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Imaging the Crustal Structure Beneath the Northwest Yunnan From a High‐Density Seismic Array

Emeishan igneous province (ELIP) is the only one widely recognized LIP in China, which can be divided into three different regions: inner zone, intermedia zone and outer zone. Previous studies show that the inner zone is characterized by a Moho doming, and a lower crustal high-velocity and high-density anomaly, which may be result from the mantle plume underplating. Chenghai fault (CHF) is located at the eastern boundary of the inner zone of ELIP. Previous studies show that CHF is at the boundary of Bouguer gravity anomaly. And high-speed anomalies of lower crust are mainly exist in the east of CHF. These suggest that CHF may be in the position of thickness gradient of intrusive rock. However, this is in contradiction with the severe erosion of Maokou Formation in Binchuan. The study of the structure of ELIP inner zone, especially the fine structure around the CHF, will help us understand the thickening mechanism and evolution of the Yunnan crust. However, subject to the sparse observation, there were few studies on the fine structure of the inner zone. From March to May 2017, we deployed the dense short-period seismic array in the original position of Yunxian-Ninglang DSS profile which northern part is roughly parallel to the CHF and southern part is nearly perpendicular to the Red River Fault (RRF). In this study, 1873 receiver functions were extracted and then imaged by CCP stack. We find the Moho is continuous cross the RRF. However, we observed strong Vp/Vs contrast cross the RRF. Combined with other evidence, we inferred that the RRF has cut through the Moho. Two interfaces have been recognized under the CHF, one of which we recognized as an artifact of multiples generated by the sedimentary layer, and the other is a inter crust interface with a depth of ~ 35 km. Combined with the Ariy isostasy along the profile, we speculated that the inter crust interface is the underplating interface formed by the ancient mantle plume. The results show that CHF was strongly underplated during the formation of ELIP.

Presenting Author: Tianwei Sun

Student Presenter: Yes

Day: 4/20/2021

Time: 4:15 PM - 5:15 PM Pacific

Additional Authors