Crustal Structure of Southwest China and Northern Vietnam From Ambient Noise Tomography: Implication for the Large‐Scale Material Transport Model in SE Tibet
Crustal Structure of Southwest China and Northern Vietnam From Ambient Noise Tomography: Implication for the Large‐Scale Material Transport Model in SE Tibet
复制标题
DOI：
10.1029/2018tc004957
复制
发表时间：
2018-05
期刊：
影响因子：
4.2
通讯作者：
Lei Qiao;H. Yao;Y. Lai;Bor‐Shouh Huang;Ping Zhang
中科院分区：
文献类型：
--
作者：
Lei Qiao;H. Yao;Y. Lai;Bor‐Shouh Huang;Ping Zhang
人们提出了几种模型来描述西藏东南部及其边缘地区的构造演化。因此，高分辨率地壳速度模型对于解决这一争议至关重要。利用来自中国西南部和越南北部 73 个宽带站的波形数据，我们通过环境噪声断层扫描反演了地壳和上地幔的 3D 剪切波速度模型。我们的模型显示，小江断裂带的中下地壳低速带向南延伸越过红河断裂到达越南，东边大致以小江断裂和奠边府断裂为界。我们认为，观测到的低速区代表中下地壳的机械薄弱区，它可能作为青藏高原东南部物质高效南下的通道。根据我们的结果和之前的证据，我们提出了一个结合刚性块挤压和地壳通道流的组合模型来描述西藏东南部的大规模物质传输。我们进一步提出了印度-欧亚板块碰撞后西藏东南部的两相物质输运模型：（1）早渐新世-早中新世期间实皆右旋断裂和左旋红河断裂之间的刚性块体挤压；（2）晚中新世至今中下地壳刚性块体挤压和物质通道流的组合模型。向南的地壳物质输送很可能沿着峨眉山大型火成岩省内区下方较坚硬的地壳周围的两条主要通道转移。
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.