Tectonophysics xxx (2015) xxx–xxx

TECTO-126720; No of Pages 14

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Tectonophysics

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Paleomagnetism of the Central AtlanticMagmatic Province in the Algarvebasin, Portugal: First insights

Eric Font a,⁎, Susana Fernandes a, Marta Neres a,b, Claire Carvallo c, Línia Martins a,d,José Madeira a,d, Nasrrddine Youbi a,e

a IDL-FCUL, Instituto Dom Luíz, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, Lisbon, Portugalb IPMA, Instituto Português do Mar e da Atmosfera, Lisboa, Portugalc Institut deMinéralogie, de Physique desMinéraux et de Cosmochimie, SorbonneUniversités-Pierre andMarie Curie, University of Paris 06, UMRCNRS7590,MuséumNational d'Histoire Naturelle,IRD UMR 206, Paris, Franced Departamento de Geologia, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Lisbon, Portugale Faculty of Sciences-Semlalia, Geology Department, Cadi Ayyad University, Prince Moulay Abdellah Boulevard, P.O. Box 2390, 40 000 Marrakech, Morocco

⁎ Corresponding author at: IDL-FCUL, Instituo DomUniversidade de Lisboa, Edifício C8-8.3.22, Campo Grande

E-mail address: font_eric@hotmail.com (E. Font).

http://dx.doi.org/10.1016/j.tecto.2015.07.0360040-1951/© 2015 Elsevier B.V. All rights reserved.

Please cite this article as: Font, E., et al., PaleoTectonophysics (2015), http://dx.doi.org/10

a b s t r a c t

a r t i c l e i n f o

Article history:Received 4 February 2015Received in revised form 24 July 2015Accepted 29 July 2015Available online xxxx

Keywords:CAMP lavasAlgarve basinTriassicVertical-axis rotationMagnetic mineralogyPaleomagnetism

We present new rockmagnetic and paleomagnetic data of the Central Atlantic Magmatic Province (CAMP) lavascropping out in the Algarve basin (southern Portugal). Our results show that the magnetic mineralogy of the se-lected samples is primary and dominated by an assemblage of single-domain (SD) tomulti-domain (MD)Ti-poortitanomagnetites. All samples carry a characteristic remanent magnetization of normal (positive) magnetic po-larity, similarly to other circum-Atlantic CAMP lava sequences. Except for the sites located in the central part ofthe Algarve basin, site-basedmean directions (5 sites, Group A) are comparable to the giantMessejana dyke's di-rections, suggesting that both lavaflows and dykewere emplaced during the same geological interval (~200Ma).However, sites located in the central part of the basin (4 sites; Group B), just east of the São Marcos-Quarteirafault zone, show a systematic discrepancy in the declination values, which is indicative of a significant vertical-axis rotation that we estimated to be ~30° clockwise. We suggest that the observed clockwise vertical-axis rota-tion was produced by a Riedel dextral shear zone of the São Marcos-Quarteira faults acting during the N-Scompression that affected the Southern Portuguese margin in the Cenozoic. Our results provide important in-sights to unravel the complex history of the Algarve basin since the Mesozoic.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The Central Atlantic Magmatic Province (CAMP) is one of the largestMesozoic continental Large Igneous Provinces associated with the dis-ruption of Pangea and the opening of the central Atlantic Ocean(Marzoli et al., 1999, 2004). Similarly to the Siberian and DeccanTraps, the CAMP is coeval with one of the five most severe mass extinc-tion of the Phanerozoic, namely, the end-Triassic Mass Extinction thatoccurred at around 200 Ma ago (Deenen et al., 2010; Marzoli et al.,2004; Ruhl et al., 2010). The synchronism between the onset of CAMPvolcanismand the end-TriassicMass Extinction has been established in-directly, by comparing radiometric (Verati et al., 2007), paleomagnetic(Kent and Olsen, 1999; Knight et al., 2004) and geochemical data fromcircum-Atlantic CAMP lavas flows, as well as from underlying Triassicred beds (Dal Corso et al., 2014; Deenen et al., 2010) (Fig. 1A, B).Paleomagnetic data of the CAMP relics are well documented in North

Luiz, Faculdade de Ciências,, 1749-016, Lisboa, Portugal.

magnetism of the Central At.1016/j.tecto.2015.07.036

America (Deenen et al., 2011; Donohoo-Hurley et al., 2010; Kent andOlsen, 1999, 2008), Morocco (Font et al., 2011; Knight et al., 2004;Ortas et al., 2006; Ruiz-Martinez et al., 2012) and South America (deMin et al., 2003; Ernesto et al., 2003) but are still poorly constrained inIberia. Actually, the sole reliable paleomagnetic pole comes from theMessejana dyke (Ortas et al., 2006), a giant dolerite intrusion thatobliquely cuts across the South Portuguese, Ossa-Morena and CentralIberian zones of the Variscan Iberian Massif for more than 530 km(Fig. 1B, C). Paleomagnetic data of the CAMP volcanic successions(pyroclastic deposits, lava flows, dykes) cropping out in the Algarveand Santiago do Cacém basins, which represent potential candidate tounravel the chronological framework of the CAMP eruptions in Iberia,are still lacking. This paper aims to provide the first rock magnetic andpaleomagnetic data from the CAMP lava flows in the Algarve basin.Our objectives are (i) to assess whether the magnetic signal is primary,and thus suitable for further paleomagnetic investigation, byconducting a detailed magnetic mineralogy investigation from tensites along aW-E transect from Sagres (western Portugal) to Ayamonte(Spain) (Fig. 1C), and (ii) to discuss the implications of the correspond-ing virtual geomagnetic poles (VGPs) in terms of chronological and tec-tonic constraints.

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

Fig. 1. (A)Map of Pangea at 201Ma showing the distribution of theCentral AtlanticMagmatic Province (modified fromMarzoli et al. (2011) and Bertrand et al. (2014)). (B) Onset showingthe distribution of sub-surface Triassic–Jurassic basin and exposed CAMP lavas in North America, Northwest Africa and Iberia (palaeogeographic reconstruction is based on the model ofTorsvik et al. (2012)). (C) Map of southern Portugal showing the location of the studied sites from the Algarve basin (modified fromMartins et al. (2008)) and the main tectonic features(modified from Terrinha et al. (2013)). The onset (right upper corner) shows the position of the giant Messejana dyke.

2 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

2. Geological setting

The E–W trending Algarve basin is a pull-apart basin located onthe northern part of a left-lateral transtensional shear zone accom-modating the opening of the central Atlantic rift system to the SEand the Neotethys rift system to the NW (Terrinha, 1998; Terrinhaet al., 2013) (Fig. 1A, B). During the lattermost Triassic, the Algarvebasin was tectonically active and affected by graben structures filledby continental sandstones (Grès de Silves; Palain, 1976), restingunconformably on Carboniferous shales and graywackes of theVariscan basement. From Late Triassic to Early Jurassic (Hettangian),a volcano-sedimentary sequence constituted by tholeiitic lava flowsand pyroclastic deposits interbedded within red mudstones, silt-stones and sparse limestones or dolostones overlie the Triassic red

Please cite this article as: Font, E., et al., Paleomagnetism of the Central AtTectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

sandstones or locally rests directly on the Paleozoic basement(Martins et al., 2008; Palain, 1976; Rocha, 1976; Youbi et al., 2003).

The oldest CAMP magmatism in Iberia is represented by the giantMessejana dyke, dated at 203 ± 2 Ma by 40Ar/39Ar method (Dunnet al., 1998) and thought to be the feeder of part of the eruptive productscropping out in the Algarve and Santiago do Cacém basins (Terrinhaet al., 2013). The ages of these volcanics are poorly constrained andhampered by the probable presence of several (diachronous?) eruptivecenters (Martins et al., 2008; Youbi et al., 2003) aswell as by severe rockalteration, making the calibration of a reliable chronological frameworkfor the emplacement of these extrusive rocks extremely difficult.Actually, we were not able to collect samples in the Santiago do Cacémbasin, due to the severe alteration of the rocks as well as to the lack ofoutcrops displaying continuous sections across the whole thickness of

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

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the volcanic sequence. In rare localities of the Algarve basin, the CAMPlava flows show a more preserved aspect (hard rock) marked byapparent preservation of pyroxene and plagioclase in hand specimens,thus representing suitable candidates for preliminary paleomagneticinvestigation.

Recent radiometric (40Ar/39Ar) data (furnace step heating method)of three lava samples from the Algarve basin and two from the Santiagodo Cacém basin were provided by Verati et al. (2007). Samples from thearea of Alte (Fig. 1C) yielded ages of 198.9± 0.7Ma and 197.7±0.4Ma.Samples from Tavira and Santiago do Cacém basin yielded ages of196.3 ± 1.3 Ma and 198.2 ± 0.7 Ma, respectively. Verati et al. (2007)considered the weighted mean age of the two plateau ages from Alteat 198.1 ± 0.4 Ma (2σ) as the best estimate of the age of the CAMP vol-canism in Portugal.

In terms of geochemical composition, theAlgarve lavaflows are clas-sified as low Ti- basalts enriched in large ion lithophile elements, whichsuggests partial melting of heterogeneous mantle sources (Martinset al., 2008). Their geochemical signature (TiO2, SiO2, La/Yb, Y/Nb,Lu/Hf) is comparable to the intermediate and upper basalt unitsfrom Morocco and to the oldest (intermediate) units from the Newarkbasin (Orange Mountains) (Deenen et al., 2010; Martins et al., 2008;Marzoli et al., 2004). Geochemical and radiometric ages thus indicatea younger age for the onset of the CAMP volcanism in Portugal com-pared to the Moroccan and USA basalts units.

Froma tectonic point of view, theAlgarve basin is segmented by sev-eral fault systems oriented approximately N-S, NE-SW, E-Wand NW-SE(Fig. 1C) (Terrinha et al., 2013), being the most important the post-Variscan N-S Aljezur and Portimão faults, the NW-SE São Marcos-Quarteira fault and the NE-SW Carcavai fault (Terrinha, 1998; Terrinhaet al., 2013). The comparison of these fault systems with those affectingthe paleozoic basement suggests that they already exist during theVariscan orogenic and tardi-orogenic episodes and were active sincethe Jurassic (Terrinha et al., 2013). The N-S faults developed duringthe extensional phases related to the opening of the Atlantic Ocean,while the transtensive stretching resulting from the separation betweenEurasia and Africa led to the formation of E-W toWNW-WSW-orientedbasins, observable fromMorocco to the Pyrenees, including the Algarvebasin. Tectonic inversion occurred during the Cenozoic by compressivereactivation of the fault systems due to crustal shortening. The succes-sive deformation events that affected the Algarve basin and the lack ofoutcrop continuity in the field hindered the definition of a clear strati-graphic and chronological framework for the volcanism across thebasin.

Table 1Geographic coordinates of the sites from theAlgarve basin under study; attitude of the beddingand tilt-corrected coordinates (Dec=Declination (°), Inc= Inclination (°),N and n are the numK is the precision parameter and a95 is the interval of confidence; and coordinates of the correstions (Plat = Paleolatitude (°), Plong = Paleolongitude (°) and Dp, Dm are the ellipsoid of con

Area Site Geographiccoordinates

Tilt correction(Strike/Dip)

N ChRM

Lat.(N)

Long.(W)

n Dec

São Bartolomeu de Messines SB 37.257 8.299 N80°/16° 117 117 344Alte I (top) AL 37.286 8.167 N290°/19° 23 22 7.2Alte II (base) RL 37.235 8.176 N108°/28° 14 13 11.9Caminho velho de Alte FP 37.241 8.188 N170°/20° 22 22 29.9Atalaia AA 37.248 8.179 N120°/5° 26 26 15.1Jardim del Gonduana JG 37.226 7.410 N70°/14° 17 17 345.6Quinta da Ombria QO 37.194 8.018 N110°/28° 11 11 356.8Ayamonte (Spain)* AY 37.227 7.404 N90°/15° 21 20 12.3Hortas do Tabual HT 37.073 8.876 N0°/0° 30 30 347.8Rio Arade RA 37.220 8.370 N100°/10° 30 30 336.5All sites 9 359.3Group A(SB + HT + JG + RA + QO)

5 346.3

Group B (AA + RL + FP + AL) 4 17

Please cite this article as: Font, E., et al., Paleomagnetism of the Central AtTectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

3. Sampling

We have sampled the Algarve basin volcanics at 9 sites: Quinta daOmbria (QO), São Bartolomeu de Messines (SB), Atalaia (AA), Hortasdo Tabual (HT), Rio Arade (RA) and Alte (Alte base—RL; Alte top—AL;and Caminho Velho de Alte – FP) (Fig. 1C; Table 1).

The SB, RA and HT sites are located in the western Algarve basin,west of the São Marcos-Quarteira fault (Fig. 1C). Site SB correspondsto a 20- to 30-m-thick lava flow cropping out in a quarry near the vil-lage of São Bartolomeu de Messines (Figs. 1C and 2A, B). The absenceof discontinuities across the whole thickness suggests that this out-crop corresponds to a single flow. We sampled in detail the base(SB1, SB2, SB3 and SB4) and the top (SB5) of the outcrop (Fig. 2).The base of the lava flow with the underlying sediments is not ob-served in the field, hampering the direct measurement of the bed-ding attitude. We thus oriented the lava flow by measuring thestrike and dip of columnar and platy flow joints, which are usuallyperpendicular and parallel, respectively, to the topographic surfaceon which the lava was emplaced (Fig. 2B). Although the topographicsurface on which the lava was emplaced could be erosive, most of thevisited outcrops of the Algarve basin show a conformable contact be-tween the lavas and the stratification in the underlying sediments.The HT site is located near the village of Sagres, where the CAMPsequence is less developed and outcrops are less abundant. Itcomprises two thin (metric-scale) basaltic flows separated by a~1-m-thick dolostone layer (Fig. 1C, 2J). Bedding is easily measur-able at the contact between the lava flows and the dolomitic layer.Site RA is located in an agricultural flat area, northeast of Silves(Fig. 1C). We sampled three outcrops from the western (RA1) andeastern sides (RA2 and RA3) of the plateau. Bedding was retrievedby measuring platy and columnar joints.

In the central part of the Algarve basin, near the village of Alte, athick (~15–20 m) basalt unit is observed from the highest topo-graphic levels (site AL; Fig. 2C–E) down to the Alte river (sites RL1and RL2; Fig. 2F–H). However, there is no outcrop continuity be-tween the AL and RL sites, making it impossible to discriminate ifthe basalts correspond to a single massive lava flow or to the super-position of several flows from a single eruption or from multipleeruptive events. At the RL1 site, the lava structure is marked by thepresence of platy and columnar joints (Fig. 2). At RL2 site, there areno observable structural criteria and we thus used the bedding atti-tude in RL1 site since lavas flows are continuous from RL1 to RL2.Two others sites corresponding to single thin basalt flows were

plane (tilt correction; Strike andDip), characteristic remanentmagnetization in geographicber of total and selected samples, respectively, R is the length of the addition of unit vectors,ponding virtual paleomagnetic poles calculated based upon tilt-corrected site-mean direc-fidence).

s (geographic coordinates) ChRMs (tilt corrected) VGPs (tilt corrected)

Inc R K a95 Dec Inc K a95 Plat. Plong. Dp Dm

41.4 116.1 123.7 1.2 341.6 57.3 123.7 1.2 75.4 270.1 1.3 1.765.1 21.7 74.6 3.6 12.2 46.6 74.4 3.6 76.1 120.6 3.0 4.624.4 13.0 222.3 2.8 8.9 52.2 222.0 2.8 81.5 110.3 2.6 3.835.7 21.6 47.0 4.6 14.9 46.6 47.0 4.6 74.4 114.2 3.8 5.933.5 25.9 255.8 1.8 14.1 38.4 256.5 1.8 70.2 129.9 1.2 2.143.4 16.9 118.0 3.3 347.5 57.3 118.2 3.3 80.1 270.5 3.5 4.833.3 10.9 100.5 4.6 342 57.7 100.4 4.6 75.8 272.1 4.9 6.760.8 19.1 21.8 7.2 23.9 75.1 21.8 7.2 61.1 15.8 12.0 13.142.7 29.4 47.2 3.9 347.8 42.7 47.2 3.9 73.9 215.1 3.0 4.837.1 29.7 98.7 2.7 343.7 42.1 98.5 2.7 71.0 223.5 2.0 3.340.8 8.6 21.2 11.4 357.9 49.8 43.8 7.939.8 5.0 126.7 6.8 344.7 51.5 92.4 8 76.4 244.2 7.4 10.9

39.8 3.8 18.3 22.1 12.7 45.9 185.4 6.8 75.4 120.8 5.5 8.6

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

Fig. 2. Field photographs of sampled sites from the Algarve basin. The strike and dip of columnar and platy flow joints in the lavas flows are indicated, as well as the bedding of the un-derlying sediments when observable.

4 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

sampled at the “Atalaia” (AA) and “Caminho Velho de Alte” (FP) loca-tions, some kilometers northward of the village of Alte (Fig. 1C). Atsite FP, the bedding attitude was measured at the contact betweenthe lava flow and the underlying sediments (Fig. 2I).

In the eastern Algarve basin, outcrops are located north of the city ofAyamonte (Fig. 1C). We collected samples from two localities: Jardinsdel Gonduana (JG) and Ayamonte (AY) (Fig. 1C and Table 1). At siteAY, the outcrops are severely affected by tectonics, making it difficultto obtain accurate attitudes of the lava flows.

Please cite this article as: Font, E., et al., Paleomagnetism of the Central AtTectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

4. Methods

The magnetic mineralogy was investigated by using rock mag-netic techniques, namely, Isothermal Remanent Magnetization(IRM) curves, low and high temperature dependence magnetic sus-ceptibility (K-T curves), hysteresis curves and first-order reversalcurves (FORCs) diagrams. Representative samples were previouslydemagnetized by an alternated magnetic field (AF) at 100 mT andfurther submitted to a progressive uniaxial and constant magnetic

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

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field up to 1 T following approximately 25 steps at constant temper-ature, using a pulse magnetizer (ASC Scientific IM-10-30). Rema-nence was measured with a JR6 magnetometer (sensitivity of2.4 × 10−6 A/m). IRM curves were treated by a cumulative log-Gaussian function (Kruiver et al., 2001; Robertson and France,1994). K-T curves were conducted under Argon-controlled atmo-sphere using an MFK1 (AGICO) apparatus, and reported in SI units.All techniques (except hysteresis curves and FORC diagrams) wereperformed at the Paleomagnetic laboratory of the Institute DomLuis, in Lisbon, Portugal. Hysteresis curves and FORC diagramswere measured using a magnetometer (μ-VSM) from PrincetonMeasurements Corporation at the IPGP-IMPMC (Institut de Phy-sique du Globe de Paris-Institut de Minéralogie, de Physique desMinéraux et de Cosmochimie) Mineral Magnetism Analytical Facil-ity. Data were treated using the VARIFORC software (Egli, 2013).Demagnetization treatment included stepwise alternating fieldsup to 100 mT using an LDA-3A demagnetizer (AGICO) and thermalcleaning by using a homemade shielded furnace. Themeasurementswere subjected to principal component analysis of the naturalremanent magnetization (NRM) by using the Remasoft (AGICO)software.

Table 2Isothermal remanentmagnetic parameters after treatment by the cumulative log-Gaussian func(mT), DP is the dispersion parameter, and % represents the percentage of contribution in the to

Component 2 (soft magnetite) Component 2 (hard mag

SIRM Log B1/2 B1/2 DP Contribution (%) SIRM Log B1/2 B1/2

HT1.G4 318.00 1.30 19.95 0.26 100.00HT2.E2 285.00 1.14 13.80 0.33 91.94 25.00 1.75 56.2HT2.F3 340.00 1.23 16.98 0.33 93.54 23.50 1.85 70.7HT3.A3 433.00 1.25 17.78 0.23 100.00AL1A 20.00 1.25 17.78 0.28 3.64 530.00 1.73 53.7AL1B 85.00 1.26 18.20 0.30 16.67 425.00 1.60 39.8AL1C 100.00 1.26 18.20 0.27 22.22 350.00 1.64 43.6AL1D 100.00 1.30 19.95 0.30 21.60 363.00 1.65 44.6AL1E 90.00 1.27 18.62 0.28 24.86 272.00 1.61 40.7AL1F 80.00 1.22 16.60 0.28 18.82 345.00 1.60 39.8AL1G 50.00 1.28 19.05 0.28 9.09 500.00 1.68 47.8SB1A 138.00 1.69 48.9SB1C 142.00 1.66 45.7SB1D 115.00 1.59 38.9SB1E 141.00 1.67 46.7SB1G 120.00 1.61 40.7SB1H 125.00 1.66 45.7SB2A 139.00 1.59 38.9SB2B 149.00 1.57 37.1SB2C 126.00 1.60 39.8SB2D 129.00 1.61 40.7SB3A 133.00 1.59 38.9SB3B 125.00 1.58 38.0SB3C 133.00 1.59 38.9JG1.B2 415.00 1.53 33.8JG1.C1 452.00 1.51 32.3JG1.D4 485.00 1.52 33.1FP1.C2 300.00 1.67 46.7FP1.B1 282.00 1.70 50.1FP1.E1 382.00 1.71 51.2RL1.E3 319.00 1.62 41.6RL1.B4 420.00 1.60 39.8RL2.G3 254.00 1.57 37.1AY1.C3 275.00 1.52 33.1AY2.C3 289.00 1.43 26.9AY2.B3 305.00 1.43 26.9AA1.E4 150.00 1.77 58.8AA1.A3 244.00 1.78 60.2AA1.C1 140.00 1.76 57.5RA1.A1 45.00 1.74 54.9RA1.B3 22.00 1.75 55.5RA2.E2 303.00 1.79 61.6QO2.B3 232.00 1.72 52.4QO2.E3 281.00 1.75 56.2QO2.F2 222.00 1.74 54.9

Please cite this article as: Font, E., et al., Paleomagnetism of the Central AtTectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

5. Rock magnetism

5.1. Isothermal remanent magnetization

IRM curves were acquired for 44 specimens (13 in SB; 7 in AL and 3 inHT, AA, RA, RL, AY, JG, FP and QO; Table 2) for which typical behaviors arerepresented in Fig. 3. One or two components of low, medium and highcoercivity ranges are isolated after unmixing raw IRM curves by using acumulative log-Gaussian function (Kruiver et al., 2001; Robertson andFrance, 1994). The main magnetic component has B1/2 (mean coercivity)of 27–58mT and is identified in almost all samples (except in HT). It con-tributes tomore than 75% of the total remanence, except in samples fromsite RA, where a high coercive component contributes to more than 90%of the total remanence (Fig. 3B). The values of B1/2 are comparable tothose from the Moroccan CAMP lavas and lie within the typical range oftitanomagnetite (Font et al., 2011). We called this IRM component“hard magnetite” (relative to the lower coercive component) (Fig. 3).The values of the dispersion parameter (DP, the width of distributiongiven by one standard deviation) of the hardmagnetite are homogeneouswithin-site, suggesting a homogeneous distribution of grain size andcomposition of the magnetite population, but differing from site to site.

tion. SIRM is the saturation isothermal remanentmagnetization, B1/2 is themean coercivitytal remanence.

netite) Component 3 (Hematite)

DP Contribution (%) SIRM Log B1/2 B1/2 DP Contribution (%)

3 0.30 8.069 0.30 6.46

0 0.24 96.361 0.25 83.335 0.24 77.787 0.24 78.404 0.24 75.141 0.25 81.186 0.24 90.918 0.36 100.001 0.34 95.95 6.00 2.70 501.1872 0.37 4.050 0.33 100.007 0.33 93.38 10.00 2.60 398.1072 0.38 6.624 0.33 100.001 0.35 100.000 0.33 100.005 0.33 100.001 0.33 100.004 0.32 100.000 0.33 100.002 0.33 100.000 0.33 100.008 0.31 100.006 0.28 100.001 0.27 100.007 0.25 100.002 0.26 100.009 0.25 100.009 0.37 100.001 0.36 100.005 0.35 100.001 0.29 100.002 0.28 100.002 0.27 100.008 0.32 88.76 19.00 2.75 562.3413 0.37 11.246 0.31 100.004 0.32 85.37 24.00 2.60 398.1072 0.45 14.635 0.30 70.31 19.00 2.40 251.1886 0.21 29.699 0.30 86.27 3.50 2.48 301.9952 0.29 13.736 0.30 100.008 0.32 100.003 0.29 100.005 0.29 91.74

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

6 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

Please cite this article as: Font, E., et al., Paleomagnetism of the Central Atlantic Magmatic Province in the Algarve basin, Portugal: First insights,Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

Fig. 4. Examples of low and high temperature dependence of magnetic susceptibility (K in SI) of the CAMP lava flows from the Algarve basin. All heating cycles show a systematic andabrupt decrease in K between 560 °C and 580 °C, typical of the Curie point of magnetite. In some samples (e.g., AL1.C), the heating curve shows a hump at around 300 °C suggestingthe admixture of maghemite. Sample AL1.C show another hump at ~540 °C, typical of the Hopkinson peak. Few mineralogical transformations occurred during heating, as noted bythe almost reversible behavior of the heating and cooling curves. Low temperaturemeasurements show a systematic and rapid K decrease at ~−150 °C, characteristic of the Verwey tran-sition of magnetite.

7E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

For example, SB samples have a DP of 0.33, whereas AL samples havemean DP values of 0.24 (Fig. 3). These variations probably arose from dif-ferences in magma composition and/or cooling rates.

A lower coercive magnetic component with B1/2 of 14–20 mT is ob-served in specimens from the HT and AL sites (Fig. 3). In HT specimens,this low coercive phase contributes to 100% of the remanence, while itcontributes to 4–25% in the AL samples (75–96% being carried by thehard magnetite; Fig. 3A). This “soft” component may correspond to alow coercive (titano-) magnetite. Within-site DP values of this “softmagnetite” are comparable to those from the hard magnetite.

A high coercive component with B1/2 of 250–500 mT, interpreted ashematite, is accessorily present in someAA and SB specimens, becomingdominant in the RA1 specimens where it contributes up to 30% of thetotal remanence (Fig. 3). In the AA, SB and RA1-RA2 samples, this hema-tite has a minor contribution in the remanence (b11%; Fig. 3C). Thevalues of DP show a wide data dispersion (0.21–0.45), probablyresulting from the noisy character of the IRM curves in higher inductionfields (Fig. 3A) or due to the presence of heterogeneous populations ofsecondary hematite.

5.2. K-T curves

K-T curves were conducted in one sample per site (Fig. 4). All K-Tcurves show an abrupt decrease in magnetic susceptibility at around560–580 °C, indicative of the Curie point of Ti-poor titanomagnetite.Samples AA1.C, AY1.B and AL1.C show a hump at around 250 °C, follow-ed by a gradual decrease of K values up to 350 °C, which is attributed tothe presence of maghemite. At low temperatures, K-T curves show a

Fig. 3. (A) Examples of characteristic isothermal remanentmagnetization (IRM) acquisition curthe mean coercivity (Log B1/2) in function of the dispersion parameter (DP) and of the contribuercivity (B1/2=27–58mT, called “hardmagnetite” and represented by the grey IRM-CLG curve(B1/2= 14–20mT) ferromagnetic phase (probablymagnetite) is identified in theAL (contributia hard magnetic component (B1/2 = 250–560 mT) lying in the typical coercivity range of hem

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systematic and abrupt hump at−150 °C followed by a gradual decreaseof K values, which is characteristic of the Verwey transition of magne-tite. Few mineralogical transformations occurred during heating, asshown by the almost reversible behavior of the heating/cooling curves.

5.3. First-order reversal curves and hysteresis

FORC diagramsweremeasured on 11 characteristic samples with anaveraging time of 100 ms and a saturating field of 1 T. 100 FORCs wereused to calculate each FORC diagram. They were analyzed with theVARIFORC software (Egli, 2013) and a variable smoothing factor. Thevariable smoothing considerably reduces the noise levels by applyinglarger smoothing factors to the background, while preserving theareas along the axes with relatively small smoothing factors.

An example of FORC diagrams for each unit is plotted in Fig. 5. All theFORC diagrams are characteristic of pseudo-single-domain magneticgrains in their broad lines: the innermost contours are closed, whilethe outermost ones diverge away from the horizontal axis. This is con-sistent with the hysteresis parameters plotted on a Dunlop diagram(Fig. 6). All the samples from each lava flow have very similar FORC di-agrams, but there are some slight differences between the samples fromthe different lava flows. Sample FR1-A seems to have a smaller grainsize: the coercivity peak is higher than in the SB and AL samples. Both,AL1 and FR1 samples have an important high coercivity component,with the outermost contour extending up to 120 mT. This outermostcontour extends only to 90 mT in the case of sample SB3. The spreadalong the Hu axis is significant for all samples, with full width athalf maximum around 25 mT, which indicates that the amount of

ves after treatment by the cumulative log-Gaussian (CLG) function. (B) Diagrams showingtion (%) in the total remanence. Most of the samples show the presence of a medium co-in (A) ferromagnetic phase that contributes tomore than 70% of the total remanence. A softng to 3–25% of the total remanence) and HT (100% of the remanence) samples. Accessorily,atite is identified in some samples from the RA, SB and AA sites.

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

Fig. 5. First-order reversal curves (FORC) diagrams of representative samples plotted with a variable smoothing factor (Egli, 2013). The Hc and Hu scales are the same for all the FORCdiagrams.

Fig. 6.Hysteresis data of the studied samples plotted on the theoretical unmixing diagramof Dunlop (2002) and showing a typical SD + MD trend.

8 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

magnetostatic interactions is substantial in these rocks. Sample AL1-C(not shown) is more multi-domain-like than the other samples, withcoercivity contours that do not extend after 50 mT.

6. Paleomagnetism

Paleomagnetic data are illustrated in Figs. 7 and 8 and presented inTable 1. After stepwise AF cleaning, more than 99% of the studied sam-ples yielded stable and reliable magnetic directions. More than 90% ofthe remanence were cleaned below 100mT, confirming magnetite asthe main magnetic carrier, as suggested by our rock magnetic results(Figs. 3–5). Due to high content of hematite previously identified byusing the IRM-CLG curves in the RA samples, these latter were cleanedby thermal demagnetization (Fig. 7). After stepwise AF and thermaldemagnetization, one or two magnetic vectors are observed inthe Zijderveld diagrams: a low temperature (b100 °C) and a high

Fig. 7. Stereographic and orthogonal projections and remanence intensities during alternating fiafter tilt correction. Stereographic projection of sample-based mean direction for each site andthe interval of confidence; K is the precision parameter; n is the number of samples used in theNRM is the natural remanent magnetization.

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temperature (unblocking temperatures of 350 °C, 560 °C and 640 °C)magnetic component. Unblocking temperatures of ~560 °C and 640 °Cindicate the presence of titanomagnetite and titanohematite, respec-tively (Fig. 7). The decrease in the remanence observed at ~350 °C isprobably due to thepresence ofmaghemite. The orthogonal plot of sam-ple RA2-E4 is almost linear from 250 °C up to 640 °C (Fig. 7), suggestingthat titanomagnetite and titanohematite locked the magnetizationwithin a relatively short time interval (cooling) in these samples.

Magnetic directions illustrated in stereographic projections are pos-itive (normal) in all sites and cluster approximately at N0° with a meaninclination of 40–50° (Figs. 7 and 8). The exceptions are the Ayamonteand Hortas do Tabual samples (site AY and HT, respectively), forwhich remanence is carried by a very low coercive phase with mediandestructive field (MDF) of 5–8 mT (Fig. 7). This low coercive phase isalso identified in our IRM-CLG analyses (Fig. 3). Characteristic remanentmagnetization (ChRM) directions of the HT samples are comparable tothose from the other sites under study, but the AY samples definitivelyshowmore scattered (precision parameter as low as k=15) and anom-alously high inclination directions.We thus excluded the AY site for fur-ther calculation of mean magnetic components.

We calculated the mean characteristic remanent magnetization(ChRM) directions for each site, except for the AY site (Table 1). Insitu site-mean ChRM directions are reported in Table 1, while tilt-corrected site-mean ChRM directions are illustrated in Figs. 7 and 8.The number of specimens used for the calculation of site-mean direc-tions varies between 11 and 30, but reach 117 in the São Bartolomeude Messines (SB) site (i.e. the thicker lava flow). At site SB, we sampledin details the base and the top of the outcrop in order to check for thepresence of one or several events (Fig. 2A, B). However, our results indi-cate no significant difference in the ChRM from the base and to the topof the outcrop, suggesting that the 30-m-thick basalt represents a singleeruptive event. Site-meanmagnetic directions have satisfactory statisti-cal values, namely, alpha95 comprised between 1.2° and 4.6° and preci-sion parameter (K) between 47 and 256 (Table 1). Individual virtualgeomagnetic poles per site are reported in Table 1 and illustrated inFig. 9.

7. Discussion

Our magnetic mineralogy study shows that the main magnetic car-riers of the CAMP lavas from the Algarve basin are moderately coercive

eld (AF) and thermal demagnetization of the samples from the AA, RA, QO, HT and AY sites,the associated statistical values of the mean component are represented on the left. a95 iscalculation of the mean component, while N corresponds to the total number of samples.

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

9E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

Please cite this article as: Font, E., et al., Paleomagnetism of the Central Atlantic Magmatic Province in the Algarve basin, Portugal: First insights,Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

10 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

(Hc ~ 20–40mT) magnetite grains, except in the HT and AL sites whereIRM-CLG curves show the presence of a low coercive (Hc b 18mT)mag-netite population (Fig. 3). Thermal demagnetizations of RA samplesshowed Curie temperatures of 560–580 °C and 640 °C, indicating thepresence of titanomagnetite and titanohematite, respectively (Fig. 4).Curie temperatures at around 580 °C and the systematic presence ofthe Verwey transition observed in the low temperature thermomagnet-ic analyses of most of samples corroborate the presence of Ti-poortitanomagnetite (Fig. 4). The grain size of the magnetite population es-timated from hysteresis data and FORC diagrams are in the range of PSDparticles. Hematite is also identified in the IRM-CLG curves and thermaldemagnetization curves in sites SB, AA and RA. In RA samples, hematitecontributes to more than 90% of the remanence, whereas its contribu-tion is minor in samples SB and AA. After thermal demagnetization ofRA samples, directions isolated in the range of the Curie temperatureof hematite (580–680 °C) are similar to those carried by the magnetitepopulations, suggesting that both magnetite and hematite populationslocked the magnetization during a short time interval (cooling). Theremanence carried by hematite can be thus primary (thermal origin)or acquired soon after cooling (by early deuteric oxidation and chemicalremanent magnetization acquisition) (Dunlop and Özdemir, 1997).Themean ChRM calculated based upon all sites (except AY; N = 9) hasK = 21.2 and a95 = 11.4° in geographic coordinates, and K = 43.8and a95 = 7.9° after tilt correction (Table 1, Fig. 9A), which suggestsa primary (pre-tectonic) origin for the magnetization recorded inthese rocks. However, no significance test was achievable: no foldedstructures were observed in the field, whereas a baked contact test ishampered by the severely altered state of the underlying sediments.Magnetic polarities are all normal (positive), similarly to circum-Atlantic CAMP lavas (with a few exceptions in the Messejana dykenear Juromenha, where Ortas et al. (2006) reported three sites show-ing reversed polarities) and probably corresponding to the magneticchron E24n identified in the Newark Basin, USA (Deenen et al., 2010,2011; Font et al., 2011; Kent and Olsen, 1999; Knight et al., 2004).

Since radiometric data suggested that the CAMP lava flows and theMessejana dyke were emplaced together within a short time interval(~203–198 Ma; Dunn et al. (1998);Verati et al. (2007)), they shouldcarry the same paleomagnetic pole directions. We thus compared thesite-mean virtual geomagnetic poles (VGPs) obtained by Ortas et al.(2006) in the Messejana dyke with our data (Fig. 9B). Results showthat only 5 sites (SB, HT, QO2, RA, JG, called “Group A”) are compatiblewith the geomagnetic directions recorded by the Messejana dyke,while 4 sites (AA, AL, RL, FP, called “Group B”) have declination valuesrotated approximately 30° clockwise (Fig. 9B). Following theMcFadden and Lowes (1981) test, the null hypothesis of a commonmean direction between both groups (Group A, N = 5; Group B,N = 4) may be rejected at the 95% confidence level (as the test isclearly negative). This also allows analyzing the two groups indepen-dently. Interestingly, all the sites belonging to the Group B are locat-ed in the central part of the Algarve basin near the village of Alte, justeast of the major São Marcos-Quarteira Fault (Fig. 1C). Such strikingcoincidence can be due to one of the following two reasons: (i) rockswere affected by remagnetization and (ii) the rocks from this areawere affected by post-emplacement vertical-axis tectonic rotation.

In order to test these hypotheses, we calculated a mean VGP foreach Group (A and B; Table 1) and compared themwith the apparentpolar wander path (APWP) of Iberia (Fig. 8C), which is based on acompilation from Neres et al. (2012) and Osete et al. (2011) (70–142 Ma and 180–203 Ma paleomagnetic poles, respectively). TheVGP of Group A (Plat = 76.4°, Plong = 244.2°, Dp = 7.4, Dm =10.9) overlaps the Iberia APWP at 180–200 Ma, comforting the ideathat both, CAMP lavas and the Messejana dyke emplacement, aremore or less coeval (Fig. 8C). However, it also overlaps the 100- to120-Ma poles, suggesting that a Cretaceous remagnetization is a pos-sible scenario. Globally, two magmatic episodes affected the WestIberian Margin during the Cretaceous alkaline magmatic episodes

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(Miranda et al., 2009): the first one (94–88 Ma) occurred duringthe opening of the Bay of Biscay and consequent rotation of Iberiaand clusters above N38° 20′; the second pulse (75–72 Ma) has awider geographical distribution, from N37° to N39°, and includesthe Monchique intrusion (Fig. 1C). The Monchique Alkaline Complexis the most voluminous alkaline intrusion that affected the regionduring the Cretaceous and is associated to a huge 0- to 3.5-km-deep laccolith-oriented E-W and measuring 200 km in length andmore than 50 km in width (Gonzalez-Castillo et al., 2014). Crustalfaulting of this laccolith may have provided conduits for the circula-tion of hydrothermal fluids, acting as a remagnetization agent in theAlgarve basin (Elmore et al., 2006; Font et al., 2012). A basin-scaleremagnetization event would have affected all sites located close tothe intrusion or close to the crustal faults of Portimão and SãoMarcos-Quarteira faults, including those from Group A (RA, SB) andthose from Group B (AA, FP, AL, RL) (Fig. 1). However, the fact thatGroup A and Group B magnetic directions and paleomagnetic polesare statistically different between them and when compared to the88- and 70-Ma Iberian mean poles (Fig. 1C) argues against a Creta-ceous remagnetization event linked to the Monchique laccolith.Note that although some small Cretaceous intrusions are observedalong the Algarve littoral, there are no Cretaceous intrusions inmost of the studied area. Therefore, we suggest that the discrepancyobserved between the Group A and Group B directions is not the resultof a remagnetization but is rather due to complex tectonic processesthat affected the Algarve basin during Mesozoic and Cenozoic.

The VGP of Group B (Plat = 75.4°; Plong = 120.8°; Dp = 5.5°,Dm = 8.6°) does not fit any Iberia APWP pole from 200 to 70 Ma(Fig. 9C). Although the VGP of Group B is close to the reference pole at70 Ma, the latest episode of magmatism affecting the Iberian margin,they are statistically distinct (no overlap of their respective confidenceintervals; Fig. 1C). Neither paleomagnetic data are documented after70 Ma nor major deformation events that could have led to widespreadremagnetization of pre-Cretaceous rocks. Therefore, we propose thatlocal vertical-axis block rotation is the alternativemechanism to explainthe discrepancy observed between Group A and Group B declina-tions. In order to better quantify the amount of rotation due to tec-tonic deformation, we calculated the difference in the tilt-corrected declination and inclination values between Group A(Dec = 344.7°; Inc = 51.5°; a95 = 8°) and Group B (Dec = 12.7°;Inc = 45.9°; a95 = 6.8°) and the respective significance (Beck,1980; Butler, 1992; Demarest, 1983). The confidence limit on

vertical-axis rotation is given by ΔR ¼ 0:8√ ½ðΔDAÞ2 þ ðΔDBÞ2� , inwhich ΔD ≈ α95/cos I. The flattening of inclination (F) is given by

ΔR ¼ 0:8√ ½ðΔIAÞ2 þ ðΔIBÞ2�, in which ΔI= α95. In our case, the differ-ence in inclination, ± ΔF= 5.6°± 8.4°, is not significant and thus arotation along horizontal axis is not favored. However, the differ-ence in declination, R ± ΔR = 28.0° ± 12.9°, (clockwise) is highlysignificant, thus suggesting vertical-axis rotation of the sites corre-sponding to Group B with respect to the rest of the basin. Compar-ison of the Messejana pole (35 sites, Dec = 339.9°, Inc = 46.9°,a95 = 3.5°) with Group A yielded R ± ΔR = 4.8° ± 11.1° and F ±ΔF = 4.6° ± 7.0°, suggesting that both declination and inclinationof Group A are statistically undistinguishable from the Messejanapole (the uncertainties are greater than the difference values).Conversely, comparison of the Messejana pole with Group Byielded R ± ΔR = 32.8° ± 8.8° and F ± ΔF = −1.0° ± 6.1°, whichindicates a significant clockwise rotation.

Group B sites are located in a complex faulted zone, limited by the70-km long N140° E-striking São Marcos-Quarteira Fault (SMQF) tothe west and the NE-SW trending Carcavai Fault to the south (Fig. 10).The Carcavai Fault is considered as an active fault zone and the probablesource of the 1856 Loulé earthquake (Carvalho et al., 2012). These on-shore faults are connected to major offshore structures identified inthe Gulf of Cádiz from geological survey and played an important role

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

Fig. 8. Stereographic and orthogonal tilt-corrected projections and remanence intensities during alternating field (AF) cleaning of the samples from the SB, JG, FP, AL and RL sites. Samelegend as in Fig. 7.

11E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

Please cite this article as: Font, E., et al., Paleomagnetism of the Central Atlantic Magmatic Province in the Algarve basin, Portugal: First insights,Tectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

12 E. Font et al. / Tectonophysics xxx (2015) xxx–xxx

Please cite this article as: Font, E., et al., Paleomagnetism of the Central AtTectonophysics (2015), http://dx.doi.org/10.1016/j.tecto.2015.07.036

in the segmentation of the Algarve Basin (Carvalho et al., 2012; Lopeset al., 2006; Terrinha, 1998; Terrinha et al., 2009; Terrinha et al.,2013). The tectonic evolution of the Algarve basin is complex and in-cludes halokinesis, fault reactivation and tectonic inversion fromMesozoic to Cenozoic. From the Triassic to the Early Cretaceous, themajor faults behaved as extensional structures linked to the openingof the central Atlantic rift and of theWestern Tethys. Tectonic inversionoccurred from Late Paleogene, followed by Cenozoic compression(Terrinha, 1998). According to Terrinha (1998), the SMQF is aninherited Variscan thrust reactivated as a dextral transtensional faultduring E-W Mesozoic extension and as a dextral transpressive strike-slip fault during the Cenozoic tectonic inversion. If we assume that themain deformation of the studied area is controlled by the NW-SEmajor faults, such as the SMQF, the clockwise rotation is consistentwith a Riedel shear zone (Fig. 10). The basic geometry of Riedel shearstructures consists of conjugate shear bands arranged in en-échelon ar-rays and are common features of active continental deformation involv-ing vertical-axis crustal block rotation (Katz et al., 2004; Nicholson et al.,1986; Riedel, 1929; Schreurs, 1994) (Fig. 10A). In our case, the westernboundary of the rotated blocks is represented by the N140º E trendingdextral strike-slip SMQF, and to the east by a hypothetical fault parallelto the SMQF. Antithetic Riedel shear faults (R′) would correspond toE-W and NE-SW faults segmenting the area (i.e., Loulé and Carcavaifaults; cf. Fig. 10) andwould act as left-lateral strike-slip faults. In ad-dition, the vertical-axis rotation of crustal fragments may have beenfacilitated by the presence of Triassic salt deposit, which acted as adecollement level at the scale of the basin. The age of the vertical-axisrotationwould be therefore linked to the N-S compression that affectedthe Algarve basin during the Cenozoic. However, note that the SãoMarcos-Quarteira Fault does not displace significantly the geologicalcontacts shown on geologicalmaps (Fig. 10), and its slip is quitemodestto account for a 30° rotation. We suggest that the real offset may havebeen masked by tectonic inversion of prior extensional faults.

8. Conclusion

Our rock magnetic study indicates that the remanence of the select-ed sites of the CAMP lavas from Portugal is primary (thermal remanentmagnetization origin) and carried by pseudo-single-domain magnetite,and aminor contribution of accessory hematite. After stepwise alternat-ing field and thermal cleaning, sample-basedmeanmagnetic directionsare positive (normal), oriented approximately N-S, and interpreted ascorresponding to the magnetic chron E24n recorded in most ofcircum-Atlantic CAMP basalts. Virtual geomagnetic poles calculatedfrom site-basedmean characteristic remanentmagnetization directions(n=9) show two distinct magnetic groups (A and B).The VGP of GroupA lies close to the distribution of individual VGPs of theMessejana dykepreviously published and overlaps the a95 confidence interval of theMessejana dyke paleomagnetic pole, suggesting that the intrusion ofthe dyke and the extrusion of the lava flows occurred almost simulta-neously. However, VGPs of Group B does not match any mean Iberianpole and correspond to the sites located in the Carcavai-Quarteira faultzone. Themain difference between Group A and B resides in declinationvalues, for which calculated rotation is ~30° clockwise, while the differ-ence in inclination is statistically insignificant. The virtual geomagneticpole of Group B sites is statistically distinct from the mean Iberian

Fig. 9. (A) Site-based mean directions and associated a95 confidence cones of the studiedsites (except AY) in geographic coordinates and after tilt correction. The difference in dec-lination between Groups A and B implies a vertical-axis rotation of ~30°. (B) Comparisonof the virtual geomagnetic poles (VGP) of the Messejana dyke (modified from Ortas et al.,2006) and of the CAMP lavas from the Algarve basin. The paleomagnetic pole of theMessejana dyke is also shown (blue circle). Group A (sites QO, HT, RA, JG and SB; GroupA) shares the same magnetic directions than the Messejana dyke, whereas sites locatedin the central part of the basin (RL, FP, AL and AA; Group B) show a distinct orientation.(C) Comparison of the VGP of Group A and Group B with the apparent polar wander pathof Iberia (compilation from Neres et al. (2012) and Osete et al. (2011)).

lantic Magmatic Province in the Algarve basin, Portugal: First insights,

Fig. 10. Present-day architecture of onshore and offshore major faults of the Southern Portuguese margin (modified from Carvalho et al., 2012; Terrinha et al., 2013), including a putativemodel to explain vertical-axis rotation of Group B sites.

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poles at 88 and 70 Ma, suggesting that remagnetization linked to theCretaceous alkaline magmatic pulse is not the best scenario, but is notexcluded. Alternatively, we suggest a scenario involving clockwisecrustal bloc rotations in relation to the reactivation of major faults. Weexplained the observed clockwise vertical-axis rotation by proposing aconceptual model based on a Riedel shear pattern involving NW-SEdextral strike-slip Riedel faults, like the São Marcos-Quarteira Fault,and sinistral NE-SW to E-W strike-slip anti-Riedel faults, such as theLoulé and Carcavai Faults. Such a model is compatible with the N-Scompression that affected the South Portuguese margin during theCenozoic. These new evidences provide new perspectives to unravelthe complex history of the Algarve basin since the Mesozoic.

Acknowledgments

This work was funded by FCT (ref. PTDC/CTE-GIX/117298/2012).Partial funding was provided by a bilateral Portugal (FCT)–Morocco(CNRST) cooperation project (ref. SDU No. 1/2015-2016). We thankCelia Lee and Ana Sousa for administrative support. We thank AdriaRamos, José Carlos Kullberg and Pedro Terrinha for fruitful discussionsabout the tectonic evolution of the Algarve Basin. We acknowledgethe Guest Associate Editor Antonio Azor for handling and improvingour manuscript, as well as Juan José Villalaín and Vicente Carlos Ruiz-Martínez for their detailed and helpful reviews.

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lantic Magmatic Province in the Algarve basin, Portugal: First insights,