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

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.

New Identity of the Kimberlite Melt: Constraints from Unaltered Diamondiferous Udachnaya –East Pipe Kimberlite, Russia

“…Three Sr isotope analyses of UV31k-05 perovskite by solution-mode average 0.70305±7 (2σ, age-corrected), similar to laser ablation MC-ICPMS results for 20 individual perovskite grains (average 0.70312±5, 2σ, age-corrected). These 87 Sr/ 86 Sr i ratios are lower than those for the host kimberlite (0.7043-0.7049, Kostrovitsky et al, 2007;Maas et al, 2005;Pearson et al, 1995), although results for acid-leached kimberlite (0.7034-0.7037, Maas et al, 2005) provide a closer match. Such offsets between perovskite and host kimberlite were also noticed elsewhere (Paton et al, 2007), and probably reflect minor disturbance of bulk rock Rb-Sr systems.…”

The basalt pipes of the Tunguska Basin (Siberia, Russia): High temperature processes and volatile degassing into the end-Permian atmosphere

“…The latest brines were generated from a buried bittern of the evaporite basin, which underwent metamorphism in the water-rock system during the subsequent geochemical evolution of the basin (Alexeev et al, 2007). Regional scale brecciation and silicification occurs throughout the Vendian-Cambrian evaporitic rocks and is primarily attributed to ancient weathering as opposed to local processes such as pipe formation, which could account for only a small proportion of the observed alteration (Pisarchik et al, 1975).…”

Repeated kimberlite magmatism beneath Yakutia and its relationship to Siberian flood volcanism: Insights from in situ U–Pb and Sr–Nd perovskite isotope analysis

“…In the latter province, there is mounting evidence for the evolution of carbonate-rich residual magmas from kimberlitic Yakutian kimberlites and from published worldwide kimberlite occurrences: South Africa (Donnelly et al, 2012;Wu et al, 2013b); North China (Yang et al, 2009);Greenland (Tape et al, 2011, 2012; North America (Heaman, 1989;Wu et al, 2010) and India (Chalapathi Rao et al, 2013). Bulk kimberlite Sr-Nd isotope data from the Yakutian kimberlites are from Kostrovitsky et al (1999), Agashev et al (2000), Bogatikov et al (2004), Carlson et al (2006), Kostrovitsky et al (2007). parent melts.…”

“…7, we are comparing the newly obtained Sr and Nd isotope compositions of perovskites from the Yakutian kimberlite province with available Sr-Nd isotope data from bulk Siberian kimberlites (Kostrovitsky et al, 1999;Bogatikov et al, 2004;Carlson et al, 2006;Kostrovitsky et al, 2007). In general, the Sr-Nd isotope data of the kimberlitic perovskites show much less variation (initial 87 Sr/ 86 Sr of 0.70282-0.70375; 143 Nd/ 144 Nd of 0.51229-0.51271; ε Nd of +1.8 to +5.4) than the equivalent data for the bulk kimberlites (initial 87 Sr/ 86 Sr of 0.70318-0.70641; 143 Nd/ 144 Nd of 0.51048-0.51270; ε Nd of −4.2 to +7), although the difference is less pronounced for the Nd isotope compositions.…”