Dating the Sedimentary Protolith of the Daldyn Group Quartzite, Anabar Shield, Russia: New Detrital Zircon Constraints

geosciences

Article Dating the Sedimentary Protolith of the Daldyn Group Quartzite, Anabar Shield, Russia: New Detrital Zircon Constraints

Nikolay I. Gusev 1,*, Lyudmila Yu. Sergeeva 1 and Sergey G. Skublov 2,3

1 Karpinsky Russian Geological Research Istitute of Geology (VSEGEI), 199106 St. Petersburg, Russia; [email protected] 2 Institute of Precambrian Geology and Geochronology, Russia Academy of Sciences (IPGG RAS), 199034 St. Petersburg, Russia; [email protected] 3 Saint-Petersburg Mining University (Mining University), 199106 St. Petersburg, Russia * Correspondence: [email protected]; Tel.: +7-81232-89-124

Received: 16 April 2020; Accepted: 26 May 2020; Published: 30 May 2020

Abstract: Quartzites and paragneisses of the Archean granulite series of the Anabar Shield (Siberian Craton, Russia) are described geochemically. The Sm-Nd isotope systematics of the rocks and the U-Pb age (SHRIMP II) and geochemistry of zircons from quartzites and paragneisses are studied. Newly formed zircons from quartzites display geochemical characteristics of the magmatic type and were produced by rock anatexis upon granulite-facies metamorphism. The Paleoproterozoic age of the latest detrital zircons, 2250 24 Ma, constrains the maximum age of sedimentary rock ± deposition. The anatectic rims around detrital zircons were formed ca. 2000 9 Ma ago. The time ± of deposition of the sedimentary protolith of gneisses and quartzites falls within the age interval of the above-mentioned dates and is tentatively accepted as 2.1 Ga. The presence of Paleoproterozoic metasedimentary rocks in the Daldyn Group implies the tectonic heterogeneity of the series and the existence of Paleoproterozoic rock bodies among the predominant Archean rock sequences.

Keywords: Anabar Shield; granulites; Archean; Paleoproterozoic; quartzites; zircon; geochemistry; U-Pb age; Sm-Nd systematics

1. Introduction Siberian Craton is the largest Precambrian continent in the north of Asia. The basement of the Siberian Craton represents a Paleoproterozoic collage of Precambrian highly metamorphosed terranes [1–3], which is overlain by Mesoproterozoic to Lower Cretaceous sedimentary rocks and Mesozoic ﬂood-basalts (traps). The current understanding of the age and structure of the Siberian cratonic basement has been outlined mostly through studies of exposed rocks in the Anabar and Aldan shields and the Olenek, Kan, Birusa, and Sharyzhalgai uplifts (Figure1). According to a number of studies, the Siberian craton is composed of several Archean and Early Proterozoic superterranes (Tungus, Anabar, Aldan, Stanovoy) that are believed to have assembled into a single structure and ﬁnally stabilized at 1.8–2.1 Ga. Superterranes are suggested to have an ancient granulite-gneiss or granite-greenstone basement. The assembling event is marked by a widespread collision-related granulite metamorphism and collisional and post-collisional granitic magmatism [1]. The Siberian Craton is also divided into several tectonic provinces (Figure1: Tungus, Anabar, Olenek, Aldan) consisting of heterogeneous terranes [1]. The Anabar Shield is an exposed block of the basement of the Anabar province.

Geosciences 2020, 10, 208; doi:10.3390/geosciences10060208 www.mdpi.com/journal/geosciences Geosciences 2020, 10, 208 2 of 17 Geosciences 2020, 10, x FOR PEER REVIEW 2 of 18

FigureFigure 1.1. GeologicalGeological scheme scheme of of the the Siberian Siberian craton craton (m (modifiedodified after after [1–3]. [1–3 ].Green Green lines lines delineate delineate the theboundaries boundaries of the of theSiberian Siberian craton craton and and its its majo majorr units. units. Red Red stars stars represent represent kimberlite fields:fields: 1—Kuoyka1—Kuoyka field;field; 2—Muna 2—Muna field; field; 3—Daldyn 3—Daldyn field; field; 4—Alakit 4—Alakit field; field; 5—Nakyn 5—Nakyn field; field; 6—Kharamai 6—Kharamai field. Paleoproterozoicfield. Paleoproterozoic intracratonic intracratonic rift zones: ub-Ulakano-Billikean, rift zones: ui-Urik-Iya.ub-Ulakano-Billikean, Archean-Paleoproterozoic ui-Urik-Iya. basementArchean-Paleoproterozoic uplifts: B—Birusa basement block; Bk—Baikal uplifts: B—Birusa uplift; K—Kann block; Bk—Baikal uplift; S—uplift; uplift; Y—Yenisey K—Kann uplift.uplift; RipheanS—uplift; sedimentary Y—Yenisey succession uplift. areas:Riphean bp—Baikal-Patom; sedimentary um—Uchur-Maya.succession areas: bp—Baikal-Patom; um—Uchur-Maya. The Anabar shield (Figure2) is composed mainly of rocks metamorphosed in the granulite facies,According which areto a combinednumber of studies, into the the Archean Siberian Daldyncraton is andcomposed Upper of Anabarseveral Archean groups and and Early the PaleoproterozoicProterozoic superterranes Khapchan (Tungus, Group Anabar, [1,4]. The Aldan, Daldyn Stanovoy) and Upper that are Anabar believed groups to have consist assembled mostly ofinto hypersthene a single structure plagiogneisses and finally and subordinatestabilized at amounts 1.8–2.1 Ga. of orthopyroxene-clinopyroxene-plagioclase Superterranes are suggested to have an schistsancient (metabasites), granulite-gneiss with or quartzite granite-greenstone beds and, locally, basement. beds ofThe aluminous assembling schists event and is silicate marked marble. by a Thewidespread Khapchan collision-related Group is made granulite up of metasedimentary metamorphism garnet and collisional gneisses, bedsand ofpost-collisional metacarbonate granitic rocks, andmagmatism rare horizons [1]. ofThe hypersthene Siberian Craton plagiogneisses. is also Thedivided Early into Proterozoic several sheartectonic zones provinces comprise (Figure reworked 1: ArcheanTungus, granulitesAnabar, Olenek, (including Aldan) anorthosites, consisting tectonites, of heterogeneous and granite-migmatites) terranes [1]. The metamorphosed Anabar Shield to is the an amphiboliteexposed block facies of the [5]. basement Numerous of the U-Pb Anabar zircon province. dates and data on the Sm-Nd isotopic systems [1,4–8] showThe that Anabar the dominant shield rocks (Figure of the 2) Daldynis composed and Upper mainly Anabar of rocks groups metamorphosed are granulites, whosein the protolithsgranulite havefacies, an which age of are 3.0–2.8 combined Ga. Metamorphosed into the Archean anatectic Daldyn granitoids and Upper with anAnabar age of groups 3.34 Ga and are lessthe commonPaleoproterozoic [7,8]. Sometimes Khapchan mafic Group xenoliths [1,4]. containingThe Daldyn Eoarchean and Upper zircon Anabar are foundgroups in consist them [ 8mostly]. of hypersthene plagiogneisses and subordinate amounts of orthopyroxene-clinopyroxene-plagioclase schists (metabasites), with quartzite beds and, locally, beds of aluminous schists and silicate marble. The Khapchan Group is made up of metasedimentary garnet gneisses, beds of metacarbonate rocks, and rare horizons of hypersthene plagiogneisses. The Early Proterozoic shear zones comprise

Geosciences 2020, 10, x FOR PEER REVIEW 3 of 18 reworked Archean granulites (including anorthosites, tectonites, and granite-migmatites) metamorphosed to the amphibolite facies [5]. Numerous U-Pb zircon dates and data on the Sm-Nd isotopic systems [1,4–8] show that the dominant rocks of the Daldyn and Upper Anabar groups are granulites, whose protoliths have an age of 3.0–2.8 Ga. Metamorphosed anatectic granitoids with an age of 3.34 Ga are less common [7,8]. Sometimes mafic xenoliths containing Eoarchean zircon are found in them [8]. The oldest Daldyn Group comprises the Bekelekh and Kilegir sequences, which contain various quantities of crystalline schist and gneisses. The Bekelekh sequence is dominated by meso and melanocratic two-pyroxene and hypersthene plagiogneisses. The Kilegir sequence displays a more diverse petrographic composition; it contains such characteristic rocks as quartzite (up to 5%), which forms lenses and beds stretching for several kilometers. The quartzites exhibit signs of sedimentary origin and are used as indicators for distinguishing between the Kilegir and Bekelekh sequences. The detrital zircons are studied in the quartzites, and their U-Pb age is estimated to constrain the maximum sedimentation age of original parental rocks and obtain evidence for the source area toGeosciences describe2020 ,the10, 208tectonomagmatic evolution and conduct paleogeographic reconstructions 3and of 17 correlations [9–13].

Figure 2. SchematicSchematic geological geological map map of the Anabar Shield.Shield. (1–3) (1–3) Archean Archean and and Early Proterozoic metamorphic rocks: (1) (1) Daldyn Daldyn Group; Group; (2) (2) Upper Upper Anabar Anabar Group; Group; (3) (3) Khapchan Group; (4) Early Proterozoic shearshear zones.zones. (5)(5) Intrusive Intrusive rocks: rocks: (A) (A anorthosite) anorthosite and and (G) (G) gabbroids. gabbroids. (6) autochthonous(6) autochthonous and andparautochthonous parautochthonous granitoids. granitoids. (7) Major (7) Major faults: faults: (a) steep (a) steep faults faults and (b) and overthrusts. (b) overthrusts. (8) platform (8) platform cover; cover;(9) area (9) of area Figure of 2Figure. 2.

DetritalThe oldest zircons Daldyn in Groupthree quartzite comprises samples the Bekelekh from the and Anabar Kilegir Shield sequences, showing which the contain oldest various (Paleo andquantities Eoarchean of crystalline Nd-model schist age of and the gneisses.protolith [7,14]) The Bekelekh were dated sequence to estimate is dominated the time of by formation meso and of themelanocratic Siberian Craton’s two-pyroxene continental and hypersthene crust. The plagiogneisses.oldest detrital zircons The Kilegir from sequence quartzites displays in the aupper more reachesdiverse petrographicof the Nalim-Rassokha composition; River it contains yield an such age characteristic of 3570 Ma, rocks but asthe quartzite sedimentary (up to protolith 5%), which of Daldynforms lenses quartzites and beds is not stretching older than for several3254 ± kilometers.38 Ma [8]. TheTwo quartzites Daldyn exhibitquartzite signs samples of sedimentary from the Khatarykorigin and River are used mouth as indicators(Figure 3, forsamples distinguishing 820 and 832- between1) are thedominated Kilegir and by detrital Bekelekh zircons sequences. dated at 3487 The± 21 detritalMa [15], zircons but the aredepositional studied in age the of quartzites, the sedimentary and their protolith U-Pb ageof quartzites is estimated is unknown. to constrain the maximum sedimentation age of original parental rocks and obtain evidence for the source area to describe the tectonomagmatic evolution and conduct paleogeographic reconstructions and correlations [9–13]. Detrital zircons in three quartzite samples from the Anabar Shield showing the oldest (Paleo and Eoarchean Nd-model age of the protolith [7,14]) were dated to estimate the time of formation of the Siberian Craton’s continental crust. The oldest detrital zircons from quartzites in the upper reaches of the Nalim-Rassokha River yield an age of 3570 Ma, but the sedimentary protolith of Daldyn quartzites is not older than 3254 38 Ma [8]. Two Daldyn quartzite samples from the Khataryk River mouth ± (Figure3, samples 820 and 832-1) are dominated by detrital zircons dated at 3487 21 Ma [15], but the ± depositional age of the sedimentary protolith of quartzites is unknown. The analysis of zircons from quartzites metamorphosed under granulite facies conditions is complicated by the polygenetic structure of grains, the latter consisting of detrital zircon cores reworked to a diﬀerent extent via granulite facies metamorphism and metamorphic shells. Some of the zircon grains analyzed possess several metamorphic shells, which indicate multiple metamorphisms. Typically, the metamorphic shells of the Anabar Shield granulites result from the latest Paleoproterozoic metamorphism [4,5]. The aim of the present study is to date the sedimentary protolith of quartzites in Daldyn granulites at the Khataryk River mouth and in the transition zone between the Bekelekh and Kilegir sequences. Geosciences 2020, 10, 208 4 of 17 Geosciences 2020, 10, x FOR PEER REVIEW 4 of 18

Figure 3. GeologicalFigure 3. Geological map of map the of estuary the estuary part part of of the the KhatarykKhataryk River. River. (1) Quaternary(1) Quaternary rocks; rocks; (2) kimberlites;(2) (3) kimberlites; charnockites, (3) charnockites, enderbites, enderbites, and and alas alaskankan granites;granites; (4) metamorphosed(4) metamorphosed peridotites peridotites and and pyroxenites. (5,6) Daldyn Group: (5) Kilegir sequence, including two-pyroxene schists, plagiogneisses, pyroxenites.and (5,6) quartzites; Daldyn (6) Bekelekh Group: sequence, (5) includingKilegir hypersthene, sequence, two-pyroxene including plagiogneisses, two-pyroxene and schists, plagiogneisses,schists. and (7) Paleoproterozoicquartzites; (6) metasedimentary Bekelekh se rocks;quence, (8) migmatization; including (9)hypersthene, clinopyroxene andtwo-pyroxene plagiogneisses,scapolite-clinopyroxene and schists. (7) plagiogneisses; Paleoproterozoic (10) garnet metasedimentary and pyroxene plagiogneisses; rocks; (11)(8) quartzites;migmatization; (9) (12) orthopyroxene, two-pyroxene, and hornblende-pyroxene plagiogneisses; (13) strike and dip of clinopyroxenegneissosity and scapolite-clinopyr and foliation. (14) Localitiesoxene and plagiogneisses; numbers of samples: (10) (a) quartzitesgarnet and previously pyroxene studied plagiogneisses; [9]; (11) quartzites;(b) presented (12) orthopyroxene, in this paper. two-pyroxene, and hornblende-pyroxene plagiogneisses; (13)

strike and2. Materials dip of andgneissosity Methods and foliation. (14) Localities and numbers of samples: (a) quartzites previously studied [9]; (b) presented in this paper. The concentrations of the major and trace elements in rocks were determined by XRF («Thermo Fisher Scientiﬁc (Ecublens) SARL», Ecublens, Switzerland) and ICP-MS (PerkinElmer Life and The analysisAnalytical of Sciences, zircons Inc., from Waltham, quartzites MA, USA) atmetamorphosed a laboratory of the Karpinsky under Institute.granulite The facies analytical conditions is complicateduncertainties by the polygenetic of the XRF analysis structure were no greaterof grains than, 5the relative latter %. The consisting detection limits of detrital of the trace zircon cores reworked toelements a different were 0.005 extent to 0.1 via ppm, granulite and the analyses facies were metamorphism accurate to 2–7 relative and metamorphic % on average. shells. Some of The U-Pb dating of zircons was conducted on a SHRIMP-II probe at the Center of Isotopic Research the zirconof thegrains Karpinsky analyzed Institute followingpossess conventional several methodsmetamorphic [16]. Areas (spots)shells, for datingwhich were indicate selected multiple metamorphisms.using optical Typically, (in transmitted the metamorphic and reﬂected light) shells and cathodoluminescenceof the Anabar Shield (CL) images granulites that showed result from the latest Paleoproterozoicthe inner structure metamorphism and zoning of the zircons.[4,5]. The The intensityaim of ofthe the present primary molecular study is oxygen to date beam the was sedimentary 4 nA, the diameter of the spot (crater) was 25 µm, and its depth was 2 µm. The raw data were processed protolith ofwith quartzites the SQUID in software Daldyn (Berkeley granulites Geochronology at the Khataryk Center, Berkeley, River CA, mouth USA) [ 17and]. The in206 thePb/ 238transitionU zone between the Bekelekh and Kilegir sequences.

2. Materials and Methods The concentrations of the major and trace elements in rocks were determined by XRF («Thermo Fisher Scientific (Ecublens) SARL», Ecublens, Switzerland) and ICP-MS (PerkinElmer Life and Analytical Sciences, Inc., Waltham, MA, USA) at a laboratory of the Karpinsky Institute. The analytical uncertainties of the XRF analysis were no greater than 5 relative %. The detection limits of the trace elements were 0.005 to 0.1 ppm, and the analyses were accurate to 2–7 relative % on average. The U-Pb dating of zircons was conducted on a SHRIMP-II probe at the Center of Isotopic Research of the Karpinsky Institute following conventional methods [16]. Areas (spots) for dating were selected using optical (in transmitted and reflected light) and cathodoluminescence (CL) images that showed the inner structure and zoning of the zircons. The intensity of the primary molecular oxygen beam was 4 nA, the diameter of the spot (crater) was 25 µm, and its depth was 2

Geosciences 2020, 10, 208 5 of 17 ratios were normalized to 0.0668, a value for the TEMORA zircon standard dated at 416.75 Ma [18]. The uncertainties of individual analyses (ratios and ages) are reported at a 1σ level, the uncertainties of the calculated values of concordant ages and intercepts with a concordia are presented at a 2 σ. level. The plots were constructed using the ISOPLOT/ET program (Berkeley Geochronology Center, Berkeley, CA, USA) [19]. The zircons were analyzed for trace elements by secondary ion mass spectrometry (SIMS) on a Cameca IMS-4f probe at the Yaroslavl Branch of the Physical—Technical Institute, Russian Academy of Sciences; the procedure is described in [20]. The analysis was conducted accurate to better than 10% for elements whose concentrations were higher than 0.1 ppm and 30–50% at concentrations lower than 0.1 ppm. The zircon crystallization temperature was determined by the Ti-in-Zrn thermometer [21]. The Sm–Nd isotope composition was studied using conventional procedures for the separation of elements. The isotope measurements were conducted on a TRITON TI mass spectrometer (ThermoQuest Finnigan MAT, Bremen, Germany) at the Center of Isotopic Research at the Karpinsky Institute. Calculation according to the formula ε (T) = [(143Nd/144Nd /143Nd/144Nd ) 1] 104 is Nd SAMPLE,t CHUR,t − × performed using the following values of isotope ratios for the chondritic uniform reservoir (CHUR): 147 144 143 144 Sm/ Nd = 0.1967 and Nd/ Nd = 0.512638 [22]. The single-stage model age TNd(DM) is deﬁned as follows:   143Nd/144Nd 143Nd/144Nd  sample,today DM,today  1  −  TNd(DM) = ln + 1 λ  (147Sm/144Nd) (147Sm/144Nd)  sample,today − DM,today

147 144 The TNd(DM) was calculated relative to the depleted mantle, with Sm/ Nd = 0.2136 and 143Nd/144Nd = 0.51315 [23]. The studied rocks have a sedimentary protolith; therefore, to determine the age of the rocks in the denudation area, a two-stage model age TNd(DM-2st) was calculated. The two-stage model age (TNd(DM-2st)) can be obtained from the single stage (TNd(DM)) model age by the equation [23]: " # fCC fsample TNd(DM 2st) = TNd(DM) – (TNd(DM) TSTRAT) − − f fDM CC − where T is the sample evolution from the time of deposition; f = 0.4, f = 0.08592 is the STRAT CC − DM f Sm/Nd value of the DM reservoir. Mineral symbols are according to [24].

3. Sample Descriptions

Rocks in the transition zone between the oldest Bekelekh sequence (AR2bk) and the younger Kilegir sequence (AR2kl) were studied. In the coarse-grained Grt-Cpx gneiss exposure (Figures3 and4, outcrop 823), milky-white quartzites, occurring as 5–10 cm thick intercalations, alternate with clinopyroxene gneisses enriched in coarse garnet aggregates (Figure4). On the hanging wall, they are in contact with schist (Figure4, sample 823-2) which passes upwards into migmatized orthopyroxene gneisses. Geosciences 2020, 10, 208 6 of 17

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Figure 4. Outcrop 823. 1—coarse-grained Grt-Cpx gneisse gneissess (sample 823); 2—the contact of Grt-Cpx gneisses with quartzites; 3—Cpx-Opx schists (sample 823-2). Coordinates: 69°43'20''N, 110°29'33''E. gneisses with quartzites; 3—Cpx-Opx schists (sample 823-2). Coordinates: 69◦43020”N, 110◦29033”E.

4. Petrography Petrography Coarse-grained Grt-Cpx gneisses (sample (sample 823) 823) contain Qtz Qtz (50–53% (50–53%,, The content is given in volume%), PlPl (An36)(An36) (20%),(20%), CpxCpx (18%), (18%), Grt Grt (5–7%), (5–7%), Bt Bt (2%), (2%), and and Mag Mag (2%). (2%). The The rock rock is is thick-banded thick-banded in inthe the thin thin section. section. Its melanocratic Its melanocratic portion portion contains contains clinopyroxene-plagioclase clinopyroxene-plagioclase aggregates, aggregates, with relatively with relativelyequal Cpx equal and Pl Cpx concentrations. and Pl concentrations. Garnet aggregates Garnet withaggregates abundant with Qtz, abundant Pl, and CpxQtz, inclusions Pl, and Cpx are inclusionsconﬁned to are siliciﬁcation confined to bands silicification composed bands of coarse composed isometric of coarse quartz isometric grains. Thequartz late grains. crystallization The late crystallizationstage is characterized stage is bycharacterized coarse grained by coarse biotite grained and garnet. biotite The and quartzite garnet. ofThe sample quartzite 823-1 of consistssample 823-1of Qtz consists (68–70%), of Qtz Cpx (68–70%), (15%), Grt Cpx (7–10%), (15%), BtGrt (3%), (7–10%), and MagBt (3%), (2%). and The Mag other (2%). quartzite The other (sample quartzite 523) (sampleconsists 523) of Qtz consists (80%), of Mi Qtz (10%), (80%), Pl Mi (An7) (10%), (8%), Pl and(An7) Bt (8%), (1%). and The Bt quartzite (1%). The of quartzite sample 820 of sample consists 820 of consistsQtz (90%), of Qtz Sill (4%),(90%), Mi Sill (4%), (4%), Bt Mi (1%), (4%), and Bt Ilm(1%), (1%). and TheIlm quartzite(1%). The ofquartzite sample of 831-1 sample consists 831-1 of consists quartz (98%),of quartz Sill (98%), (1%), Sill and (1%), Bt (1%). and Bt The (1%). two-pyroxene The two-pyroxene schists (sampleschists (sample 823-2) consist823-2) consist of Pl (An70) of Pl (An70) (40%), (40%),Cpx (7%), Cpx Opx (7%), (35%), Opx and (35%), Mag (6%).and Mag Single (6%). large Single apatite large grains apatite are found grains sporadically; are found superimposedsporadically; superimposed minerals are presented by Qtz (10%) and Bt (2%). The boundary with quartzite in thin section is sharp, but coarse elongated quartz grains contain crystalline schist inclusions and garnet grains elongated concordantly with quartz grains.

Geosciences 2020, 10, 208 7 of 17 minerals are presented by Qtz (10%) and Bt (2%). The boundary with quartzite in thin section is sharp, but coarse elongated quartz grains contain crystalline schist inclusions and garnet grains elongated concordantlyGeosciences 2020,with 10, x FOR quartz PEER grains. REVIEW 7 of 18

5.5. GeochemicalGeochemical DataData Coarse-grainedCoarse-grained Grt-Cpx Grt-Cpx gneisses gneisses (sample (sample 823) 823) were identiﬁedwere identified as para-rocks as para-rocks based on based the following on the ratios: MgO/CaO = 2; P O /TiO = 0.03 [25]. Elevated Cr (114 ppm), Y (157 ppm), Zr (541 ppm), following ratios: MgO/CaO2 5 = 2; 2P2O5/TiO2 = 0.03 [25]. Elevated Cr (114 ppm), Y (157 ppm), Zr (541 andppm), Nb and (7.92 Nb ppm)(7.92 ppm) concentrations concentrations may may be ascribed be ascribed to theto the enrichment enrichment of of chromite, chromite, zircon, zircon,and and monazitemonazite detritusdetritus inin sedimentarysedimentary rocksrocks (Table(Table S1).S1). TheThe spiderspider diagramdiagram ofof samplesample 823823 shownshown onon FigureFigure5 5indicates indicates a a positive positive U U anomaly anomaly and and a a negative negative P P anomaly. anomaly. The The rare rare earth earth elements elements (REE) (REE) distributiondistribution ((ΣΣREEREE= = 141141 ppm)ppm) displaysdisplays thethe predominancepredominance ofof heavyheavy rarerare earthearth elementselements (HREE)(HREE) overover lightlight rarerare earthearth elementselements (LREE), which which is is possibly possibly associated associated with with garnet garnet detritus detritus and and the the growth growth of ofmetasomatic metasomatic garnet; garnet; the the Eu-minimum Eu-minimum (Eu/Eu* (Eu/Eu* == 0.560.56)) is is well-defined. well-deﬁned. The garnet quartzitequartzite fromfrom samplesample 823-1 823-1 contains contains less less REE REE (Σ (REEΣREE= 30.16= 30.16 ppm) ppm) and and displays displays a distribution a distribution pattern pattern similar similar to that to ofthat coarse-grained of coarse-grained gneiss. gneiss. The spiderThe spider diagram diagram in Figure in Figure5a shows 5a shows positive positive Ba and Ba Zr and anomalies Zr anomalies and negativeand negative Sr and Sr Tiand anomalies. Ti anomalies.

FigureFigure 5.5. (a(,ac),) Primitive(c) Primitive mantle-normalized mantle-normalized abundances abunda ofnces trace of elements;trace elements; [26](b ,d[26]) chondrite- (b), (d) normalizedchondrite-normalized [26] REE patterns [26] REE for patterns zircons. for zircons.

TheThe quartzites quartzites (samples (samples 523, 523, 820, 820, 831-1) 831-1) generally generally display display low values low (Al values2O3/SiO (Al2) (0.01–0.05)2O3/SiO2) (0.01–0.05)and are consistent and are consistentwith the values with the(Na values2O/Al2O (Na3) (0.01–0.20)2O/Al2O3) in (0.01–0.20) terrigenous in terrigenousrocks [27]. The rocks values [27]. The(Fe2 valuesO3+FeO+MnO/Al (Fe2O3+FeO2O+3+TiOMnO2/)Al (0.05–0.14)2O3+TiO2) (0.05–0.14)indicate the indicate alumin theous aluminous composition composition of pelites. of pelites. The Thechemical chemical alteration alteration index index value, value, (Al(Al22O3/(Al/(Al22OO33+CaO+Na+CaO+Na2O+K2O+2O),K2O), varies varies considerably considerably (43–90),(43–90), indirectlyindirectly indicating indicating a a di differenceﬀerence in in source source areas. areas. TheThe totaltotal REEREE concentrationconcentration inin thethe quartzitequartzite isis inin thethe rangerange ofof 24–3624–36 ppmppm (except(except forfor samplesample 831-1—9831-1—9 ppm). ppm). The The REE REE distribution distribution displays displays a diﬀerentiated a differentiated pattern (LapatternN/YbN (La= 9–39).N/YbN The= 9–39). quartzites The fromquartzites samples from 820 samples and 523 820 show and Eu 523/Eu* show= 0.93–1.29, Eu/Eu* = while0.93–1.29, sample while 831-1 sample exhibits 831-1 the exhibits most negativethe most negative Eu anomaly (Eu/Eu* = 0.42). The rocks contain low Th (0.76–3.03 ppm) and U (0.10–0.46 ppm) concentrations; the Th/U ratio is 4.52–9.77. Orthopyroxene-clinopyroxene schists (sample 831-2) contain elevated Cr (177 ppm) and Ni (126 ppm) concentrations (Table S1); the spider diagram in Figure 5 shows positive U and Pb anomalies. The REE concentration is low (ΣREE = 49.94 ppm) and the distribution shows a flat pattern (La/Yb)N = 1.98 with a slight minimum Eu anomaly (Eu/Eu* = 0.82).

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Eu anomaly (Eu/Eu* = 0.42). The rocks contain low Th (0.76–3.03 ppm) and U (0.10–0.46 ppm) concentrations; the Th/U ratio is 4.52–9.77. Orthopyroxene-clinopyroxene schists (sample 831-2) contain elevated Cr (177 ppm) and Ni (126 ppm) concentrations (Table S1); the spider diagram in Figure5 shows positive U and Pb anomalies. The REE concentration is low (ΣREE = 49.94 ppm) and the distribution shows a ﬂat pattern (La/Yb)N = 1.98 with a slight minimum Eu anomaly (Eu/Eu* = 0.82).

6. U-Pb Data Age dating was performed for zircons from coarse-grained Grt-Cpx gneisses (sample 823), garnet quartzite (sample 823-1), and quartzite (sample 523) (Table S2). In outcrop 823, a similar zircon monofraction from coarse-grained Grt-Cpx gneisses and garnet quartzite consists of yellow transparent and semi-transparent prismatic and rounded idiomorphic and sub-idiomorphic crystals and fragments. The crystals are 200–400 µm long, with a coefficient of elongation (Ky) of 1–2. The zircon grains are polygenetic in CL image; three zircon generations were identified (Figure6). The cores dominantly display poor luminescence, sometimes (grain, point with analysis 8.1) with fine rhythmic zoning. Some of the cores are surrounded by thin brightly luminescent rims (analytical points 9.2 and 7.2) varying in width, partly dissolved upon being overgrown by rims, which shows grey luminescence. The grey rims are much thicker; such grey luminescent zircons make up individual coarse grains with coarse concentric zoning and the sectorial structure of the central portions of crystals. Grey zircons from gneisses display a concentric structure and finer rhythmic zoning around the black cores. The internal rhythmic zones and lighter external rims of the gneisses were dated separately. The neoformation of zircon in the quartzites is well-defined, but detrital zircons in the cores are much worse preserved. The radial fracturing in the back-scattered electron (BSE) image is conspicuous. Fractures begin to form at the boundary of cores that are dark in CL and spread into zircon grain, which is grey in CL, towards the grain margins. The fracturing was caused by a differentiated and more intense zircon metamictization and by the increasing volume in the U- and Th-enriched cores, and was followed by the alteration of low U- and Th rims [28]. The cores and rims of 14 zircon grains from Grt-Cpx gneisses were analyzed. The cores are mainly black in CL, but they sometimes contain zircon fragments with well-defined rhythmic zoning (grains with analyses 1.1, 4.1, 5.1, 6.1, 7.1), in which Th/U = 0.13–0.91. The maximum 207Pb/206Pb age value in the core from the analysis 6.1 is 2723 9 Ma, but it is highly ± discordant (D = 8%). The age of 2364–2250 Ma was obtained for three cores; it should be noted that analysis 4.1 yielded an age of 2316 19 Ma with a low discordance (D = 1%). The black homogeneous ± cores dated (2107–2048 Ma) display low Th/U ratios of 0.04–0.10, typical of metamorphic zircons. The zircon cores in garnet quartzite from sample 823-1 show the age range 207Pb/206Pb of 2758–2566 Ma; the smaller value of 2214 11 Ma, at a point with analysis 3.1, is due to the trapping ± of the surrounding grey zircon by the analytical crater (Figure7). The oldest value of 2758 11 Ma ± (D = 3%) was obtained for a zircon core with analysis 8.1 with a well-defined rhythmic zoning. In the − REE distribution diagram (Figure7), it is characterized by the composition of magmatic zircons and Zir by the lowest Ti-in-Zrn temperature (TTi ) of 760 ◦C. Other zircon cores are enriched in LREE and are shifted towards hydrothermal zircons with respect to the trace element composition (Figure8a). The cores display a Th/U ratio of 0.38 and mean U concentrations of (102 ppm); Th (256 ppm); Y (1404 ppm); Hf (7446 ppm); ΣREE 976 (ppm) (Table S3). The temperature reaches a maximum value of 858 ◦C for the most enriched REE zircon with 5.1 analysis. Geosciences 2020, 10, 208 9 of 17

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FigureFigure 6. Cathodoluminescence 6. Cathodoluminescence (CL) (CL) images imag andes and ages ages of zirconsof zircons from from the garnet–clinopyroxenethe garnet–clinopyroxene gneiss (samplegneiss 823). (sample White 823). circles White mark circles analytical mark analytical craters, cr andaters, the and nearby the nearby numerals numerals are theare the numbers numbers of the 207 206 Geosciencesanalyticalof the 2020 spotsanalytical, 10, x (numerators) FOR spots PEER (numerators) REVIEW and 207Pb and/206 PbPb/ age (denominators).Pb age (denominators). The craters The craters are 20 areµm 20 in µm diameter. in10 of 18 diameter.

The zircon cores in garnet quartzite from sample 823-1 show the age range 207Pb/206Pb of 2758–2566 Ma; the smaller value of 2214 ± 11 Ma, at a point with analysis 3.1, is due to the trapping of the surrounding grey zircon by the analytical crater (Figure 7). The oldest value of 2758 ± 11 Ma (D = −3%) was obtained for a zircon core with analysis 8.1 with a well-defined rhythmic zoning. In the REE distribution diagram (Figure 7), it is characterized by the composition of magmatic zircons and Zir by the lowest Ti-in-Zrn temperature ( TTi ) of 760 °C. Other zircon cores are enriched in LREE and are shifted towards hydrothermal zircons with respect to the trace element composition (Figure 8a). The cores display a Th/U ratio of 0.38 and mean U concentrations of (102 ppm); Th (256 ppm); Y (1404 ppm); Hf (7446 ppm); ΣREE 976 (ppm) (Table S3). The temperature reaches a maximum value of 858 °C for the most enriched REE zircon with 5.1 analysis. The grey rims and the individual grains of CL-grey zircon show a REE distribution pattern and indicator ratios (Sm/La)N and Ce/Ce* which are consistent with those of magmatic zircons (Figure 8b). In contrast to the cores, the grey zircon of the rims contains low concentrations (mean values in ppm)—U 89, Th 86, Y 616, ΣREE 296—but displays a higher Th/U ratio of 1.0 and Hf concentration of 9278–10,182 ppm. Grey zircons, in contrast to typical magmatic zircons, are poor in HREE (flattening of the spectra from Er to Lu) and display a low (Lu/Gd)N ratio of 2.6–9.2, which indicates zircon growth in the presence of garnet (Gd-concentrating mineral), i.e., under granulite-facies conditions of metamorphism. A quite sustained value = 781–793 °C is noted. The age of 2000 ± 9 Ma with a high concordance (probability of concordance = 0.75) was obtained from eight analyses. It is understood as the crystallization time of grey zircon grains and rims.

FigureFigure 7. CL7. CL images images and and age age ofof zirconszircons from th thee garnet garnet quartzite, quartzite, sample sample 823-1. 823-1.

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Figure 8. (a), (b)—Chondrite-normalized REE patterns of zircon from the garnet quartzite, sample Figure 8. (a,b)—Chondrite-normalized REE patterns of zircon from the garnet quartzite, sample 823-1. 823-1. Pattern numbers correspond to the numbers of analytical spots in Figure 6. The grey field Pattern numbers correspond to the numbers of analytical spots in Figure6. The grey field corresponds corresponds to the composition of magmatic zircon according to [29]. (c), (d)—Diagrams for to the composition of magmatic zircon according to [29]. (c,d)—Diagrams for distinguishing magmatic distinguishing magmatic zircon from the hydrothermal one according to [29]. zircon from the hydrothermal one according to [29]. The zircons from quartzite in sample 523 are brown-colored, and their sub-idiomorphic oval The grey rims and the individual grains of CL-grey zircon show a REE distribution pattern grains are transparent to semi-transparent and fractured (Figure 9). The grains are 100–200 µm long and indicator ratios (Sm/La)N and Ce/Ce* which are consistent with those of magmatic zircons with a Ky of 1–2.5. The zircons dominantly display a poor luminescence in CL, a black color prevails, (Figure8b). In contrast to the cores, the grey zircon of the rims contains low concentrations (mean there is no luminescence, and the metamorphic rims are either thin or poorly-defined. Zoning in values in ppm)—U 89, Th 86, Y 616, ΣREE 296—but displays a higher Th/U ratio of 1.0 and Hf crystals is mainly observed as a combination of fine and coarse banding with signs of sectorial concentrationzoning (point of 12.1). 9278–10,182 Zoning ppm.is mainly Grey truncated zircons, inby contrast the grain to margins; typical magmatic zoning subparallel zircons, are to poorgrain in HREEmargins (flattening is less common of the spectra (6.1, 12.1, from 13.1–2326 Er to Lu) Ma, and 19.1). display a low (Lu/Gd)N ratio of 2.6–9.2, which indicates zircon growth in the presence of garnet (Gd-concentrating mineral), i.e., under granulite-facies conditions of metamorphism. A quite sustained value = 781–793 C is noted. The age of 2000 9 Ma ◦ ± with a high concordance (probability of concordance = 0.75) was obtained from eight analyses. It is understood as the crystallization time of grey zircon grains and rims. The zircons from quartzite in sample 523 are brown-colored, and their sub-idiomorphic oval grains are transparent to semi-transparent and fractured (Figure9). The grains are 100–200 µm long with a Ky of 1–2.5. The zircons dominantly display a poor luminescence in CL, a black color prevails, there is no luminescence, and the metamorphic rims are either thin or poorly-defined. Zoning in crystals is mainly observed as a combination of fine and coarse banding with signs of sectorial zoning (point 12.1). Zoning is mainly truncated by the grain margins; zoning subparallel to grain margins is less common (6.1, 12.1, 13.1–2326 Ma, 19.1).

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FigureFigure 9. CLCL images images and and age age of of zircons zircons fr fromom the quartzite, sample 523.

Twenty-three cores of zircon grains from the quartzite quartzite of of sample sample 523 523 were were dated dated (Figure (Figure 99).). Four discordant PaleoarcheanPaleoarchean analysesanalyses (points (points with with analyses analyses 2.1, 2.1, 5.1, 5.1, 7.1, 7.1, and and 20.1) 20.1) dated dated at 3347at 3347 7± to7 ± to3166 3166 8± Ma 8 Ma (D =(D3–7%) = 3–7%) in the in upperthe upper part part of Figure of Figure9 are the9 are oldest. the oldest. Two of Two the oldest of the grains oldest display grains ± displaywell-preserved well-preserved rhythmic rhythmic zoning (grains zoning with (grains points with 2.1 points and 7.1), 2.1 showand 7.1), REE show spectra REE (Figure spectra 10 (Figurea) most 10a)similar most to similar magmatic to magmatic type pattern type [ 29pattern](ΣREE [29]= (441–666ΣREE = 441–666 ppm), and ppm), are and characterized are characterized by the lowestby the value of TZir = 768–784Zir C in comparison with other analyses. The two other oldest grains (5.1, 20.1) lowest valueTi of TTi = ◦768–784 °C in comparison with other analyses. The two other oldest grains are black in CL and are more enriched in Y 2277–3214 and REE (ΣREE = 1588–2136 ppm) due to an (5.1, 20.1) are black in CL and are more enriched in Y 2277–3214 and REE (ΣREE = 1588–2136 ppm) increase in HREE (ΣHREE = 1555–2096 ppm) and other factors (P, Th, Table S4). due to an increase in HREE (ΣHREE = 1555–2096 ppm) and other factors (P, Th, Table S4). Rhythmic zoning in a population of six grains dated at 2981–2858 Ma with analytical points 17.1 and 21.1 is similar to the magmatic pattern. Other grains display a spotted luminescence in CL, but they also lie in the magmatic zircons ﬁeld in the REE distribution diagram (Figure 10b). The discordia line, based on four analyses from this population, shows an upper intersection at 2870 21 Ma ± (MSWD = 1.14). In a group of zircons dated 2769–2609 Ma (Figure9), seven analyses yielded a mean age of 2695 25 Ma (MSWD = 3.4). Rhythmic zoning in grains with analyses 8.1, 9.1, 15.1, and 16.1 was ± observed. Grains that are black in CL contain elevated LREE concentrations and display a decline in Eu-minimum (points 6.1, 18.1 23.1), suggesting zircon growth under ﬂuid saturation conditions, Zir and the maximum value of TTi = 817–858 ◦C is noted. As the age decreases from 2680 Ma, the Y (1231–1407 ppm) and HREE (826–1016 ppm) concentration increases respectively (Table S4). Magmatic zircons in the REE distribution diagram predominate (Figure 10c).

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Figure 10. ((aa––dd)—Chondrite-normalized)—Chondrite-normalized REE REE patterns patterns of of zi zirconsrcons from from the the quartzite, quartzite, sample sample 523. 523. Pattern numbersnumbers correspond correspond to theto numbersthe numbers of analytical of analytical spots inspots Figure in9. TheFigure grey 9. ﬁeld The corresponds grey field correspondsto the composition to the composition of magmatic of zircons magmatic according zircons to [according29]. to [29].

RhythmicZircons with zoning a minimum in a population age of 2535–2326 of six grains Ma dated yield at a 2981–2858 poor luminescence Ma with analytical (Figure9). points Rhythmic 17.1 andzoning 21.1 is is only similar discernible to the magmatic in a grain pattern. with analysis Other 3.1grains (dated display at 2535 a spotted13 Ma). luminescence The REE distribution in CL, but ± theyspectra also (Figure lie in 10 thed) aremagmatic most similar zircons to thefield magmatic in the REE type. distribution The zircons withdiagram analysis (Figure 22.1 10b). (2451 The Ma) discordiahave elevated line, Y,based U, and on REEfour concentrationsanalyses from this and population, exhibit a decrease shows inan Eu-minimum.upper intersection at 2870 ± 21 Ma (MSWD = 1.14). 7. Sm-Nd Isotope Systematics In a group of zircons dated 2769–2609 Ma (Figure 9), seven analyses yielded a mean age of 2695 ± 25 MaThe (MSWD Sm-Nd = isotope 3.4). Rhythmic system ofzoning rocks in is grains considered with analyses in comparison 8.1, 9.1, with15.1, and other 16.1 granulites was observed. of the GrainsKilegir andthat Bekelekhare black sequences in CL contain of the Daldynelevated Group LREE (Figureconcentrations 11). The and Sm-Nd display isotope a decline system in Eu-minimumquartzites commonly (points 6.1, indicates 18.1 23.1), a low suggesting147Sm/144 ziNdrcon ratio growth of 0.0724–0.1111 under fluid sa (Tableturation S5). conditions, However, and the Zir 147 144 therocks maximum in samples value 823 andof T 823-1Ti = show817–858 high °C isSm noted./ Nd As ratio the values age decreases of 0.1815–0.2541, from 2680 exceeding Ma, the the Y 147 144 (1231–1407Sm/ Nd ppm) in chondrite. and HREE This makes(826–1016 it impossible ppm) concentration to determine increases the Nd-model respectively age of protolith (Table and,S4). Magmaticas a consequence, zircons in the the age REE of thedistributi rocks inon thediagram denudation predominate area. All (Figure the rocks 10c). display negative εNd(T) values of 4.2 to 11.3 (Table S5). Considerable diﬀerences in the Nd-model age of the rock protolith Zircons− with− a minimum age of 2535–2326 Ma yield a poor luminescence (Figure 9). Rhythmic zoningare observed is only in discernible two cases (samplesin a grain 820 with and analysis 831-1) when3.1 (dated the T Ndat (DM-2st)2535 ± 13 =Ma).3.69–3.71 The REE Ga, distribution and also for spectrathe quartzites (Figure of 10d) sample are most 523, wheresimilar the to TtheNd (DM-2st)magmatic= type.3.02 Ga.The zircons with analysis 22.1 (2451 Ma) have elevated Y, U, and REE concentrations and exhibit a decrease in Eu-minimum.

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7. Sm-Nd Isotope Systematics The Sm-Nd isotope system of rocks is considered in comparison with other granulites of the Kilegir and Bekelekh sequences of the Daldyn Group (Figure 11). The Sm-Nd isotope system in quartzites commonly indicates a low 147Sm/144Nd ratio of 0.0724–0.1111 (Table S5). However, the rocks in samples 823 and 823-1 show high 147Sm/144Nd ratio values of 0.1815–0.2541, exceeding the 147Sm/144Nd in chondrite. This makes it impossible to determine the Nd-model age of protolith and, as a consequence, the age of the rocks in the denudation area. All the rocks display negative εNd(T) values of −4.2 to −11.3 (Table S5). Considerable differences in the Nd-model age of the rock protolith Geosciencesare observed2020, 10in, two 208 cases (samples 820 and 831-1) when the TNd(DM-2st) = 3.69–3.71 Ga, and also13 of for 17 the quartzites of sample 523, where the TNd(DM-2st) = 3.02 Ga.

Figure 11. εNd versus age diagram for granulites of the Daldyn Group. Additionally, orthogneisses Figure 11. εNd versus age diagram for granulites of the Daldyn Group. Additionally, orthogneisses and sapphirine schists of the Kilegir sequence [30] and granulites of the Bekelekh sequence of the and sapphirine schists of the Kilegir sequence [30] and granulites of the Bekelekh sequence of the Daldyn Group are shown [7]. Daldyn Group are shown [7].

Sapphirine schists and orthogneisses of the Kilegir sequence [[30],30], like the quartzites we studied, were characterized by negative values of εNd(T) from −7.4 to −5.1 and a model age of protolith were characterized by negative values of εNd(T) from 7.4 to 5.1 and a model age of protolith TNd(DM-2st) = 3.43–3.25 Ga. Thus, the protolith of the granulites− − of the Kilegir sequence studied by TNd(DM-2st) = 3.43–3.25 Ga. Thus, the protolith of the granulites of the Kilegir sequence studied by us andus and [30 ][30] was was formed formed due due to theto the processing processing of theof the Archean Archean and and Eoarchean Eoarchean continental continental crust. crust. Granulites ofof the the Bekelekh Bekelekh sequence sequence are represented are represented by the prevailing by the clinopyroxene- prevailing orthopyroxeneclinopyroxene-orthopyroxene gneisses, containing gneisses, interlayers containing of in maﬁcterlayers and of ultramaﬁc mafic and schists. ultramafic The schists. age of The the magmaticage of the zirconsmagmatic varies zircons from varies 3.40 tofrom 2.86 3.40 Ga. to The2.86 granulitesGa. The granulites have a magmatic have a magmatic protolith protolith and are characterizedand are characterized by slightly by slightly negative negative and predominant and predominant positive positiveε (T) ε valuesNd(T) values from from1.5 − to1.5+ 7.5to +7.5 [7]. Nd − The[7]. protolithThe protolith of granulites of granulites of the Bekelekhof the Bekelekh sequence sequence indicates theindicates formation the offormation a juvenile of Archean a juvenile and EoarcheanArchean and crust Eoarchean with the crust participation with the ofparticipation a depleted mantleof a depleted source. mantle source.

8. Discussion Quartzite beds in the Daldyn Group occur in association with the two-pyroxene plagiogneisses, whichwhich areare consistentconsistent in in chemical chemical composition composition with with andesite andesite or or quartz quartz diorite, diorite, with with a U-Pba U-Pb zircon zircon age age of 2960 22 Ma [7]. The quartzites vary in the Nd-model age of the protolith and the age of detrital zircon. ± Quartzites in samples 820 and 831-1 with the model age of the protolith TNd(DM-2St) = 3.69–3.71 Ga are dominated by Paleoarchean detrital zircons dated at 3.5 Ga [15], indicating the age of predominant magmatic rocks in the feeding province. The zircons in these quartzites, dated at 2778 16 Ma, are ± metamorphic [15]. It is not clear whether this zircon formed prior to or after deposition in the sediment during Archean granulite-facies metamorphism. Therefore, the lower age boundary for the deposition of the sedimentary protolith of the quartzites is unknown. In the quartzite of sample 523, whose model age of the protolith TNd(DM-2St) is 3.02 Ga, the age of detrital zircon grains varies from Paleoarchean (3347 7 Ma) to Paleoproterozoic (2451–2326 Ma). ± Geosciences 2020, 10, 208 14 of 17

No zircons with an age of 3.5 Ga have been revealed. The most numerous analyses of zircon grains show age peaks of 2870 21 Ma (N = 6) and 2695 25 Ma (N = 7), and are confined within the epochs ± ± of large-scale magmatism and metamorphism. For example, 2870 Ma detrital zircons were produced by the scour of the rocks formed by granulite-facies metamorphism and enderbitization (in sense of [31]) provoked by magmatism caused by the accretion of juvenile crust on the Anabar Shield and the reworking of the earlier crust in the age range 2878 11–2858 9 Ma [6,7]. The second peak of detrital ± ± zircons dated at 2695 25 Ma is more likely to be associated with a new stage during the formation ± of juvenile crust, which is indicated by ultramafic intrusions dated at 2726 15 Ma and potassium ± granitoid magmatism (2705 12 charnockites [6], sanukitoids 2702 9 [32], and the formation of ± ± anatectic alaskitic granite-gneiss dated at 2618 10 Ma [7]. ± The 2535–2326 Ma zircons occur as scarce grains. Intrusions and metamorphic rocks of this age have not been established on the Anabar Shield. Detrital zircon cores in sample 823-1 are 2758–2566 Ma old. Only zircons dated at 2758 11 Ma ± are reliably identified as magmatic by rhythmic zoning and trace element concentrations. In the quartzite (sample 831-1), zircons dated at 2778 16 Ma are metamorphic and seem to have ± been produced by the same event as magmatic zircons dated at 2758 11 Ma. It is this event that ± was identified as 2.75 Ga granulite-facies metamorphism at early stages in the study of the Anabar Shield [4]. Zircons, which are grey in CL, overgrow black cores in CL and form independent grains. These zircons yields a concordant age of 2000 9 Ma, suggesting that the protolith of the quartzites ± cannot be younger than 2 Ga. The trace element composition of zircon of 2000 9 Ma is consistent with a magmatic type ± but displays a low Lu/GdN ratio of 2.6–9.2. These zircons were produced by partial rock melting under garnet stability conditions, i.e., granulite-facies metamorphism. Our findings confirm the results of studies presented by Peck et al. [33], which showed that the zircon growth in quartzites among granulites takes place in melt, and their U-Pb age shows the age of rock anatexis. However, the anomalous REE distribution spectra with negative LREE-anomalies on Figure4 in quartzites and garnet-clinopyroxene gneisses (sample 823) suggest a metasomatic process similar to silicification with the removal of LREE [14]. Furthermore, in contrast to Peck et al. [33], the amount of overgrowth and the quantity of newly formed zircons is greater in SiO2-enriched quartzites than in clinopyroxene gneisses, although the reverse pattern was expected [33]. It seems that rock anatexis in sample 823 at the postmagmatic stage was followed by silicification with the removal of LREE. It should be noted that, although the Archean model age of the protolith TNd(DM-2St) is 3.25–3.43 Ga, the scarce age values for the cores of detrital zircon in sapphirine-bearing schist from the Kilegir sequence of the Anabar Shield yield a Paleoproterozoic age and show an age of 2217 6 Ma ± (D = 1%) in the least discordant zircon [30]. Thus, the sedimentation time for the sedimentary protolith of the para-rocks in the Daldyn Group is between the age of the youngest detrital zircons, 2250 24 Ma (2217 6 Ma, as dated by [30]), and ± ± the time of quartzite anatexis under the granulite-facies conditions of metamorphism (2000 9 Ma). ± The time of formation for the sedimentary protolith of quartzites and paragneisses could tentatively be accepted as 2.1 Ga. It is not yet clear whether other quartzite bodies (Figure3) in which no Paleoproterozoic detrital zircons were revealed are Proterozoic; however this possibility is not ruled out [15]. The occurrence of Paleoproterozoic metasedimentary rocks in the Daldyn Group suggests that the Daldyn granulite group, as it looks like now, is tectonically heterogeneous and contains Paleoproterozoic rock bodies among predominant Archean rocks. A similar situation has been described from the well-studied Jack Hills sedimentary belt in Australia, where ~3 Ga conglomerates host the Earth’s oldest zircons. It gradually became obvious that rocks with Proterozoic zircons make up 12% of the belt, suggesting the tectonic alternation of Archean and Proterozoic rock sequences [12]. Geosciences 2020, 10, 208 15 of 17

9. Conclusions Quartzites occurring at the boundary between the Bekelekh and Kilegir sequences in the Daldyn Group differ markedly in the Nd-model age of the protolith and the U-Pb age of detrital zircons. One group of rocks with the Nd-model age of the protolith with a TNd(DM-2St) of 3.69–3.71 Ga contains predominant detrital zircons dated at 3487 21 Ma. Another group with a T (DM-2St) of ± Nd 3.02 Ga hosts Paleoproterozoic zircons. Furthermore, Paleoproterozoic detrital zircons were revealed in paragneisses and quartzites with a disturbed isotope system, whose model age is not clear. These rocks have been altered metasomatically, and the zircon neoformation in them is well-defined. Newly formed zircons display geochemistry of magmatic type in spite of zoning typical of granulite zircons. The age of the youngest detrital zircons is 2250 24 Ma and the age of the anatectic rims is ± 2000 9 Ma. The formation time for the sedimentary protolith of gneisses and quartzites lies within the ± interval between the two age values specified above and is provisionally taken as 2.1 Ga. The presence of Paleoproterozoic metasedimentary rocks in the Daldyn Group has led us to conclude that the Daldyn granulite group, as it now looks, is tectonically heterogeneous and contains Paleoproterozoic rock bodies among predominant Archean rock sequences.

Supplementary Materials: The following are available online at http://www.mdpi.com/2076-3263/10/6/208/s1: Table S1: Concentrations of major oxides (wt %) and trace elements (ppm) in granulites; Table S2: Results of U-Pb geochronological studies of zircons; Table S3: Trace element concentrations (ppm) and the calculated temperature in zircons from the quartzite (sample 823-1); Table S4: Trace element concentrations (ppm) and the calculated temperature in zircons from the quartzite (sample 523); Table S5: Sm and Nd isotope composition. Author Contributions: Conceptualization, N.I.G.; formal analysis, N.I.G., S.G.S.; writing—original draft preparation, N.I.G.; writing—review and editing, N.I.G., S.G.S. and L.Yu.S.; visualization, L.Yu.S. All authors provided input to the evaluation and discussion of the data and to the final version of this report. All authors have read and agreed to the published version of the manuscript. Funding: This study was supported by the Russian Foundation for Basic Research, project No. 18-35-0029/19 mol-a. This study was conducted under a state contracts No. 0153-2019-0002 (Institute of Precambrian Geology and Geochronology of Russian Academy of Sciences). Acknowledgments: The authors thank the reviewers of Geosciences for constructive criticism, which led us to significantly improve the manuscript. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analysis, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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