Geochemistry and Petrology of Crust and Mantle Xenoliths and Xenocrysts in the Trans-Khamar-Daban Zone

The volcanic rocks from Cenozoic Trans-Khamar-Daban volcanic zone (TKDVZ) in Russia and their xenocrysts and crust-mantle xenoliths were investigated by electron microprobe (EPMA) and laser-ablation inductively coupled mass-spectrometry (LA ICP MS) and other methods. They were used to show the composition and reconstructions of structure of the crust and mantle. Volcanism started from Central Part of ridge at 23 Ma and distributed to the shoulders (18–16 Ma) rift margins (13–16 Ma) and top of volcanoes (12–10 Ma), followed by rift valleys (5–2 Ma) and culminated in cinder cones volcanoes (0.8–0.15 Ma). Lavas evolved from sub-alkali to alkaline basalts and tephrites. Lherzolitic xenoliths are nearly primitive, having relics of garnets and simplectites which represent the material of mantle diapirs. The volcanics from Tunka and Dzhida valleys carry abundant cumulate xenoliths related to 2.0–1.0 GPa. The geothermal regimes reconstructed using electron probe (EPMA) mineral analyses and mineral thermobarometry is close to the South-Eastern Australian Geotherm (SEA). At the first stage, it shows heating to 1350 ◦C near Baikal Lake (Sukhoy volcano). The trace elements in the lherzolites are close to primitive mantle being more depleted near Tunka valley and showing ancient subduction related depletion and hydration in Dzhida. The cumulates show fractionation trends for pyroxenes, garnets amphiboles. The megacrysts show high La/Yb ratios increasing with Fe# for clinopyroxenes and garnets and LILE enrichments for amphiboles and Ti-biotites. The volcanism was caused by deep plume generated with the influence of the subduction from the Pacific and correlated with the events of India- Eurasia collision.