Crustal Anisotropy Beneath the Trans-North China Orogen and its Adjacent Areas From Receiver Functions

Xiaoming Xu,Fenglin Niu,Li Li,Zhifeng Ding

doi:10.3389/feart.2021.753612

Abstract

As an important segment of the North China Craton, the Trans-North China Orogen (TNCO) has experienced strong tectonic deformation and magmatic activities since the Cenozoic and is characterized by significant seismicity. To understand the mechanism of the crustal deformation and seismic hazards, we determined the crustal thickness (H), Vp/Vs ratio (κ) and crustal anisotropy (the fast polarization direction φ and splitting time τ) beneath the TNCO and its adjacent areas by analyzing receiver function data recorded by a dense seismic array. The (H, κ) and (φ, τ) at a total of 309 stations were measured, respectively. The Moho depth varies from ∼30 km beneath the western margin of the Bohai bay basin to the maximum value of ∼48 km beneath the northern Lüliang Mountain, which shows the positive and negative correlations with the elevation and the Bouguer anomaly. The average φ is roughly parallel to the strikes of the faults, grabens and Mountains in this study area, whereas a rotating distribution is shown around the Datong-Hannuoba volcanic regions. Based on the φ measured from the Moho Ps and SKS/SKKS phases, we propose that the crustal deformation and seismic hazards beneath the TNCO could be due to the counterclockwise rotation of the Ordos block driven by the far-field effects of the India-Eurasian collision.

Highlights

The North China Craton (NCC) as the largest and oldest known Archean craton in China is located in the eastern margin of the Eurasian plate (Zhao et al, 2001)
The estimated (H, κ) at 309 stations were interpolated into 1,419 meshed grids of 0.25° × 0.25° to show the lateral variations of Moho depth (Figure 4A) and Vp/Vs ratio (Figure 4B) beneath the study area, respectively
We further argue that the observed crustal anisotropy, associating with other parameters, reflects the complex crustal deformation beneath the Trans-North China Orogen (TNCO) and its adjacent areas

Summary

Introduction

The North China Craton (NCC) as the largest and oldest known Archean craton in China is located in the eastern margin of the Eurasian plate (Zhao et al, 2001). The NCC consists of the western NCC (WNCC) and the eastern NCC (ENCC), which are separated by a Paleoproterozoic orogen, the Trans-North China Orogen (TNCO) (Figure 1). Crustal Anisotropy Beneath the TNCO and Ai, 2009) and gravity anomalies (Deng et al, 2014) between the ENCC with lithospheric thinning and the WNCC remaining stable cratonic roots, the TNCO has been accompanied by complicated tectonic deformation and magmatic activity during the episodic geological evolution (Ren et al, 2002; Xu et al, 2004; Zhu et al, 2011). The mechanism of crustal deformation is important in understanding the tectonic evolution and seismic hazards in this study area. Further studies on crustal structure and anisotropy are essential for constraining the crustal deformation mechanism

Methods

Results

Discussion

Conclusion