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Russian Geology and Geophysics

2018 year, number 12

GEOCHEMICAL MODEL FOR THE FORMATION OF THE MEDEK PLATINUM-BEARING DUNITE-WEHRLITE MASSIF (East Sayan, Russia)

A.S. Mekhonoshin, T.B. Kolotilina, A.A. Doroshkov
A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
Keywords: Элементы группы железа, ЭПГ, композиционные тренды, процессы дифференциации, объемная геохимическая модель, Siderophile elements, PGE, composition trends, differentiation, 3D geochemical model

Abstract

We study the behavior of a number of siderophile elements, including platinum-group elements, during the formation of the Medek dunite-wehrlite massif. Its structural position, internal structure, and mineralogical composition are presented; a 3D geochemical model is constructed. The forsterite content of olivine varies from 90 to 73% from top to bottom of the vertical cross section of the massif. In addition, there are a decrease in the volume content of olivine and the appearance of ilmenite instead of accessory Cr-spinel. The observed zonation in variations in the composition of rocks and minerals is consistent with magmatic differentiation in a sheet-like body, which changed its primary occurrence. A geodynamic scenario is proposed, which links the formation of the massif with the break-up of Rodinia and the further changes in the primary occurrence with subsequent accretion-collision events on the southern and southwestern margins of the Siberian craton in the period 600-450 Ma.