Accepted Manuscript

Geochronological constraints on the polycyclic magmatism in the Bou Azzer-El Graara inlier (Central Anti-Atlas Morocco)

O. Blein, T. Baudin, P. Chèvremont, A. Soulaimani, H. Admou, P. Gasquet, A.Cocherie, E. Egal, N. Youbi, P. Razin, M. Bouabdelli, P. Gombert

PII: S1464-343X(14)00127-7DOI: http://dx.doi.org/10.1016/j.jafrearsci.2014.04.021Reference: AES 2033

To appear in: African Earth Sciences

Received Date: 1 July 2013Revised Date: 5 April 2014Accepted Date: 24 April 2014

Please cite this article as: Blein, O., Baudin, T., Chèvremont, P., Soulaimani, A., Admou, H., Gasquet, P., Cocherie,A., Egal, E., Youbi, N., Razin, P., Bouabdelli, M., Gombert, P., Geochronological constraints on the polycyclicmagmatism in the Bou Azzer-El Graara inlier (Central Anti-Atlas Morocco), African Earth Sciences (2014), doi:http://dx.doi.org/10.1016/j.jafrearsci.2014.04.021

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26 novembre 2013

Geochronological constraints on the polycyclic magmatism in the 1

Bou Azzer-El Graara inlier (Central Anti-Atlas Morocco) 2

O. Blein1*, T. Baudin1, P. Chèvremont1, A. Soulaimani2, H. Admou2, P. Gasquet3, A. 3

Cocherie1, E. Egal1, N. Youbi2, P. Razin4, M. Bouabdelli5, P. Gombert1. 4

1 BRGM, BP 6009, 45060 Orléans Cédex, France 5

2 Faculty of Science, Cadi Ayyad University, Marrakech, Morocco 6

3 Laboratoire EDYTEM, Université de Savoie, CNRS, Campus Scientifique, 73376 Le Bourget du Lac 7

Cedex, France. 8

4 EGID, Université de Bordeaux 3, 33607 Pessac Cedex, France. 9

5 GEODE Terre et Patrimoine, B.P. 7004, 40014 Marrakech, Morocco. 10

* Corresponding author. 11

Keywords. Anti-Atlas, Cryogenian, Ediacaran, Bou Azzer, Pan-African, U-Pb geochronology. 12

ABSTRACT 13

New U-Pb SHRIMP zircon ages from the Bou Azzer-El Graara onlier constrains the Neoproterozoic 14

evolution of the Anti-Atlas during Pan-African orogenesis. Within the Central Anti-Atlas, the Bou Azzer-15

El Graara inlier exposes a dismembered ophiolite, long considered to mark a late Neoproterozoic 16

suture between the West African Craton in the south, and Neoproterozoic arcs to the north. From 17

north to south, this inlier includes four main geological units: a volcanic-arc, an ophiolite, a 18

metamorphic complex and a continental platform. Several plutons intrude the volcanic-arc, the 19

ophiolite, the metamorphic complex, and post-orogenic volcanic and sedimentary deposits 20

unconformably cover these terranes. 21

The age of the volcanic-arc is reported here for the first time. Analyses of zircon of two rhyolites 22

provide ages of 761 ± 7 Ma and 767 ± 7 Ma. Zircons from two gneisses provide dates of 755 ± 9 Ma 23

and 745 ± 5 Ma. Both dates are considered best estimates of the crystallization ages of their igneous 24

protoliths. Analyses of zircon from two granitic bodies, which crosscut gneisses, provide younger dates 25

of 702 ± 5 Ma and 695 ± 7 Ma. The age of an aplitic body of the ophiolite is reported here for the first 26

time, as 658 ± 8 Ma (SHRIMP U-Pb on zircons). Theses ages suggest the existence of three distinct 27

orogenic events during Cryogenian times: (i) 770-760 Ma Tasriwine-Tichibanine orogeny with rollback 28

of the subducting oceanic plate, leading to the formation of back-arc basins; (ii) 755-695 Ma Iriri-29

n’Bougmmane orogeny; and (iii) the 660-640 Ma Bou Azzer orogeny involving the formation and the 30

emplacement of the Bou Azer ophiolite. 31

During Ediacaran times, the Bou Azzer-El Graara inlier is characterized with the development of a 32

continental volcanic arc between 630 and 580 Ma (Bou Lbarod Group, 625 ± 8 Ma ; Bleïda 33

granodiorite, 586 ± 15 Ma), and strike-slip pull-apart basins (Tiddiline Group, 606 ± 4 Ma and 34

606 ± 5 Ma). These volcanic and sedimentary Lower Ediacaran sequences are deformed before the 35

felsic pyroclastic deposits of the Ouarzazate Group (567 ± 5 Ma and 566 ± 4 Ma). Finally, the 36

Ouarzazate Group is overlain by early Cambrian volcanic deposits of the Jbel Boho Formation 37

(541 ± 6 Ma). 38

1. INTRODUCTION 39

Located on the northern edge of West African Craton (WAC), the Anti-Atlas belt of Morocco is 40

characterised by a Proterozoic basement unconformably underlying by late Ediacaran to Paleozoic 41

sedimentary rocks in several inliers (Bas Dra, Ifni, Kerdous, Akka, Igherm, Sirwa, Zenaga, Bou Azzer-42

El Graara, Saghro and Ougnat; Figure 1). This Proterozoic basement consists of: (i) Paleoproterozoic 43

metamorphic and igneous rocks; (ii) Cryogenian rocks affected by the main Pan African orogenic 44

events; (iii) Early Ediacaran sedimentary and volcanic rocks deformed by the latest tectonic event of 45

the Pan African orogeny; and (iv) and late Ediacaran volcanic rocks (Ouarzazate Group). However, 46

two main structural domains have been recognised part of the NW-SE Anti-Atlas Major Fault (AAMF; 47

Choubert, 1963). 48

In Western Anti-Atlas (Figure 1), Paleoproterozoic basement (2030-2200 Ma) has been recognised 49

and recently confirmed by U–Pb zircon dating in several inliers (Ait Malek et al., 1998; Charlot-Prat et 50

al., 2001; Thomas et al., 2002; Walsh et al., 2002; Barbey et al., 2004, Gasquet et al. 2004). This 51

Paleoproterozoic basement, consisting of schists, gneisses, migmatites and plutonic rocks, is 52

unconformably overlain by Early Ediacaran sedimentary and volcanic rocks and/or Late Ediacaran 53

volcanic rocks. 54

The Eastern Anti-Atlas domain, including Sirwa, Bou Azzer-El Graara and Saghro inliers (Figure 1), is 55

characterised by the lack of Paleoproterozoic rocks (except as relics in the inherited cores of zircon 56

from Ediacaran volcanic rocks, Gasquet et al; 2005; Pelleter et al. 2007), and by Cryogenian rocks 57

affected by the main Pan African orogenic events, Early Ediacaran sedimentary and volcanic rocks 58

affected by the latest stage of Pan African orogeny, and late Ediacaran volcanic rocks. In the Sirwa 59

inlier, two dismembered ophiolite sequences (Tasriwine and N’Qob ophiolites) include ultramafic 60

cumulates, gabbros, a sub-vertical sheeted dyke complex and plagiogranite intrusions (Admou, 2000). 61

Samson et al. (2004) dated two plagiogranite intrusions within the Tasriwine ophiolite, 761 Ma and 62

762 Ma, which were interpreted to date formation of oceanic crust. In the central part of the Sirwa 63

inlier, medium to high grade metamorphic rocks are thought to represent the roots of an arc complex 64

estimated to be 743 Ma (Thomas et al., 2002). The relationships of the ophiolites in the Sirwa inlier to 65

the main Bou Azzer–El Graara ophiolite are unclear. 66

Recent mapping in the Bou Azzer-El Graara inlier and the western edge of the Saghro massif, within 67

the framework of the Moroccan National Project of Geological mapping (1/50 000-scale sheet maps of 68

Bou Azzer, Alougoum, Aït Ahmane and AlGlo’a) gave opportunities to acquire new field, geochemical 69

and geochronological data. Therefore, the aims of this paper are: (i) a re-appraisal of the lithological 70

units of the Bou Azzer-El Graara inlier; (ii) to present new geochronological data on magmatic rocks; 71

and (iii) to discuss the geodynamical evolution of the West African Craton during Proterozoic times. 72

The new geochronological data have allowed us to clarify the timing of polycyclic magmatism 73

observed in several terranes of Pan-African belt. 74

2. LITHOLOGICAL UNITS OF THE BOU AZZER-EL GRAARA INLIER 75

The Bou Azzer-El Graara inlier is a key element of the Anti-Atlas area for the understanding of Pan-76

Africa events. It is believed to expose the dismembered relics of a Neoproterozoic suture zone 77

(Leblanc, 1981; Saquaque et al., 1989; Hefferan et al., 2000) marking the boundary between the 78

Paleoproterozoic Eburnean basement of the WAC to the south, and Neoproterozoic accreted arcs to 79

the north. Composed of tectonic blocks separated by oblique slip faults, the Bou Azzer-El Graara inlier 80

is structurally the most complex part of the whole Anti-Atlas (Leblanc, 1981; Saquaque et al., 1989, 81

1992). 82

Nine main lithological units were identified in the Bou Azzer-El Graara inlier: (i) a gneissic basement 83

composed of deformed meta-igneous and metasedimentary rocks, including augen granite gneiss, 84

and leucogranite (Assif n’Bougmmane gneiss complex); (ii) a plateform sequence of quartzite and 85

stromatolitic limestones overlain by mafic lavas and volcano-sedimentary rocks, interpreted as a 86

Tonian and/or Cryogenian passive margin cover sequence (Tachdamt-Bleida Group); (iii) a 87

Cryogenian mafic–ultramafic complex, interpreted as a dismembered ophiolite fragment (Bou Azzer 88

Group); and (iv) a Cryogenian metasedimentary sequence with subordinate volcanic units (Tichibanine 89

Group). These pre-Ediacaran units are deformed by the main Pan-African shortening tectonic event, 90

and are intruded by granitoid bodies, (v) the Ousdrat Suite, which are believed to have been emplaced 91

syn-tectonically during the main period of Pan-African orogenesis (Saquaque et al., 1989). This 92

collisional event is generally considered to have been the major Pan-African orogenic phase (PA1), 93

with the southward obduction of the Bou Azzer ophiolite onto the WAC at about 685 Ma (Leblanc, 94

1975; Leblanc and Lancelot, 1980), 663 Ma (Thomas et al., 2002), or 653-640 Ma (Inglis et al., 2004). 95

The above units are unconformably overlain or intruded by successively: (vi) mafic volcanic rocks (Bou 96

Lbarod Group); (vii) the terrigeneous sediments with local pyroclastic rocks (Tiddiline Group); (viii) 97

undeformed intrusions such as the Bleïda granodiorite (Bleïda Suite); (ix) a late Ediacaran volcano-98

clastic sequence (Ouarzazate Group). 99

The lithostratigraphic system used for the Anti-Atlas orogen is summarised in Table 1, where it is 100

compared to the previous chronostratigraphic nomenclature. 101

2.1. Tonian and/or Cryogenian lithological units 102

The Tachdamt-Bleïda Group is characterized by the following succession from the base to the top: a 103

stromatolitic limestone and quartzite unit; a tholeiitic basalt unit; a schist unit; and a schist and 104

sandstone unit (Leblanc and Billaud, 1978; Mouttaqi and Sagon, 1999). The limestone and quartzite 105

unit comprises: an alternation of sandstones and limestones; massive quartzites; and an alternation of 106

sandstones and pelites. This group is interpreted as the local Neoproterozoic passive margin of the 107

West African Craton (Saquaque et al., 1989; Leblanc and Moussine-Pouchkine, 1994; Hefferan et al., 108

2002; Bouougri and Saquaque, 2004). 109

2.2. Cryogenian lithological units 110

The southern part of the Bou Azzer-El Graara inlier consists of a variety of deformed igneous, meta-111

igneous and metasedimentary rocks, including augen granite gneiss, paragneisses, low-grade 112

amphibolites, muscovite pegmatite and leucogranite. The five main outcrops occur at Bou Azzer, 113

Oumlil, Tazigzaout, Ightem and assif n’Bougmmane. On the basis of their deformational state and 114

lithological similarities with rocks of the nearby Zenaga Massif these units have been considered to be 115

2 Ga Eburnean WAC basement by all previous workers (Leblanc, 1981; Saquaque et al., 1989; 116

Saquaque, 1991). 117

Recently determined ages by SHRIMP on zircons have been performed on metagabbro, augen 118

granite gneiss, and crosscutting leucogranites bodies of the Tazigzaout complex (D’Lemos et al., 119

2006). Three concordant U–Pb analyses of zircon from an augen granite gneiss provide a date of c. 120

753 Ma. Zircons from a nearby metagabbro provide a similar age date of c. 752 Ma. Both dates are 121

considered best estimates of the crystallization ages of their igneous protoliths. Analyses of zircon 122

from two crosscutting leucogranite bodies provide younger dates of 701 and 705 Ma. 123

The ophiolite defined by Leblanc (1975, 1981a) is a composite terrane, involving three separate units: 124

(i) an oceanic crust and upper mantle, i.e. the true ophiolite; (ii) a northern belt made up of calc-125

alkaline volcanic rocks (Saquaque et al., 1989b), the Tichibanine Group; and (iii) late Cryogenian syn-126

kinematic granitoïd plutons (Ousdrat Suite), intruding both oceanic and arc units (Beraaouz et al., 127

2004). 128

In this paper, we restricted the term of Bou Azzer ophiolite to the oceanic-type crust and upper mantle. 129

This ophiolite comprises the following rock units: upper mantle tectonite peridotites, mafic-ultramafic 130

cumulates, submarine basaltic pillow lava, and volcano-sedimentary sequence (Leblanc, 1976; 131

Bodinier et al., 1984). This mafic-ultramafic complex is interpreted as a dismembered ophiolite 132

fragment (Leblanc, 1975, 1981) later on interpreted as a mélange complex (Saquaque et al., 1989; 133

Hefferan et al., 2002), taking place at blueschist metamorphic conditions (Hefferan et al., 2002). 134

Until recently no precise radiometric dates exist for any magmatic rocks of the Bou Azzer ophiolite. 135

Admou (2000) considered on extensive mapping and structural studies the Sirwa inlier as a westward 136

extension of the Bou Azzer-El Graara inlier. Within the Sirwa inlier, crop out two small highly 137

tectonized ophiolites, the N’qob and Tasriwine ophiolites (Thomas et al., 2002). Samson et al. (2004) 138

obtained two ages of 762 Ma on plagiogranites. El Hadi et al. (2010) place the age of the formation of 139

the Bou Azer ophiolite at 697 Ma. 140

The Tichibanine Group outcrops on the northern part of the Bou Azzer-El Graara inlier, and 141

corresponds to the northern terrane of Saquaque et al. (1989b). This group consists of a complex 142

tectonic assemblage of metagraywackes with basalts, andesites, rhyolites and tuffs (Tekiout et al., 143

1991), bearing calc-alkaline and island arc tholeiitic signatures (Naidoo et al., 1991). A thick series of 144

layered cinerites has been evidenced. The rocks are metamorphosed at greenschist-facies to lower 145

epidote-amphibolite facies conditions. 146

The late Cryogenian granitoïds of the Ousdrat Suite are organized in massifs and stocks that are 147

either roughly circular in plan (Ousdrat) or, more commonly, WNW-ESE elongated (Ait Ahmane and 148

Bou Frokh), and intrude sedimentary and volcano-sedimentary Cryogenian rocks. The intrusions, 149

generally more intermediate than felsic rocks, include diorites, quartz-diorites and monzodiorites. 150

Published ages for these granitoïds are 667 ± 11 Ma (Mrini, 1993) and 653 ± 1.5 Ma (Inglis et al., 151

2003) for quartz-diorites from Bou Frokh, 640 ± 1.5 Ma for quartz-diorites from Ousdrat (Inglis et al., 152

2003), 650 ± 2 Ma for diorite from Ait Ahmane (Samson et al., 2004), and 646 ± 8 Ma and 646 ± 6 Ma 153

for diorites from Tamellalet and Tafrawt (Yazidi et al., 2008). These late Cryogenian (650-670 Ma) 154

medium-K calc-alkaline diorites were produced by partial melting of subducted oceanic crust followed 155

by interaction of the melt with the overlying mantle wedge (Beraaouz et al., 2004). 156

2.3. Ediacaran lithological units 157

Three volcano-sedimentary or volcanic groups occurred during that Ediacaran period: the Bou Lbarod, 158

the Tiddiline and the Ouarzazate groups. 159

The Bou Lbarod Group outcrops in the Bou Azer-El Graara inlier and in the western edge of the 160

Saghro massif (Figure 2). This group is composed of volcanic rocks with andesitic to rhyolitic 161

compositions, and corresponds to the lower member of the Ouarzazate Group defined by Choubert 162

(1953b). In the Saghro massif, the Issougri complex (the lower member of the Ouarzazate Group), a 163

great thickness of andesitic volcanic rocks, is folded with local sub-vertical bedding (Choubert and 164

Faure-Muret, 1970). The middle member of the Ouarzazate Group unconformably overlies the Issougri 165

complex. 166

The Tiddiline Group is a clastic sedimentary succession characterized by a coarsening upwards 167

sequence of siltstones to conglomerates with local diamictites interpreted as marine tilloids with 168

dropstones (Leblanc, 1975). This group unconformably overlies Cryogenian rocks deformed by the 169

Pan African orogeny. The Tiddiline Group is tilted, faulted and folded with local development of axial-170

plane cleavage. In the eastern part of the Bou Azzer-El Graara inlier, the two main outcrops of the 171

Tiddiline Group are the Dwaïssa basin on the northern border and the Trifya basin on the southern 172

border. Hefferan et al. (1992) suggest that the upper members of the Tiddiline Group contain clasts 173

derived from the underlying tectonic blocks, including boulders of the Ediacaran granodioritic and 174

dioritic intrusions (such as Bleïda granodiorite), and thus the tectonic blocks were thrust over the 175

Tiddiline basins. On this basis Hefferan et al. (1992) argued for a continuation in collision within the 176

Bou Azzer region during deposition of the Tiddiline Group. 177

Recent mapping permit to observe that the conglomerates of the upper members are not stratified and 178

unconformably overlain typical stratified conglomerates of the Tiddiline Group. In the ultimate 179

conglomerates, the lithology of the boulders varies from west to east, from gneisses, to quartzite and 180

diorite. Such lithological variation reflects variations in local Cryogenian rocks and is frequently 181

observed at the base of the Ouarzazate Group. This formation is characterized by basal sedimentary, 182

volcano-sedimentary or volcanic breccias with boulders of local Cryogenian to Ediacaran basement. 183

These petrographic observations and U-Pb ages obtained on Bleïda granodiorite (Inglis et al., 2004) 184

suggest that ultimate conglomerates of the Tiddiline Group are in fact basal conglomerates of the 185

Ouarzazate Group. 186

The Ediacaran granodioritic and dioritic intrusions (Bleïda Suite) occur within each of the tectonic 187

blocks of the Bou Azzer-El Graara inlier and several of the intrusions carry a weak to moderately 188

developed foliation that is co-planar to the main regional fabric observed in the surrounding host-rocks 189

(Admou, 2000). 190

The Bleïda granodiorite is exposed in the eastern wedge of the inlier, emplaced within the Tachdamt-191

Bleïda Group. The bulk of the intrusion is a medium grained granodiorite consisting of plagioclase, 192

quartz, hornblende, alkali-feldspar, apatite and zircon. Tonalitic and dioritic compositions occur within 193

the intrusion; without definite boundaries, they result from variation in the relative proportion of quartz, 194

hornblende and plagioclase. A fine-grained granodiorite phase is evident in the south of the intrusion, 195

forming sheets running parallel to the southern boundary. The granodiorite exhibits primary igneous 196

features. Internal magmatic fabrics are weak and discontinuous, defined by the alignment of lath 197

shaped hornblende, and possess no predominant structural orientation across the intrusion. In the 198

south-east of the body the magmatic fabrics are sub-vertical and trend to the WNW. In the north-west 199

fabrics rotate into parallelism with the boundary of intrusion. Ducrot (1979) provided the first U–Pb age 200

(615 ± 12 Ma) of the Bleïda granodiorite. Recently, Inglis et al. (2004) provided a younger age of 201

597 ± 2 Ma. 202

The relationship of the Bleïda Suite to deformation in the Bou Azzer inlier has remained open to 203

question. Leblanc (1981) argued that the lack of penetrative deformation within the intrusion implied 204

that its emplacement post-dated thrusting and pervasive greenschist facies metamorphism. Saquaque 205

et al. (1989) regarded the intrusion as having been emplaced and deformed during the greenschist 206

facies deformation event. Inglis et al. (2004) argued that the granodiorite was emplaced after the end 207

of greenschist facies metamorphism and the development of the pervasive regional fabrics in the Bou 208

Azzer inlier. However, they suggested that the intrusion could conceivably have been emplaced during 209

late brittle transcurrent faulting, and in this regard the granodiorite is better identified as being syn-210

tectonic only with late brittle deformation in the region, rather than pervasive regional fabric 211

development (Inglis et al., 2004). 212

The Ouarzazate Group consists of potassic to high-potassic basaltic andesites, andesites, dacites, 213

and rhyolites interstratified with chaotic breccia, polygenic conglomerates and arkosic sandstones. 214

Felsic volcanics were dated in several inliers: 565 Ma in the Tagragra of Tata (Walsh et al., 2002); 215

563 Ma and 580 Ma in the Central Anti-Atlas (Mifdal and Peucat, 1985); between 560 and 575 Ma in 216

the Sirwa massif (Thomas al., 2002); 550 Ma in the Imiter inlier (Cheilletz et al., 2002) and 552 ± 5 Ma 217

in the Bou Madine inlier (Gasquet et al., 2005). The Ouarzazate Group has not recorded the Pan-218

African deformations (PA1 and/or PA2), but was deposited on a highly variable basement topography, 219

which, coupled with the important and rapid thickness variations of the volcano-sedimentary deposits, 220

suggests that this group was deposited during active tectonics, most probably transtensional 221

movements (Maacha et al., 1998; Gasquet et al., 2005). This late Neoproterozoic magmatic activity 222

constitutes the Ediacaran Atlasic Volcanic Chain that built across the whole Anti-Atlas (Pouclet et al. 223

2007). This chain extends from the Atlantic coast to the border of Algeria, with a total length reaching 224

850 km and the width, 80-150 km. 225

2.4. Paleozoic sedimentary cover and intercalated volcanics 226

The Ediacaran-Cambrian transition is recognized in the Moroccan Anti-Atlas throughout a carbonate-227

dominated succession (Adoudou and Lie-de-vin formations; Choubert, 1952, 1953a, b) that 228

unconformably overlies the late Ediacaran Ouarzazate Group. 229

Volcanic ashes and flows also occur interbedded with the Adoudou and Lie-de-vin strata (Choubert 230

and Faure-Muret, 1970). One source for these ashes is preserved in the Alougoum volcanic complex 231

located on the Al Glo’a area (Choubert, 1952; Boudda et al., 1979), in which volcanic 232

paleotopographies cover directly the Adoudou dolostones and were progressively onlapped by the 233

breccias, dolostones, variegated shales and sandstones of the Lie-de-vin Formation. An early U/Pb 234

date of 529 ± 3 Ma from the Boho volcano (Recalculated from Ducrot and Lancelot, 1977) and 235

531 ± 5 Ma (Gasquet et al., 2005) suggests that deposition of the uppermost part of the Adoudou 236

Formation took place in the pre-trilobite earliest Cambrian. As a result, the location of the Ediacaran-237

Cambrian boundary (defined by the first appearance of the ichnospecies Treptichnus (former 238

Phycodes pedum; Narbonne et al., 1987) remains problematical in Morocco because it lies within the 239

thick carbonate-dominated Adoudou Formation, extremely poor in shelly metazoans and ichnofossils. 240

The boundary has been tentatively correlated with carbon isotope signatures (Tucker, 1986; Latham 241

and Riding, 1990; Kirshvink et al., 1991; Magaritz et al., 1991) above the medusoid-like imprints of the 242

‘Série de base’ or Basal series (Adoudou Formation; Houzay, 1979) and below the occurrence of 243

Atdabanian (sensu Spizharski et al., 1986), shelly metazoan fossils in the Tiout Member (Sdzuy, 1978; 244

Schmitt, 1979; Debrenne and Debrenne, 1995). 245

The carbonate to clastic sedimentary cover comprises from bottom to top: (i) the transgressive late 246

Proterozoic to early Paleozoic Taroudannt Group; (ii) the Cambrian Tata Group; and (iii) the Cambrian 247

to Ordovician transgressive groups of internal Feijas, Tabanite, external Feijas, first and second Bani 248

and Ktaoua. 249

2.5. Main objectives and sampling 250

This paper provides new high-precision zircon U-Pb ages for Cryogenian and Ediacaran magmatic 251

rocks of the Bou Azzer-El Graara inlier to constrain the magmatic events and deformation phases of 252

Pan-African events in the Anti-Atlas area. 253

In a first stage, we will focus on Cryogenian period. Recent U-Pb analyses of zircon of an augen 254

granite gneiss and metagabbro exposed in the Tazigzaout area provide dates of 753 and 752 Ma, and 255

dates of 701 and 705 Ma for crosscutting leucogranite bodies (D’Lemos et al., 2006). We selected two 256

samples of orthogneisses (BOPC028 and AADG4) in Bou Azzer and assif n’Bougmmane areas, and 257

two samples of crosscutting granitic bodies (BOPC076 and AAPC140) in Oumlil and assif 258

n’Bougmmane areas to confirm these new ages in others outcrops of metamorphic rocks. 259

Bodinier et al. (1984) and El Hadi et al. (2010) suggested that the Tichibanine volcanic island-arc may 260

be contemporaneous from the Bou Azzer ophiolite. Then, we selected two rhyolites in the Tichibanine 261

Group, and a leucogranodiorite within the Bou Azzer ophiolite to test this hypothesis. 262

In a second stage, we will try to precise timing of Ediacaran volcanic rocks, intrusions and deformation 263

phase recorded in part of Ediacaran rocks. The sample AAYN55a represents a small diorite pluton 264

within the Bou Lbarod Group composed of volcano-sedimentary and volcanic rocks of andesitic 265

compositions. Three samples were selected in the Tiddiline Group. Sample ALDG21 is a rhyolitic 266

welded tuff observed at the top of the Tiddiline Group conformably overlaying cross-bedded quartzo-267

feldspathic sandstones. Sample ALDG4 is a trachytic dyke which cross-cutting the Tachdamt-Bleïda 268

Group. And the sample AGEE24 is a sandstone sampling in the Dwaissa basin. 269

The sample AGDG1 is a quartz diorite which outcrops in the Trifya basin of Tiddiline Group. The 270

relationships between conglomerates of the Tiddiline Group and dioritic intrusions are unclear. 271

However, cobbles and boulders of granodiorite and diorite occur within conglomerates of upper 272

members of the Tiddiline Group. Hefferan et al. (1992) suggest that they came from the Bleïda 273

granodiorite. Recently, Inglis et al. (2004) obtained two well constrained ages of 579.4 ± 1.2 Ma and 274

578.5 ± 1.2 Ma for two samples of the Bleïda granodiorite. 275

Two rhyolitic welded tuffs of the Ouarzazate Group have been sampled in the Bou Azzer-El Graara 276

inlier and the Saghro massif. In the Bou Azzer-El Graara inlier, the ignimbrite (ALDG20) 277

unconformably overlies folded ignimbrite (ALDG21) of the Tiddiline Group, and occurs at the local 278

base of the Ouarzazate Group. In the western edge of the Saghro massif, the ignimbrite (BODG6) 279

occurs closer to the top of the ignimbritic sequence of the Ouarzazate Group. To the north of the Bou 280

Azzer mine, basalts and volcanic breccias are interlayered with dolomies at the base of the Adoudou 281

formation. Sample BOPC343 is one of these volcanic clasts. 282

Finally, we will present a geodynamic reconstruction of the Anti-Atlas during Cryogenian and 283

Ediacaran times. 284

3. ANALYTICAL METHOD 285

Two different ion microprobes were used for this study: a Neptune MC-ICP-MS at BRGM 286

(Orléans, France) and a SHRIMP II at the Australian National University, Canberra 287

(Australia). For each sample, about 30 grains were mounted in epoxy and polished for U and 288

Pb isotopes to be analysed by the ion microprobe. Spot analyses were carried out on zircon 289

grains with both instruments. Only the most homogeneous parts of the zircons, without any 290

cracks, were investigated after a careful checking of cathodoluminescence images and 291

reflected light photomicrographs of the sectioned zircon grains. Within the zircons, 292

patches showing alteration domains were avoided. 293

Three analyses on single grains were made using the Neptune MC-ICP-MS (ThermoElectron, 294

Bremen, Germany) at BRGM (Orléans, France) equipped with a multi-ion counting system, allowing a 295

very high sensitivity (Cocherie and Robert, 2007), and a laser ablation system (New Wave frequency-296

quintupled Nd:YAG UV laser, distributed by VG, UK) operating at 213 nm. The ablation pit was 20 µm 297

in diameter and 15-20 µm deep. Argon gas was used as carrier gas. Zircon standard used is 91500 298

(Wiedenbeck et al., 1995). Standard bracketing was applied in order to correct both elemental 299

fractionation during the ablation process and mass bias originating from the MC-ICP-MS itself. 300

Detailed instrumentation and analytical accuracy descriptions are given in Cocherie and Robert (2008) 301

and Cocherie et al. (2009). 302

The SHRIMP II was used for the thirteen others analyses. The SHRIMP analyses were 303

performed following the analytical procedure described by Claoué-Long et al. (1995) and 304

Willliams (1998). The zircon standards used to calibrate the U–Pb ratio were the 91500 305

zircon from Ontario (Canada) for the CAMECA ion microprobe (1062.4 ± 0.4 Ma; Wiedenbeck et 306

al., 1995), and the Duluth gabbro (USA) for the Australian microprobe (1099.1 ± 0.5 Ma; Paces 307

and Miller, 1993). 308

Whatever analytical approach was used, all the uncertainty calculations were made at the 309

2σ level (95% confidence limit) using the ISOPLOT/EX program (version 3.6) of Ludwig 310

(2008). 311

Two methods were used to build the histogram diagram. For ages younger than 1000 Ma, the plotted 312

data correspond to 206

Pb*/238

U ages of the analyses involved in the calculation of obtained ages in the 313

Terra-Wasserburg Inverse Concordia diagram. For ages older than 1000 Ma, the plotted data 314

correspond to the 207

Pb*/206

Pb* ages for concordant analysis or extrapolated ages in case of Discordia 315

mixing line. 316

4. GEOCHRONOLOGICAL RESULTS 317

4.1. Tichibanine Group 318

Two samples of rhyolites (AGEE298 and AGEE094) from the Tichibanine Group were dated. Sample 319

AGEE298 is a rhyolite with quartz phenocrysts. The outcrop is a succession of felsic pyroclastic tuffs 320

and rhyolitic flows. Sample AGEE094 is a dacitic coarse pyroclastic tuff with feldspar clasts. The 321

outcrop is a succession of lapilli, coarse and fin pyroclastic tuffs. 322

Zircons in AGEE298 are limpid, euhedral crystals with little well-developed 50-100 µm prisms. 323

Thirteen spot analyses were carried out on 12 zircon grains. All the analyses show a low common lead 324

contribution, and no loss of radiogenic lead. Thirteen sub-concordant points gave a weighted mean 325

age of 767 ± 7 Ma for the rhyolite AGEE298 (Figure 3a, Table 2). 326

Zircons in AGEE094 are quite similar in size and morphology to those of AGEE298, but are light pink 327

to pink in colour. Fourteen spot analyses were carried out on 13 zircon grains. The analysis of grain 10 328

shows a level in common lead significative and a radiogenic Pb-loss. It will not be taken into 329

consideration. Two other analyses, 4.1 and 9.1, close to the Concordia curve, have not been 330

considered in the calculation of the age. Ten sub-concordant points gave a weighted mean age of 331

761 ± 7 Ma for the rhyolite AGEE094 (Figure 3b, Table 2). 332

These ages of 761 and 767 Ma correspond to the emplacement age of the rhyolites in the Tichibanine 333

volcanic arc. 334

4.2. Assif n’Bougmmane gneiss complex 335

The five main outcrops of the assif n’Bougmmane gneiss complex occur at Bou Azzer, Oumlil, 336

Tazigzaout, Ightem and Tamaliout in the Bou Azzer-El Graara inlier (Figure 2). In the Bou Azzer area, 337

foliated gneisses are associated with augen gneisses, amphibolites and metagabbros. Sample 338

BOPC028 is a foliated fine- to coarse grained gneiss consisting of 3-5 mm-sized crystals of 339

plagioclase, quartz and hornblende. Sample AADG4 is an orthogneiss collected in the assif 340

n’Bougmmane area, where orthogneisses are associated with paragneisses, amphibolites, 341

metagabbros. Sample AADG4 is an augen gneiss with large plagioclase feldspar and/or quartz and 342

muscovite. Gneisses are crosscutted by leucogranites bodies. 343

Zircons in BOPC028 are small (~100 µm), limpid, and rounded. Fifteen spot analyses were carried 344

out on 15 zircon grains. The analyses show low U contents (20 to 30 ppm) and the lack of 345

common lead. Two analyses (9.1 and 10.1) with significant younger ages will not be taken 346

into consideration. Thirteen sub-concordant points gave a weighted mean age of 755 ± 9 Ma 347

(Figure 4a, Table 2). 348

Separated zircons in AADG4 are small to coarse-grained (~100 to 400 µm). They show two zircon 349

populations. The first one consists of colored, massive and metamict zircons, and the second one of 350

clear, colorless and small zircons. This second population has been selected for datation. Thirteen 351

spot analyses were carried out on 12 zircon grains. These thirteen sub-concordant points gave a 352

weighted mean age of 745 ± 5 Ma (Figure 4b, Table 2). 353

These ages of 745 and 755 Ma correspond to the emplacement age of the granitic protoliths of these 354

orthogneisses. 355

Samples AAPC140 and BOPC076 are porphyric granitic bodies exposed in the assif n’Bougmmane 356

and Oumlil areas respectively. Sample AAPC140 is a coarse-grained granodiorite consisting of 357

crystals of potassic feldspar, plagioclase feldspar and quartz. Sample BOPC076 is a coarse-grained 358

granite consisting of crystals of potassic feldspar, plagioclase feldspar, quartz, muscovite and biotite. 359

Zircons in AAPC140 are rare and small (~100 to 150 µm). They are sometimes elongated with a 360

concentric zonation. Fifteen spot analyses were carried out on 15 zircon grains. The analyses do not 361

show common lead, but the data show two distinct populations. Four analyses give a significative old 362

age of 743 ± 9 Ma (Figure 4c, Table 2) observed in orthogneiss AADG4. The main groups of eleven 363

zircons gave a weighted mean age of 702 ± 5 Ma (Figure 4c, Table 2). This age corresponds to the 364

emplacement of the granodiorite, whereas the older ages reflect the crustal inheritance. 365

Zircons in BOPC076 are rare and small (~50 to 150 µm). They are limpid with a concentric zonation. 366

Thirteen spot analyses were carried out on 13 zircon grains. The analyses show very low common 367

lead. Four analyses give a significative old age of 752 ± 10 Ma (Figure 4d, Table 2) observed in 368

orthogneiss BOPC028. The main groups of eight zircons gave a weighted mean age of 695 ± 7 Ma 369

(Figure 4d, Table 2). This age corresponds to the emplacement of the granite, whereas the older ages 370

reflect the crustal inheritance. 371

4.3. Bou Azzer Group 372

Sample AADG12 is a light granodiorite dyke in a small exposure in cumulative gabbro of the ophiolitic 373

complex. This dyke is two hundred meters in length and fifteen meters in width, and has a foiled 374

contact with a cumulative gabbro. Sample AADG12 is a coarse-grained granodiorite consisting of 1-375

4 mm sized crystals of potassic feldspar, plagioclase feldspar, quart and biotite. According to the 376

presence of potassic feldspar, sample AADG12 is not a plagiogranite, however potassic feldspar is not 377

abundant. 378

Zircons in AADG12 are clear, thick, often broken and small (<150 µm). The U contents are low, and 379

typical of oceanic material. Fifteen spot analyses were carried out on 15 zircon grains. The 15 380

analyses show the absence of common lead and fall very close to the Concordia curve. Four analyses 381

(5.1, 6.1, 13.1 and 15.1) give younger ages around 590 Ma. These zircons have an uncertain 382

radiogenic Pb-loss, or these ages are significative of an event which affected the rock after its 383

emplacement. Finally, the main population gave a weighted mean age of 658 ± 8 Ma (Figure 5, Table 384

2). This age corresponds to the emplacement of the leucogranodiorite. 385

4.4. Early Ediacaran intrusions 386

Sample AAYN55a was collected from small dioritic intrusions crosscutting andesitic flow and rhyolitic 387

pyroclastic tuffs from the Bou Lbarod. The Bou Lbarod Group unconformably overlies the Tichibanine 388

Group, and is unconformably overlain by the Ouarzazate Group. Sample AAYN55a is a coarse-389

grained diorite consisting of crystals of plagioclase feldspar, clinopyroxènes, hornblende and quartz. 390

Zircons in AAYN55a are relatively abundant and small (80 to 200 µm). The analyses show a 391

homogeneous population, with very low common lead and lack of radiogenic Pb-loss. Sixteen spot 392

analyses were carried out on 15 zircon grains. The analyses reflect a homogeneous zircon population. 393

The contribution of common lead is very low, as potential radiogenic Pb-loss. However, three analyses 394

showing a light loss of radiogenic lead (7.1, 8.1 and 11.1) and one sample with an old age (4.1: 395

659 ± 18 Ma) have not been taken into consideration. Finally, twelve analyses gave a weighted mean 396

age of 625 ± 8 Ma (Figure 6, Table 3). This age corresponds to the crystallisation of zircons and the 397

emplacement of the diorite. 398

4.5. Tiddiline Group 399

Sample ALDG21 is a rhyolitic welded tuff observed at the top of the Tiddiline Group conformably 400

overlaying cross-bedded quartzo-feldspathic sandstones in the eastern part of the Bou Azer-El Graara 401

inlier. An ignimbrite of the Ouarzazate Group (ALDG20) unconformably overlies the rhyolitic welded 402

tuff (ALDG21) of the Tiddiline Group. Sample ALDG4 is a trachytic dyke which cross-cutting the 403

Tachdamt-Bleïda Group. And the sample AGEE24 is a sandstone sampling in the Dwaissa basin. 404

Zircons in ALDG21 are relatively abundant and small (100 to 150 µm), clear and without concentric 405

zonations. Fifteen spot analyses were carried out on 15 zircon grains. They do not show common lead 406

or radiogenic Pb-loss. These fifteen analyses gave a weighted mean age of 606 ± 4 Ma (Figure 7a, 407

Table 2). This age corresponds to the emplacement of the volcanic rock. 408

Zircons in ALDG4 are abundant, homogeneous and medium-grained (~200 µm). Twelve spot 409

analyses were carried out on 11 zircon grains. All the analyses fall very close to the Concordia curve. 410

Only two analyses (7.1 and 11.1) show a light radiogenic Pb-loss. Ten analyses remaining gave a 411

weighted mean age of 606 ± 5 Ma (Figure 7b, Table 2). This age corresponds to the crystallisation of 412

zircons and the emplacement of the trachyte. 413

Zircons in AGEE24 are abundant and almost rounded. Some grains are clear or purplish red. Fifteen 414

spot analyses were carried out on 13 zircon grains. The ages are essentially Paleoproterozoic, only 415

two ages realised on grain 7 gave a weighted mean age of 606 ± 14 Ma (Figure 7c, Table 4). All the 416

other analyses fall on the Concordia curve. Nine analyses gave a weighted mean age of 2045 ± 13 Ma 417

(Figure 7d, Table 4). These ages reflect a crustal inheritance, with a significative episode around 418

2045 Ma for the history of this rock. 419

4.6. Bleïda Suite 420

The Ediacaran granodioritic and dioritic intrusions of the Bleïda Suite occur within each of the tectonic 421

blocks of the Bou Azzer-El Graara inlier. One intrusion was observed in the eastern edge of the inlier 422

and is overlain by coarse volcano-sedimentary breccia of the Ouarzazate Group. Sample AGDG1 is a 423

coarse grained diorite consisting of crystals of plagioclase feldspar, quartz, hornblende, biotite and 424

rare potassic feldspar. 425

Zircons in quartz diorite AGDG1 are abundant but little (50 to 200 µm). Grains are clear and rounded. 426

The analysed grains are often very little and fractured. Only ten grains could be dated. Zircon 5 is a 427

typical inherited grain. Two analyses (4.1 and 6.1) have not been taken into consideration, because 428

they could present radiogenic Pb-loss. Finally, seven analyses gave a weighted mean age of 429

586 ± 15 Ma, interpreted as the age of the diorite emplacement (Figure 8, Table 3). 430

4.7. Ouarzazate Group 431

Samples ALDG20 and BODG6 are welded tuffs collected in the Bou Azzer-El Graara inlier and the 432

Saghro massif, respectively. In the Saghro massif, sample BOG6 is collected at the top of the 433

Ouarzazate Group, and sample ALDG20 outcrops at the base of the Ouarzazate Group. However, 434

these two welded-tuffs are mapped as ignimbrites of the Jbel Timeskrine member of the Aourz 435

Formation. Both ignimbrites exhibit a ≤ mm-scale eutaxitic fabric, welded Y-shaped shards, and crystal 436

fragments of quartz, without lithic fragments. 437

Zircons in ALDG20 are clear and elongated (200 à 300 µm). Ten analyses gave a weighted mean age 438

of 567 ± 5 Ma (Figure 9a, Table 2). This age corresponds to the emplacement of the rhyolite. One 439

analysis shows a high common lead contribution (8.1: 737 ± 32 Ma). This zircon is rounded, very poor 440

in U like zircons in orthogneiss. It could reflect a crustal inheritance. 441

Zircons in BODG6 are medium-grained (~200 to 250 µm), abundant, clear with a concentric zonation. 442

Eleven spot analyses were carried out on 10 zircon grains. These analyses do not show significative 443

common lead contribution, or radiogenic Pb-loss. Eleven analyses gave a weighted mean age of 444

566 ± 4 Ma (Figure 9b, Table 2). This age corresponds to the emplacement of the rhyolite. 445

The obtained ages in the Bou Azzer-El Graara and Saghro inliers, respectively of c. 567 Ma and c. 446

566 Ma are thus similar. 447

4.8. Adoudou Formation 448

In the area of the mine of Bou Azzer, the base of the Adoudou Formation is characterized by a 449

pyroclastic breccia with basaltic clasts. Sample BOPC343, one of these clasts, is a porphyric basalt 450

with plagioclase feldspar phenocrysts. 451

Zircons in BOPC343 are reworked, few and little (~50-150 µm). Grains are clear and colorless. 452

Eighteen spot analyses were carried out on 16 zircon grains. All the analyses show a low common 453

lead contribution. An important loss in radiogenic lead has been observed on one sample, which has 454

not been taken into consideration. Two analyses record an old inheritance (8.1 and 16.1). Sample 8.1 455

give an inherited age of 2795 ± 10 Ma (Table 4). The other analyses range from 540 to 650 Ma. The 456

seven younger zircons gave a weighted mean age of 541 ± 6 Ma (Figure 10, Table 4). This 457

crystallisation age corresponds to the last registred volcanic activity in accordance with the age 458

previously published by Ducrot and Lancelot (1977) from the Jbel Boho syenite and by Gasquet et al. 459

(2005) from the contemporaneous Aghbar trachyte. Moreover, this age is in agreement with the 460

stratigraphic position of the volcanic breccia, which was at the base of the Cambrian series. Several 461

volcanic episodes were opportunity for crystallisation of other zircons around 560, 580 and 630 Ma. 462

5. DISCUSSION 463

5.1. Tectonic models 464

5.1.1. Tonian and/or Cryogenian passive margin 465

During Tonian and/or Cryogenian, rifting affects the West African Craton (WAC). The precise timing of 466

this event is poorly constrained. Undated rift-related doleritic and basaltic intrusive rocks intrude the 467

Paleoproterozoic basement rocks of the WAC and the Taghdout Group platform sedimentary rocks at 468

about this time (El Aouli et al., 2001; Thomas et al., 2004; Gasquet et al., 2008). Without quantitative 469

age constraints on the timing of platform sedimentation, Thomas et al. (2004) suggest the time of 470

passive margin formation between about 800 and 700 Ma, and Bouougri and Saquaque (2004) place 471

it between about 800 and 750 Ma. Gasquet et al. (2008) place the time of deposition of the Taghdout 472

Group at between about 1000 and 880 Ma by comparison with the Char and Atar groups of the 473

Taoudenni basin. Recently, Youbi et al. (2013) suggest that the Taghdout Group may be equal to or 474

older than 1.75 Ga. However, these ages have been obtained on dykes which intrude the 475

Paleoproterozoic rocks, not the Taghdout Group. 476

5.1.2. Cryogenian arc ophiolite genesis 477

A subduction zone and volcanic arc formed along the margin of the WAC, creating the Iriri arc of 478

Thomas et al. (2002, 2004), after the development of the early Neoproterozoic passive margin 479

(Taghdoud Group). The polarity of this first Neoproterozoic period of subduction has been a matter of 480

debate (Ennih and Liégeois, 2001; Hefferan et al., 2000; Gasquet et al., 2005, 2008), but north-dipping 481

subduction is now generally accepted (Saquaque et al., 1989; Saquaque, 1992; Hefferan et al., 2000; 482

Soulaimani et al., 2006; Benziane, 2007; Gasquet et al., 2008; Bousquet et al., 2008; El Hadi et al., 483

2010) and the present-day deep structure supports the hypothesis of a north-dipping subduction zone 484

(Soulaimani et al., 2006) during the initial stages of Pan-African tectonics. Relict early high-T low-P 485

metamorphism was probably associated with subduction, and may have reached blueschist facies 486

conditions (Hefferan et al., 1992), although accurate assessment of P-T conditions is still debated 487

(Bousquet et al., 2008; El Hadi et al., 2010). 488

Modern dates for oceanic crust and ophiolite formation range from about 760 to 740 Ma in the Sirwa 489

inlier (Thomas et al., 2004; Samson et al., 2004) to about 700 Ma in the Bou Azzer–El Graara inlier (El 490

Hadi et al., 2010). Granitoids and metagabbro formed juvenile crust at this time, with Nd and Hf 491

isotopic data indicating a depleted-mantle source with limited to no interaction with WAC source 492

material in the Sirwa (Samson et al., 2004), and Bou Azzer inliers (D’Lemos et al., 2006). The 493

tectonics may have involved an extensional fore-arc (Naidoo et al., 1991, 1993; El Hadi et al., 2010) or 494

volcanic arc setting (Thomas et al., 2004). 495

The onset of collisional deformation is referred to as phase 1 of Pan-African orogenesis (PA1). 496

Obduction of ophiolite fragments onto the margin of the WAC was associated with arc-continent 497

collision, and took place sometime after the ages of ophiolite-related magmatism, or after about 750-498

700 Ma. D’Lemos et al. (2006) suggest that the timing of this deformation occurred between 750 and 499

700 Ma and was accompanied by dextral transpression and greenschist to amphibolite facies 500

metamorphism. El Hadi et al. (2010) place the timing of obduction of the Bou Azzer ophiolite to after 501

the age of the metagabbro there at about 700 Ma. There is still a question as to whether ophiolite 502

obduction took place during PA1 or PA2 times (i.e. Samson et al., 2004). In the Bou Azzer–El Graara 503

inlier, calc-alkaline granodiorite and quartz diorite, dated at 650-646 Ma, are syn- to post-tectonic with 504

respect to the second period of Pan-African orogenesis (PA2), arc-continent accretion, and related 505

greenschist facies metamorphism. Thomas et al. (2002) suggest that the ophiolite obduction took 506

place at about 660 Ma based on a U–Pb SHRIMP age of metamorphic overgrowths on zircon from the 507

Iriri Migmatite. Villeneuve and Cornée (1994) suggest that it occurred between about 685 and 660 Ma, 508

and Gasquet et al. (2005, 2008) place the timing of obduction at about 690-660 Ma. 509

Late to syn-tectonic calc-alkaline arc-related plutonism produced granodiorites to quartz diorites dated 510

in this study at about 650-645 Ma. Other ages place the time of this plutonism to as young as about 511

640-630 Ma in the Bou Azzer–El Graara inlier (Inglis et al., 2005; El Hadi et al., 2010; Walsh et al., 512

2012). Older ages occur in the Saghro inlier and range from about 677 to 645 Ma (Massironi et al., 513

2007; Schiavo et al., 2007). Slab break-off and lithospheric delamination may have provided the 514

source for the supra-subduction calc-alkaline plutons during this second period of Pan-African 515

magmatism (Benziane, 2007; Gasquet et al., 2008). 516

5.1.3. Ediacaran volcanism 517

The final stages of Pan-African tectonism produced the large volume of Ediacaran volcanic and sub-518

volcanic plutonic rocks which occupy the majority of the exposed rocks in the western and eastern 519

Anti-Atlas in the Ifni, Kerdous, Igherm, Agadir-Melloul, Sirwa, Bou Azzer, Saghro, and Ougnat inliers. 520

Although this event may have involved the formation of a continental volcanic arc along the northern 521

margin of the WAC (Benziane, 2007), Gasquet et al. (2005, 2008) argue that there was no arc. 522

Extension, rifting, block faulting, and weak folding in a post-collisional setting occurred during 523

transpressive to transtensional deformation (Thomas et al., 2002, 2004; Gasquet et al., 2005, 2008). 524

Continued high-K calc-alkaline magmatism post-dated earlier Cryogenian Pan-African deformation 525

and metamorphism and began at about 615 Ma (Thomas et al., 2004). 526

This period has long been considered post-collisional with respect to the arc-continental collision of the 527

PA1 and PA2 Pan-African events. Chemically, the volcanic and plutonic rocks plot in the field for 528

volcanic arc granite with some overlap into the field for within plate granite (Walsh et al., 2012); this 529

overlap zone also characterizes post-collisional granites (Pearce, 1996). New geochemical data 530

corroborate earlier findings (i.e. Thomas et al., 2002; El Baghdadi et al., 2003; Gasquet et al., 2005, 531

2008) and show high-K calc-alkaline to shoshonitic plutonism and volcanism. High-K calc-alkaline 532

granitic rocks are likely to come from a post-collisional tectonic setting (Liégeois et al., 1998; Frost et 533

al., 2001). Liégeois et al. (1998) note that high-K calc-alkaline and shoshonitic magmatism is 534

characteristic of post-collisional settings at the end of orogenic events, with more evolved granitic 535

rocks plotting within the fields for A-type granitoids. According to Walsh et al. (2012), most of the 536

Ediacaran granites and felsic volcanic rocks largely plot in the fields for I- to S-type granites with 537

limited overlap into the A-type field. A finding also supports by El Baghdadi et al. (2003). Thomas et al. 538

(2002) reported similar chemistry for the Assarag and Toufghrane Suite plutonic rocks and the 539

Ouarzazate volcanic rocks in the Sirwa inlier, and attributed the chemical signatures to a rifted, post-540

collisional setting without subduction where the compositions were derived largely from the earlier 541

subduction related arc rocks. Gasquet et al. (2005, 2008) refer to this period of late Ediacaran 542

magmatism as a metacratonic event with igneous activity attributed to asthenospheric rise beneath a 543

modified portion of the WAC, without subduction. El Baghdadi et al. (2003) and Benziane (2007) both 544

favor a model involving subduction of oceanic crust, with Benziane (2007) suggesting polarity flip from 545

northward to southward subduction. Walsh et al. (2012) suggest that this southward subduction may 546

have occurred beneath the crust of the WAC, in agreement with more traditional models of high-K 547

calc-alkaline magmatism beneath thickened continental crust in a setting comparable to an Andean-548

type active margin (Dewey and Burke, 1973; Thompson et al., 1984; Wilson, 1989). 549

5.2. Cryogenian oceanic and volcanic-arc sequences 550

5.2.1. No eburnean basement in the Bou Azzer-El Graara inlier 551

The meta-igneous units and leucogranites of the Asssif n’Bougmmane gneissic complex have been 552

previously considered to be c. 2 Ga Eburnean basement (Choubert, 1963; Leblanc, 1981; Saquaque 553

et al., 1992). This interpretation was made on the basis of lithological and deformational similarities to 554

WAB basement units exposed to the west of the Bou Azzer-El Graara inlier (e.g. Zenaga inlier). 555

D’Lemos et al. (2006) demonstrate that the protoliths of the gneissic and igneous basement rocks 556

within the Tazigzaout complex (part of the Bou Azzer-El Graara inlier) were emplaced at c. 755-557

750 Ma, and recorded transpressive deformation after c. 750 Ma and before 700 Ma. Our U–Pb zircon 558

data on the gneissic rocks from Bou Azzer, Oumlil and assif n’Bougmmane areas confirm and precize 559

these results. Effectively, an Eburnean basement is not exposed in the Bou Azzer-El Graara inlier. 560

Protoliths of the gneisses from Bou Azzer and assif n’Bougmmane areas were emplaced at c. 755-561

745 Ma like in Tazigzaout area. Meta-igneous gneisses within the Bou Azzer-El Graara inlier were 562

emplaced at c. 755-745 Ma, and recorded transpressive deformation after c. 745 Ma and before 563

700 Ma as suggested by D’Lemos et al. (2006). 564

Similar emplacement ages at 755-745 Ma have been observed in the Sirwa inlier. Medium to high 565

grade metamorphic rocks comprising gneisses with interlayered migmatites are thought to represent 566

the roots of an arc complex estimated to be 743 + 14 Ma in age, based on a SHRIMP U–Pb zircon 567

date from the Iriri migmatite (Thomas et al., 2002). 568

5.2.2. Age of the Bou Azzer ophiolite and neighbouring arc-volcanic rocks 569

According to Bodinier et al. (1984) and El Hadi et al. (2010), the Bou Azzer oceanic crust and the 570

adjacent volcanic arc rocks of the Tichibanine Group might have been formed in connection. 571

Saquaque et al. (1989) pointed out that the Bou Azzer ophiolite is in fault contact with volcanic-arc 572

rocks of Tichibanine Group. Thus, the relative displacements between the ophiolite and the arc cannot 573

be established. On the other hand, Saquaque et al. (1989), Hefferan et al. (2002) and Bousquet et al. 574

(2008) have suggested that a great part of the oceanic terrane lacks geometric coherence and must 575

be considered as a melange. Ahmed et al. (2005) interpreted the mantle section of the Bou Azzer 576

ophiolite as a supra-subduction setting, either representing the mantle wedge or the sub-arc mantle. 577

These conclusions suggest a close connection between the Bou Azzer ophiolite and the Tichibanine 578

Group; they might have formed contemporaneously or the volcanic arc might be younger. 579

We interpret our U-Pb zircon data as demonstrating that the volcanic rocks of the Tichibanine Group 580

were emplaced at c. 770-760 Ma. The ages of this volcanic arc activity is similar than the ophiolites of 581

the Sirwa inlier. Samson et al. (2004) obtained two emplacement ages of 761 ± 2 Ma and 762 ± 2 Ma 582

on plagiogranites of the N’qob and Tasriwine small highly tectonized ophiolitic bodies which belong to 583

the Sirwa inlier. From extensive mapping and structural studies, Admou (2000) considered the Sirwa 584

inlier as a westward extension of the Bou Azzer-El Graara inlier. The proximity of the Tasriwine and 585

N’qob ophiolites and the larger Bou Azzer ophiolite to the east raises the possibility that they may all 586

simply be dismembered pieces of a single larger ophiolite body. Structurally, the Tasriwine ophiolite 587

and the Tichibanine arc have an outer position relative to the Iriri migmatite and the assif 588

n’Bougmmane gneissic complex, which are characterized by emplacement ages bracketed between 589

755 and 745 Ma. This relationship suggests the development of a back-arc domain between the 590

Tichibanine arc and the WAC, and closure of this back-arc domain before the Tichibanine arc-591

continent collision. 592

In the Bou Azzer inlier, the main ophiolite outcrop is characterized by small aplitic bodies crosscutting 593

cumulative gabbros, but it is not yet clear whether these bodies are younger leucogranitic intrusions, 594

possibly related to the quartz diorites of the inlier, or true plagiogranites within the ophiolitic succession 595

(Samson et al., 2004). These aplitic bodies have a granodioritic composition, and a foiled contact with 596

crosscutting cumulative gabbro. This contact suggests contemporaneous ages between the 597

granodioritic intrusion and cumulative gabbro. Moreover, low U contents of zircon from sample 598

AADG12 (Table 2), and major and trace elements chemistry from granodioritic intrusion are typical of 599

oceanic material (Admou et al., 2013). We interpret our U-Pb zircon data as demonstrating that the 600

Bou Azzer granodioritic intrusion and cumulative gabbro were emplaced at c. 660 Ma. Recently, El 601

Hadi et al. (2010) obtained an age of 697 ± 8 Ma on a metagabbro of the ophiolite. This metagabbro 602

do not outcrop in the main exposure of the Bou Azzer ophiolite, but south of the meta-igneous and 603

meta-sedimentary rocks of the Tamaliout area. U-Pb geochronological data of El Hadi et al. (2010) 604

and our study clearly establish a gap of at least 60 Ma between the Bou Azzer ophiolite and the 605

magmatic activities of the Tasriwine and N’qob ophiolites in the Sirwa inlier (760-770 Ma), or the 606

Tichibanine volcanic arc in the Bou Azzer-El Graara inlier (760-770 Ma). El Hadi et al. (2010) 607

suggested that the Bou Azzer oceanic crust might have been formed in connection with the adjacent 608

volcanic-arc (Tichibanine Group), or the volcanic-arc might be younger and have evolved over the 609

previous oceanic crust of Bou Azzer. We demonstrate that magmatic activities of the Bou Azzer 610

ophiolite and the Tichibanine Group were not contemporaneous. The Tichibanine Group is clearly 611

older than the Bou Azzer oceanic crust. They have not been formed in connection, and the relative 612

displacement of these two terranes has probably been important. 613

In Sirwa and Bou Azzer-El Graara inliers, Cryogenian rocks are characterized by two distinct activities 614

with juvenile source (such as ophiolite and intra-oceanic arc) dated at c. 770-760 Ma and at 755-615

745 Ma. Thus, the Pan African Cryogenian rocks represent an accretionary orogen that formed along 616

the leading edge of a dispersing continent, and that evolved in response to peri-supercontinental 617

subduction systems from 770 to 660 Ma (peripheral orogen of Murphy and Nance, 1991). According to 618

geochronological data (D’Lemos et al., 2006; this study), two distinct accretionary events might be 619

observed. The first event, characterized by the accretion on the continental margin of ophiolitic and 620

volcanic-arc sequences dated at c. 755-745 Ma, occurs prior 700 Ma. This first arc-continent collision 621

corresponds to the first period of Pan-African orogenesis (PA1). A second accretionary event may 622

occur at c. 650-640 Ma, and is characterized by the obduction of the Bou Azzer ophiolite, and 623

corresponds to the second period of Pan-African orogenesis (PA2). High-resolution ages of rocks of 624

SSZ ophiolites comprising accreted arc terranes provide details of the timing of the onset of intra-625

oceanic subduction and hence place important constraints in relevant tectonic reconstructions. 626

Arc-continent collision (Dewey, 2005; Brown et al., 2006) involves the collision of a volcanic arc with a 627

continental margin. In many places, ophiolite fragments are now recognized as components of island 628

arc complexes that formed in distinct tectonic basins over brief periods of time (Hawkins, 2003; 629

Pearce, 2003 and references therein). Such ophiolite fragments that display supra subduction zone 630

(SSZ) affinities are characteristic of many arc-continent collisional terranes; and trace element 631

geochemistry of rocks of many SSZ ophiolites are consistent with their formation in the upper plate at 632

a convergent plate boundary (Alabaster et al., 1982; Pearce et al., 1984) analogous to the forearc of 633

modern island (i.e. intra-oceanic) arc systems (e.g., Miyashiro, 1973). The obduction of the ophiolitic 634

fragments onto the two Sirwa and Bou Azzer-El Graara inliers of the WAC presumably occurred during 635

the accretion of the ophiolite-island arc complexes. Determining precisely the timing of these 636

accretionary events remains important as the precise determination of the formation of the ophiolites 637

themselves. The fact that the majority of SSZ ophiolites are emplaced within ~10 Ma of their formation 638

via arc-continent collision (Dewey, 2003) suggests a direct link between SSZ ophiolite formation and 639

intra-oceanic arc-continent collision. 640

5.3. Ediacaran volcano-sedimentary sequences 641

In the Bou Azzer-El Graara inlier, Ediacaran sedimentary, volcano-sedimentary and volcanic rocks of 642

the Ouarzazate Supergroup have been subdivided in three groups, Bou Lbarod, Tiddiline and 643

Ouarzazate. 644

The Bou Lbarod Group unconformably overlies the Tichibanine Group, and is unconformably overlain 645

by the Ouarzazate Group. The Bou Lbarod Group is crosscutted by dioritic intrusions dated at 646

625 ± 8 Ma. This U-Pb zircon age suggests that the Bou Lbarod Group may be correlated with the 647

Saghro Group. In the Saghro massif, the Saghro Group corresponds to a great thickness of siliciclastic 648

turbidites. These deposits alternated with basaltic flows having the signatures of rift tholeiites and 649

alkaline intraplate basalts (Fekkak et al., 2001). U-Pb ages of detrital zircon recently realized (Liégeois 650

et al., 2006) show that the Saghro Group was deposited between 630 and 610 Ma. Moreover, the 651

zircon became younger toward the top of the group, suggesting that the Saghro Group was deposited 652

during the uplift of the WAC and the beginning of the Ediacaran magmatism that culminated during the 653

Ouarzazate Group (Gasquet et al., 2008). 654

The Tiddiline Group, which outcrops in southern and northern basins part of the Bou Azzer ophiolite, 655

consists of coarsening-upwards sequences of siltstones, sandstones and conglomerates with local 656

ignimbrites. Hefferan et al. (1992) suggested that this group has been deposited within small syn-657

orogenic basins, and documented the destruction of the relict forearc basin as a result of the collision 658

of a Proterozoic volcanic arc to the north with the WAC to the south. In this study, an ignimbrite and a 659

trachytic dyke have been dated at 606 ± 4 Ma and 606 ± 5 Ma. In the western edge of the Bou Azzer-660

El Graara inlier, folded ignimbrite (606 ± 4 Ma) of the Tiddiline Group is unconformably overlain by 661

ignimbrite (567 ± 5 Ma) of the Ouarzazate Group. The deformation which affected the Tiddiline Group 662

is bracketed between 606 and 567 Ma. These new U-Pb zircon ages suggest that the Tiddiline Group 663

may be correlated with the Bou Salda and Anzi Groups, which are volcano-sedimentary sequences 664

with local rhyolitic lavas. In the Sirwa region, the sedimentary and volcanic rocks of the Bou Salda 665

Group occur in narrow fault-bound grabens, and tend to have high tectonic dips of 70° and vertical. It 666

is suggested that the grabens were strike-slip pull-apart basins (Thomas et al., 2004). 667

The 580 Ma old (U-Pb zircon) Bleïda granodiorite which cross-cuts the regional fabric provides a firm 668

constraint on the latest stage of transpressive brittle movements in the Bou Azzer-El Graara inlier 669

(Inglis et al., 2004). The relationships between the Tiddiline Group and the Bleïda granodiorite are not 670

directly observed in the field, but Hefferan et al. (1992) report within conglomerates of upper member 671

of the Tiddiline Group occurrence of cobbles and boulders of granodiorite probably coming from the 672

Bleïda granodiorite. Recent mapping permit to observe that these conglomerates are not stratified, 673

and unconformably overlain typical stratified conglomerates of the Tiddiline Group. Such 674

conglomerates rich in boulders of Cryogenian and early Ediacaran lithofacies are typically observed at 675

the base of the Ouarzazate Group. Then, boulders of the Bleïda granodiorite are not within the upper 676

conglomerate member of the Tiddiline Group, but within the base of the Ouarzazate Group. 677

A diorite overlain by conglomerates of the base of the Ouarzazate Group has been dated at 678

586 ± 15 Ma (this study). This new age is closely similar to the ages (579.4 ± 1.2 Ma and 679

578.5 ± 1.2 Ma) of the Bleïda granodiorite (Inglis et al., 2004). Regional deformation observed in the 680

Tiddiline Group was completed before c. 585-580 Ma, and followed by an erosional phase before the 681

deposition of the Ouarzazate Group over Bleïda type granodiorites. 682

The Ouarzazate Group consists of detrital deposits, such as chaotic breccia polygenic conglomerates 683

and sandstones, and abundant intermediate to felsic volcanic rocks. This magmatic activity is calc-684

alkaline to shoshonitic with moderately potassic andesites, high-potassic dacites and rhyolites. Felsic 685

volcanics were dated in several inliers, and the ages range from 580 ± 12 to 543 ± 9 Ma (Charlot, 686

1982; Mifdal et al., 1982; Mifdal and Peucat, 1985; Aït Malek et al., 1998; Levresse, 2001; Cheilletz et 687

al., 2002; Thomas et al., 2002; Walsh et al., 2002; Gasquet et al., 2005). The Ouarzazate Group has 688

not recorded the Pan-African deformation, but was deposited on highly variable basement topography. 689

Rapid variations in thickness of the Ouarzazate Group suggest that it was deposited during active 690

tectonics. 691

The obtained ages on rhyolitic welded tuffs are similar 566 and 567 Ma, but in the Bou Azer inlier this 692

age is observed at the base of the Ouarzazate Group, and at the top of the volcanic activity in the 693

Saghro massif. In the Bou Azzer inlier, the magmatic activity is bracketed between 566 and 541 Ma, 694

the age of the base of the jbel Boho alkaline magmatism. By contrast, in the western edge of the 695

Saghro massif, the magmatic activity is mainly older than 567 Ma, older than in the Bou Azzer-El 696

Graara inlier. According to old authors, Ediacaran granites and felsic volcanic rocks are related to: (i) a 697

rifted, post-collisional setting without subduction (Thomas et al., 2002); (ii) a metacratonic event with 698

igneous activity attributed to asthenospheric rise beneath a modified portion of the WAC (Gasquet et 699

al., 2008); or (iii) a subduction of oceanic crust beneath thickened continental crust (El Baghdadi et al., 700

2003; Benziane, 2007; Walsh et al., 2012). 701

We suggest a new model with: (i) a subduction beneath the thickened continental crust of the WAC 702

during lower Ediacaran; (ii) the cessation of the subduction between 580-575 Ma related to a ridge-703

trench collision; and (iii) an upper Ediacaran felsic magmatism attributed to asthenospheric rise, 704

related to the development of a slab-window. The transition between the early Ediacaran subduction 705

magmatism and the upper Ediacaran felsic magmatism was locally accompanied by deformation, but 706

no evidence exists for a regional orogenesis, crustal shortening, and crustal thickening and uplift 707

characteristic of continental collision zones during Ediacaran. Instead, deformation is localized and 708

resulted only in the inversion of some of the lower Ediacaran pull-apart basin successions, such as the 709

Tiddiline Group deposits. 710

To account for such a tectonic transition in the apparent absence of a major collisional event, we 711

propose that the lower Ediacaran subduction was terminated as a result of transform activity. In their 712

model, the main phase of lower Ediacaran magmatism at c. 630-590 Ma occurred as the result of 713

oblique subduction, leading to the development of an extensional magmatic arc and a variety of 714

volcanic arc basins. Subsequently, the interaction of a continental margin transform system with the 715

subduction zone resulted in the termination of subduction, the structural inversion of some pull-apart 716

basins, and the formation of new rift- and wrench-related basins in the interval c. 580-550 Ma. We 717

propose ridge-trench collision as a mechanism for the transition, to account for the cessation of arc 718

volcanism, the apparent reversal of kinematics on major basin-bounding faults, and the development 719

of silicic magmatism in a transtensional context. The ridge-trench collision product the initiation of a 720

slab window and an upwelling of the asthenospheric mantle. The upper Ediacaran magmatism is 721

attributed to asthenospheric rise beneath WAC or accreted Neoproterozoic arcs. A similar model has 722

been proposed by Nance et al. (2008) to explain the evolution of Ediacaran Avalonian subduction. 723

5.4. Ediacaran-Cambrian transition volcano-detritic groups 724

In the Anti-Atlas, the Ediacaran-Cambrian transition is recognized throughout a carbonate-725

dominated succession (Adoudou Formation) that unconformably overlies the Ouarzazate Group. 726

Volcanic ashes and flows also occur interbedded with the Adoudou strata (Choubert and 727

Faure-Muret, 1970). One source for these ashes is preserved in the jbel Boho volcanic 728

complex (Choubert, 1952). An early U/Pb date of 529 ± 5 Ma from the Boho volcano (Ducrot 729

and Lancelot, 1977) suggests that deposition of the uppermost part of the Adoudou 730

Formation took place in the earliest Cambrian. Recently, a trachytic sill at the base of 731

the Adoudou Formation gives an age of 531 ± 5 Ma (Gasquet et al., 2005). 732

The analyses obtained on a pyroclastic breccia at the base of the Adoudou Formation give 733

several cristallisation ages. The younger zircons gave an age of 541 ± 6 Ma, the last registred 734

volcanic activity, the pyroclastic breccia emplacement. The transition between the Ouarzazate Group 735

and the Adoudou Formation outlines in the Bou Azzer-El Graara inlier the Ediacaran-Cambrian 736

transition. Several volcanic episodes were dated around 560, 580 and 630 Ma. Moreover, a zircon 737

gives an inherited age of 2795 ± 10 Ma. Eburnian outcrops have not been observed in the Bou Azzer-738

El Graara inlier, but such age suggests the presence at depth of the Eburnian basement as previously 739

identified in other inliers of the eastern Anti-Atlas (Gasquet et al., 2008). 740

6. CONCLUSIONS 741

New U–Pb SHRIMP zircon ages from rocks of the Bou Azzer–El Graara inlier provide new constraints 742

on the Neoproterozoic evolution of the Anti-Atlas. We herein propose the following distinct orogenic 743

events: (i) 770-760 Ma Tasriwine-Tichibanine orogeny with rollback of the subducting oceanic plate, 744

leading to the formation of several back-arc basins; (ii) 755-695 Ma Iriri-n’Bougmmane orogeny 745

involving a first episode of north-dipping subduction and rollback of back-arc basin lithosphere; (iii) 746

660-640 Ma Bou-Azzer orogeny involving a second episode of north-dipping subduction and rollback 747

of back-arc basin lithosphere. This second episode is characterized by the total closure of the back-arc 748

basin domain, and collision of the 770-760 Ma Tasriwine-Tichibanine arc with the margin of the WAC. 749

With the Ediacaran ages, we propose the following distinct orogenic events: (iv) 630-585 Ma peri-750

Gondwanan orogeny resulting from subduction beneath the amalgamated West African Craton; (v) 751

580-575 Ma ridge-trench collision with the cessation of the subduction; (vi) 575-550 Ma Ouarzazate 752

magmatic event attributed to asthenospheric rise related to the development of a slab-window. 753

Acknowledgments 754

Support for this work was provided by the Ministère de l’Energie, des Mines, de l’Eau et de 755

l’Environnement, Direction du Développement Minier, Division du Patrimoine Géologique, Rabat, 756

Morocco under contract 17-2005/DG under the Plan National de Cartographie Géologique (PNCG). 757

758

759

References 760

Admou, H., 2000. Structuration de la paléosuture ophiolitique panafricaine de Bou Azzer-Siroua (Anti-761

Atlas central, Maroc). Ph.D. Dissertation. Université Cadi Ayyad, Marrakech, Maroc, 201 pp. 762

Admou, A., Fekkak, A., Razin, Ph., Egal, E., Youbi, N., Soulaimani, A., Blein, O., Baudin, T., 763

Chèvremont, Ph. (2013) Carte géologique au 1/50 000), feuille Aït Ahmane. Notes et Mémoires 764

Serv. Géol. Maroc 533, 154. 765

Aït Malek, H., Gasquet, D., Bertrand, J.-M., Leterrier J., 1998. Géochronologie U-Pb sur les 766

granitoïdes éburnéens et panafricains dans les boutonnières protérozoïques d'Igherm, du Kerdous 767

et du Bas Drâa (Anti-Atlas occidental, Maroc). Comptes Rendus de l’Académie des Sciences 327, 768

819-826. 769

Barbey, P., Oberli, F., Burg, J.-P., Nachit, H., Pons, J., Meier, M., 2004. The Palaeoproterozoic in 770

western Anti-Atlas (Morocco): a clarification. Journal of African Earth Sciences 39, 239-245. 771

Benziane, F., 2007. Lithostratigraphie et évolution géodynamique de l’Anti-Atlas (Maroc) du 772

Paléoprotérozoïque au Néoprotérozoïque: exemples de la boutonnière de Tagragra de Tata et du 773

Jbel Saghro. PhD thesis. Université de Savoie CISM, Chambéry, France, 320 pp. 774

Beraaouz, E.H., Ikenne, M., Mortaji, A., Madi, A., Lahmam, M., Gasquet, D., 2004. Neoproterozoic 775

granitoïds associated with the Bou-Azzer ophiolitic melange (Anti-Atlas, Morocco. evidence of 776

adakitic Magmatism in an arc segment at the NW edge of the West-African craton. Journal of 777

African Earth Sciences 39, 285-293. 778

Bodinier, J.L., Dupuy, C., Dostal, J., 1984. Geochemistry of Precambrian ophiolites from Bou Azzer, 779

Morocco: Contributions to Mineralogy and Petrology 87, 43-50. 780

Boudda, A., Choubert, G., Faure-Muret, A., 1979. Essai de stratigraphie de la couverture sédimentaire 781

de l’Anti-Atlas : Adoudounien-Cambrien inférieur. Notes et Mémoires du Service Géologique du 782

Maroc 271, 96 p. 783

Bouougri, E.H., Saquaque, A., 2004. Lithostratigraphic framework and correlation of the 784

Neoproterozoic northern West African Craton passive Margin sequence (Siroua–Zenaga–785

Bouazzer Elgraara Inliers, Central Anti-Atlas, Morocco): an integrated approach. Journal of African 786

Earth Sciences 39, 227-238. 787

Bousquet, R., El Mamoun, R., Saddiqi, O., Goffé, B., Möller, A., Madi, A., 2008. Mélanges and 788

Ophiolites during the Pan-African Orogeny: the Case of the Bou-Azzer Ophiolite Suite (Morocco). 789

Special Publications 2008, 297. Geological Society, London, pp. 233-247. 790

Cahen, L., Snelling, N.J., Dalhal, J., Vail, J.R., 1984. The geochronology and evolution of Africa. 791

Claredon Press, Oxford. 792

Chalot-Prat, F., Gasquet, D., Roger, J., Hassenforder, B., Chèvremont, P., Baudin, T., Razin, P., 793

Benlakhdim, A., Benssaou, M., Mortaji, A., 2001. Carte géologique du Maroc au 1/50 000. Feuille 794

de Sidi Bou’Addi avec Mémoire explicatif. Notes et Mémoires du Service Géologique du Maroc 795

414 et 414 bis, 84 p. 796

Cheilletz, A., Levresse, G., Gasquet, D., Azizi Samir, M.R., Zyadi, R., Archibald, D.A., 2002. The Imiter 797

epithermal deposit (Morocco): new petrographic, microtectonic and geochronological data. 798

Importance of the Precambrian–Cambrian transition for Major precious metals deposits in the Anti-799

Atlas. Mineralium Deposita 37, 772-781. 800

Choubert, G., 1952. Histoire géologique du domaine de l’Anti-Atlas. In: Géologie du Maroc. Notes et 801

Mémoires du Service Géologique du Maroc 100, 75-194. 802

Choubert, G., 1953a. Histoire géologique du domaine de l’Anti-Atlas. Notes et Mémoire de Service 803

géologique du Maroc 100, 1-77. 804

Choubert, G., 1953b. Le Précambrien III et le Géorgien de l’Anti-Atlas. Notes et Mémoire de Service 805

géologique du Maroc 103, 7-39. 806

Choubert, G., 1963. Histoire géologique du Précambrien de l'Anti-Atlas. Notes et Mémoires du Service 807

Géologique du Maroc 162, 443 p. 808

Claoué-Long, J. C., Compston, W., Roberts, J., Fanning, C. M., 1995. Two Carboniferous ages: a 809

comparison of SHRIMP zircon dating with conventional zircon ages and 40

Ar/39

Ar analysis. 810

Geochronology Time Scales and Global Stratigraphic Correlation. SEPM Special Publication 54, 811

1-21. 812

Cocherie, A., Robert, M., 2007. Direct measurement of lead isotope ratios in low concentration 813

environmental samples by MC-ICPMS and multi-ion counting. Chemical Geology 243, 90-104. 814

Cocherie, A., Robert, M., 2008. Laser ablation coupled with ICP-MS applied to U–Pb zircon 815

geochronology: a review of recent advances. Gondwana Research 14, 597-608. 816

D’Lemos, R.S., Inglis, J.D., Samson, S.D., 2006. A newly discovered orogenic event in Morocco : 817

Neoproterozoic ages for supposed Eburnean basement of the Bou Azzer inlier, Anti-Atlas 818

Mountains. Precambrian Research 147, 65-78. 819

Debrenne, F., Debrenne, M., 1995. Archaeocyathid fauna of the lowest fossiliferous levels of Tiout 820

(Lower Cambrian, Southern Morocco). Geological Magazine. 115, 101-119. 821

Dewey, J., Burke, K., 1973. Tibetan, Variscan, and Precambrian basement reactivation; products of 822

continental collision. Journal of Geology 81, 683-692. 823

Ducrot, J., 1979. Datation à 615 Ma de la granodiorite de Bleïda et conséquences sur la chronologie 824

des phases tectoniques, métamorphiques et Magmatiques pan-africaines dans l’Anti-Atlas 825

Marocain. Bulletin Société Géologique France 7, 495-499. 826

Ducrot, J., Lancelot, J.R., 1977. Problème de la limite Précambrien-Cambrien : étude radio-827

chronologique par la méthode U-Pb sur zircons du volcan du Jbel Boho (Anti-Atlas Marocain). 828

Canadian Journal of Earth Sciences 14, 2771-2777. 829

El Aouli, E.H., Gasquet, D., Ikenne, M., 2001. Le magmatisme basique de la boutonnière d’Igherm 830

(Anti-Atlas occidental, Maroc); un jalon des distensions neoproterozoiques sur la bordure nord du 831

craton ouest-africain. Bulletin de la Société Géologique de France 172 (3), 309-317. 832

El Baghdadi, M., El Boukhari, A., Jouider, A., Benyoucef, A., Nadem, S., 2003. Calc-alkaline arc I-type 833

granitoid associated with S-type granite in the Pan-African belt of eastern Anti-Atlas (Saghro and 834

Ougnat, South Morocco). Gondwana Research 6 (4), 557-572. 835

El Hadi, H. Simancas, J.F., Martínez-Poyatos, D., Azor, A., Tahiri, A., Monterod, P., Fanning, C.M., 836

Bea, F., González-Lodeiro, F., 2010. Structural and geochronological constraints on the evolution 837

of the Bou Azzer Neoproterozoic ophiolite (Anti-Atlas, Morocco). Precambrian Research 182, 1-838

14. 839

Ennih, N., Liégeois, J.P., 2001. The Moroccan Anti-Atlas: the West African craton passive margin with 840

limited Pan-African activity. Implications for the northern limit of the craton. Precambrian Research 841

112, 289-302. 842

Fekkak, A., Pouclet, A., Ouguir, H., Ouazzani, H., Badra, L., Gasquet, D., 2001. Géochimie et 843

signification géotectonique des volcanites du Cryogénien inférieur du Saghro (Anti-Atlas oriental, 844

Maroc). Geodinamica Acta 13, 1-1. 845

Frost, B.R., Barnes, C.G., Collins, W.J., Arculus, R.J., Ellis, D.J., Frost, C.D., 2001. A geochemical 846

classification for granitic rocks. Journal of Petrology 42 (11), 2033-2048. 847

Gasquet, D., Chevremont, P., Baudin, T., Chalot-Prat,

F., Guerrot, C., Cocherie, A., Roger, J., 848

Hassenforder, B., Cheilletz, A., 2004. Polycyclic Magmatism in the Tagragra and Kerdous-849

Tafeltast inliers (Western Anti-Atlas, Morocco). Journal of African Earth Sciences 39, 267-276. 850

Gasquet, D., Levresse, G., Cheilletz, A.. Azizi-Samir, M.R., Mouttaqi, A., 2005. Contribution to a 851

geodynamic reconstruction of the Anti-Atlas (Morocco) during Pan-African times with the 852

emphasis on inversion tectonics and metallogenic activity at the Precambrian-Cambrian transition. 853

Precambrian Research 140, 157-182. 854

Gasquet, D., Ennih, N., Liégeois, J-P., Soulaimani, A., Michard, A., 2008. The Panafrican belt, in: 855

Michard, A., Saddiqi, O., Chalouan, A., Frizon de Lamotte, D. (Eds.), Continental Evolution: The 856

Geology of Morocco. Structure, Stratigraphy, and Tectonics of the Africa-Atlantic-Mediterranean 857

Triple Junction. Springer Verl., Berlin, Heidelberg, pp. 33-64. 858

Hefferan, K.P., Karson, J.A., Saquaque, A., 1992. Proterozoic collisional basins in a Pan-African 859

suture zone, Anti-Atlas mountains, Morocco. Precambrian Research 54, 295-319. 860

Hefferan, K.P., Admou, H., Karson, J.A., Saquaque, A., 2000. Anti-Atlas (Morocco) role in 861

Neoproterozoic Western Gondwana reconstruction. Precambrian Research 103, 89-96. 862

Hefferan, K.P., Admou, H., Hilal, R., Karson, J.A., Saquaque A., Juteau, T., Bohn, M., Samson, S.D., 863

Kornprobst, J., 2002. Proterozoic blueschist-bearing mélange in the Anti-Atlas Mountains, 864

Morocco. Precambrian Research 118, 179-194. 865

Houzay, J.P., 1979. Empreintes attribuables à des méduses dans la série de base de l’Adoudounien 866

(Précambrien terminal de l’Anti-Atlas, Maroc). Géologie Méditerranéenne 6, 379-384. 867

Inglis, J.D., Samson, S., D’Lemos, R.S., Admou, H., 2003. Timing of regional greenschist facies 868

deformation in the Bou Azzer Inlier, Anti-Atlas: U–Pb constraints from syn-tectonic intrusions. First 869

meeting of IGCP 485, 1-2 December, El Jadida, Morocco, 40-42. 870

Inglis, J.D., MacLean, J.S., Samson, S.D., D’Lemos, R.S., Admou, H., Hefferan, K., 2004. A precise U-871

Pb zircon age for the Bleïda granodiorite, Anti-Atlas, Morocco: implications for the timing of 872

deformation and terrane assembly in the eastern Anti-Atlas. Journal of African Earth Sciences 39, 873

277-283. 874

Inglis, J.D., D’Lemos, R.S., Samson, S.D., Admou, H., 2005. Geochronological constraints on late 875

Precambrian intrusion, metamorphism, and tectonism in the Anti-Atlas Mountains. Journal of 876

Geology 113 (4), 439-450. 877

Kirshvink, J.L., Magaritz, M., Ripperdan, R.L., Zhuravlev, A.Yu., 1991. The Precambrian/Cambrian 878

boundary: Magnetostratigraphy and carbon isotopes resolve correlation problems between 879

Siberia, Morocco, and South China. GSA Today 1, 69-71. 880

Kröner, A., Todt, W., Hussein, I.M., Mansour, M., Rashwan, A.A., 1992. Dating of late Proterozoic 881

ophiolites in Egypt and the Sudan using the single grain zircon evaporation technique. 882

Precambrian Research 59, 15-32. 883

Landing, E., Bowring, S.A., Davidek, K.L., Westrop, S.R., Geyer, G., Heldmaier, W., 1998. Duration of 884

the Early Cambrian: U–Pb ages of volcanic ashes from Avalon and Gondwana. Canadian Journal 885

Earth Sciences 35, 329-338. 886

Latham, A., Riding, R., 1990. Fossil evidence for the location of the Precambrian/Cambrian boundary 887

in Morocco. Nature 344, 752-754. 888

Leblanc, M., 1975. Ophiolites précambriennes et gîtes arseniés de cobalt (Bou Azzer - Maroc). Ph.D. 889

Dissertation. Paris, France, Université de Paris VI, 329 pp. 890

Leblanc, M., 1976. Proterozoic oceanic crust at Bou Azzer. Nature 261, 34-35. 891

Leblanc, M., 1981. The late Proterozoic ophiolites of Bou Azzer (Morocco): evidence for Pan African 892

plate tectonics, in: Kroner A. (Ed.), Precambrian Plate Tectonics. Elsevier, Amsterdam, pp. 436-893

451. 894

Leblanc, M., Billaud, P., 1978. A volcano-sedimentary copper deposit on a continental Margin of upper 895

Proterozoic age; Bleïda (Anti-Atlas, Morocco). Economic Geology 73, 1101-1111. 896

Leblanc, M., Lancelot, J.R., 1980. Géodynamique du domaine panafricain (Précambrien terminal) de 897

l’Anti-Atlas (Maroc) à partir de données géologiques et géochronologiques. Canadian Journal 898

Earth Sciences 17, 142-155. 899

Leblanc, M., Moussine-Pouchkine, A., 1994. Sedimentary and volcanic evolution of a Neoproterozoic 900

continental Margin (Bleïda, Anti-Atlas, Morocco). Precambrian Research 70, 25-44. 901

Liégeois, J.P., Navez, J., Hertogen, J., Black, R., 1998. Contrasting origin of post-collisional high-K 902

calc-alkaline and shoshonitic versus alkaline and peralkaline granitoids; the use of sliding 903

normalization. Lithos 45, 1–28. 904

Liégeois, J.P., Fekkak, A., Bruguier, O., Errami, E., Ennih, N., Abstr. 2006. The Lower Ediacaran (630-905

610 Ma) Saghro group: an orogenic transpressive basin development during the early 906

metacratonic evolution of the Anti-Atlas (Morocco). In: IGCP485 4th meeting, Algiers. 907

Ludwig KR, 2008. Users manual for ISOPLOT/EX, version3.6. A geochronological toolkit for Microsoft 908

Excel. Berkeley Geochronology Center, Special Publication, 4. 909

Maacha, L., Azizi-Samir, M.-R., Bouchta, R., 1998. Gisements cobaltifères du district de Bou Azzer 910

(Anti-Atlas). Structure, minéralogie et conditions de genèse. Chronique de la Recherche Minière, 911

531-532, 65-75. 912

Magaritz, M., Kirschvink, J., Latham, A., Zhuravlev, A., Rozanov, A., 1991. Precambrian/Cambrian 913

boundary problem : Carbon isotope correlations for Vendian and Tommotian time between Siberia 914

and Morocco. Geology 19, 847-850. 915

Massironi, M., Moratti, G., Algouti, A., Benvenuti, M., Dal Piaz, G.V., Eddebbi, A., El Boukhari, A., 916

Laftouhi, N., Ouanaimi, H., Schiavo, A., Taj-Eddine, K., Visonà, D., 2007. Carte Géologique du 917

Maroc au 1/50 000, feuille Boumalne. Notes et Mémoires Service Géologique du Maroc 521, 80. 918

Mouttaqi, A., Sagon, J.-P., 1999. Le gisement de cuivre de Bleïda (Anti-Atlas central); une interférence 919

entre les processus de remplacement et d'exhalaison dans un contexte de rift: Chronique de la 920

Recherche Minière, 536-537, 5-21. 921

Mifdahl, A., Peucat, J.J., 1985. Datations U-Pb et Rb/Sr du volcanisme acide de l’Anti-Atlas Marocain 922

et du socle sous-jacent dans la région de Ouarzazate. Apport au problème de la limite 923

Précambrien-Cambrien. Sciences Geologiques Bulletin, 38, 185-200. 924

Mrini, Z., 1993. Chronologie (Rb-Sr, U-Pb), traçage isotopique (Sr-Nd-Pb) des sources des roches 925

Magmatiques éburnéennes, panafricaines et hercyniennes du Maroc. Thèse Doctorat es 926

Sciences, Université Cadi Ayad, Marrakech, 227 p. 927

Murphy, J.B, Nance, R.D., 1991. Supercontinent model for the contrasting character of Late 928

Proterozoic orogenic belts. Geology 19, 469-472. 929

Naidoo, D.D., Bloomer, S.H., Saquaque, A., Hefferan, K.P., 1991. Geochemistry and significance of 930

metavolcanic rocks from the Bou Azzer-El Graara Ophiolite (Morocco). Precambrian Research 53, 931

79-97. 932

Naidoo, D.D., Bloomer, S.H., Saquaque, A., Hefferan, K., 1993. Geochemistry and significance of 933

metavolcanic rocks from the Bou Azzer-El Graara ophiolite (Morocco)-reply. Precambrian 934

Research 62, 369-371. 935

Nance, R.D., Murphy, J.B., Strachan, R.A., Keppie, J.D., Gutiérrez-Alonso, G., Fernández-Suárez, J., 936

Quesada, C., Linnemann, U., D’Lemos, R., Pisarevsky, S.A., 2008. Neoproterozoic-early 937

Palaeozoic Tectonostratigraphy and Palaeogeography of the Peri-Gondwanan Terranes: 938

Amazonian v. West African Connections. Special Publications 297. Geological Society, London, 939

pp. 345-383. 940

Narbonne, G.M., Landing, E., Anderson, M.M., 1987. A candidate stratotype for the Precambrian–941

Cambrian boundary, Fortune Head, Burin Peninsula, southeastern Newfoundland. Canadian 942

Journal of Earth Sciences 24, 1277-1293. 943

Pearce, J.A., 1996. Sources and settings of granitic rocks. Episodes 19, 120-125. 944

Pouclet, A., Aarab, A., Fekkak, A., Benharref, M., 2007. Geodynamic evolution of the northwestern 945

Paleo-Gondwanan margin in the Moroccan Atlas at the Precambrian-Cambrian boundary, in: 946

Linnemann, U., Nance, R.D., Kraft, P., and Zulauf, G., (Eds.), The evolution of the Rheic Ocean: 947

From Avalonian-Cadomian active margin to Alleghenian-Variscan collision: Geological Society of 948

America Special Paper 423, pp. 27-60 949

Samson, S.D., Inglis, J.D., D'Lemos, R.S., Admou, H., Blichert-Toft, J., Hefferan, K., 2004. 950

Geochronological, geochemical, and Nd-Hf isotopic constraints on the origin of Neoproterozoic 951

plagiogranites in the Tasriwine ophiolite, Anti-Atlas orogen, Morocco. Precambrian Research 135, 952

133-147. 953

Saquaque, A., Admou, H., Karson, J.A., Hefferan, K., Reuber, I., 1989. Precambrian accretionary 954

tectonics in the Bou Azzer-El Graara region, Anti-Atlas, Morocco. Geology 17, 1107-1110. 955

Saquaque, A., Benharref, M., Abia, H., Mrini, Z., Reuber, I., Karson, J. A., 1992. Evidence for a 956

Panafrican volcanic arc and wrench fault tectonics in the Jbel Saghro, Anti-Atlas, Morocco. 957

Geologische Rundschau 81, 1-13. 958

Schiavo, A., Taj-Eddine, K., Algouti, Ah., Benvenuti, M., Dal Piaz, G.V., Eddebbi, A., El Boukhari, A., 959

Laftouhi, N., Massironi, M., Moratti, G., Ouanaimi, H., Pasquarè, G., Visonà, D., 2007. Carte 960

Géologique du Maroc au 1/50 000, feuille Imtir. Notes et Mémoires du Service Géologique du 961

Maroc 518, 96. 962

Schmitt, M., 1979. The section of Tiout (Precambrian/Cambrian boundary beds, Anti-Atlas, Morocco): 963

stromatolites and their biostratigraphy. Arb. Paläontology Institut Würzburg 2, 1-188. 964

Sdzuy, K., 1978. The Precambrian /Cambrian boundary beds in Morocco (preliminary report). 965

Geological Magazine 115, 83-94. 966

Soulaimani, A., Jaffal, M., Maacha, L., Kchikach, A., Najine, A., Saidi, A., 2006. Modélisation 967

magnétique de la suture ophiolitique de Bou Azzer-El Graara (Anti-Atlas central, Maroc). 968

Implications sur la reconstruction géodynamique panafricaine. Comptes Rendus Geoscience 338, 969

153-160. 970

Spizharski, T.N., Zhuravleva, I.T., Repina, L.N., Rozanov, A.Yu., Tchernysheva, N.Ye, Ergaliev, G.H., 971

1986. The stage scale of the Cambrian system. Geological Magazine 123, 387-392. 972

Tekiout, B., 1991. Stratigraphie, pétrographie, géochimie et structure de l’ensemble arc/avant arc de la 973

Boutonnière de Bou Azer-El Graara (unité nord) Anti-Atlas Maroc. Thèse 3ème

Cycle, Université 974

Cadi Ayyad, Marrakech, 151p. 975

Thomas, R.J., Chevallier, L.C., Gresse, P.G., Harmer, R.E., Eglington, B.M., Armstrong, R.A., de 976

Beer, C.H., Martini, J.E.J., de Kock, G.S., Macey, P., Ingram, B., 2002. Precambrian evolution of 977

the Siroua Window, Anti-Atlas Orogen, Morocco. Precambrian Research 118, 1-57. 978

Thomas, R.J., Fekkak, A., Errami, E., Loughlin, S.C., Gresse, P.G., Chevallier, L.P., Liégeois, J.-P., 979

2004. A new lithostratigraphic framework for the Anti-Atlas Orogen, Morocco. Journal of African 980

Earth Sciences 39, 217-226. 981

Thompson, R.N., Morrison, M.A., Hendry, G.L., Parry, S.J., 1984. An assessment of the relative roles 982

of crust and mantle in magma genesis: an elemental approach. Philosophical Transactions of the 983

Royal Society of London Mathematical and Physical Sciences A310, 549-590. 984

Tucker, M.E., 1986. Carbon isotope excursions in Precambrian/Cambrian boudary beds, Morocco. 985

Nature 319, 48-50. 986

Villeneuve, M., Cornée, J.J., 1994. Structure, evolution and palaeogeography of the West African 987

Craton and bordering belts during the Neoproterozoic. Precambrian Research 69, 307-326. 988

Walsh, G.E., Aleinikoff, J.N., Benziane, F., Yazidi, A., Armstrong, T.R., 2002. U-Pb zircon 989

geochronology of the Paleoproterozoic Tagragra de Tata inlier and its Neoproterozoic cover, 990

western Anti-Atlas, Morocco. Precambrian Research 117, 1-20. 991

Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W. L., Meier ,M., Oberli, F., von Quadt, A., Roddick, J. C., 992

Spiegel, W., 1995. Three natural zircon standards for U–Th–Pb, Lu–Hf, trace element and REE 993

analysis. Geostandard Newsletter 19, 1-23. 994

Williams, I.S., 1998. U–Th–Pb geochronology by ion microprobe, in: McKibben, M.A., Shanks III, 995

W.C., Ridley, W.I. (Eds.), Applications of Microanalytical Techniques to Understanding 996

Mineralizing Processes. Reviews of Economic Geology 7, 1-35. 997

Wilson, M., 1989. Igneous Petrogenesis, a Global Tectonic Approach. Unwin Hyman, London, 466 pp. 998

Wingate, M.T.D., Giddings, J.W., 2000. Age and palaeomagnetism of the Mundine Well dyke swarm, 999

Western Australia: Implications for an Australia-Laurentia connection at 755 Ma. Precambrian 1000

Research, 100, 335–357. 1001

Yazidi, A., Benziane, F., Walsh, G.J., Harrisson,R.W., Saadane, A., Yazidi, M., Quick, J.E., El Fahssi, 1002

A., Aleinikoff, J.N., Ejjouani, H., Kalai, M., 2008. Carte géologique du Maroc au 1/50 000 – feuille 1003

Aït Semgane. Mémoire explicatif. Notes et Mémoires du Service Géologique du Maroc 472bis, 1004

113 p. 1005

Youbi, N., Kouyaté, D., Söderlund, U., Ernst, R.E., Soulaimani, A., Hafid, A., Ikenne, M., El Bahat, A., 1006

Bertrand, H., Rkha Chaham, K., Ben Abbou, M., Mortaji, A., El Ghorfi, M., Zouhair, M., El Janati, 1007

M., 2013. The 1750 Ma magmatic event of the West African Craton (Anti-Atlas, Morocco). 1008

Precambrian Research 236, 106-123. 1009

1010

List of figures 1011

Figure 1: Simplified geological map of the Anti-Atlas showing the location of the Bou Azzer-El Graara 1012

inlier (modified from Walsh et al. 2002 and Gasquet et al. 2008). 1013

Figure 2: Simplified geological map of the Bou Azer-El Graara inlier showing the main lithotectonic 1014

units. The localities cited in the text are indicated, as well as the location of samples for 1015

geochronology. 1016

Figure 3: Age determination for zircon from the rhyolites AGEE298 (a) and AGEE094 (b) of the 1017

Tichibanine Group using SHRIMP II. 1018

Figure 4: Age determination for zircon from the orthogneisses BOPC028 (a) and AADG4 (b) of the 1019

gneissic basement, and granitic bodies BOPC067 (c) and AAPC140 (d) using SHRIMP II. 1020

Figure 5: Age determination for zircon from the leucogranite AADG12 of the Bou Azzer ophiolite using 1021

SHRIMP II. 1022

Figure 6: Age determination for zircon from diorite AAYN55a using LA-MC-ICPMS. 1023

Figure 7: Age determination for zircon from the rhyolite ALDG21 (a), the trachyte ALDG4 (b) and the 1024

sandstone AGEE24 (c) of the Tiddiline Group using SHRIMP II (a). Concordia diagram for SHRIMP 1025

analyses of zircon from the sandstone AGEE24 of the Tiddiline Group. 1026

Figure 8: Age determination for zircon from quartz diorite AGDG1 using LA-MC-ICPMS. 1027

Figure 9: Age determination for zircon from the rhyolitic welded tuffs ALDG20 (a) and BODG6 (b) of 1028

the Ouarzazate Group using SHRIMP II. 1029

Figure 10: Age determination for zircon from the volcanic breccia BOPC343 of the Adoudou 1030

Formation using SHRIMP II. 1031

1032

1033

List of tables. 1034

Table 1: Comparative lithostratigraphic nomenclature of the Anti-Atlas Orogen, with the scheme 1035

proposed by this study. 1036

Table 2: Summary of SHRIMP U–Pb data on zircons of the orthogneisses, granitic bodies, 1037

plagiogranite, rhyolites, trachyte and rhyolitic welded tuffs of the Bou Azzer-El Graara inlier. 1038

Table 3: Summary of LA-MC-ICPMS data on zircons of the diorite and quartz diorite of the Bou Azzer-1039

El Graara inlier. 1040

Table 4: Summary of SHRIMP U–Pb data on zircons of the sandstone from the Tiddiline Group and 1041

volcanic breccia from the Adoudou Formation. 1042

1043

1044

1045

1046

1047

1048

1049

1050

1051

1052

1053

1054

1055

1056

1057

1058

1059

1060

1061

1062

1063

Table 1.

Comparative lithostratigraphic nomenclature of the Anti-Atlas Orogen, with the scheme proposed by this study.

Kerdous and Bas

Dra inliers Bou Azer inlier

Saghro inlier

Age and

settings

Ouarzazate

Supergroup

basalt,

gabbro Takartat Suite

upper Ediacaran

Ait Baha, Anzi,

Tanalt, Flyzirt,

Oufoud, Jbel Guir

and Taarotihate

groups

Imlas, Mancour

subgroups 550-575 Ma

syn-

Ouarzazate

granites

Guelba suite

Tabghourt suite younger than

580 Ma

HKCA

granitoids

Bleïda suite Bardouz suite 615-580 Ma

lower

Ediacaran

Tafrawt, Ansi groups Tiddiline group

strike-slip pull-

apart basins

Sarhro group Bou Lbarod group Sarhro group

active margin

and

sediments

Anti-Atlas

Supergroup

Bou Azer group

ocean floor,

arc

upper

Cryogenian

Tichibanine group,

Assif

n'Bougmmane

gneiss complex

ocean floor,

arc

lower

Cryogenian

dolerite,

gabbro Toudma suite

extension

Jbel Lkst group Tachdamt-Bleïda

group

Taghdout

group

passive

margin

Tonian and/or

Cryogenian

Basement

complexes

Granitoids

Kerdous, Draa

complexes:

Tazeroualt and

Mechebbouk suites

not present not present

Paleoproterozoi

c

Schists Had-n- Tahala and

Draa groups not present

not present

Table 2.

Grain U Th Th/U206

Pb*204

Pb/ f206

238U/

207Pb/

206Pb/

206Pb/

spot (ppm) (ppm) (ppm)206

Pb %206

Pb ±206

Pb ±238

U ±238

U ±

Rhyolite Tichibanine Group (AGEE298)

1.1 124 105 0.87 13.5 0.000112 0.176 7.932 0.115 0.06619 0.00120 0.1258 0.0019 764 11

1.2 206 263 1.32 22.4 0.000128 0.275 7.891 0.109 0.06702 0.00083 0.1264 0.0018 767 10

2.1 321 188 0.61 35.1 0.000065 0.151 7.866 0.099 0.06599 0.00057 0.1270 0.0016 770 9

3.1 38 18 0.48 4.2 - - 7.779 0.151 0.06426 0.00164 0.1287 0.0026 780 15

4.1 29 20 0.71 3.1 0.000434 0.292 8.025 0.168 0.06715 0.00192 0.1242 0.0027 755 15

5.1 50 25 0.52 5.5 0.000166 0.236 7.822 0.141 0.06669 0.00144 0.1276 0.0024 774 14

6.1 50 33 0.68 5.3 0.000179 0.166 8.125 0.147 0.06611 0.00149 0.1228 0.0023 747 13

8.1 30 20 0.68 3.2 0.000374 0.535 7.857 0.159 0.06916 0.00183 0.1266 0.0026 768 15

9.1 84 45 0.56 9.0 0.000113 0.122 8.005 0.123 0.06575 0.00108 0.1247 0.0020 758 11

10.1 59 46 0.80 6.5 0.000433 0.409 7.807 0.144 0.06812 0.00153 0.1276 0.0024 774 14

11.1 18 8 0.46 1.9 0.000706 0.786 7.742 0.225 0.07124 0.00289 0.1282 0.0039 777 22

12.1 51 39 0.79 5.6 0.000202 0.632 7.796 0.150 0.06996 0.00165 0.1275 0.0025 773 14

13.1 33 14 0.45 3.6 0.000438 0.676 7.894 0.181 0.07033 0.00212 0.1258 0.0030 764 17

Rhyolite Tichibanine Group (AGEE094)

1.1 110 45 0.42 11.8 - - 8.038 0.115 0.06405 0.00090 0.1245 0.0018 756 10

2.1 166 51 0.32 17.8 0.000113 0.161 8.007 0.108 0.06589 0.00076 0?1247 0.0017 757 10

3.1 177 147 0.86 25.2 0.000085 0.128 6.023 0.082 0.07357 0.00068 0.1658 0.0023 989 13

4.1 79 46 0.60 7.2 0.000116 0.321 9.499 0.160 0.06264 0.00121 0.1049 0.0018 643 11

5.1 52 12 0.23 5.7 0.000152 0.213 7.921 0.138 0.06632 0.00138 0.1260 0.0023 765 13

5.2 109 31 0.30 11.8 - 0.000 7.918 0.115 0.06456 0.00094 0.1263 0.0019 767 11

6.1 82 56 0.70 8.8 0.000067 - 8.018 0.125 0.06455 0.00111 0.1247 0.0020 758 11

7.1 122 29 0.25 13.2 - - 7.929 0.114 0.06434 0.00090 0.1261 0.0019 766 11

8.1 117 35 0.31 12.6 - 0.049 7.986 0.116 0.0497 0.00093 0.1252 0.0019 760 11

9.1 188 98 0.54 16.4 0.000158 0.267 9.863 0.142 0.06219 0.00096 0.1011 0.0015 621 9

10.1 166 104 0.65 13.7 0.000774 1.363 10.386 0.153 0.07115 0.00110 0.0950 0.0014 585 8

11.1 146 50 0.36 15.8 0.000114 0.268 7.959 0.118 0.06677 0.00099 0.1253 0.0019 761 11

12.1 164 66 0.41 17.3 0.000147 0.191 8.153 0.119 0.06614 0.00095 0.1224 0.0018 744 10

13.1 109 39 0.37 11.9 - 0.041 7.834 0.126 0.06490 0.00116 0.1276 0.0021 774 12

Orthogneiss Assif n'Bougmmane gneissic complex (BOPC028)

1.1 23 11 0.47 2.4 0.000155 0.11 8.051 0.238 0.0653 0.0020 0.1241 0.0038 754 22

2.1 24 12 0.50 2.5 0.000416 0.46 8.319 0.180 0.0674 0.0019 0.1197 0.0027 729 15

3.1 26 12 0.47 2.8 - <0.01 7.846 0.170 0.0638 0.0018 0.1276 0.0029 774 16

4.1 39 35 0.87 4.2 0.000525 <0.01 8.062 0.156 0.0640 0.0014 0.1241 0.0025 754 14

5.1 18 9 0.49 2.0 0.000860 <0.01 8.053 0.191 0.0629 0.0020 0.1244 0.0030 756 17

6.1 26 12 0.46 2.8 0.000146 <0.01 8.085 0.173 0.0601 0.0017 0.1243 0.0027 755 16

7.1 20 10 0.51 2.1 0.000872 0.01 8.100 0.237 0.0651 0.0020 0.1233 0.0037 750 21

8.1 24 11 0.46 2.6 - <0.01 8.005 0.174 0.0632 0.0018 0.1251 0.0028 760 16

9.1 36 22 0.62 3.5 - <0.01 8.846 0.342 0.0609 0.0027 0.1133 0.0045 692 26

10.1 78 47 0.60 7.8 - 0.25 8.680 0.163 0.0648 0.0014 0.1149 0.0022 701 13

11.1 17 6 0.37 1.8 - <0.01 7.909 0.200 0.0630 0.0023 0.1267 0.0033 769 19

12.1 20 10 0.50 2.2 - <0.01 8.149 0.192 0.0635 0.0021 0.1228 0.0030 747 17

13.1 23 11 0.46 2.4 - <0.01 8.266 0.203 0.0637 0.0020 0.1210 0.0031 736 18

14.1 28 12 0.45 3.0 0.000425 <0.01 7.889 0.175 0.0639 0.0018 0.1269 0.0029 770 17

15.1 25 12 0.48 2.6 - <0.01 8.106 0.188 0.0617 0.0019 0.1238 0.0029 752 17

Orthogneiss Assif n'Bougmmane gneissic complex (AADG4)

1.1 310 134 0.45 32.3 0.000078 0.096 8.254 0.102 0.06489 0.00050 0.1210 0.0015 737 9

2.2 346 160 0.48 36.3 0.000035 0.066 8.198 0.101 0.06489 0.00045 0.1219 0.0015 741 9

3.2 379 187 0.51 40.1 0.000064 0.048 8.136 0.101 0.06489 0.00055 0.1229 0.0016 747 9

4.1 346 163 0.49 37.2 0.000071 0.125 7.993 0.099 0.06489 0.00107 0.1250 0.0016 759 9

5.1 204 82 0.41 21.6 0.000071 0.055 8.121 0.104 0.06489 0.00059 0.1231 0.0016 748 9

6.1 385 172 0.46 40.6 0.000078 0.072 8.149 0.100 0.06489 0.00042 0.1226 0.0015 746 9

7.1 115 22 0.20 12.0 0.000041 0.156 8.204 0.111 0.06489 0.00079 0.1217 0.0017 740 10

8.1 379 192 0.52 39.9 0.000064 0.088 8.146 0.100 0.06489 0.00042 0.1227 0.0015 746 9

8.2 386 193 0.52 41.1 0.000046 0.150 8.178 0.100 0.06489 0.00041 0.1221 0.0015 743 9

9.1 391 203 0.54 35.1 0.000064 0.104 7.901 0.098 0.06489 0.00045 0.1265 0.0016 767 9

10.1 322 142 0.46 44.5 0.000045 0.054 8.228 0.100 0.06489 0.00038 0.1214 0.0015 739 9

11.1 426 192 0.47 79.2 0.000032 0.064 8.223 0.098 0.06489 0.00028 0.1215 0.0015 739 9

12.1 758 376 0.51 39.7 0.000030 0.098 8.332 0.101 0.06489 0.00039 0.1198 0.0015 730 9

Granitic intrusion (AAPC140)

1.1 159 96 0.62 16.5 0.000138 0.192 8.234 0.111 0.06562 0.00077 0.1216 0.0017 738 10

2.1 214 83 0.40 20.7 0.000000 - 8.901 0.116 0.06280 0.00068 0.1126 0.0015 686 9

3.1 275 166 0.62 27.0 0.000090 0.026 8.751 0.111 0.06308 0.00059 0.1146 0.0015 697 9

4.1 518 443 0.89 50.9 0.000014 - 8.735 0.105 0.06284 0.00043 0.1148 0.0014 699 8

5.1 507 437 0.89 50.3 0.000032 0.044 8.670 0.105 0.06323 0.00043 0.1156 0.0014 703 8

6.1 303 252 0.86 30.6 0.000080 0.141 8.515 0.107 0.06403 0.00057 0.1177 0.0015 715 9

7.1 409 203 0.51 41.0 0.000056 0.060 8.581 0.132 0.06336 0.00048 0.1168 0.0018 710 11

8.1 163 10 0.06 16.1 0.000084 0.103 8.691 0.116 0.06372 0.00074 0.1153 0.0016 701 9

Summary of SHRIMP U–Pb data on zircons of the orthogneisses, granitic bodies, plagiogranite, rhyolites, trachyte and rhyolitic

welded tuffs of the Bou Azzer-El Graara inlier.

Total Radiogenic Age (Ma)

9.1 239 158 0.68 24.9 0.000030 - 8.249 0.105 0.06333 0.00059 0.1217 0.0016 738 9

10.1 424 321 0.78 41.8 0.000022 0.046 8.705 0.106 0.06325 0.00047 0.1152 0.0014 701 8

11.1 118 49 0.43 12.3 0.000092 0.125 8.226 0.116 0.06507 0.00087 0.1218 0.0018 739 10

12.1 545 497 0.94 53.8 - 0.100 8.702 0.104 0.06369 0.00042 0.1151 0.0014 701 8

13.1 418 390 0.96 42.1 0.000040 0.074 8.517 0.104 0.06348 0.00047 0.1177 0.0015 715 8

14.1 214 187 0.80 23.6 0.000055 0.080 8.767 0.112 0.06353 0.00062 0.1143 0.0015 696 9

15.1 355 200 0.58 37.9 - - 8.043 0.099 0.06395 0.00050 0.1248 0.0016 756 9

Granitic intrusion (BOPC 076)

1.1 82 20 0.26 8.0 0.000114 0.342 8.794 0.133 0.06533 0.00108 0.1133 0.0018 692 10

2.1 165 2 0.01 16.1 0.000111 0.379 8.779 0.117 0.06566 0.00076 0.1135 0.0015 693 9

4.1 201 63 0.33 19.7 0.000080 0.190 8.754 0.121 0.06421 0.00115 0.1140 0.0016 696 9

5.1 483 207 0.44 51.2 0.000050 0.066 8.107 0.101 0.06478 0.00052 0.1233 0.0016 749 9

6.1 394 161 0.42 42.6 0.000008 0.012 7.954 0.101 0.06476 0.00058 0.1257 0.0016 763 9

7.1 100 9 0.10 9.9 0.000262 0.567 8.688 0.141 0.06738 0.00125 0.1144 0.0019 699 11

8.1 293 15 0.05 29.2 0.000054 0.136 8.623 0.114 0.06406 0.00113 0.1158 0.0016 706 9

10.1 190 4 0.02 18.4 0.000121 0.316 8.861 0.132 0.06498 0.00090 0.1125 0.0017 687 10

11.1 161 54 0.35 17.0 0.000086 0.189 8.137 0.119 0.06568 0.00096 0.1227 0.0018 746 11

12.1 142 39 0.29 13.7 0.000096 0.231 8.890 0.136 0.06424 0.00108 0.1122 0.0018 686 10

13.1 80 27 0.35 8.5 0.000061 0.125 8.115 0.124 0.06523 0.00106 0.1231 0.0019 758 11

14.1 97 44 0.47 9.6 - 0.096 8.733 0.129 0.06349 0.00100 0.1144 0.0017 698 10

Plagiogranite Bou Azzer ophiolite (ADG12)

1.1 41 22 0.53 3.8 0.000476 0.13 9.214 0.182 0.0627 0.0015 0.1084 0.0022 663 13

2.1 38 23 0.62 3.6 0.001016 0.25 8.947 0.234 0.0642 0.0028 0.1115 0.0030 681 17

3.1 91 100 1.10 8.3 0.000093 <0.01 9.379 0.154 0.0611 0.0009 0.1067 0.0018 653 10

4.1 45 29 0.65 4.2 0.000084 <0.01 9.217 0.179 0.0609 0.0015 0.1086 0.0022 665 13

5.1 58 29 0.51 4.7 0.000534 0.09 10.561 0.196 0.0602 0.0013 0.0946 0.0018 583 11

6.1 39 31 0.81 3.1 0.000389 0.29 10.597 0.210 0.0617 0.0016 0.0941 0.0019 580 11

7.1 20 10 0.53 1.8 - 0.36 9.700 0.229 0.0637 0.0022 0.1027 0.0025 630 15

8.1 56 48 0.85 5.2 - <0.01 9.290 0.168 0.0613 0.0012 0.1077 0.0020 659 12

9.1 42 39 0.91 3.9 0.000191 0.03 9.330 0.180 0.0617 0.0015 0.1072 0.0021 656 12

10.1 48 49 1.02 4.3 - <0.01 9.534 0.178 0.0610 0.0014 0.1049 0.0020 643 12

11.1 24 13 0.54 2.3 0.000556 0.58 8.997 0.201 0.0668 0.0020 0.1105 0.0025 676 15

12.1 36 28 0.80 3.3 0.000360 <0.01 9.336 0.197 0.0609 0.0016 0.1072 0.0023 656 13

13.1 84 67 0.80 7.1 0.000094 0.03 10.143 0.174 0.0603 0.0011 0.0986 0.0017 606 10

14.1 56 28 0.49 5.2 0.000175 0.27 9.265 0.179 0.0638 0.0015 0.1076 0.0021 659 12

15.1 60 54 0.90 5.1 - 0.29 10.148 0.476 0.0624 0.0014 0.0983 0.0047 604 28

Rhyolitic welded tuff Tiddiline Group (ALDG21)

1.1 143 68 0.49 11.9 0.000085 0.023 10.340 0.146 0.06020 0.00091 0.0967 0.0014 595 8

2.1 128 58 0.47 11.1 0.000118 0.206 9.952 0.145 0.06170 0.00098 0.1003 0.0015 616 9

3.1 68 24 0.37 5.7 0.000208 0.296 10.176 0.169 0.06243 0.00133 0.0980 0.0017 603 10

4.1 163 88 0.55 13.8 0.000062 0.098 10.185 0.140 0.06081 0.00084 0.0981 0.0014 603 8

5.1 120 70 0.60 10.1 0.000068 0.053 10.175 0.147 0.06044 0.00097 0.0982 0.0015 604 9

6.1 154 56 0.38 13.0 0.000077 0.200 10.220 0.142 0.06164 0.00087 0.0976 0.0014 601 8

7.1 184 104 0.59 15.7 0.000079 0.023 10.095 0.136 0.06020 0.00077 0.0990 0.0014 609 8

8.1 128 75 0.60 10.6 0.000133 0.248 10.367 0.149 0.06203 0.00096 0.0962 0.0014 592 8

9.1 99 52 0.54 8.4 - - 10.176 0.155 0.05965 0.00108 0.0983 0.0015 605 9

10.1 101 52 0.53 8.6 - 0.124 10.106 0.169 0.06102 0.00131 0.0988 0.0017 608 10

11.1 103 52 0.53 8.8 - 0.152 10.010 0.167 0.06125 0.00130 0.0997 0.0017 613 10

12.1 172 95 0.57 14.6 0.000085 0.024 10.062 0.148 0.06021 0.00099 0.0994 0.0015 611 9

13.1 146 82 0.58 12.4 0.000103 0.120 10.129 0.155 0.06099 0.00109 0.0986 0.0015 606 9

14.1 252 140 0.57 22.1 0.000132 0.226 9.811 0.136 0.06186 0.00085 0.1017 0.0014 624 8

15.1 378 221 0.60 31.5 0.000047 0.050 10.305 0.133 0.06042 0.00067 0.0970 0.0013 597 8

Trachyte Tiddiline Group (ALDG4)

1.1 341 147 0.45 28.6 0.000028 0.050 10.243 0.127 0.06042 0.00048 0.0976 0.0012 600 7

2.1 286 68 0.24 24.3 0.000099 0.209 10.127 0.127 0.06171 0.00069 0.0985 0.0013 606 7

3.1 260 82 0.33 22.3 0.000143 0.209 10.021 0.126 0.06172 0.00056 0.0996 0.0013 612 8

4.1 416 106 0.26 35.1 0.000023 0.030 10.179 0.125 0.06026 0.00043 0.0982 0.0012 604 7

5.1 390 146 0.39 33.1 0.000034 0.030 10.105 0.126 0.06026 0.00045 0.0989 0.0013 608 7

6.1 409 160 0.40 34.4 - 0.02 10.210 0.125 0.06002 0.00044 0.0979 0.0012 602 7

7.1 314 105 0.34 25.6 0.000052 0.099 10.538 0.131 0.06082 0.00050 0.0947 0.0012 584 7

8.1 430 142 0.34 36.3 - 0.003 10.177 0.124 0.06003 0.00042 0.0983 0.0012 604 7

9.1 260 82 0.33 22.1 0.000041 0.073 10.120 0.127 0.06061 0.00055 0.0988 0.0013 607 7

10.1 220 55 0.26 18.6 0.000000 0.055 10.186 0.128 0.06046 0.00056 0.0981 0.0013 603 7

10.2 865 270 0.32 74.0 - 0.071 10.039 0.120 0.06059 0.00029 0.0996 0.0012 612 7

11.1 285 86 0.31 23.3 0.000054 0.109 10.487 0.141 0.06090 0.00054 0.0952 0.0013 587 8

Rhyolitic welded tuff Ouarzazate Group (ALDG20)

1.1 578 173 0.30 46.0 0.000009 <0.01 10.794 0.157 0.0590 0.004 0.0927 0.0014 571 8.0

2.1 391 61 0.15 31.3 0.000095 <0.01 10.726 0.158 0.0586 0.005 0.0933 0.0014 575 8.2

3.1 776 160 0.21 63.7 0.000041 <0.01 10.468 0.165 0.0593 0.004 0.0956 0.0015 588 9.0

4.1 680 155 0.23 53.7 0.000009 0.05 10.874 0.156 0.0594 0.004 0.0919 0.0013 567 7.9

5.1 1022 248 0.24 81.6 0.000032 <0.01 10.762 0.159 0.0586 0.003 0.0930 0.0014 573 8.2

6.1 829 324 0.39 59.0 0.000214 0.58 12.065 0.173 0.0622 0.004 0.0824 0.0012 511 7.1

7.1 732 268 0.37 56.3 0.000008 0.08 11.171 0.160 0.0593 0.004 0.0894 0.0013 552 7.7

8.1 28 19 0.68 3.3 0.007429 9.72 7.452 0.155 0.1440 0.064 0.1211 0.0028 737 16.3

9.1 271 57 0.21 21.2 - 0.01 10.963 0.165 0.0590 0.006 0.0912 0.0014 563 8.2

10.1 963 139 0.14 75.9 0.000009 <0.01 10.892 0.160 0.0588 0.003 0.0918 0.0014 566 8.1

11.1 793 178 0.23 60.1 0.000026 0.09 11.324 0.248 0.0591 0.004 0.0882 0.0020 545 11.6

12.1 555 107 0.19 43.2 - 0.03 11.037 0.160 0.0590 0.004 0.0906 0.0013 559 7.9

13.1 682 321 0.47 51.6 0.000005 0.07 11.350 0.163 0.0590 0.004 0.0880 0.0013 554 7.6

14.1 475 103 0.22 34.6 0.000085 0.29 11.801 0.173 0.0602 0.005 0.0845 0.0013 523 7.5

15.1 437 61 0.14 34.2 0.000048 0.14 10.982 0.161 0.0600 0.005 0.0909 0.0014 561 8.0

Rhyolitic welded tuff Ouarzazate Group (BODG6)

1.1 258 71 0.28 20.8 0.000079 0.099 10.634 0.134 0.05975 0.00055 0.0939 0.0012 579 7

2.1 695 118 0.18 55.6 0.000032 0.039 10.736 0.130 0.05925 0.00034 0.0931 0.0011 574 7

3.1 619 250 0.42 49.0 0.000028 - 10.852 0.130 0.05849 0.00035 0.0922 0.0011 569 7

4.1 176 66 0.39 13.8 0.000080 0.161 10.930 0.142 0.06025 0.00067 0.0913 0.0012 563 7

5.1 201 36 0.19 15.8 0.000119 0.200 10.904 0.170 0.06057 0.00063 0.0915 0.0015 565 9

6.1 217 35 0.17 17.3 0.000035 0.062 10.766 0.170 0.05945 0.00060 0.0928 0.0015 572 9

6.2 184 30 0.17 14.4 0.000048 0.098 10.990 0.141 0.05974 0.00066 0.0909 0.0012 561 7

7.1 554 114 0.21 43.9 0.000023 0.040 10.835 0.131 0.05927 0.00038 0.0923 0.0011 569 7

8.1 613 143 0.24 48.3 0.000034 0.031 10.901 0.131 0.05919 0.00047 0.0917 0.0011 566 7

9.1 960 357 0.38 74.6 0.000035 0.010 11.057 0.132 0.05902 0.00041 0.0904 0.0011 558 7

10.1 454 140 0.32 34.9 - 0.024 11.174 0.154 0.05914 0.00042 0.0895 0.0013 552 7

f206 % is the percentage of 206

Pb that is common lead. Uncertainties are given at the one σ level. Correction for common lead is

made using the measured 204

Pb/206

Pb ratio. For % conc., 100% signifies a concordant analysis.

Table 3.

Grain U Th Th/U206

Pb*204

Pb/ f206238

U/207

Pb/206

Pb/206

Pb/

spot (ppm) (ppm) (ppm)206

Pb %206

Pb ±206

Pb ±238U

±238

U ±

Diorite Ediacaran intrusions (AAYN55a)

1.1 134 127 0.95 11.3 1,763 0.208 9.829 0.155 0.06273 0.00034 0.1015 0.0015 623 9

1.2 84 67 0.80 7.4 964 0.154 9.423 0.187 0.06300 0.00032 0.1060 0.0019 649 11

2.1 52 46 0.89 4.4 - 0.198 9.939 0.136 0.06247 0.00056 0.1004 0.0013 617 7

3.1 171 149 0.87 14.2 3,650 0.108 10.046 0.174 0.06159 0.00035 0.0994 0.0016 611 9

4.1 90 70 0.78 8.0 5,905 0.003 9.290 0.146 0.06200 0.00036 0.1076 0.0016 659 9

5.1 101 75 0.75 8.3 3,467 0.130 10.031 0.162 0.06177 0.00053 0.0996 0.0015 612 9

6.1 69 54 0.79 5.9 25,305 0.192 9.667 0.121 0.06285 0.00052 0.1032 0.0012 633 7

7.1 123 97 0.79 9.9 - 0.314 10.291 0.146 0.06286 0.00039 0.0969 0.0013 596 7

8.1 82 86 1.06 6.7 4,263 0.156 10.179 0.121 0.06174 0.00063 0.0981 0.0011 603 6

9.1 102 107 1.05 8.4 1,052 0.290 10.060 0.173 0.06299 0.00057 0.0991 0.0016 609 9

10.1 124 102 0.83 10.7 2,836 0.080 9.631 0.111 0.06215 0.00045 0.1037 0.0011 636 6

11.1 89 58 0.65 7.1 - 0.248 10.430 0.107 0.06226 0.00047 0.0956 0.0009 589 5

12.1 121 120 0.99 10.1 - 0.329 9.957 0.124 0.06354 0.00032 0.1001 0.0011 615 7

13.1 139 130 0.93 11.6 - 0.152 9.968 0.122 0.06206 0.00043 0.1002 0.0011 615 7

14.1 78 66 0.85 6.8 5,403 0.073 9.563 0.112 0.06205 0.00050 0.1045 0.0011 641 7

15.1 25 15 0.60 2.2 5,781 0.248 9.715 0.205 0.06323 0.00075 0.1027 0.0020 630 12

Quartz diorite Ediacaran intrusions (AGDG1)

1.1 93 63 0.68 7.3 3,252 0.299 10.586 0.123 0.06233 0.00064 0.0942 0.0010 580 6

2.1 91 40 0.44 7.0 1,166 0.241 10.842 0.147 0.06151 0.00044 0.0920 0.0012 567 7

3.1 86 50 0.58 6.7 2,636 0.588 10.600 0.130 0.06470 0.00096 0.0938 0.0011 578 6

4.1 87 47 0.54 6.5 1,028 0.351 11.073 0.140 0.06215 0.00051 0.0900 0.0010 555 6

5.1 96 62 0.64 18.2 - - 4.378 0.080 0.10907 0.00082 0.2284 0.0038 1326 20

6.1 103 51 0.50 7.8 1,235 0.291 10.933 0.143 0.06174 0.00085 0.0912 0.0011 563 7

7.1 165 107 0.65 13.6 5,156 0.136 10.104 0.111 0.06168 0.00032 0.0988 0.0010 608 6

8.1 107 55 0.51 8.3 - 0.123 10.707 0.122 0.06073 0.00045 0.0933 0.0010 575 6

9.1 105 70 0.66 8.7 3,290 0.020 10.067 0.132 0.06077 0.00056 0.0993 0.0012 610 7

10.1 122 86 0.71 9.5 1,272 0.201 10.633 0.128 0.06146 0.00034 0.0939 0.0010 578 6

f206 % is the percentage of 206

Pb that is common lead. Uncertainties are given at the one σ level. Correction for common lead is

made using the measured 204

Pb/206

Pb ratio. For % conc., 100% signifies a concordant analysis.

Summary of LA-MC-ICPMS data on zircons of the diorite and quartz diorite of the Bou Azzer-El Graara inlier.

Total Radiogenic Age (Ma)

Table 4.

Grain U Th Th/U206

Pb*204

Pb/ f206

238U/

207Pb/

206Pb/

207Pb/

207Pb/

206Pb/

207Pb/

207Pb/ %

spot (ppm) (ppm) (ppm)206

Pb %206

Pb ±206

Pb ±238U

±235U

±206U

± ρ238

U ±235

U ±206

U ± Conc

Sandstone Tiddiline Group (AGEE24)

1.1 72 20 0.28 23.9 0.000158 0.24 2.584 0.042 0.1259 0.0008 0.3861 0.0062 6.590 0.121 0.1238 0.0011 0.884 2105 29 2058 16 2012 15 105

2.1 103 53 0.52 34.4 0.000059 0.09 2.563 0.040 0.1320 0.0007 0.3898 0.0060 7.053 0.117 0.1312 0.0008 0.935 2122 28 2118 15 2115 10 100

3.1 75 21 0.27 24.7 - <0.01 2.613 0.042 0.1280 0.0008 0.3828 0.0061 6.763 0.117 0.1281 0.0008 0.928 2089 29 2081 15 2073 11 101

4.1 112 28 0.25 36.1 0.000001 <0.01 2.656 0.042 0.1253 0.0007 0.3765 0.0059 6.504 0.109 0.1253 0.0007 0.945 2060 28 2046 15 2033 10 101

5.1 535 23 0.04 185.4 0.000004 0.01 2.476 0.036 0.1318 0.0003 0.4038 0.0058 7.338 0.107 0.1318 0.0003 0.986 2186 27 2153 13 2122 4 103

5.2 47 31 0.65 17.2 - <0.01 2.359 0.046 0.1458 0.0010 0.4240 0.0083 8.547 0.177 0.1462 0.0010 0.939 2279 37 2291 19 2302 12 99

6.1 149 14 0.09 48.3 - <0.01 2.644 0.040 0.1253 0.0006 0.3782 0.0057 6.537 0.104 0.1254 0.0006 0.952 2068 27 2051 14 2034 9 102

7.1 159 135 0.85 13.7 0.000083 0.15 9.996 0.170 0.0607 0.0007 0.0999 0.0017 0.819 0.018 0.0595 0.0009 0.760 614 10 608 10 585 32 105

7.2 113 78 0.69 9.4 - <0.01 10.294 0.169 0.0592 0.0009 0.0972 0.0016 0.799 0.019 0.0596 0.0010 0.704 598 9 596 10 590 36 101

8.1 113 46 0.41 36.3 - <0.01 2.669 0.041 0.1269 0.0007 0.3747 0.0058 6.554 0.107 0.1269 0.0007 0.946 2052 27 2053 14 2055 9 100

9.1 132 44 0.33 42.4 - <0.01 2.683 0.055 0.1273 0.0006 0.3729 0.0077 6.567 0.139 0.1277 0.0006 0.973 2043 36 2055 19 2067 9 99

10.1 1042 52 0.05 333.0 0.000013 0.02 2.689 0.041 0.1257 0.0002 0.3718 0.0057 6.434 0.100 0.1255 0.0002 0.993 2038 27 2037 14 2036 3 100

11.1 526 180 0.34 168.3 0.000008 0.01 2.683 0.039 0.1259 0.0003 0.3727 0.0054 6.462 0.095 0.1258 0.0004 0.982 2042 25 2041 13 2040 5 100

12.1 248 21 0.09 79.0 - <0.01 2.695 0.040 0.1257 0.0005 0.3711 0.0055 6.445 0.100 0.1260 0.0005 0.962 2035 26 2038 13 2042 7 100

13.1 119 86 0.72 38.2 - <0.01 2.683 0.043 0.1275 0.0008 0.3727 0.0059 6.559 0.111 0.1276 0.0008 0.933 2042 28 2054 15 2066 11 99

Volcanic breccia Jbel Boho (BOPC343)

1.1 137 55 0.40 10.3 0.000757 0.80 11.405 0.187 0.0647 0.0024 0.0870 0.0015 538 9

2.1 850 262 0.31 63.5 0.000028 <0.01 11.500 0.162 0.0578 0.0003 0.0870 0.0012 538 7

2.2 555 160 0.29 41.7 - <0.01 11.433 0.165 0.0580 0.0004 0.0875 0.0013 541 8

3.1 111 114 1.03 3.6 - 0.16 26.207 0.490 0.0523 0.0014 0.0381 0.0007 241 4

4.1 333 68 0.20 27.1 0.000031 <0.01 10.530 0.155 0.0589 0.0005 0.0950 0.0014 585 8

5.1 170 76 0.45 12.9 - <0.01 11.293 0.180 0.0579 0.0008 0.0886 0.0014 547 8

6.1 340 65 0.19 27.3 0.000023 <0.01 10.722 0.158 0.0574 0.0005 0.0935 0.0014 576 8

7.1 229 60 0.26 18.0 0.000006 0.04 10.917 0.167 0.0593 0.0007 0.0916 0.0014 565 8

8.1 219 71 0.33 102.2 - <0.01 1.843 0.027 0.1960 0.0006 0.5426 0.0080 14.684 0.222 0.1963 0.0006 0.979 2794 33 2795 14 2795 5 100

9.1 421 87 0.21 32.1 0.000038 <0.01 11.279 0.165 0.0579 0.0005 0.0887 0.0013 548 8

9.2 252 48 0.19 19.7 - <0.01 11.023 0.169 0.0579 0.0006 0.0908 0.0014 560 8

10.1 35 16 0.45 3.2 0.000219 0.25 9.410 0.207 0.0634 0.0017 0.1060 0.0024 649 14

11.1 385 93 0.24 29.0 - 0.14 11.413 0.168 0.0595 0.0005 0.0875 0.0013 541 8

12.1 253 43 0.17 20.4 0.000024 0.09 10.647 0.162 0.0601 0.0006 0.0938 0.0014 578 9

13.1 120 51 0.43 9.4 0.000296 <0.01 10.912 0.183 0.0589 0.0009 0.0916 0.0016 565 9

14.1 565 104 0.18 49.6 0.000046 <0.01 9.804 0.140 0.0605 0.0004 0.1020 0.0015 626 9

15.1 42 14 0.34 3.1 0.000421 0.11 11.613 0.250 0.0589 0.0019 0.0860 0.0019 532 11

16.1 154 52 0.34 19.4 - <0.01 6.818 0.108 0.0919 0.0011 0.1467 0.0023 1.858 0.037 0.0919 0.0011 0.795 882 13 1066 13 1465 23 60

f206 % is the percentage of 206

Pb that is common lead. Uncertainties are given at the one σ level. Correction for common lead is made using the measured 204

Pb/206

Pb ratio. For % conc., 100% signifies a concordant analysis.

Summary of SHRIMP U–Pb data on zircons of the sanstone from the Tiddiline Group and volcanic breccia from the Adoudou Formation.

Age (Ma)Total Radiogenic ratios

Highlights 1064

1065

● Multiple Cryogenian (lower and upper) volcanic-arc sequences. 1066

● At least two distinct accretion of volcanic arc to the WAC margin. 1067

● A late Cryogenian Bou Azzer ophiolite. 1068

● An Ediacaran active margin of the WAC. 1069

● A tectonic deformation with an erosional phase separating lower and upper Ediacaran. 1070

1071

1072