Crustal Structure of Southwest China and Northern Vietnam From Ambient Noise Tomography: Implication for the Large‐Scale Material Transport Model in SE Tibet

Abstract

Several models have been proposed to describe the tectonic evolution of SE Tibet and its marginal areas. Hence, high-resolution crustal velocity models are essential to address this controversy. With waveform data from 73 broadband stations in southwest China and northern Vietnam, we invert for a 3-D shear wave velocity model of the crust and uppermost mantle from ambient noise tomography. Our model reveals that the midlower crustal low-velocity zone in the Xiaojiang Fault Zone extends farther southward across the Red River Fault to Vietnam and is approximately bounded by the Xiaojiang and Dien Bien Phu faults to the east. We suggest that the observed low-velocity zone represents a mechanically weak zone in the mid-lower crust, which may serve as a channel for efficient southward material transport in SE Tibet. With our results and previous evidence, we propose a combined model that integrates rigid block extrusion and crustal channel flow to describe the large-scale material transport in SE Tibet. We further propose a two-phase material transport model in SE Tibet after the India-Eurasia plate collision: (1) rigid block extrusion between the right-lateral Sagaing Fault and left-lateral Red River Fault during the early Oligocene-early Miocene and (2) a combined model of rigid block extrusion and material channel flow in the mid-lower crust from the late Miocene to the present. The southward crustal material transport is likely to be diverted along two major channels around the more rigid crust beneath the inner zone of the Emeishan large igneous province.

Deep crust analysis beneath northern Vietnam by using receiver functions: Implications for SE Asia continental extrusion

“…8a). On a large scale, the presence of a LVZ in this sector is probably associated with a LVZ beneath central and southeastern Tibet (Ozacar and Zandt 2004;Xu et al 2007;Bai et al 2009;Li and van der Hilst 2010;Qiao et al 2018;Deng et al 2019). This evidence is also consistent with findings reported by Le et al (2008Le et al ( , 2009.…”

“…Furthermore, Bai et al (2010) reported that they detected a LVZ in the northwestern part of the Indochina Peninsula. Recently, Qiao et al (2018) reported this LVZ extended to western side of the Dien Bien Phu fault based on results of ambient noise tomography. However, because of limited observations, the question of whether this LVZ extends to a broad area of northern Vietnam remains unanswered.…”

Transversely Isotropic Lower Crust of Variscan Central Europe imaged by Ambient Noise Tomography of the Bohemian Massif

“…Therefore, we can explain the discrepancy between the CSS and our ANT model by anisotropic structure (transverse isotropy with slow vertical symmetry axis) in the LPC (see the text below). Weak VTI anisotropy explaining the velocity drop in the lower crust is in agreement with results of other authors elsewhere (e.g., Luo et al, 2013;Shapiro et al, 2004;and Qiao et al, 2018). The subtle v S decrease in the top of the LPC of the ANT model (see Figs.…”

Viscosities of the crust and upper mantle constrained by three-dimensional GPS rates in the Sichuan–Yunnan fragment of China

“…Additionally, the specific distribution, dynamic source and movement mechanism of the channel flow are not completely clear. In particular, the distribution of the channel flow given by different studies (Bai et al 2010;Bao et al 2015;Liu et al 2014;Qiao et al 2018) has significant differences. Thus, it is impractical to quantitatively study crustal vertical movement caused by the channel flow.…”