Tectonic framework of continental subduction - testing hypotheses and developing criteria

大陆俯冲的构造框架 - 检验假设和制定标准

基本信息

批准号：
248980730
负责人：
Professor Dr. Nikolaus Froitzheim
金额：
--
依托单位：
Institut für Geologie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2014
资助国家：
德国
起止时间：
2013-12-31 至 2016-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/248980730?language=en
关键词：
Tectonic framework continental subduction testing

项目摘要

The initiation of subduction and the subduction of continental crust are two key processes of global tectonics which are unsufficiently understood. This project will test three alternative hypotheses (intracontinental subduction, continent collision, and ablative subduction), and develop criteria to distinguish between these.In most instances where continental crust has been subducted, this occurred after the subduction of oceanic lithosphere, when a continental margin entered the subduction zone. In some cases it has been proposed that continental subduction started within continental lithosphere, triggered by compressive stresses acting on pre-existing weaknesses or by density heterogeneities. Intracontinental subduction has also been proposed for the subduction of the Eo-alpine (Cretaceous) high-pressure belt of the Eastern Alps, an eclogite-bearing thrust sheet discontinuously cropping out over a distance of ca. 400 km in Austria, Italy, and Slovenia, because of an apparent lack of oceanic crust and the relatively high thermal gradient in the subduction zone. Other authors have interpreted the high-pressure belt as the result of continent collision after subduction of a narrow ocean embayement, or as the result of ablative subduction, that is, down-dragging of upper-plate rocks into the subduction zone. These three models are testable working hypotheses for our project.To test them and to develop criteria to distinguish between them, we will (1) date protoliths of subducted rocks using LA-ICPMS on zircon and characterize them geochemically, in order to find evidence for either a continental or oceanic nature of the subducted crust; (2) determine the P-T-evolution of eclogites using microprobe analysis and thermodynamic modeling; (3) date their prograde metamorphism using Lu/Hf geochronometry in order to increase the accuracy of age information and to find if the terrane was subducted in one piece or in several pieces; and (4) study the kinematics of shear zones delimiting the high-pressure terrane in order to define how it was emplaced after high-P metamorphism. This study builds on our long-standing collaboration with the Cologne isotope geochemistry group and the methods developed in this collaboration, to determine and date the structural and pressure-temperature history of eclogite-facies rocks with the highest precision possible at the present state of the art. We use the Alpine field example because of the unrivaled wealth of structural, petrological, and geochronological data that is already available for this area.

俯冲起始和大陆地壳俯冲是全球构造运动的两个关键过程，目前尚未得到充分了解。该项目将测试三种替代假设（陆内俯冲、大陆碰撞和烧蚀俯冲），并制定区分这些假设的标准。在大多数大陆地壳俯冲的情况下，这发生在大洋岩石圈俯冲之后，此时大陆边缘进入俯冲带。在某些情况下，有人提出大陆俯冲始于大陆岩石圈内，是由作用于预先存在的弱点的压应力或密度异质性引发的。大陆内俯冲也被提议用于东阿尔卑斯山的始高山（白垩纪）高压带的俯冲，这是一个含榴辉岩的逆冲片，不连续地露出大约 100 米的距离。奥地利、意大利和斯洛文尼亚的距离为400公里，因为明显缺乏洋壳且俯冲带的温度梯度相对较高。其他作者将高压带解释为狭窄海湾俯冲后大陆碰撞的结果，或者是烧蚀俯冲的结果，即将上板块岩石向下拖入俯冲带。这三个模型是我们项目可测试的工作假设。为了测试它们并制定区分它们的标准，我们将 (1) 使用锆石上的 LA-ICPMS 对俯冲岩石的原岩进行测年，并对它们进行地球化学表征，以便找到证据俯冲地壳的大陆性或海洋性； (2) 利用微探针分析和热力学模型确定榴辉岩的 P-T 演化；（3）利用Lu/Hf测年法测定其进行变质作用的年代，以提高年龄信息的准确性，并确定地体是一块还是几块俯冲； (4) 研究界定高压地体的剪切带的运动学，以确定高压地体在高磷变质作用后如何就位。这项研究建立在我们与科隆同位素地球化学小组的长期合作以及在这次合作中开发的方法的基础上，旨在以目前可能的最高精度确定和测定榴辉岩相岩石的结构和压力-温度历史。艺术。我们使用阿尔卑斯地区的例子是因为该地区已经拥有无与伦比的丰富的结构、岩石学和地质年代学数据。