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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.

俯冲的起始和大陆地壳的俯冲是全球构造的两个关键过程，人们对这两个过程的认识还不够充分。该项目将测试三种可供选择的假设（大陆内俯冲、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，这发生在海洋岩石圈俯冲之后，大陆边缘进入俯冲带。在某些情况下，有人提出大陆俯冲开始于大陆岩石圈内，是由作用于预先存在的薄弱处的压缩应力或密度非均质性引起的。大陆内俯冲也被认为是东阿尔卑斯的古阿尔卑斯（白垩纪）高压带俯冲的原因，这是一个含榴辉岩的逆冲片，在奥地利、意大利和斯洛文尼亚的距离约为400公里，因为明显缺乏海洋地壳和相对较高的热梯度。另一些作者将高压带解释为一个狭窄的海洋海湾俯冲后大陆碰撞的结果，或者是烧蚀性俯冲的结果，即上板块岩石向下拖入俯冲带。对于我们的项目，这三个模型是可测试的工作假设。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，以寻找俯冲地壳的大陆或海洋性质的证据；(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年代学对其前变质作用进行定年，以提高年龄信息的准确性，确定地块是整体俯冲还是多块俯冲；(4)研究划分高压地块的剪切带运动学，以确定高压地块在高p变质作用后的侵位方式。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基础上，以及在合作中开发的方法，以目前最先进的技术水平，以最高的精度确定榴辉岩相岩石的结构和压力-温度历史。我们以阿尔卑斯油田为例，是因为该地区已经拥有无与伦比的丰富的构造、岩石学和地质年代学数据。