DEEP ELECTRIC STRUCTURE BENEATH NORTHEASTERN BOUNDARY AREAS OF THE NORTH CHINA CRATON

Magnetotelluric data are collected along a NW-SE trending and about 900km long profile within northeastern boundary areas of the North China craton(NCC). This profile extends from the Hegenshan belt within the Central Asian orogenic belt(CAOB), across the Baolidao arc, Solonker-Linxi suture zone, Ondor Sum accretion complex, Bainaimiao arc, Inner Mongolia paleo-uplift, Yanshan belt, and ends on the Liaohe depression of the NCC. Impedance tensor decomposition methods are used to study the dimensionality and geo-electric strike of MT data of the region. Two-dimension (2D) analysis is appropriate for this profile. The 2-D subsurface electrical resistivity structure along profile is obtained using the non-linear conjugate gradient (NLCG) algorithm. The electrical resistivity structure is characterized by lateral segmentation, and divided into high resistive, low resistive, and high resistive areas; The lateral variation of electrical resistivity is significant within the CAOB, but it is smooth in the NCC; The extensive high conductive body(HRB)is observed in the mid-low crust beneath the Solonker-Linxi suture zone and Inner Mongolia paleo-uplift, respectively; The low resistivity could be due to the partial melts and crustal flows. Based on our electrical resistivity structure and other geological, geophysical observations, we speculate that (1)the final suturing of the Siberian craton to the NCC could be along the areas between Xilinhot Fault and Xar Moron Fault; (2)the relatively thick high resistive body beneath the Yanshan belt may serve as a tectonic barrier separating the on-craton and off-craton regions into different upper mantle convection system, and lower the effect of tectonic evolution of CAOB on the destruction to NCC.