Lateral extrusion of the northern Tibetan Plateau interpreted from seismic images, potential field data, and structural analysis of the eastern Kunlun fault

Abstract

The extrusion model suggests that the India-Eurasia collision triggered lateral escape of the Tibetan Plateau via strike-slip faults from south to north. However, questions remain as to how the collision resulted in the different geological settings of northern Tibet. The area between the Haiyuan fault and the eastern Kunlun fault is ideal for investigating whether major strike-slip faults contributed to lateral extrusion of the plateau. This study uses a deep seismic profile spanning a 257km transect, along with regional geologic, gravity, and magnetic data. Examining our results integrated with those of previous studies, we propose that the block between the Elashan and Riyueshan faults extruded southward under the background of a large-scale eastward extrusion of the Tibetan Plateau. According to regional tectonic events, the north-dipping intracrustal seismic reflectors that appear beneath the Western Qinling orogen are the remnants of the Indosinian Mianlue suture zone. The subduction of the Mianlue Ocean led to the underthrusting of South China beneath the Qinling orogen, similar to the process that occurred in the Western Kunlun Range and central Alps. As a result, the Moho was duplicated beneath the Western Qinling orogen. Southward extrusion resulted in the offset of the eastern Kunlun fault from the Diebu-Bailongjiang fault, which transferred part of the Western Qinling orogen to the Ruo'ergai basin and pulled the Ruo'ergai basin as well. Based on interpretations of structures and other evident features, we develop a kinematic model to specifically explain how the northern Tibetan Plateau between the Elashan and Riyueshan faults, located between the Haiyuan and Kunlun faults, accommodates southwesterly compression.