~, • LITHOS

ELSEVIER Lithos, 34 (1995) 61-88

Magma differentiation and mineralisation in the Siberian continental flood basalts

C.J. Hawkesworth a, P.C. Lightfoot b, V.A. Fedorenko c, S. Blake a, A.J. Naldrett d, W. Doherty e, N.S. Gorbachev f aDepartment of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, UK bOntario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 6B5 CTsNIGRL 129B VarshavskoyeSh., Moscow 113545, Russia dDepartment of Geology, University of Toronto, Toronto, Ontario, Canada, M5S 1A 1 CGeological Survey of Canada, 501 Booth St, Ottawa. Canada, KIA OE8 flnstitute for Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, Russia Received 1 November, 1993, revised version accepted 28 March, 1994

Abstract

New major, trace element and Sr and Nd isotope data are presented for selected lavas from the three uppermost formations in the Siberian Trap, and on over 60 samples of the associated intrusive rocks. The lavas from a 1400 m section are remarkably homogeneous and, apart from four samples of basaltic andesites, SIO2=48.4-49.6%, MgO= 8.1-6.3%, and Mg°= 54-58, TiO2= 1.05-1.6%, esr= 1-7 and end= 3.8-1.3. There is no significant deple- tion in Ni and Cu, or coupled increase in SiO2 and La/Sm, which so characterise the underlying Nadezhdinsky formation rocks. The intrusive rocks are considered in 5 groups, following Naldrett et al. The alkaline rocks (Group 1 ), dolerites with a range of Ti contents (Groups 2 and 3), and differentiated intrusions not associated with ore junctions (Group 4), all exhibit restricted initial esr and eNa values of 3-32 and 3.5 to -3.2, respectively. In contrast, the intrusions related to ore junctions (Noril'sk- and Lower Talnakh-types, 5A and 5B) trend towards higher esr and lower end, with esr= 17-59 and end 2.9 to --3.4 in the Norirsk-type, and 41-66 and -3.7 to -6.2 respectively in the Lower Talnakh-type. The roles of crustal contamination and partial melting in the continental mantle lithosphere are briefly reviewed. A minimum of three components are required to explain the basalt data, which are therefore inconsistent with simple mixing between plume derived magmas and crustal material. Rather, magmas were derived from both the mantle lithosphere and the underlying asthenosphere, and crustal contami- nation modified the composition of specific magma types. The minor and trace element characteristics of the contaminant appear to have been similar to those of an inferred deep-seated crustal melt, rather than an upper crustal melt, or a bulk sediment. The between-suite variations in the intrusions are similar to those in the lavas but, in addition, there are within-suite variations attributed to late stage, open system differentiation within the Noril'sk and Lower Talnakh-type intrusions. In the preferred model in which sulphide precipitation occurred in response to the crustal contamination processes responsible for the elevated La/Sm and lower end of the Lower Talnakh and Nadezhdinsky rocks, sulphide precipitation took place before the crystallisation of the silicate phases currently preserved in the intrusive rocks.

1. Introduction basalts have demonstrated that they may be sub- divided into chemically defined magmatic units. A number of recent studies of continental flood These may be mapped out over large areas, and

0024-4937/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI0024-4937(94)00033-6 62 C.J. Hawkesworth / Lithos 34 (1995) 61-88 at least in some instances they appear to repre- volatile-absent melting of major element de- sent chronostratigraphic units. Thus, they have pleted peridotite (Turner and Hawkesworth, been used to investigate chemical changes with 1995, and references therein). In the context of time in the evolution of individual magmatic tectonic models for melt generation, it is striking provinces, and to show how these changes may that the Deccan CFB have well established fast be used to constrain models of magma genera- eruption rates (Courtillot et al., 1988), and un- tion and differentiation (Watts and Cox, 1989; contaminated magmas similar to those of the as- Peate et al., 1990). The Siberian Trap is of par- sociated Reunion hot spot (the Ambenali For- ticular interest both because of the considerable mation, Mahoney, 1988 ). In contrast, the Paran~i thickness of lavas preserved (~ 4000 m), and lavas were erupted over ~ 10 Ma (Turner et al., because of the mineralisation associated with 1994) and there is no compelling evidence for a contemporaneous intrusions. This paper pre- significant contribution from melts similar to sents new data on selected samples of the younger those associated with the Tristan da Cunha hot lavas, and a number of the intrusive suites, and spot (Peate et al., 1990, 1992; Hawkesworth et seeks to evaluate the relationship between the in- al., 1992). Such data are consistent with melt trusive and extrusive rocks, and the nature of the generation in the Deccan being triggered by the contamination processes which appear to have emplacement of the Reunion hot spot, and that been responsible for the sulphide mineralisation. in the Paran~i being triggered by lithospheric ex- The origins of continental flood basalts (CFB) tension over the area of the Tristan hot spot have been the subject of considerable debate. In (Richards et al., 1989; White and McKenzie, general, the large volumes of magma, and the 1989; Hawkesworth and Gallagher, 1993 ). The clear association between many of the Mesozoic Siberian CFB may be too old for precise mea- CFB and hot spot traces on the ocean floor, in- surements of eruption rates, but it is important dicate that the majority were generated in the to establish whether the associated mineralisa- presence of a mantle plume. However, many CFB tion primarily reflects magma source regions, and have major, trace element and radiogenic iso- the causes of melt generation, or the nature of tope compositions which are different from those potential contaminants in that segment of the of oceanic basalts, and there is increasing evi- continental crust. dence for differences in chemical composition, and eruption rates, between CFB in different provinces. Crustal contamination has signifi- 2. Background geology cantly modified the compositions of mantle de- rived magmas in many areas, and Arndt et al. The Siberian Trap basalts are located on the ( 1993 ), for example, have sought to attribute the Siberian platform, which is dominated by Ar- differences between CFB and oceanic basalts to chaean to Lower Proterozoic gneisses and crys- different crustal contamination processes acting talline schists overlain by Ripheian sediments on plume-related magmas. Others, however, have and volcanics. The platform is surrounded by argued that (i) the effects of crustal contamina- major faults to the north and west, and the No- tion can be evaluated and stripped off and (ii) ril'sk region lies close to a possible triple junc- in some areas the uncontaminated magmas have tion at the northwestern margin of the Trap. In major, trace element and radiogenic isotope the western part of the platform, lower Palaeo- compositions which reflect distinct source re- zoic dolomites, limestones and argillites of ma- gions in the sub-continental mantle. Many CFB rine origin are overlain by extensive Devonian have low Na20, F%O~, TiP2 and high SiO2 at calcareous and dolomitic marls, dolomites and 8% MgO, relative to oceanic basalts (Hergt et al., sulphate-rich evaporites and lower Carbonifer- 1991; Turner and Hawkesworth, 1995). Such ous shallow water limestones. These are uncon- differences are not readily explained by crustal formably overlain by the middle Carboniferous contamination of plume-related melts, but they to upper Permian Tungusskaya series composed are consistent with the experimental data for oflagoonal and continental sediments, including CJ. Hawkesworth / Lithos 34 (1995) 61-88 63 siltstone, sandstone, conglomerate and coal Naldrett et al., 1992; Wooden et al., 1993; Fedor- measures (Smirnov, 1966; Glazkovsky et al., enko, 1994). It now appears that five principal 1977). On the Siberian platform the emergent magma types are present in the eleven forma- sedimentary sequence is covered by the volumi- tions, and so the relation between stratigraphic nous (~ 1 × 10 6 km 3) Siberian Trap lavas in formations and magma types is different from which magmatic activity peaked in the early those in several of the major CFB provinces. In Triassic at 248-250 Ma (Dalrymple et al., 1991; the Deccan and the Parami, for example, strati- Renne and Basu, 1991; Campbell et al., 1992 ). graphic units were defined on the basis of changes The largest basin in the region of the Siberian in magma compositions (Cox and Hawkes- Trap is the Tunguska basin in which the thick- worth, 1985; Beane et al., 1986; Peate et al., ness of the lava pile ranges from ~ 3500 km in 1992). However, in the Siberian Trap forma- the northwest, to only a few tens of metres in the tions were in part described prior to detailed mi- southeast in the area of the Tunguska river. A few nor and trace element investigations, and one thick flows, and many of the flow packages, have consequence is that not every stratigraphic break been recognised over distances of tens to some is associated with a significant change in magma hundreds of kilometres. In the centre of the basin chemistry (Table 1 ). the flows consist predominantly of tholeiitic ba- Lightfoot et al. (1990) grouped the alkalic and salt, whereas to the northwest, as in the Noril'sk sub-alkalic basalts of the Ivakinsky, the tholei- region, picritic, alkalic and sub-alkalic variants ites of the Syverminsky, and the tholeiitic and are developed (Fedorenko, 1981 ). Tufts occur pricritic basalts of the Gudchikhinsky into a irregularly across the basin, and they dominate Lower Series, primarily on the basis of their more the southern margin. Fedorenko (1994) and fractionated rare earth element (REE) patterns. Lightfoot et al. (1994) have discussed the thick- The overlying tholeiites of the Nadezhdinsky, ness variations of different formations in the Morongovsky and Mokulaevsky were placed in Noril'sk region, and the implications for models the Upper Series (Table 1 ), as were the rocks of of magma generation. It appears that magmatic the Kharaelakhsky, Kumginsky and Samoedsky, activity was focussed along discrete lineaments, for which there were relatively few data at that including the North Kharaelakh, Noril'sk-Khar- time. Naldrett et al. ( 1992 ) reviewed the major aelakh and Imangda faults (Fig. 1 ). Feeder dykes and trace element data and suggested that five for the individual formations are not observed, major magma types were involved in the gener- but the sequence in which the flows were erupted ation of the lavas of the formations up to and in- and the lateral variations in their thickness sug- cluding the Mokulaevsky. From the base to the gest that the centres of activity switched episod- top, the five principal magma types are: ( 1 ) the ically between different eruptive sites, rather than Ivakinsky and Syverminsky magma type of al- continuously as, for example, when a plate moves kalic to sub-alkalic affinity, (2) the Gudchikhin- across a mantle plume. Specifically within the sky Ni-rich suite which includes picritic basalts, Noril'sk area, there is no systematic migration in (3) the primitive but Ni-depleted Tuklonsky magmatic activity until after the eruption of the suite, which is characterised by flat REE profiles Morongovsky, whereupon the volcanic edifice and also includes picritic basalts, (4) the Lower appears to have migrated towards the northeast Nadezhdinsky type, which is LREE-enriched and and all the basalts have very similar has low Nd and high Sr isotope ratios, and which compositions. has been consistently modelled by crustal con- Previous studies recognised eleven formations tamination processes and (5) the Mokulaevsky in the 3.5 km vertical thickness of extrusive rocks type, which is primitive and has close similari- of the Noril'sk region (Fedorenko, 1981; Fedor- ties to the Tuklonsky type. In the Upper Nadezh- enko et al., 1984; Fedorenko and Petrukhov, dinsky and the Morongovsky there are flows with 1988), and subsequently sought to characterise compositions transitional between the Moku- their geochemical and isotopic compositions in laevsky type and the crustally contaminated more detail (Lightfoot et al., 1990, 1993, 1994; Lower Nadezhdinsky. The Mokulaevsky is fol- o~ o~ C.J. Hawkesworth / Lithos 34 (1995) 61-88 65

LEGEND Jurassic and Cretaceous sediment I~ Bolgokhtoksky granodiorlte intrusion Mokytgevsky, Kharaelakhsky,Kumginsky ~ Northwest trending faults and Samoedskyvolcanic suites Khakanchansky, Tuklonsky Nadezhdinsky ~ Main Northeastand North northeast I:::::::1 and Morongovsky volcanic suites I~'~I_ trending laults Ivakinsky, Syverminsky and Minor northeastand North northeast V//////A Gudchikhinsky volcanic suites 1.11 trending faults Cambrian to Upper Permian sediments

Fig. 1. Geological Map of the Norirsk area (based on Lightfoot et al., 1993 ). lowed by the tuffs and basalts of the Kharae- have been emplaced relatively late in the period lakhsky, Kumginsky and Samoedsky formations of Siberian Trap magmatism. Fedorenko (1994) (Table 1 ), for which new data are presented as provides a more detailed analysis of the links be- part of this study, in addition to new isotope and tween different intrusions and the lava stratig- trace element data on samples from selected raphy based on bulk rock geochemistry and cross- intrusions. cutting relations in the field. The relative ages of The intrusive facies crop out predominantly at the intrusive rocks summarised in Table 1 are the margins of the Trap, but they are also well based partly on his work. developed along fault lines such as the Noril'sk- Kharaelakh, North Kharaelakh and Imangda faults (Fig. 1 ). Most of the thicker differentiated 3. Samples analysed and analytical techniques and undifferentiated sills occur in the Devonian Tungusskaya sediments, and to a lesser extent in The lava samples are from sections 15 F and the associated volcanic rocks. Sills vary in thick- 16 F through the Kharaelakhsky (Hr), Kumgin- ness from a few metres up to at least 300 m in the sky (Km) and Samoedsky (Sm) formations (lo- Noril'sk region and to 500 m in the south of the cated in Fig. 1 ). Representative samples were Trap basin. In some areas the thickness of sedi- also taken from examples of the intrusion types ments and volcanics has been increased by > 50% described by Naldrett et al. (1992) and sum- by the intrusion of Trap-related sills (Zolotu- marised in Table 1. The samples were collected khin and Al'mukhamedov, 1988 ). Fedorenko et by Fedorenko from drill core and outcrop in the al. (1984) and Fedorenko (1994) subdivided the course of his work with NKGRE (Noril'sk Com- intrusions into 14 types, and Naldrett et al. plex Geological Exploration Expedition) and ( 1992 ) identified five main groups: ( 1 ) those of TsNIGRI (Central Research Institute of Geo- alkaline and sub-alkaline affinity, (2) Ti-rich logical Prospecting for Base and Precious Met- dolerite dykes that are only found in the north- als): weather surfaces and altered zones were re- eastern part of the Noril'sk region, (3) dolerite moved, and the remaining material was crushed, sills and dykes found throughout the Noril'sk re- ground and analysed as described by Lightfoot et gion, (4) differentiated intrusions that are not al. ( 1990, 1993 ). The major element oxides were related to the ore junctions and (5) differen- determined by wavelength dispersive X-ray flu- tiated mafic-ultramafic intrusions that occur orescence, the REE, Y, Zr, Nb, Rb, Sr, Cs, Th, only in the vicinity of the ore junctions. Naldrett U, Ta and Hf were determined by inductively- et al. ( 1992 ) sought to evaluate whether the dif- coupled plasma mass spectrometry (Doherty, ferent intrusion types could be linked to specific 1989); Ni, Cu, Co, Sc, V and Zn, were deter- magma types in the lava pile, and hence into a mined by inductively-coupled plasma optical chronological sequence. For example, the Ni-Cu emission spectroscopy, and Ba and Cr were de- ores are associated with Ni- and Cu-rich type 5 termined by flame atomic absorption. Quality intrusions that are geochemically similar to the control tests indicate that both the accuracy and Mokulaevsky lavas, and they therefore appear to precision were better than 5% r.s.d, over the pe- Table 1 Summaryof the lava stratigraphy,and the relativeages of the differentintrusive suites (after Fedorenko, 1994). The numbersafter the intrusiveunits refer to the five groups of Naldrett et al. ( 1992): ( 1 ) alkalic intrusions,(2) Ti-rich dolerite dykes, (3) dolerite sills and dykes, (4) differentiatedbodies not related to ore junctions,and (5) differentiatedbodies related to ore junctions.(5A) and (5B) are here termedthe Noril'sk-and the LowerTalnakh-types respectively

Volcanic formations Volcanic Volcanicrocks Intrusivetypes and core/section Intrusiverocks Grouping subunits lithology sampled lithology Naldrettet (indexes) al., and thickness ( 1992 ) (m)

No volcanics Ostrogorskytype lamprophyre Ageof intrusions ( Core NP- 12 ) unknown Severokharaelakhskytype picrite (Core TL- (5B) 6) (CoresTL-3, TL-6) to subalkaline dolerite (Core TL-3)

Bolgokhtokhskytype (BG-26) granodiorite No volcanics Avamskytype dolerite ( 2 ) Post lava age (SamplesAV-5, AV-6) intrusions Daldykanskytype doleritesand ( 3 ) (Cores NP-37,NP-49) pegmatoids Ruinnytype gabbro-dolerite- (4) 4~ (SampleM 1-5, Core SG-11 ) picrite Kulgakhtakhskytype picrite and dolerite (4) x~ (Core UK-35) Samoedsky(Sm) TtSm3 Aphyric,poikilophyitic, >200 porphyriticand TiSm2 glomeroporphyriticbasalts 230-280 and tufts TiSml 150-180 Kumginsky(Km) T~Km Glomeroporphyritic 160-210 basahsand tufts Kharaelakhsky T~ H~ Aphyric,poikilophyitic, Ambarninskytype II dolerite (3) (Hr) porphyriticbasalts and many 95-215 tufts Ikonskybasaltic andesite (Ik) TI Hr3 Poikilophytic,porphyritic, aphyric,glomeroporphyritic 205-365 basalts Tl H~ Glomeroporphyriticbasalts 15-120 Tt Hrt Porphyritic,aphyric 60-105 and poikilophyticbasalts, thick tufts Mokulaevsky 40-165 Porphyritic, (Mk) TtMI~ poikilophytic,aphyric and Ambarninskytype I dolerite (3) 140-265 glomeroporphyriticbasalts, TiMk3 and a few tufts 40-290 T~Mk2 35-275 TjMk~ Morongovsky Yuryakhskytrachybasahs (Mr) (Ur) and Kaltaminsky Upper ankaramites(Kt) TIMr2 175-640 Aphyric,poikilophytic and porphyriticbasalts and tufts

TiMrff TuffbetweenTiMr I and TtMr2 Noril'sktype: TIMr2 15-100 (i) Talnakh subtype: Main Talnakh intrusion(Core KZ-1739 ); NW Talnakhintrusion gabbro-dolerite- ( Core SG-18 ); sillsof NW picrite (5A) Talnakh intrusion (Cores KZ- (ore bearing) 997, SG-23); Noril'skI intrusion ( SamplesN 1 to N 17 ) (ii) Chernogorskysubtype: Tangaralakh intrusion (Core SG-10); Imangdaintrusion (Core KP-4) (iii) Zubovskysubtype: Zubovskyintrusion: (Core 624)

LowerTalnakh type: gabbro-dolerite- (SB) 7" LowerTalnakh intrusion picrite (Core SG-2k); sills of LowerTalnakh intrusion(Cores SG-5k, SG-7k);Lower Noril'sk intrusion(Core NP-37) Lower Aphyric,poikilophytic and TtMrt porphyriticbasalts and tufts 45-150

Nadezhdinsky(Nd) Upper Glomeroporphyriticand one TiNd3 flowof porphyriticbasalts 25-150 tufts Middle Porphyriticbasalts TiNd2 75-260 tufts Lower Porphyriticand tholeitic -,-.I TiNd~ basalts 50-260 oo

Table 1 (continued)

Volcanic formations Volcanic Volcanicrocks Intrusivetypes and core/section Intrusiverocks Grouping subunits lithology sampled lithology Naldrettet (indexes) al., and thickness (1992) (m)

Tuklonsky(Tk) T tTK Picriticbasalts Irbinskytype dolerite (3) 0-220 Tholeites (Core NM-7) Khakanchansky TtHk Mainlytufts with rare 0-260 tuklonsky-likebasalts Gudchikhinsky Upper Picriticand olivinophyricbasalts Fokinskytype picrites-dolerites (1) (Gd) TiGd2 (Core TL-3) 0-190 Lower Porphyritic and poikilophytic T~Gdt basalts 0-160 Glomeroporphyriticbasalts Syverminsky(Sv) P ~Sv Tholeiticbasalts 0-195 lvakinsky(IV) Upper Two-plagioclase,andesite P21v3 and labradoriticbasalts o~ 0-135 tufts 7" Middle Ti-augiteand sub-alkaline Yergalakhskytype II Sub-alkaline (1) P2Iv2 poikilophyticbasalts (SampleIF-45 ) Ti-augitedolerite 0-100 tufts Lower Trachybasalts,tufts and tuff Yergalakhskytype I Alkaline (1) P2Iv~ breccia (Cores SG-9, SG-10, NM-7) trachydolerite 0-240

The Lower, Middleand UpperSequences of Fedorenko (1994) are IV-Gd, Hk-Mr~ and Mr2-Sm, respectively C.J. Hawkesworth / Lithos 34 (1995) 61-88 69 riod of this study (Lightfoot et al., 1993, 1994). sky and the Mokulaevsky formations, which have Radiogenic isotopes were determined at the Open very similar compositions. Fig. 3a illustrates the University, using standard chemical separation new data from the Kharaelakhsky, Kumginsky techniques and a Finnigan MAT 261 multi-col- and Samoedsky formations, and compares them lector mass spectrometer in static mode. Results with the fields for the other formations. A key have been normalised to NBS 987 = 0.71022 for feature of the diagram is that it highlights the rel- 87Sr/86Sr, and J and M=0.51185, BCR- atively low HREE contents, and hence high Gd/ 1 =0.51262 for ~43Nd/la4Nd. The standard de- Yb, in the Ivakinsky, Syverminsky and Gudchi- viations for repeat analyses of the Sr and Nd iso- khinsky rocks, compared with those of the lavas tope standards were 4 and 3 ppm respectively in higher in the sequence. The differences in Gd/ the period of this study. Yb encouraged Lightfoot et al. (1990) to argue that there was a major change in magma com- position at the end of the Gudchikhinsky, and to 4. Lava geochemistry subdivide the succession broadly into the Lower (Ivakinsky, Syverminsky, Gudchikhinsky) and The analytical results on selected samples from Upper (Nadezhdinsky, Morongovsky, Moku- the Kharaelakhsky, Kumginsky and Samoedsky laevsky) Series. The displacement to high La/Sm formations over a combined section of 800 m are in the Nadezhdinsky is accompanied by marked summarised in Table 2, and Ne results on the full increases in Th abundances, and changes in ra- section of 15F are illustrated in Fig. 2. Apart from diogenic isotopes, and it has been consistently four basaltic andesite samples with SiO2 = 53.1- attributed to crustal contamination processes 54.5% from a single flow within the Kharae- (Lightfoot et al., 1990, 1993; Naldrett et al., lakhsky Formation, most of the Kharaelakhsky 1992; Wooden et al., 1993 ). Apart from the four to Samoedsky rocks analysed have restricted Kharaelakhsky samples with higher silica con- major element compositions with SIO2=48.4- tents, the Kharaelakhsky-Samoedsky samples 49.6%, MgO = 8.1-6.3% and Mg*= 54-58, simi- have low Gd/Yb and La/Sm similar to those in lar to the underlying rocks of the Mokulaevsky the underlying Mokulaevsky and Upper Moron- and Upper Morongovsky (Mr2). In the context govsky rocks. of other CFB suites, all the rocks are low-Ti tho- A distinctive feature of many CFB is that they leiites with TiO2 = 1.05-1.6%, and Ti/Zr = 70-86 have relatively low HFSE contents, and hence compared with Ti/Zr= 116 in primitive mantle. negative Ta and Nb anomalies on mantle nor- Throughout the 15F section the rocks exhibit re- maliSed diagrams, compared With oceanic ba- markably restricted ranges in element abun- salts. This is illustrated on a plot of Ta/La-La/ dances, although there is a significant increase in Sm (Fig. 3b) on which it is clear that, with the Ta/La at the base of the Kharaelakhsky forma- exception of the Gudchikhinsky rocks, all the Si- tion (Fig. 2). With the exception of the four berian Trap lavas have relatively low Ta abun- samples from the basaltic andesite flow, there is dances. The Gudchikhinsky formation includes no significant depletion in Ni and Cu, or coupled picritic basalts and, since they also have minor increase in SiO2 and La/Sm, which so character- and trace element ratios similar to oceanic ba- ise the underlying Nadezhdinsky Formation salts, these rocks arguably exhibit least evidence (Lightfoot et al., 1990, 1993; Naldrett et al., for any interaction with material from either the 1992; Wooden et al., 1993 ). mantle or crustal portions of the continental lith- Lightfoot et al. ( 1990, 1993) discussed the osphere. In detail, the rocks of the Kharae- minor and trace element features of the different lakhsky-Samoedsky formations tend to have formations within the Siberian Trap, and con- slightly lower La/Sm and higher Ta/La than cluded that rocks from different formations could those of the underlying Mokulaevsky and Upper be most easily distinguished on a diagram of La/ Morongovsky. Thus, it could be argued that they Sm-Gd/Yb. The only rocks which could not be contain a greater contribution from mantle sim- separated were those from the Upper Morongov- ilar to that sampled by oceanic basalts, i.e. with- Table 2 Extrusiverocks

Sm3 Sm2 Sm 1 Samoedsky Kumginskybasalt

Section 16F 16F 16F 16F 16F 16F 16F 15F 15F 16F 15F 15F 15F Sampleno. 20 18 14 13 9 7 2 40 39 1 38 36 32 Depth (m) 18 77 217 245 409 473 575 25 38 595 60 132 215

SiO2 48.9 48.4 48.8 48.9 48.4 48.6 48.5 48.4 48.5 48.2 49.2 49.1 48.9 TiO2 1.43 1.4 1.45 1.57 1.66 1.4 1.37 1.36 1.39 1.31 1.49 1.49 1.5" A1203 15.1 15.08 15.36 15.2 15.45 15.2 15.3 15.42 15.3 16.91 15.3 15.23 15.5 Fe203 13.6 13.65 13.54 13.9 14.39 13.4 13.2 13.15 13.3 12.35 13.4 13.49 13.5 MgO 7.15 7.09 6.88 6.8 6.27 7.14 7.52 7.49 7.28 6.75 6.44 6.42 6.39 CaO 10.9 11.42 11.14 10.3 10.5 11.4 11.3 11.41 11.4 11.48 11.2 11.22 10.93 Na20 2.29 2.28 2.26 2.44 2.53 2.28 2.14 2.21 2.2 2.35 2.39 2.36 2.45 K20 0.45 0.3 0.21 0.49 0.36 0.33 0.28 0.24 0.26 0.27 0.24 0.27 0.46 P2Os 0.15 0.16 0.17 0.17 0.24 0.16 0.15 0.16 0.19 0.14 0.2 0.2 0.19 MnO 0.2 0.21 0.21 0.21 0.21 0.22 0.21 0.19 0.2 0.19 0.2 0.21 0.2 4~ LOI 1.59 2.97 2.32 1.7 1.47 1.78 2.21 1.54 2.31 1.88 2.62 2.5 1.93 Sr 182 193 198 187 206 164 166 184 212 189 188 203 201 Y 27.2 25.6 26.0 27.6 31.3 25.7 24.9 25.0 26.2 24.5 28.6 28.9 • 29.3 O~ Zr 108 107 ll0 115 133 97 99 103 110 101 122 127 130 7" Nb 4.56 4.61 4.73 5.07 6.72 4.3 4.5 4.51 4.92 4.53 5.85 6.12 6.24 Rb 10 14.2 4 10.6 8.9 1.7 3.9 9 6.8 10.3 6.2 7.2 5.8 Ba 123 106 139 153 188 118 136 175 162 107 167 132 194 Cr 141 160 100 104 108 151 223 189 190 184 109 108 113 Zn 103 96 100 105 121 105 97 100 99 93 117 110 104 V 304 275 286 301 298 279 261 287 276 245 318 302 294 Sc 40 37 37 36 33 36 35 38 37 31 43 40 37 Ni 101 110 107 101 97 113 124 130 124 119 92 90 87 Cu 181 163 144 186 154 167 161 236 186 151 166 170 157 Co 45 43 44 43 44 45 43 46 45 40 47 44 41 La 7.53 7.44 7.59 8.26 11.26 7.14 7.22 7.13 7.78 7.34 9.14 9.38 9.4 Ce 19.2 18.9 18.9 20.4 26.6 17.9 18.1 17.8 19.0 18.4 22.6 22.2 22.9 Pr 2.74 2.6 2.66 2.89 3.61 2.53 2.53 2.55 2.62 2.5 3.13 3.14 3.14 Nd 12.5 12.3 12.1 13.5 16.1 11.8 11.7 11.8 12.2 11.7 13.8 13.8 13.6 Sm 3.64 3.51 3.4 3.69 4.17 3.44 3.42 3.57 3.55 3.36 3.67 3.87 3.92 Eu 1.26 1.21 1.24 1.4 1.44 1.26 1.17 1.2 1.2 1.16 1.26 1.32 1.33 Gd 4.38 4.12 4.31 4.64 5.07 4.06 4.01 4.03 4.28 3.91 4.64 4.58 4.61 Tb 0.76 0.71 0.74 0.82 0.85 0.72 0.72 0.73 0.76 0.67 0.81 0.82 0.84 Dy 5.12 4.95 4.85 5.38 5.69 4.85 4.77 4.79 4.95 4.53 5.19 5.28 5.39 Ho 1.02 0.97 0.98 1.06 1.18 1.01 0.96 0.94 0.98 0.94 1.08 1.07 1.09 Tm 0.42 0.41 0.42 0.45 0.51 0.43 0.42 0.41 0.44 0.39 0.47 0.45 0.47 Er 2.84 2.73 2.69 2.97 3.25 2.8 2.81 2.71 2.77 2.8 3.11 3 3.02 Yb 2.6 2.68 2.6 2.86 3.22 2.57 2.61 2.6 2.7 2.5 2.9 2.95 2.99 Lu 0.41 0.38 0.4 0.43 0.49 0.39 0.4 0.37 0.4 0.39 0.44 0.47 0.43 Cs 0.1 0.56 0.08 0.27 0.43 0.1 0.1 0.27 0.23 0.31 0.37 0.35 0.1 Hf 2.75 2.56 2.79 2.93 3.33 2.7 2.74 2.51 2.55 2.6 3.04 3.07 3.08 Ta 0.27 0.27 0.28 0.3 0.39 0.29 0.27 0.27 0.28 0.3 0.34 0.35 0.37 Th 0.9 0.89 0.89 0.98 1.57 0.98 1.04 0.99 1.05 1.03 1.36 1.31 1.38 U 0.32 0.33 0.32 0.38 0.8 0.39 0.42 0.37 0.62 0.43 0.59 0.56 0.6 Mg* 0.55 0.55 0.54 0.53 0.50 0.56 0.57 0.57 0.56 0.56 0.53 0.53 0.52 87Sr/86Sra 0.70539 0.70491 0.70529 0.70530 0.70532 0.70518 0.70509 143Nd/144Nda 0.51267 0.51270 0.51272 0.51272 0.51273 0.51271 ESr b 6.1 7.1 9.1 8.5 7.9 8.7 8.4 ENd b 1.39 2.08 2.89 2.34 2.66 2.11

4~

O~ Table 2 (continued)

Hr4 Hr3 Hr2 Hrl Kharaelakhsky

Section 15F 15F 15F 15F 15F 15F 15F SG-9 15F 15F 15F Sample no. 31 29 28 23 25 21 22 16 15 12 Depth (m) 239 315 347 410 410 445 449 85.6 715 725 805

SiO2 48.9 48.5 48.2 54.1 54.5 48.7 48.6 48.4 49.0 49.3 48.6 TiOz 1.62 1.5 1.47 2.28 2.28 1.31 1.32 1.33 1.4 1.41 1.4 A1203 14.7 15.36 15.4 13.87 14.06 15.48 15.3 16.42 15.36 15.4 15.3 Fe203 14.0 13.93 14. 12.88 12.74 13.28 13.2 13.36 13.63 13.5 13.7 MgO 6.62 7.11 7.26 3.72 3.7 7.39 7.55 6.83 6.67 6.29 7.39 CaO 10.9 10.29 10.5 7.46 7.3 10.84 11.0 11.02 11.02 11.2 10.4 Na20 2.44 2.32 2.33 3.28 3.01 2.21 2.33 2.17 2.3 2.33 2.42 K20 0.36 0.59 0.53 1.76 1.81 0.47 0.36 0.23 0.23 0.2 0.42 PzO5 0.23 0.18 0.18 0.48 0.49 0.13 0.14 0.1 0.15 0.17 0.15 MnO 0.21 0.2 0.22 0.17 0.15 0.19 0.21 0.18 0.21 0.21 0.21 LOI 2.84 1.74 2.2 1.21 2.17 1.44 0.57 1.4 2.19 1.85 1.23 Sr 203 216 176 436 425 179 169 165 180 192 170 Y 33.0 28.1 28.3 40.4 41.5 25.8 25.9 24.9 24.7 26.0 25.8 o~ 7" Zr 151 122 111 312 315 96 98 93 103 105 106 oo Nb 7.99 5.43 4.95 23.4 24.0 3.84 3.95 4.3 4.18 4.28 4.29 Rb 2.2 9.2 9 43.5 45.9 8.3 7.5 2.8 1.4 4.9 8.7 Ba 206 160 168 568 518 119 151 216 142 93 111 Cr 103 96 114 50 43 146 185 206 107 140 117 Zn 115 117 110 134 139 103 96 108 105 102 102 V 302 308 297 179 190 283 276 262 299 298 292 Sc - 1 40 41 24 25 42 40 36 41 42 40 Ni 90 124 110 24 25 124 118 123 88 77 116 Cu 134 207 154 19 53 116 168 215 189 182 177 Co 44 50 47 27 28 48 45 44 45 43 46 La 11.9 8.04 7.26 33.21 33.73 5.96 5.95 5.54 6.54 6.46 6.84 Ce 28.2 19.7 17.9 77.0 78.5 14.9 15.7 14.4 16.6 16.5 17.2 Pr 3.8 2.85 2.6 10.4 10.52 2.16 2.23 2.22 2.43 2.43 2.47 Nd 16.5 12.9 12.0 42.5 43.4 10.5 10.2 10.5 11.2 11.3 11.4 Sm 4.52 3.79 3.58 10.13 10.02 3.21 3.27 3.34 3.4 3.4 3.55 Eu 1.42 1.34 1.24 3.05 2.98 1.05 1.14 1.07 1.21 1.27 1.22 Gd 4.96 4.67 4.38 9.36 9.64 4.22 4.11 4.17 4.07 4.12 4.34 Tb 0.93 0.83 0.79 1.45 1.47 0.7 0.74 0.68 0.73 0.77 0.73 Dy 5.87 5.48 5.35 8.34 8.3 4.93 4.74 4.72 5.09 4.87 4.94 Ho 1.2 1.07 1.05 1.54 1.54 0.96 0.97 1.01 1.05 1.03 1.02 Tm 0.53 0.48 0.43 0.56 0.58 0.4 0.41 0.43 0.43 0.43 0.42 Er 3.39 3.1 3.1 3.98 3.98 2.65 2.7 2.95 2.84 2.81 2.96 Yb 3.25 2.76 2.81 3.42 3.35 2.62 2.64 2.65 2.8 2.85 2.63 Lu 0.51 0.44 0.43 0.5 0.52 0.37 0.39 0.38 0.41 0.43 0.42 Cs 0.07 0.05 0.03 0.35 0.34 0.01 0.11 0.11 0.19 0.35 0.09 Hf 3.58 2.88 2.74 7.57 7.56 2.36 2.44 2.47 2.58 2.58 2.63 Ta 0.43 0.31 0.29 1.39 1.35 0.28 025 0.24 0.32 0.32 0.25 Th 1.77 1.08 0.92 4.32 4.48 0.79 0.84 0.75 0.87 0.83 0.91 U 0.89 0.47 0.43 1.04 1.1 0.26 0.29 0.25 0.29 0.31 0.32 Mg* 0.52 0.54 0.55 0.40 O.40 0.56 0.57 0.54 0.53 0.52 0.56 875r/S6Sra 0.70536 0.70671 0.70685 0.70532 0.70466 0.70480 143Nd/144Nda 0.51246 0.51244 0.51276 0.51282 0.51274 .q ESrb 10.2 21.1 21.9 9.1 4.0 7.4 ENdb - 1.80 -2.04 2.73 3.67 2.40

Analyticalresults on selectedKharaelakhsky to Samoedskylavas. a-presentday; b-initialE values

t.,o 4~

7" Oo 74 C.J. Hawkesworth / Lithos 34 (1995) 61-88

0 ,¢ Sm Km 200' I. t g 400, o QO g Hr 600' ° o g %• ¢ ( Q e~ 800 t o o o o o o o o o o o o o o % o O 1000 o o o o o o o o o o o o o o o o Mk o o o o o o 1200 o o o o S g, O o o o o o o o o 1400 i i i i i i i 0.35 0.45 0.55 0.65 5O 55 2 4 2 0.04 0.06 100 2~ 3~

Mg* SiO2 TiO2 La/Sm Ta/La Cu (ppm) Fig. 2. Geochemical variations with height in the 15F section. Dots: Kharaelakhsky-Samoedsky formations; circles: Mokulaev- sky formation. The thicknesses of the Kharaelakhsky, Kumingsky and Samoedsky formations are 600 m, 200 m and > 580 m, respectively.

3 Gd~ 4 • •

Gd/Yb ~Nd ~, 0 o o ~Mr-Sm o ...... oiB "~s-~-]~ ...... ~.~ea.~ 2

Siberian Basalts i Mamle -8 1 , I I I I I I I I I I I I [ -20 20 40 60 0.06 --;~.~'~ ...... Esr Ta/La Fig. 4. Initial eNd-ESr variations in the lavas of the Siberian 0.05 Trap, compared with fields for MORB and OIB. Filled tri- angles: Gudchikhinsky (Gd); open triangles: Tuklonsky ( Tk ); ' " •:? Mr-Mk~. ~0 open diamonds: Syverminsky (Sv) and Ivakinsky (Iv); filled 0.04 - diamonds: Nadezhdinsky (Nd); circles: Morongovsky (Mr) and Mokulaevsky (Mk); dots: Kharaelakhsky (Hr), Kum- 0.03 - ginsky (Km) and Sarnoedsky (Sin). Data from Lightfoot et al. (1993) and this work. 0.02 I I I I 2 3 4 5 La/Sm out significant negative Ta anomalies, and that interpretation is consistent with their slightly higher Nd and lower Sr isotope ratios, compared Fig. 3. Gd/Yb-La/Sm and Ta/La-La/Sm for the lavas of with those from the Mokulaevsky and Upper the Siberian Trap. The filled symbols are for samples from the Kharaelakhsky, Kumginsky and Samoedsky formations. Morongovsky rocks (Fig. 4). Stratigraphically Data from Lightfoot et al. ( 1990, 1993) and this work. there is a marked increase in Ta/La at the base CJ. Hawkesworth / Lithos 34 (1995) 61-88 75 of the Kharaelakhsky formation (Fig. 2), and which may be used to constrain the nature of end- thus that appears to mark a significant pulse of member components. magma from the sub-lithospheric mantle. The A striking feature of the Siberian lavas is that higher silica samples from within the Kharae- they include a remarkably homogeneous se- lakhsky formation also have distinctive isotope quence of lavas which is > 2000 m thick (Upper ratios with Csr and end values of ~ + 20 and -2 Mokulaevsky-Samoedsky). These rocks typi- respectively. Possible causes for these variations cally have Mg numbers of 0.55 _+ 3 and they have are discussed further below. clearly evolved in equilibrium with plagioclase feldspar, and hence within the continental crust. It has been suggested that because the site of 5. Crustal contamination vs. partial melting of homogenisation was within the crust, the conti- the continental mantle lithosphere nental crust was the source of their distinctive trace element and isotope signatures (Wooden et Many CFB have major, trace element and ra- al., 1993 ). However, the very fact that these rocks diogenic isotope compositions which are differ- are homogeneous, and therefore do not preserve ent from those commonly observed in oceanic trends which may be used to constrain possible basalts (Hawkesworth et al., 1984, 1986; Maho- components, makes such arguments unusually ney, 1988; Ellam and Cox, 1989; Carlson, 1991; difficult to test. Where there appears to be more Hergt et al., 1991 ). The extent to which these re- general agreement is in the role of crustal con- flect contributions from crustal material en route tamination in the generation of the Nadezhdin- to the surface, or from distinctive source regions sky rocks (Lightfoot et al., 1990, 1993, 1994; in the continental mantle lithosphere, is often Naldrett et al., 1992; Wooden et al., 1993 ). These difficult to establish, and it has resulted in lengthy rocks are characterised by elevated La/Sm, Th, and often complex debates in the literature. A SiO2 and Sr isotopes, together with unradiogenic central problem is that many of those CFB which Nd, and relatively low Cu and Ni abundances. It have enriched radiogenic isotope ratios also have is envisaged that the addition of crustal material relatively low Ti, Ta and Nb abundances, and el- either introduced additional sulphur, or at least evated SIO2. Such features may be modelled both triggered the precipitation of sulphides (Nal- by the addition of granitic material from the drett et al., 1992). However, in detail the continental crust (Arndt et al., 1993; Wooden et amounts of crustal material introduced, and the al., 1993), and by partial melting of melt-de- nature of parental magmas, varies significantly pleted and trace element enriched source regions between different models. in the mantle lithosphere (Hergt et al., 1991; Most attempts to model crustal contamina- Turner and Hawkesworth, 1995 ). In the context tion have noted trends such as the general de- of the Siberian Trap the debate is of particular crease in Ti/Zr with increasing SiO2 (Fig. 5). importance in view of the associated mineralis- The Nadezhdinsky rocks have among the highest ation, and the need to understand whether sig- SiO2 and lowest Ti/Zr, and the overall shift to nificant quantities of sulphur were added to the high SiO2 and low Ti/Zr is accompanied by in- magmas and, if so, from where and under what creases in esr and decreases in end (Figs. 4 and conditions. Published models indicate that sig- 5 ). The arrays in both diagrams suggest that they nificant amounts of partial melting will not oc- might be explained by mixing between two com- cur within the continental mantle lithosphere, ponents, and in the simplest models it is often unless small amounts of volatiles are present assumed that the mantle end-member has minor (McKenzie and Bickle, 1988; Arndt and Chris- and trace element ratios similar to those of tensen, 1992; Gallagher and Hawkesworth, oceanic basalts (Lightfoot et al., 1990, 1993; 1992). However, at present there is no a priori Wooden et al., 1993 ). In detail, and as discussed way to evaluate the volatile content in the source further below (Fig. 8), there is compelling evi- of CFB, and so the approach adopted here is to dence that a minimum of three components were identify trends within the geochemical data involved in the generation of the Siberian Trap 76 C.J. Hawkesworth /Lithos 34 (1995) 61-88

140 primitive mantle, and in many oceanic basalts.

AA • • However, they cannot represent the mantle com- Ti/Zr lA:~t Gd • ponent in any two component mixing model for Aa~A AOL a A~I'A the overlying rocks because they have, for ex- ample, higher Gd/Yb ratios than the Upper Se- ries basalts (Fig. 3a). The Upper Series Nadezh- o 60 dinsky-Samoedsky formation lavas are displaced from the primitive mantle Ta/La ratio, and this Sv-lv can be modelled by crustal contamination. Two 20 I I I l I l I I I I I I component mixing results in linear arrays on ele- 45 50 55 SiO? ment-element diagrams, and in the simplest model being explored here the displacement to Fig. 5. Ti/Zr-SiO2 for the Siberian Trap lavas. Symbols as low Ta/La ratios may be solely attributed to for Fig. 4. mixing with a crustal component. The mantle component is assumed to have been derived from J G~,,2,, . o the sub-lithospheric mantle, and hence to have 1.(1 t 0 O0 0 O •O Sv Iv had a Ta/La ratio similar to that in primitive Ta o.8 mantle and oceanic basalts. The Ta and La abun- i I O ppm AA ,. 8 dances of that model mantle component in the 0.6 Siberian CFB may then be estimated by extrap- 11.4 olation of the linear arrays on Fig. 6 back to Ta/ ¢~ °IMr-Mk La = 0.13. This procedure was repeated for other 0.2 t / Hr-Sm elements plotted against Ta, and the calculated 0 I I I t I I minor and trace element pattern for the model 10 20 3(I La ppm mantle end-member is illustrated in Fig. 7. It

Fig. 6. Ta vs. La for the Siberian Trap lavas. With the excep- tion of those from Gudchikhinsky, all samples analysed have lower Ta/La ratios than that of primitive mantle (see also Fig. 3b). Those in the Kharaelakhsky-Samoedsky, Moron- govsky-Mokulaevsky and the Nadezhdinsky formations may be modelled by bulk mixing with material similar to the gran- = odiorite samples from the Bolgokhtokhsky Intrusion (Light- "vE foot et al. 1993; Table 3). Symbols as in Fig. 4. basalts. However, it is useful to explore the im- plications of a simple two component model to evaluate the general nature of the inferred man- tle and crustal end-members. A number of Rb Ra K I'h "Ia Nb I,a Cc Sr Nd P Sm Zr Hf Ti Y Yh models infer that the dominant mantle compo- Fig. 7. Mantle normalised minor and trace element diagram nent was derived from a mantle plume, and that illustrating one possible crustal contamination model for the at least some of the crustal material was from the generation of the Nadezhdinsky lavas. The pre-contamina- tion magma was calculated from from trends on element- upper crust which provides a suitable source for element diagrams such as Fig. 6, assuming that the pre-con- the associated sulphur (see discussions in God- tamination magma did not have a significant negative Ta levski and Grinenko, 1963; Grinenko, 1985; anomaly. The crustal end-member is that required if the av- Campbell and Griffiths, 1990; Arndt et al. 1993; erage Nadezhdinsky lava was generated by mixing of the cal- Wooden et al., 1993 ). culated pre-contamination magma with 40% crust (e.g. Lightfoot et al., 1993). The calculated pattern is similar to Fig. 6 illustrates the variations in Ta and La in that of the granodiorite from the Bolgokhtokhsky Intrusion the Siberian lavas. The Gudchikhinsky rocks (e.g. Table 3 ), rather than to typical sediments (e.g. Post Ar- have Ta/La ratios similar to that in estimated chaean Shale, Taylor and McLennan, 1985 ). C.J. Hawkesworth / Lithos 34 (1995) 61-88 77 necessarily has no HFSE anomalies, but it also abundances (e.g. Hawkesworth and Clarke, has relatively low trace element abundances, 1994). In detail, Sr is difficult to model in open typically 10-15 times primitive mantle, and sig- system fractionation, because it is so sensitive to nificantly less than those in plume-related ba- the amounts of plagioclase involved. However, salts in oceanic areas. Thus, if all the enriched the low Rb/Ba and HREE abundances of the isotope and trace element signatures in the Si- Bolgoldatoldasky granodiorite and the calculated berian CFB are attributed to crustal contamina- contaminant indicate that both were derived tion, the parental magmas appear to require a from relatively deep levels in the continental more depleted source region than those com- crust. monly inferred for plumes in oceanic areas, and/ Fig. 8 summarises the variation in Ta/La with or higher degrees of partial melting. end. In most models the sub-lithospheric mantle The minor and trace element abundances in is inferred to have high Ta/La and end similar to the mantle end-member may also be used to cal- oceanic basalts (Lightfoot et al., 1990, 1993; culate those in the crustal component in this two Wooden et al., 1993), whereas both the conti- component model. If the high silica and low Ti/ nental crust and old trace element enriched por- Zr of the Nadezhdinsky rocks (Fig. 5 ) primarily tions of the continental mantle lithosphere often reflect bulk assimilation of a high silica compo- have low Ta/La and eNd. Two component mix- nent (tonalite or granodiorite) then they require ing should result in broadly linear arrays on Fig. a maximum of ~ 40% contamination (Lightfoot 8, and it is clear that no one such array is ob- et al., 1990). The minor and trace element abun- served. Rather, the data are scattered, and if they dances in the crustal component have therefore are interpreted in terms of mixing, at least two been calculated assuming, for the sake of this mixing arrays are present. The upper basalts of discussion, that the Nadezhdinsky rocks were the Morongovsky to Samoedsky formations may generated by the addition of 40% of a crustal reflect mixing between a high Ta/La, high end component to the mantle end-member with no component, as also sampled by the Gudchikhin- HFSE anomalies. The actual abundances of ele- sky rocks, and low Ta/La material with eNd close ments in this component are not well con- to that of the bulk Earth. However, the contami- strained. However, the estimated minor and trace nation processes responsible for the enriched elements ratios are much more robust and, as il- characteristics of the Nadezhdinsky rocks ap- lustrated in Fig. 7, these are broadly similar to pear to have acted on magmas which already had those in a typical granodiorite. The actual gran- low Ta/La, and low Ti/Zr (not shown), and eso odiorite plotted in Fig. 7 is a granodiorite from values less than those commonly observed in the Bolgokhtokhsky Intrusion used by Lightfoot oceanic basalts. This point has been developed et al. ( 1993 ) and Fedorenko (1994) in their dis- in more detail by Lightfoot et al. (1993), and cussion of crustal contamination in the same after earlier suggestions that the Morongovsky rocks. Its initial Sr isotope ratios are too low basalts might have been parental to the Nadezh- (~ 0.706, Table 3) to be a precise analogue of dinsky suite, most recent studies have favoured the proposed contaminant, but such trace ele- the Tuklonsky picrites as the parental magmas ment patterns can be used qualitatively to eval- (Naldrett et al., 1992; Lightfoot et al., 1993, uate whether the contaminant was derived from 1994). Fedorenko (1994) used the available the upper or lower continental crust. major and trace element data to argue that the Upper crustal rocks, such as shales and many Lower and Middle Nadezhdinsky rocks could leucogranites, have high Rb/Ba and Rb/Sr ra- have been generated by gabbro fractionation and tios, and relatively low Sr abundances and un- 7.5% contamination with the Bolgokhtokhsky fractionated HREE (Taylor and McLennan, granodiorite, from Tuklonsky, but not Moku- 1985; Harris and Inger, 1992). At deeper levels laevsky/Upper Morongovsky,u parental mag- garnet replaces plagioclase feldspar, and thus the mas. Both the Tuklonsky and Mokulaevskly- lower crustal melts typically have higher Sr con- Upper Morongovsky magmas have distinctive tents, low Rb/Ba and Rb/Sr, and low HREE isotope and trace element signatures, and Light- Table 3 - lntrusives

Ostro- ¢vero- Bolgokhtoki'~kytype Avamskytype Daldykanskytype Ruinny type Kulgakhtaksky Ambarninsky Noril'sktype gorsky :harae- IBolgokhtokh intrusion a dyke a thick sill dykes MorongoTulaektaas intrusion type type II ~khsky int. Magnitnyint. Ambarnayaint. Main Talnakhintrusion ype ill

NP-12 TL-3 BG-26 BG-26 BG-26 AV4 AV~ NP-49 NP-49 NP-49 NP-37 N20 MI-5 SG-11 SG-11 SG-11 UK-35 UK-35 4F 4F KZ-1739 KZ-1739 KZ-1739 KZ-1739

1508 721.5 80.5 350 546 1379 1405 1439 1598 7 142 202 82.3 199.5 6 10 1693.5 1709.3 1722 1732

SiO2 46.3 47.91 66.1 66.6 67.4 49.1 48.1 48.2 47.2 47.6 47.8 48.9 47.9 46.8 47.3 46.4 48.0 46.1 49.0 49.7 49.7 50.0 49.9 49,5 TiO2 1.10 3.761 0.41 0.38 0.32 3.23 2.47 1.81 2.89 1.26 1.85 1.62 1.30 1.29 1.26 1.58 0.46 0.71 1.41 1.51 0.58 1.17 0.93 0.78 A1203 10.57 14.03[ 15,56 16.11 15.72 12.2 13.1 14.65 10.88 15.24 15.06 15.32 17.29 16.29 17.64 13.49 14.49 10.38 15.75 14.65 17.38 15.27 14.82 17.3 i Fe203 7.90 17.07[ 3.8 3.56 3.22 18.04 16.94 15.35 23.78 14.14 15.27 14.24 13.35 13.86 13.25 16.09 10.13 14.39 13.86 14.13 11.28 12.4 11.41 9.45 MgO 6.03 4.941 1.8 1.58 1.58 4.52 5.43 6.34 2.14 7.79 6.15 5.85 5.79 9.44 6.94 10.19 15.7 20.13 6.36 6.2 7.55 6.26 7.59 7.09 CaO 18.11 7.48[ 2.96 2.62 2.4 8.6 9.87 10.23 7.78 10.66 10.35 10.73 10.72 9.65 10.5 9.14 9.87 6.74 10.35 10.51 9.85 10.64 11,96 12.8 Na20 0.97 2.82[ 3,75 3.49 4.03 2.57 2.76 2.47 2.7 2.61 2.55 2.41 2.67 1.96 2.47 2.36 0.93 0.9 2.42 2.35 2.46 2.78 2,01 1.94 i K20 7.13 1.43 5.16 5.3 5.05 1.12 0.86 0.54 0.9 0.33 0.57 0.50 0.58 0.32 0.34 0.4 0.19 0.35 0.5 0.58 0.93 1.13 1.1 0.84 P"206 1.67 0.39 0.43 0.28 0.27 0.43 0.25 0.22 1.37 0.15 0.22 0.19 0.16 0.14 0.14 0.16 0.05 0.09 0.17 0.18 0.09 0.15 0.11 0.1 MnO 0.26 0.211 0.05 0.05 0.04 0.25 0,22 0.23 0.41 0.21 0.24 0.23 0.21 0.2 0.t6 0.23 0.15 0.19 0.21 0.22 0.18 0.21 0.21 0.19 LOI 1.71 0.9 1.2 7 0.71 0.28 1.4 3.50 0.65 1.7 4.8 4.3 0.3 1.7 1.9 1.4 1.5

S 0.1 i 0.06 0.35 0.11 0.1 4.91 14.1 3.17 4.68 0.16 3.70 3.17 3.01 3.63 0.01 0.11 0.02 0.02 0.2 0.21 0.1 0.09 Sr 1518 576] 1625 1689 1605 266 306 208 220 198 208 217 266 222 228 193 166 151 203 201 364 413 324 348 i Y 19.7 32.2] 16.8 15.4 13.7 49.3 31.3 32.1 83.9 23.5 31.9 27.9 27.1 20.9 21.0 27.7 9.5 13.5 27.9 31.0 15.2 23.1 I8,6 16.9 Zr 291 276] 266 253 241 288 173 137 235 88 144 119.9 71 91 75 112 53 66 117 122 70 95 81 72 L Nb 27.0 261I 26 26 23 17.5 ll.0 7.07 23.5 4.7 6.19 5.45 5.03 4.47 4.19 5.39 3 3 Rb 120 351 147 158 136 30.5 21.7 14.6 23.6 8.2 17.8 14.7 17.3 9 8.6 10.7 10 32 16 18 33 31 36 Ba 6050 5721 3960 3875 3705 330 220 212 321 130 137 162 164 110 115 124 163 165 168 173 133 200 201 168 Cr 298 36i 40 33 29 49 5(3 187 5 244 135 96 133 101 91 113 810 1800 170 225 -10 38 135 198 Zn 83 1651 44 43 39 158 14(3 135 22I 114 133 124 122 97 95 113 65 91 113 110 95 75 115 118 V 155 66 57 48 435 393 335 38 275 326 303 249 211 206 273 127 172 304 325 120 275 236 216 Sc 28 9 8 5 33 32 37 30 34 35 34.0 35 23 24 30 19 8 34 38 25 36 39 39 Ni 57 991 27 28 22 43 62 94 6 128 89 85 79 243 197 263 482 775 91 85 75 62 80 83 Cu 103 1981 39 230 29 343 271 234 563 167 232 199 188 143 142 431 94 83 184 190 122 98 96 79 Co 28 581 15 15 10 49 35 52 47 43 61 54 66 59 84 44 42 49 37 40 35

La 55.1 31.81 99.1 94.0 77.9 28.0 15.5 9.9 26,2 6.21 9.49 8.95 7.67 6.73 6.78 8.05 5.09 6.04 8.55 9.05 6.08 9.09 6.37 6.02 Ce 123 75.2] 192 187 155 62.20 37.8 25.0 71,0 15.9 23.9 21.77 19.2 16.2 15.9 19.4 11.8 14.5 21.4 22.9 13.9 21.0 14.7 13.5 Pr 13.4 8.831 19.0 18.6 15.8 8.84 5.28 3.63 10.67 2.38 3.36 3.10 2.61 2.32 2.31 2.78 1.44 1.8 2.8 3 1.68 2.66 1.82 1.71 Nd 58.8 43.3] 69.1 66.5 57.0 38.2 23.5 16.3 50.5 10.8 15.7 14.04 12.3 10.6 10,5 13.1 6.7 8.5 13.9 14.5 7.9 12.3 9.0 8.2 Sm 10.6 9.71 10 9.4 8.47 9.55 5.92 4.91 14.14 3.17 4.68 3.91 3.70 3.17 3.01 3.63 1.66 2.22 3.82 4.22 213 3.33 2.58 2.31 Eu 2.85 3.18 2.41 2.26 2.07 2.89 2.01 1.56 4.31 1.25 1.52 1.38 1.36 1.16 1.14 1.27 0.62 0.75 1.37 1.41 0.91 1.18 0.99 0.84 Gd 6.88 9.11 5.6 5.27 4.41 10.4 6.55 5.91 16.6 4.03 5.64 4.72 4.52 3.99 3.71 4.48 1.63 2.2 4.4 4.68 2.5 3.75 3.04 2.73 Tb 0.90 1.21 0.68 0.63 0.5 1.64 1.12 0.98 2.61 0.68 0.96 0.81 0.73 0.65 0.61 08 0.26 0.38 0.75 0.79 0.4 0.61 0.48 0.45 Dy 4.48 7.14 3.52 3.22 2.71 10.5 6.94 6.26 16.4 0.3 6.31 5.64 4.93 4.08 4.02 5.03 1.75 2.51 4.91 5.2 2.7 4.09 3.49 3.09 Ho 0.77 1.29 0.61 0.53 0.48 2.10 1.33 1.38 3.53 0.93 1.33 1.14 1.08 0.9 0.87 1.07 0.38 0.5 1.03 1.1 0.58 0.86 0.7 0.61 Trn 0.27 0.42 0.2 0.18 0.15 0.84 0.54 0.56 1.33 0.39 0.56 0.47 0.41 0.37 0.35 0.44 0.14 0.21 0.41 0.44 023 0.35 0.29 0.25 Er 1.97 3.25 1.45 1.32 1.19 5.69 3.50 3.98 9.72 2.65 3.88 3.12 3.04 2.55 2.44 3.21 1.0,5 1.48 2.77 2.91 1.59 2.35 1.93 1.75 Yb 159 2.57 1.26 1.17 1.05 5.11 3.27 3 8.82 2.54 3.63 3.01 2.71 2.29 2.19 2.84 1.1 1.49 2.84 2.97 163 2.34 1.99 1.7 Lu 0.25 0.35 0.18 0.15 0.13 0.80 0.48 0.56 1.31 0.38 0.51 0.47 0.41 0.38 0.33 0.44 0.14 0.21 0.41 0.42 0.23 0.34 0.29 0.24

Cs 0.6t3 0.82 0.66 0.41 0.58 0.2 1.19 1:09 0.99 0.33 0.38 0.4 Hf 7.45 2.12 2.04 2.34 7.03 4.33 3.9 6.52 2.52 3.86 3.11 2.05 2.61 2.2 3.21 1.17 1.54 2.93 3.15 1.61 2.18 1.94 1.8 Ta 1.61 2.73 2.67 2.41 0,99 0.68 0.45 1.3 0.29 0.36 0.33 0.30 0.28 0.31 0.34 0.09 0.13 0.29 0.32 0.21 0.27 0.2 0.18 Th 1.23 U

Mg* 0.64 0.40 0.53 0.51 0.53 0.37 0.43 0.49 0.17 0.56 0.48 0.49 0.50 0.61 0.55 0.60 0.78 0.77 0.52 0.51 0,61 0.54 0.61 0.64 87Sr/86Sra 0.7070410.70720 0.70703 0.70686 0.70531 0.70530 0.70560 0.70481 0.70578 0.70490 0.70484 0.70503 0.70739 0.70735 0.70555 0.70568 0,70778 0.70863 0.70817 0,70769 143Nd/144Nda 0.51193 0.51237[ 0.51173 0.51258 0.51259 0.51276 0.51274 0.51275 0.51273 051258 0.51272 0.51274 0.51277 051193 0.51218 0.51262 0.51263 0.51258 0.51261 0.51249 ESr b 31.5 29.4 26.5 21.0 5.4 5.4 4.2 2.6 9.9 4.0 3.6 3.7 36.5 13.8 7.6 7.9 37.6 51.9 56.8 34.4 ENd b -13.0 -3.19 -I4.2 0.13 033 2.91 2.78 2.87 2.22 -0,26 2.09 2.72 3.51 -12.32 -7.68 0.61 0.50 43.16 0.21 -2.17 qW Talnakhintrusion N!oril'skI int. Tangara-Zubovsky Imangda akh int. intrusion intrusion

KZ-1739 KZ-1739 KZ-1739 KZ-1739 KZ-1739 KZ-1739 KZ-1739 KZ-1739 SG-18 SG-18 SG-18 SG-18 NI N3 N4 N5 N6 N10 N13 N15 NI7 SG-10 I 624 624 KP-4 KP--4

1744 1757 1790 1807.1 1818.5 1838.7 1851.6 1852.4 1934.5 1980.8 1982 2002.7 2330 I 212.0 236.8 1447.4 1450.1

49.0 48.4 45.3 41.7 46.4 44.4 47.8 48.2 48.0 45.1 44.5 45.0 45.6 49.6 49.5 47.1 41.8 42,2 41.1 46.6 48.3 49.11 42.2 45.2 43.l 43.0 0.7 0.65 0.76 0.54 0.62 0.93 1.22 1.21 0.49 0.73 0.61 0.49 0.49 1.05 1.13 0.71 0.45 0.61 0.66 0.82 1.16 o 91 0.45 0.72 0,66 0.63 17.85 19.28 15.89 8.09 14.5 13.84 16.16 15.77 18.26 11.74 10.69 9.7 22.75 14.52 14.39 16.96 7.23 8.47 9.13 16.68 16.49 16A51 15.08 13.02 9,50 9.64 9A7 8.47 12.49 20.17 16.22 18.24 13.82 12.84 10.11 14.65 14.15 16.16 6.22 10.82 11.21 9.27 16.69 18.41 22.51 12.52 12.45 10.261 10.49 13.59 16.20 16.61 7.78 7.49 13.84 23.08 10.51 10.84 6.62 6.94 9.68 18.26 21.99 20.05 6.73 7.19 6.95 11.85 27.78 22.49 18.97 9.75 7.74 7.63T 16.77 17.01 22.12 21.56 13.25 13.03 9.94 5.1 9.5 8.65 10.09 9.81 10.5 7.92 6.78 7.31 15.94 12.85 12.86 11.25 4.74 6.35 6.11 11.11 10.63 12.69[ 13.51 8.23 6.53 6.88 1.53 2.01 1.12 0.6 1.26 1.74 2.54 1.47 1.96 1.02 0.84 0.79 1.52 3.03 3.06 1.71 0.70 0.60 0.90 1.86 2.35 2.4E 0.65 1.59 1,31 1.20 0.48 0.51 0.41 0.29 0.7 0.97 1.44 3.41 0.84 0.31 0.24 0.21 0.58 0.67 0.59 0.98 0.33 0.60 0.34 0.36 0.58 0.381 0.38 0.32 0,28 0.21 0.09 0.07 0.08 0.1 0.06 fill 0.13 0.12 0.02 0.06 0.06 0.05 0.10 0.12 0.13 0.07 0,05 008 0.10 0.10 0.12 o.o91 0.10 0m~ 0.07 0.07 0.16 0.13 0.16 0.28 0.23 0.28 0.22 0.26 0.18 0.17 0.15 0.23 0.08 0:15 0.19 0.14 0.21 0.22 0.23 0.18 0.20 0.151 0.35 0.20 0.22 0.22 0.9 1.2 1.1 6.1 2.7 4.6 1.5 1.6 4.4 0.2 1.3 0.6 4.29 2.27 1.86 2.76 4.09 2.92 5.20 1.57 1.74 0.51 3.38 1.80 0.13 0.05

0.08 0.08 0.19 0.22 0.09 0.07 0.09 0.07 0.67 0.12 0.12 0.05 0.60 0.08 0.80 0.80 0.10 2.381 0.34 0.15 0.80 0.57 241 259 219 133 286 326 461 542 228 146 125 132 246 393 362 285 99.3 133 100 223 322 2381 403 211 153 128 14.8 13,0 12.1 10.4 12.3 16.3 21.7 21.6 9.4 13.0 11.0 9.9 11.5 19.5 20,1 11.8 6.4 9.3 10.6 13.4 24.5 16.91 10.5 10.9 10.6 9.7 60 61 57 50 54 69 91 97 39 61 45 41 48.1 79.8 76.9 43.4 27.0 37.2 42.4 54.5 60.6 .~31 65.1 44.4 44.6 36.5 1.25 2.26 1.98 1 .(aft 3.01 3.91 4.15 2.22 1.38 2.05 2.19 2.96 4.07 2.881 2.79 2.34 2.10 1.72 25 17 14 12 10 23 53 37 24.4 8.7 7.4 6 15.7 22.1 17.5 33.7 12.1 22.9 11.1 10.3 16.3 9.81 11.0 8.6 6.65 4.87 201 122 135 68 136 171 202 353 147 157 208 112 102 120 115 185 65 87 78 107 138 1291 84 84 78 67 420 79 3000 229 284 186 133 132 450 4220 2930 505 395 105 110 343 2730 1150 286 263 149 770l 61 510 4000 3160 94 69 124 105 101 118 118 118 57 103 92 101 51 61 93 53 101 138 147 111 137 76~ 164 114 109 114 185 175 226 102 183 222 288 273 163 192 136 126 66 231 249 143 115 133 154 175 243 2361 68 154 193 207 32 28 20 6 30 29 34 33 27 6 10 16 10.0 44.0 44.0 21.0 13.0 17.0 20.0 24.0 29.0 3.~1 9.0 19.0 21.0 23.0 118 122 479 2948 3563 1620 832 155 335 730 875 810 1241 71 63 314 2083 3519 9052 1980 233 1091 524 653 2180 1984 87 66 127 3876 6009 3127 1985 443 285 84 103 105 2230 76 85 18 2126 4488 13560 3818 301 83~ 389 141 2153 1702 38 37 70 172 164 132 74 46 46 90 97 99 4}1

4.52 4.37 4.38 4.39 4.28 5.31 7.74 6.52 3.7 4.6 3.7 3.2 5.18 6.78 7.19 3.75 2.51 3.35 3.90 4.90 6.78 5.371 8.44 4.18 3.80 3.07 10.8 10.0 10.3 9.9 9.9 12.7 16.2 16.0 7.9 II.0 8.6 7.5 13.2l 16.96 17.60 9.91 5.92 8.37 9.09 11.87 15.98 12.71 19.62 9.77 8.78 7.16 1.37 1.34 1.28 1.21 1.22 1.64 2.09 2.07 I01 1.4 1.1 0,97 1.84 2.27 2.38 1.38 0.82 1.20 1.24 1,67 2.19 1.761 2.40 1.37 1.23 1.03 4.5 6.4 6.2 5.7 5.9 8.1 10.3 10.2 4.7 6.7 5.1 4.6 8.09 10.50 11.11 6.31 3.70 5.09 5.60 7.59 9.55 8.21 9.34 5.92 5.48 4.56 1.91 1.79 1.72 1.47 1.64 2.28 3.04 3.01 1.3 1.8 1.5 1.3 2.10 2.97 3.09 1.81 1.03 1.49 159 2.09 2.90 2.381 2.12 1.74 1.62 1.24 0.75 0.66 0.61 0.5 0.75 0.83 1.12 1.07 0.56 0.65 0.53 0.5 0.76 1.03 1.10 0.61 0.37 0.50 0.63 0.81 1.04 0.83l 0.67 0.72 0.60 0.51 2.3 2.19 1.99 1.61 1.93 2.59 3.37 3.53 1.5 2.2 1.8 1.6 2.54 3.71 3.69 2.25 1.22 1.73 1 88 2.54 3.51 2.93[ 2.11 2.06 1.81 1.63 0.39 0.36 0.32 0.26 0.32 0.43 0.58 0.56 0.28 0.37 0.32 0.27 0.42 0.61 065 0.36 0.22 033 032 0.42 0.57 0.471 0.34 0.34 0.32 0.29 2.65 2.4 2.28 1.85 2.24 3.14 3.96 3.89 1.8 2.3 2 1.8 2.70 3.97 4.24 2.32 1.44 2.12 2.21 2.80 3.91 3.13[ 2.26 2.32 2.15 1.92 0.53 0.47 0.47 0.39 0.45 0.61 0.8I 0.79 0.37 0.51 0.43 0.37 0.53 0.83 0.89 0.52 0.30 0.45 0.46 0.60 0.80 0.67[ 0.46 0.47 0.46 0.40 0.21 0.2 0.19 0.15 0.18 0.26 0.33 0.33 0.16 0.22 0.18 0.16 0.22 0.35 0.37 0.22 0.11 0.18 0.19 0.24 0.33 0.26[ 0.20 0.21 0.20 0.17 1.54 1.31 1.28 1.08 1.27 1.68 2.27 2.27 1.1 1.5 1.2 1.2 1.50 2.36 2.37 1.34 0.86 1.21 1.19 1.62 2.29 1.95[ 1.23 1.30 1.24 1.07 1.49 1.37 1.32 1.15 1.29 1.71 2.31 2.32 0.99 1.4 1.2 1 1.33 2.12 2.25 1.34 0.87 1.27 1.25 1.56 2.26 1.791 1.29 1.29 1.25 1.14 0.2 0.19 0.18 0.17 0.18 0.24 0.33 0.33 0.15 0.22 0.17 0.17 0.17 0.34 0.35 0.21 0.12 0.18 0.19 0.24 0.34 0.261 0.19 0.19 0.19 0.17

0.51 0.39 0.26 0.25 0.79 0.60 0.42 1.33 0.49 0.94 0.79 0.69 0.91 0.31 [ 0.64 0.81 0.23 0.19 1.42 1 A4 1.43 1.36 1.16 1.59 2.19 2.29 1.21 1.77 1.41 1.27 1.29 2.10 2.03 1.22 0.73 0.97 1.06 1.40 1.59 1.681 1.63 1.09 1.13 0.91 0.15 0.14 0.14 0.13 0,12 0.19 0.27 0.24 0.1 0.17 0.18 0.14 0.23 0.23 0.23 0.15 0.08 0.14 0.12 0.19 0.25 0.181 0.19 0.14 0.14 0.11 0.4 0.9 0.6 0.5 0.82 1.01 1.08 0.53 0.32 0.51 0.55 0.70 0.92 1.72 0.53 0.58 0.43 0.1 0.3 0.2 0.2

0.66 0.67 0.72 0.73 0.60 0.58 0.53 0.56 0.69 0.74 0.78 0.74 0.72 0.61 0.59 0.75 0.80 0.74 0.66 0.64 0.59 0.631 0.74 0.76 0.75 0.70686 0.70671 0.70720 0.70767 0.70737 0.70873 0.70813 0.70906 0.70878 0.70654 0.70629 0.70629 0.70771 0.70750 0.70719 0.70738 0.70798 0.70790 0.70669 0.70594 0.70659 0.70628[ 0.79 0.70658 0.70665 0.70620 0.51263 0.51262 0.51270 0.51263 0.51241 0.51267 0.51260 0.51263 0.51264 0.51257 0.51266 0.51266 0.51264I 0.70835 0.51263 0.51264 0.51268 22.6 26.0 33.3 36.1 39.9 54.0 39.0 59.0 49.4 24.5 21.0 23.0 40,5 38,6 35.4 27.9 35.9 27.5 19.1 17.9 26.5 23.5I 22.1 23.1 16.7 0.73 0.28 1.85 0.79 -3.36 1.23 0.13 0.72 0.91 -0.45 1.31 1.31 0.79I 47.2 0.72 2.07 2.85 80 C.J. Hawkesworth / Lithos 34 (1995) 61-88

Lower Talnakh type lrbinsky type :okinsky Yergalaskytype Lower Talnakh intrusion sill of Lower Noril'sk a sill YPe Lower,, intrusion , sill

SG-2k SG-2k SC-2k SG-2k SG-2k S( NP-37 NP-37 NM-7 NM-7 TL-3 1F-45 SG-9 SG-10

2475.3 2497.5 2533.5 2554.5 2571,8 2 1526 1574 1308 1356.8 1040 68 2200 1515

76.2 47,3 45.0 46.3 45.2 50.4 44.2 49.2 49.5 47.6 47.93 46.2 43.6 0.22 0.49 0.42 0.67 0.46 0.88 0.5 0.96 0.91 1.32 2.47 3.35 3.11 6,01 16.79 10.93 15.11 6.79 15.38 9.58 16.64 16.12 10.63 15.91 16.43 19.8 2.96 10 13.18 11.9 15.05 10.21 15.08 11.29 11.19 13.91 14.26 15.31 14.98 122 12.46 21.35 15.53 25.64 7.7 2135 7.83 8.44 15.59 5,62 4.04 3.82 12.66 11.12 7.73 8.45 5.92 11.66 7.79 11.4 11.39 8.79 8.88 8 7.62 0.04 1 0.79 1.23 0.36 2.54 0.64 2.05 1.89 1.38 3.26 3.09 3.32 0,04 0.65 0.38 0.59 0.35 1.01 0.32 0.38 0.36 0.43 1.12 2.22 2.09 0.01 0.04 0.07 0.07 0.04 0.1 0.08 0.07 0.05 0.12 0.37 1.13 1.45 0.2 0.15 0.18 0.17 0.23 0.18 0.24 0.17 0.17 0.18 0.18 0.21 0.19 2.8 2.8 1.9 2.8 3.6 2.5 2.1 0.2 0.6 0.7 2.7 1.4 2,4

0.08 0.2 0.13 0.24 2.93 1.6 0.06 0.02 0.02 0.08 0.14 0.14 307 223 135 208 114 239 149 244 241 233 475 465 491 18.0 11.0 10.0 13.0 8.8 17.5 9.4 19.1 17.3 16.0 26.7 43.7 39.0 78 44 47 66 37 86 58 64 61 95 202 346 353 4.53 2.76 2.4 4.34 2.29 4.54 2.69 3.3 3.3 16 24.5 39.03 25 16.9 10.3 15.6 9.4 42.3 10.2 8.4 7.6 12 18.9 55,3 57.9 290 194 188 358 244 142 130 332 189 102 431 985 67 89 I29 73 129 154 97 340 388 800 48 31 38 82 93 82 82 230 55 106 95 98 105i 122 173 174 214 125 116 143 116 224 129 248 240 241 212 180 119 32 16 9 19 5 35 19 36 36 181 23 24 18 41 230 475 290 400 50 679 95 106 7191 35 36 22 77 101 238 132 295 62 671 121 121 1331 31 39 39 28 65 101 79 120 38 112 47 49 71 43 31 36

9,7 6.2 6 8.2 4.9 8.09 5.49 5.54 5.25 7.42 22.9 51.95 50.62 22,0 14.0 14,0 18.0 11.0 19.3 11.7 13.4 12.3 18.4 54.7 115.4 106.1 2,36 1.61 1.49 1.84 1.21 2.29 1.37 1.64 1.61 2.47 6.47 12.64 12.02 12,0 7.3 7.5 9.0 58 10.7 6.4 8.3 7.9 12.5 27.7 56,0 50.4 3 1.8 1.8 2.2 1.4 2.93 1.6 2.32 2.21 3.31 6.29 11.23 9.89 0.93 0.61 0.56 0.68 0.45 0.88 0.53 0.95 0.91 1.12 204 2.87 2.63 3.1 1.9 1,7 2.2 1.5 3,09 1.73 2.95 2.83 3.49 5.94 974 8.83 0.54 0.3 03 0.37 0.26 0.51 0.29 0.52 0.49 0.53 0.89 1.56 1.42 3.1 2 1.9 2.3 1.6 3.43 1.86 3.17 2,92 3.17 5.51 8.54 7,62 0.7 0.43 0.4 0.49 0.34 0.71 04 0.7 0.61 0.62 11 1.77 1.59 0.28 0.17 0.15 0.19 0.13 0.29 017 0.27 0.27 0.21 0.39 0,66 0.59 2 1.2 1.1 1.4 0.97 1.93 112 1.89 1.84 1.67 2.79 4.66 4.12 1.7 1 0.94 1,2 0.89 1.84 109 1,7 1.69 1.46 2.56 4.3 3.72 0.27 0.17 0.15 0,19 0.12 0.27 0.16 0.27 0.26 0.2 0.36 0.68 0.52

0.3 0.8 0.29 0,9 0.81 0.37 0.53 0.56 0.61 2.06 3.13 239 2.21 1,44 1,42 1.88 1.22 2.34 1.65 1.8 1.76 2.57 4.95 7.61 7.23 0.25 0.22 0.15 0.26 0.15 0.26 0.15 0.19 0.23 0.36 0.84 2.04 2.09 1.6 1.2 1 1.5 0.8 0.83 2.01 6.82 6.05 0.5 0.5 0.3 0.5 0.3 0.2 0.61 324 2.81

0.57 0.74 0.79 075 0.80 0.64 0.77 0.62 0.64 0.72 0.48 0.38 0.37 0.70915 070891 0.70864 0.70871 0.70829 0.; 0.71005 0.70832 0.70600 0.70553 0.70604 0.70705 0.70713 0.51227 0.51227 0.51231 0.51259 0.51255 0.51276 0.51255 0.51251 58.4 55.8 51.9 53.1 46.0 57.2 48.5 20.5 14.3 18.6 23.1 24.4 ~.62 -6.19 -5.01 -0.08 -0.82 3.57 0.69 0.00 foot et al. (1993) marshalled previous argu- their different Nd isotope ratios. In the model of ments to suggest that such magmas could have Lightfoot et al. (1993), the presence of an en- been derived from sources within the continen- riched mantle component in the parental mag- tal mantle lithosphere (e.g. Hergt et al., 1991 ). mas to the Nadezhdinsky rocks reduces the esti- These arguments need not be repeated here, but mated amounts of crustal contamination to we emphasise that the Ta/La--ENd data arrays ap- ~ 10%, but the minor and trace element ratios of pear to require a minimum of three components. the contaminant remain similar to that of a ton- In the model of Wooden et al. (1993) we infer alite or granodiorite. that two of these components would be different Finally in this section, there is the question of contaminants from the continental crust, and how the Cu contents of the magmas vary with that they would be of different ages to explain the minor and trace element ratios which have C.J. Hawkesworth / Lithos 34 (1995) 61-88 81

at low Ti/Zr. Many of the Syverminsky and Ivakinsky rocks are sub-alkalic and their low Ni

4 and Cu abundances could be due to trace resid- • u ENd ual sulphides in their source regions. However, arth 0 r .... _~c I the Nadezhdinsky rocks also have markedly low , Cu, and Ni, contents (Lightfoot et al., 1990, Sv-lv -4- i 1993; Naldrett et al., 1992) and so their Cu/Zr i i and Ti/Zr ratios may reflect crustal contamina- ) Siberian Basalts -8" i tion. The data in Fig. 9 might be modelled in t I I I I I terms of two components with progressive con- 0.(12 0.03 0.04 0.05 0.06 0.07 Ta/La tamination of mantle derived magmas resulting Fig. 8. CNd--Ta/La for the lavas of the Siberian Trap. Two in lower Ti/Zr and SiO2 (Fig. 5), until the component mixing will result in linear arrays, provided that amounts of contamination were great enough for the end members have similar La/Nd ratios. Data sources sulphides to precipitate, and to scavenge the Cu. and symbols as in Fig. 4. However, the case for the presence of at least three components has been outlined above, and on that basis it is concluded that the Cu/Zr-Ti/ Zr trends reflect a similar number of compo- Itl Sibctian Basalts nents. In the model of Lightfoot et al. (1993, CII/ZI- Mu'-Sm q_~ Tk . 1994) the Gudchikhinsky to Morongovsky-Sa-

...... moedsky array is due to contributions from dif- ferent mantle source regions, and the displace- $ • o ment to relatively low Cu in the Nadezhdinsky Nd rocks reflects sulphide precipitation and segre- Sv-lv gation in response to crustal contamination. The t I ~ I I I 4(~ 8t~ 120 evidence from the minor and trace element vari- Ti/Zr ations is that the contaminant was an interme- Fig. 9. Cu/Zr-Ti/Zr for the lavas of the Siberian Trap. Sym- diate to acidic igneous rock; presumably it there- bols and data sources as in Fig. 4, except that the dots repre- fore had relatively low S contents, and so it is sent the Morongovskyto Samoedskyrocks plotted together. Cu and Zr have similar distribution coefficients into com- inferred that sulphide saturation was in response mon silicate phases, and so the relatively low Cu/Zr in the to the changes in the bulk composition of the Nadezhdinsky and Syverminsky-Ivakinskyrocks is inferred contaminated magma, rather than to the addi- to be due to the presence of fractionated, or residual sulphides. tion of large amounts of sulphur. been used to identify contributions from differ- ent crustal and mantle sources. Cu increases with 6. Intrusive phases Zr in rocks which have neither fractionated nor accumulated magmatic sulphides, and Fedor- Fedorenko et al. (1984) and Naldrett et al. enko (1994) has also demonstrated a strong cor- (1992) provided comprehensive studies of the relation between Cu and TiO2 in the unmineral- different intrusive rocks of the Norirsk region in ised rocks of the Noril'sk region. Fig. 9 illustrates which they summarised the available geological Cu/Zr vs. Ti/Zr in the Siberian Trap lavas and, and geochemical data, and addressed specific as with the Ta/La-ENd data, it appears that two questions about how different intrusive types trends can be identified. The Gudchikhinsky and might be associated with different magmas re- the Upper Series rocks of the Upper Morongov- cognised in the lava stratigraphy. New radi- sky to Samoedsky formations have relatively ogenic isotope data on samples from a number constant Cu/Zr over a range of Ti/Zr, and then of different intrusions may be used to re-evalu- the Nadezhdinsky, and the Syverminsky and ate how the origins of the different intrusion- Ivakinsky, lavas have significantly lower Cu/Zr types might be linked to current models for the 82 C.J. Hawkesworth / Lithos 34 (1995) 61-88

extrusive rocks. The geology of individual intru- and they plot broadly within the field for the No- sions, and the locations of the samples analysed, ril'sk-type rocks in Fig. 10. The Lower Talnakh- are described in Naldrett et al. (1992). Fedor- type rocks are consistently displaced to higher enko et al. (1984), and Fedorenko (1994), re- SiO2 than those from the Noril'sk-type. cognised 14 types of intrusions, but here they are REE abundances decrease with increasing Mg* considered in the five groups outlined by Nal- within the intrusive phases, and presumably re- drett et al. (1992) (Tables 1 and 3). For clarity flect both the amount of trapped liquid in each the results from the alkaline rocks are not plotted sample, and the degree of differentiation of the on several of the diagrams, and the dolerites of magma that is trapped. Nonetheless, the Lower Groups 2 and 3 are given the same symbols. Of Talnakh-type rocks consistently have higher La particular interest are the variations within the abundances than those from the Noril'sk-type. In intrusions related to ore junctions (Group 5, Ta- addition, the Lower Talnakh-type samples are bles 1 and 3), and these are subdivided into the characterised by elevated La/Sm, and lower Ti/ (5A) and (5B) subgroups of Naldrett et al. Zr, than the Noril'sk-type (Fig. 11 ). Even though (1992), here termed the Noril'sk- and Lower many of these samples presumably do not rep- Talnakh-types (Fedorenko, 1994). The former resent liquid compositions, it would appear that consists of the different intrusions comprising the particular major element features, such as rela- Cr-rich Talnakh subtype, and it includes the well tively high SiO2, are associated with changes in differentiated Chernogorsky and the Zubovsky minor and trace element ratios that should pri- subtypes (Table I ), whereas the Lower Talnakh- marily reflect variations in the interstitial mag- type is Cr-poor and it is characterised by weakly disseminated sulphides. Fig. 10 summarises the Mg*-SiO2 data for the Siberian Trap lavas, and selected intrusion types. 3 The Lower Series lavas, and the Upper Series Gd/Yb rocks of the Tuklonsky and Nadezhdinsky for- mations, have higher SiO2 contents, at a partic- ular Mg*, than those of the Morongovsky-Sa- o moedsky formations. The dolerites and differentiated intrusions not associated with ore [] junctions typically have Mg* in the range 55-40, Man e 1 0 I I I I 0 Differentiated rrarusions

Ti/Zr 0.8 A 100 Mg* 0 • Dolerites ril'sk typ~ (].7 0 •• • A A

60 0.6

0.5 -Iv 20 I i I i 2 3 4 5 La/Sm 0.4 40 45 sio2 Fig. 11. Gd/Yb-La/Sm and Ti/Zr-La/Sm to demonstrate that most of the intrusions analysed have ratios similar to Fig. 10. Mg*-SiO2 for the intrusive and extrusive rocks of the those of the lavas. In particular, most of the intrusions have Norirsk region. Gabbro fractionation results in steep nega- low Gd/Yb similar to the Upper Series rocks in the Tuklon- tive trends, as observed in selected samples of the dolerites sky to Samoedsky formations. Filled triangles: Noril'sk type; and differentiated intrusions, and crustal contamination tends open triangles: Lower Talnakh-type; circles: dolerites; open to generate very shallow negative arrays. diamonds: differentiated, unmineralised intrusions. C.J. Hawkesworth / Lithos 34 (1995) 61-88 83 mas. In the context of possible links between dif- the Lower Series lavas into the Nadezhdinsky ferent extrusive formations and intrusion types, formation, and then the steady decrease in 875r/ the Lower Talnakh-type rocks have both major 868r with stratigraphic position in the upper for- and trace element features similar to those of the mations. The alkaline intrusives (Group 1 ), the Nadezhdinsky rocks. The dolerites in Groups 2 dolerites (Groups 2 and 3), and the differen- and 3, the differentiated intrusions not associ- tiated intrusions not related to ore junctions ated with ore junctions (Subgroup 4), and the (Group 4) all have relatively restricted initial Noril'sk-type intrusions (Group 5A) have simi- 87Sr/86Sr=0.7044-0.7064. In contrast, the No- larities with the Morongovsky to Samoedsky ex- ril'sk-type rocks (Subgroup 5A) have higher and trusives, suggesting that they are stratigraphi- more variable 87Sr/86Sr, 0.7054-0.7084, and the cally younger than the Lower Talnakh-type rocks Lower Talnakh-type rocks (Subgroup 5B) have (Table 1 ). initial 87Sr/86Sr=0.7074-0.7089. The Noril'sk- Initial Sr isotope ratios are summarised in Fig. and Lower Talnakh-type rocks are the only in- 12. This highlights the increase in a7Sr/86Sr from trusive samples analysed which have Sr isotope ratios similar to those of the Nadezhdinsky for- mation lavas (Fig. 12). Overall, Esr values range

Intrusive Suites from +3 to +66, with end=+4 to -12 (Fig. o amp o (5B) 13 ). The alkaline rocks have eSr and end values of 19 to 32 and 0.7 to -3.2 respectively and, t~t:n:t~0¢~ (5A) since these rocks have relatively high incompat- o o (4) ible element contents, they are less sensitive to cm~oooo (3) the effects of crustal contamination. They may o o (2) therefore provide independent evidence for the o© o (1) presence of mantle with enriched radiogenic iso- tope ratios in the Noril'sk region. The dolerites Lavas and samples from differentiated intrusions not • Sm associated with ore junctions have broadly simi- Ku lar esr and eNd values of 3 to 21 and 3.6 to -0.8. • Hr These tend to overlap the Nd and Sr isotope field ~e Mr of the Morongovsky-Samoedsky basalts, rather ~e• Mk than those of the Tuklonsky and Nadezhdinsky formations (Fig. 13 ). ,~ ~e~ Nd A/~x Tk :7, 2, ~ '" at ~ Gd 8 _", MOR B ' ', ,~--,.Q\

0 O0 Sv 4 .... -.re----Alkaline O~ Iv ENd I I I _~tk ~o.r~ .... '~ .... 0.703 0.705 0.707 0.709 . Dotenws oral type

87Sr] 86 Sr -4- ', ',,,~ ~ L,r ,~kh " \ J type Fig. 12. Initial Sr isotope ratios in the lavas and intrusive suites • Tk I of the Siberian Trap. The iavas are presented in stratigraphic -R" sequence, and the intrusive rocks are in the five groups of Naldrett et al. ( 1992 ): ( 1 ) alkalic intrusions, (2) Ti-rich do- I I ~ I I I I -20 0 20 4() 6(I lerite dykes, (3) dolerite sills and dykes, (4) differentiated bodies not related to ore junctions and (5) differentiated gSr bodies related to ore junctions. (5A) and (5B) are here Fig. 13. ~Na-ESr for selected samples of the intrusive suites. termed the Noril'sk- and the Lower Talnakh-types respec- Filled triangles: Noril'sk type; open triangles: Lower Tal- tively. The symbols for lavas are as in Fig. 4, except that Hr- nakh-type; circles: dolerites; dots: alkaline intrusives; open Sm and Mk-Mr are both represented by dots. diamonds: differentiated, unmineralised intrusions. 84 C.J. Hawkesworth / Lithos 34 (I 995) 61-88

Although the Lower Talnakh-type samples intrusive rocks tend to have higher Sr/Sm than have Sr isotope ratios similar to some of the No- the lavas, and within both the Noril'sk- and ril'sk-type rocks, they have markedly different erda Lower Talnakh-types 878r/86Sr increases with Sr values. The latter have relatively restricted CNO, contents (Fig. 14c). Sr increases with increasing but a wide range in ~Sr, whereas the Lower Tal- A1203, and so the arrays in Fig. 14c are inter- nakh-types are characterised by high Esr and low preted in terms of varying proportions of modal ~Na (Fig. 13). The range in 87Sr/86Sr in the No- plagioclase and interstitial magma. This presum- ril'sk and Lower Talnakh rocks is similar to that ably reflects open system differentiation within in the Nadezhdinsky lavas, but there is increas- the individual intrusions but, in addition, the ing evidence that the cause of the elevated 87Sr/ data in Fig. 14b and c indicate that 875r/86Sr was 86Sr ratios in the intrusives differs from that in significantly higher in the initial magmas of the the lavas. Fig. 14a demonstrates that for Nd iso- Lower Talnakh-type rocks, consistent with their topes and La/Sm the intrusive rocks plot in the lower average eNd, than in the Noril'sk-type. field for the basalts. However, many of the No- In summary, two overall trends can be identi- ril'sk- and Lower Talnakh-type samples are dis- fied. First, there is the between-suite variations placed to higher S7Sr/S6Sr than the basalts on a in, for example, REE and Nd isotopes, in the in- diagram of STSr/S6Sr-La/Sm (Fig. 14b). These trusions which are similar to those observed in the basalts and second, the within-suite displace- ment to high 87Sr/86Sr and Sr/Sm in the No- ril'sk- and Lower Talnakh-type rocks. The be- tween-suite variations are dominated by the trend to the Nadezhdinsky basalts, and that has been consistently attributed to crustal contami- nation (Lightfoot et al., 1990, 1993; Naldrett et ~ype al., 1992; Wooden et al., 1993). By analogy it is inferred that the differences between the Lower I I I I (b) Talnakh and the other intrusion types are also O.709" A primarily due to crustal contamination pro- • •• A ~A 87Sr/~6Sr •" &/~" 5 cesses (Naldrett et al., 1992). The within-suite 0.7O7. displacement to higher 87Sr/86Sr and Sr/Sm is attributed to subsequent, shallow level, open sys- tem differentiation within individual intrusions. 0.705. A major priority is to establish whether sulphide mineralisation was particularly associated with 0.703 I I I I the processes responsible for one or other of the 2 3 4 5 La/Sm two overall trends, but this cannot be resolved on the available data. The Noril'sk-type rocks are 0.7O9 (c) associated with much more sulphide mineralis- 87Sr/~Sr ation than the Lower Talnakh-type, and yet the (1.7117 latter appear to have undergone more crustal contamination (Naldrett et al., 1992). It might, therefore, be inferred that sulphide mineralisa- 0.705 tion was more closely associated with the late

n ru tc,~ stage, open system differentiation, but there is no clear trend of increasing 878r/86Sr with Cu/Zr or [[.7([3 J p I I I 0 2IX) 400 6(10 Cu/Sm within the Noril'sk-type rocks. Sr ppm Fig. 14. eya-La/Sm, S7Sr/S6Sr-La/Sm and S7Sr/S6Sr-Sr for the intrusive rocks analysed. Symbols as in Fig. 1 1. CJ. Hawkesworth / Lithos 34 (1995) 61-88 85

7. Concluding discussion (Arndt et al., 1993; Wooden et al., 1993). How- ever, the argument that because such CFB mag- This paper offers a progress report on one of a mas were homogenised within the continental number of parallel studies currently being car- crust, the crust is also the source of their distinc- ried out on the extrusive and intrusive rocks of tive trace element and isotope signatures, is not the Siberian Trap. It is a time of tantalising in- particularly compelling. Moreover, we are reluc- sights which are sometimes difficult to test, in tant to invoke two crustal components, which many cases because different data are available would appear to have been of different ages to on different rock suites. For example, in the ac- explain their different end values. Rather we pre- cepted models the crustal contamination pro- fer the model in which most of the parental mag- cesses which were responsible for the distinctive mas were derived from source regions within the trace element and isotope signatures of the Na- continental mantle lithosphere (Lightfoot et al., dezhdinsky lavas triggered the precipitation of 1993), as has been argued for a number of the the sulphides that were subsequently emplaced low-Ti CFB associated with the break-up of as the ore bodies (e.g. Naldrett et al., 1992). Gondwana, (e.g. Hawkesworth et al., 1988; Hergt However, sulphur isotopes have only been deter- et al., 1991; Turner and Hawkesworth, 1995). mined on the ore minerals, and the models de- (iii) The Nadezhdinsky formation rocks are veloped from the sulphur isotope data and from characterised by elevated SiO2, La/Sm, Th and the trace element and radiogenic isotope varia- eSr, and relatively low Ni and Cu abundances. An tions in the Nd samples appear to be contradic- analysis of the nature of the contaminant re- tory [see (iii), below]. There is not room here quired if the parental magmas had smooth man- to reproduce the details of the current debates on tle normalised minor and trace element patterns, the origins of the Siberian Trap CFB, but there indicates that the contaminant would have been are a number of points which should be similar to a deep-seated crustal melt, such as the highlighted. granodiorite from the Bolgokhtokhsky Intru- (i) In the Siberian CFB, the variations in Ti sion, rather than to an upper crustal melt, or bulk appear to be relatively independent of those of sediment. This is in contrast to the sulphur iso- HFSE such as Nb and Ta (see, for example, the tope data on ore minerals which suggests a large different trends of Ti/Zr-La/Sm and Ta/La-La/ component of sulphur was derived from the un- Sm in Figs. 11 and 3. This is a feature of a num- derlying evaporites (Grinenko, 1985). How- ber of CFB and of certain island arc suites (e.g. ever, as indicated above, this cannot be resolved Hawkesworth et al., 1993 ). Its origins are not well until sulphur isotope data are also available on understood, but, in the context of the Siberian the lavas. CFB the apparently separate behaviour of Ti and (iv) The geochemistry of individual intru- Ta, or Nb, makes it difficult to model the avail- sions can often be matched with that of particu- able data in any simple two component mixing lar lava units, and such correlations are used to model, such as between plume-derived magma evaluate the chronology of different intrusion and upper continental crust. types (Naldrett et al., 1992; Fedorenko, 1994; (ii) The eNd--Ta/La arrays further emphasise Table 1 ) Thus, for example, the Yergalakhsky has that a minimum of three components were in- been correlated with the Ivakinsky lavas, and the volved in the generation of the Siberian CFB. The Fokinsky with the Gudchikhinsky (Group l, Ta- large volumes of basaltic magma, and the in- ble l ). The dolerites and differentiated intru- ferred high eruption rates, suggest that a mantle sions of Groups 2 to 5 have low Ti/Y and Gd/ plume was present, and plume-derived magmas Yb ratios (Fig. 11 ), and so they all appear to have are assumed to have high Ta/La and eNd values. crystallised from magmas associated with the The other two components have low Ta/La and generation of the Upper Series lavas, i.e. after the variable end, and it has been suggested that all extrusion of the Gudchikhinsky picrites. such enriched signatures are due to the addition (v) Two overall trends have been identified. of crustal material to plume-derived melts First, the between suite variations in the intru- 86 C.J. Hawkesworth /Lithos 34 (1995) 61-88 sions are similar to those in the lavas, and the tinental flood basalts. Isotope research at the general increase in Th and La/Sm, and decrease Open University is funded by the NERC. The in ~Nd, as best developed in the Nadezhdinsky isotope analyses were carried out by Mabs John- rocks, has been widely modelled by crustal con- ston and Marcel Regelous and the manuscript tamination processes (Lightfoot et al., 1990, was prepared by Janet Dryden. 1993; Naldrett et al., 1992; Wooden et al., 1993; Fedorenko, 1994). Second, within-suite varia- tions in the Noril'sk- and Lower Talnakh-type References rocks are different from those in the lavas. They are characterised by elevated 87Sr/S6Sr and Sr/ Amdt, N.T. and Christensen, U., 1992. The role of litho- Sm attributed to late stage, open system differ- spheric mantle in continental flood volcanism. J. Geo- phys Res., 97: 10,967-10,981. entiation with individual intrusions. The Lower Arndt, N.T., Czamanske, G.K., Wooden, J.L. and Fedor- Talnakh-type magmas experienced greater de- enko, V.A., 1993. Mantle and crustal contributions to grees of crustal contamination, similar to the continental flood volcanism. Tectonophysics, 223: 39-52. Nadezhdinsky lavas, (Naldrett et al., 1992) and Beane, J.E., Turner, C.A., Hooper, P.R., Subbarao, K.V. and this took place prior to the final emplacement and Walsh, J.N., 1986. Stratigraphy, composition and form of the Deccan basalts, western Ghats, India. Bull. Volcanol., crystallisation responsible for the within-suite 48: 61-83. variations of 875r/86Sr and Sr observed in Fig. Campbell, I.H. and Griffiths, R.W., 1990. Implications of 14b and c. mantle plume structure for the evolution of flood basalts. (vi) The Lower Talnakh- and Noril'sk-type Earth Planet. Sci. Lett., 99: 79-93. rocks crystallised a similar range in olivine com- Campbell, I.H., Czamanske, G.K., Fedorenko, V.A., Hill, R.I., Stepanov, V. and Kunilov, V.E., 1992. Synchronism of the positions, but the Lower Talnakh magmas were Siberian traps and the Permian-Triassic boundary. Sci- characterised by significantly lower Ni and Cr ence, 258: 1760-1763. contents. In the model in which sulphide precip- Carlson, R.W., 1991. Physical and chemical evidence on the itation occurred in response to the crustal con- cause and source characteristics of flood basalt volca- tamination processes that were responsible for nism. Aust. J. Earth Sci., 38: 525-544. Courtillot, V., Feraud, G., Maluski, H. Vandamme, D., Mo- the elevated La/Sm and lower EN~ of the Lower reau, M.G. and Besse, J., 1988. Deccan flood basalts and Talnakh (and Nadezhdinsky) rocks, sulphide the Cretaceous/Tertiary boundary. Nature, 333: 843-846. precipitation and segregation took place before Cox, K.G. and Hawkesworth, C.J., 1985. Geochemical stra- the crystallisation of the low Ni olivines sampled tigraphy of the Deccan traps at Mahabaleshwar, Western in the Lower Talnakh rocks, and before the de- Ghats, India, with implications for open system mag- matic processes. J. Petrol., 26: 355-377. velopment of the within-suite trends to elevated Dalrymple, G.B., Czamanske, G.K., Lanphere, M.A., Stepa- S7Sr/868r (Fig. 14b and c). Within individual in- nov, V. and Fedorenko, V., 1991.4°Ar/39Ar ages of sam- trusions massive sulphides typically cross cut the ples from the Noril'sk-Talnakh ore-bearing intrusions and silicates. Thus, while the initial crystallisation of the Siberian flood basalts. Eos, 72:570 (abstr.). sulphides appears to have pre-dated that of oliv- Doherty, W., 1989. An internal standardization procedure for the determination of Yttrium and the rare earth elements ine within the intrusions, the final emplacement in geological materials by inductively coupled plasma mass of the massive sulphides post-dates crystallisa- spectrometry. Spectrochim. Acta, 44B: 263-280. tion of the silicate component (Naldrett et al., Ellam, R.M. and Cox, K.G., 1989. A Proterozoic lithospheric 1992). source for Karoo magmatism: evidence from the Nu- anetsi picrites. Earth Planet. Sci. Lett., 92: 207-218. Fedorenko, V.A., 1981. Petrochemical series of extrusive rocks of the Noril'sk region. Sov. Geol. Geophys., 22(6): 66- Acknowledgements 74. Fedorenko, V.A., Stifeeva, G.T., Makeeva, L.V., Sukhareva, The manuscript was improved by the con- M.S. and Kuznetsova, N.P., 1984. Basic and alkali-basic structive and patient comments of three anony- intrusions of Noril'sk area in connection with their com- agmatism with effusive formations. Geol. Geophys., 6: 56- mous referees. We thank Janet Hergt, Graham 65. Pearson, Nick Rogers and Simon Turner for Fedorenko, V.A. and Petrukhov, I.E., 1988. Generalized many discussions on the generation of the con- scheme for the diagnosis of effusive rocks from Noril'sk C.J. Hawkesworth / Lithos 34 (1995) 61-88 87

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