LI BaoChun,
ZHANG LeTian,
YE GaoFeng et al
.2020.Upper mantle thermal structure beneath the eastern margin of the Tibetan Plateau inferred from electrical structure model Chinese Journal of Geophysics(in Chinese),63(3): 1043-1055,doi: 10.6038/cjg2020N0234
基于电性结构模型的青藏高原东缘上地幔热结构研究
李宝春, 张乐天, 叶高峰, 金胜, 魏文博, 谢成良, 陈显荣
中国地质大学(北京)地球物理与信息技术学院, 北京 100083
Upper mantle thermal structure beneath the eastern margin of the Tibetan Plateau inferred from electrical structure model
LI BaoChun, ZHANG LeTian, YE GaoFeng, JIN Sheng, WEI WenBo, XIE ChengLiang, CHEN XianRong
School of Geophysics and Information Technology, China University of Geosciences(Beijing), Beijing 100083, China
Abstract：The eastern margin of the Tibetan Plateau plays a significant role in controlling the uplift and expansion of the plateau. Previous Magnetotelluric (MT) studies have been conducted to better understand the lithospheric structure and physical properties of this region. In this study, to interpret the previously published MT models more quantitatively, we establish a quantitative relationship between the electrical conductivity and temperature, as well as melt fraction of the upper mantle, by combining the two-dimensional MT inversion model with laboratory derived formulae for electrical conductivity of major upper mantle minerals and melts using the mixing law of Hashin-Shtrikman (HS) bounds. The resultant upper mantle thermal structure as well as distribution model of upper mantle melt fraction suggest that the upper mantle conductors observed from previous MT studies can be interpreted as regions with partial melting under high temperature. The large scale upper mantle conductor beneath Songpan-Garzê terrane corresponds to temperature ranges between 1300 and 1500℃, with melt fraction as high as 10%, which is consistent with the qualitative interpretations of partial melting from previous MT studies. A smaller conductive region in the upper mantle beneath the western Sichuan Basin represents a region with the temperature of 1200~1400℃ and 1%~5% melt fraction, which indicate upwelling of the asthenosphere and modification of the western margin of the Yangtze Craton. The upper mantle resistor beneath the Longmen Shan fault zone corresponds to a relatively cold region with temperature around 1100℃, and very limited amount of melt fraction (0~0.1%), which is consistent with its rigid behavior as a seismogenic zone. The coldest region locates beneath the eastern Sichuan Basin with upper mantle temperature of 800~900℃ and no partial melting, which represents the ancient, stable, cratonic Yangtze block.
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