MINERALOGICAL AND ISOTOPE-GEOCHEMICAL CHARACTERISTICS OF THE ZHARNICHIKHA BASANITES (southern Transbaikalia)
A.Ya. Medvedev, S.I. Dril’, A.A. Karimov, V.A. Belyaev
Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
Keywords: Basanites, plume, isotope, Cenozoic, xenoliths, Transbaikalia
Abstract
Cenozoic alkali basaltoids are developed in southern Transbaikalia (Daur-Hentiyn Range). They are represented by thin flows and nappes. Unlike the volcanic fields of the South Baikal volcanic region (SBVR), the investigated fields are not related to rifting. The volcanics from the Zharnichikha River flow were studied. By composition, they are referred to as basanites. The mineral compositions of the volcanics have been determined for the first time. In geochemical parameters the basanites correspond to mafic volcanics of oceanic islands. The P - T parameters of the equilibrium crystallization of olivine and clinopyroxene phenocrysts have been determined. For the calculated parent melt, the formation temperature was 1536 ºС, and the pressure was 3.28 GPa. The obtained original data on the isotopy of Sr, Nd, and Pb showed that the isotopic composition of the magmatic melt formed from the PREMA source, with a strong subordinance of the latter. Olivine clinopyroxenites (Ol + Cpx + Grt) were the probable mantle source for the studied basanites. The generation of basaltoid melts occurred under the influence of the mantle plume, which caused Cenozoic activation.
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