Late Cenozoic development characteristics and dynamic mechanism of the main faults in the Midu area, northwestern Yunnan[BP(]Development characteristics of the main faults of the late cenozoic in the Midu area, northwestern Yunnan, and their dynamic mechanism

Abstract

The Midu area is located at the southeast end of the northwestern Yunnan fault depression zone, the intersection of the Red River fault zone and the Chenghai fault. It is a key area for uncovering the formation mechanism of the Northwest Yunnan fault depression zone as well as its kinematic relationship with the Red River fault zone. Based on remote sensing interpretation and field investigation, we found five faults in the study area, namely the NE-trending Maolipo fault, NW-NNW-trending Fengyi-Dingxiling fault, Midu fault, Mizhi fault and Yinjie fault. We made statistical analysis of the fault slipping geological-landscape bodies and slickensides, and the results are produced in three aspects. Firstly, the Maolipo fault are mainly characterized by left lateral strike-slip activity with normal fault component in Quaternary. Secondly, the arc-shaped Midu fault and the NW-trending Yinjie fault are dominated by normal fault activity in Quaternary. Thirdly, during the Pliocene the Fengyi-Dingxiling fault was characterized by dextral strike-slips, while the Mizhi fault by extensional normal faults, and there was no obvious activity in both faults during the Quaternary. We inferred both from the geometry and kinematics of the main faults in the Midu area and the activity evolution of the Red River fault zone that, in the Late Cenozoic the main Quaternary active faults, such as the Midu fault and Yinjie fault, were formed on the basis of inheriting and remaking the original fault trace of the Red River fault zone. These active faults controlled the distribution of the Midu basin. The fault activity and transtensional deformation in the Midu area and the Northwest Yunnan fault depression zone during the Pliocene or even earlier could be affected by the extensional deformation at the end of the Red River fault zone. However, during the Quaternary the Chenghai fault basically controlled the development of main active faults in the Midu area. The crustal transtensional deformation in this period might be driven by the clockwise rotation of the Sichuan-Yunnan inner arc belt and the regional strike-slip pull-apart caused by the Nantinghe fault, Wanding fault and Litang fault.

Keywords

• fault depression zone in northeastern yunnan
• chenghai fault
• red river fault zone
• late cenozoic
• block rotation