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.

俯冲的启动和大陆地壳的俯冲是全球构造学的两个关键过程，这些过程是无法充分理解的。该项目将测试三个替代假设（注入大陆俯冲，大陆碰撞和消融性俯冲），并制定标准以区分这些假设。在大多数情况下，大陆岩石层俯冲后发生在大陆岩石圈的俯冲后，当大陆缘伸入大陆缘后，这发生在大陆岩石圈后。在某些情况下，已经提出，大陆俯冲始于大陆岩石圈，这是由作用于预先存在的弱点或密度异质性的压缩应力引起的。还提出了肠内俯冲，以使东阿尔卑斯山的EO-α（白垩纪）高压带的俯冲，这是一种含有依云虫的推力板，不连续地在Ca的距离内裁剪出来。在奥地利，意大利和斯洛文尼亚的400公里，由于显然缺乏海洋壳，并且在俯冲带中的热梯度相对较高。其他作者已经解释了高压带，这是由于狭窄的海洋嵌入或消融俯冲的结果，即将上层岩石拖放到俯冲带的垂直下，是由于大陆碰撞的结果。这三个模型是我们项目的可检验的工作假设。要测试它们并制定标准以区分它们，我们将使用LA-ICPMS上的La-iCPMS在锆石上使用俯冲岩石的质量石材，并在地球上进行表征，以便找到俯冲壳的大陆或海洋性质的证据；（2）使用微探针分析和热力学建模确定息肉的p-t进化；（3）使用LU/HF地球运动学来约会他们的训练变质，以提高年龄信息的准确性，并找到地层是否被一块或几块俯冲；（4）研究剪切区域的运动学，以划定高压地形，以定义高-P变质化后如何分配它。这项研究建立在我们与科隆同位素地球化学组的长期合作基础上，以及在此合作中开发的方法，以确定和日期，以确定和日期，在当前艺术状态下，eclogite-Facies岩石的结构和压力温度历史具有最高的精度。我们之所以使用高山现场示例，是因为该领域已经可用的结构，岩石学和年代学数据无与伦比的财富。