Structural features and tectonic evolution of the Nenjiang–Balihan fault in the western margin of the Songliao Basin, NE China, inferred from 2D inversion of magnetotelluric data

Abstract

Located in the famous gravity gradient belt ranging from the Mt. Great Xing'an through Mts. Taihang and Wuling in East China, the Nenjiang-Balihan (NJBLH) fault is important for the understanding of the formation and evolution of Mesozoic and Cenozoic basins in NE China. The distribution and deep structure of the middle and northern segments of this fault are poorly known because of thick sedimentary cover. In this paper, an electrical structure across the western margin of the Songliao Basin and eastern margin of the Great Xing’an Range is revealed on the basis of three magnetotelluric (MT) sounding survey profiles. The results show the development of a low-resistivity layer (L2) and two low-resistivity strips with opposite dip (L1 and L3) in the lower portion of the small-scale basins or sags. The west-dipping low-resistivity strip L1 is considered to be the trace of a paleo-suture zone. The transverse low-resistivity layer L2 may reflect the Palaeozoic sedimentary strata in the basin, and the east-dipping low-resistivity strip L3 represents the NJBLH fault, the presence of which exhibits a gentle sloping tendency from the shallow to the deep portion of the fault cut through the Moho. The NJBLH fault is segmented on the plane, with an overall left-slip NE-trending en echelon arrangement. Presumably, the NJBLH fault began to form during the Jurassic under the influence of the closure of the Mongolia–Okhotsk Ocean in the northwest, and the fault subsequently experienced left-lateral strike-slip movements due to the NW-trending subduction of the Paleo-Pacific Izanagi Plate toward the Eurasian Plate.