Crust and upper mantle electrical structure of the eastern Central Asian Orogenic Belt revealed by the MT line from Zhangwu County to East Ujimqin Banner

Abstract

The Central Asian Orogenic Belt is bounded on the north by the Siberian Craton and on the south by the North China Craton and the Tarim Craton. It is one of the largest Phanerozoic accretionary orogenic belts on Earth. Since the early Paleozoic, its eastern part has experienced the compound orogenesis and mineralization of three major tectonic systems: the closure of the Paleo-Asian Ocean, the closure of the Mongolian–Okhotsk Ocean, and the subduction of the Paleo-Pacific Plate. From Zhangwu County in the south to East-Ujimqin Banner in the north, a 500 km magnetotelluric profile adjacent to Northeast China has been studied. With 100 sites of magnetotelluric data processing and analysis, we apply a two dimensional inversion in TE and TM modes and obtain a resistivity model up to a 100 km depth. We have discovered two high-resistivity anomalies with opposite dip directions in the upper mantle on both sides of the Solonker Suture Zone, which provide an evidence of the bi-directional subduction pattern of the oceanic crust and the position of the closure of the Paleo-Asian Ocean. In addition, the whole study area presents an approximate basin-range coupling relationship. In the northern part of the study area, the low-resistivity anomalies below it have an apparent north-dipping characteristic, which may be related to the asthenosphere upwelling from west to east. In addition, they may be related to the upwelling of mantle materials, and provide sources of ore-forming material for the Baiyinnuoer mining area through post-collision extension. In the central part of the study area, there are several large-scale high-resistivity anomalies below the Baolidao Belt. The different dip directions reveal the experiences of several subductions and collisions. In the southern part of the study area, the Bainaimiao Belt is located between the southern margin of the Songliao Basin and the northern margin of North China Craton. The main resistivity anomalies below are all south-dipping.Graphical