Tectonic origin of supra-subduction zone ophiolites from the three-dimensional geochemical structure of the lava pile

从熔岩堆三维地球化学结构看超俯冲带蛇绿岩的构造成因

基本信息

批准号：
290488493
负责人：
Privatdozent Dr. Marcel Regelous
金额：
--
依托单位：
Geotieteiden ja maantieteen osasto
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2015
资助国家：
德国
起止时间：
2014-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/290488493?language=en
关键词：
Tectonic origin supra subduction zone

项目摘要

Ophiolites are fragments of oceanic crust preserved on land, and are often used to infer the internal structure of the oceanic crust and the processes by which it is formed. However, most ophiolites were not formed in typical mid-ocean ridge settings, and instead appear to have formed close to former subduction zones. The exact tectonic setting in which they were formed has been debated for over 40 years. If ophiolites represent fore-arc crust formed during subduction initiation events, then they provide insights into the initiation of subduction zones, an outstanding unresolved question in plate tectonics. If ophiolites were formed in back-arc or plate edge settings they may represent useful analogues for the internal structure of oceanic crust. If they were formed at a ridge-trench-trench or ridge-trench-transform triple junction then they could be used to investigate mantle wedge structure and processes. Different tectonic models predict different geochemical variations in ophiolite lavas with space and time. We will map out the 3D gechemical structure of the Troodos Ophiolite of Cyprus, one of the best preserved and exposed ophiolites. We will use major and trace element microanaysis of fresh volcanic glass in order to avoid the effects of alteration. Detailed high resolution sampling of sections through the Troodos volcanic section on both the northern and southern margins of the ophiolite will be used to determine the chemical evolution of magmatism. New 39Ar-40Ar ages for lavas from different stratigraphic levels in the Troodos lava sequence will be used to determine the age and duration of the volcanism, and rates of chemical evolution of magmatism with time. Our new geochemical and geochronological data will be used to test hypotheses for the tectonic origin of the Troodos ophiolite.

蛇绿岩是陆地上保存的洋壳碎片，常被用来推断洋壳的内部结构及其形成过程。然而，大多数蛇绿岩并不是在典型的洋中脊环境中形成的，而是似乎是在以前的俯冲带附近形成的。它们形成的确切构造环境已经争论了 40 多年。如果蛇绿岩代表了俯冲起始事件期间形成的弧前地壳，那么它们就可以深入了解俯冲带的起始，这是板块构造中一个尚未解决的突出问题。如果蛇绿岩是在弧后或板块边缘环境中形成的，那么它们可能代表了洋壳内部结构的有用类似物。如果它们是在脊-海沟-海沟或脊-海沟-转换三重连接处形成的，那么它们可用于研究地幔楔结构和过程。不同的构造模型预测了蛇绿岩熔岩随空间和时间的不同地球化学变化。我们将绘制塞浦路斯特罗多斯蛇绿岩的 3D 地球化学结构，该蛇绿岩是保存最完好、暴露程度最高的蛇绿岩之一。我们将对新鲜火山玻璃进行主量和微量元素微量分析，以避免蚀变的影响。对蛇绿岩南北边缘的特罗多斯火山剖面进行详细高分辨率采样，将用于确定岩浆作用的化学演化。特罗多斯熔岩序列中不同地层层熔岩的新 39Ar-40Ar 年龄将用于确定火山活动的年龄和持续时间，以及岩浆作用随时间的化学演化速率。我们新的地球化学和地质年代学数据将用于检验特罗多斯蛇绿岩构造起源的假设。