Relationship between the regional tectonic activity and crustal structure in the eastern Tibetan plateau discovered by gravity anomaly

Xiao Xu,Xiaoyu Guo,Rui Gao

doi:10.1007/s11589-016-0142-7

Xiao Xu, Xiaoyu Guo + Show 1 more

Open Access

https://doi.org/10.1007/s11589-016-0142-7

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Abstract

The eastern Tibetan plateau has been getting more and more attention because it combines active faults, uplifting, and large earthquakes together in a high-population region. Based on the previous researches, the most of Cenozoic tectonic activities were related to the regional structure of the local blocks within the crustal scale. Thus, a better understanding of the crustal structure of the regional tectonic blocks is an important topic for further study. In this paper, we combined the simple Bouguer gravity anomaly with the Moho depths from previous studies to investigate the crustal structure in this area. To highlight the crustal structures, the gravity anomaly caused by the Moho relief has been reduced by forward modeling calculations. A total horizontal derivative (THD) had been applied on the gravity residuals. The results indicated that the crustal gravity residual is compatible with the topography and the geological settings of the regional blocks, including the Sichuan basin, the Chuxiong basin, the Xiaojiang fault, and the Jinhe fault, as well as the Longmenshan fault zone. The THD emphasized the west margin of Yangtze block, i.e., the Longriba fault zone and the Xiaojiang fault cut through the Yangtze block. The checkboard pattern of the gravity residual in the Songpan-Garze fold belt and Chuandian fragment shows that the crust is undergoing a southward and SE-directed extrusion, which is coincident with the flowing direction indicated from the GPS measurements. By integrating the interpretations, the stepwise extensional mechanism of the eastern Tibetan plateau is supported by the southeastward crustal deformation, and the extrusion of Chuandian fragment is achieved by Xianshuihe fault.

Highlights

The eastern Tibetan plateau has been divided into three subunits by four major left-lateral strike-slip faults, including the red river fault, the Xianshuihe fault, the Kunlun fault, and the Haiyuan fault (Fig. 1b)
The low gravity anomaly in the Songpan-Garze fold belt and Chuandian fragment has a checkerboard-like pattern, which shows that the crust is
The crustal gravity residual is compatible with the topography and distribution of regional tectonic units, including the Sichuan basin, Chuxiong basin, Xiaojiang fault, Jinhe fault, Longmenshan fault zone, Longriba fault zone, and the thrust faults in the northern Tibetan plateau

Summary

Introduction

The eastern Tibetan plateau has been divided into three subunits by four major left-lateral strike-slip faults, including the red river fault, the Xianshuihe fault, the Kunlun fault, and the Haiyuan fault (Fig. 1b). Based on the observed Global Positioning System (GPS) measurements, the Tibetan plateau is dominated by lateral movement (Gan et al 2007). These four dominant left-lateral strike-slip fault systems control the directions of extrusion from southeast to northeast (Fig. 1a) (Wang et al 2014; Tapponnier et al 1986, 2001). Based on the focal mechanism, the Sichuan basin is under compression from eastern Tibet, and the inner part of the Chuandian fragment extends in a southeast direction (Wang et al 2014).

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