Electrical resistivity structure of the Trans-North China Orogen: implications for lithospheric deformation history

Wednesday, 17 December 2014: 10:20 AM
Yaotian Yin, Wenbo Wei, Sheng Jin and Gaofeng Ye, China Univ. of Geosciences, Beijing, China
The North China Craton (NCC) is composed of the Eastern Block (WB) and Western Block (EB) amalgamated along the Central Orogenic Belt (Trans-North China Orogen, TNCO). A magnetotelluric (MT) profile crossing the eastern margin of WB, southern TNCO and western margin of EB, combined with a subset of SinoProbe MT array near this profile is used in our study. Dimensionality analysis indicates that (a) the resistivity structure is nearly 2-D with geoelectric strike directions varying in different tectonic units, and that (b) electrical anisotropy may exist in the mid-lower crust beneath the Shanxi Rift and Qinshui Basin. Isotropic and anisotropic 2-D inversion and isotropic 3-D inversions have been conducted. The most significant resistivity features in the inversion models are a series of mid-lower crustal sub-horizontal blob-like conductors beneath Shanxi Rift and an east-dipping conductor extending from mid crust to a depth greater than 150 km beneath the southern Taihang Mountains. Inversions show that the crustal conductor series may represent an anisotropic layer, likely caused by conductive materials filling a network of fractures with preferred spatial orientation. The dipping conductor may represent a conduit of hot asthenospheric materials transporting upwards, which is interpreted to the leading edge of the eastward escape mantle flow caused by Indian-Asia collision. The hot materials are inferred to be resulted from the westward mantle convection associated with the westward subducting Pacific Slab, going upward into the mid-lower crustal detachment zone and heat the rock, generating partial melts filling the fractures beneath Shanxi rift. The rift system is believed to be associated with NW–SE-trending extensional stress field resulted from the rapid convergence of India–Eurasia. Thus, conclusion can be drawn that the deformation of the lithosphere beneath NCC, especially the TNCO, may be a far-field effect of Indian-Asia collision.