The continental lithospheric mantle beneath early precambrian and late proterozoic - phanerozoic structures of the earth crust: chemical composition, thermal state, evolution

Vestnik Otdelenia nauk o Zemle RAN VOL. 2, NZ6009, doi:10.2205/2010NZ000027, 2010

The continental lithospheric mantle beneath early precambrian and late proterozoic - phanerozoic structures of the earth crust: chemical composition, thermal state, evolution

Vrevskij A. B., V. A. Glebovitskij, A. G. Goncharov, L. P. Nikitina, Yu. D. Pushkarev

Abstract

The chemical composition and thermal state of the continental lithospheric mantle (CLM), beneath Early Precambrian and Late Proterozoic-Phanerozoic fold structures, were estimate on the basis of a bulk composition of mantle xenoliths and on P, T – crystallization conditions of their mineral assemblage. The thermal state in mantle beneath each structure are characterized by geotherms for considerable intervals of depths and geothermal gradients (TG), which are determined by T/H (C/km) ratio, where H – depth (km), are calculated in compliance with PREM model. Usage same geothermobarometer for all examined xenoliths secures the estimation comparability of mantle states beneath different structures. The heterogeneity of chemical composition of CLM beneath uneven-aged fold structures are observed, and also the even difference of chemical composition for each studied structure are established. The main cause of a chemical heterogeneity of CLM are the processes of primitive mantle melting in different P, T, f_O2 conditions, which occur with various intensity in mantle under Early Precambrian (till 60–65% of partial melting) and under Late Proterozoic-Phanerozoic structures (till 20–25%). The CLM beneath Early Precambrian structures is characterized by weak differentiation of thermal state (TG = 8.0÷8.6 C/km), while in mantle under Late Proterozoic and Phanerozoic structures it is observed a variety of thermal conditions (TG = 8.4÷13.3 C/km) and more high temperatures on the same depths. These data is evidence that chemical composition and physical state of continental lithospheric mantle are evolved in a history of the Earth and allow to guess the change of mantle dynamics and, first of all, change of convection style on bound of an Early Precambrian and Late Proterozoic-Phanerozoic.

Received 28 April 2010; published 5 June 2010.

Citation: Vrevskij A. B., V. A. Glebovitskij, A. G. Goncharov, L. P. Nikitina, Yu. D. Pushkarev (2010), The continental lithospheric mantle beneath early precambrian and late proterozoic - phanerozoic structures of the earth crust: chemical composition, thermal state, evolution, Vestn. Otd. nauk Zemle, 2, NZ6009, doi:10.2205/2010NZ000027.