科研之友
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摘要
As a part of the East Asian Rift System, Songliao basin experienced major geological events of Mesozoic lithospheric thinning together with the North China craton. The overall understanding of the state and structure of continental lithosphere and asthenosphere is the key to studying the dynamics of continental lithosphere thinning. Based on the 106 broadband and 30 long period magnetotelluric sounding data from the Songliao basin, we complete the calculation and analysis of the data about two-dimensional deviation degree, the structural trend and so on. We further use the nonlinear conjugate gradient algorithm for 2D combined inversion of the mode data of TE and TM to obtain the crust-mantle electrical structure along the profile, and then we are able to build crust-mantle structure model of the Songliao basin. The results are summarized as follows. (1) The lithosphere thickness is about 160 km in Da Hinggan Ling area, about 45 km in Songliao basin, and is between 70 and 100 km in the Zhang Guangcai Ling. The Moho and the bottom interface of lithosphere do not have a mirror image relationship. The overall property of the asthenosphere shows middle and low resistivity anomalies, and the resistivity value is about 30 Omega m, The abnormality shaped like a mushroom presents a westerly dip of 30. It indicates an upwelling of the asthenosphere which is different from the traditional understanding of the vertical upwelling asthenosphere. (2) There are double high conductivity anomalies in the deep part of Songliao basin (the resistivity is less than 5 Omega m). The upper high conductivity layer is in the crust, which is snake-like distributed, and we infer that it is the bottom of the magma invasion zone. The lower high conductivity layer in the mantle is dumbbell shaped, and it is the asthenosphere upwelling area. The asthenosphere is characterized by two dumbbell shaped high resistivity anomalies, which are inferred to be the delaminated lithospheric mantle. The accumulation of cold, high-density descending flow of material and the insertion of deladimated blocks beneath the mountains on the two sides caused the rapid uplifting of the Da Hinggan Ling and Zhang Guangcai Ling in Mesozoic extensional environments. (3) The Songliao basin experienced lithospheric thinning event; compared with the Da Hinggan Ling, the Songliao basin lithosphere thinned near 100 km, or 70 km compared to the Zhang Guangcai Ling on the east, and compared to 100 km of the Mesozoic lithosphere in North China platform the thinning is near 50 km; it experienced a dynamic process of lithosphere extension, rifting, delamination, and growth.
- 出版日期2018-6
- 单位中国地质科学院; 吉林大学
