Unraveling the Dynamic Processes beneath the Northern Tibetan Plateau: Paleozoic Collision and Cenozoic Destruction of Mantle Lithosphere and Plateau Uplift

我们建议在青藏高原北方进行一个中德合作的地震实验，以解决造山带下修改和破坏大陆岩石圈和控制岩石圈动力学过程的基本问题。与西藏其他地区相比，北方地区具有广泛的新生代火山活动、Sn波传播不良和Pn波速度低、浅部地幔地震速度低和地震各向异性强等特点。提出了两种端元模型来解释这些观测结果：（1）印度和欧亚地幔岩石圈的俯冲、叠加或纯剪切增厚;（2）欧亚地幔岩石圈的拆沉或对流去除。另一个问题涉及古生代特提斯洋俯冲的极性重建，这可以通过研究古生代缝合带的深部结构来解决。以前在西藏进行的实验分辨率不足以解决这些问题，估计的地震速度和岩石圈厚度仍存在很大差异。本文计划在西藏东北部部署和分析两个线性被动震源地震台阵：（1）可可西里和北方羌塘的NW-SE宽频带台阵，由50个台距10 km的台站组成;（2）横跨金沙江缝合带的N-S密集台阵，由300个短周期台站组成，台距500 m。将对宽带阵列采用各种地震方法，包括接收器功能、地震体波层析成像、利用环境噪声和地震的表面波层析成像以及横波分裂，以探测地壳和地幔岩石圈的地震结构，并确定岩石圈的厚度。我们将应用和开发利用短周期波形相干性的方法，例如，使用连续波场的叠加互相关和不同的转换相位来获得金沙江缝合带的详细图像。

We propose a collaborative Sino-German seismic experiment in the northern Tibetan plateau in order to address fundamental questions on the processes that modify and destroy continental lithosphere and control lithospheric dynamics beneath orogenic belts. Northern Tibet is characterized, with respect to the rest of Tibet, by the widespread Cenozoic volcanism, poor Sn wave propagation and low Pn wave velocity, low seismic velocities in the shallow mantle and strong seismic anisotropy. Two end member models were proposed to explain the these observations beneath the northern Tibetan plateau involve (1) underthrusting, stacking or pure-shear thickening of Indian and Eurasian mantle lithosphere and (2) delamination or convective removal of Eurasian mantle lithosphere. A further question relates to the reconstruction of the polarity of Paleozoic Tethys ocean subduction, which can be resolved from examining the deep structure of Paleozoic sutures. The resolution of previous experiments in Tibet was not sufficient to resolve theses questions and large discrepancies remain in the estimated seismic velocities and thickness of the lithosphere. Here, we plan to deploy and analyse two linear passive-source seismic arrays in northeastern Tibet: (1) a NW-SE broadband array in Hoh Xil and northern Qiangtang, consisting of 50 stations with a station spacing of 10 km; and (2) a dense N-S array across the Jinsha River Suture, comprising 300 short-period stations with a station spacing of 500 m. A variety of seismic methods will be applied to the broadband array, including receiver functions, teleseismic body wave tomography, surface wave tomography using ambient noise and earthquakes and shear wave splitting to explore seismic structures in the crust and mantle lithosphere and to determine the thickness of the lithosphere. We will apply and develop methodologies that exploit the coherence of waveforms at short period, for example to obtain detailed images of the Jinsha River Suture using stacked cross-correlations of the continuous wavefield and distinct converted phases from teleseismic earthquakes.