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.

帕米尔-阿莱地区长期以来一直被认为是活跃的陆内俯冲带的最佳例子，此类区域是人们最不了解的板块边界类型，因为现代的例子很少，而且古代的类似物已被随后的构造和侵蚀过程所覆盖。在过去的十年中，人们在仍然鲜为人知的帕米尔造山带中出现了大量的新观测结果，提出了两个已发表的模型来解释帕米尔北部下方发生明显中深度地震的南倾地震带。主流观点认为，下降的板片代表了北帕米尔和天山之间约300公里的新生代俯冲作用。在新生代早期，北帕米尔和西昆仑山是连续的。该模型预测了北帕米尔和西昆仑山的显着缩短和折返。此外，如果板片中出现比正常情况更致密的地壳，那么 KYTS 就会同时或稍后开始——沿着其长度同步地发生俯冲。基于广泛的地球物理数据库的新研究表明，下地壳和岩石圈地幔分层可以解释该模型中的帕米尔板块。帕米尔岩石圈的下部由地幔和下地壳组成，通过剥离、变陡和向北滚动，形成连续的片状，下沉的下岩石圈形成类似于俯冲作用产生的板块。分层是由印度克拉通向北楔入亚洲地壳所驱动的，因为该模型不允许现在的北帕米尔和天山之间的大幅缩短，因此北帕米尔似乎不太可能。西昆仑山在印度-亚洲碰撞之前形成了一个连续的带，因此，KYTS应该从南部开始并向北发展，最近到达北帕米尔，如果亚洲大陆地壳很厚，则分层模型最有效。如果这个模型是正确的，它将对地球动力学概念产生深远的影响，因为帕米尔高原被用作解释古代造山带的陆内俯冲的类比，这两个模型对空间和浮力做出了不同的预测。变形和折返的时间模式以及形成板块的地壳性质我们的目标是系统地进行地质观测并从垂直剖面中收集样本进行热年代学分析，以限制北帕米尔变形的开始和程度。西昆仑山和 KYTS，从而确定了更合理的模型。