The first results of U/Pb dating and isotope geochemical studies of detrital zircons from the neoproterozoic sandstones of the Southern Timan (Djejim-Parma Hill)

ISSN 1028�334X, Doklady Earth Sciences, 2010, Vol. 435, Part 2, pp. 1676–1683. © Pleiades Publishing, Ltd., 2010.Original Russian Text © N.B. Kuznetsov, L.M. Natapov, E.A. Belousova, U.L. Griffin, S.Y. O’Relly, K.V. Kulikova, A.A. Soboleva, O.V. Udoratina, 2010, published in DokladyAkademii Nauk, 2010, Vol. 435, No. 6, pp. 798–805.

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In the eastern and northeastern framework of theEast European Platform (EEP), including the Uralwestern slope, Timan, and the basement of thePechora basin, Neoproterozoic complexes (pre�uralides) are quite abundant (Fig. 1) [1, 2]. Their ageanalogues are known on peninsulas of the Kola coastsof the Barents Sea (the Srednii, Rybachii, and

Varanger peninsulas) and adjacent islands (IslandKil’din, etc.), at the Pai�Khoi Mts., and on theNovaya Zemlya and Svalbard archipelagoes. More�over, by geological data, pre�uralides and their ageanalogues form the upper levels of the consolidatedcrust on the Barents Sea shelf. Many aspects of thegeological structure of these formations have been wellstudied by now using the classic techniques [2, 5, etc.].However, until now, no pre�uralide–timanide sedi�mentary stratum within the borders of the Timan andPechora basin was studied by means of a modern tech�nique such as the geochemical and isotope study ofdetrital zircons from sedimentary rocks. The applica�tion of this method may provide important informa�tion allowing one both to verify the notion of the age ofthe stratum considered as such and to make conclu�sions on the ablation sources and paleotectonic condi�

The First Results of U/Pb Dating and Isotope Geochemical Studies of Detrital Zircons from the Neoproterozoic Sandstones

of the Southern Timan (Djejim–Parma Hill)N. B. Kuznetsova, b, L. M. Natapovc, E. A. Belousovac, U. L. Griffinc, S. Y. O’Rellyc,

K. V. Kulikovad, A. A. Sobolevad, and O. V. Udoratinad

Presented by Academician Yu.G. Leonov February 25, 2009

Received March 24, 2009

Abstract—This report presents the first results of U/Pb dating, isotope–geochemical, and geochemical studiesof detrital zircons from the Neoproterozoic clastic rocks of the Southern Timan. Sixty�one zircon grains weretreated, including 51 from red�colored sandstones and 10 grains from aleurosandstones of the Djejim Formationof the southern Chetlas–Djejim zone (Djejim�Parma Hill). It was found that the U/Pb–ages of zircons fromthe rocks of the Djejim Formation, varied from ~2.97 to ~1.20 Ga. The studies of microelement composition in47 grains (of 61 U/Pb isotope ages obtained), on the basis of several empirical regularities found formerly, showthat the detrital zircons had originated from “granites” (22 grains), “diorites” (12 grains), or their volcanic ana�logues, or more rarely, from “syenites” and “basites” (5 and 8 grains, respectively). The Lu/Hf isotope system

of zircons allows one to estimate the model ages ( ) of the substrate magmatic rocks being parental to thezircons considered. In particular, Archean zircons are characterized by ~2.84–3.36 Ga model ages of magma�forming rocks. For some of the grains, their model ages (~2.84 Ga) are close to those of zircons as such (~2.7–2.8 Ga), which points to the juvenile character of the substrate from which the parent magma of the zirconstreated was fused. For Proterozoic (to Middle Riphean) zircons, the Lu/Hf isotope system allows one to esti�mate the model age of the substrate of their parental rocks within ~2.00–3.36 Ga, which shows that these rockswere formed under the recycling of the Archean and Early�Proterozoic crust. The ages obtained for detrital zir�cons, as well as model ages of the substrate of the corresponding parental magmatic rocks, are quite comparableto the age of crystalline complexes of the ancient framework of the East European Platform (EEP), formed inthe course of the Archean, Early�Proterozoic, and Early–Middle Riphean tectonomagmatic events. This per�mits us to conclude that the Neoproterozoic detrital complexes of the Timan were formed owing to the erosionof earlier Neoproterozoic and Early Precambrian complexes constituting the Neoproterozoic Baltica conti�nent, presenting complexes of the passive margin of this continent. A variety of ages of detrital zircons fromsandstones and aleurosandstones from the Djejim Formation of Djejim�Parma Hill, and of the estimates ofmagmatic rocks parental to these zircons, may be characterized as a Baltic Provenance signal.

DOI: 10.1134/S1028334X10120263

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a Geological Institute, Russian Academy of Sciences, Moscow, Russiab The Peoples’ Friendship University of Russia, Moscow, Russiac GEMOS Center, Macquarie University, Sydney, Australiad Institute of Geology, Komi Scientific Center, Ural Division, Russian Academy of Sciences, Syktyvkar, Russiae�mail: [email protected]

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Fig. 1. Complexes and structures of the East European platform (crystalline basement and dissecting aulacogenes and rift sys�tems), as well as of Neoproterozoic and Paleozoic folded belts of its framing. As a basis, the tectonic scheme of Late Paleoprot�erozoic–Early Neoproterozoic EEP complexes by Bogdanova [8] was used. The spatial disposition of Late Precambrian com�plexes of the eastern and northeastern framings of the platform by [2]. 1—Paleozoic complexes of uralides (variscides) of theEastern Urals; 2—Paleozoic (Caledonian) complexes of middle and upper nuppes of Scandinavian caledonides; 3—Neoprot�erozoic complexes (cadomides) of the southeastern framing of the platform; 4–5—Neoproterozoic complexes (pre�uralides–timanides) of the Western Urals and the Timan–Pechora region, as well as their age analogues in the Near�Ural part of the plat�form, Caspian region, and Scandinavia: 4—mainly sedimentary complexes; 5—the complexes of the structures with a consider�able contribution of volcanogenic and volcano�sedimentary formations, as well as granitoids and rare ophiolites; 6—Mesoprot�erozoic forming the riftogenic structures within the platform; 7–10—Riphean forming the accretionary and collision structuresin the western part of the platform: 7—Early and Late�Precambrian complexes transformed under the Sveconorwegian (1.14–0.90 Ga) collision tectogenesis (Sveconorwegian orogeny); 8—Telemarkian event complexes (1.52–1.48 Ga) of accretionary tec�togenesis; 9—Danopolonian event complexes (1.50–1.40 Ga) of accretionary tectogenesis; 10—Gothian event complexes(1.75–1.55 Ga) of accretionary tectogenesis; 11—Neoproterozoic intrusive associates of anorthosite–mangerite–charnokite–granite composition (AMCG) and A�type granitoids of age intervals of 1.55–1.44 (a), 1.60–1.58 (b), and 1.67–1.65 Ga (c); 12—Early�Proterozoic complexes of Fennoscandia (1.95–1.65 Ga), Volgo�Uralia and Sarmatia (2.2–2.0 Ga); 13—Archean com�plexes of Fennoscandia, Volgo�Uralia, and Sarmatia (3.70–2.60 Ga); 14–15—the complexes of Early�Proterozoic collision oro�genes: 14—Lapland–Kola orogenic belt welded the Karelian and Kola protocratons (1.95–1.65 Ga); 15—the orogenic beltwelded Sarmatia and Volgo�Uralia (2.1–2.0 Ga); 16—Central Russian orogenic belt welded Fennoscandia and Volgo�Sarmatia(1.8–1.7 Ga); 17—main tectonic scissions (firm lines) and their probable locations (dotted lines): a—sutures at the outer limitsof the ancient core of the EEP outer framework; b—block boundaries inside the ancient EEP framework; the boundaries of col�lision orogenic belts welded these blocks; tectonic limits of Neoproterozoic (1.6–0.8 Ga) riftogenic structures (aulacogenes)within the platform (rift systems: WSRS is the White Sea system by [14], KB is Kama–Belaya system; aulacogenes: MR is MiddleRussian, M is Moscow, VO is Volyn–Orsha, SA is Sernovodsk–Abdulino, Pa is Pachelma belts; La is Ladoga graben); 18—con�tours of the pre�uralide–timanide protrusions onto the daylight surface in the Western Ural (B is Bashkir uplift, K is Kvarkushanticlinorium, and L is Lyapin anticlinorium), Timan, and Kanin Peninsula; 19—location of the sampling site (samples 301 and301A) in Southern Timan (Djejim–Parma hill). The inset contains the contours of protocratons (Fennoscandia, Sarmatia, andVolgo�Uralia) involved into the structure of the EEP ancient framework [8].

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8 9 10 11 12 13 14

15 16 17 18 19

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Bolshezemel megablock

Timan megablock

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km

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a n d C e n t r a lE u r o p e

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BU

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tions of its formation, and to test on this basis the tec�tonic models describing the paleotectonic nature ofthe complex considered. This report presents the pri�mary results of integrated studies of detrital zirconsfrom one of the Neoproterozoic clastic rocks of south�ern Timan.

Within the bounds of the Timan and adjacent partsof the basement of Pechora basin on the basis of thefeatures of composition, structure, and completenessof the sections of Neoproterozoic strata, a series ofstructural and material zones is distinguished (fromSW to NE): the Obdyrsko–Nivsherskaya, Cheglass–Djejim–Parma, Tsilma–Ropcha, and Vymsko–Vol�skaya zones [3, 4]. In the Southern Timan, within thebounds of the Djejim–Parma hilly area, the Neoprot�erozoic formations presented by red�colored sand�stones and aleurosandstones of the Early–Neoprot�erozoic Djejim Formation [4] are protruding in someplaces from under a loose Cenozoic sedimentary cover(the southern part of the Cheglass–Djejim–Parmazone).

In the quarry of the Asy�Vozha rubble�stonedeposit (61°47′11.5″ N, 54°06′35.2″ E), the samplesfor analyzing the detrital zircons were collected fromDjejim red�colored obliquely�laminated quartz sand�stones and aleurosandstones with plentiful wave marks(samples 301A and 301, respectively). The sampleswere crushed manually in a cast�iron mortar andcleansed with water to a gray schlich from which a zir�con�enriched concentrate of heavy minerals wasobtained using bromoform at the Geological Institute(analyst T.D. Zelenova). A further separation of indi�vidual zircon grains and the analyses of the separatedzircons were carried�out at the GEMOS Center of theMacquarie University (Sydney, Australia) using theTerraneChron procedure, including (1) U/Pb datingof zircons, (2) studies of the Lu/Hf isotope system in

zircons, (3) the estimation of the model age ( )considered as the minimum age of the substrate ofparental magma from which a zircon was crystallized,and (4) the determination of the content of impurity

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Fig. 2. Concordance diagram for zircons from aleuro�sandstones (301, grey ellipses) and sandstones (301A, light ellipses) of theDjejim Formation. The images of examined zircon crystals (in back�scattered electrons), their nos. and values of U/Pb isotopeage are given.

0.05

40 8 12 16207Pb/235U

0.15

0.25

0.35

0.45

0.55

0.65

206Pb/238U

301A�22(1042 ± 18 Ma)

301A�25(1129 ± 20 Ma)

301�103(1663 ± 34 Ma)

301A�46(2747 ± 40 Ma)

301�47R(2687 ± 24 Ma)301�101

(1592 ± 48 Ma301�98(1578 ± 26 Ma)

301A�06(1617 ± 30 Ma)

301A�39(2673 ± 52 Ma)

301A�40(2595 ± 36 Ma)

301�26(2709 ± 22 Ma)

301A�14(1931 ± 36 Ma)

301�97(1804 ± 18 Ma)

301�99(2777 ± 34 Ma)

301�06(2666 ± 22 Ma)

301A�37(2759 ± 44 Ma)

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50 µm50 µm

100 µm50 µm

100 µm

50 µm

100 µm

50 µm

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100 µm

100 µm

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301A�12

301�57C

301�47C

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elements in zircons allowing one to characterize thetype of zircon parental rocks.

The U/Pb system in zircons was studied by meansof an LUV 213 laser ablation system (manufactured byNew Wave/Merchantek) combined with an Agilent7500cs IPC mass spectrometer. The Lu/Hf system inzircons was studied in situ by means of a New Wave UP

213 nm laser ablation microprobe equipped with a NuPlasma multicollector ICP mass spectrometer. Theablation crater was of ~50 μm diameter. All the analyt�ical measurements were performed in helium atmo�sphere. The measured values of the U/Pb isotope sys�tem were processed using the Isoplot software. To cal�culate the initial 176Hf/177Hf ratios, the measured

Fig. 3. Occurrence frequency diagram (histogram) of U/Pb isotope ages of detrital zircons from sandstones and aleurolites of theDjejim Formation or Southern Timan (61 analyses). The numbers (301A�16, 301A�12, 301A�57C, 301A�57R, and 301�47) markthe zircons for which the off�grade data were obtained (C is a core, and R is a rim of zircon). Over the histogram, the time intervalsare shown (using the data by [7–13 etc.]): black bands are the collision events of Baltica assembling; gray bands are the accretion�ary phases (Gothian, Telemarkian, Danopolonian) and other less important tectonomagmatic events revealed on the westernedge of Baltica (in the Sveconorwegian area); light�gray bands are the formation times of the Korosten’ pluton (K), Ovruch (O),Navysh (N), and Mashak (M) riftogene complexes, the Kusinsk–Kopan complex (KK), AMCG and A�granites (AMCG andand A�granites), synmetamorphic granitoids of Volgo�Uralia (SMg V�U), leucogranites of Volgo�Uralia (LG V�U) of granulitemetamorphism of Volgo�Uralia (GM V�U). The shaded rectangles are the Archean complexes of Fennoscandia, Volgo�Uralia,and Sarmatia.

1

12001100

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3

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6

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1300 1400 1500 1600 1700 1800 1900 2000 2200 23002100 2400 2500 2600 2700 2800 2900 3000

301A�16301A�12301A�57R

301A�47C

D6D5D4D3D2D1

O MKK H K GM VU LG V–UAMCG andA�granites SMg VU

TTG

GrenvilleProtobalticaassembling

~2.1−1.7 Ма

Granitoids and granite�metamorphiccomplexes (Sarmatia)

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norweg

ian

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opolonia

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mar

kian

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ian

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n of F

ennosc

andia

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fennia

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and V

olgo�S

arm

atia

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oro

geny

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n of V

olgo�

Fen

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dia

Sanukitoids (intrusions)

Alkaline magmatism in

Volgo�Uralia

Age, Ma

“Granites” “Diorites” “Syenites” “Basites” Lack of parameters

Sample 301

301A�57C

Orogeny(Rodinia assembling)

~1.3−1.0 Ma

Ura

lia an

d Sar

mat

ia

(Karelian province)

Keivi area (Kola province)

for classification

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176Lu/177Hf values were used. The error (2σ) of theunique analysis for 176Lu/177Hf amounted to ±1–2%,including the analytical uncertainties and spatial vari�ations of the Lu/Hf value in zircons. The technicali�ties, methodical modes, and constants used in calcu�

lating the εHf values and model ages ( ), as well asthe references to original publications, are given in [1].

In total, the authors tested 61 zircon grains fromthe rocks of the Djejim Formation. The results of fourisotope analyses (301A–16, 301A–12, 301A–57C,and 301–47C) were not used because of their consid�erable discordance. The results of the study of theU/Pb system in other zircons show that their age var�ied from 2.972 to 1.175 Ga (Figs. 2, 3). Most of the zir�cons were of Neoproterozoic ages, with 4 and 7 grainsof Mezoproterozoic and (Neo)Archean ages, respec�tively. The age distribution of zircons of sample 301

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(10 grains) showed no peculiarities compared to theages of sample 301A (51 grains).

The acceptable data on the content of rare andtrace elements were obtained only for 47 of 61 grainstested. The geochemical characteristics of zircons(according to methodical approaches presented in [1,6] point to the origin of 34 grains from granitic rocksor their volcanic equivalents (including 22 grains fromthe rocks of 70–75% SiO2 content (“granites”) and 12from those containing less than 65% of SiO2 (“dior�ites”), 5 grains from the rocks of syenitic composition(“syenites”), and 8 from the rocks of basic composi�tion (“basites).

For 47 grains, acceptable results allowing one tocharacterize the Lu/Hf isotope system were obtained.The analysis of these data revealed a wide scattering ofεHf values (from +8 to –15). Positive εHf values in zir�cons show their origin from magmatic rocks of mantlegenesis. However, negative εHf values point to the par�

Fig. 4. Model ages of the substrate of magmatic rocks parental to the zircons considered. The squares are zircons from aleuro�sandstones (sample 301), and the circles are zircons from coarse�grained sandstones (sample 301A). The numerals in rectangular

frames are the values of model age ( , Ga) of the substrate of magmatic rocks parental to the zircons considered.TDMC

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1000500 1500 2000 30002500 35000.2805

0.2815

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176Hf/177Hfinit

DM

CHUR

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1.52 1.82 2.00

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2.80

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Age, Ma

Types of zircon parental rocks: “Granites”

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ticipation of ancient matter in the substrate, the melt�ing of which formed the magmas primary to eruptiverocks that were parental to these zircons.

The model ages ( ) of the substrate of mag�matic rocks parental to zircons under study, obtainedon the basis of the analysis of U/Pb isotope systemparameters, resulted in data scattering from 1.40 to3.24 Ga (Fig. 4). For several zircons examined, the

ages of the proper zircons and values appeared tobe almost coincident (a close position of figurativepoints to the DM line in Fig. 4). This points to the factthat the substrate from which the primary magmaparental to the zircons considered was fused may becharacterized as juvenile. The other zircons are char�acterized by pronounced disagreement in isotope ages

and values; i.e., they contain considerableamounts of radiogenic matter of the Lu/Hf isotopesystem. This points to a sufficient contribution of theancient crust matter to the substrate magmatic rocksbeing parental to these zircons.

On the basis of the results of isotope dating of detri�tal zircons collected from clastic rocks of the DjejimFormation, six groups of different ages (populations)were distinguished (D1–D6). The determination of atype of parental rock and the features of Lu/Hf systemin zircons allowed us to realize a supplementary classi�fication of zircons within the populations distin�guished.

Within the youngest population D1 (~1.18–1.35 Ga), the zircons are of diorite origin (2 grains),with one grain each of basites and syenites. The dioritezircons originated from the rocks characterized by avery low accumulation of radiogenic matter, and basiteand syenite ones came from rocks that may be treatedas juvenile.

Population D2 is presented by both granite anddiorite zircons (6 grains in all) of the ages within

~1.53–1.64 Ga and of εHf and values varyingfrom –3 to +5 and within 1.82–2.12 Ga, respectively.

Population D3 (~1.70–1.83 Ga) are presented bytwo basite, four granite, and one diorite zircon. Forone of the grains, we failed to determine the composi�tion of the parental rock. The diversity of the types ofparental rocks for the zircons of this population wasnot represented in significant variations of the param�eters of the Lu/Hf isotope system. The εHf values inzircons of this population varied only from 0 to +5,

and the values were about 2.12 Ga.

The most abundant population D4 is characterizedby age ranges of ~1.88–2.15 Ga. The zircons of thisgroup originated from parental rocks of various types,and are characterized by pronounced variations in theparameters of the Lu/Hf isotope system. Thus, twodiorite zircons show εHf values of –12 and –15, whichpoints to the formation of a melt that was later crystal�

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lized to form the parental rocks for these zircons from

isotopically mature ancient crust matter ( of3.08–3.25 Ga). On the contrary, many granite zirconscontain small amounts of the radiogenic componentof the Lu/Hf isotope system, or are substantially juve�nile. More than half of zircons are characterized byLu/Hf isotope parameters close to CHUR, and their

varies from 2.6 to 2.8 Ga.

Population D5 is presented by two granite zircons(both of highly discordant ages) and one unidentifiedzircon (the age was obtained for its shell). For zircons

as such, εHf values are close to –8, and values areabout 1 Ga more ancient than the proper zircons.

The Archean zircons (population D6) are pre�sented by 12 grains of ~2.53–2.80 Ga age and onegrain of 2.972 ± 0.064 Ga. Five zircons of this grouporiginate from diorite, two from syenite, and one fromgranite source. Five zircons including the mostancient one were not identified. The syenite zircons

are characterized by values of over 3.0 Ga. Thediorite zircons contain moderate amounts of radio�genic matter, and the parental rock of granite zircon

may be considered as juvenile. A value for themost ancient zircon was not determined.

According to the notions based upon the analysis ofthe spatial distribution of various Early Neoprotero�zoic structural and material complexes along theTiman periphery of Baltica (Pre�Cambrian EEP core),the sedimentary basin existing at that time consisted ofan asymmetric basin of a sort of a continental marginof the passive (Atlantic) type, opening towards theTiman Ocean (northeastwards in present�day coordi�nates) [3, 4, etc.]. The primary obtained results of thestudies of isotope�geochronological, isotope�geochem�ical, and geochemical parameters of detrital zirconsfrom clastic rocks of the Djejim Formation providefirst a basic opportunity to characterize the distributiveprovince, the complexes of which formed the Neopro�terozoic clastic rocks of the Southern Timan owing tothe products of the destruction of its complexes. Evi�dently, this allows one to examine the notions that theTiman edge of Baltica was its passive margin in theEarly Neoproterozoic, within which the destructionproducts of the complexes of its ancient frameworkwere accumulated.

First, one must note that the ages of the greatmajority of the studied zircons (populations D3 andD4) fall into the range of ~1.70–2.15 Ga. This timeinterval corresponds to the stages of the “assembling”of Baltica owing to the collision of the Sarmatia andVolgo�Uralia protocratons (~2.1–2.0 Ga) to formtheir agglomerate (Volgo�Sarmatia), and further colli�sion of Volgo�Sarmatia and Fennoscandia (1.8–1.7 Ga).At that time, large volumes of granitoid rocks werefused in collision orogenes which “welded” the proto�

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cratons. Moreover, ~2.00–1.95 Ga ago, a large super�subduction formation occurred along the northwest�ern edge of Sarmatia (an orogen of the accretionarytype with super�subduction magmatism and meta�morphism) [7, 8, and references therein].

Juvenile basite and syenite zircons of the youngestpopulation D1 may conform either to the intrusions ofthe mantle substance at the earliest stages of the Gren�ville Orogeny of West Baltica, or, most probably, to theMashak rifting event of East Baltica (its magmaticcomplexes are now exposed in the western SouthernUrals in the Bashkir uplift). Two diorite zircons ofpopulation D1 might have originated from magmaticcomplexes formed under the later tectomomagmaticevents that proceeded in the Svecofennian area in WestBaltica.

Granite and diorite zircons from population D2 of1.82–2.12 Ga model ages, probably, originated fromthe rocks formed either during the accretionary events(the Gothian orogenic event) in West Baltica, or, as forgranite zircons, may be the products of the destructionof rapakivi granites developed widely over its north�western part. Some of the basite and diorite zircons ofpopulation D3 might have originated from the rocks ofthe Korosten’ pluton (North Sarmatia) presented bygabbroids, anorthosites, and rapakivi�like granites,which is supported by the comparable model ages ofthe granite and basite substrates (~2.12 Ga).

Zircons of the most ancient (Neo)Archean popula�tion D6 might possibly have originated from theancient crystalline complexes of Fennoscandia (theknown ages of 2.60–3.5 Ga [8–10]), Volgo�Uralia(2.60–3.5 Ga [8, 11–13]), and Sarmatia (2.50–3.8 Ga[7, 8]). The most likely sources of syenite zirconsmight be alkaline granitoids and gabbro�anorthositesof 2.63–2.75 Ga in age [10] from Keiva tundras (Kolaprovince of Fennoscandia).

CONCLUSIONS

(1) The age of the youngest grain (1042 ± 18 Ma) ofthe examined zircons we sampled from the clasticrocks of the Djejim Formation of the Djejim–Parmahill in the Southern Timan does not contradict thepresent notions [3, 4] on the Early�Neoproterozoicattribution of this formation.

(2) The tested detrital zircons are characterized bya prevalence of the grains of two age groups (Paleopro�terozoic D4 and Neoarchean D6). The age interval ofthe former group correlates to the events of Balticaassembling from Sarmatia, Volgo�Uralia, and Fennos�candia, and that of the latter group, to the events offormation and evolution of Fennoscandia. In thiscase, there are almost no zircons of 2.15–2.65 Ga agesamong the samples treated. Combined with theobtained values, the ages of the tested zirconspoint to a high probability of their origin from crystal�line complexes formed during the Archean, Early Pro�terozoic, and Mesoproterozoic tectonomagmatic

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events, which caused the formation of the ancientEEC framework. This may be considered as a reliableand completely independent confirmation of the pre�vious assumption [4] that the Early�Neoproterozoicterrigenous complexes of the Timan were formed fromthe products of destruction of more ancient crystallinecomplexes of the EEP basement.

(3) The products of destruction of the most ancientcomplexes of Sarmatia (3.8 Ga; the Aul complex ofthe Middle Dnieper block of the Ukrainian shield)and of Volgo�Uralia (3.5 Ga; the Taratash complex ofthe Taratash protrusion at the Bashkir uplift) wererevealed neither in the ages of zircons from the Djejim

Formation rocks (<3.00 Ga) nor in values of theirparental rocks (<3.36 Ga). This might be caused by thefact that the Djejim Formation rocks were mainlyformed owing to the erosion of crystalline complexesof North and Central Baltica (primarily of Fennos�candia and the areas of its coupling to Volgo�Sarma�tia), and almost no products of the erosion of South�ern Volgo�Sarmatia were supplied onto the Timanmargin of the paleocontinent.

ACKNOWLEDGMENTS

The authors are sincerely grateful to K.E. Degt�yarev and I.N. Burtsev for their organizational andlogistic support of the performed studies.

This study was supported by the Russian Founda�tion for Basic Research (project nos. 09�05�00812 and09�05�01033), and by Program 16 of the Presidium ofthe Russian Academy of Sciences (Project 4.1. “Geo�logical History and Lithosphere of Polar Regions”directed by Academician Yu.G. Leonov).

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