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地表地质观测与阿尔卑斯山的深层结构联系起来。密集的 AlpArray 地震网络和进一步致密化的相关部署 (SWATH D) 将以前所未有的细节对深层结构进行 3D 成像。然而，对这些图像的地质解释只有在引起地震观测的岩石类型和结构的合理模型的基础上才有可能。根据地震数据和板块构造重建，我们可以期望找到目前下方俯冲的大陆地壳阿尔卑斯山。在小规模上，这些俯冲岩石的地震特性取决于（a）作为压力、温度和流体可用性条件的函数而变化的矿物组合，以及（b）由变形引起的不断演变的岩石结构（例如，糜棱岩剪切导致各向异性） ）。因此，在更大的尺度上，地震速度变化的模式是由地壳基底中高应变域和低应变域的分布和/或岩性变化决定的。量化地震特性需要当前俯冲地壳的可接近的类似物，这些类似物可以在现在暴露在地表的高压（HP）和超高压（UHP）基岩中找到。为了实现 4D-MB 的主要目标，我们的目标是将这些 (U)HP 单元的构造变质演化与其不断变化的地震特性联系起来。我们将重建它们的几何形状，并对埋藏和掘出过程中的运动学进行数值模拟 (WP1)，然后将这些信息与 (U)HP 样本的岩石物理数据相结合，以获得不同埋藏深度的大陆基底单元的合成地震图像 (WP2)。然后，这些合成图像将根据由 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，该阵列使东阿尔卑斯山 (WP3) 的台站密度增加了近十倍。我们将重点关注在弹性不连续性处转换的地震波，因为这些地震波对地幔深处的地壳结构具有最高的敏感性，但会用当地地震记录对其进行补充。通过这种跨学科方法，我们的目标是破译目前在 U(HP) 处大陆地壳的状态） 深度。我们特别想了解推覆层的形成和流体-岩石相互作用如何导致矿物组合的变化，进而决定变形和俯冲地壳的地震可见性。该项目旨在从运动学、岩石物理学和地震学三个不同角度解决这一问题，旨在探索用地震方法解析地幔深度地壳尺度结构的可行性和局限性。它开辟了在地表收集的地质观测和岩石样本与深层结构的地球物理图像之间提供可靠的定量联系的视角，以寻求重建阿尔卑斯造山带的变形历史。