Isotope-geochemical systematics of kimberlites and related rocks from the Siberian Platform

Russian Geology and Geophysics 48 (2007) 272–290 www.els\e\vier.com/locate/rgg\

Isotope-geochemical systematics of kimberlites and related rocks from the Siberian Platform S.I. Kostrovitsky a, *, T. Morikiyo b, I.V. Serov c, D.A. Yakovlev a, A.A. Amirzhanov d a

Institute of Geochemistry, Siberian Branch of the RAS, 1a ul. Favorskogo, Irkutsk, 664033, Russia b Shinshu University, Matsumoto, 390-8621, Japan c ALROSA Ltd., 6 ul. Lenina, Mirny, 678170, Russia d Institute of the Earth’s Crust, Siberian Branch of the RAS, 128 ul. Lermontova, Irkutsk, 664033, Russia Received 27 February 2006

Abstract Using the ICP-MS method we have studied the isotope systematics of Sr and Nd as well as trace element composition of a representative collection of kimberlites and related rocks from the Siberian Platform. The summarized literature and our own data suggest that the kimberlites developed within the platform can be divided into several petrochemical and geochemical types, whose origin is related to different mantle sources. The petrochemical classification of kimberlites is based on persistent differences of their composition in mg# and in contents of indicator oxides such as FeOtot, TiO2, and K2O. The recognized geochemical types of kimberlites differ from one another in the level of concentration of incompatible elements as well as in their ratios. Most of isotope characteristics of kimberlites and related rocks of the Siberian Platform correspond to the earlier studied Type 1 basaltoid kimberlites from different provinces of the world: Points of isotopic compositions are in the field of primitive and weakly depleted mantle. An exception is one sample of the rocks from veins of the Ingashi field (Sayan area), which is characterized by the Sr and Nd isotopic composition corresponding to Type 2 micaceous kimberlites (orangeites). The most important feature of distribution of isotopic and trace-element compositions (incompatible elements) is their independence of the chemical rock composition. It is shown that the kimberlite formation is connected with, at least, two independent sources, fluid and melt, responsible for the trace-element and chemical compositions of the rock. It is supposed that, when rising through the heterogeneous lithosphere of the mantle, a powerful flow of an asthenosphere-derived fluid provoked the formation of local kimberlite chambers there. Thus, the partial melting of the lithosphere mantle led to the formation of contrasting petrochemical types of kimberlites, while the geochemical specialization of kimberlites is due to the mantle fluid of asthenosphere origin, which drastically dominated in the rare-metal balance of a hybrid magma of the chamber. © 2007, IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: Kimberlites; petrochemical and geochemical types; isotope systematics

Introduction To study kimberlites is quite a difficult task. The hybrid nature of the rock, abundance of mantle- and crust-derived xenogenous matter, and different degree of secondary hydrothermal-metasomatic alteration are the main factors distorting the primary composition of kimberlites. This is why the kimberlite nature cannot be understood without a detailed and correct analysis of data on their isotopic and trace-element compositions. The very early studies (Borodin et al., 1976; Ilupin et al., 1978; Kostrovitsky, 1986) have shown that

* Corresponding author. E-mail address: [email protected] (S.I. Kostrovitsky)

kimberlites are characterized by an extremely wide range of variability in contents of trace elements. It has been established that two kimberlite subprovinces including southern diamondiferous and northern diamond-poor fields significantly differ in the level of concentrations of incompatible elements. To characterize kimberlites from individual pipes and from fields as a whole, analysts used, as a rule, averaged parameters of the composition. It is not clear, however, what is reflected by kimberlite differences in average compositions: different degree of contamination or different degree of secondary alteration of rocks, or different mantle sources? Similar questions arise when interpreting isotopic data. In the last years, the works placing an emphasis upon isotopic geochemical characteristics became more abundant

1068-7971/$ - see front matter D 2007, IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.rgg.2007.02.011

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

(Kostrovitsky et al., 1999; Agachev et al., 2001; Bogatikov et al., 2004; Kononova et al., 2005). The authors came to an important conclusion that there are chiefly basaltoid-type kimberlites (of Type 1) within the Yakutian Province, whose appearance is related to a weakly depleted mantle source, while Type 2 micaceous kimberlites, called orangeites by Mitchell (1996), are absent. On the other hand, the authors indicated sufficiently wide variations of isotope ratios of Sr and Nd, which are beyond the ranges typical of classical kimberlites. A question arises again: What is the cause of these deviations? Some authors (Agashev et al., 2000) believe that relatively high 87Sr/86Sr values are specific for the mantle source of the Yakutian kimberlites. But is this the case? There is evidence (Kostrovitsky, 1986; Khar’kiv et al., 1998) that secondary metasomatic processes play an important role in the change of the isotopic composition of the kimberlites. The posed questions prompted us to characterize the primary magma component in terms of isotopic geochemistry. Here, we summarize a host of data on chemical, trace-element, and isotope-geochemical compositions of kimberlites from most occurrences of kimberlite volcanism on the Siberian Platform. These data are our own as well as borrowed from the literature. The study is based on the collection of samples of kimberlites and related rocks little altered by secondary processes. They were taken from different fields, including the Malaya Botuobiya, Daldyn, Alakit, Upper Muna, Nakyn, Kuoika, Malya Kuonamka, Luchakan, Dyuken, Ary-Mastakh, Staraya Rechka, Orto-Yhargyn, Kharamai, and Ingashi. The rock compositions were analyzed by the chemical (RFA) and trace-element (ICP-MS) methods at the Institute of Geochemistry (Irkutsk). The Sr-Nd isotopy in the rocks was studied using a Finnigan MAT 262 mass spectrometer, at Shinshi University (Japan). The isotopic composition of Sr in kimberlites of the Upper Muna field was instrumentally analyzed on a Finnigan MAT 262 mass spectrometer at the Institute of Geochemistry (Irkutsk).

Short description of kimberlites Most occurrences of kimberlite volcanism within the Siberian Platform are united (Khar’kiv et al., 1998) into the Yakutian Diamond Province. Beyond the province, kimberlites have been found in the Krasnoyarsk Territory (Kharamai and Kotui fields) and in the East Sayan region (Ingashi field). The kimberlite fields of the Yakutian Province are situated within three mineragenic zones (Fig. 1): Vilyui-Markha, Daldyn-Olenek, and Olenek-Anabar. The kimberlite occurrence constrain four main stages: (1) Proterozoic (for the Ingashi veins only); (2) Middle Paleozoic (for the majority of kimberlites of the Daldyn-Olenek and Vilyui-Markha zones); (3) Lower Mesozoic (for kimberlites and related rocks of the Olenek-Anabar zone as well as Kotui abd Kharamai fields); (4) Upper Mesozoic (for some kimberlites from the Kuoika and Upper Molodo fields). In composition, the studied rocks can be divided into four genetic groups: (1) kimberlites that belong to southern diamon-

273

diferous fields of the Yakutian Province (the first five fields in the above list); (2) nondiamondiferous and diamond-poor kimberlites of the northern fields of the Yakutian Province (the rest of the list but the last field); (3) Type 2 kimberlites (orangeites) of the Ingashi field (Sayans); (4) carbonatites that form individual pipes within the kimberlite fields of the Anabar region (Dyuken, Staraya Rechka, and Orto-Yhargyn). Some uncertainty arises in recognizing the third group. On the basis of mineral and geochemical compositions of the rocks, Sekerin et al. (1991) came to the conclusion that the veined kimberlites of the Ingashi field should be referred to as lamproites. However, analysis of the rocks shows that the Ingashi veins are not homogeneous in composition. Most of them are rich in SiO2, TiO2, and K2O (>40, 2.2–3.9, and 1.4–2.8 wt.%, respectively), have no carbonate component, and contain accessory minerals (priderite, armalcolite), which actually makes them similar to olivine lamproites. In our opinion, however, one of the veins (Pravoberezhnaya or no.6) is filled with compositionally typical kimberlite (Sekerin et al. referred them to as carbonatized phlogopite-olivine lamproites). Mineralogically, this is essentially phlogopite-carbonateolivine (with serpentine substituting for olivine) rock of fine porphyraceous texture. Its chemical composition is typical of kimberlites, with 26.34 wt.% SiO2, relatively low content of TiO2 (to 1 wt.%), and rather high K2O (1.44 wt.%). We have studied the isotope-geochemical composition of the rock filling only vein 6. Kimberlite classifications are usually based on differences in structure and texture and in mineralogy. According to structural and textural signature, Russian authors divide the kimberlite rocks into: (1) kimberlites with massive structure; (2) kimberlite breccia, including autolith kimberlite breccia; (3) tuff breccia, xenotuff breccia, tuffs. The pipes of southern diamondiferous fields of the Yakutian Province are largely (except for the Upper Muna field) filled with the breccia-type kimberlites and, much less frequently, with the massive variety. In the pipes of northern fields, the volume percentage of massive kimberlites considerably increases: Many bodies are filled only with porphyraceous massive kimberlite. For this reason some authors (Nikishov, 1984) called them stocks. According to mineral composition, essentially olivine, montichellite-, pyroxene-, melilite-, calcite- and phlogopite-olivine varieties of kimberlites are recognized. The southern fields are dominated by essentially olivine kimberlites with carbonateolivine (or carbonate-serpentine) mesostasis. Montichellitebearing kimberlites play an important role in the Upper Muna field only. The northern fields harbor all the above varieties of kimberlites.

Petrochemical types of kimberlites First of all, the question arises whether or not it is reasonable to distinguish petrochemical types of kimberlites. The universally accepted classifications of kimberlites are based on distinctions in structure, texture, mineralogy or facies but not in petrochemistry. Though some Russian authors

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Fig. 1. A synoptic map of location of kimberlite fields within the Siberian Platform (after A.D. Khar’kiv et al. (1998), with our supplements). Boundary of: 1 — Siberian Platform, 2 — Yakutian Kimberlite Province, 3 — boundary between subprovinces of southern (I) and northern (II) fields of Yakutian Province: 4–6 — ovals corresponding to kimberlite fields of different ages: 4 — Proterozoic, 5 — Middle Paleozoic, 6 — Mesozoic. Fields: 1 — Malaya Botuobiya, 2 — Nakyn, 3 — Alakit-Markha, 4 — Daldyn, 5 — Upper Muna, 6 — Chomurdakh, 7 — Severnei, 8 — West Ukukit, 9 — East Ukukit, 10 — Ogoner-Yuryakh, 11 — Merchimden, 12 — Kuoika, 13 — Upper Molodo, 14 — Toluop, 15 — Khorbusuonka, 16 — Luchakan, 17 — Kuranakh, 18 — Dyuken, 19 — Ary-Mastakh, 20 — Staraya Rechka, 21 — Orto-Yhargin, 22 — Kotui, 23 — Kharamai, 24 — Taichikun-Nemba, 25 — Chadobets, 26 — Ingashi, 27 — Chompolin, 28 — Tobuk-Khatystyr. Hatched bands — mineragenic zones: A — Vilyui-Markha, B — Daldyn-Olenek, C — Olenek-Anabar.

(Blagul’kina, 1971; Milashev, 1965) suggested that petrochemical types are to be recognized, their recommendations were ignored. The use of petrochemical parameters for classification of kimberlites is reasonable only if these parameters are stable and the distinguished petrochemical types of kimberlites have their own genetic significance. Kimberlite rocks are known to be characterized by wide variations in rock-forming oxides (Ilupin et al., 1978; Khar’kiv et al., 1991; Nikishov, 1984; Vasilenko et al., 1997). There are some factors that are responsible for the diversity of chemical compositions of rocks. One of the factors can be conventionally called primary-magmatic. It implies that the regional differences in the composition of kimberlites recorded either throughout the Yakutian Province or within its separate fields stem from the originally different compositions of the initial kimberlite fluxed melts. The other factors are related to the secondary redistribution of chemical components of kim-

berlites. They include all processes of fractionation of the kimberlite melt on its ascending from the mantle depths such as liquation, leading uplift of carbonate-saturated fluid, fractional crystallization, and gravity settling of pheno- and xenocrysts, extrusive-explosive formation of different structural-textural varieties of kimberlites in pipe and crater environments. The secondary factors include the processes of contamination of host rocks as well as hydrothermal-metasomatic processes of carbonatization and serpentinization of various intensity. It seems reasonable to distinguish a certain petrochemical type only if it reflects the specific primary composition of the kimberlite. Seemingly, the abundance of secondary factors of redistribution of petrochemical oxides should completely mutilate the primary composition of kimberlites and, hence, there is no sense in distinguishing any petrochemical types. However, this is not the case. Such oxides as TiO2, FeOtot, K2O, Al2O3, and P2O5 are relatively

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inert in secondary processes (Ilupin et al., 1978; Khar’kiv et al., 1991). The first three oxides are to be taken into account when comparing compositions of kimberlites. Within each kimberlite field in both southern and northern Yakutian Province, there are pipes and even clusters of pipes filled by kimberlites with relatively high or low contents of TiO2, FeOtot, and K2O. For example, in the Malaya Botuobiya field the kimberlites from the Mir and Anomaliya-21 pipes are enriched in TiO2 (averaged 1.7 and 2.5 wt.%, respectively) and in FeOtot (9.5 and 7 wt.%, respectively) (Khar’kiv et al., 1991). The kimberlites depleted in TiO2 and FeOtot fill the Internatsional’naya and Imeni Dvadtsat’ Tret’ego S’ezda KPSS (23 CPSU Meeting) pipes (0.4 and 0.7 wt.% TiO2 and 6 and 5 wt.% FeOtot). In both groups of pipes, however, they are poor in K2O (less than 1 wt.%). The kimberlites from the Dachnaya pipe of the Malaya Botuobiya field are poor in Fe and rich in K (to 5 wt.% FeOtot and more than 2 wt.% K2O). Remarkably, the contents of TiO2 and FeOtot in pipes with high-Mg kimberlite vary in a narrow range, within the fluctuations typical of this type of rocks. For instance, the contents of TiO2 in the kimberlites of the Internatsional’naya and Aikhal pipes vary from 0.2 to 1.26 and from 0.1 to 0.96 wt.% as estimated from 163 and 313 analyses, respectively (Vasilenko, 1997). Most data (80–90%) fall on the interval 0.1–0.7 wt.% TiO2. On the contrary, the kimberlites enriched in TiO2 and FeOtot (Mir and Udachnaya pipes) are characterized by a wide range of contents of these oxides (0.1–2.5 wt.% TiO2 and 3–15% FeOtot, respectively), which suggests an ability of this type to differentiation. The pipes of this kind are often multiphase. Thus, there are solid grounds to conclude that the differences in composition of the kimberlites from the two groups of pipes are quite distinct and sufficient for attributing them to different petrochemical types. Similar groups of pipes, usually close in space, have been established nearly in all kimberlite fields. The expediency of recognition of petrochemical types is confirmed by the study of the composition characteristics of rock-forming and accessory minerals. For example, the Feand Ti-rich kimberlite usually contains olivine with a widely varying composition (from 7 to 14% fayalite end-member), picroilmenite being predominant in the heavy fraction. The high-Mg kimberlites contain olivine with usually no more than 8–9% fayalite, the heavy fraction being dominated by garnet and Cr-spinel rather than by picroilmenite (e.g., in the Aikhal and Internatsional’naya pipes). According to chemical composition, the following contrasting types of kimberlites and related rocks have been recognized within the Yakutian Province (Table 1): (1) high-Mg, low-Ti, low-K; (2) high-Mg, low-Ti, high-K; (3) Mg-Fe, high-Ti, low-K; (4) Fe-Ti, low-K; (5) Fe-Ti, high-K. In the southern fields, the high-Mg and Mg-Fe kimberlites are varieties with 5–6 and over 6 wt.% FeOtot, respectively, while the low- and high-K kimberlites contain under and over 1 wt.% K2O, respectively. The Fe-Ti type of kimberlites is characterized by limit values of over 8 wt.% FeOtot and over 1.5 wt.% TiO2. Proportions of petrochemical types are different for differ-

275

ent kimberlite fields. Of eight pipes in the Malaya Botuobiya field, four are filled by kimberlite of the third Mg-Fe type, three — of the first type, and one, of the second type. Two pipes are known from the Nakyn field which are represented by Type 2 kimberlite alone. The Daldyn field is dominated by Type 3 kimberlite, while Type 1 and 2 kimberlites form only few pipes. The pipes of the Alakit-Markha field are filled with Type 1 and 3 kimberlites approximately in equal parts. In the Upper Muna field, Type 3 kimberlites are predominant. Type 4 and 5 kimberlites occur in the northern Yakutian Province, especially, in the Anabar region. Kimberlites of the first three types occur there less frequently. An exception is the Kuoika field, where the Type 1 kimberlites are rather abundant (e.g., in the Obnazhennaya, Olivinovaya, Ruslovaya, and other pipes). The most contrasting stable differences in contents of TiO2, FeOtot, K2O, and P2O5 are recorded between the kimberlites filling the southern diamondiferous and northern diamondpoor kimberlite fields. It is still unclear what is the source of kimberlite alkalis. The basaltoid type of kimberlites developed chiefly within the southern diamondiferous fields is characterized by a low content of alkalis. The kimberlites from the northern fields are considerably richer in them. In both southern and northern fields the distribution of alkalis is extremely uneven, though quite specific. In the southern fields, the maximum concentrations of alkalis are observed in high-Mg low-Ti type of kimberlite (pipes of the Nakyn field; Dachnaya pipe from the Malaya Botuobiya field; Zagadochnaya and Kusova pipes from the Daldyn field), whereas the opposite correlation is observed in the northern fields — the maximum concentrations of alkalis are observed in the Fe- and Ti-richest varieties of kimberlites. Possibly, the sources of alkalis for the southern and northern fields were different. Another problem to be addressed is alkali budget. A typical ratio of alkali oxides in kimberlites is a significant predominance of K2O over Na2O (3:1 to 10:1) with a very low content of Na2O (in kimberlites of southern fields it does not usually exceed 0.1 wt.%). There are, however, exceptions. Elevated concentrations of Na2O (up to 0.5–0.7 wt.%) are documented in the kimberlites of deep horizons of some diamondiferous pipes, e.g., in the Internatsional’naya, Udachnaya pipes and in pipes of the Upper Muna field. We are sure that these anomalous values are due to contamination of halite from the evaporite sequence of enclosing rocks or to the interaction of kimberlites with brines established at corresponding horizons. However, some authors (Kamenetsky et al., 2004) believe that the chlorine source is the mantle. Quite a specific approach to the petrochemical study of kimberlites was used by Vasilenko (1997). He proposed to classify kimberlites on the basis of their TiO2 contents. In our opinion, Vasilenko overestimates the importance of TiO2 for dividing kimberlites into “populations” of genetic significance. Within the same pipe, he recognizes sometimes several populations of kimberlites whose generation is supposed to be related to different levels of the lithosphere mantle. Actually, though TiO2 is an inert oxide, its content in kimberlites varies

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Table 1 Petrochemical types of kimberlites distinguished within the Yakutian Province PetroDescription chemical type

Content of indicator oxides (wt.%) FeOtot

TiO2

K2O

Pipe (examples)

Area of occurrence

1

High-Mg, low-Ti, low-K

<6

<1

<1

Aikhal, Internatsional’naya, Obnazhennaya

All southern diamondiferous fields but Nakyn

2

High-Mg, low-Ti, high-K

<6

<1

1–2.5

Dachnaya, Zagadochnaya, Bukovinskaya, Nyurba

Malaya Botuobiya, Daldyn, and Nakyn fields

3

Mg-Fe, high-Ti, low-K

6–9

1–2.5

<1

Mir, Udachnaya, Dal’nyaya, Zarnitsa, Sytykan, Yubileinaya, Zapolyarnaya

All diamondiferous fields but Nakyn

4

Fe-Ti, low-K

8–15

1.5–7

<1,5

Druzhba (Chomurdakh field), Kosmicheskaya (Ary-Mastakh field), Viktoriya (Staraya Rechka field)

Northern fields

5

Fe-Ti, high-K

8–15

1.5–7

1.5–5

Lychkhan, Pozdnyaya (Luchakan Northern fields field), Rudny Dvor, Bargydymalakh (Ary-Mastakh field)

as function of carbonatization degree. The plots TiO2 versus CaO and TiO2 versus CO2 for the Dyuken and Upper Muna kimberlites show (Fig. 2) a distinct opposite correlation. It is quite another matter if kimberlites are characterized by a stable content of TiO2 within one pipe, cluster of pipes or field as a whole. Then this oxide can be successfully used as a classification sign (Bogatikov et al., 2004; Kononova et al., 2005).

Geochemical typification of kimberlites Trace-element compositions of kimberlites from different pipes are difficult to compare because of their great variability even within the same pipe. The reported contents of some

trace elements in kimberlite from such pipes as Aikhal, Internatsional’naya, and Obnazhennaya often differ by a factor of 2–5 and even by an order of magnitude. The main agencies that change the composition are processes involved with differentiation of the kimberlite fluxed melt during its uplifting from the mantle chamber and emplacement in the pipe space as well as with the secondary alteration of rocks (serpentinization and carbonatization, weathering). By sampling the freshest specimens we tried to minimize the action of the second factor. The influence of the first factor cannot be properly estimated. For this reason the compositions are to be compared according to the level of concentrations typical of grouped samples rather than according to the absolute contents of trace elements in individual samples. The main signature of the trace-element composition of

Fig. 2. Correlation of contents of oxides in kimberlites: A — TiO2 and CaO of the Dyuken field (tie lines join composition points of kimberlite from the same pipe); B — TiO2 and CO2 from the Upper Muna field.

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

277

Fig. 3. Spidergrams of distribution of primitive-mantle-normalized trace elements (McDonough and Sun, 1995). For kimberlites of geochemical type 1 from: a — diamondiferous pipes: 1 — Aikhal, 2 — Internatsional’naya, 3 — Lipa, 4 — Mir, 5 — Udachnaya; 6 — Upper Muna field. Hereafter, hatched field is range of compositions from diamondiferous kimberlites of geochemical type 1.

kimberlites is the presence of two groups of elements drastically contrasting in behavior — compatible and incompatible with respect to the ultrabasic nature of rocks. As the main concentrator of compatible elements is the rock-forming mineral, olivine, there seem to be a relationship between the pattern of their distribution and the discriminated petrochemical types of kimberlites. In fact, as compatible elements are more “sensitive” to secondary alteration than major oxides, this relationship is not sufficiently distinct. For this reason, the geochemical typification of kimberlites was based on distribution pattern of incompatible elements. Analysis of trace-element composition of kimberlites and related rocks developed within the Siberian Province indicates the presence of six main geochemical types that differ in concentration of incompatible elements. The first type comprises the most typical kimberlites, which compose most of the diamondiferous southern fields (Malaya Botuobiya, Daldyn, Alakit-Markha, and Upper Muna). The trace-element composition of kimberlites and specific values of indicator ratios of elements are given in Tables 2–4. Despite wide variations of nearly all incompatible elements in kimberlites, their distribution on spidergrams (Fig. 3) shows stable plots characterized by steep slopes in both sides beginning with Th, U, and Nb. The longer right branch is complicated by a minimum of HFSE (Hf, Zr, and Ti). The REE distribution pattern is indicative of high fractionation coefficients (La/Yb), averaging 146 to 196 in all diamondiferous fields but the Nakyn one. The spidergram for the Upper Muna field is somewhat complicated because of errors of the ICP-MS analyses. Among the kimberlites of diamondiferous and diamondfree fields, the maximum concentrations of incompatible elements are recorded (Fig. 4, Table 2) in the micaceous kimberlites of the Zagadochnaya pipe (Daldyn field) recognized as Type 2. In the Daldyn field, micaceous kimberlites

also compose the Kusova, Bukovinskaya and Gornyatskaya pipes. In the contents of such elements as Rb, Sr, Zr, Nb, REE, U, and Th, micaceous kimberlites are considerably superior to the classical kimberlites of geochemical Type 1 (including the kimberlite varieties most enriched in these elements). It should be noted, however, that the indicator ratios of trace elements for micaceous kimberlites as a whole (see Table 3) little differ from the corresponding ratios specific for Type 1 kimberlites, which just makes the plots for the two types of kimberlites quite conform (see Fig. 4). Type 3 kimberlites occur in the highly diamondiferous Nakyn field. They differ (see Table 2) from Type 1 kimberlites

Fig. 4. Spidergram of distribution of primitive-mantle-normalized trace elements (McDonough and Sun, 1995). For kimberlites of geochemical types 2 and 6 from Zagadochnaya pipe (Daldyn field) (1) and Pravoberezhnaya vein (Ingashi field) (2), respectively.

89

96

71

801

21.6

Cu

Zn

Rb

Sr

Y

71.8

11.7

3.23

Nd

Sm

Eu

178

18.8

Pr

La

Ce

704

97

Ba

0.9

303

Ni

Cs

54

Co

287

495

Cr

157

190

V, ppm

Nb

96.79

Total

Zr

5.64

2.39

8.9

63.7

18.2

184

105

895

0.2

181

139

11.4

947

26

60

414

1182

97

945

160

97.30

9.97

10.13

5.03

CO2

1.09

0.07

1.30

8.78

24.74

H2O

0.09

0.42

Na2O

P2O5

7.57

24.72

MgO

1.59

0.20

MnO

CaO

9.46

10.62

K2O

2.35

2.52

Al2O3

FeOtot

0.14

30.18

2.25

29.57

2.90

SiO2, wt.%

30.64

4.51

17.9

132.4

37.9

365

209

1496

1.0

237

246

21.2

1307

66

109

55

1048

74

816

130

98.69

4.93

7.40

1.14

0.16

1.78

9.11

28.27

0.18

9.17

2.78

1.86

—

—

—

—

—

—

870

—

—

—

—

1400

48

—

63

1000

93

830

130

—

4.79

6.87

1.14

0.17

1.74

8.38

29.18

0.18

9.49

2.75

1.8

31.69

4

—

—

—

—

—

—

830

—

—

—

—

1800

86

—

110

690

72

760

360

—

10

6.94

1.15

0.15

2.1

15.35

19.69

0.17

8.5

4.69

1.87

25.98

5

3.58

13.7

98.4

28.0

268

143

2086

1.2

249

180

16.2

513

130

100

46

994

84

783

112

98.38

4.93

6.84

0.41

0.15

3.49

7.62

22.91

0.17

9.59

4.83

3.87

32.26

6

5.41

20.2

142.2

39.7

365

220

3663

0.5

330

413

24.6

679

51

126

144

648

75

751

123

100.56

4.62

7.68

0.32

0.13

1.22

12.42

23.58

0.21

11.68

3.18

4.16

29.86

7

4.25

16.3

112.9

31.4

295

164

1054

1.6

262

299

21.3

747

49

98

31

527

75

791

182

99.96

6.78

7.20

0.93

0.10

0.98

12.08

23.99

0.22

13.13

2.90

3.97

25.42

8

3.8

15.1

106.6

29.9

293

163

740

1.7

230

501

20.0

632

72

177

185

651

84

790

135

99.77

11.59

6.31

3.30

0.1

0.68

19.06

18.40

0.21

11.03

3.19

2.03

22.43

9

3

1

2

99-14

78-1003 78-1215 78-1185 78-1166 78-1316 78-1380 78-1395 99-3

TiO2

Component

Table 2 Chemical and trace-element compositions of kimberlites and related rocks of the Siberian Platform

4.9

19.7

129.7

33.0

301

174

2290

0.3

196

341

27.4

704

42

121

80

628

80

543

163

98.93

11.69

3.31

0.79

0.1

0.81

14.74

23.44

0.25

12.23

2.83

3.01

25.12

10

8.7

33.6

232.6

66.6

671

423

1640

0.6

532

342

43.9

571

82

157

183

600

76

685

216

98.57

4.29

4.46

1.99

0.1

1.96

10.58

26.95

0.26

13.03

2.69

4.21

27.34

11

4.3

16.2

110.7

30.9

294

164

2107

0.8

208

325

21.1

951

76

92

76

540

63

429

136

98.97

10.75

4.3

1.42

0.1

1.89

15.77

22.91

0.2

11.02

3.05

2.23

24.78

12

97-192 97-128 97-90

2.9

10.6

72.2

19.9

191

105

990

0.6

170

262

16.5

621

59

119

138

821

90

745

226

99.96

2.68

7.99

0.64

0.37

2.02

8.34

21.66

0.19

14.03

2.81

5.78

31.45

13

—

—

—

—

—

—

1690

—

—

—

2020

60

—

63

470

51

280

240

—

14.33

5.65

1.71

0.28

2.28

19.2

14.02

0.21

10.68

4.6

2

23.78

14

78-1534 90-15

3.3

11.9

78.7

21.5

204

111

1333

0.8

174

353

19.8

1284

106

149

161

643

89

614

268

—

1.06

4.91

0.77

0.61

2.92

11.1

20.95

0.19

13.81

4.6

5.07

33.5

15

90-21

6.3

23.0

152.1

41.2

435

222

2141

1.0

301

419

28.9

1303

35

94

177

330

55

293

176

—

5.54

7.11

0.56

0.14

1.87

12.6

20.95

0.21

11.28

5.2

3.44

30

16

90-55

—

—

—

—

—

—

1140

—

—

—

—

1320

60

—

61

460

49

1100

220

—

18.06

5

1.05

0.22

2.02

25.04

11.4

0.15

8.89

4.16

3.1

20.24

17

2.4

9.3

68.7

18.8

184

103

513

0.4

99

108

10.6

535

31

83

32

1398

81

524

45

99.72

3.98

10.74

0.42

0.06

1.17

5.60

31.86

0.13

8.38

1.20

1.42

33.53

18

90-60-1 Xp-10

4.1

15.6

109.9

30.9

299

166

1397

0.9

212

447

19.3

307

76

102

51

1157

81

760

128

99.96

0.37

7.57

0.20

0.15

2.43

11.10

23.94

0.16

9.65

4.80

1.99

36.52

19

Xp-8

4.6

18.3

130.8

37.1

344

190

1719

0.6

219

294

21.1

1244

67

93

47

1019

72

833

113

100.81

5.48

7.68

0.98

0.24

1.92

12.90

27.22

0.17

8.76

2.60

2.04

30.14

20

Xp-11

3.9

13.6

84.6

22.8

218

126

2505

1.0

200

329

23.1

1881

121

120

126

706

68

620

173

99.96

2.15

2.25

1.18

1.15

3.32

12.5

21.11

0.21

10.1

6.4

2.14

36.75

21

01-11

278 S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

1.93

0.25

1.36

Er

Tm

Yb

6.88

7-191

23

11.57

3.20

7-460

22

Th

U

Component

8.44

0.13

—

107

723

Total

V, ppm

Cr

455

328

98.63

6.59

10

—

—

0.92

H2O

P2O5

1.12

16.32

22.14

CO2

<0.1

0.54

Na2O

10.81

26.9

MnO

MgO

1.26

0.11

FeOtot

CaO

10.71

8.66

Al2O3

K2O

3.25

2.39

TiO2

0.2

22.11

4.2

30.36

2.11

SiO2, wt.%

2.92

13.26

16.08

7.46

8.78

Pb

3.37

0.07

0.54

0.10

0.89

0.40

2.63

0.68

Ta

0.16

0.91

Ho

7.56

4.93

Dy

Hf

1.13

Lu

9.74

Gd, ppm

13.80

787

143

99.28

7.05

4.51

0.77

0.06

0.14

10.3

27.9

0.26

15.56

2.9

4.07

24.55

24

7-483

5.96

26.19

15.91

10.46

5.87

0.14

0.96

0.21

1.78

0.85

5.39

1.45

865

218

99.85

7.66

5.53

0.54

0.05

0.07

11.5

29.4

0.18

10.79

2.2

2.46

28.58

25

7-487

6

23

—

—

—

—

—

—

—

—

—

—

—

4

811

89

99.37

14.97

5.87

0.76

0.11

0.87

15.24

25.17

0.17

7.46

2.12

1.03

25.06

26

7-78

9

34

—

—

—

—

—

—

—

—

—

—

—

5

858

111

99.57

12.98

4.61

0.83

0.15

1.35

16.52

25.25

0.26

8.16

2.65

1.35

24.56

27

7-384

4.41

24.04

5.32

15.17

5.17

0.13

1.07

0.20

1.48

0.65

4.38

1.04

10.38

6

1057

183

99.8

3.58

8.62

0.17

0.15

2.28

4.56

28.71

0.12

9.73

3.72

4.75

32.34

28

7-388

7.97

30.58

14.15

12.50

8.54

0.18

1.24

0.28

2.06

1.05

6.34

1.61

15.82

7

910

110

—

14

6.25

0.47

0.11

1.03

18

24.13

0.24

7.11

1.97

0.93

24.59

29

7-276

5.56

22.01

10.04

13.85

7.51

0.16

1.24

0.23

1.76

0.83

5.04

1.27

11.93

8

350

220

—

4.85

9.92

0.75

1.13

0.4

11.84

24.79

0.22

11.9

3.8

4.09

24.73

30

7-93

3.6

24.4

7.9

13.6

12.5

0.2

1.2

0.2

1.8

0.8

4.8

1.2

11.3

9

3

1

2

99-14

78-1003 78-1215 78-1185 78-1166 78-1316 78-1380 78-1395 99-3

Tb

Component

Table 2 (continued)

515

185

—

1.18

4.63

0.7

0.25

0.65

14.4

24.7

0.23

12.13

4.4

3.76

30.57

31

7-473

3.6

34.4

18.0

8.8

7.8

0.2

1.4

0.2

2.1

1.0

5.9

1.5

14.1

10

7.9

28.3

11.6

9.3

7.7

0.2

1.0

0.2

1.7

0.9

5.3

1.4

13.0

12

2.8

12.6

5.1

10.5

6.8

0.1

0.9

0.2

1.4

0.7

3.9

0.9

8.3

13

—

—

—

—

—

—

—

—

—

—

—

—

—

14

78-1534 90-15

3.1

13.7

10.6

9.4

9.0

0.1

1.1

0.2

1.7

0.8

4.5

1.1

9.7

15

90-21

694

111

—

—

—

0.69

0.41

0.37

8.62

37.3

0.1

6.36

1.56

0.57

30.74

32

843

62

—

—

—

0.93

<0.2

0.47

17.3

25.71

0.07

5.57

1.66

0.55

26.58

33

699

46

—

—

—

0.65

0.2

0.35

8.34

35.36

0.1

6.19

1.49

0.54

29.52

34

645

162

—

—

—

1.05

0.2

1.41

8.73

26.39

0.16

9.68

2.73

2.41

31.28

35

505

298

99.73

0.77

7.61

0.63

0.77

1.45

10.30

16.55

0.20

12.25

7.10

5.16

35.98

36

406

107

99.48

5.14

11.11

0.22

0.56

0.41

12.60

28.74

0.18

8.74

2.70

1.70

26.36

37

01-280 01-361 00-289 01-163 9-200 9-154

12.4

46.7

20.0

15.4

7.4

0.2

1.7

0.4

3.7

1.9

12.2

2.9

27.2

11

97-192 97-128 97-90

—

—

—

—

—

—

—

—

—

—

—

—

—

17

2.8

11.3

3.5

5.5

3.1

0.0

0.5

0.1

0.9

0.5

3.0

0.8

7.0

18

90-60-1 Xp-10

4.4

22.5

8.1

8.7

10.7

0.2

1.2

0.3

1.7

0.8

5.1

1.3

11.7

19

Xp-8

5.2

22.3

14.6

8.9

6.7

0.1

1.0

0.2

1.6

0.8

5.2

1.4

13.7

20

Xp-11

4.2

13.8

20.6

8.4

8.1

0.2

1.2

0.2

1.8

0.8

4.9

1.2

11.0

21

01-11

32

50

—

30.8

2.24

3.55

0.28

0.51

28.14

9.5

1.04

11.72

1.33

0.18

4.89

38

32

29

99.77

28.16

1.66

1.83

1.2

1.19

28.38

9.78

0.88

7.88

3.47

0.17

13.64

39

662

89

100.2

12.78

12.02

0.42

0.06

0.6

14.55

22.34

0.19

7.39

2.7

1.18

25.1

40

98

150

—

22.85

1.73

1.91

0.4

1.76

30.29

7.8

0.39

9.66

3.4

0.78

17.86

42

1010

58

—

—

—

1.76

0.2

1.44

9.66

26.48

0.15

7.94

2.06

0.98

26.34

43

(continued on next page)

106

97

99.32

26

5.1

0.54

0.19

1.25

31.36

8.21

0.23

8.74

2.58

1

13.07

41

78-1555 78-1565 90-67 78-1610 90-74 Ing-1

5.0

20.1

41.2

12.4

11.1

0.2

1.5

0.3

2.4

1.2

7.4

1.9

17.8

16

90-55

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290 279

65

2.0

0.3

1.2

0.2

5.3

7.1

20.5

15.3

4.3

Er

Tm

Yb

Lu

Hf

Ta

Pb

Th

U

7.4

36.8

11.2

17.7

5.3

0.2

1.3

0.3

2.1

1.0

6.2

1.6

15.1

5.2

18.3

131.8

36.6

361

229

3768

1.2

402

227

78

6.7

70.0

11.3

27.3

8.4

0.2

1.4

0.3

2.5

1.2

8.1

2.1

21.6

7.0

29.4

224.7

65.2

577

369

1326

0.2

433

366

31.1

701

14

139

74

611

97

24

7-483

2.6

12.0

5.3

10.2

3.7

0.1

0.6

0.1

1.0

0.5

3.0

0.7

7.1

2.4

9.1

62.6

17.7

174

99

578

0.2

198

160

12.8

627

4

102

86

1087

101

25

7-487

3.3

16.1

6.2

6.5

3.1

0.1

0.5

0.1

0.9

0.4

2.7

0.7

7.1

2.5

9.4

66.3

19.0

194

119

1624

0.5

166

145

11.4

1033

42

68

43

1358

82

26

7-78

5.9

29.9

11.2

10.6

3.4

0.1

1.1

0.2

1.7

0.8

5.3

1.3

12.1

3.9

14.9

111.6

33.0

367

207

2405

0.6

294

148

22.6

1903

69

77

73

833

69

27

7-384

1.5

7.0

3.6

11.4

1.6

0.0

0.3

0.0

0.5

0.2

1.3

0.3

3.4

1.0

3.8

28.2

8.4

89

54

578

1.2

139

56

5.9

435

144

110

219

1415

110

28

7-388

11.0

25.0

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

1100

—

—

—

—

2400

38

—

95

1400

90

29

7-276

9.0

27.0

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

450

—

—

—

—

530

14

—

103

520

95

30

7-93

11.0

18.0

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

1460

—

—

—

—

1280

56

—

150

880

80

31

7-473

2.4

16.6

4.4

10.9

3.9

0.1

0.6

0.1

0.9

0.5

3.0

0.8

7.9

2.6

10.6

80.2

22.7

227

124

686

0.2

223

165

11.6

919

17

86

67

1062

78

32

5.5

24.0

2.8

9.2

3.4

0.1

0.8

0.1

1.3

0.6

4.1

1.1

10.8

3.5

14.2

110.1

32.3

325

193

936

0.3

263

143

17.5

618

24

42

11

1363

62

33

2.3

16.8

5.1

6.9

3.5

0.1

0.6

0.1

1.1

0.5

3.6

0.9

8.5

3.0

11.7

81.1

23.1

221

122

469

0.2

166

151

14.1

539

20

48

21

1423

75

34

5.9

24.6

17.2

10.5

5.5

0.1

1.1

0.2

1.7

0.8

5.5

1.3

12.6

4.2

16.3

120.4

34.8

343

200

938

0.5

234

236

21.8

736

52

79

55

1006

74

35

2.9

10.1

5.1

8.8

7.7

0.2

1.1

0.2

1.5

0.7

3.8

0.9

8.0

2.8

9.7

61.2

16.7

156

81

3051

1.0

144

301

18.0

768

102

123

114

346

66

36

4.4

16.6

8.0

10.6

5.0

0.1

0.9

0.2

1.4

0.6

4.0

1.0

9.3

3.1

12.4

88.6

24.8

238

134

740

1.0

234

225

17.5

1648

86

85

44

972

69

37

01-280 01-361 00-289 01-163 9-200 9-154

39.0

86.0

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

1500

—

—

—

—

6500

89

—

7

63

19

38

20.4

122.4

42.0

25.1

5.3

0.6

5.0

0.9

9.1

4.2

28.5

7.8

87.7

26.7

118.5

1029.5

269.1

3032

1929

1807

2.1

1012

235

108.3

2104

27

362

109

19

15

39

2.8

18.4

7.2

5.6

3.3

0.3

2.2

0.4

3.0

1.2

6.3

1.2

9.1

2.6

10.2

81.4

24.9

271

171

594

0.6

234

133

33.8

618

34

79

61

705

60

40

3.1

32.1

34.4

4.1

3.0

0.5

3.4

0.6

4.8

2.1

10.4

1.9

12.8

3.5

12.9

104.0

32.6

345

250

536

1.1

321

118

57.1

624

31

111

52

51

20

41

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

—

1410

—

—

—

—

3950

45

—

21

37

18

42

5.6

24.5

45.1

7.9

9.8

0.1

1.2

0.2

2.2

1.0

6.2

1.8

20.9

6.8

29.5

295.9

88.9

814

433

1119

0.8

225

446

25.6

2168

74

80

77

1109

81

43

78-1555 78-1565 90-67 78-1610 90-74 Ing-1

Note. Samples taken from fields: 1–5 — Kuranakh; 6–9 — Luchakan; 10–12 — Dyuken; 13–17 — Ary-Mastakh; 18–20 — Kharamai; 21 — Bol’shaya Kuonamka headwaters; 22 — Chomurdakh; 23–31 — Kuoika; 32 — Daldyn; 33 — Alakit-Markha; 34–35 — Malaya Botuobiya; 36–37 — Upper Muna; 38–41 — Staraya Rechka (Nomokhtookh site); 42 — Orto-Yhargin; 43 — Ingashi (Sayan region). Names of pipes are reported in Table 6.

5.9

0.9

Tb

Ho

1.4

Gd

Dy

4.1

12.0

Eu

94.8

15.4

Sm

Pr

Nd

234

25.6

Ce

966

125

La

0.9

Cs

Ba

166

Nb

27.5

25.2

213

Y

Sr

Zr

910

60

825

Rb

131

105

58

85

Zn

356

Cu

77

1043

23

22

Co, ppm

7-191

7-460

Ni

Component

Table 2 (continued)

280 S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

357 0.2 2.3 0.5 0.7 4.0 28 171 0.5 0.3 17 71 21 87 40 0.03 0.14

Cav

Daldyn (5)

292–481 0.1–0.4 1.5–3.7 0.3–0.9 0.5–0.7 2.3–5.9 16–44 124–208 0.4–0.6 0.2–0.4 14–19 45–92 16–30 21–179 34–42 0.01–0.03 0.13–0.14

Interval

538 0.2 6.4 1.3 0.9 6.8 75 196 0.7 0.6 17 57 20 47 41 0.03 0.13

Cav 127–799 0.2 1.0–12.9 0.2–2.7 0.5–1.9 3.4–15.1 15–298 53–247 0.4–1.0 0.2–1.3 7–21 19–85 2–29 14–112 35–47 0.01–0.04 0.12–0.14

Interval

Alakit-Markha (7)

441 0.2 2.1 0.4 1.0 4.3 35 146 0.7 0.3 15 56 16 35 47 0.03 0.14

Cav 154–743 0.1–0.3 0.6–3.3 0.2–0.7 0.7–1.1 1.3–7.6 10–124 69–201 0.5–0.9 0.1–0.7 8–23 36–108 7–27 0–126 40–57 0.02–0.05 0.11–0.16

Interval

Malaya Botuobiya (10)

401 0.2 26.0 5.5 1.2 8.2 28 167 0.7 0.4 16 57 15 60 52 0.02 0.13

Cav 216–840 0.1–0.3 0.7–482 0.2–104 0.9–2.1 0.1–25.3 3–109 74–336 0.6–1.1 0.1–1.3 9–23 37–70 5–99 33–115 39–81 0.01–0.04 0.1–0.16

Interval

Upper Muna (22)

40 0.1 0.7 0.1 3.3 52.3 4 12 0.8 0.2 3 139 4 46 46 0.14 0.19

Cav

Glimmerite, Upper Muna (1)

REEtot U/Th Th/Pb U/Pb Zr/Nb Ba/Nb Ba/Rb La/Yb La/Nb Ce/Sr Ce/Y Nb/U Nb/Ta Ti/Zr Zr/Hf Lu/Hf Sm/Nd

Parameter

Interval

584–10282 0.1–0.6 0.9–3.8 0.1–2.2 0.2–0.6 1.7–2.5 17–116 73–883 0.7–4.5 0.4–1.4 6–57 18–104 16–78 0.5–53 40–53 0.08–0.15 0.09–0.13

Cav

4550 0.2 2.6 0.8 0.4 2.0 54 354 2.0 0.9 25 64 44 27 44 0.12 0.11

Nomokhtookh site, carbonatites (4)

863 0.2 2.4 0.5 1.5 7.0 28 167 0.8 0.6 14 47 24 48 43 0.02 0.15

Cav

Dyuken (4)

633–1486 0.1–0.3 1.9–3.1 0.2–0.7 0.6–2.2 3.1–11.7 10–55 125–253 0.7–0.9 0.3–1.2 11–15 27–63 17–35 24–74 40–46 0.01–0.03 0.14–0.15

Interval 663 0.2 1.6 0.3 1.0 4.8 21 179 0.7 0.3 15 60 19 63 41 0.02 0.14

Cav 394–897 0.2–0.3 0.8–2.7 0.2–0.5 0.5–1.8 3.6–6.3 10–34 71–241 0.4–0.9 0.2–0.5 8–18 40–100 12–23 44–97 38–45 0.02–0.03 0.14–0.16

Interval

Kuranakh (5)

579 0.2 2.6 0.6 1.0 6.9 32 133 0.5 0.4 13 58 20 92 40 0.02 0.14

Cav 221–839 0.2–0.3 1.1–4.5 0.3–1.1 0.7–1.3 3.2–15.7 13–82 88–177 0.4–0.8 0.2–0.5 10–16 41–83 16–26 55–129 35–48 0.02–0.03 0.13–0.16

Interval

Luchakan (8)

688 0.2 3.1 0.7 1.4 6.8 34 155 0.8 0.4 17 41 23 40 43 0.02 0.14

Cav

399–917 0.2–0.3 1.5–5.9 0.4–1.6 1.1–2.1 5.2–8.2 17–76 2–222 0.5–1.0 0.2–1.0 15–19 33–48 18–25 14–79 35–52 0.01–0.02 0.13–0.14

Interval

Kharamai (5)

Table 4 REE contents (ppm) and indicator ratios for kimberlites and related rocks from northern kimberlite fields of the Siberian Platform

Note. Hereafter in tables: parenthesized is number of analyses, Cav — averaged content.

REEtot U/Th Th/Pb U/Pb Zr/Nb Ba/Nb Ba/Rb La/Yb La/Nb Ce/Sr Ce/Y Nb/U Nb/Ta Ti/Zr Zr/Hf Lu/Hf Sm/Nd

Parameter

Table 3 REE contents (ppm) and indicator ratios for kimberlites and related rocks from southern kimberlite fields of the Siberian Platform

502 0.2 2.7 0.5 0.7 7.2 43 160 0.6 0.3 14 72 21 130 40 0.04 0.14

Cav

124–1310 0.1–0.2 1.6–6.2 0.3–0.7 0.1–1.5 1.8–35 4–130 77–259 0.3–1.8 0.1–0.8 10–19 19–125 2–59 30–512 30–48 0.02–0.1 0.13–0.16

1365 0.2 9.1 2.2 1.0 11.4 39 190 1.2 0.3 22 29 11 15 61 0.05 0.13

Cav

424 0.2 1.6 0.3 1.2 5.7 15 167 0.5 0.2 9 69 23 91 40 0.03 0.16

Cav

152–599 0.2–0.3 0.7–3.3 0.2–0.5 0.3–4.0 0.5–15.7 12–19 46–658 0.3–0.8 0.1–0.3 5–11 39–113 15–37 42–192 35–42 0.02–0.05 0.15–0.17

Interval

1702 0.2 0.5 0.1 2.0 5.0 15 364 1.9 0.4 32 40 29 13 46 0.01 0.10

Cav

Ingashi (1)

489 0.2 2.1 0.5 1.4 6.2 23 115 0.6 0.3 11 68 19 71 39 0.02 0.15

Cav

220–912 0.2–0.3 0.5–5.9 0.1–1.5 0.7–2.0 1.6–13.8 10–61 65–207 0.2–1.0 0.1–0.6 8–16 39–109 15–24 10–132 36–43 0.01–0.03 0.14–0.16

Interval

Ary-Mastakh (11)

1140–1484 0.2–0.3 5.2–11.7 1.3–2.8 0.8–1.2 8.9–14.1 36–44 168–216 0.9–1.6 0.3 21–23 22–34 8–13 14–15 60–62 0.05 0.13–0.14

Interval

Zagadochnaya pipe (3)

Chomurdakh, OgonerYuryakh field (8)

89–149 0.1–0.2 0.2–9.1 0.0–2.0 1.8–2.6 14.8–31.3 8–140 24–40 0.5–0.7 0.0–0.2 3–6 76–148 2–19 59–69 39–46 0.04–0.06 0.18–0.21

Interval

Interval

Kuoika (12)

110 0.2 3.0 0.6 2.2 20.2 42 32 0.6 0.1 4 109 14 63 42 0.05 0.2

Cav

Nakyn (4)

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290 281

282

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

Fig. 5. Spidergram of distribution of primitive-mantle-normalized trace elements (McDonough and Sun, 1995). For kimberlites of geochemical type 3: 1 — from pipes of the Nakyn field, 2 — glimmerite of the Upper Muna field, 3 — alkaline basaltoid (sp. An-446) from the Malaya Botuobiya field.

in having low concentrations of incompatible elements such as U and Th, HFSE (Zr, Nb, Ta, Hf), and REE (Fig. 5). In trace element composition these kimberlites are similar to the kimberlites of the Arkhangel’sk Province and kimberlites filling the Snap Lake diamondiferous sill (Canada). The anomalous nature of this kind of kimberlites is characterized in detail by Russian authors (Pokhilenko et al., 2000; Serov et al., 2001; Bogatikov et al., 2004; Kononova et al., 2005). The Nakyn field kimberlites are distinguished not only by low concentrations of incompatible elements but, more importantly, by absolutely different values of indicator ratios of trace elements and, first of all, by a relatively low coefficient of REE fractionation (La/Yb) (see Table 2). It is still debatable whether it is worthy to classify the kimberlites and related rocks of the northern fields of the Yakutian Province as an individual geochemical type. It is known (Borodin et al., 1976; Ilupin et al., 1978; Bogatikov et al., 2004) that the kimberlites of the northern fields are generally distinguished by higher concentrations of incompatible elements. Our data (see Table 2) confirm this conclusion. However, the variations in composition for individual samples as well as variations of averaged indicator ratios of trace elements for individual fields typical of southern diamondiferous and northern diamond-free fields (Table 5) suggest that, though the differences exist, they are not significant. The maximum differences are recorded for the rocks of the Dyuken field, which often contain a carbonatite component, possibly, somewhat related to the close Mal’dangar carbonatite massif and to other, still hidden, magmatic occurrences of carbonatites. On the other hand, the wide occurrence of kimberlites with a high concentration of trace elements in the northern fields is explained by the considerable denudation owing to which massive rocks were exposed to the day. These rocks were little altered by superimposed hydrothermal metasoma-

tism considerably decreasing the concentration of trace elements. Nevertheless, though the kimberlites from different northern fields of the Yakutian Province are close to the 1st geochemical type, there are certain differences between them, which is illustrated by corresponding spidergrams of distribution of incompatible elements (Figs. 6 and 7). All the distributions of incompatible elements from kimberlites of the Kuranakh, Luchakan, Dyuken, Ary-Mastakh, Kharamai, Kuoika, Chomurdakh, and Ogoner-Yuryakh fields are quite similar and are characterized by a very wide region of coincidence with the distribution for diamondiferous kimberlites. At the same time, many of the analyses are distinguished in higher concentrations of such elements as Cs, Rb, Sr, Ba, Zr, Nb, Ta, and Hf. Thus, it seems reasonable to distinguish the 4th geochemical type for some kimberlites and related rocks within the northern fields. Distinct geochemical differences are recorded in carbonatite breccia filling some pipes within the kimberlite fields of the Anabar region (Marshintsev, 1974). It is supposed (Chernysheva and Kostrovitsky, 1981) that they were formed when the kimberlite pipes intruded the carbonatite massifs occurring at depth. As compared with kimberlites (see Figs. 3–7), the carbonatite breccia is distinguished by the higher level of such elements as Sr, Ba, REE, U, Th, Nb and Ta (see Table 2, Fig. 8). In contents of Cs, Rb, Ba, Hf, and Zr the carbonatites are comparable to kimberlites. Striking differences in most indicator ratios of carbonatites (see Table 4) strongly suggest that we deal with the 5th geochemical type, which is characterized, first of all, by a very high La/Yb parameter of fractionation of REE, averaging 354. Wide variations in compositions (see Table 2) are due to different proportions of kimberlite and carbonatite components in the studied breccia samples. The micaceous rocks of the Ingashi field referred by different authors to as kimberlites (Vladimirov, 1987) or lamproites (Sekerin et al., 1991), in distribution of trace elements are most similar (see Table 2, Fig. 4) to the micaceous kimberlites of the Zagadochnaya pipe (2nd geochemical type). At the same time, some specific features of their composition give grounds for recognizing them as the 6th geochemical type. They differ from the 1st geochemical type in having more Sr, Hf, Zr, Pb, and REE and, mainly, a higher La/Yb parameter of fractionation of REE (364). The rocks of the Ingashi field differ from the kimberlites of the Zagadochnaya pipe in having relatively low concentrations of Ba, Th, U, Nb, Ta, and are distinguished by values of most indicator ratios, including La/Yb and Nb/U. Thus, according to contents of incompatible elements the kimberlites and related rocks within the Siberian Platform are divided into six geochemical types of rocks. The most abundant rocks are of types 1 and 4. They compose the overwhelming majority of pipes in the southern and northern fields of the Yakutian Province. The other four geochemical types of kimberlites and related rocks, including the micaceous kimberlites of the Daldyn field (as few as two clusters of pipes), kimberlites of the Nakyn field (Nyurbinskaya and Botuobinskaya pipes), carbonatite breccia (some pipes from

283

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290 Table 5 Trace-element composition (ppm) and indicator ratios of elements from kimberlites of southern and northern fields of Yakutian Province Parameter

Southern diamondiferous field

Northern diamond-poor fields

Interval

Interval

total

field averaged

total

field averaged

Sr

178–2152

526–803

307–2587

695–1106

Ba

51–3939

775–1316

162–4847

1140–1871

Zr

68–508

131–218

18–690

143–377

Nb

69–378

172–207

67–555

204–292

Ta

5–33

10–26

2–46

9–18

Hf

2–8.8

3.3–4.3

0.4–16.5

3.5–8.9

Rb

1–169

26–65

4–223

48–81

Cs

0.2–3.6

0.4–0.9

0.2–2.3

0.5–1.1

REE

127–840

357–538

152–1486

424–863

U

0.7–6.8

3–4.1

1.7–12.4

3.2–6.9 15–33

Th

4.5–34

13–20

4.9–70

U/Th

0.1–0.4

0.2

0.1–0.3

0.2

Th/Pb

0.6–48

2.3–6.4

0.5–6.2

1.6–3.1

U/Pb

0.2–2.7

0.5–1.3

0.2–1.6

0.3–0.7

Zr/Nb

0.5–2.1

0.7–1.2

0.1–4.0

0.7–1.5

Ba/Nb

1.3–25.3

4–8.2

0.5–35

4.8–7.2

Ba/Rb

15–298

28–75

10–130

15–43

La/Yb

53–336

146–196

46–158

115–179

Ce/Sr

0.2–1.3

0.3–0.6

0.1–1.2

0.2–0.6

Ce/Y

7–23

15–17

5–19

9–17

Nb/U

19–108

56–71

19–125

41–72

Nb/Ta

2–99

15–21

2–59

19–24

Ti/Zr

10–179

35–87

10–512

40–92

Zr/Hf

34–81

40–52

35–52

39–43

Lu/Hf

0.01–0.05

0.02–0.03

0.01–0.1

0.02–0.04

Sm/Nd

0.1–0.16

0.13–0.14

0.13–0.17

0.14–0.16

the Staraya Rechka and Dyuken fields), and micaceous kimberlites (veins of the Ingashi field) are actually of narrow local distribution. The most striking feature of the distribution of incompatible elements in kimberlites of the 1st and 4th geochemical types is that the element concentration does not depend or depends weakly on petrochemical composition (Kostrovitsky et al., 2004). The reported spidergrams for diamondiferous kimberlites (see Fig. 3) demonstrate that both high-Mg low-Ti low-K varieties from the Aikhal and Internatsional’naya pipes and Fe-enriched, high-Ti kimberlites from the Mir and Udachnaya pipes (1st and 2nd petrochemical types, respectively) are characterized by the close level of concentrations of incompatible elements and similar distribution patterns. The same is displayed by spidergrams for the kimberlites from the northern fields (Kostrovitsky et al., 2004).

Isotope studies We have studied the Sr and Nd isotope systematics for a representative collection of kimberlites and related rocks (44

samples) from different fields of the Siberian Platform. To summarize the obtained results, we used our own (Table 6) and literature (Agashev et al., 2000; Bogatikov et al., 2004; Kostrovitsky et al., 1999) data, with a total of 22 additional samples. On the (86Sr/87Sr)0–εNd plot (Fig. 9) the isotope characteristics of kimberlites and related rocks of the Yakutian Province correspond to those of the earlier studied (Mitchell, 1986; Smith, 1983; Tainton and McKenzie, 1994) Type 1 kimberlites from different provinces of the world, for most points of isotopic compositions fall on the field of primitive and weakly depleted mantle. However, some values of isotopic composition of Sr (more than 0.705) evidently depart from the signature of this source. For this reason some authors (Agashev et al., 2000) suggest that, along with the depleted source, a more enriched source existed for the kimberlites of the Yakutian Province. To understand the nature of relatively high values of 87Sr/86Sr, we additionally studied a collection of kimberlite samples from the Zapolyarnaya pipe of the Upper Muna field distinguished by a different degree of carbonatization (Table 7). Earlier, we (Kostrovitsky, 1986) made a conclusion on the dominating role of the enclosing frame of carbonate rocks of the

284

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

Fig. 6. Spidergrams of distribution of primitive-mantle-normalized trace elements (McDonough and Sun, 1995). For kimberlites and related rocks of geochemical types 1 and 4 from different fields of the Anabar region: a — Dyuken (1), Kuranakh (2), b — Luchakan (1), Kharamai (2), c — Ary-Mastakh.

sedimentary cover in the change of the primary isotopic composition of Sr in kimberlites. The measured 87Sr/86Sr (Kostrovitsky, 1986) in the carbonate and silicate phases of kimberlite from the Komsomol’skaya-Magnitnaya pipe (0.706 and 0.705, respectively) corroborates the conclusion that high Sr isotope ratios are due to the secondary process of carbonatization accompanied with the addition of sea-sedimentary Sr. It is well to bear in mind that not only carbonatization but also the secondary process of serpentinization can severely distort the primary mantle characteristics of the isotopic composition in kimberlites. Worthy of note is that diamondiferous kimberlites are distinguished by a Nd-depleted mantle source. Exceptions are kimberlites from the Zapolyarnaya pipe (Upper Muna field) and from pipes of the Nakyn field characterized by higher serpentinization. Kimberlites of the northern fields are not uniform in isotopic characteristics. The value of εNd for kimberlites and related rocks in the Anabar region varies in a

wide range (–1.58...+3.81), while for rocks of the Kuoika field, in a relatively narrow range (+3.08...+4.62), thus characterizing a generally more depleted source. The rocks of the Ingashi field from the Sayan region demonstrate the isotopic compositions of Sr and Nd similar in characteristics (see Fig. 9) to Type 2 kimberlites (orangeites), on the one hand, and to Leucite Hill lamproites, on the other. According to isotopic data, the carbonatites of the Anabar region are characterized by a relatively high degree of depletion of mantle source, commensurate nevertheless with the depletion for diamondiferous kimberlites. To study the dependence of 87Sr/86Sr and 143Nd/144Nd on the composition of the rocks in question, we have plotted these values as a function of variations of such oxides as TiO2 and K2O, which are the most inert in the secondary processes. The absence of correlation (Fig. 11) usually indicates that the isotopic characteristics do not depend on the contents of these oxides. The plot K2O–(143Nd/144Nd) demonstrates a weak

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

285

Fig. 7. Spidergrams of distribution of primitive-mantle-normalized trace elements (McDonough and Sun, 1995). For kimberlites and related rocks of geochemical types 1 and 4 from fields of Yakutian Province: a — Kuoika, b — Chomurdakh (1) and Ogoner-Yuryakh (2).

inverse dependence of the isotope ratio on K2O content. Note that the isotope ratios of Sr and Nd do not depend on the mg# of the studied kimberlites either.

Discussion

as a rule, they are separated in space, and differences in the content of indicator oxides (FeOtot, TiO2, K2O) are quite significant. It is supposed that their differences are due to the heterogeneity of the lithosphere mantle, where corresponding kimberlite magma chambers were formed. It is more difficult to estimate the significance of the geochemical types of

As regards the recognized petrochemical and geochemical types of kimberlites, we must answer, first of all, the following questions. Have they their own significance? To what extent is their formation due to the primary reasons, namely, to differences in the composition of mantle sources? The answer is positive for all petrochemical types of kimberlite, because,

Fig. 8. Spidergrams of distribution of primitive-mantle-normalized tarce elements (McDonough and Sun, 1995). For carbonatites (geochemical type 5) from fields of Anabar region: 1 — Staraya Rechka (Nomokhtookh site), 2 — Dyuken.

Fig. 9. Isotopic compositions of kimberlites and related rocks of the Siberian Platform on the plot (87Sr/86Sr)0–εNd. Composition fields for kimberlites and lamproites are borrowed from (Mitchell, 1986; Smith, 1983; Tainton and McKenzie, 1994). Kimberlites from fields of: 1 — Anabar region, 2 — Olenek (including: Kuoika, Chomurdakh, and Ogoner-Yurakh fields), 3 — southern diamondiferous fields, 4 — Nakyn, 5 — Ingashi; 6 — carbonatite pipes from Dyuken, Staraya Rechka, and Orto-Yhargyn kimberlite fields; 7 — host rocks.

78-1003 78-1215 78-1185 78-1166 78-1316 78-1380 78-1395 99-3 99-14 97-192 97-128 97-90 78-1534 90-15 90-21 90-56 90-60-1 Khr-10 Khr-8 Khr-11 001-11 7-460 7-191 7-483 7-487 7-78 7-384 7-388 7-276 7-93 7-473 01-280 01-361 00/289 01-163 9-200 9-154 78-1555 78-1565 90-67 78-1610 90-74 Ing-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Los’ Trudovaya Universitetskaya Universitetskaya Universitetskaya Otritsatel’naya Anomaliya 84 Lychkhan An 98/65 Anomaliya 4/90 Anomaliya 90/63 Anomaliya 37/89 Arktika Polyarnaya Rudny Dvor Sportivnaya Viktoriya Akhtakh-2 Ulakh-7 Bazovaya-3 Serbiyana Chomur Velikan Zenit Zhila 87/2 Vtorogodnitsa Obnazhennaya Obnazhennaya Obnazhennaya Seraya Montichellitovaya Udachnaya Aikhal Internatsional’naya Mir Novinka Zapolyarnaya Prima Tokio Dzho-sever An-41n Anomaliya 15/85 Ingashi

Pipe 19.4 9.01 18.1 17.8 15.8 14.1 25.2 20.7 25.4 20.8 37.2 18.6 11.4 23.2 14.6 15.1 11 9.3 16.4 19.3 15 15.9 20.9 32.4 9.52 9.47 15.7 4.06 14.4 19.3 16.8 10.81 11.79 12.08 11.2 10.62 12.76 125 104.96 10.22 13.49 32.4 29.84

Sm, ppm 145.7 65.7 135.4 132 113 100.7 111.4 147.7 172.4 136 260.7 114.6 77.2 153 96.6 104 66.3 68.2 119.5 141.6 93.8 97.9 125 247.8 65.6 67.8 117.3 30 108 136 116 81.51 114.17 87.42 135.51 68.11 92.84 1450 913.18 82.7 109.39 275 286

Nd, pm 0.512666 0.512587 0.512635 0.51263 0.512143 0.512611 0.512588 0.512396 0.512616 0.512664 0.512669 0.512671 0.512588 0.512663 0.512677 0.512576 0.512344 0.512534 0.512545 0.512523 0.512471 0.512564 0.512724 0.51271 0.512775 0.512744 0.512707 0.512717 0.51274 0.512745 0.512777 0.512568 0.51254 0.512608 0.51265 0.512619 0.512469 0.512701 0.512663 0.512687 0.512688 0.512678 0.511003

0.000013 0.000013 0.000014 0.000014 0.000014 0.000012 0.000013 0.000041 0.000013 0.000014 0.000013 0.000014 0.000013 0.000014 0.000014 0.000014 0.000018 0.000013 0.000014 0.000014 0.000014 0.000013 0.000013 0.000013 0.000014 0.000013 0.000013 0.000013 0.000014 0.000014 0.000012 0.000014 0.000014 0.000014 0.000014 0.000012 0.000013 0.000009 0.000014 0.000014 0.000014 0.000014 0.000013

Nd/144Nd 2σ

143

0.51255 0.512468 0.512519 0.51251 0.51232 0.512489 0.512391 0.512274 0.512488 0.512531 0.512545 0.51253 0.51246 0.51253 0.51254 0.51245 0.5122 0.512399 0.512409 0.512388 0.512332 0.512332 0.512631 0.512638 0.512695 0.512667 0.512633 0.512642 0.51265 0.51252 0.51267 0.512379 0.512393 0.512411 0.512532 0.512397 0.512273 0.51263 0.512581 0.512599 0.5126 0.51258 0.510478

3.8 2.2 3.2 3.1 –0.61 2.6 0.7 –1.58 2.6 3.4 3.7 3.4 2.0 3.5 3.7 1.9 –2.9 1.6 1.8 1.4 –0.4 3.1 3.4 3.5 4.6 4.1 3.4 3.6 4.7 5 5.2 4 4.3 4.6 7 4.3 1.9 5.3 3.4 3.8 3.8 4.3 –10.2

(143Nd/144Nd)0 εNd 55.3 31.1 72.3 62.9 114 141.3 74.1 55.2 39.7 44.2 88.2 81.8 67.5 66.8 111 97 70.7 31.7 84.5 74.7 135.4 66.8 89.2 15.2 114.8 43.3 72.6 155 48.6 20.4 73.3 18.88 27.22 21.83 57.96 116.6 93.54 12.4 25.64 36.51 33.79 40.8 84.28

Rb, ppm 1443 1170 806 1280 1900 634.6 775.7 785.4 1355.7 825.2 648.9 1109 594.8 2030 1284 1190 1360 600.6 304 1553 2063 1006 1121 849 749 1220 2191 511 1790 551 1220 1106.2 748.53 668.15 914.75 1003 1808 7070 2733.4 722.15 741.15 3860 2583

Sr, ppm 0.704161 0.706257 0.704013 0.704 0.704032 0.705869 0.704452 0.704448 0.70401 0.704299 0.705058 0.70449 0.705027 0.703997 0.704328 0.7051 0.704215 0.705132 0.706795 0.704602 0.705003 0.706005 0.70441 0.704304 0.704458 0.704644 0.70527 0.70806 0.705674 0.703869 0.704401 0.704601 0.704652 0.703905 0.704117 0.70611 0.707173 0.703476 0.703644 0.703868 0.704593 0.703712 0.70783

Sr/86Sr

87

0.000013 0.000012 0.000013 0.000013 0.000012 0.000014 0.000014 0.000014 0.000014 0.000014 0.000014 0.000014 0.000014 0.000012 0.000014 0.000012 0.000011 0.000013 0.000014 0.000014 0.000013 0.000014 0.000012 0.000013 0.000013 0.000014 0.000013 0.000013 0.000014 0.000014 0.000012 0.000014 0.000014 0.000014 0.000014 0.000013 0.000012 0.000014 0.000014 0.000013 0.000013 0.000014 0.000014

2σ

Rb/86Sr

0.110877 0.076878 0.259458 0.1416 0.1732 0.644163 0.276478 0.20332 0.084697 0.15484 0.39324 0.213278 0.328051 0.0954 0.2506 0.2351 0.1507 0.15252 0.804235 0.139183 0.189806 0.191957 0.230238 0.051747 0.443558 0.102717 0.095792 0.876137 0.0786 0.1073 0.1739 0.049365 0.105181 0.094494 0.183257 0.336241 0.149676 0.0051 0.027129 0.146221 0.131867 0.0304 0.094406

87

0.703814 0.706017 0.703201 0.7036 0.7035 0.703854 0.703587 0.703812 0.703745 0.703815 0.703828 0.703823 0.704001 0.7037 0.7035 0.7044 0.7037 0.70459 0.703935 0.704107 0.704409 0.705021 0.703952 0.704201 0.703575 0.70444 0.705079 0.706317 0.7055 0.7036 0.704 0.704348 0.704113 0.703421 0.703178 0.704387 0.706406 0.7035 0.703575 0.703494 0.704256 0.7036 0.706115

(87Sr/86Sr)0

Note. Samples 1–43 are taken from fields: 1–5 — Kuranakh, 6–9 — Luchakan, 10–12 — Dyuken, 13–17 — Ary-Mastakh, 18–20 — Kharamai, 21 — Bol’shaya Kuonamka headwaters, 22 — Chomurdakh, 23–31 — Kuoika, 32 — Daldyn, 33 — Alakit-Markha, 34, 35 — Malaya Botuobiya, 36, 37 — Upper Muna, 38–41 — Nomokhtookh, Staraya Rechka field, 42 — Orto-Yhargin, 43 — Ingashi (Sayan region).

Sample

Nos.

Table 6 Isotopic composition of Sr and Nd for kimberlites and related rocks of Siberian Platform

286 S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

287

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290 Table 7 Isotopic composition of Sr for kimberlites of Upper Muna field No.

Sp.

Pipe

Rb, ppm

Sr, ppm

Rb/Sr

1/Sr

87

Sr/86Sr

87

Rb/86Sr

(87Sr/86Sr)0

1

9-154

Zapolyarnaya

93.5

1808

0.051735

0.000553

0.707173

0.14968

0.706406

2

122/352

Zapolyarnaya

64

974

0.065708

0.001027

0.705680

0.19007

0.704706

3

122/372

Zapolyarnaya

93

1107

0.084011

0.000903

0.705670

0.24302

0.704425

4

122/383

Zapolyarnaya

24

523

0.045889

0.001912

0.705770

0.13274

0.705090

5

02-100

Poiskovaya

42

555

0.075676

0.001802

0.704180

0.21887

0.703058

6

02-144

Zimnyaya

36

802

0.044888

0.001247

0.706670

0.12986

0.706004

7

328/6

Komsomol’skaya- 40 Magnitnaya

830

0.048193

0.001205

0.706860

0.13942

0.706145

8

416/113

Komsomol’skaya- 28 Magnitnaya

906

0.030905

0.001104

0.707390

0.08941

0.706932

9

9-200

Novinka

117

1003

0.116234

0.000997

0.706110

0.33624

0.704387

10

409/145

Novinka

81

1110

0.072973

0.000901

0.706820

0.21111

0.705738

11

409/154

Novinka

38

1109

0.034265

0.000902

0.707180

0.09913

0.706672

12

415/19

Novinka

42

438

0.095890

0.002283

0.70588

0.27739

0.704458

13

423/125

Novinka

4

326

0.012270

0.003067

0.705560

0.03549

0.705378

14

423/80

Novinka

58

609

0.095238

0.001642

0.706350

0.27551

0.704938

15

8D/117

Deimos

44

2379

0.018495

0.000420

0.708010

0.05351

0.707736

16

8D/169

Deimos

19

446

0.042601

0.002242

0.706600

0.12324

0.705968

17

8D/257

Deimos

20

944

0.021186

0.001059

0.705830

0.06129

0.705516

kimberlites, as they differ from one another only in the concentration of incompatible elements. Remarkably, the representative ratios of elements (see Tables 3 and 4) also demonstrate considerable variations with a great overlap for different types. Only isotopic composition is relatively stable and homogeneous. What is the relationship between the distinguished types of kimberlites and related rocks on the basis of chemical, trace-element, and isotopic compositions? Why the isotopic and geochemical characteristics (in a group of incompatible elements) do not depend on the chemical composition of kimberlite rocks (within a field or even a group of fields)? It is usually supposed that the diversity of compositions of igneous rocks is due to melt differentiation. But this is hardly true for kimberlites. First, the kimberlites with different mg# are separated in space. As a rule, spatially close pipes, which belong to the same cluster, are characterized by similar compositions according to major oxides. Second, even if we assume that the different types of kimberlites stem from differentiation, this does not explain the paradox of independence of petrochemical and geochemical characteristics in the rocks. The differentiation in major components should be accompanied by the appropriate differentiation in trace elements. In our opinion, the absence of correlation between the isotope-geochemical and petrochemical parameters suggests the existence of independent mantle sources for major and trace incompatible elements of kimberlites. It is supposed (Kostrovitsky et al., 2004) that when a powerful flow of a fluid from an asthenospheric source ascended through the heterogeneous lithosphere, it provoked the formation of local kimberlite chambers, which were just

responsible for the formation of contrasting petrochemical types of kimberlites. In this case the geochemistry of kimberlites was controlled mostly by the same mantle fluid (common for all pipes of the field and, possibly, even for several coeval fields), which, as a rule, drastically dominated the rare-metal budget of the hybrid melt of the chamber. Thus, our model for kimberlite genesis suggests that the

Fig. 10. Isotopic composition of Sr as a function of CO2 content in kimberlites of Upper Muna field.

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Fig. 11. Isotopic compositions of Sr and Nd as a function of TiO2 and K2O in kimberlites and related rocks of the Siberian Platform. Fields: 1 — southern diamondiferous, 2 — of Anabar region, 3 — Kharamai, 4 — Kuoika; 5 — carbonatite pipes.

processes of the formation of the fluid and magma chamber were separated in space. A similar approach was earlier proposed by Russian authors (Sobolev et al., 1986), who indicated that two independent, fluid and melt, factors existed, which led to the heterogeneity of kimberlite compositions. Here, we do not consider the problem of origin of the specific composition of the asthenospheric source, certainly, related to the processes of mantle melting. What is crucially important is that the partial melting of the lithosphere mantle responsible for the specific trace-element composition of kimberlites has no relation to the formation of a kimberlite magma chamber, as supposed by many hypotheses. This conclusion is of principal importance in all petrological calculations of the models for kimberlite genesis. We must also bear in mind that the ratio of the fluid asthenospheric and melt components in

kimberlites might be different and, most likely, we cannot rule out the cases when the melt component was predominant in the total budget of trace-element composition. But these cases are rather exceptions. It is also debatable whether or not the kimberlites of the Nakyn field with their unusual trace-element composition are an exception of this kind. The lowest concentration of incompatible elements established for the Nakyn kimberlites is explained (Pokhilenko et al., 2000) by the existence of a thick keel of the lithosphere plate beneath it. We suppose for the Nakyn field that the specific trace-element composition of the kimberlites implies their intimate genetic relationship with alkaline basaltoids. The affinity of kimberlites to potassium alkaline basaltoids in geochemical parameters was earlier discussed by other authors as well (Ilupin et al., 1978; Sobolev

S.I.Kostrovitsky et al. / Russian Geology and Geophysics 48 (2007) 272–290

et al., 1986). It is known (Kiselev et al., 2002) that a spatial and temporal relationship exists between these two types of rocks of the Nakyn field. The substantial aspect of the problem of relationships between kimberlites and alkaline basaltoids is also quite remarkable. We have studied the trace-element composition of glimmerite from the kimberlites of the Zapolyarnaya pipe of the Upper Muna field and the rock from the Middle Paleozoic alkaline-basaltoid pipes (Anomaliya446) spatially conjugated with the coeval kimberlite pipes of the Malaya Botuobiya field. In their composition (phlogopite, olivine, clinopyroxene), the glimmerite inclusions correspond to the alkaline-basaltoid rocks. At the same time, they are considered (Dawson, 1983) kimberlite-related formations. Spidergram of trace-element distribution (see Fig. 5) shows that the kimberlites of the Nakyn field are much more similar to alkaline basaltoids than to classical kimberlites. The kimberlites of the Arkhangel’sk Province are also geochemically anomalous: They demonstrate (Bogatikov et al., 1999) the spatial and temporal relationship with alkaline basaltoids. The evident similarity of Sr and Nd isotope classifications for these rocks (Yarmolyuk et al., 2003) indicates the same mantle sources. Thus, the anomalous character of the kimberlites of the Nakyn field (and of the Arkhangel’sk Province) expressed in low concentration of incompatible elements and in low coefficient of REE fractionation is, most likely, due to the fact that the melt component contributed much more to their formation than the fluid one. Inspection of the spidergrams of trace-element distribution for kimberlites from most fields of the Yakutian Province reveals a similar shape of curves for all plots, with the same maxima and minima, and nearly the same concentration of elements. Deviations in the level of concentrations of incompatible elements toward their increase (expressed in the north of the Yakutian Province and in micaceous kimberlites of the Daldyn field) are possibly due to a comparatively thin lithosphere plate in these areas of the Siberian Platform and, therefore, by the relative closeness of the fluid source of kimberlites (asthenosphere mantle) to the surface horizon of formation of kimberlite chambers. Another explanation is not ruled out either: Because of mantle metasomatism, the mantle sources for micaceous kimberlites might have a very specific trace-element composition and be highly enriched in incompatible elements.

Conclusions Our study has shown that several petrochemical and geochemical types of kimberlite related to different mantle sources occur within the Siberian Platform. On the basis of stable differences in mg# and contents of indicator oxides such as FeOtot, TiO2, and K2O, we have recognized five petrochemical types of kimberlite. Though this classification is rather tentative (as it ignores variations of other oxides, e.g., Al2O3 and CaO), it is useful for understanding the kimberlite genesis, because the different types suggest compositionally different lithosphere areas of the mantle involved in the

289

chamber formation. A somewhat different situation exists in the case of six distinguished geochemical types of kimberlites and related rocks. Obviously independent geochemical types correspond to kimberlites from the southern diamondiferous fields (except for the Nakyn field and micaceous kimberlites of the Daldyn field) (Type 1), from the Nakyn field (Type 3), to carbonatites of the Anabar region (Type 5), and orangeites (possibly, lamproites) of the Sayan region (Type 6). As regards Types 2 and 4 (micaceous kimberlites of the Daldyn field and kimberlites from the northern fields of the Yakutian Province), we doubt in their independence. The reason is that they differ, chiefly, only in having higher concentrations of incompatible elements (as compared with geochemical Type 1), with their ratios being quite the same. We analyzed the isotope-geochemical data obtained for the representative collection of kimberlites and related rocks of the Siberian Platform, with an emphasis placed upon study of correlations between the isotope-geochemical and chemical compositions of the rocks, and this allowed us to refine the model for kimberlite genesis. We have shown that the formation of kimberlites is related to, at least, two independent sources — fluid and melt — responsible for the formation of trace-element (in a group of incompatible elements) and chemical compositions of the rocks. It is worthy to bear in mind that macrocrystal clastics of mantle origin also contributed much to the kimberlite composition. It is not ruled out that the source of clastics might be restite relative to the melt source. The study shows that the predominant part of the kimberlite occurences is characterized by very close isotopic and traceelement compositions. This is evidence of a relatively homogeneous asthenosphere source beneath the Siberian Platform, which initiated kimberlite volcanism there. Of course, we realize that some questions in the isotopegeochemical classification of kimberlites are yet to be answered. In particular, what is the nature of mantle fluid sources? What accounts for the relationship between the alkali contents of kimberlites and their enrichment with incompatible elements and why this relationship is absent from the Nakyn field? In our opinion, the anomalous geochemical characteristics of the kimberlites of the Nakyn field are due to their genetic relation to alkaline basaltoids. But the question arises: What is the mechanism of this relation? What particular rocks of the lithospheric mantle were the sources of certain petrochemical types of kimberlites? These and other genetic problems remain to be solved in our further studies. We thank N.N. Pakhomova, G.P Sandimirova, E.V. Smirnova, and Yu.A. Pakhol’chenko (Institute of Geochemistry, Irkutsk) as well as Dr. Varna Kumara Verakun and Professors H. Kagani and K. Shuto (Niigata University, Japan) for analyses of trace-element and isotopic compositions of rocks. We are also grateful to Academicians N.V. Sobolev and I.D. Ryabchikov for constructive criticism and friendly reviews. The study was supported by grants 02-05-64793 and 06-05-64981 from the Russian Foundation for Basic Research and by collaborative projects of the Siberian Branch of the

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RAS (no. 21) and Department of Geosciences of the RAS (no. 2.1).

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