Source rocks and provenances of the Ladoga Group siliciclastic metasediments (Svecofennian Foldbelt, Baltic Shield): Results of geochemical and Sm-Nd isotopic study

1

ISSN 0869-5938, Stratigraphy and Geological Correlation, 2009, Vol. 17, No. 1, pp. 1–19. © Pleiades Publishing, Ltd., 2009.Original Russian Text © L.N. Kotova, A.B. Kotov, V.A. Glebovitskii, V.N. Podkovyrov, V.M. Savatenkov, 2009, published in Stratigrafiya. Geologicheskaya Korrelyatsiya, 2009,Vol. 17, No. 1, pp. 3–22.

INTRODUCTION

Outcrops of metasedimentary rocks different incomposition and origin occupy considerable areas inthe Svecofennian foldbelt of the Baltic Shield. Data ontheir source complexes and provenance are fragmen-tary at present, and it is difficult therefore to elaboratean integral model of geodynamic evolution of the beltthat is one of the structures brightly exemplifying thelarge-scale process of formation of juvenile continentalcrust in the Early Proterozoic.

The Ladoga Group, metasediments of which arewidespread in the region northward of the LadogaLake, is the Kalevian stratotype of Karelia regarded asanalog of concurrent siliciclastic succession in Finland(

Geology of Karelia

, 1987;

General Stratigraphic…

,2002). Unfortunately, geochemical characteristics andisotopic systematics of the group rocks have not beensystematically studied so far, and it is impossible there-fore to identify the source rocks and provenances ofmetasediments. In this work, we made an attempt toclose this lacuna in our knowledge by means of petro-chemical, geochemical, and Sm–Nd isotopic study ofthe Ladoga Group metasediments sampled northwardof the Ladoga Lake. The results obtained are consid-ered below.

GEOLOGICAL REVIEW

Flyschoid siliciclastic deposits of the Kalevian(2.05–1.90 Ga, Huhma, 1987), the Ladoga Groupmetasediments inclusive, are confined to junction zoneof the Svecofennian foldbelt and Karelian craton. For-merly, all siliciclastic metasediments occurring withingreater part of the northwestern circum-Ladoga regionhave been attributed to the Ladoga Group (

Guide toGeological…,

1981). However, it has been shown inrecent years (Shul’diner et al., 1995; Koistinen, 1996;

Geology and Petrology…

, 2000;

Geological map…

,2001) that metasediments in northern and western sec-tors of the circum-Ladoga region are not identical incomposition and in terms of their geological history,being most likely also different in age, formation envi-ronments, and interrelated with different provenances.At present, they are attributed to the Ladoga (northernsector) and Lahdenpohja (western sector) groups(

Geology and Petrology…

, 2000) and belong in tec-tonic plane (Huhma, 1986, 1987; Gaal and Gor-batschev, 1987) to the Karelides and Svecofennides,respectively (Fig. 1). In recent Geological Map of theFennoscandian Shield (

Geological Map…,

2001), thepost-Jatulian rock complexes of the Karelides are datedat 2.06–1.96 Ga, while volcanogenic-sedimentary for-mations of the Svecofennides correspond in age to1.95–1.87 Ga. The Sm–Nd isotopic data (Huhma,

Source Rocks and Provenances of the Ladoga Group Siliciclastic Metasediments (Svecofennian Foldbelt, Baltic Shield):

Results of Geochemical and Sm–Nd Isotopic Study

L. N. Kotova, A. B. Kotov, V. A. Glebovitskii, V. N. Podkovyrov, and V. M. Savatenkov

Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, Russia

Received October 10, 2007; in final form, December 25, 2007

Abstract

—Siliciclastic metasediments of the Ladoga Group that is the Kalevian stratotype in Karelia correla-tive with the Kalevian siliciclastic succession in Finland are studied in terms of geochemistry and Sm–Nd iso-topic systematics. The results obtained show that rocks in the Ladoga Group lower part are enriched, as com-pared to rocks of the upper part, in

TiO

2

, Fe

2

O

3

, MgO, Cr, Co, Ni, and Sc, being comparatively depleted in

Al

2

O

3

and Th that is a result of compositional changes in provenances. The Sm–Nd isotopic data evidence thatsiliciclastic sediments of the Ladoga Group have accumulated during the erosion of rocks, which originated atthe time of the Archean and Early Proterozoic crust-forming processes. Siliciclastic material with the Archeanand Early Proterozoic

T

Nd

(DM)

values, which are characteristic of metasediments in the group lower part, wasderived respectively from granite gneisses of the Archean basement in the Karelian megablock of the BalticShield and from volcanic rocks of the Sortavala Group. Volcanic rocks of island-arc terranes of the Svecofen-nian foldbelt represented main source of siliciclastic material that accumulated in upper part of the succession.

DOI:

10.1134/S0869593809010018

Key words

: Early Proterozoic, siliciclastic metasediment, geochemistry, Sm–Nd systematics, source rocks,provenances, circum-Ladoga region, Baltic Shield.

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STRATIGRAPHY AND GEOLOGICAL CORRELATION

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KOTOVA et al.

1987) suggest the average model ages of 2.4 and 2.2 Gafor the rocks in provenances of the Kalevian and Sve-cofennian sediments in Finland, respectively.

The upper age limit of accumulation of the LadogaGroup sediments is estimated to be 1.89–1.88 Ga(Bogachev et al., 1999; Shul’diner et al., 2000). Byanalogy with supracrustal formations associated withthe Svecofennian island-arc complexes, the Kalevianbase is accepted to be 1.92–1.91 Ga old according toage values published in several works (Shul’diner et al.,1996;

General Stratigraphic…

, 2002;

Early Precam-brian…

, 2005). Identical age values characterizingaccumulation time of Svecofennian successions havebeen obtained for youngest detrital zircons frommetaturbidites of the Tampere belt in southern Finland(Huhma et al., 1991). However, geochronologicaldates obtained recently for rocks from northern sectorof the circum-Ladoga region evidence that lower partof the Ladoga Group (Kalevian) cannot be youngerthan 1.92 Ga (Matrenichev et al., 2006a), and thegroup base is about 2.0 Ga old (Pupkov andMatrenichev, 2006).

The Kalevian metasediments of the Ladoga Group,which are under consideration (Janisjarvi province,North Ladoga region) are confined to the schist belt(Fig. 1) that extends to the Hoytiainen Lake area in syn-

onymous province of Finland (Negrutsa, 1984;Zagorodny et. al., 1986; Kohonen, 1995; Glebovitskiiand Shemyakin, 1996). The schist belt 20–30 kmwide, extending northwestward for the distance of190 km is interpreted (Kohonen, 1995) as the EarlyProterozoic rift that originated on continental marginof the Karelian craton in the Jatulian and, maybe,Ludicovian time (Gaal and Gorbatschev, 1987;Kohonen, 1995).

In the Hoytiainen–Janisjarvi schist belt, there aredistinguished the Tohmajarvi and Sortavala complexesof the Jatulian–Ludicovian age, which are composed ofvolcanic, mostly basic rocks. Volcanics of the Tohma-jarvi Complex are dated at 2.10 Ga (Huhma, 1986),rocks of the Sortavala Group at 1.96 Ga (

Geology andPetrology…

, 2000; Shul’diner et al., 2000) that is anevidence of a long-term intermittent volcanic activity inthe Hoytiainen–Janisjarvi zone. According to mostrecent results of dating (Matrenichev et al., 2006b), vol-canic rocks of the Sortavala Group range in age from2.21 to 2.07 Ga.

The Kalevian metasediments of the Hoytiainenprovince and their relations with continental andmarine deposits of the Jatulian are described in work byKohonen (1995) who showed that the Kalevian micaschists after flyschoid sediments are younger than the

N

60 km

62°

63°

61° N

Fig. 2

Priozersk

Lahdenpohja

Imatra

30°27°

62°

61°

63°

27° 30° E

1

2

3

4

5

6

Sortavala

Tohmajarvi

Savonlina

Mikkeli

Kuopio

Janisjarvi Lake

Hoytiainen Lake

RU

SS

I A

FI

NL

AN

D

Ladoga

Lake

Fig. 1.

Geological scheme of southeastern part of the Svecofennian foldbelt (compiled based on cartographic materials from

Raahe–Ladoga Zone

, 1999;

Geological Map…

, 2001): (1) rapakivi (1.65–1.47 Ga); (2) area of widespread supracrustal island-arc associ-ations (Svecofennides, 1.95–1.87 Ga); (3) area of widespread, predominantly Upper Kalevian metasedimentary rocks (Sve-cokarelides, 1.95–1.87 Ga); (4) Outokumpu proto-ophiolites (1.96–1.95 Ga); (5) area of widespread, predominantly Lower Kale-vian metasedimentary rocks (Karelides, 2.06–1.96 Ga); (6) Karelian craton with outcrops of basement (> 2.50 Ga).


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SOURCE ROCKS AND PROVENANCES OF THE LADOGA GROUP SILICICLASTIC METASEDIMENTS 3

Jatulian platform deposits, being associated with volca-nic complexes of the Tohmajarvi type. This is indicativeof a considerable accumulation period (2.1–1.9 Ga) ofthe Kalevian succession. Kohonen (1995) distinguishedthe West and East Kalevian, the latter represented bymetasedimentary complex of a marginal rift basin,whereas metasediments of the former are correlative, inhis opinion, to graywackes of the Outokumpu region. Inconclusive remarks, Kohonen (1995) stated that genesisof the West Kalevian sediments remains unclear, andthat it is awkward to correlate lithostratigraphy of theEast Kalevian sedimentary successions. Cratonic prov-enances of these successions consisted predominantlyof the Archean rocks, whereas the Proterozoic compo-nent established by Huhma (1987) in their composi-tion may find explanation in a constrained supply ofsedimentary material, which originated as a result ofdestruction of rift-related continental mafic volcanics.In addition, some researchers (Koistinen, 1996;

Raahe-Ladoga Zone

, 1999) divide the Kalevian intothe lower (autochthonous) subgroup associated genet-

ically with rifting and the upper (allochthonous) sub-group, which presumably accumulated within a pas-sive continental margin (Savo Province; Kohonen,1995) to be transformed afterward into a rock com-plex of the Svecofennides (

Geological Map…

, 2001)or Svecokarelides.

BASIC GEOLOGICAL FEEATURESAND STRATIGRAPHY OF THE KARELIDES

IN THE NORTH LADOGA REGION

The region northwestward of the Ladoga Lake (Fig. 2)is subdivided into the Northern and Southern tectonicblocks (domains) separated by the Meyer thrust zone(Baltybaev et al., 1996; Shul’diner et al., 1997). TheSouthern block (westward of the lake) is composed ofundivided, deeply metamorphosed rocks of the EarlyProterozoic Lahdenpohja Group that is regarded atpresent as an age analog of the Ladoga Group (

EarlyPrecambrian…

, 2005). As is suggested, the Southernblock is lacking, in contrast to the Northern block, the

1 2

3 4

10 km

Sortavala

Harlu

Lahdenpohja

FIN

LAN

D

Janisjarvi Lake

L a d o g aL a k e

Janisjarvi Lake

L.

L.

L.

Harlu

Sortavala

Lahdenpohja

N

0 8 km

L a d o g aL a k e

17-12

3-6

13-15

1, 21

2

3

4 1

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

1, 2

Fig. 2.

Schematic geological map of the North Ladoga region compiled using data from works by Krats (1963), Predovskii etal.,(1967), Saranchina (1972), and Koistinen et. al. (1996): (1) Quaternary deposits; (2) microcline granitoids; (3) plagiogranites,tonalites, enderbites; (4) gabbroids, pyroxenites; (5) siliciclastic deposits of the Lahdenpohja Group; (6) siliciclastic deposits of theLadoga Group; (7) andalusite- and staurolite-bearing schists; (8) volcanogenic-sedimentary deposits of the Sortavala Group (marineJatulian); (9) predominantly siliciclastic-carbonate deposits of the continental Jatulian; (10) granite-gneiss domes; (11) granitegneisses of the Karelian craton; (12) principal faults; (13) northern boundary of ultrametamorphism zone; (14) Janisjarvi (1), Harlu(2), Ljaskelja (3) and Impiniemi (4) reference areas; (15) sampling sites for Sm–Nd isotopic-geochemical study (numbers in thefigure correspond to ordinal numbers in Table 4). The inset map illustrates metamorphic zones of the greenschist (1), epidote-amphibolite (2), amphibolite (3), and granulite (4) facies in the North Ladoga region.

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KOTOVA et al.

Archean basement, and its rocks have been formedunder control of the Early Proterozoic crust-formingevents (Shul’diner et al., 1995, 1996).

In geological structure of the Northern block(northward of the lake), the Archean basement is over-lain by variably metamorphosed rock complexes rep-resenting siliciclastic-carbonate deposits of the conti-nental Jatulian, volcanogenic-sedimentary rocks ofthe Sortavala Group (the marine Jatulian), and silici-clastic succession of the Ladoga Group (the Kale-vian). Granite-gneiss domes rimmed by outcrops ofthe Sortavala Group rocks complicate geologicalstructure of the block in coastal zone of the LadogaLake.

The Jatulian siliciclastic-carbonate deposits of theplatform type are most widespread in northern part ofthe region under consideration (the Janisjarvi Lakearea). These are quartzites, arkosic and carbonate rocksenclosing metagabbro-diabase sills and intercalationsof amphibole schists.

Volcanogenic-sedimentary rocks of the SortavalaGroup are mapped in southern part of the Northernblock, the distribution area of granite-gneiss domes ofthe Archean basement. The Sortavala Group describedin detail by Svetov and Sviridenko (1992) includes thebasal siliciclastic-carbonate succession (the Jatulian),lower and middle volcanogenic sequences composedpredominantly of basalts and basaltic tuffs, and uppersedimentary-volcanogenic succession of carbonaterocks, tuffites, and picritic basalts (the Ludicovian). Inupper part of the entire succession, these researchersindividualized the Livian Superhorizon characterizingseparate stage of volcanic activity concurrent to forma-tion of the Suisari volcanic complex in the Onega Lakeregion. Svetov and Sviridenko attributed volcanic rocksof the Sortavala Group to plateau basalts of the traptype. Oceanic basalts comparable in composition andage with pillow lavas of the Yormua ophiolites in Fin-land have been distinguished among volcanic rocks ofthat group in later works (Ivanikov et. al., 1997, 1998;

Shul’diner et al., 2000). At the base of the SortavalaGroup, there is a member of coarse-grained siliciclasticsediments comparable in geochemical parameters withthe granite-gneiss basement (Vasil’eva, 1999, 2000)and containing accessory zircon corresponding in mor-phology and age to zircon from granitoids of the base-ment (Vrevskii et al., 2006).

Rocks of the Ladoga group are in intricate ambig-uous relations with the Jatulian siliciclastic-carbon-ate deposits and with volcanic rocks of the SortavalaGroup. Quite important for understanding the rela-tions between the Jatulian and Kalevian are coarse-grained rocks (quartzites, arkosic sandstones andconglomerates) mapped in the Janisjarvi Lake area.Some researchers (Potrubovich, 1956; Predovskiiand Petrov, 1964a; Predovskii et al., 1967) attributethem to basal part of the Ladoga Group, while theothers consider them as either the intraformationalbeds (Inina, 1975), or the landslide olistostromes(Martynova, 1980; Negrutsa,1984). Contacts betweenthe Ladoga Group and underlying volcanogenic-sedi-mentary deposits of the Sortavala Group are interpretedusually as discordant or tectonic, although their con-formable character and gradual transitions betweenthe groups have been also described in some works(Predovskii and Petrov, 1964b; Predovskii et al.,1967; Negrutsa, 1984; Svetov and Sviridenko,1992).

Greater part of the Northern block is composed ofthe Kalevian rocks corresponding to rhythmically lay-ered siliciclastic sediments (turbidites) of the LadogaGroup (thickness up to 3000 m), which experiencedzonal metamorphism of the greenschist to amphibolitefacies. Several stratigraphic schemes suggested for theLadoga Group are controversial (Table 1). Manyresearchers divide the group into the Kontiosari, Pjalk-jarvi, Naatselka, and Ilola formations (sequences, hori-zons). The Kontiosari Formation is composed predom-inantly of mica schists intercalated with quartzites,arkosic sandstones, and conglomerates. Rhythmicallyalternating biotite and two-mica schists of the Pjalk-

Table 1.

Correlation of stratigraphic successions suggested in different works for the Ladoga Group

Potrubovich (1956),

Geology of Karelia

, 1987

Krats (1963),Predovskii et al. (1967) Negrutsa (1984)

Svetov and Sviridenko (1992)with reference to unpublisheddata of G.V. Makarova and

R.I. Borisova

Formation Sequence Horizon Formation

Ilola and Leppjalampi Upper (analog of Ilola) Late (Materta) Ilola

Pjalkjarvi Middle (analog of Pjalkjarvi) Middle (Naatselka) Naatselka

Naatselka Lower (analog of Naatselka) Early (Pjalkjarvi) Pjalkjarvi

Kontiosari Kontiosari


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jarvi Formation contain perceptible amount of garnet,andalusite, and staurolite. The Naatselka Formation isrepresented largely by the coarse to fine rhythmicalalternation of biotite-quartz and quartz-mica schistsand phyllites, which also bear andalusite and staurolitesometimes. The Ilola Formation mapped in the Janis-jarvi area only is of a low thickness, being composedpredominantly of para-amphibolites and quartzites(Krats, 1963). In the Ladoga Group succession of theJanisjarvi synclinorium, Inina (1975) distinguishedtwo sedimentary cycles separated by intraforma-tional conglomerates. In opinion of Negrutsa (1984),the group succession in the Janisjarvi zone can beinterpreted as exemplifying two complete transgres-sive-regressive megarhythms (horizons) with basalconglomerates and associates coarse-grained sedi-ments.

Researchers used to deny a possibility to subdividethe Ladoga Group in detail, as this objective is verydifficult because of intense structural-metamorphicreworking and absence of distinct stratigraphic mark-ers (

Guide to Geological…

, 1981;

Geology andPetrology…

, 2000). Emphasizing facies variability ofthe group rocks northward of the Ladoga Lake, Khari-tonov (1966) argued that subdivisions of the groupdistinguished based on petrographic and lithologiccriteria characterize its structure in a very generalmode only.

OBJECTS OF INVESTIGATION

In this work, we studied petrochemistry (120 sam-ple), geochemistry (30 samples), and Sm–Nd isotopicsystematics (15 sample) of siliciclastic metasedimentsin order to get insight into compositional characteriza-tion of the Ladoga Group. Rock samples were collectedin four reference areas (Janisjarvi, Harlu, Ljaskelja, andImpiniemi) situated along submeridional profile about45 km long, transecting the North Ladoga region fromthe Soanlahti Settlement (Janisjarvi Lake) on the northto the Impiniemi (Hunnaka Peninsula) on the south(Fig. 2).

In the Janisjarvi area on eastern side of the epony-mous lake (Kelenmjaki Town–Soanlahti Settlement),there are observable outcrops of quartz-biotite, biotite,and two-mica schists containing garnet sometimes incorresponding in metamorphic grade to the greenschistfacies. In many cases, the rocks are carbonaceous. TheHarlu area (between the eponymous and Hjamekoskisettlements) is composed predominantly of quartz-biotite, biotite, and two-mica schists bearing andalusiteand corresponding in metamorphic grade to the epi-dote-amphibolite facies. In the Ljaskelja area betweenthe eponymous and Lesozavodskoi settlements, rocksof the Ladoga Group are represented by quartz-biotite,biotite, and two-mica schists containing garnet andstaurolite, and metamorphosed under conditions of the

epidote-amphibolite facies. In the Impiniemi area at thesouthern extremity of the Hunnaka Peninsula (CapeImpiniemi), quartz-biotite, biotite, and two-micaschists of the Ladoga Group contain sometimes garnetand correspond in metamorphic grade to the low-tem-perature amphibolite facies.

In schematic geological map of the North Ladogaregion (Krats, 1963), the Harlu and Ljaskelja areas arewithin the field of andalusite and staurolite schists.According to stratigraphic scheme and position on themap, rocks of the designated areas belong most likelyto the Pjalkjarvi Formation, whereas rocks of the Janis-jarvi and Impiniemi areas represent the Naatselka For-mation. In other words, it is reasonable to think thatthey exemplify respectively the lower and upper partsof the Ladoga Group section.

ANALYTICAL METHODS

Concentrations of major elements in siliciclasticmetasediments of the Ladoga Group are determinedusing the XRF analytical method in the Central Chem-ical Laboratory of the VSEGEI (St. Petersburg). Anal-ysis of the REE and other trace elements is carried outon the ICP mass spectrometer PlasmaQuad 3 at theIAnP RAS (St. Petersburg). Uncertainty of the analyti-

0.1

0 0.1

a

b0.2 0.3 0.4

0.2

0.3

0.4

0.5

0.612

VI

V

IV

III

II

I

A

R

D

Fig. 3.

Diagram a–b (Al/Si–Fe + Mn + Mg + Ca; Neelov,1980) for siliciclastic metasediments of the LadogaGroup, the North Ladoga region: (1) metasediments fromlower part of the Ladoga Group (Harlu and Ljaskeljaareas); (2) metasediments from upper part of the LadogaGroup (Janisjarvi and Impiniemi areas). Fields in the dia-gram: (I) oligomictic arenites, (II) subgraywacke areni-tes, (III) graywackes, (IV) aleurolites, (V) argillites,(VI) pelites; dashed contours outline fields of volcanicrocks: rhyodacites (R), dacites (D) and andesites (A).

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KOTOVA et al.

Table 2.

Chemical composition and petrochemical parameters of representative metasedimentary rocks from the LadogaGroup, North Ladoga region

Area Janisjarvi Harlu Ljaskelja

Ordinalno. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Sample no. 6-2 6-3 124-1 10-5 10-8 115-2 107-4 112-1 113-5 114-1 118 17-1 17-2 17-4 17-6

SiO

2

58.45 66.52 69.28 88.86 57.42 62.71 60.83 66.06 68.97 58.47 59.23 82.54 54.74 60.05 58.74

TiO

2

0.73 0.6 0.64 0.31 1.29 1.04 1.02 0.67 0.57 1.09 0.97 0.57 1.17 1.13 0.98

Al

2

O

3

20.56 15.92 14.17 5.01 15.62 14.86 14.2 15.49 14.62 17.45 16.57 7.57 21.97 14.78 16.13

Fe

2

O

3

7.11 6.03 5.37 2.91 10.65 9.02 10.55 6.03 5.35 9.6 9.28 3.55 11.71 10.22 10.24

MnO 0.05 0.04 0.05 0.01 0.08 0.08 0.08 0.06 0.05 0.08 0.07 0.01 0.13 0.04 0.06

MgO 3.35 1.73 2.37 0.88 5.82 5.28 5.39 2.67 2.45 5.61 4.92 1.18 4.89 5.32 5.79

CaO 1.25 2.36 1.22 0.47 0.74 0.67 0.72 0.88 0.75 0.56 0.44 0.74 0.19 0.69 0.87

Na

2

O 2.37 3.81 3.24 0.99 2.28 0.73 2.08 3.52 1.96 1.35 1.59 2.01 0.6 2.76 1.66

K

2

O 4.23 2.1 2.26 0.8 3.43 3.59 3.74 3.34 3.36 3.29 3.34 1.19 2.76 3.61 3

P

2

O

5

0.14 0.15 0.13 0.05 0.19 0.11 0.05 0.16 0.12 0.17 0.11 0.08 0.09 0.1 0.14

L.O.I. 2.2 1.2 1.3 0.3 2.9 1.6 1.3 1.2 1.6 2.3 2.9 0.8 2.1 1.3 2.5

Sum 100.44 100.46 100.03 100.59 100.42 99.69 99.96 100.08 99.8 99.97 99.42 100.24 100.35 100 100.11

S (total) 0.01 0.01 0.02 0.08 0.03 0.3 0.02 0.01 0.18 0.05 0.47 0.02 0.04 0.05 0.12

a 0.41 0.28 0.24 0.07 0.28 0.28 0.28 0.28 0.25 0.35 0.33 0.11 0.47 0.29 0.32

b 0.2 0.16 0.15 0.07 0.29 0.26 0.28 0.16 0.14 0.28 0.26 0.09 0.28 0.28 0.3

n 0.17 0.17 0.15 0.05 0.15 0.1 0.15 0.19 0.14 0.12 0.13 0.09 0.08 0.17 0.12

k 0.54 0.27 0.31 0.35 0.5 0.76 0.54 0.38 0.53 0.62 0.58 0.28 0.75 0.46 0.54

f 0.46 0.47 0.46 0.55 0.46 0.44 0.48 0.48 0.48 0.45 0.47 0.51 0.54 0.47 0.45

Si/Al 0.45 0.62 0.69 1.25 0.62 0.63 0.63 0.63 0.67 0.53 0.55 1.04 0.4 0.61 0.56

Fe/K 0.23 0.46 0.38 0.56 0.48 0.4 0.45 0.26 0.2 0.47 0.44 0.47 0.63 0.45 0.53

F 27.3 39.2 30.1 12.2 23.3 18.4 25.9 40 20.7 18.9 24.1 20 – 33.4 25

P 54.2 31.6 34.4 11.2 55.8 48 49.2 33.8 41.3 55.3 49.5 17 83.3 45.6 48.7

Q 18.5 29.2 35.5 76.6 20.9 33.6 24.9 26.2 38 25.8 26.4 63 16.7 21 26.3

PL 21.8 34.8 29.7 9 21 6.7 18.7 32.4 18.1 12.3 14.8 18.6 – 25.4 9.7

OR 5.4 4.4 0.4 3.2 2.3 11.7 7.2 7.6 2.6 6.6 9.3 1.4 – 8 15.3

ILL 34.8 14 22.9 2.7 32 16.1 25.6 21.3 30.8 22.4 18.6 10.1 28.5 23.2 14.2

CHL 17.2 13 – 7.2 – 29.7 – – – 31 29.7 – 24.2 – 32.2

MM – – – – – – – – – – – – 20.6 – –

KN – – – – – – – – – – – – 6 – –

SRP – – 3.5 – 11.5 – 10.3 5 3.7 0.1 – 1.8 – 10.8 –

GT – – 5.5 – 10.3 – 11.4 6.4 5.2 – – 3.5 2.4 10.1 –

CAR 1.3 3.6 1.5 0.8 0.2 0.9 0.9 0.1 0.8 0.3 – 0.6 0.3 0.2 1.1

SM 1 1 1 0.5 1.8 1.3 1 1 0.8 1.5 1.2 1 1.3 1.3 1.2

A(CIA) 65.7 55.4 58.6 59.9 61.7 70.2 61.8 58.5 64 72 70.2 56 83.5 60.3 68.1

CN 19.7 36.7 31.2 29.7 22 11.4 20.6 27.9 20.1 13.4 14.5 34.5 5.1 23.7 18.2

K 14.6 7.9 10.1 10.4 16.3 18.4 17.6 13.6 15.9 14.6 15.3 9.5 11.4 16 13.7

F1 –0.58 2.41 –1.36 –5.9 –5.84 –6.54 –5.37 –1.97 –3.39 –4.44 –3.91 –4.53 0.96 –4.87 –4.11

F2 –0.51 0.74 –1.02 –5.3 –5.77 –7.16 –5.47 0.39 –1.61 –7.04 –5.87 –3.31 –8.44 –4.4 –7.37


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2009


Table 2.

(Contd.)

Area Ljaskelja Impiniemi

Ordinalno. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample no. 18-3 18-9 18-10 19-6 20-1 20-3 21-2 21-4 22-4 22-7 23-1 24-3 24-4 25-4 26-2

SiO

2

50.43 55.29 71.82 68.96 66.96 55.08 65 61.6 58.6 74.66 71.73 75.88 49.05 75.31 66.12TiO

2

0.99 0.8 0.61 0.68 0.73 0.93 1.07 0.7 0.81 0.47 0.48 0.3 1 0.38 0.85Al

2

O

3

21.19 18.68 12.48 13.96 15.27 19.81 13.88 17.26 17.54 12.91 13.71 13.17 22.22 13.1 14.8Fe

2

O

3

9.61 8.91 5.14 5.69 5.43 7.71 8.94 7.68 8.15 3.31 3.74 2.42 9.24 3.25 7.05MnO 0.08 0.1 0.05 0.04 0.05 0.08 0.05 0.03 0.08 0.03 0.08 0.03 0.12 0.02 0.08MgO 5.63 5.03 1.7 1.98 2.02 5.02 2.52 3.33 5.14 1.03 1.02 0.84 4.36 0.9 2.45CaO 0.63 1.48 1.92 2.01 1.01 1.17 0.81 0.54 0.77 1.51 4.08 1.9 1.8 2.11 1.19Na

2

O 1.17 2.54 3.06 3.16 3.82 3.53 1.46 1.58 1.61 2.91 1.91 4.29 3.22 3.73 2.53K

2

O 6.56 5.05 1.83 2.24 3.13 4.47 3.15 3.75 5.59 2.66 2.02 1.13 6.64 1.28 3.85P

2

O

5

0.08 0.14 0.14 0.15 0.18 0.17 0.1 0.06 0.07 0.15 0.25 0.12 0.05 0.14 0.16L.O.I. 2.7 2.1 1.2 1.1 1.3 2 2 2.3 1.6 0.6 1.1 0.2 2 0.5 1.2Sum 99.07 100.12 99.95 99.97 99.9 99.97 98.98 98.83 99.96 100.24 100.12 100.28 99.7 100.72 100.28S (total) 1.11 0.42 0.06 0.12 0.01 0.01 1.08 1.32 0.02 0.01 0.01 0.02 0.02 0.04 0.02

a 0.5 0.4 0.2 0.24 0.27 0.42 0.25 0.33 0.35 0.2 0.23 0.2 0.53 0.21 0.26b 0.29 0.27 0.14 0.16 0.14 0.25 0.2 0.2 0.25 0.09 0.15 0.09 0.26 0.1 0.17n 0.18 0.19 0.14 0.15 0.19 0.21 0.12 0.14 0.17 0.15 0.11 0.16 0.25 0.15 0.16k 0.79 0.57 0.28 0.32 0.35 0.45 0.59 0.61 0.7 0.38 0.41 0.15 0.58 0.18 0.5f 0.45 0.43 0.46 0.46 0.5 0.4 0.59 0.51 0.42 0.44 0.33 0.36 0.46 0.41 0.52

Si/Al 0.38 0.47 0.76 0.69 0.64 0.44 0.67 0.55 0.52 0.76 0.72 0.76 0.34 0.76 0.65Fe/K 0.17 0.25 0.45 0.4 0.24 0.24 0.45 0.31 0.16 0.09 0.27 0.33 0.14 0.4 0.26

F 21 32.9 34.6 29.2 43.6 39.3 13.8 21.6 27.3 32 13.2 40.2 42.9 34.2 37.5P 71.5 55.2 24.1 34.3 29.1 53 47.9 49.1 54.4 24.8 46.8 18.1 57.1 22.6 28.1Q 7.5 11.9 41.3 36.5 27.3 7.7 38.3 29.3 18.3 43.2 40 41.7 – 43.2 34.5

PL 10.9 23.2 28.2 28.8 35.7 32.4 13.6 14.9 14.7 26.8 13.2 39.5 28.1 34.1 33.2OR 10.1 9.7 6.4 0.4 7.9 6.9 0.2 6.7 12.6 5.2 – 0.7 14.8 0.1 4.3ILL 51.1 35 7.8 22.7 18.9 34.6 33.3 28.2 35.7 18.5 20.7 10.5 36.8 13.1 18.3CHL – – 12.7 – – – – 19.4 – – – 5 – 5.8 –MM – – – – – – – – – – 15.2 – – – –KN – – – – – – – – – – – – – – –SRP 9.9 8.3 – 1.4 3.6 9.2 3.5 – 9.2 0.2 – – – – 0.15GT 8.3 8.1 – 5.2 5.2 6.9 8.4 7.3 2.8 – – – 4.8CAR 1 2.7 2.7 4 0.3 1 1.4 0.7 1.2 2.5 9.9 2.1 19.3 3 3.9SM 1.2 1.1 0.9 1 1.1 1.3 1.3 0.8 1 0.8 1 0.5 1 0.7 0.85

A(CIA) 67.6 60.3 54.3 55.3 57 60.8 65.6 69.3 63.5 55.4 51.8 52.9 58.5 53.5 58.5CN 9.8 22.1 37.1 35.1 30.3 24.4 18.3 14.4 14.6 32.3 39.9 42.2 22.6 40.8 25K 22.6 17.6 8.6 9.6 12.7 14.8 16.1 16.3 21.9 12.3 8.3 4.9 18.9 5.7 16.5

F1 –6.06 –3.82 –0.63 –0.26 –1.17 –3.22 –1.95 –2.46 –6.91 –1.94 0.8 0.91 –2.11 0.92 –2.56F2 –2.25 –1.47 –0.9 –0.46 1.53 –0.5 –3.42 –2.54 –2.42 1.02 –0.24 1.39 3.09 0.62 –0.2

Note: (1–3) quartz-biotite and mica schists (phyllites); (4) biotite-quartz rock; (5, 6) quartz-mica schists with andalusite; (7, 8, 12) biotite-quartz schists; (10) biotite schist; (11) biotite schist with andalusite; (13) biotite schist with garnet and staurolite; (14, 15) quartz-biotite schists with staurolite; (16, 17) two-mica schists; (18–20) two-mica schists; (21) two-mica quartz schist; (22, 23) quartz-micaschists with staurolite; (24) mica schist; (25, 27, 29) mica-quartz schists; (26) quartz-biotite schist; (28) two-mica schist; (30) quartz-mica schist. Protoliths: (4, 12, 25, 27, 29) arenites; (2, 3, 5–9, 14, 15, 18–20, 22, 23, 26, 30) graywackes; (1, 10, 11, 13, 16, 17, 21,24, 28) argillites. Petrochemical parameters a, b, n, k, f are after Neelov (1980); Si/Al, Fe/K after Herron (1988); F, P, Q after Rozenand Nistratov (1984, 1993); A(CIA), CN, K after Nesbitt and Young (1982); F1, F2 after Roser and Korsch (1988). Abbreviationsfor minerals: (Q) quartz; (PL) plagioclase; (OR) orthoclase; (ILL) illite; (CHL) chlorite; (MM) montmorillonite; (KN) kaolinite;(SRP) serpentine; (GT) goethite; (CAR) carbonate; (SM) secondary minerals rutile, rhodochrosite, apatite (after Rozen and Nistra-tov, 1984, 1993); dash denotes absence of respective normative mineral.

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Vol. 17

No. 1

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KOTOVA et al.

cal procedure described earlier (Podkovyrov et al.,2002) corresponded to 5–10%.

The Sm–Nd isotopic-geochemical study is per-formed on the TRITON TI mass spectrometer at theInstitute of Precambrian geology and GeochronologyRAS in accord with procedure described by Kotov et al.(1995). Total blanks during the period of measurementscorresponded to 0.03–0.2 ng Sm and 0.1–0.5 ng Nd.The measured

143

Nd/

144

Nd

ratios are normalized to

146

Nd/

144

Nd

= 0.7219 and

143

Nd/

144

Nd

= 0.511860 inthe La Jolla Nd standard. Analytical uncertainty was

±

0.5% (2

σ

)

for Sm and Nd concentrations,

±

0.5%

for

147

Sm/

144

Nd

and

0.005%

for

143

Nd/

144

Nd

ratios. Accord-ing to results of 11 measurements, the weighted aver-age

143

Nd/

144

Nd

value in the La Jolla Nd standard isestimated to be

0.511894

±

8 (2

σ

)

. The

εNd(0) valuesand model ages TNd(DM) are calculated using isotopicratios suggested by Jacobsen and Wasserburg (1984)for the CHUR (143Nd/144Nd = 0.512638, 147Sm/144Nd =0.1967) and by Goldstein and Jacobsen (1988) for theDM (143Nd/144Nd = 0.513151, 147Sm/144Nd = 0.2136).

PROTOLITHS AND PETROCHEMISTRYOF METAMORPHIC ROCKS

FROM THE LADOGA GROUP

Chemical composition of representative metamor-phic rocks from the Ladoga Group is shown in Table2. Presumable protoliths of the rocks are identifiedusing available petrochemical classifications of meta-morphic sedimentary rocks (Neelov, 1980; Herron,1988; Rozen, 1993), which are most appropriate forthe analyzed samples. According to classification byHerron (1988), the studied rocks correspond in chem-

ical composition predominantly to wackes andclayey shales, while only few of them can be identi-fied with lithites and sublithites (arenites). Whenclassification by Rozen (1993) is applied, chemicalcomposition of the rocks suggests that their pro-toliths were wackes in most cases, more preciselygraywackes and pelitic graywackes with P index(pelitic component) values lower or higher than 50%(Table 2), whereas amount of quartz and arkosicsandstones was insignificant.

Using classification by Neelov (1980), we arrive atthe conclusion that 90% of studied samples from theLadoga Group correspond in chemical composition tograywackes and shales (Fig. 3), the boundary betweenwhich corresponds to the aluminous module (Al/Si) =0.3. Only 10% of quartz-biotite schists had protoliths ofthe arenite type, represented by feldspar and quartzsandstone varieties. The quartz varieties (oligomicticsandstones) are most characteristic therewith of theHarlu and Ljaskelja areas, i.e., of the lower and upperparts of the Ladoga Group section, respectively. Beingmoderately alkaline (n = 0.10–0.21, Table 2), lower andupper metamorphic rocks of the Ladoga Group revealeither the Na–K or K specifics (k = 0.41–0.60 and 0.60–0.75, respectively; Table 2) and insignificant prevalenceof potassium over sodium (Fig. 4).

In general, the results of above classification showthat quartz-biotite schists from the Ladoga Group of the

0 2

Na2O

K2O4 6

2

4

6

K 2O/N

a 2O =

1

Fig. 4. Diagram K2O–Na2O for metasediments of theLadoga Group, North Ladoga region (symbols as in Fig. 3).

–8

–10 –6

F2

F1–2 2 6

–6

–4

–2

4

6P3

–8 –4 0 4–10

2

0

P2

P1P4

BS

AN

DC

GR

Fig. 5. Discrimination diagram F1–F2 (Roser and Korsch,1988) for metasediments of the Ladoga Group, NorthLadoga region (symbols as in Fig. 3). Asterisks denote com-positions of basalt (BS), andesite (AN), dacite (DC) andgranite (GR). Fields P1, P2 and P3 characterize detritusapproaching in composition the source rocks of basic, inter-mediate and silicic types; field P4 corresponds to maturerecycled sedimentary material.

STRATIGRAPHY AND GEOLOGICAL CORRELATION Vol. 17 No. 1 2009


study region have been formed after graywacke pro-toliths in most cases, whereas biotite and two-micaschists are metamorphic equivalents of aleuropelites,and only small group of quartz-biotite gneisses corre-sponds in chemical composition to subacrosic and oli-gomictic sandstones of the arkose group. In addition,classification criteria suggested by Neelov (1980) pointto essential difference in composition of protoliths,which gave birth to metamorphic rocks of the LadogaGroup in separate reference areas. In the Janisjarviarea, schists correspond in chemical compositionmostly to aleuropelites. Data points characterizingschists of the Harlu and Ljaskelja areas plot in the “a–b” diagram (Fig. 3) along the trend extending fromarenite field (oligomictic sandstones) to the field ofaleurolites and argillites, whereas schists of the Impin-iemi area are divisible in two associations approachingin composition subarkoses and argillites. It is remark-able as well that graywackes and aleuropelites are com-positionally close in majority to volcanic rocks of rhy-odacite, dacite, and andesite groups. Arenites fromupper part and some graywackes from lower part of theLadoga Group section are close therewith in composi-tion to rhyodacites; graywackes from upper part and

aluminous graywackes from lower part are comparablewith dacites, and finally aleurolites from the lower partapproach andesites in composition.

The distinct compositional difference betweenmetamorphic rocks of lower and upper parts of theLadoga Group section is evident from discriminationdiagram (Roser and Korsch, 1988) demonstrating rela-tive maturity of sediments, on the one hand, and com-position of provenances for immature detrital compo-nents, on the other (Fig. 5). The diagram plotted incoordinates F1 and F2 and characterizing proportionsbetween groups of rock-forming oxides (TiO2, Al2O3,Fe2O3, MgO, CaO, Na2O, K2O) shows the following:first, rocks from the section lower part are in most casesthe metamorphic equivalents of more recycled sedi-ments, as compared to rocks from the upper part; sec-ond, less mature sediments of the upper part were closein composition to their source rocks, which were repre-sented most likely by igneous rocks of silicic and inter-mediate composition.

The CIA index after Nesbitt and Young (1982) char-acterizing the extent of chemical weathering rangesfrom 53 to 83 for all the rock samples from the Ladoga

4

50 60SiO2

80 90 100

8

12Fe2O3

070

0.4

0.8

1.6TiO2

0

2

50 60SiO2

80 90 100

4

8MgO

070

6

5

10

25Al2O3

0

15

201.2

Fig. 6. Variation diagrams for metasediments of the Ladoga Group, North Ladoga region (symbols as in Fig. 3).

10


KOTOVA et al.

Group (table 2). The average CIA values for rocks fromlower and upper parts of the section correspond to 65and 60, respectively. This is again an indication of

somewhat greater extent of weathering and recycling ofsedimentary material in protoliths of metamorphicrocks from the section lower part.

Petrochemical variation diagrams (Fig. 6) plottedfor metagraywackes and meta-argillites of the LadogaGroup (SiO2 less than 75%) show that rocks from thesection lower part are enriched in mafic components(TiO2, Fe2O3, MgO) as compared to rocks from theupper part. Variations of MnO, CaO, and Na2O contentsin rocks from both parts are irregular, whereas variationtrends of Al2O3 and K2O suggest that the increasingextent of sedimentary differentiation and chemicalweathering controlled accumulation of these oxides inthe rocks.

GEOCHEMISTRY OF SILICICLASTIC METASEDIMENTS OF THE LADOGA GROUP

Preliminary data on geochemistry and isotopicparameters of siliciclastic metasediments of the LadogaGroup have been published in resent work by Kotovet al. (2006). Concentrations of trace elements and REEin rocks from lower and upper parts of the group sectionare perceptibly different (Table 3). Argillic protolith ofrocks from the section lower part (Harlu and Ljaskeljaareas) are enriched first of all in Cr and Ni (Fig. 7) ascompared to rocks of the upper part (Janisjarvi andImpiniemi areas). In addition, the La–Th–Sc and Th–Hf–Co diagrams (Fig. 8) show that Sc and especiallyCo concentrations are higher in rocks of the lower part,which are comparatively depleted in Th and La at thesame time.

101

Cr

Ni102

102

101

I

II

OB

AN

OC

J2

J1, J3

103

Fig. 7. Diagram Ni–Cr for metasediments of the LadogaGroup, North Ladoga region (symbols as in Fig. 3). Fieldsdiscriminate the Archean (I) and post-Archean (II) schists(Taylor and MacLennan, 1988). Asterisks denote island-arc andesites (AN), oceanic basalts (OB) (Taylor andMacLennan, 1988), basic rocks of the Jormua ophiolitecomplex (OC) (Kontinen, 1987), metabasalts of the 1st,2nd and 3rd stratigraphic levels of the Jatulian (J1, J2, J3)(Malashin et al., 2003).

0 0.2

La

Sc0.4 0.6 0.8

1.01.0

Th

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1.0(a)

GR

ëGD

AN

BS

B

A

0 0.2

Th

Co0.4 0.6 0.8

1.01.0

Hf

0.8

0.6

0.4

0.2

0

0

0.2

0.4

0.6

0.8

1.0(b)

TTUC

OC

AN

CC

Fig. 8. Diagrams Sc–La–Th (a) and Co–Th–Hf (b) for metasediments of the Ladoga Group, North Ladoga region (symbols as inFig. 3). In diagram (a) asterisks denote average composition of basalts (BS), granodiorite (GD), and granite (GR) after Lopez et. al.(2005), and of andesite (AN) after Taylor and MacLennan (1988); dashed contours correspond to oceanic (A), continental (B), andmarginal-continental (C) tectonic settings after Bhatia and Crook, (1986). In diagram (b) asterisks denote average compositions ofoceanic crust (OC), continental crust as a whole (CC), lower continental crust or andesite (AN), tonalite–trondhjemite (TT) andupper continental crust (UC) after Taylor and MacLennan (1988).



Table 3. Concentrations of trace elements and REE (ppm) in representative metasedimentary rocks from the Ladoga Group,North Ladoga region

Area Janisjarvi Harlu Ljaskelja

Ordinal no. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Sample no. 6-2 6-3 124-1 10-5 10-8 115-2 107-4 112-1 113-5 114-1 118 17-1 17-2 17-4 17-6

Li 58 49 30 15.7 77 50 67 50 47 64 44 22 214 38 116Be 3.2 4.0 2.1 0.49 1.33 0.97 0.29 1.81 3.3 0.86 2.6 1.79 4.4 1.33 1.84Sc 16.7 11.5 14.4 4.8 26 12.2 12.2 9.1 11.1 10.9 6.0 8.3 13.4 21 12.1Ti 4267 3057 3954 2286 7150 5384 5349 3865 3546 3546 5674 2305 6118 5433 5356V 96 71 93 65 262 171 184 108 98 156 236 58 211 172 170Cr 82 57 140 129 275 213 221 84 100 216 216 71 227 190 166Co 17.1 13.3 9.8 8.4 32 35 34 13.0 15.9 27 29 10.7 42 30 28Ni 34 26 29 22 90 80 92 28 40 80 82 24 88 84 70Cu 17.2 12.8 11.1 40 13.3 74 3.9 13.1 36 34 100 33 150 35 40Zn 93 70 54 15.0 108 86 351 50 60 108 104 29 388 35 137Ga 24 15.1 16.2 6.0 22 21 26 19.3 20 23 20 8.2 52 12.1 24Rb 190 138 173 34 131 97 108 123 111 67 65 68 33 113 50Sr 156 236 302 65 118 39 104 134 117 72 56 127 13.9 117 90Y 24 22 29 10.4 21 9.2 9.9 11.6 20 11.6 5.6 13.5 9.5 18.8 6.1Zr 61 58 174 211 174 128 142 184 178 149 151 53 98 97 74Nb 15.9 11.9 11.1 4.5 15.7 12.5 13.2 11.5 10.2 12.6 12.9 6.6 10.2 12.2 10.9Cs 8.1 7.9 6.7 3.0 9.4 7.2 9.7 8.8 4.5 5.5 5.8 3.8 2.7 5.4 6.3Ba 625 195 426 146 444 308 294 848 824 210 124 152 265 444 147La 37 25 49 8.7 33 19.3 19.7 22 51 19.5 15.5 16.1 13.3 21 13.4Ce 77 46 101 17.8 73 46 51 54 106 45 44 32 27 44 27.7Pr 8.6 5.6 10.2 1.9 7.4 4.7 4.7 5.4 11.9 5.0 3.8 3.7 3.5 5.2 3.2Nd 32 21 38 7.5 28 17.0 18.2 20 45 18.4 13.2 14.3 14.0 19.6 11.9Sm 6.0 4.2 6.6 1.35 4.3 2.5 3.5 3.5 7.8 3.2 2.3 2.9 3.1 4.2 2.4Eu 1.09 1.18 1.37 0.50 1.20 0.48 0.69 0.88 1.30 0.64 0.47 0.75 0.50 0.96 0.41Gd 4.9 4.0 5.7 1.42 4.5 2.3 3.1 2.9 6.4 2.9 2.0 2.8 2.4 3.5 2.0Tb 0.77 0.66 0.88 0.28 0.73 0.37 0.45 0.44 0.89 0.46 0.28 0.42 0.36 0.58 0.29Dy 4.1 3.6 4.5 1.51 4.0 1.9 1.9 2.6 4.2 2.2 1.55 2.3 2.0 3.1 1.25Ho 0.86 0.72 0.89 0.41 0.83 0.40 0.44 0.48 0.79 0.42 0.23 0.47 0.42 0.65 0.26Er 2.3 2.1 2.5 1.05 2.5 1.06 1.16 1.35 2.8 1.36 0.75 1.29 1.08 1.88 0.73Tm 0.35 0.34 0.45 0.17 0.34 0.15 0.13 0.20 0.31 0.19 0.11 0.20 0.15 0.29 0.11Yb 2.3 2.2 2.6 1.18 2.5 1.10 1.36 1.45 2.2 1.40 0.60 1.20 1.08 2.1 0.70Lu 0.33 0.31 0.37 0.18 0.30 0.17 0.16 0.18 0.30 0.18 0.12 0.18 0.16 0.31 0.11Hf 3.1 3.0 5.1 6.0 5.1 3.5 4.2 5.5 5.2 4.0 4.3 2.6 4.7 4.7 3.6Ta 1.24 0.93 0.97 0.31 1.19 0.90 0.93 0.88 0.81 1.02 0.93 0.49 0.79 0.74 0.72Pb 20 23 22 7.7 17.0 21 17.9 20 23 15.7 22 13.8 5.7 21 12.6Th 11.8 9.5 15.6 4.1 11.2 6.3 6.2 8.0 11.6 5.7 4.4 5 5.5 6.6 4.7U 2.7 3.8 3.5 1.54 4.0 2.5 2.6 2.3 3.2 2.4 2.8 2.0 2.1 2.2 2.0La/Sc 2.2 2.1 3.4 1.8 1.3 1.6 1.6 2.4 4.6 1.8 2.6 1.9 1.0 1.0 1.1Th/Sc 0.71 0.83 1.08 0.85 0.43 0.52 0.51 0.88 1.05 0.52 0.73 0.60 0.41 0.31 0.39La/Th 3.2 2.6 3.1 2.1 2.9 3.1 3.2 2.7 4.4 3.4 3.5 3.1 2.4 3.2 2.8Co/Th 1.5 1.4 0.6 2.1 2.8 5.6 5.5 1.6 1.4 4.7 6.7 2.1 7.6 4.6 5.9Th/U 4.4 2.5 4.5 2.7 2.8 2.5 2.4 3.5 3.6 2.4 1.6 2.6 2.7 3.0 2.4Sc/Th 1.4 1.2 0.9 1.2 2.3 1.9 2 1.1 1 1.9 1.4 1.6 2.4 3.3 2.6Yb/Th 0.19 0.23 0.17 0.29 0.22 0.17 0.22 0.18 0.19 0.25 0.14 0.23 0.20 0.32 0.15Hf/Zr 0.05 0.05 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.03 0.05 0.05 0.05 0.05Eu/Eu* 0.61 0.88 0.68 1.10 0.83 0.61 0.64 0.84 0.56 0.63 0.67 0.82 0.56 0.77 0.57ΣΡΕΕ 177.6 116.9 224.1 44.0 161.7 97.5 106.5 115.1 240.4 100.9 84.5 78.6 69.4 107.3 64.5ΣLREE/ΣΗΡΕΕ 10.1 7.3 11.4 6.0 9.2 11.9 11.1 10.9 12.4 9.9 14 7.8 8.0 7.6 10.9Lan/Ybn 11 7.7 12.7 5 8.9 11.9 9.8 10 15.8 9.4 17.4 9.1 8.3 6.7 12.9Lan/Smn 3.9 3.7 4.6 4.1 4.8 4.8 3.5 3.8 4.1 3.8 4.2 3.5 2.7 3.2 3.5Gdn/Ybn 1.8 1.5 1.8 1 1.5 1.7 1.8 1.6 2.4 1.7 2.7 1.9 1.8 1.4 2.3

12


KOTOVA et al.

Table 3. (Contd.)

Area Ljaskelja Impiniemi

Ordinal no. 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Sample no. 18-3 18-9 18-10 19-6 20-1 20-3 21-2 21-4 22-4 22-7 23-1 24-3 24-4 25-4 26-2

Li 52 38 33 39 31 50 56 43 63 19.4 21 16.1 57 22 35Be 2.1 2.2 2.0 2.2 1.71 2.4 0.98 0.72 2.1 1.65 1.34 1.20 4.4 1.51 2.6Sc 18.6 16.9 11.3 12.3 9.9 15.7 12.7 11.1 18.2 7.4 7.8 6.2 20 7.1 12.4Ti 4422 4058 2911 3086 2777 4431 4521 4105 3887 2343 2301 1638 4462 2067 3998V 148 122 73 82 67 104 134 139 114 48 47 37 103 44 82Cr 168 107 85 70 63 101 184 131 166 65 64 34 106 58 109Co 21 19.7 11.3 12.6 10.7 17.0 31 23 19.7 6.6 6.7 4.8 15.3 7.5 14.3Ni 65 47 66 28 25 39 86 70 67 17.6 19.7 13.3 39 27 43Cu 51 56 16.5 16.9 8.5 2.3 60 75 14.4 19.2 21 1.25 1.56 19.6 2.4Zn 105 101 53 57 66 117 197 77 110 36 37 22 115 35 152Ga 24 21 12.5 13.9 13.7 23 18.6 17.5 22 12.1 12.0 10.7 25 11.4 17.5Rb 177 156 67 83 84 149 100 83 246 86 96 30 175 59 135Sr 68 145 177 178 156 162 84 81 99 226 271 304 445 234 154Y 15.0 20 16.3 17.5 17.3 17.3 16.6 10.3 17.6 11.9 21 12.3 26 11.8 17.4Zr 50 61 78 76 80 74 85 71 56 86 70 57 90 63 63Nb 11.1 11.4 7.0 8.2 8.8 15.0 10.3 12.2 11.3 8.2 7.6 5.7 16.5 6.8 11.7Cs 5.4 6.3 2.8 3.5 3.7 8.2 5.3 4.8 14.3 4.2 4.4 1.48 7.5 3.2 5.7Ba 732 806 375 524 524 627 255 314 762 615 254 533 1691 274 625La 22 30 29 27 15.3 14.7 21 19.7 24 22 26 21 41 25 24Ce 49 61 59 56 35 39 51 45 49 45 54 41 81 44 50Pr 5.3 7.0 6.7 6.3 4.1 4.0 4.9 4.5 5.6 4.7 5.6 4.6 10.0 5.3 5.7Nd 20 26 24 23 16.0 15.8 18.2 16.4 21 17.4 22 17.9 37 20 22Sm 4.0 5.0 4.1 4.2 3.5 3.4 3.6 3.2 4.4 3.0 4.1 3.0 7.1 3.3 4.3Eu 0.83 1.12 0.81 0.86 0.83 0.85 0.59 0.59 0.72 0.81 0.74 0.72 1.52 0.63 0.96Gd 3.1 4.5 3.5 3.7 3.2 3.2 3.4 2.7 3.5 2.5 3.7 2.6 5.8 2.7 3.5Tb 0.43 0.62 0.49 0.51 0.53 0.52 0.50 0.34 0.56 0.40 0.58 0.37 0.79 0.40 0.54Dy 2.8 3.2 2.8 2.7 2.9 3.0 3.0 1.78 3.0 2.0 3.5 2.0 4.4 2.1 3.0Ho 0.57 0.70 0.57 0.58 0.65 0.67 0.69 0.39 0.63 0.46 0.78 0.43 0.99 0.44 0.62Er 1.43 2.0 1.49 1.57 1.77 1.90 1.83 1.08 1.89 1.17 2.0 1.19 2.8 1.21 1.62Tm 0.25 0.32 0.27 0.28 0.31 0.30 0.29 0.19 0.29 0.21 0.36 0.19 0.46 0.21 0.28Yb 1.67 2.0 1.62 1.58 1.83 2.1 1.65 1.28 1.64 1.31 2.3 1.22 2.8 1.23 1.72Lu 0.22 0.30 0.24 0.25 0.27 0.28 0.25 0.19 0.25 0.17 0.32 0.17 0.44 0.18 0.26Hf 2.7 3.1 3.7 3.5 3.8 3.8 4.1 3.6 2.8 4.3 3.4 2.6 4.4 2.9 3.1Ta 0.75 0.83 0.59 0.59 0.67 1.16 0.71 0.79 0.94 0.63 0.59 0.45 1.24 0.53 1.05Pb 11.9 14.1 16.6 14.8 15.7 20 14.1 16.9 15.4 19.2 8.9 10.1 21 13.2 31Th 7.8 8.0 8.6 8.3 8.5 9.5 6.6 7.3 9.4 9.9 7.2 6.5 14.2 7.0 7.7U 3.3 2.7 2.3 2.0 1.84 3.0 2.6 2.7 2.5 1.25 1.76 1.53 3.9 1.53 2.3La/Sc 1.2 1.8 2.6 2.2 1.6 0.9 1.7 1.8 1.3 3.0 3.4 3.4 2.1 3.4 1.9Th/Sc 0.42 0.47 0.76 0.67 0.86 0.61 0.52 0.66 0.52 1.34 0.92 1.05 0.71 0.98 0.62La/Th 2.9 3.7 3.4 3.3 1.8 1.6 3.2 2.7 2.1 2.2 3.7 3.3 2.9 3.5 3.1Co/Th 2.7 2.5 1.3 1.5 1.3 1.8 4.8 3.1 3.7 0.7 0.9 0.7 1.1 1.1 1.9Th/U 2.4 3.0 3.8 4.1 4.6 3.2 2.5 2.7 2.0 7.9 4.1 4.3 3.7 4.6 3.3Sc/Th 2.4 2.1 1.3 1.5 1.3 1.7 1.9 1.5 2.0 0.8 1.1 1.0 1.4 1.0 1.6Yb/Th 0.21 0.24 0.19 0.19 0.22 0.22 0.25 0.18 0.18 0.13 0.32 0.19 0.19 0.18 0.22Hf/Zr 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.05Eu/Eu* 0.72 0.72 0.65 0.67 0.75 0.79 0.52 0.62 0.56 0.9 0.59 0.78 0.72 0.65 0.75ΣΡΕΕ 111.6 143.6 135.2 129.0 86.2 89.8 110.8 97.6 116.3 101.7 126.0 97.1 196.1 106.8 118.5ΣLREE/ΣΗΡΕΕ 9.6 9.5 11.2 10.5 6.4 6.4 8.5 11.3 8.8 11.2 8.4 10.7 9.6 11.5 9.1Lan/Ybn 9.1 10.2 12.3 11.8 5.7 4.7 8.7 10.4 9.8 11.4 7.8 11.7 10.1 13.5 9.3Lan/Smn 3.5 3.8 4.5 4.1 2.7 2.7 3.7 3.9 3.4 4.7 4.1 4.4 3.7 4.7 3.4Gdn/Ybn 1.5 1.9 1.8 1.9 1.4 1.2 1.6 1.7 1.8 1.6 1.3 1.7 1.7 1.8 1.7Note: Ordinal numbers as in Table 2.



The Cr and Ni concentrations in the studied rocksare variable, though comparable in general with con-centrations of these elements in the post-Archeanschists (Fig. 7). In concentrations of both elements,rocks from the section upper part are comparable withisland-arc andesites and upper continental crust,whereas rocks of lower part contain much higher Crand Ni concentrations approaching those in the oceanicor lower continental crust (Taylor and MacLennan,1988). Accordingly, it is possible to assume that one ofsources of siliciclastic material accumulated in lowerpart of the Ladoga Group corresponded to basic rocks,maybe to analogs of metabasalts occurring at differentstratigraphic levels of the Jatulian Superhorizon inKarelia (Malashin et al., 2003) or to basic rocks of theYormua ophiolite complex in Finland (Kontinen,1987). Distribution of Cr and Ni in rocks of the LadogaGroup upper part suggests that respective provenancesof original sediments included rocks close in composi-tion to island-arc andesites.

In concentration levels of La, Th, Sc, Hf and Co(Fig. 8), rocks from the group lower part correspond togranodiorite (and/or andesite) and to continental crustas a whole; rocks of the upper part to tonalite andtrondhjemite or to the upper continental crust. Abun-dance rates of La, Th and Sc (Fig. 8a) are indicative tofirst approximation of geodynamic settings, which con-trolled accumulation of siliciclastic sediments (Bhatiaand Crook, 1986). For instance, rocks from both partsof the Ladoga Group section are similar in distribu-tion trends of La, Th and Sc to rocks of continental

island arcs and exclude at least the possibility of theirformation in a passive continental margin or oceanicisland arc.

Rocks of the Ladoga Group upper part are enrichedto some extent in Th and La as compared to rocks of thelower part (Table 3). The La/Th ratio is slightly variable(Table 3), corresponding in average to 3.0 in both sec-tion parts. The Th/U average ratio is somewhat reducedin lower relative to upper part (2.9 versus 4.1), althoughU concentrations are slightly variable throughout thesection (Table 3).

In the section lower part, La/Sc and Th/Sc ratios(Table 3, Fig. 9) are lower in average than in upper partof the Ladoga Group section (0.61 and 1.8 versus 0.88and 2.6 respectively). In the La/Sc–Th/Sc diagram(Fig. 9), data points depict general trend overlappingpoints, which characterize average composition of theArchean and post-Archean siliciclastic metasediments(Taylor and MacLennan, 1988) so that the former isclustering center for the studied lower rocks and the lat-ter for the upper ones.

In the Zr–Hf diagram (Fig. 10), there are two dis-tinct trends corresponding to different Hf/Zr ratios(0.03 and 0.05). The lower ratio (Hf/Zr = 0.03) is char-acteristic only of rocks from the Harlu area and south-ern part of the Janisjarvi area (Hjamekoski outcrops). Itis remarkable therewith that the Hf/Zr average ratio cal-culated for the Jatulian trap complex of Karelia corre-sponds to 0.024 (Malashin et al., 2003). In other silici-

0 2

Th/Sc

La-Sc3 4

0.4

0.8

1.2

1 5

Ar

PAr

1.6

Fig. 9. Diagram La/Sc–Th/Sc for metasediments of theLadoga Group, North Ladoga region (symbols as in Fig. 3):(Ar) Archean rocks, (PAr) post-Archean rocks (Taylor andMacLennan, 1988).

2 4

Zr

Hf5 6

80

120

160

3

JV

Hf/Zr =

0.03

240

40

Hf/Zr = 0.05

200

Fig. 10. Diagram Hf–Zr for metasediments of the LadogaGroup, North Ladoga region with indicated average compo-sition of Jatulian volcanics (JV) in Karelia after Malashinet al. (2003) (symbols as in Fig. 3).

14


KOTOVA et al.

clastic metasediments of the Ladoga Group, the Hf/Zrratio is close to 0.05.

Chondrite-normalized REE distribution patterns inmetamorphic rocks of the Ladoga Group sampled infour reference areas are shown in Fig. 11. These pat-terns are identical in general to the REE distributionpatterns in averaged aleuritic sandstone of the Russianplatform (Migdisov et al., 1994) and in the Phanerozoicgraywacke with intermediate quartz content (Taylorand MacLennan, 1988) that is most clearly seen in thediagrams for rocks from upper part of the LadogaGroup section (Janisjarvi and Impiniemi areas). As forrocks from the section lower part (Harlu and Ljaskeljaareas), their REE distribution patterns are of the sametype, but summary REE concentrations are much morevariable, characterizing more diverse composition ofprotoliths, among which there were oligomictic sand-stones.

The lowest ΣREE and Gdn/Ybn values along withabsence of europium anomaly (Eu/Eu* = 1.10) are typ-ical of quartz sandstone from the Harlu area (Table 3,no. 4) and characterize most likely a peculiar composi-tion of source. Characteristic of the other rock samplesstudied are negative europium anomalies (Eu/Eu* =0.52–0.90) and considerable ranges of ΣREE (64–240),ΣLREE/ΣHREE (6.4–14) and Lan/Ybn (4.7–17.4),whereas ratios Lan/Smn (2.7–8.0) and Gdn/Ybn (1.2–2.7) are less variable. The highest fractionation ofLREE and twofold lower fractionation of HREE estab-lished in the rocks is inherent in general to the post-Archean sedimentary rocks. The LREE distributiontrends are similar therewith in contrast to more variabledistribution of HREE. The respective variations ofLan/Ybn ratio depend ultimately on abundance of con-crete accessory minerals in the rocks.

Spider-diagrams (Fig. 12) plotted using normalizingto the Phanerozoic graywacke (Taylor and MacLennan,

100Eu

III

Dy Er

101

La Lu

12

Ce Pr Nd Sm Gd Tb Ho Tm Yb

102

1314151617

181920212223

100Eu

IV

Dy Er

102

La Lu

24

Ce Pr Nd Sm Gd Tb Ho Tm Yb

101

103

252627282930

100

II

4

101

567891011

102

103Rock/chondrite

100

IAS

101

Rock/chondrite

102

103

PG123

Fig. 11. Chondrite-normalized REE distribution patterns in metasediments of the Ladoga Group, North Ladoga region(chondrite normalizing values after Taylor and MacLennan, 1988). Numbers in diagrams correspond to ordinal numbers inTable 3. Reference areas: (I) Janisjarvi, (II) Harlu, (III) Ljaskelja, (IV) Impiniemi; (AS) average composition of aleuriticsandstones in the Russian platform cover after Migdisov et al. (1994); (PG) Phanerozoic graywacke after Tailor andMacLennan (1988).



1988) also reveal difference in concentrations of certaintrace element between siliciclastic metasediments fromlower and upper parts of the Ladoga group section.Rocks of the lower part reveal higher concentrations ofsiderophile elements (V, Cr, Co, Ni) and Cu. In addi-tion, all studied rocks are enriched in Rb and Ba relativeto the Phanerozoic graywacke. Variations in concentra-tion of other elements (Sc, Zn, Ga, Sr, Y, Nb, Hf, Pb, Th,and U) are nether significant, nor anomalous. An excep-tion is Zr most concentrated in rocks of the Harlu–Hjamekoski area.

Sm–Nd ISOTOPIC SYSTEMATICS OF STUDIED ROCKS

The results of Sm–Nd isotopic study (Table 4) showthat TNd(DM) model ages calculated for siliciclasticmetasediments from lower and upper part of the

Ladoga Group section range within 2.5–2.7 and 2.4–2.5 Ga, respectively. An extreme TNd(DM) = 3.1 Ga isestimated for the only metagraywacke sample fromthe section lower part. In the “εNd–Age” diagram(Fig. 13), lines of Nd isotopic evolution plotted formost studied rocks appear to be in the field of Nd iso-topic evolution of the Kalevian metasediments in Fin-land (Huhma, 1987) or between the fields of Nd isoto-pic evolution of the Svecofennian metasediments inFinland (Lahtinen et al., 2002) and of the Archeancontinental crust in the Karelian megablock of theBaltic Shield (Early Precambrian…, 2005). Two sam-ples from lower part of the Ladoga Group section rep-resent exception, and lines of their isotopic evolutionare close to or inside the field characterizing the Ndisotopic evolution of the Archean continental crust inthe Karelian craton.

10–2Cu

III

Y Nb

101

Sc Pb

12

V Cr Co Ni Ga Rb Zr Ba Hf

1314151617

181920212223

10–1

IV

101

24252627282930

10–1

II4567891011101

Rock/Phanerozoic graywacke

10–1

I

100

Rock/Phanerozoic graywacke

123

Zn Sr Th U

10–1

100

102

Cu Y NbSc PbV Cr Co Ni Ga Rb Zr Ba HfZn Sr Th U

101 102

100

100

102

Fig. 12. Spider-diagrams for metasediments of the Ladoga Group, North Ladoga region (see explanations to Fig. 11).

16


KOTOVA et al.

CONCLUSIONS

The results of petrochemical analysis used to recon-struct primary composition of sedimentary protolithsfor metamorphic rocks of the Ladoga Group showedthat they corresponded along the studied profile mostlyto rocks of graywacke-argillite association (90%) witha minor proportion of arenites (10%). Characteristic ofthe protoliths was moderate alkalinity with insignifi-cant prevalence of potassium over sodium.

In chemical composition, siliciclastic metasedi-ments of the Ladoga Group are divisible in two differ-ent groups. One group includes rocks sampled in prox-imity to outcrops of the Sortavala Group rocks (Harluand Ljaskelja areas), which are enriched in trace ele-ments of the iron group and characterize lower part ofthe Ladoga Group section. The other group of morealuminous rocks sampled away from these outcrops(Janisjarvi and Impiniemi areas) exemplifies upper partof the group under consideration. In terms of chemicalcomposition, rocks from lower part of the LadogaGroup section are metamorphic equivalents of morerecycled sedimentary protoliths, which have been rela-tively enriched, being interrelated with source rocks ofbasic composition, in TiO2, Fe2O3, and MgO butdepleted in Al2O3 as compared to rocks representingthe section upper part.

Lower and upper parts of the Ladoga Group sectiondiffer also in geochemical characteristics of their rocks.Rocks of the section lower part are enriched in V, Cr,Co, Ni, and Cu, and this suggests, along with petro-chemical data, that rocks of basic composition were

Table 4. Result of Sm–Ng isotopic-geochemical study of metasedimentary rocks from the Ladoga Group, North Ladoga region

Ordinal no.

Sample no.

Sm,ppm

Nd,ppm

147Sm/144Nd 143Nd/144Nd ± 2σ εNd(0) TNd(DM), Ma

Type ofprotolith Area

1 6-2 7.36 42.6 0.1088 0.511459 ± 9 –23.0 2449 Argillite Janisjarvi (upper part of the section)2 6-3 4.91 25.7 0.1204 0.511522 ± 8 –21.8 2648 Graywacke

3 114-1 6.22 32.4 0.1161 0.511433 ± 5 –23.5 2671 Argillite Harlu (lower part of the section)4 107-4 5.17 26.2 0.1195 0.511479 ± 5 –22.6 2697 Graywacke

5 112-1 4.59 25.3 0.1097 0.511398 ± 4 –24.2 2558 Graywacke

6 10-5 1.29 6.87 0.1138 0.511399 ± 9 –24.2 2661 Arenite

7 20-1 4.19 20.0 0.1317 0.511447 ± 5 –23.2 3149 Graywacke Ljaskelja (lower part of the section)8 21-4 5.27 29.3 0.1130 0.511471 ± 4 –22.8 2532 Argillite

9 18-10 5.04 30.1 0.1052 0.511332 ± 4 –25.5 2544 Graywacke

10 18-3 5.67 31.1 0.1147 0.511418 ± 9 –23.8 2655 Argillite

11 17-4 4.59 24.4 0.1182 0.511438 ± 7 –23.4 2721 Graywacke

12 17-1 2.75 14.5 0.1193 0.511468 ± 9 –22.8 2704 Arenite

13 23-1 5.22 29.2 0.1125 0.511430 ± 7 –23.6 2582 Graywacke Impiniemi (upper part of the section)14 24-4 7.30 41.9 0.1097 0.511430 ± 14 –23.6 2511 Argillite

15 25-4 4.23 25.6 0.1040 0.511311 ± 5 –25.9 2546 Arenite

Note: 143Nd/144Nd ± 2σ—uncertainty corresponds to last significant digits after point.

–8

1.8 1.9

εNd

Age, Ga2.0 2.1

1 2 3 4 5

–6

–4

–2

0

2

4

6

CHUR

DM

Fig. 13. Diagram “εNd–age” for metasediments of theLadoga Group, North Ladoga region: (1) metasedimentsfrom upper part of the Ladoga Group section; (2) metased-iments from lower part of the Ladoga Group section; (3)field of Nd isotopic evolution in Archean continental crustof the Karelian megablock, Baltic Shield (Early Precam-brian…, 2005); (4) field of Nd isotopic evolution in EarlyProterozoic siliciclastic metasediments of southern and cen-tral Finland (Lahtinen et al., 2002); (5) field of Nd isotopicevolution in Early Proterozoic siliciclastic metasediments,the Kalevian of Finland (Huhma, 1987).



sufficiently widespread in respective provenances ofclastic material. In contrast, rocks of the upper part areenriched in Th and La, and consequently their prove-nances were composed predominantly of silicic rocks.In concentration ranges of La, Th and Sc, rocks of theupper and lower parts of the studied succession arecomparable with granite and granodiorite, respectively.

Distribution trends of Zr, Hf, Cr, and Ni are of spe-cial importance for identification of source rocks forsedimentary protoliths of the Ladoga Group metamor-phites. According to close Hf/Zr ratios, the Jatulian pla-teau basalts appear to be most appropriate source rocksfor those siliciclastic metasediments of the LadogaGroup, which are relatively enriched in Zr. Compara-tively high Cr and Ni concentrations in lower metamor-phites of the Ladoga Group also evidence in favor oftheir connection with a provenance composed of theJatulian and Livian basalts. In turn, some rocks fromthe group lower part with lowered Cr and Ni concentra-tion suggest that one of their source corresponded prob-ably to andesites of the Svecofennian island-arc com-plexes in Finland.

The Sm–Nd isotopic data imply that protoliths ofthe Ladoga Group metasediments included clastic com-ponents with both the Archean and Early ProterozoicNd model ages. In other words, siliciclastic successionsof the Ladoga Group accumulated at the expense oferosion in provenances composed of rocks, which orig-inated under influence of crust-forming processes ofthe Archean and Early Proterozoic time. Metamorphicrocks from the section lower part reveal therewith themuch greater relative contribution of sedimentarymaterial with the Archean TNd(DM) than siliciclasticmetasediments of the Ladoga Group upper part.

Taking into consideration the Sm–Nd isotopic-geochemical data available at present for the Svecofen-nian foldbelt (Fig. 13), we can state that provenances ofsiliciclastic material with the Archean TNd(DM) valueswere situated within the Karelian craton during theaccumulation time of sedimentary protoliths for theLadoga Group metamorphites. For lower and upperparts of the Ladoga Group section, main source of thismaterial should be of granitoid composition, i.e., corre-sponding to granite gneisses of the Archean basementwithin the Karelian megablock of the Baltic Shield.Influx of the Early Proterozoic sedimentary materialinto the Kalevian basin of sedimentation was controlledmost likely by erosion of the Sortavala Group rocks andEarly Proterozoic island-arc associations in eastern partof the Svecofennian foldbelt. Volcanic rocks of the Sor-tavala Group should be considered therewith as mainsource of siliciclastic material with the Early Protero-zoic TNd(DM) values for sediments accumulated inlower part of the Ladoga Group, whereas sediments ofthe upper part included material derived by erosionfrom island-arc terranes of the Svecofennian belt. Sum-marizing up the aforesaid, we may conclude that prov-

enances of siliciclastic material transformed into theKalevian metamorphic rocks of the Ladoga Group weresituated not far away from the basin of sedimentation.

ACKNOWLEDGMENTS

The work was supported by the Program for Supportof Scientific Schools, grant NSh-4732.2006.5, and bythe Program “Isotopic Geology: Geochronology andmatter Sources” of the Earthscience Division RAS.

Reviewer A.V. Maslov

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Documents

Source rocks and provenances of the Ladoga Group siliciclastic metasediments (Svecofennian Foldbelt, Baltic Shield): Results of geochemical and Sm-Nd isotopic study