Deep electrical structure and geological significance of Beishan Orogenic Belt, Southern CAOB

Abstract:

The Beishan Orogenic Belt is a collage of multiple active continental margins, island arcs, and ophiolite belts during the closure of the ancient Asian Ocean since the Paleozoic era. In terms of geotectonic setting, the study area experienced polycyclic lateral orogeny and vertical accretion as well as complex splicing and strike-slip processes of blocks. Although a lot of studies have improved the overall research level of the Beishan ophiolite belts, there are still controversies about how the ophiolite belts are spread and buttressed on a regional scale, and about the subduction polarity of the ocean basins. Therefore, to better document the subsurface crustal structure of the Beishan Block, including the down‐dip orientation of the ophiolite belts, we carried out a 280‐km‐long Magnetotelluric (MT) survey from the Hexi Corridor to the northern Beishan with 16 stations along the overall survey length. The acquired data underwent rigorous analysis using ModEM software, The results of the profile analysis demonstrate that the southern and northern regions of the Beishan area exhibit divergent electrical structural characteristics, demarcated by low resistivity bodies indicative of ophiolite mélange zones. The northern part of the area is distinguished by a low-high-low resistivity pattern, which may suggest the presence of a colluvial accretionary crustal structure. Conversely, the southern part of the northern hill exhibits a more structurally intact high-resistivity body, which is hypothesised to potentially represent a more rigid and ancient landmass.

Key words:Electrical structure；Magnetotelluric;Beishan Orogenic Belt;

Acknowledgments: This research was supported by Phase I of the Northwest Region Magnetotelluric Subnetwork(Grant No.2024ZD1000201), the China Geological Survey for Regional Geophysical Survey in Beishan and Adjacent Areas (Grant No. DD20230254).