Did the Pamir slab form by intracontinental subduction or lithospheric delamination? Clues from the deformation and thermal history

帕米尔板块是由陆内俯冲或岩石圈拆沉形成的吗？

基本信息

批准号：
336677747
负责人：
Professor Dr. Jonas Kley
金额：
--
依托单位：
Abteilung Strukturgeologie und Geodynamik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2021-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/336677747?language=en
关键词：
Did Pamir slab form intracontinental

项目摘要

The Pamir-Alai has long been considered to represent the best example of an active intracontinental subduction zone. Such zones are the least understood type of plate boundaries because modern examples are few, and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes. During the past decade, a significant body of new observations have emerged from the still poorly-known Pamir orogen. Two published models have been proposed to explain the south-dipping seismic zone with prominent intermediate-depth earthquakes beneath the northern Pamir. The dominant view is that the downgoing slab represents intracontinental subduction which has accommodated ca. 300 km of Cenozoic convergence between the North Pamir and the Tien Shan. In the early Cenozoic, the North Pamir and the Western Kunlun Shan were contiguous; they are now offset by the Kashgar-Yecheng Transfer System (KYTS). This model predicts that significant shortening and hence exhumation in the North Pamir and the Western Kunlun Shan commenced synchronously. Furthermore, the KYTS would have initiated either at the same time or later - synchronously along its length. Intracontinental subduction is facilitated if denser than normal crust occurs in the slab. We propose to investigate evidence for a Mesozoic oceanic backarc basin subducted beneath the Pamir in Cenozoic time. New work based on an extensive geophysical database suggests that lower crustal and lithospheric mantle delamination could explain the Pamir slab. In this model, the lower part of the Pamir lithosphere, consisting of the mantle and lower crust, delaminates as a continuous sheet from the upper crust. By peeling off, steepening and rolling back northwards, the sinking lower lithosphere forms a slab resembling that produced by subduction. This forced delamination is driven by northward wedging of the Indian craton into Asian crust. Since this model does not allow for substantial shortening between the present North Pamir and the Tien Shan, it seems unlikely that the North Pamir and the Western Kunlun Shan formed a continuous belt prior to the India-Asia collision. Therefore, the KYTS should have started in the south and grown northward, reaching the North Pamir recently. The delamination model works best if Asia´s continental crust was thick and buoyant. If this model is correct, it has profound implications for geodynamical concepts, because the Pamir is used as an analogue to explain intracontinental subduction in ancient orogens. The two models make different predictions about the spatial and temporal pattern of deformation and hence exhumation and about the nature of the crust forming the slab. Our goal is to systematically make geological observations and collect samples from vertical profiles for thermochronologic analysis in order to constrain the onset and magnitude of deformation in the North Pamir, the Western Kunlun Shan, and the KYTS and thereby identify the more plausible model.

长期以来，Pamir-Alai被认为是活动室内俯冲带的最佳例子。这样的区域是板块边界的最不知情的类型，因为现代例子很少，而古老的类似物被随后的构造和侵蚀过程广泛覆盖。在过去的十年中，从仍然鲜为人知的帕米尔造山基因出现了大量的新观察结果。已经提出了两种已发表的模型来解释北部帕米尔下方明显的中间地震的南倾阵区。主要的看法是，下去的平板代表了在CA中发生的注型室内俯冲。北帕米尔（North Pamir）和蒂恩（Tien Shan）之间的300公里的新生代收敛。在早期的新生代，北帕米尔和昆伦山是连续的。现在，它们被Kashgar-Yecheng转移系统（KYTS）所抵消。该模型预测，北帕米尔（North Pamir）和昆伦（Kunlun Shan）的大幅缩短并因此挖掘出来。此外，KYTS将同时或以后 - 沿其长度同步。如果比正常地壳发生比正常地壳发生比正常地壳发生，则可以制备透明俯冲。我们建议调查在帕米尔（Cenozoic）时代下方俯冲的中生代海洋后水盆地盆地的证据。基于广泛的地球物理数据库的新工作表明，下层地壳和岩石圈地幔分层可以解释Pamir板。在此模型中，由岩层和下层地壳组成的Pamir岩石圈的下部将其作为连续薄板从上皮中分离出来。通过剥离，钢和向北滚动，下沉的下岩石圈形成了俯冲产生的平板。由印度克拉顿向北楔入亚洲地壳驱动。由于该模型不允许在目前的北帕米尔和蒂恩山之间进行大幅缩短，因此北帕米尔和昆伦·山（North Pamir）和西部昆伦（Kunlun Shan）似乎不太可能在印度 - 亚洲碰撞之前形成一条连续的皮带。因此，Kyts应该从南部开始，向北种植，最近到达北帕米尔。如果亚洲的连续地壳厚而浮力，则分层模型最有效。如果该模型是正确的，它对地球动力学概念具有深远的影响，因为Pamir被用作解释古代牛根群体内大陆俯冲的类似物。这两个模型对变形的空间和临时模式进行了不同的预测，因此挖掘以及形成板的外壳的性质。我们的目标是系统地进行地质观察，并从垂直轮廓中收集样品，以进行热力学分析，以限制北帕米尔（North Pamir），西部昆伦·山（Western Kunlun Shan）和kyts的变形的开始和变形幅度，从而确定了更合理的模型。