Petrology and Geochemistry of Granulite Xenoliths from Udachnaya and Komsomolskaya Kimberlite Pipes, Siberia

Petrology and Geochemistry of GranuliteXenoliths from Udachnaya and KomsomolskayaKimberlite Pipes, Siberia

M. Yu. KORESHKOVA1*, H. DOWNES2, L. K. LEVSKY3 ANDN.V.VLADYKIN4

1GEOLOGICAL FACULTY, ST PETERSBURG STATE UNIVERSITY, ST PETERSBURG 199034, RUSSIA2DEPARTMENT OF EARTH AND PLANETARY SCIENCES, BIRKBECK UNIVERSITY OF LONDON, LONDON WC1E 7HX, UK3INSTITUTE OF PRECAMBRIAN GEOLOGY AND GEOCHRONOLOGY, RUSSIAN ACADEMY OF SCIENCES,

ST PETERSBURG 199034, RUSSIA4VINOGRADOV INSTITUTE OF GEOCHEMISTRY AND ANALYTICAL CHEMISTRY, RUSSIAN ACADEMY OF SCIENCES,

IRKUTSK 664033, RUSSIA

RECEIVED MAY 29, 2010; ACCEPTEDJUNE 8, 2011ADVANCE ACCESS PUBLICATION JULY 27, 2011

Lower crustal xenoliths from the Udachnaya and Komsomolskaya

kimberlite pipes in Siberia are mainly meta-igneous mafic garnet

granulites, with subordinate feldspar-rich garnet granulites.

Pressure and temperature estimates are interpreted as the conditions

in the lower crust at the time of the last granulite-facies metamorphic

event (800^8908C) followed by cooling to 610^7208C with a pres-

sure decrease from 1·2 to 0·8 GPa. Most of the xenoliths show minor

alteration. Leaching experiments demonstrate that their isotopic,

major and trace element compositions have been affected by inter-

action not only with the host kimberlite but also with a fluid mobi-

lized from local sedimentary country rocks. To obtain unambiguous

compositional data we have calculated the composition of selected

samples using modal analyses, electron microprobe and laser ablation

inductively coupled plasma mass spectrometry data for constituent

minerals. The reconstructed protoliths of most of the xenoliths were

Fe-tholeiites of intraplate affinity, similar to some Archean basalts,

whereas the others show characteristics of subduction-related

magmas. However, the mafic granulites are strongly depleted in Rb,

Th and U, which were removed by a small-degree partial melt. A

protolith age of c. 3 Ga is supported by a disturbed Sm^Nd isochron,

Nd and Hf model ages, and published U^Pb ages of zircon cores.

KEY WORDS: lower crust; xenoliths; petrology; geochemistry; Siberian

craton

I NTRODUCTION ANDGEOLOGICAL BACKGROUNDThe composition and history of the lower crust of anArchaean craton can be deduced from a study ofgranulite-facies rocks entrained as xenoliths by kimberliticeruptions. Xenoliths represent the lower crust at the timethey were brought to the surface. However, geologicalevents could have overprinted the composition of thelower crust during the time between its formation and thekimberlite eruption. Interaction with the kimberlitic hostcan also strongly affect xenolith compositions. Here we at-tempt to infer the origin of kimberlite-hosted granulitexenoliths that represent the lower crust of the Siberiancraton, taking into account possible changes in theircomposition.Granulite xenoliths have been investigated from many

cratonic regions such as South Africa (Huang et al., 1995;Schmitz & Bowring, 2003), Fennoscandia (Kempton et al.,1995, 2001; Ho« ltta« et al., 2000; Peltonen et al., 2006), NorthAmerica (Chen & Arculus, 1995; Davis et al., 2003; Bolharet al., 2007) and others (Rudnick & Gao, 2003), but little isyet known about the lower crust beneath the Siberiancraton (Shatsky et al.,1990, 2005). However, the craton con-tains numerous kimberlite pipes (Bobrievich et al., 1964;

*Corresponding author.Telephone:7 812 3289479.E-mail: [email protected]

� The Author 2011. Published by Oxford University Press. Allrights reserved. For Permissions, please e-mail: [email protected]

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Griffin et al., 1999) that have brought upper mantle andlower crustal xenoliths to the surface (Sobolev, 1974;Spetsius & Serenko, 1990). The origin and original tectonicsetting of the protoliths of the xenoliths is unclear.Spetsius & Serenko (1990), Shatsky et al. (1990, 2005) andBuzlukova et al. (2004) investigated mafic granulitexenoliths from the Zagadochnaya, Udachnaya andLeningradskaya pipes, and considered them to be frag-ments of deep-seated intrusions formed by underplating ofbasaltic magmas. In contrast, Solov’eva et al. (2004)

concluded that granulite xenoliths from Udachnaya arethe metamorphosed equivalents of basalts of enrichedmid-ocean ridge basalt (E-MORB) and ocean-islandtholeiite affinity. In this paper, we have studiedgranulite-facies xenoliths from the Udachnaya andKomsomolskaya kimberlite pipes (Fig. 1) for their pet-rology, mineral chemistry, bulk-rock compositions, and Srand Nd isotope compositions. Details of zircon geochemis-try and geochronology for the same samples have beenpresented previously by Koreshkova et al. (2009), who

Fig. 1. Geological sketch map of Siberia showing the locations of kimberlite fields and the main features of the surface geology (after Rosenet al., 2006). Grey areas are outcropping Precambrian rocks, the white area is post-Riphean sedimentary cover, diagonally shaded areas arePhanerozoic mobile belts. Stars represent kimberlite fields: 1, Kuoyka field (Obnajennaya pipe); 2, Muna field (Novinka and Zapolyarnayapipes); 3, Daldyn field (Udachnaya, Leningradskaya and Zarnitsa pipes); 4, Alakit field (Aikhal, Komsomolskaya, Yubileinaya andSytykanskaya pipes); 5, Nakyn field (Nurbinskaya and Botuobinskaya pipes); 6, Mirny field (Mir pipe).

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showed that, although they contain rare discordant mag-matic cores with ages of c. 3 Ga, the zircons mostly yieldmetamorphic ages of 1·8^1·9 Ga.The Siberian craton is composed of four major provinces

(Fig. 1): the Anabar in the north, the Aldan in the south,the Tungus in the west and the Olenek in the NE (Rosenet al., 2002; Pisarevsky et al., 2008). The ProterozoicAkitkan fold belt divides the Aldan from the northernprovinces. Much of the Siberian craton is covered by thick(2^14 km) sedimentary sequences, together with volumin-ous Triassic basaltic lavas. Basement outcrops occur onlyin the Aldan and the Anabar shields and in uplifted areasalong the craton boundaries. The crustal thickness is40^45 km (Suvorov et al., 2006), with the lower crusthaving a P-wave velocity of 6·8^6·9 km s�1 and an upperboundary at 25^30 km depth.Kimberlite pipes occur in the Anabar and Olenek prov-

inces. Several major terranes have been identified withinthe Anabar province (Rosen et al., 2002). These are theMagan terrane in the south and west, and the Daldyn(granulite^gneiss) and the Markha (granite^greenstone)terranes in the north and east. The Udachnaya andKomsomolskaya kimberlite pipes are situated within theMarkha terrane, near its boundary with the Daldyn ter-rane, and belong to the Daldyn and Alakit kimberlitefields respectively (Rosen et al., 2002).The Udachnaya pipewas intruded in late Devonian times (Kinny et al., 1997).The Komsomolskaya pipe lies 80 km west of Udachnaya,and is also late Devonian in age (Griffin et al.,1999).

ANALYTICAL TECHNIQUESThe xenoliths are ellipsoidal and 10^20 cm long. Theirouter parts (about 1cm thickness) were removed bysawing, after which the samples were washed and thencrushed to �2 cm size with a stainless steel screw pressand reduced to fragments �0·4mm size with a jaw crusher(stainless steel jaws). The crushed material was dividedinto two parts for separation of minerals and for X-rayfluorescence (XRF), inductively coupled plasma massspectrometry (ICP-MS) and isotope analyses. Samples forbulk-rock analysis were ground in an agate mill. Modalproportions (Table 1) were estimated from thin-sectionsusing an integration stage and ImageScope software.Major element analyses of garnet, clinopyroxene, ortho-

pyroxene, amphibole, plagioclase and accessoryK-feldspar, rutile and ilmenite (Electronic Appendix 1,available for downloading at http://www.petrology.oxfordjournals.org) were performed using a scanning electronmicroscope (ABT-55 Akashi) at the Institute ofPrecambrian Geology and Geochronology (IPGG, StPetersburg) equipped with an energy-dispersive detector(Link AN 10000/S85). Analytical conditions were 15 kVaccelerating voltage, a spot diameter of 1^5 mm and a

counting time of 100 s. Major element mineral analyses ofzircons and their inclusions were obtained using a JEOL8100 Superprobe (wavelength-dispersive spectrometer) atBirkbeck, using an accelerating voltage of 15 kV, currentof 2·5 nA and a beam diameter of 1 mm. In both cases, theanalyses were calibrated against standards of natural sili-cates, oxides and Specpure metals with the data correctedusing a ZAF program. The data were used for pressureand temperature estimates that are presented inTable 2.We used laser ablation (LA)-ICP-MS to determine trace

elements in constituent minerals in eight representativesamples (mafic granulites Uk1, Uk21, Uk35, Uk37 andY6,and feldspar-rich granulites Uk5, Y7 and Y53; see Fig. 2).Analyses were made at Birkbeck using a New WaveResearch UP213 laser aperture imaged frequency quin-tupled Nd:YAG solid state laser operating at 213 nm,coupled to an Agilent 7500 a quadrupole ICP-MS system.Time-resolved analysis was employed during data acquisi-tion and the raw data were processed using GEMOCGLITTER software (Griffin et al., 2008). A laser diameterof 55 mm, pulse frequency of 20Hz and a dwell time of25 s were used. Ablation was carried out in He mixed withAr carrier gas before the plasma torch. The synthetic glassreference material NIST 612 was used for external calibra-tion (Pearce et al., 1997). An internal calibration elementdetermined by electron microprobe was used: Ti for ilmen-ite and rutile and Ca for other minerals. Limits of detec-tion provided by the GLITTER software are included inthe Electronic Appendix 3 (http://www.petrology.oxfordjournals.org). Trace element concentrations were deter-mined on two separate occasions in 2007 and 2008, whichare indicated as session I and II in the data table.Minerals analysed included garnet, clinopyroxene, plagio-clase, K-feldspar, orthopyroxene, amphibole, ilmenite,rutile and apatite. Results are presented in ElectronicAppendix 2 (http://www.petrology.oxfordjournals.org)and in Fig. 3. The trace element composition of zircon hasbeen discussed by Koreshkova et al. (2009).Major element data were obtained by XRFat VSEGEI

(St Petersburg) for samples prefaced by Uk (except forUk35a) and samples Y59, Kom72 and 286/78, and at theVinogradov Institute in Irkutsk for samples prefaced byY(except for Y59) and samples Uk35a, Kom11 and Kom70.Fusion with LiBO2 was used to homogenize powders inboth laboratories. The precision of the XRF analysis is0·5% for SiO2, 1·5% for Al2O3 and CaO, 5% for Na2O,and 2^2·5% for the rest of the oxides. Two samples (Uk35,Uk37) were analysed in both Irkutsk and St Petersburg.Agreement is very good, except for MgO (for which thevalues obtained in Irkutsk are slightly lower) and Na2O(for which the concentrations from St Petersburg areslightly lower). Results are presented in Table 3. The ana-lyses of international standards and limits of detection arereported in Electronic Appendix 3.

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Trace element concentrations were determined by aquadrupole ICP-MS ELAN-6100-DRC (Perkin Elmer) atVSEGEI, St Petersburg, for samples Uk1, Uk4, Uk5,Uk11, Uk20, Uk21, Uk23, Y6, Y6a, Y7, Y59 and Kom72,and by ELEMENT 2 (Finnigan MAT) at Irkutsk forUk35, Uk35a, Uk37, Kom11, Kom70 and samples pre-faced by Y (except for Y59 and Y6a). Thus analyses ofY6 and Y7 were repeated. Both laboratories used fusionwith LiBO2 and dissolution in ultrapure HNO3 to pre-pare sample solutions. TOTALQUANT software wasused to process data, and certified multi-element solutionswere employed for constructing calibration graphs.Purification of water for solutions was achieved using amembrane technique device ‘Labconco Water Pro PS’ inSt Petersburg and a Millipore-ELIX-3 device in Irkutsk.An internal Rh standard was used to correct signal drift.The isotopes of elements were selected with regard to pos-sible interferences with isobaric and molecular ions.Interference corrections were routinely applied to correctanalyte isotopes 151Eu (from BaO, BaOH) and 159Tb(from NdO, NdOH). Oxide production ratio was �3%.Uncertainties are estimated to be better than 2^10%.The analyses of international standards, blanks andlimits of detection are reported in Electronic Appendix3. Trace element analyses for samples Uk20 and Uk23were repeated by ICP-MS at the University ofMontpellier using a VG-PQ2 spectrometer, following themethod of Ionov et al. (1992) and Godard et al. (2000),who reported on the accuracy and reproducibility of themethod based on repeated analyses of internationalstandards.Comparison of the data obtained in different labora-

tories shows good agreement for most elements. The differ-ence in values does not exceed the precision of the methodfor most elements. Larger discrepancies are observed be-tween Zr and Hf concentrations determined in VSEGEI(St Petersburg) and Montpellier, and for Zr, Hf, Nb andTa concentrations determined in St Petersburg andIrkutsk. In both cases the VSEGEI laboratory gave lowervalues. Zr contents determined by ICP-MS are lower thanthe XRF values, pointing to possible incomplete dissol-ution of zircon. We have used the data from Montpellierfor Uk20 and Uk23 and average values for Y6 and Y7 inthe subsequent discussion.To remove intergranular carbonate films, leaching ex-

periments were performed on fresh-looking samples Uk35and Y6. Approximately 5 g of crushed material of sampleUk35 were attacked with 0·1N HCl solution, for 15min atroom temperature, after which the material was rinsed inpure distilled water, dried and ground to a powder. Sixgrams of the powder made from sample Y6 were leachedwith 2N double sub-boiled HCl for 2 h at 208C. The pow-ders were given sample numbers Uk35a and Y6a respect-ively and analysed as normal.

Isotope analyses were undertaken on whole-rock samplesat the IPGG (St Petersburg). Samples were broken downusing a mixture of nitric and hydrofluoric acids. Sr separ-ation was performed by means of cation chromatographicexchange resin AG50W-X8. Separation of Sm and Ndwas carried out in two stages: first using AG50W-X8 resinto separate the rare earth elements (REE), followed by achromatographic extraction on a Teflon medium. Rb, Sr,Sm and Nd concentrations were obtained by isotope dilu-tion using a mixed spike solution of 85Rb^84Sr and149Sm^150Nd. Isotopic analyses of Rb, Sr, Sm and Ndwere made on eight-collector MAT261 and Triton massspectrometers in static mode. Corrections for isotopic frac-tionation of Sr were made by normalizing to a value of88Sr/86Sr¼ 8·37521. Corrections for isotopic fractionationof Nd were made to a value of 148Nd/144Nd¼ 0·241578.During the course of the measurements the weighted aver-age of nine NBS-987 standard runs was 0·710249�8 (2s)for 87Sr/86Sr and of nine La Jolla Nd-standard runs was0·511852�8 (2s) for 143Nd/144Nd. Errors are estimated tobe 0·5% for Rb, Sr, Sm and Nd concentrations. Blanklevels were 30 pg for Rb, Sr and Sm and 70 pg for Nd.Analysis of BCR-1 yielded the following results: Rb con-tent¼ 45·9 ppm, Sr¼ 329 ppm, 87Rb/86Sr¼ 0·4027�9,87Sr/86Sr¼ 0·705013�6 (average of six analyses), Sm con-tent¼ 6·45 ppm, Nd¼ 28·4 ppm, 147Sm/144Nd¼ 0·1383�3,143Nd/144Nd¼ 0·512654� 8 (average of 10 analyses).Agreement between Rb, Sr, Sm and Nd values determinedby isotope dilution and by ICP-MS in xenoliths is verygood.Samples Uk5, Uk21, Uk35a, Uk37 andY6 were leached

prior to analysis, otherwise the samples were unleached.Leaching was carried out on two aliquots of powder(0·5 g each) with 2N HCl for 2 h at room temperatureand at 608C. Unleached whole-rock and two residues wereanalysed for each sample. Leachates were analysed forsamples Uk5, Uk21 and Y6. The data are reported inTable 4.For Hf isotope analysis, samples were fused with lithium

metaborate flux to ensure dissolution of zircon and subse-quently dissolved in 3M HCl. Samples were spiked with amixed 176Luþ180Hf isotopic tracer. Hf was separatedusing the method of Mu« nker et al. (2001), modified to elutemore Zr from the sample prior to Hf collection. Lu wasseparated from the heavy REE (HREE) cut from the Hfseparation, and was further purified using LN-SPEC ionexchange columns. Hf was analysed on a ThermoScientific Neptune Plus mass spectrometer at the NERCIsotope Geoscience Laboratory (Keyworth, UK).Correction for Lu interference on mass 176 was negligible.Minor Yb interference on mass 176 was monitored using173Yb/176Yb values empirically determined using dopedJMC475 solutions. A total of 54 analyses of the JMC475standard solution gave a value of 0·282160� 0·000007


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(23 ppm, 1s) during the period of analysis. Seven analysesof standard BCR-2 gave a value of 0·282867�0·000005(16 ppm, 1s) at the time of analysis. Lu was also measuredon a Thermo Scientific Neptune Plus mass spectrometer.Lu samples were doped with sufficient natural Yb to allowmass bias correction using measured 172Yb/173Yb. Hf iso-tope data are presented inTable 4.

RESULTSPetrographyPetrographic examination of 58 samples fromKomsomolskaya and 40 samples from Udachnaya allowedus to identify and exclude highly altered rocks.We selected22 xenoliths from Udachnaya (samples prefaced by Ukand Y and sample 286/78) but only three fromKomsomolskaya (prefaced by Kom) because the litho-logical types are the same, but the Komsomolskaya xeno-liths are more altered. The samples are mostlytwo-pyroxene garnet granulites, or garnet granulites lack-ing orthopyroxene; two samples (Uk4 and Uk11) areamphibolized garnet granulites.The modal abundance of garnet ranges from 7 to 46%;

typically it forms 20^30% of the samples. Clinopyroxeneaccounts for 11^53% (amphibolized garnet granuliteshave only 2^9%); orthopyroxene is much less abundant(1^9%, and not present in all the xenoliths). Plagioclaseforms 7^73% of the rock, but most samples contain�50%. Samples Uk5,Y7 and Y53 contain �60% feldsparand are here termed ‘feldspar-rich granulites’. Severalxenoliths contain pargasite, generally forming55% of therock, except for amphibolized granulites Uk4 and Uk11,which contain 18 and 34% amphibole, respectively. Allother minerals are present in minor amounts, except forgranulites Y53, Kom11 and Kom72, which contain30^59% of alteration products (Table 1). They wereincluded to trace the change of chemical compositionowing to alteration. Minor and accessory primary min-erals are K-feldspar, quartz, scapolite, ilmenite, rutile, sul-fides, apatite, zircon and baddeleyite.Textures of the granulites are coarse- to medium-

grained, granoblastic to porphyroblastic, foliated orbanded (Fig. 2a^d). All minerals are in textural equilib-rium except for amphibole that replaces clinopyroxene insome samples (Fig. 2e). Orthopyroxene is often mantledby clinopyroxene (Fig. 2g). Garnet has numerous inclu-sions of all phases. It sometimes shows skeletal forms atcontacts with plagioclase (Fig. 2f). Rutile is present to-gether with ilmenite and often has ilmenite rims.All of the samples show some degree of alteration.

Minimal alteration this is in the form of thin cracks filledwith carbonate and serpentine (� phlogopite, barite andother minerals). In strongly altered rocks, calcite andsome phyllosilicates replace the rock-forming minerals,leading to the formation of pseudomorphs that preserve

the shape and cleavage of the former mineral.The most re-sistant minerals are garnet, apatite, ilmenite, rutile andzircon. The less resistant minerals are orthopyroxene,clinopyroxene and feldspars (Opx5Cpx�Pl, Kfs).

Mineral major element compositionsGarnets are almandines containing 23^44% pyrope and16^20% grossularite components. Garnet grains frommedium-grained rocks with an average grain size of0·5^0·7mm show negligible zoning. The most prominentzoning is observed in samples Y7,Y59, Uk20 and Uk23, inwhich garnet porphyroblasts are 5^7mm in diameter(Electronic Appendix 1). They exhibit variable increasesin CaO and decreases in MgO and Mg-number fromcore to rim. Traverses across single porphyroblasts aretrough-like for XCa and convex upward for XMg andMg-number. In sample Y7, small garnet grains from thematrix have CaO contents similar to porphyroblast rimsbut with lower Mg-numbers. No change in MnO contenthas been detected in any of the garnet grains. A garnet in-clusion in zircon was found in sample Y53, situated withinthe homogeneous textured inner part of the zircon. Inthis sample and Y7, which is similar, two generations ofmetamorphic zircon have been recognized (Koreshkovaet al., 2009). Homogeneous zircon belongs to an early gen-eration whereas the final generation is in the form ofzircon overgrowths with a convoluted to fir-tree texture.The composition of the garnet inclusion differs from thegarnet in the rest of the rock by its higher Mg-numberand lower CaO content (5·5 vs 6·7wt %).Clinopyroxenes are NaÂl-diopsides or Al-diopsides

with 0·9^2·1wt % Na2O and 3·1^6·7wt % Al2O3

(Electronic Appendix 1). They show gradually decreasingAl2O3 contents (by 1^2wt %) and increasingMg-numbers from core to rim. Na2O content does notchange significantly, which results in a decrease of the cal-culated amount of Al in the tetrahedral site.Clinopyroxene inclusions in garnet have compositionssimilar to the rims of clinopyroxene grains. In samplesY7 and Y53, the composition of clinopyroxene inclusionsin convolute-textured zircon is similar to the average clino-pyroxene composition; however, an inclusion in an olderhomogeneous zircon has a much higher Al2O3 content(6·8 vs 4·8wt %) and lower Mg-number. No domains ofpreviously existing pyroxenes have been detected withingrains.Orthopyroxenes have 0·9^2·9wt % Al2O3 and

Mg-numbers of 0·54^0·69 (Electronic Appendix 1).Mg-number increases and Al2O3 content decreases fromcore to rim. In samples containing single orthopyroxenegrains (Y7, Uk23 and Kom70), they are much smallerthan the clinopyroxene and their composition probablycorresponds to rims rather than cores. In sample Uk37,zircon of the final metamorphic generation contains an


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Table 1: Modal mineralogy of granulite xenoliths from Udachnaya and Komsomolskaya kimberlite pipes

Sample Texture Grt Opx Cpx Pl Kfs Qtz Prg Rt Ilm Ap Zrn Scp Secondary minerals

Measured modes (vol. %)

Udachnaya

Uk1 m/g, banded, g/b 20 3 20 47 x x 3·0 0·3 x x 7

Uk4 c–m/g, foliated, p/b 18 9 50 18 x 0·3 5 x

Uk5 m/g, foliated, p/b 10 13 72 2 x x 2·0 0·5 x 1 (7 after Cpx)

Uk11 c–m/g, foliated, p/b 8 2 50 1 34 1·5 0·8 x 3

Uk20 c/g, foliated, p/b 27 41 24 x 4 2·0 0·4 1 1

Uk21 c/g, foliated, p/b 25 3 35 31 x x 1 2·5 0·4 x 2

Uk23 c/g, foliated, p/b 23 x 45 25 x x 4·0 0·5 x 2

Uk35 c/g, foliated, p/b 28 38 29 x 2 0·4 0·4 0·1 2

Uk37 c–m/g, foliated, g/b 10 9 26 50 x x 3·0 0·3 x 2

Y-5 c/g, foliated, p/b 34 34 23 1 4·0 0·4 x 4

Y-6 c/g, foliated, p/b 25 38 26 x 2 1·5 3·0 0·3 x 4

Y-7 c-m/g, banded, p/b 23 x 11 59 1 x 2 x 0·5 0·6 x 3

Y52 c/g, foliated, p/b 22 1 16 39 6 4·5 0·5 x 11

Y53 m/g, foliated, g/b 13 13 73 0·4 0·5 0·4 x (7 after Grtþ 3 after Cpxþ 30 after Pl)

Y54 c/g, foliated, p/b 24 44 17 5 3·9 0·2 5

Y55 c/g, foliated, p/b 20 42 30 2 2·4 x 4

Y56 c/g, foliated, p/b 26 3 38 24 2·0 0·3 7 (after Pxs)

Y59 c/g, foliated, p/b 46 28 7 x x 1·3 1·2 0·6 x 2 14

Y60 c/g, foliated, p/b 34 37 23 2 3·2 0·3 0·5

Y61 c/g, foliated, p/b 37 2 34 22 1·5 2·5 0·2 x 1

Y62 c/g, foliated, p/b 24 53 14 4 4·0 x 1

286/78 c/g, foliated, p/b 23 1 34 33 1 4·0 x x 4

Komsomolskaya

Kom11 c/g, foliated, p/b 28 27 40 2 x 2·8 0·2 (21 after Cpxþ 38 after Pl)

Kom70 c/g, foliated, p/b 23 x 40 28 x 3·6 x x 5

Kom72 m/g, foliated, p/b 22 36 41 0·5 0·5 x x x (30 after Cpx)

Modes used for calculations (vol. %)

Uk1 18 7 24 48 1·8 0·4 0·002

Uk4 17 10 55 18·0 0·2 0·1 not calc.

Uk5 9 15 71 3·0 1·2 0·8 0·002

Uk11 10 3 50 1·0 34·0 1·0 1·1 not calc.

Uk20 26 42 26 4·0 1·9 0·3 not calc.

Uk21 22 5 35 33 0·5 1·9 2·4 0·4 0·004

Uk23 25 44 25 0·5 4·0 0·5 not calc.

Uk35 32 38 28 0·5 2·0 0·2 0·2 0·2 0·001

Uk37 9 13 26 49 1·0 1·6 0·2 0·007

Y5 35 36 23 2·5 3·0 0·5 not calc.

Y6 25 35 33 2·5 2·1 2·0 0·3 0·001

Y7 21 12 60 3·0 2·0 0·5 0·4 0·9 0·005

Y53 14 11 74 0·4 0·2 0·4 0·010

Y59 45 38 13 0·3 1·5 1·5 0·8 not calc.

Kom70 24 2 40 30 1·5 2·5 0·3 not calc.

Secondary minerals in parentheses are included in mineral modes. m/g, medium-grained; c/g, coarse-grained;g/b, granoblastic; p/b, porphyroblastic; x, 50·5 vol. %; not calc., not calculated. Mineral symbols are according toKretz (1983).


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inclusion of orthopyroxene, with a composition similar tothe grain cores.Amphiboles are potassic pargasites with 1·4^2·4wt %

K2O. They contain significant amounts of TiO2

(1·5^3·0wt %). MnO content is below the detection limit.There are some minor variations in pargasite compositionfrom sample to sample but no essential difference is

observed between amphibole-rich and amphibole-poorgranulites (Electronic Appendix 1).Plagioclase is andesine to oligoclase. Anorthite content

either decreases slightly from core to rim or shows nochange. Feldspar inclusions in garnet are within the rangeof plagioclase in the rocks. K-feldspar occurs at the bound-aries between Fe^Mg-silicates and plagioclase, and

Fig. 2. Photomicrographs of granulite xenoliths from Udachnaya and Komsomolskaya: (a) sample Uk37, granoblastic texture; (b) sample Y7,banded porphyroblastic texture; (c) sample Uk23, porphyroblastic texture; (d) sample Kom70, porphyroblastic texture; (e) sampleY6, parga-site replacing diopside; (f) sample Uk37, skeletal forms of garnet at the contact with feldspars; (g) sample Uk1, orthopyroxene mantled by clino-pyroxene. Plane-polarized light.


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sometimes as lamellae within plagioclase. K-feldspar con-tains up to 0·2wt % CaO, 2·1wt % Na2O and 1·5wt %BaO. Both plagioclase and K-feldspars are present as inclu-sions in zircon. In sample Uk37, they are similar to thefeldspars within the rock matrix. In sample Y53, an inclu-sion from a homogeneous domain within a complexzircon grain is slightly more sodic than the plagioclase inthe rest of the rock. Average compositions of plagioclase(in Electronic Appendix 1) include analyses of K-rich rimsfor those samples where separate K-feldspar grains areabsent.Ilmenite is present in all samples. In rutile-free rocks,

ilmenite contains 1·1^2·3wt % MgO; it is richer in FeOthan ilmenite from rutile-bearing rocks. In the latter,MgO contents are 1·9^3·8wt %. Rutile contains0·5^2·1wt % FeO.

P^T determinationsTo give a first approximation of pressure and temperatureof equilibrium of the granulite assemblages, we have usedthe formulations of the Grt^Cpx geothermometer (Ai,1994; Krogh Ravna, 2000), Grt^Pl^Cpx^Qtz geobarom-eter (Newton & Perkins, 1982), GrtÔpx geobarometer[Nickel & Green, 1985; modified version byTaylor (1998)]and Amph geobarometer (Anderson & Smith, 1995).Because of mineral zoning, we have chosen for calculationsaverage core and rim compositions for all samples and ex-treme core compositions (of garnet porphyroblasts andthe largest grains of clinopyroxene and plagioclase) forcoarse-grained granulites Y7, Y59, Uk20 and Uk23. Insample Y7, we have separately used porphyroblasts andminerals from the groundmass. The results are presentedin Table 2. In general, extreme core compositions give800^8908C, 0·9^1·2GPa, average cores 710^8408C,0·9^1·2GPa, and average rims 610^7208C, 0·7^1·1GPa.The lowest values belong to the amphibolized granulites.The amphibole barometer yields 0·8GPa at the tempera-ture inferred for rim compositions in all pargasite-bearingsamples. Pargasite was probably formed when the tem-perature fell below 7008C.

Trace elements in mineralsGarnets mostly have similar HREE-enriched, light REE(LREE)-depleted compositions. Garnets from maficgranulites are richer in HREE than those fromfeldspar-rich granulites, except for Uk35, and displayweak positive slopes from Gd to Lu in primitive mantlenormalized trace element patterns (Fig. 3a). Garnets fromfeldspar-rich granulites are similar but Uk5 shows a nega-tive slope from Gd to Lu. Garnet from sample Uk35 hasthe lowest trace element contents, reflecting both its highmodal quantity and low whole-rock concentrations.Garnet in sample Uk37 shows a decrease of 20^30% inTi, Y and HREE concentrations within grain rims in

comparison with the cores. This is also observed in othersamples but the difference is smaller (ElectronicAppendix 2).Clinopyroxenes show strong LREE enrichment but with

the peak at Ce, Pr or Nd rather than at La. The highestLREE concentrations are observed in clinopyroxenesfrom feldspar-rich granulites and the mafic granulites Uk1and Uk37, in which the HREE are also elevated. Thelowest REE concentrations are in Uk35 (Fig. 3b).Variations between cores and rims are small but consistent.Most rims have 30^40% lowerTi,Yand overall REE con-tents than the core compositions; the HREE decreasefaster towards the rim than LREE. Small grains insampleY7 are not zoned.Orthopyroxene is poor in trace elements except for Ti,

Mn, Co and Zn. REE concentrations are 0·2^1·5 timeschondrite or below detection limits. Orthopyroxene fromsamples Uk21 and Uk37 is slightly LREE-enriched andthat from Uk1 is slightly LREE-depleted.Amphibole in samples Y6, Y7 and Uk35 displays a very

similar REE pattern to that of clinopyroxene, but the con-centrations of LREE are 1·5^2 times higher. It is enrichedin Ti, Ba, Rb and Sr. Its Zr and Hf contents are lowerthan in clinopyroxene but the Zr/Hf ratio is similar. Nbvaries from 0·02 to 20·6 ppm.Plagioclase is Ba, U, Sr, Pb and LREE enriched with a

large positive Eu anomaly (Fig. 3c). The La content ofplagioclase is 20^80 times chondrite values. Largeion lithophile elements (LILE), Th and U concentrationsvary widely. Plagioclase contains 0·3^19 ppm Rb,482^1565 ppm Sr, 113^452 ppm Ba and 2^32 ppm Pb. Bacorrelates roughly with La. Concentrations of LILE andLREE are generally higher in plagioclase fromfeldspar-rich granulites. K-feldspar shows a similar traceelement pattern to plagioclase but with much lower valuesfor trace elements other than Rb, Pb, Sr and Ba (4000^12000 ppm).Apatite shows strong LREE enrichment and HREE de-

pletion (Fig. 3d). It is rich in both Th (2·4^12 ppm) andU (0·04^3·1ppm). Rutile and ilmenite are major V-, Nb-and Ta-bearing phases. Rutile also contains significantamounts of Zr (1200^1500 ppm), Hf (33^47 ppm) andU (0·2^7·9 ppm).

Major element whole-rock compositionsThe granulite xenoliths contain 37^53wt % SiO2

(Table 3). The lowest SiO2 contents are found in samplesY5, Y59 and Kom11, and the highest in feldspar-richgranulite Uk5. The general range in MgO contents in thesamples is 6·0^17·4wt %; the lowest values are fromfeldspar-rich granulites (Uk5,Y7) and highest from alteredxenoliths Y53 and Kom11; much of this is due to replace-ment with serpentine. FeOt contents are 5·2^7·4wt % inthe feldspar-rich granulites and 8·0^18·7wt % in themafic granulites. Al2O3 ranges from 12·8 to 20·4wt %;


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the highest content is in feldspar-rich granulite Uk5. Na2Ocontents generally exceed those of K2O, except in alteredsamples (e.g. Y53). Typical loss on ignition (LOI) valuesrange from 0·1 to 3·0wt %, but higher values are found insome highly altered granulites. However, LOI values of2^3wt % are still too high for granulites that lack amphi-bole. Unusually high K2O contents (42wt %) are foundin several samples, probably owing to alteration or

contamination from the host kimberlite, particularly asthose samples with high K2O contents also show highLOI values. Generally MgO contents increase and SiO2,CaO and Na2O contents decrease with increasing LOI.However, there is no systematic correlation between K2Oand LOI; instead, two trends are observedçwith andwithout enrichment in K2O. In contrast, TiO2, FeOt andAl2O3 contents change little with progressive alteration.

Table 2: P^T determinations for granulite xenoliths from Udachnaya and Komsomolskaya kimberlite pipes

Sample Location T P T P T P T P P

(8C) (GPa) (8C) (GPa) (8C) (GPa) (8C) (GPa) (GPa)

Ai NP KR NP KR NG Ai NG AS

Uk1 cores 780 1·0 810 1·0 820 1·2 790 1·1

rims 670 0·9 690 0·9 700 1·0 660 0·8

Uk4 cores 770 0·9 790 0·9

rims 610 0·6 650 0·6 0·8

Uk5 cores 740 0·9 760 0·9

rims 650 0·7 670 0·7

Uk11 cores 720 1·0 750 1·0

rims 610 0·8 640 0·9 0·8

Uk20 cores, porphyroblasts 800 0·9 830 0·9

cores 780 0·9 810 0·9

rims 630 0·8 660 0·8 0·8

Uk21 cores 720 0·9 750 0·9 770 1·2 740 1·1

rims 640 0·9 670 0·9 680 1·2 640 1·0 0·8

Uk23 cores, porphyroblasts 800 1·1 830 1·1

cores 720 0·9 760 1·0 770 1·2 730 1·0

rims 630 0·8 660 0·8 660 0·9 620 0·7

Uk35 cores 760 1·0 780 1·0

rims 690 1·0 710 1·0 0·8

Uk37 cores 750 0·9 780 0·9 790 1·1 750 0·9

rims 680 0·8 700 0·8 710 0·9 680 0·8 0·8

Y5 cores 760 1·0 780 1·0

rims 690 0·9 710 1·0 0·8

Y6 cores 740 0·9 770 0·9

rims 650 0·8 680 0·8 0·8

Y7 cores, porphyroblasts 820 1·2 830 1·2

cores, groundmass 710 1·1 730 1·1 740 1·2 710 1·1

rims, porphyroblasts 670 1·1 700 1·1 690 1·0 660 0·9

rims, groundmass 650 1·0 670 1·0 660 0·9 630 0·8 0·8

Y53 cores 770 1·2 790 1·2

rims 730 1·1 750 1·1

Y59 cores, porphyroblasts 870 1·2 890 1·2

cores 820 1·1 840 1·2

rims 700 1·1 720 1·1

Abbreviations for P–T methods: Ai, Ai (1994); NP, Newton & Perkins (1982); KR, Krogh Ravna (2000); NG, Nickel &Green (1985), modified version by Taylor (1998); AS, Anderson & Smith (1995).


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Fig. 3. Trace element concentrations in the constituent minerals of the Udachnaya granulite xenoliths determined by LA-ICP-MS, normalizedto primitive mantle abundances (Sun & McDonough,1989): (a) garnet; (b) clinopyroxene; (c) feldspar (plagioclase and K-feldspar); (d) apatite(d). Missing symbols correspond to values below the detection limit.


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To evaluate the distortion of compositions caused byalteration and contamination, we have calculated thebulk-rock composition of several xenoliths using theirmodal abundances, average mineral compositions andmineral density values (Dortman, 1992). We based our

calculations on the resistance to alteration of garnet,zircon, Ti oxides and apatite, and the relative immobilityof TiO2, FeOt and Al2O3. We adjusted the abundances ofilmenite and rutile to agree with the measured TiO2 con-tent taking into account TiO2 in diopside and pargasite.

Fig. 3. Continued.


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Table 3: Bulk-rock geochemistry (XRF and ICP-MS) of granulite xenoliths from Udachnaya and Komsomolskaya

kimberlite pipes

Sample: Uk1 Uk1 Uk4 Uk4 Uk5 Uk5 Uk11 Uk11 Uk20 Uk20 Uk20 Uk21 Uk21

SPb calc SPb calc SPb calc SPb calc SPb MtP calc SPb calc

SiO2 (wt %) 48·2 50·4 46·6 49·1 53·2 53·7 44·8 49·3 45·6 46·7 46·4 48·2

TiO2 1·26 1·30 0·558 0·644 0·989 1·00 1·49 1·54 1·24 1·59 1·59 1·46

Al2O3 15·7 15·9 20·3 20·5 20·4 20·3 17·2 18·1 13·7 14·4 13·3 13·8

Fe2O3 10·2 8·85 5·81 12·2 13·7 15·9

FeO 12·4 8·47 5·73 9·41 13·5 14·6

MnO 0·252 0·244 0·126 0·128 0·048 0·069 0·115 0·099 0·157 0·176 0·229 0·263

MgO 9·63 6·15 9·33 6·11 6·05 3·11 10·5 6·16 11·5 8·23 9·96 7·39

CaO 6·95 9·75 9·02 10·3 5·08 10·5 6·29 8·57 11·1 12·8 10·0 11·2

Na2O 2·26 3·36 2·35 3·23 3·58 4·44 2·28 4·24 1·32 2·12 1·76 2·62

K2O 2·66 0·322 1·40 0·77 3·00 0·697 2·34 1·13 0·678 0·317 0·603 0·282

P2O5 0·170 0·172 50·05 0·057 0·358 0·356 0·503 0·486 0·090 0·104 0·148 0·148

LOI 2·85 1·61 1·72 2·55 1·07 0·24

Sum 100·1 100·0 100·1 99·3 100·2 99·9 100·3 99·0 100·2 99·9 100·1 99·9

Mg/(Mgþ Fe) 0·65 0·47 0·68 0·56 0·67 0·49 0·63 0·54 0·62 0·52 0·55 0·47

Sc (ppm) 28·8 33·4 13·9 23·8 49·1 54·1

V XRF 188 157 98·0 163 257 284

V 279 231 256 152 97·0 237 374 398 274

Cr 6·70 10·0 24·5 27·2 22·8 16·0 116 83·7 78·4

Co 31·8 40·3 18·2 37·4 57·5 55·3

Ni 8·12 20·0 30·4 33·4 61·3 86·6

Rb 75·1 1·28 23·2 49·0 14·6 56·4 12·2 11·5 5·55 0·57

Sr 1560 346 813 1278 626 884 816 940 196 160

Ba 776 46·2 524 1496 471 1035 212 249 168 61·0

Y 23·8 47·2 12·9 6·81 12·4 21·2 14·9 19·5 37·8 35·1

Zr XRF

Zr 62·5 72·2 37·5 41·5 58·6 62·9 56·9 80·9 80·4 83·7

Hf 1·79 2·25 1·08 1·24 1·81 1·98 1·74 2·35 2·36 2·52

Nb 8·69 10·0 4·17 7·62 8·47 9·18 6·98 7·01 14·7 16·0

Ta 0·490 0·150 0·330 0·380 0·360 0·449 0·790

La 13·2 11·1 11·4 25·0 22·0 50·9 8·42 8·91 8·56 6·93

Ce 29·6 31·5 24·1 52·0 43·8 119 21·6 24·6 20·4 20·5

Pr 4·34 4·87 2·86 6·03 6·31 16·3 2·93 3·24 3·31 3·37

Nd 21·0 24·9 12·0 24·9 28·5 67·1 13·0 15·1 16·0 16·0

Sm 5·29 7·51 2·77 4·16 6·17 12·6 3·23 3·47 4·36 4·36

Eu 1·34 1·96 0·83 1·53 1·44 2·69 0·87 1·12 1·24 1·42

Gd 4·82 8·15 2·61 3·02 4·85 8·83 3·16 3·77 5·21 5·20

Tb 0·860 1·42 0·410 0·39 0·55 1·12 0·580 0·586 0·960 0·894

Dy 4·53 9·49 2·44 1·48 2·77 4·79 3·19 3·59 6·16 6·53

Ho 0·910 2·01 0·490 0·270 0·458 0·820 0·570 0·693 1·45 1·45

Er 2·35 5·52 1·40 0·680 1·06 2·03 1·44 1·73 4·22 4·48

Tm 0·370 0·846 0·200 0·090 0·140 0·260 0·190 0·200 0·600 0·684

Yb 2·27 5·39 1·18 0·440 0·824 1·71 1·16 1·10 4·49 4·74

Lu 0·340 0·779 0·160 0·080 0·111 0·210 0·130 0·149 0·690 0·700

Pb 5·08 4·21 2·83 8·94 21·5 5·28 0·66 1·13 0·440 0·846

Th 0·040 0·102 0·520 0·380 0·397 4·50 0·090 0·149 0·070 0·053

U 0·110 0·061 0·240 0·150 0·238 0·580 0·070 0·069 0·030 0·076

(continued)


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Table 3: Continued

Sample: Uk23 Uk23 Uk23 Uk35 Uk35 Uk35a Uk35 Uk37 Uk37 Uk37 Y5 Y5 Y6 Y6

SPb MtP calc SPb Irk Irk calc SPb Irk calc Irk calc Irk SPb

SiO2 (wt %) 44·1 45·7 46·5 46·4 45·9 48·3 48·7 49·3 51·5 39·6 44·9 46·9

TiO2 2·47 1·90 0·668 0·722 0·726 0·742 1·16 1·18 1·25 1·69 2·19 1·61

Al2O3 13·7 13·2 15·7 15·9 15·8 16·9 13·2 13·5 14·4 14·2 15·0 14·0

Fe2O3 17·6 12·1 11·9 12·4 14·9 14·4 17·8 14·2

FeO 15·8 9·21 11·5 15·9

MnO 0·230 0·219 0·183 0·185 0·189 0·187 0·208 0·211 0·177 0·300 0·295 0·220

MgO 10·1 8·17 9·81 9·62 10·00 9·69 7·57 6·91 6·90 11·9 7·32 8·91

CaO 9·56 12·3 11·7 11·8 11·9 12·4 10·2 9·99 10·4 8·77 11·9 10·2

Na2O 1·40 2·17 1·40 1·74 1·34 2·29 2·70 3·19 3·42 1·15 1·86 1·96

K2O 0·718 0·212 0·978 0·902 0·906 0·237 0·947 0·975 0·307 0·300 0·194 0·920

P2O5 0·218 0·206 50·05 0·063 50·05 0·065 50·05 0·079 0·079 0·200 0·196 0·110

LOI 0·14 0·66 0·78 0·50 0·10 0·39 4·25 1·49

Sum 100·2 99·9 99·7 100·0 99·7 100·0 99·7 100·1 100·0 100·2 99·9 100·4

Mg/(Mgþ Fe) 0·53 0·48 0·62 0·61 0·62 0·65 0·50 0·49 0·52 0·57 0·45 0·55

Sc (ppm) 41·7 41·9 42·4 33·4 56·3 46·2

V XRF 264 178 185 236

V 364 236 237 237 301 187 342 395

Cr 157 266 289 298 149 148 115 193 142

Co 59·8 53·0 58·7 53·3 51·3 47·0

Ni 49·4 197 230 78·4 74·6 66·8 60·6

Rb 7·99 7·05 21·3 19·9 0·324 9·01 1·98 7·19 10·2 6·5

Sr 227 233 630 564 177 207 215 187 233 232

Ba 214 229 93·5 87·1 57·0 294 221 258 173 233

Y 33·0 37·4 13·5 13·2 12·5 20·4 26·0 40·5 28·2 29·6

Zr XRF 580 114

Zr 84·2 95·2 31·7 33·6 33·2 58·7 92·6 93·8 84·5 65·4

Hf 2·42 2·89 1·22 1·16 1·02 1·92 2·66 3·04 2·93 2·00

Nb 16·7 14·5 0·524 0·668 1·348 6·64 7·46 10·6 12·3 9·3

Ta 0·960 0·933 0·031 0·034 0·386 0·740 0·906 0·590

La 10·4 10·1 3·79 3·65 3·79 12·6 13·3 20·1 6·65 6·58

Ce 26·7 29·2 11·3 12·1 13·3 28·9 34·0 35·0 17·5 15·6

Pr 4·03 4·13 1·63 1·48 2·01 3·31 4·23 4·04 2·49 2·43

Nd 19·4 20·8 7·3 8·0 8·9 13·1 17·7 16·5 11·4 11·0

Sm 5·48 5·08 1·84 1·81 2·03 2·73 4·03 4·45 3·41 2·90

Eu 1·38 1·73 0·66 0·63 0·71 0·97 1·24 1·30 1·01 1·00

Gd 5·66 6·24 2·00 2·29 2·20 3·83 4·04 6·20 4·49 3·70

Tb 1·01 1·00 0·358 0·324 0·352 0·533 0·76 1·20 0·780 0·770

Dy 5·73 6·80 2·23 2·28 2·32 3·21 5·24 8·35 5·89 4·71

Ho 1·23 1·36 0·512 0·507 0·484 0·728 1·10 1·81 1·23 1·11

Er 3·37 3·59 1·29 1·33 1·38 2·40 3·10 5·47 3·90 3·35

Tm 0·490 0·477 0·195 0·217 0·213 0·358 0·484 0·759 0·594 0·490

Yb 3·05 3·02 1·15 1·43 1·49 2·35 3·36 4·90 3·83 3·03

Lu 0·410 0·475 0·178 0·238 0·215 0·311 0·504 0·757 0·551 0·520

Pb 0·550 1·04 0·501 0·829 0·660 28·9 4·45 3·55 4·87 1·77

Th 0·070 0·101 0·022 0·023 0·014 0·480 0·143 0·180 0·062 50·1

U 0·030 0·023 50·003 0·003 0·021 0·115 0·124 0·133 0·110 50·1

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Table 3: Continued

Sample: Y6a Y6 Y7 Y7 Y7 Y52 Y53 Y53 Y54 Y55 Y56

SPb calc Irk SPb calc Irk Irk calc Irk Irk Irk

SiO2 (wt %) 48·3 51·6 52·5 44·1 48·5 56·3 39·5 45·0 45·1

TiO2 1·65 0·850 1·21 2·22 0·602 0·755 2·64 1·64 1·43

Al2O3 15·2 18·4 20·1 15·0 14·6 20·4 12·8 14·4 14·0

Fe2O3 8·39 16·0 6·03 20·1 16·6 15·5

FeO 12·4 7·43 5·44

MnO 0·252 0·100 0·136 0·187 0·180 0·101 0·262 0·220 0·278

MgO 6·94 5·87 4·63 8·85 15·79 3·14 11·1 9·29 9·76

CaO 12·4 6·12 8·22 8·27 3·61 7·83 9·51 7·63 9·86

Na2O 2·34 3·78 4·62 1·91 1·25 4·82 1·04 1·95 1·49

K2O 0·173 2·72 0·642 1·39 3·32 0·964 0·672 0·921 0·808

P2O5 0·111 0·420 0·386 0·427 0·203 0·204 0·163 0·127 0·130

LOI 1·68 1·72 5·52 2·25 2·22 1·53

Sum 99·8 99·9 99·9 100·0 99·6 99·9 100·1 100·0 99·8

Mg/(Mgþ Fe) 0·50 0·58 0·53 0·52 0·84 0·51 0·52 0·53 0·55

Sc (ppm) 42·2 52·6 12·1 22·6 33·6 10·8 18·2 47·5 47·1 46·1

V XRF

V 336 114 161 296 84·8 112 373 361 304

Cr 153 157 63·2 56·0 43·6 316 57·7 84·6 276 82·8 148

Co 20·5 46·9 13·9 51·4 40·6 36·2

Ni 63 31·7 45·0 172 41·7 130 91·0 139

Rb 4·61 1·41 21·5 22·9 1·91 2·24

Sr 194 159 1056 986 851 565 1060 842 118 219 396

Ba 219·0 66·3 965 1000 403 501 3033 304 136 214 991

Y 33·6 32·9 9·01 9·54 21·9 21·7 7·31 16·2 26·3 24·8 21·5

Zr XRF 103 132 102 95·0 122

Zr 60·2 73·6 95·8 71·5 102 71·1 60·9 108 112 81·4 110

Hf 1·80 2·00 2·99 1·94 3·40 2·17 1·80 3·30 3·18 2·50 2·90

Nb 9·2 11·8 13·7 10·2 2·45 9·41 11·5 5·24 21·3 10·4 18·9

Ta 0·750 0·551 0·360 0·295 0·555 0·927 0·576 0·916

La 4·60 5·99 26·5 26·9 20·0 19·8 13·4 14·3 13·5 7·56 12·4

Ce 12·3 17·2 52·9 52·8 50·0 44·6 28·7 33·0 32·6 19·9 30·8

Pr 1·99 2·57 6·10 6·16 6·34 5·04 3·61 4·46 4·25 2·42 3·97

Nd 9·4 12·6 24·2 22·9 26·6 23·8 16·6 20·4 18·0 11·0 17·2

Sm 2·90 3·61 4·14 3·80 5·54 4·48 2·89 4·93 4·11 2·34 4·00

Eu 1·05 1·28 1·48 1·54 2·03 1·47 1·00 1·46 1·45 1·05 1·13

Gd 3·80 4·50 3·10 3·11 4·98 4·91 2·46 4·33 4·95 3·69 4·39

Tb 0·750 0·777 0·38 0·41 0·75 0·716 0·331 0·632 0·865 0·665 0·749

Dy 5·15 5·64 2·32 2·09 4·61 4·17 1·73 3·68 5·29 4·73 4·30

Ho 1·18 1·23 0·374 0·330 0·97 0·940 0·305 0·736 1·15 1·07 0·940

Er 3·50 3·66 1·03 0·81 2·65 2·36 0·80 1·95 3·05 2·95 2·38

Tm 0·520 0·569 0·132 0·120 0·406 0·374 0·118 0·271 0·491 0·455 0·361

Yb 3·45 3·88 0·880 0·740 2·70 2·22 0·65 1·72 2·90 2·93 2·11

Lu 0·535 0·590 0·132 0·130 0·431 0·331 0·084 0·257 0·472 0·471 0·319

Pb 1·99 0·69 5·32 5·78 6·48 2·98 9·11 9·65 1·33 1·78 1·63

Th 50·1 0·100 1·21 1·29 0·125 0·692 0·791 0·144 0·168 0·183 0·354

U 0·130 0·080 0·378 0·330 0·023 0·049 1·42 0·079 50·003 50·003 50·003

(continued)


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Table 3: Continued

Sample: Y59 Y59 Y60 Y61 Y62 286/78 Kom11 Kom70 Kom70 Kom72

SPb calc Irk Irk Irk SPb Irk Irk calc Irk

SiO2 (wt %) 38·1 43·7 42·8 46·3 39·7 42·1 36·5 42·4 46·5 44·8

TiO2 3·24 2·85 1·80 1·13 2·76 3·49 1·28 1·65 1·89 1·31

Al2O3 14·9 14·8 14·2 14·5 13·3 12·8 14·8 15·2 14·3 16·5

Fe2O3 20·8 19·3 15·0 19·9 19·4 15·0 17·3 16·8

FeO 16·0 14·0

MnO 0·291 0·285 0·291 0·206 0·289 0·298 0·231 0·255 0·236 0·125

MgO 11·9 8·26 8·83 8·41 10·7 7·72 17·4 9·48 7·54 7·74

CaO 7·21 12·3 10·3 9·66 7·57 10·6 4·80 7·05 13·2 5·19

Na2O 0·32 1·22 1·52 2·31 1·91 2·06 0·260 1·52 1·84 1·19

K2O 0·261 0·211 0·535 1·16 0·641 0·663 0·848 0·884 0·224 3·11

P2O5 0·291 0·299 0·165 0·121 0·271 0·339 0·141 0·137 0·134 0·061

LOI 2·64 0·49 1·19 3·11 0·23 8·93 4·11 3·64

Sum 100·0 99·8 100·2 100·0 100·2 99·7 100·2 100·0 99·9 100·5

Mg/(Mgþ Fe) 0·53 0·48 0·48 0·53 0·52 0·44 0·70 0·52 0·49 0·48

Sc (ppm) 39·4 48·2 40·1 44·7 32·2

V XRF 520 657

V 348 257 392 231 347 138

Cr 79 281 93·6 44·5 205 78·6 46·8

Co 54·9 38·0 42·6 35·8 51·2 39·9

Ni 37 109 70·7 64·5 183 54·7 214

Rb 4·99 2·58 7·01

Sr 49·2 130 297 252 203 398 733

Ba 64·2 98·2 237 196 338 1403 640

Y 45·4 28·1 20·2 36·1 22·8 36·4 26·1

Zr XRF 86·0 102 148 215 129 580 151

Zr 127 85·0 87·8 140 122 97·4 204

Hf 3·61 2·45 2·55 3·88 3·80 2·55 5·35

Nb 26·8 12·1 5·13 27·9 11·3 10·1 7·65

Ta 1·75 0·595 0·229 1·18 0·424 0·667 0·472

La 22·0 6·73 8·82 12·6 34·9 8·14 16·8

Ce 51·9 19·4 21·7 30·8 65·2 22·6 31·3

Pr 6·86 2·34 2·96 4·12 6·94 2·82 3·83

Nd 27·9 13·6 13·0 18·3 25·3 12·5 16·3

Sm 7·12 3·49 3·18 4·55 4·66 3·16 3·93

Eu 1·62 1·29 0·977 1·62 1·50 1·14 1·16

Gd 8·09 4·98 3·71 6·01 5·06 4·69 5·50

Tb 1·49 0·893 0·658 1·05 0·793 0·861 0·892

Dy 8·44 6·02 4·00 6·95 5·05 6·36 5·95

Ho 1·63 1·26 0·870 1·57 0·966 1·41 1·18

Er 4·27 3·66 2·25 4·39 3·06 4·52 3·28

Tm 0·600 0·518 0·359 0·635 0·455 0·629 0·473

Yb 3·99 3·59 2·11 3·96 3·27 4·13 2·97

Lu 0·610 0·586 0·332 0·571 0·467 0·661 0·453

Pb 2·64 1·26 1·97 1·44 3·43 50·283 3·89

Th 1·35 0·158 0·103 0·610 1·57 0·094 0·154

U 0·440 0·077 50·003 0·145 2·69 0·015 0·337

calc, calculated; MtP, analyzed in Montpellier; Irk, analyzed in Irkutsk; SPb, analyzed in St Petersburg.


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Garnet abundance was restricted by the MnO content.Weintroduced the maximum reasonable amounts ofK-feldspar and pargasite to approximate the upper limitof K2O content. Average compositions of feldspars wereused in cases where the abundance of K-feldspar was hardto estimate. We adjusted the amount of apatite to agreewith the measured P2O5 content because apatite is pre-served even in strongly altered samples. The calculatedcompositions are presented inTable 3.The method above was applied to 16 samples.

Agreement between the calculated and observed valuesfor FeOt and Al2O3 is generally very good, particularlyafter the effect of LOI is taken into account. However,most samples have higher observed MgO contents thancalculated ones. This effect is particularly strong in thefeldspar-rich granulites and disappears in the least alteredmafic granulites (Uk35 and Uk37). Similarly, the observedK2O contents greatly exceed the calculated values inalmost all samples.

Trace element whole-rock compositionsMafic granulites generally show flat to somewhatLREE-enriched REE patterns with LaN/YbN¼1·0^21·3(Fig. 4). The highest REE contents occur in amphibolizedgranulite Uk11 and altered xenolith Kom11 (Table 3).Most samples lack Eu anomalies or have small negativeones (Eu/Eu*¼ 0·7^1·0). The feldspar-rich granulites Uk5,Y7 and Y53 have strongly fractionated REE patternsshowing LREE enrichment and HREE depletion withLaN/YbN¼15^41 (Fig. 4); their HREE concentrations(0·08^0·13 ppm Lul; Table 3) resemble those of the hostkimberlite (0·075 ppm Lu; Bogatikov et al., 2004). UsingLOI as a measure of alteration, a general increase in Sr,

Th, U and LREE is observed in all altered samples. No de-pendence of Eu anomaly with LOI is seen. Like K2O con-tents, Rb and Ba contents show two trends with moderateand strong enrichment with increasing LOI.Using modal analyses and average trace element con-

centrations in minerals, we have calculated the trace elem-ent composition of five mafic granulites (Uk1, Uk21,Uk35, Uk37 and Y6) and three feldspar-rich granulites(Uk5, Y7 and Y53), and compared the observed resultswith our calculated values (Fig. 5).The major LILE-bearing phase is plagioclase. Its Pb

and Sr contents make up 80^99% of total amount in therock, whereas its Rb and Ba account for 20^99%.Wherepresent, K-feldspar provides 10^70% of the bulk-rock con-centrations of Rb and Ba. We used the lowest Ba contentin K-feldspar (4008 ppm) for mafic granulites Uk21 andUk35, and Ba concentrations determined by energy-dispersive spectrometry for the other samples, which areof similar order to the highest LA-ICP-MS values. Thussome uncertainty with respect to the calculated Rb andBa contents remains. U and Th are distributed betweenclinopyroxene (10^50% of Th), plagioclase (5^70% of Thand 10^80% of U), apatite (10^60% of Th) and rutile(10^70% of U). Calculated concentrations of these elem-ents are comparable with the measured ones in most sam-ples, but much lower in the strongly altered xenoliths suchasY53 (Table 3).Clinopyroxene is the major host of Zr (30^70%) and Hf

(50^80%). Its Zr/Hf ratio varies between samples from13 to 32 and is lower than in the whole-rocks. Garnet hasa Zr/Hf ratio in the range of 39^113 but it hosts only3^9% of the bulk Zr. Rutile, if present, provides 8^14%of the Zr. We adjusted the quantity of zircon to agreewith both the measured Zr content and the Zr/Hf inthe whole-rock. Zircon provides 17^74% of the Zr contentin the bulk-rock analyses. Its Zr/Hf value varies from45 to 63. The inferred zircon abundances are realistic:0·001^0·010 vol. %. If zircon is excluded from thecalculations, Zr/Hf declines significantly from the mea-sured values. In samples Uk5, Y7 and Y53, the calculatedamount of Zr is higher by 40% than the observedone. This is due to the necessary introduction of zirconto maintain the observed Zr/Hf ratio and may relate tothe difficulty of fully dissolving zircon for the ICP-MSanalysis.Samples Y53 and Y7 show much lower calculated con-

centrations of Nb than their measured ones. Modallyaltered samples Uk1, Uk5, Y53 and Y7 also show variableenrichment in LREE and depletion in HREE incomparison with the calculated compositions. However, inthe less altered samples REE, Zr, Hf and Nb agree well.Assuming low initial La/Yb, addition of kimberliteplus alteration of the rock-forming minerals, includinggarnet, could cause extreme HREE depletion. We see

Fig. 4. REE patterns of whole-rock granulite xenoliths from theUdachnaya and Komsomolskaya kimberlite pipes, normalized tochondrite (Sun & McDonough, 1989).


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almost no alteration of garnet in thin-section (Fig. 2);however, alteration increases towards the xenolith edges,so we cannot avoid this completely in the bulk-rockpowders.

Sr, Nd and Hf isotopic resultsSr and Nd isotope analyses were made on two feldspar-richand seven mafic granulites (Table 4 and Figs 6 and 7).Analyses of Sr isotopes in samples Uk20 and Y6 were

Fig. 5. Comparison of observed and calculated trace element patterns in granulite xenoliths from the Udachnaya kimberlite pipe. Values arenormalized to the primitive mantle composition (Sun & McDonough, 1989).


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repeated and showed good agreement. Measured 87Sr/86Srvalues range from 0·7055 to 0·7087. However, samples Uk1and Uk5 with 87Sr/86Sr 40·708 have elevated LOI. Thepresent-day 143Nd/144Nd values of the xenoliths rangefrom 0·51099 to 0·51232 (i.e. mostly lower than the valuefor the host kimberlite). The sample showing the lowest

143Nd/144Nd value is the feldspar-rich granulite Uk5. Thehighest value belongs to mafic granulite Y6. From theweak correlation between 143Nd/144Nd and LOI, it followsthat the Sm/Nd ratio and Nd isotopes are much less af-fected by alteration and contamination. Leaching with2N HCl reduced Rb and Sr concentrations, Rb/Sr and

Table 4: Sr and Nd isotope compositions of granulite xenoliths from Udachnaya kimberlite pipe

Sample Sm

(ppm)

Nd

(ppm)

147Sm/144Nd 143Nd/144Nd �2s TDM

Nd

(Ma)

eNd,

360 Ma

Rb

(ppm)

Sr

(ppm)

87Rb/86Sr 87Sr/86Sr �2s eSr,

360

Ma

Uk1 whole-rock 4·41 18·5 0·1444 0·511633 3 3314 �17 53·6 1460 0·1060 0·708692 6 55

Uk5 whole-rock 3·73 22·7 0·0991 0·510992 4 2856 �28 33·3 1258 0·0764 0·708483 6 54

dry residue, 208C 1·47 9·01 0·0982 0·510989 4 32·5 1250 0·0751 0·708420 8

leachate, 208C 0·1019 0·510996 4 0·1410 0·708980 11

dry residue, 608C 2·12 8·68 0·1475 0·511525 6 24·6 1097 0·0649 0·708382 7

leachate, 608C 0·0982 0·510984 5 0·1515 0·708757 9

Uk20 whole-rock 3·05 12·8 0·1445 0·511956 5 2617 �11 11·6 859 0·0390 0·708232 7 53

Uk20* whole-rock 11·6 845 0·0398 0·708163 9 52

Uk21 whole-rock 4·18 15·6 0·1617 0·512279 4 2548 �5 5·27 200 0·0762 0·705509 6 12

dry residue, 208C 3·60 11·7 0·1853 0·512509 5 3·03 161 0·0544 0·704670 8

leachate, 208C 0·1037 0·511762 5 0·1704 0·707825 12

dry residue, 608C 3·53 11·6 0·1838 0·512510 6 2·62 166 0·0456 0·704633 7

leachate, 608C 0·1169 0·511866 6 0·1784 0·707446 8

Uk23 whole-rock 5·23 20·1 0·1574 0·512077 6 2889 �9 7·86 241 0·0943 0·706402 6 23

Uk35a whole-rock 2·18 9·15 0·1437 0·511737 5 3062 �15 23·0 706 0·0943 0·707971 8 46

dry residue, 208C 2·10 8·48 0·1493 0·511742 6 17·1 577 0·0855 0·707759 7

dry residue, 608C 2·11 7·95 0·1601 0·511809 6 9·65 417 0·0668 0·707606 6

Uk37 whole-rock 3·57 15·7 0·1372 0·511591 5 3091 �18 8·38 242 0·0999 0·705537 7 11

dry residue, 208C 3·61 14·3 0·1521 0·511748 5 3·76 161 0·0673 0·705219 9

dry residue, 608C 3·66 14·1 0·1567 0·511802 5 4·01 189 0·0613 0·705157 10

Y7 whole-rock 3·96 20·1 0·119 0·512318 3 1337 �3 24·1 1031 0·0675 0·705751 7 16

Y6 whole-rock 3·46 13·0 0·1605 0·512305 4 2411 �5 8·21 270 0·0879 0·705892 11 16

Y6* whole-rock 8·22 268 0·0886 0·705851 8 17

dry residue, 208C 2·78 9·28 0·1809 0·512528 3 6·69 234 0·0826 0·705440 9

dry residue, 608C 3·33 10·4 0·1942 0·512631 2 3·70 209 0·0513 0·705154 10

leachate, 208C 0·1103 0·511777 4 0·1339 0·708354 7

Y6a dry residue 6 g, 208C 3·02 10·4 0·1749 0·512455 3 2718 �3 6·74 236 0·0824 0·705508 11 12

Sample Lu

(ppm)

Hf

(ppm)

176Lu/177Hf 176Hf/177Hf �2s TDM

Hf

(Ma)

eHf, 360 Ma

Uk1 whole-rock 0·29 1·72 0·0239 0·282104 4 4074 �24

Uk5 whole-rock 0·07 6·13 0·0017 0·281117 2 3026 �54

Uk37 whole-rock 0·40 2·35 0·0238 0·282189 6 3772 �21

Y6 whole-rock 0·51 2·39 0·0301 0·282719 6 3328 �4

*Repeated analyses.


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Fig. 6. (a) 87Sr/86Sr vs 87Rb/86Sr and (b) 143Nd/144Nd vs 147Sm/144Nd, for whole-rock granulite xenoliths from the Udachnaya pipe. Data for thehost Udachnaya kimberlite are from Agashev et al. (2000), Shatsky et al. (2005), Rosen et al. (2006) and Kostrovitsky et al. (2007). Open symbols,leachates; filled symbols, residues.


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87Sr/86Sr ratios. Sm concentrations in the residues re-mained nearly constant but Nd concentrations decreasedand Sm/Nd and 143Nd/144Nd ratios increased (Table 4).Figure 7 shows the similarity between the Siberian granu-lite xenoliths (at 360 Ma) and those from other cratonicregions worldwide. The Siberian xenoliths are more en-riched in radiogenic Sr than those from the Arkhangelskkimberlite field in NW Russia (Markwick & Downes,2000). All of the Udachnaya granulites have eNd360values lower than the host kimberlite, and eSr360 valueslower than the local sedimentary carbonate rocks.Four samples (Uk1, Uk5, Y6 and Uk37) were analysed

for 176Hf/177Hf ratios. Their present-day eHf values rangefrom ^1·9 (Y6) to ^58 (feldspar-rich granulite Uk5), corre-lating with their 143Nd/144Nd values. Samples Uk1 andUk37 show very similar values of both eNd and eHf; thisfinding suggests that the high 87Sr/86Sr value for Uk1 isdue to alteration.

DISCUSS IONAre the granulite xenoliths from theDevonian lower crust?The Siberian kimberlites are well known for their abun-dant mantle xenoliths (Sobolev, 1974) as well as many

types of crustal xenolith. The entire crustal xenolith suitefrom several kimberlite pipes in the Daldyn and Alakitfields comprises a large variety of metamorphic rocksincluding Bt-, Hbl^Bt-, Opx-gneisses, felsic Grt-gneisses,schists, amphibolites, kinzigites and garnet-free granulitesin addition to the Grt-granulites. Pressure estimates forthe amphibolites and Hbl^Bt-gneisses (Shatsky et al.,2005) and for kinzigites (Koreshkova et al., 2009) do notexceed 0·8GPa. These estimates obviously reflect the con-ditions of a Palaeoproterozoic metamorphic event and donot correspond directly to the position of these rocks inthe modern crustal section. Drilling within these kimber-lite fields has shown that the surface of the basement inthis area (to a depth of 2·5^3·1km) is composed ofgarnet-free Cpx^Bt-, Hbl^Bt- and CrdÔpx-gneisses(Rosen et al., 2002). The nearest granulite outcrops lie sev-eral hundreds kilometers to the north, in the Anabarshield. These granulites include metasediments andmeta-igneous rocks ranging from komatiite to rhyolites incomposition. The mafic granulites are mostly garnet-free(Luts & Oksman, 1990).However, the thermal history of presumed upper crustal

and lower crustal rocks diverges significantly. The crustalrocks as a whole have recorded several metamorphicevents during the Palaeoproterozoic collision of the

Fig. 7. eSr vs eNd for whole-rock granulite xenoliths from Udachnaya compared with other lower crustal xenolith suites from Precambrianareas. Data sources: Arkhangelsk, Markwick & Downes (2000); Kola, Kempton et al. (2001); South Africa, Huang et al. (1995); ColoradoPlateau, Chen & Arculus (1995); northern Scotland, Halliday et al. (1993); Snake River Plain, Leeman et al. (1985). BSE, Bulk Silicate Earth.


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Magan and Daldyn^Markha terranes. No thermal eventsare known in them since the Paleoproterozoic metamorph-ism until the kimberlite eruption. Sm^Nd mineral iso-chron ages determined for schists and gneisses present asxenoliths are from 1880�30 Ma to 1840�70 Ma, whereasthe Grt-granulite xenoliths yield much younger ages from1756�6 Ma to 1627�18 Ma (Neymark et al., 1992; Rosenet al., 2006). Regarding these values as cooling ages, thispoints to a longer residence of the garnet granulites at ele-vated temperature in comparison with the upper tomiddle crustal gneisses and schists, suggesting derivationfrom a deeper crustal level.Moreover, in the Grt-granulite xenoliths, the U^Pb age

of the final metamorphic zircon generation is youngerthan the Sm^Nd mineral isochron ages of the schists andgneisses (Koreshkova et al., 2009). Inclusions of pyroxeneand plagioclase in this zircon have compositions identicalto these minerals in the granulites. From the REE compos-itions of zircon and clinopyroxene, we know that theywere in equilibrium with garnet and plagioclase. We canconclude that the growth of these minerals occurredduring this final metamorphic episode at 1·81^1·83 Ga.However, inclusions in earlier formed metamorphiczircon (samples Y7 and Y53) point to higher P^T condi-tions during an event at about 1·90 Ga (zircon ages fromKoreshkova et al., 2009) and provide evidence forlong-term residence within the lower crust.We do not consider the appearance of pargasite as an in-

dependent, superimposed event. Such an event wouldhave led to the formation of a new zircon generation; how-ever, metamorphic zircons from amphibolized granuliteUk11 yield the same age of 1831�16 Ma (Koreshkovaet al., 2009).

P^T estimates and zoning in mineralsPetrographic observations point to garnet growth andpossible plagioclase consumption. The decrease ofMg-number in the rims of garnet grains may be due togrowth with decreasing temperature and/or diffusional ex-change with pyroxenes during cooling. The rate of Ca dif-fusion in garnet is comparable with, or lower than, that ofFe and Mg (Freer & Edwards, 1999). In the case of theslower rate, garnet may preserve growth zoning. The in-crease in CaO from cores to rims may be the result ofgarnet growth at the expense of plagioclase, but this isnot linked to the appearance of pargasite as seen fromamphibole-free granulites (e.g. Y59). The strong Al andMg^Fe zoning in pyroxenes was also formed during theirgrowth under conditions of decreasing temperature.Diffusional exchange of Mg and Fe would lead to the de-velopment of narrower rims in clinopyroxene than ingarnet owing to slower rates of diffusion in clinopyroxene(Duchene & Albare' de, 1999). This is directly opposite tothe observed large difference between Mg-numbers ofcores and rims in clinopyroxene in comparison with

garnet. Diffusional exchange could make a minor contri-bution to the Mg^Fe zoning.The difference in trace element contents between cores

and rims of garnet grains is weak relative to some growthzoning examples (Pyle et al., 2001; Rubatto & Hermann,2003; Whitehouse & Platt, 2003) in which it is up to anorder of magnitude. Clinopyroxene has slightly moreprominent zoning.Taking into account the slower diffusionrates of trivalent elements in comparison with divalentelements in garnet and that those in clinopyroxene areeven slower (Van Orman et al., 2002), it is probable thatthe zoning was formed during mineral growth. The de-crease inYand HREE within clinopyroxene rims may re-flect their growth together with garnet. We suggest thatthe zoning in minerals was formed during their growthunder decreasing temperature conditions but we cannotexclude the possibility that some modification of the Mg^Fe zoning in the garnet grains was caused by diffusionduring the cooling stage.The complementary character of the trace element pat-

terns in all the minerals, and in their cores and rims, indi-cates that they were in mutual equilibrium. The majorand trace element compositions of the cores of differentgrains of a single mineral species are similar to eachother. The cores of the largest porphyroblasts differ signifi-cantly from the previously existing garnet and clinopyrox-ene found as inclusions in zircon. These cores are likely toapproach the compositions at the beginning of their forma-tion. The growth of the minerals could have occurredduring the last metamorphic event, including subsequentcooling, which is reflected in the rim compositions.P^T estimates demonstrate cooling of 100^2008C from800^8908C with only a minor decrease in pressure from0·9^1·2GPa to 0·8GPa. The lower temperatures obtainedfor average cores in medium-grained rocks in comparisonwith coarse porphyroblasts probably reflect partial hom-ogenization of Mg^Fe zoning in garnet grains.

Factors influencing the compositionof the xenolithsTo some extent the trace element concentrations in theminerals must reflect the whole-rock compositions. For ex-ample, low Cr in bulk-rock Uk1 is confirmed by its lowcontent in the minerals from this sample. At the sametimeYand HREE contents in garnet are inversely propor-tional to garnet abundance in the xenoliths. In samplesUk37, Uk21 and Y6, which have almost identicalwhole-rock compositions, Y concentrations in garnet de-crease from 194 ppm to 99 ppm as the amount of garnet in-creases from 10 to 25%. Both the difference in traceelement composition of a mineral between samples and itsdependence on mineral abundance allow us to exclude thepossibility of distortion of mineral modes during samplingby the host kimberlite or metamorphic layering as factorsinfluencing the bulk-rock composition. The same


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conclusion follows from covariations of elements in thebulk-rock compositions. FeOt and Al2O3 correlate inverse-ly, which cannot be due to enrichment in garnet. Also, if il-menite enrichment is suggested, and ilmenite from thesexenoliths contains 1^6 ppm Zr, there should be an inversecorrelation of Ti (or V) and Zr that is opposite to theobserved trend.Petrographic investigations indicate that the granulite

xenoliths interacted with the host kimberlite magma. Totake this into account, we have calculated bulk compos-itions from the modal mineralogy and mineral chemicaldata. We obtain good agreement between the measuredand calculated compositions for the least altered samplesUk21, Uk35 and Uk37. In the moderately altered rocks,the calculated compositions have lower MgO and K2Oand higher SiO2, CaO and Na2O contents than the mea-sured ones, but the concentrations of high field strengthelements (HFSE) and REE agree remarkably well (e.g.Y6), given the uncertainties in the mineral proportions ofthe minor phases that host these elements (Fig. 5). The cal-culated compositions hence closely approach the compos-itions of the unaltered rocks. Feldspar-rich granulites Y53and Y7 are more altered than the other xenoliths. Theyhave much lower calculated concentrations of Nb, Th andU than their measured values, pointing to kimberlite con-tamination. However, the observed contents of Rb andsometimes Ba and Sr in all samples (Fig. 5) are severaltimes higher than the calculated ones. This cannot be dueto the uncertainties in K-feldspar modes and its compos-ition, and indicates that the xenoliths have beencontaminated.Leaching is a widely applied method to remove contam-

ination but it is possible both to dissolve the alterationproducts and to distort the mineral abundances in alteredsamples. Compared with the analysis of the unleached ma-terial of sample Uk35, there was a negligible effect on themajor elements after leaching with 0·1N HCl (Uk35a,Table 3). For trace elements the main effect was in reducingthe Sr content from 630 ppm to 564 ppm (Table 3, Fig. 5),presumably as small amounts of Sr-bearing calcite wereremoved.The REE and other trace elements were general-ly unaffected. The measured Ba content does not differ sig-nificantly from the calculated one but the concentrationsof Rb and Sr in the primary minerals cannot provide themeasured whole-rock values. Leaching with 0·1N HCl istherefore insufficient to completely remove intergranularcarbonate films and an inferred Rb-bearing secondarymineral.Another sample, the fresh-looking granulite Y6, was

leached with 2N HCl; this resulted in reduced Rb, Sr andLREE contents. The Ba content was not changed but themeasured Ba, Rb and Sr (to a lesser extent) concentrationsare higher than the calculated values. Nevertheless, thedifference in REE, Zr and Nb between unleached,

leached (Y6a) and calculated compositions is small(Table 3, Fig. 5).The Eu/Eu* ratio is unchanged. It is prob-able that an intergranular material was dissolved, ratherthan the rock-forming minerals or their alterationproducts.The effect of leaching samples with 2N HCl for isotopic

study is to reduce Rb and Sr concentrations, and Rb/Srand 87Sr/86Sr ratios. Residues from leaching at 608C ex-hibit lower values than those processed at room tempera-ture. The 87Sr/86Sr ratios in the leachates are higher thanin the unleached samples and the Udachnaya kimberlite.The lines ‘residue^whole-rock^leachate’ show steeperslopes for experiments at 208C than at 608C (Fig. 6a). Thechange in the slopes demonstrates that different propor-tions of components entered the solutions at 208C and608C. At room temperature a component relatively richin Rb and radiogenic Sr was preferentially dissolved.Samples Uk21 and Y6 exhibit steeper slopes than Uk5.Moreover, the slopes correspond to an age older than 1·8Ga [i.e. older than the Sm^Nd mineral isochron ages ob-tained for the the granulite xenoliths from Udachnaya(Neymark et al. 1992; Rosen et al., 2006)], which is clearlyimpossible. The dissolved component hence is not arock-forming feldspar. Also, it clearly differs from the kim-berlite and may have a crustal origin. One possible sourceis the local limestone country rocks around the pipe. Thekimberlite intrusion could have mobilized a fluid fromthese sedimentary rocks that reacted with the kimberliteand the xenoliths. The leachate points plot between thesedimentary carbonate composition and the kimberlite.The mafic granulites have significantly lower Rb and Srcontents than the feldspar-rich granulite Uk5. Thus thiscomponent may have affected the composition of Sr iso-topes in them more strongly than in Uk5 and caused thesteeper slopes. No age information can be obtained fromthe Rb^Sr data, but they do show that the samples aredivided into two groups with higher and lower present-day87Sr/86Sr ratios (Fig. 6a).In the leached residues, Sm concentrations remain

nearly constant but Nd concentrations decrease, whereasSm/Nd and 143Nd/144Nd ratios increase in comparisonwith the unleached samples. In feldspar-rich granuliteUk5, the residue after leaching at 208C and the leachatehave isotope ratios almost identical to the whole-rock.This implies no preferential dissolution of a componentresponsible for the Nd isotope composition of the rock.In this sample, the major Nd-bearing phases are diop-side (50% of Nd) and apatite (40% of Nd). At 608Csignificant amounts of these minerals dissolved, and theresidue moved towards higher 143Nd/144Nd and147Sm/144Nd values, in the direction of the probable garnetcomposition (Fig. 6b). The slope of the line ‘residue^whole-rock^leachate’ corresponds to an age of 1·67 Ga,similar to the mineral isochron age (Neymark et al., 1992).


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No kimberlite contamination is seen for this sample, butcontamination with carbonate country-rocks could havebeen missed owing to the low concentrations of Sm andNd in them (1·8 and 10 ppm respectively; Agashev et al.,2000).The residues of the other samples are also displaced

towards higher 143Nd/144Nd and 147Sm/144Nd values(Fig. 6b). The lines ‘residue^whole-rock’ show variousslopes corresponding to ages of 0·70^1·64 Ga.The shallow-est slope is observed in sample Uk35a, revealing some con-tamination by the host kimberlite or country-rocks orboth. In samples Uk21 and Y6, 143Nd/144Nd and147Sm/144Nd values for the leachates are lower than in thewhole-rocks, sedimentary carbonate and Udachnaya kim-berlite. The slopes of the lines ‘residue^whole-rock^leach-ate’ are slightly shallower than in Uk5 and reflect a minorcontribution of contamination to the leaching isochrons.

143Nd/144Nd values show a positive correlation with147Sm/144Nd (Fig. 6b) excluding sample Y7, which is dis-placed towards the kimberlite field. The contaminationwith kimberlite also explains the excess Nb, La, Rb, Ba,Sr, Th and U in its measured composition in comparisonwith the calculated one (Table 3).Shatsky et al. (2005) also performed leaching experi-

ments for three strongly altered granulite xenoliths fromthe Udachnaya and Leningradskaya pipes, using 6N HCl.For one sample an approximation to a mineral isochronwas obtained.Two other samples demonstrated strong con-tamination with kimberlite and the possible presence ofan additional component that we believe may originatefrom the sedimentary country rocks.

The composition of the protolithsMost of the mafic granulite xenoliths share similar com-positional characteristics, with high contents of MgO andFeOt (6·4^8·6wt % and 11·5^16·2wt % respectively inthe calculated compositions), a narrow range of Al2O3

and CaO contents, and common trends on variation dia-grams (Fig. 8). Six samples deviate from these trends,having higher Al2O3 and lower FeO and TiO2 at a givenMg-number. Three of these samples are feldspar-richgranulites, whereas the others are amphibolized granulitesand mafic granulite Uk35. A larger group of Fe-rich rockscan thus be distinguished within the suite (samples Uk1,Uk20-23, Uk37, Y5, Y6, Y52, Y54-62, 286/78 and Kom70).Many granulite xenoliths from the same locality reportedin the literature compare well with these Fe-rich rocks.Wehave selected five analyses with LOI51·2wt % from thework of Solov’eva et al. (2004) for comparison. Trace elem-ent data are available for three of these samples.Unfortunately, it is not possible to use the data of Shatskyet al. (2005) because their analyses were recalculated on awater-free basis.The low Mg-numbers (0·42^0·52) of the Fe-rich rocks

suggest that they are not primary mantle-derived melts.

In these rocks, MgO and Al2O3 decrease and FeOt andTiO2 contents increase strongly with decreasingMg-number (Fig. 8). These variations are consistent withcrystallization from evolved melts that followed a tholeiiticdifferentiation trend. In Figs 8 and 9, we have comparedthe xenoliths with gabbros from slow-spreading mid-oceanridges (Coogan et al., 2001), arc lower crustal complexes(Garrido et al., 2006; Greene et al., 2006) and variousFe-tholeiitic magmas: continental flood basalts (Farmer,2003), Proterozoic passive margin magmatic complexes(Nykanen et al., 1994; Ivanikov et al., 2008) andPaleoarchean volcanic rocks (Smithies et al., 2009). TheFe-rich xenoliths can be distinguished from arc gabbrosand granulites by their higher MgO and TiO2 and lowerAl2O3 at a given Mg-number. Their MgO content ishigher than in MOR gabbros, and they are significantlyricher in LREE and HFSE than arc and MOR gabbros.Their trace element concentrations are similar to those ofFe-tholeiites except for Rb,Th and U.The REE patterns of the Fe-rich granulites (Fig. 4) are

smooth, with low negative slopes and absent or smallnegative Eu anomalies (LaN/YbN¼1·0^4·2, LaN/SmN¼1·0^2·9, Eu/Eu*¼ 0·9^1·1). Incompatible elementcontents increase with decreasing Mg-number (Fig. 9);this may be explained by enrichment in a melt with pro-gressive differentiation. Most samples have La/Nb ratiosin the range 0·5^0·8, but in a few samples (excluding thestrongly altered ones) this ratio is 1·1^1·8. Some of themost Fe-rich rocks have a stronger Eu anomaly (Eu/Eu*¼ 0·7^0·8) and high V and Ti contents, similar tomagnetite-rich Fe-dolerites from differentiated Kareliansills (Ivanikov et al., 2008). According to experimentaldata (Villiger et al., 2007), fractional crystallization leadingto strong Fe enrichment is achieved at pressures50·8GPa.We therefore suggest that these Fe-rich rocks were formedin relatively shallow intrusions.Basic granulite Uk35 is characterized by a higher Al2O3

content and Mg-number (0·65) and lower FeOt and TiO2

in comparison with the Fe-rich granulites (Fig. 8). It hashigher Cr, much lower HFSE and Ycontents (Fig. 9), anda lower (10^20 times chondrite), slightly fractionated REEpattern (LaN/YbN¼1·8, LaN/SmN¼1·2, Eu/Eu*¼ 1·0).The composition of both major and trace elementsmatches those of primitive basaltic melts. Similar compos-itions can be found among previously published data forthe granulite xenoliths (Solov’eva et al., 1994, 2004;Shatsky et al., 2005), although those samples are suspectedto be more altered.The compositions of amphibolized granulites Uk4 and

Uk11 correspond to gabbros. They have higher calculatedAl2O3, Na2O and K2O and lower MgO and FeOt thanthe other basic granulites. Sample Uk4 has a smooth,LREE-enriched REE pattern (LaN/YbN¼ 6·9, LaN/SmN¼ 2·7, Eu/Eu*¼ 0·9). It is depleted in HFSE, which


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may reflect the characteristics of its source. It is similar inZr/Y, La/Nb and Sm/Nd to the feldspar-rich granulitesand Mg-rich granulite Uk35 (Fig. 10). Sample Uk11 hasmuch higher LREE, Rb, Ba, Th and U contents andseems to be contaminated with the host kimberlite.

The calculated compositions of the feldspar-rich granu-lites Uk5, Y7 and Y53 are poorer in MgO and FeOt andricher in Al2O3 and alkalis than the basic granulites.They resemble leucogabbros and diorites in major elementcomposition. However, they have smooth, strongly

Fig. 8. Whole-rock major element variations (wt %) vs Mg-number [100MgO/(MgOþFeOt) calculated on a molar basis] for Siberian granu-lite xenoliths (Udachnaya and Komsomolskaya kimberlite pipes), xenoliths from the Baltic Shield, gabbroic complexes from island arc terranesand mid-ocean ridges and continental flood basalts. Data sources: Fe-rich granulites, this study (calculated and measured compositions withLOI 52wt %) and Solov’eva et al. (2004); altered Fe- rich granulites, this study; Mg-rich granulite Uk35, amphibolitized granulites andfeldspar-rich granulites, this study; Fe-rich granulites from the Baltic Shield, Ho« ltta« et al. (2000) and unpublished data on xenoliths from theKola Peninsula (Koreshkova); Paleoarchean Fe-rich basalts, Smithies et al. (2009); Fe-dolerite differentiated sill, NW Russia, Ivanikov et al.(2008); Fe-dolerite dyke complex, eastern Finland, Nykanen et al. (1994); continental flood basalts, Farmer (2003); gabbros from the SouthwestIndian Ridge, Coogan et al. (2001); gabbronorites of the Talkeetna arc section, Greene et al. (2006); gabbroic rocks of the Kohistan arc section,Garrido et al. (2006).


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fractionated REE patterns (LaN/YbN¼ 5·3^19·1,Eu/Eu*¼ 0·8^1·2) and thus differ from xenoliths ofgabbroânorthosite composition (Solov’eva et al., 2004;Shatsky et al., 2005) and other plagioclase-rich intru-sive rocks. These granulites are enriched in LILE

(calculated contents) and depleted in HFSE. Their traceelement patterns are similar to that of amphibolizedgranulite Uk4. Their Mg-numbers (0·49^0·53), and lowMgO and Cr contents suggest that they cannot be primarymantle melts.

Fig. 9. Whole-rock trace element variations vs Mg-number [100MgO/(MgOþFeOt) on a molar basis] for Siberian granulite xenoliths(Udachnaya and Komsomolskaya kimberlite pipes), xenoliths from Baltic Shield, gabbroic complexes and continental flood basalts. Symbols,fields and data sources as for Fig. 8.


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Crystal fractionation, partial melting andamphibolizationThe compositions of protoliths to the granulites that wehave reconstructed are those of rocks that experiencedgranulite metamorphism at about 1·8 Ga, by which timethey had already low Rb, Th and U contents. The deple-tion in these elements may reflect partial melting of granu-lites. In this case an important question is whether theobserved compositional variations are due to this process.In the Fe-rich granulites, Nb increases with increasing Ycontent. A restite from partial melting should thereforecontain garnet and ilmenite or rutile. However, Y is alsoproportional to Zr and Nd (and other LREE) and inverse-ly proportional to Sm/Nd as expected in evolving melts.In Fig. 10 most Fe-rich granulites show variations in Sm/Nd at nearly constant La/Nb, which is least dependent oncrystal fractionation but most sensitive to contamination.Partial melting would increase Sm/Nd and decreaseLa/Nb in restites. The plausible presence of garnet in therestite allows us to suggest production of a trondhjemite-like melt and to calculate these ratios in restites frombatch melting. Sample Uk37, with a relatively high LREEcontent, and an Fe-rich Archaean basalt (Smithies et al.,2009) were taken as the initial compositions.The set of dis-tribution coefficients reported by Smithies et al. (2009) wasused. The degree of melting cannot exceed 10^15% tomaintain the calculated Rb contents and LaN/YbN andLaN/SmN ratios �1. The calculated restites show a nar-rower range of Sm/Nd and a steeper decrease of La/Nbthan the granulites. Moreover, in the latter, Y content in-creases with decreasing Sm/Nd. Hence, the observed vari-ations of trace elements, except for LILE, Th and U, aremore consistent with crystal fractionation.

Amphibolization could make its own imprint on thewhole-rock compositions. Calculations demonstrate thatamphibole contributes mainly Rb and Ba. Amphibole-bearing Fe-rich granulites have the same low calculatedRb concentrations as the amphibole-free rocks.Amphibole-rich granulites Uk4 and Uk11 cannot beamphibolitized Fe-rich rocks because the amphibole isricher inTi and Nb than the clinopyroxene that it replaces.ThusTi- and Nb-poor rocks like these cannot be produced.There is no clear evidence of metasomatism linked withthe appearance of pargasite, unlike in the lower crustalxenoliths from the Kola peninsula (NW Russia) where en-richment in some elements has been linked to pargasiteand phlogopite introduction (Kempton et al., 2001).

Age and origin of the protoliths to thegranulites143Nd/144Nd values show a positive correlation with147Sm/144Nd values (Fig. 6b) excluding sample Y7. Thistrend can be considered as a disturbed isochron corres-ponding to an age of 3·02�0·62 Ga. An initial eNd valueof three has been determined for this trend.The ages of os-cillatory zoned zircon cores are up to 3·15�0·11 Ga formafic granulite Uk1 (Koreshkova et al., 2009), similar toits TDM Nd model age. The age inferred from the trend onthe Sm^Nd diagram does not contradict these data. Theunexposed Markha terrane is composed of a granite^greenstone association, formed at 3·3^2·5 Ga (Rosen et al.,2000; Pisarevsky et al., 2008). Thus the lower crustal rocksrepresented by the xenoliths could have formed as a partof the crust of this terrane.TDM Hf model ages are in the range 3·0^4·0 Ga, eHf (at

3·0 Ga) varies from þ3 to ^7. TDM Nd model ages formost of the xenoliths range between 2·4 and 3·3 Ga(Table 4). The youngest value of 1·3 Ga is meaningless, asit is from the contaminated sample Y7. Rosen et al. (2006)and Neymark et al. (1992) reported TDM Nd model agesaround 2·5^2·6 Ga for the granulite xenoliths fromUdachnaya. Data reported by Shatsky et al. (2005) alsodemonstrate that the model ages became younger owingto kimberlite contamination.Udachnaya granulites show a general similarity to lower

crustal xenoliths from Precambrian regions worldwide interms of their Sr^Nd isotope compositions (Fig. 7). At thetime of formation the rocks yield positive eNd values,with eSr in the range of 12^59. Low concentrations of Rbrequire its removal by a small-degree partial melt. It isgenerally accepted that the lower crust is severely depletedin heat-producing elements (Rudnick & Gao, 2003).Bolhar et al. (2007) have demonstrated that this is necessaryto form a stable crust. They proposed that Archaeanlower crustal rocks of theWyoming craton lost these elem-ents by partial melting during Palaeoproterozoic meta-morphism or earlier. In our case, if partial melting tookplace, it must have occurred before the last metamorphic

Fig. 10. Whole-rock La/Nb variations vs Sm/Nd for Siberian granu-lite xenoliths (Udachnaya and Komsomolskaya kimberlite pipes).Symbols and data sources as for Fig. 8. Lines with bars representtrends for restites from partial melting. The numbers next to the barsindicate the degree of melting.


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event at 1·8 Ga. Assuming 10% batch melting and usingthe calculated Rb and Sr concentrations and isotopic datafor leached residues, calculations of eSr for a two-stageevolution give values of 10^22 for the Fe-rich rocks and46^56 for samples Uk35 and Uk5 (Fig. 7). The enrichmentin radiogenic Sr of the latter may be an artefact if leachingwas not sufficient or may be evidence for an initial enrich-ment in Rb.Overall, within the suite of xenoliths studied, we have

two groups of rocks with contrasting geochemical charac-teristics: Fe-rich rocks, with low La/Yb and La/Nb, andhigh Sm/Nd; and basic to intermediate rocks with higherLa/Yb, La/Nb and Sr/Nd, and lower Sm/Nd.Contamination with crustal material could be suggestedfor the magmatic protoliths of the latter group; however,sample Uk35 has very low incompatible element contents,high Cr and MgO and initial eNd¼1·7. Because it is mostsimilar to a primitive basalt in composition its characteris-tics probably reflect those of its source and are typical forsubduction-related magmas. This may point to significantcrust production within subduction systems in Archaeantimes. Evolved Fe-tholeiites may form an important partof the lower crust of the studied area and the lower crustof ancient platforms in general. Very similar xenolithsfrom the Lahtojoki kimberlite pipe in eastern Finlandwere reported by Ho« ltta« et al. (2000). A few xenoliths fromthe Kola Peninsula (NW Russia) share the same features(M. Koreshkova, unpublished data). The significance ofFe-basalts of similar composition in the Paleoarcheancrust has been discussed by Smithies et al. (2009), whonoted their similarity to volcanic rocks from other green-stone belts and considered them as a source for the tonal-ite^trondhjemite^granodiorite series. This suggestsincorporation of shallow intrusive or volcanic rocks intothe lower crust.

CONCLUSIONSGranulite xenoliths from the Udachnaya andKomsomolskaya kimberlite pipes are considered to repre-sent samples of the lower crust beneath the Markha ter-rane within the Siberian craton. The observed mineralassociation was formed during a granulite-facies meta-morphic event at about 1·8 Ga followed by subsequentcooling and minor amphibolization of the granulites.The reconstructed bulk-rock compositions correspond to

those of the granulites at 1·8 Ga. By that time the granu-lites had lost Rb, Th and U, which could be the result ofsmall-degree partial melting. Partial melting, however,does not explain the observed variations in major andtrace elements, which are more consistent with a processof crystal fractionation. No clear evidence of metasoma-tism linked with amphibolitization has been found.However, the xenoliths have been variably enriched inLILE, LREE, Th and U, and in certain cases Nb, owing

to interaction with the host kimberlite, as demonstratedby leaching experiments and the calculated compositions.The Rb and Sr isotopic compositions provide evidence forinteraction with local sedimentary rocks in addition tokimberlite contamination.The reconstructed protoliths are divided into two groups

with contrasting geochemical characteristics: Fe-richrocks, with low La/Yb and La/Nb, and high Sm/Nd; andbasic to intermediate rocks with higher La/Yb, La/Nband Sr/Nd, and lower Sm/Nd. The Fe-tholeiitic rocks arerelated by crystal fractionation and are geochemicallysimilar to continental flood basalts and basalts withinArchaean greenstone belts. The abundance of these granu-lite xenoliths within the host kimberlites suggests that theycould be an essential component of the Archaean crust ofthe Markha terrane. The other xenoliths have characteris-tics of subduction-related magmas, which could suggestsignificant crust production within subduction systems inArchaean times. The magmatic protoliths of these rocksmust be older than 1·94 Ga according to dating of meta-morphic zircon. Based on U^Pb ages of zircon cores, TDM

Nd and Hf model ages and a Sm^Nd disturbed isochron,the protoliths were formed at about 3 Ga.

ACKNOWLEDGEMENTSWe thank Dr A. Beard and Dr A. Carter (BirkbeckCollege) for assistance with microprobe and laser ablationanalyses, Dr J.-L. Bodinier for ICP-MS analyses atMontpellier, Dr G. A. Oleynikova for ICP-MS analyses atSt Petersburg and discussion of the techniques, Dr E. S.Bogomolov for Sr and Nd isotope analyses, Dr A. K.Saltykova for assistance with sample preparation, Dr L.V.Solovjeva for discussion and providing sample 286/78, andDr I. Millar for analysing the Hf isotope compositions.We are grateful to Dr L. P. Nikitina (with whomwe startedthis work) for her constant support and guidance. We ac-knowledge the detailed reviews of R. L. Rudnick, W. L.Griffin and A. Ulianov.

FUNDINGThe research was supported by funding from the RoyalSociety (a Joint Project Grant) and Russian Foundationfor Basic Research (grant 07-05-00974-a;). Hf isotope ana-lyses were supported by a NERC Isotope FacilityGrant-in-kind.

SUPPLEMENTARY DATASupplementary data are available at Journal of Petrology

online.


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http://petrology.oxfordjournals.org/cgi/content/full/egr033/DC1


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Petrology and Geochemistry of Granulite Xenoliths from Udachnaya and Komsomolskaya Kimberlite Pipes, Siberia