Understanding subduction by linking surface exposures of subducted and exhumed crust to geophysical images of slabs

通过将俯冲和挖出的地壳的表面暴露与板片的地球物理图像联系起来来了解俯冲作用

• 批准号: 365204690
• 负责人: Professor Dr. Mark R. Handy
• 金额: --
• 依托单位: Institut für Geologische Wissenschaften
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/365204690?language=en
• 关键词: Understanding; subduction; linking; surface; exposures

One of the prime goals of 4D-MB is to link surface geological observations to the deep structure of the Alps. The deep structure will be imaged in 3D in unprecedented detail by the densely spaced AlpArray seismic network and further densified associated deployments (SWATH D). A geological interpretation of these images, however, will only be possible on the basis of a plausible model of the rock types and structures causing the seismic observations.From seismic data and plate-tectonic reconstructions, we can expect to find subducted continental crust currently beneath the Alps. On the small scale, the seismic properties of these subducted rocks depend on (a) changing mineral assemblages as a function of pressure, temperature and fluid availability conditions, and (b) the evolving rock fabric induced by deformation (e.g., mylonitic shearing causing anisotropy). On a larger scale, the pattern of changing seismic velocities is therefore determined by the distribution of high- and low-strain domains and/or lithological changes in the crustal basement. Quantifying seismic properties requires accessible analogues of presently subducted crust, which can be found in high-pressure (HP) and ultrahigh-pressure (UHP) basement rocks now exposed at the surface. In order to address the prime goal of 4D-MB, we aim to link the tectonometamorphic evolution of these (U)HP units to their changing seismic properties.We will reconstruct their geometries and numerically model the kinematics during burial and exhumation (WP1), then combine this information with rock-physical data of (U)HP samples to obtain synthetic seismic images of continental basement units at various burial depths (WP2). These synthetic images will then be compared and updated according to actual seismic images derived from data recorded by the SWATH D array, which offers a nearly tenfold increase in station density in the Eastern Alps (WP3). We will focus on seismic waves converted at elastic discontinuities, as these have the highest sensitivity for crustal structures at mantle depths, but supplement them with local earthquake records.With this interdisciplinary approach we aim to decipher the state of continental crust currently at U(HP) depth. We especially want to understand how nappe formation and fluid-rock interaction lead to changes in mineral assemblages, which in turn determine the seismic visibility of the deforming and subducting crust. By tackling this question from three different angles, namely the kinematic, petrophysical and seismological views, the project is designed to explore the feasibility, but also the limitations, of resolving crustal-scale structures at mantle depth by seismic methods. It opens the perspective of providing a solid quantitative connection between the geological observations and rock samples collected at the surface to the geophysical images of the deeper structures in the quest to reconstruct the deformation history of the Alpine orogen.

4D-MB的主要目标之一是将表面地质观测与阿尔卑斯山的深层结构联系起来。深度结构将通过密度间隔的Alparray地震网络和进一步致密相关的部署（Swath D）以前所未有的细节成像。然而，只有基于岩石类型和结构的合理模型，对这些图像的地质解释才有可能。从地震数据和板块构造重建中，我们可以期望找到目前在阿尔卑斯山下方的大陆壳。在小尺度上，这些俯冲岩石的地震特性取决于（a）矿物质组合，这是压力，温度和流体可用性条件的函数，以及（b）因变形引起的不断变化的岩石织物（例如，肌lon虫剪切造成各向异性）。因此，在更大范围内，地震速度变化的模式取决于地下室中高压和/或岩性变化的分布和/或岩性变化。量化的地震特性需要目前俯冲的地壳的可访问类似物，可以在高压（HP）和超高压（UHP）地下室岩石中发现，现在暴露在地面上。为了解决4D-MB的主要目标，我们的目的是将这些（U）HP单元的构态化学演变与它们不断变化的地震属性联系起来。我们将重建其几何形状，并在数值上对埋葬和挖掘过程中的运动学进行建模（WP1），然后将这些信息与Rock-phys of Remittion Contiction Contiction（u）HP组合（U）HP组合（U）HP组合（U）HP组合（U）HP。埋葬深度（WP2）。然后，将根据从Swath D阵列记录的数据得出的实际地震图像进行比较和更新这些合成图像，该图像从Swath D Array记录的数据中，该图像在东阿尔卑斯山（WP3）中提供了近十倍的站点密度增长。我们将专注于在弹性不连续性上转化的地震波，因为这些波浪对地幔深度的地壳结构具有最高的敏感性，但用局部地震记录补充了它们。我们旨在破译当前在U（HP）深度的大陆壳状态（HP）深度。我们特别想了解纳普的形成和流体岩石相互作用如何导致矿物组合的变化，这又决定了变形和俯冲外壳的地震可见性。通过从三个不同角度（即运动学，岩石物理和地震学观点）来解决这个问题，该项目旨在通过地震方法探索可行性，但同样是局限性，也是通过地震方法在地幔深度上解决地壳尺度结构的局限性。它开辟了一个观点，即提供在地面上收集的地质观测和岩石样品之间与更深层结构的地球物理图像之间提供扎实的定量联系，以寻求重建高山造成的变形历史。