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SS04 – THE GEOLOGIC EVOLUTION OF NE ASIA


Thu-02 Jul 2020 | 13:30 – 15:30 | Tower B, Lavender II

Tatsuki TSUJIMORI
Tohoku University (DLR)

“Tectonic Evolution of Ne Asia: a View from the Bottom of Cratonic Lithosphere”

Tatsuki TSUJIMORI1#+, Nozomi SHINBORI1, Hafiz Ur REHMAN2, Malkovets VLADIMIR3

1Tohoku University, 2Kagoshima University, 3Sobolev Institute of Geology and Mineralogy of the Siberian Branch of the RAS

In order to better understand tectonic evolution of NE Asia, numerous studies have been conducted in various aspects, especially surface geology of orogenic belts. However, the deepest 'continental lithospheric mantle (CLM)' material beneath craton can also preserve important records of the regional tectonic history. The Archean Siberian Craton is located in northern central Asia. At a large-scale, NE Asian geology shows a growth pattern from the craton as a core to the younger orogenic belts and to the modern convergent palate margin. We have investigated mantle xenoliths transported from the bottom of the CLM to surface through plume volcanism to decipher regional tectonic history. Sheared garnet peridotite xeoliths from Siberian Craton are characterized by mylonitic deformed texture and the presence of high-Cr garnet and very low-Al orthopyroxene. Geothermobarometry suggests an equilibrium condition at P= ~6 GPa. Mylonitized olivine-dominant matrix shows a C-type crystallographic preferred orientation (CPO), indicating infiltration of water-rich fluids that enhanced deformation in the CLM. This possible fluid infiltration is also supported by trace element zoning of porphyroblastic garnet and clinopyroxene. Wemeasured the anisotropy of the elastic wave velocity of our deformed xenolith sample, which also indicates C-type olivine CPO that formed under a wet condition. However, water content in olivines show only a little amount water that contradicts the expectation of 'wet' condition. Considering these observations together with regional geological history, we proposed a scenario from the initial stage of 'wet' condition due to gain of slab-derived fluids with some trace element signature from a deeply subducted lithosphere, to the late stage of dehydration process by heating. We hypothesize that large-scale plume magmatism activity in Siberia heated and dehydrated the CLM.An integrated study among petrology, mineralogy, geochemistry, rheology and rock physics provide a great potential to understanding hidden history beneath the stable continental crust.


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