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Structural-kinematic history of crustal-scale lineaments along the South Atlantic continental margins

南大西洋大陆边缘地壳尺度线状结构运动学历史

基本信息

批准号：
172804908
负责人：
Professor Dr. Hartwig E. Frimmel
金额：
--
依托单位：
Sektion 2.2: Geophysikalische Abbildung des Untergrunds
依托单位国家：
德国
项目类别：
Priority Programmes
财政年份：
2010
资助国家：
德国
起止时间：
2009-12-31 至 2014-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/172804908?language=en
关键词：
Structural kinematic history crustal scale

项目摘要

The aim of the project is to reconstruct the mode of opening of the South Atlantic. Using the Mesozoic structures as a reference frame it will be tested whether the break-up of southwestern Gondwana followed pre-existing older lithospheric structures or not. Several different tectonic scenarios appear possible: (i) the South Atlantic opened along Pan-African suture zones that had formed between the southern African continental cratonic blocks and the South American Rio de la Plata Craton during the assembly of Gondwana, i.e. within a former subduction and continental collision zone, (ii) break-up may have commenced along a former back-arc along the western margin of the Kalahari palaeocontinent along a thermally and rheologically softened crustal domain or, (iii) it may turn out that inherited lithospheric anisotropies did not play any significant role for initiation and location of Mesozoic continental rifting. In order to achieve the set goal, the kinematic evolution of the Mesozoic structures associated with the South Atlantic opening need to be determined first. This will serve as a reference frame for comparison with the structural-kinematic history of pre-rift structures, which needs to be inferred from field observations. Integral to the proposed study is to infer the orientations (and their change) of the palaeostress fields that produced the Mesozoic and pre-Mesozoic structures. This will be done with an algorithm developed by the PI that uses robust regression techniques, which are capable of detecting outliers, to calculate geologically meaningful palaeostress orientations (i.e. the reduced stress tensor) from field data. This structural-kinematic study will be augmented by petrological and geochemical investigations on selected samples. In addition, the proposed study should demonstrate whether pre- Mesozoic structures influenced rift-related magma emplacement. Furthermore, an effort will be made to directly date the age of movement along the major fault and shear zones using the Rb-Sr and Ar-Ar isotope systems.

该项目的目的是重建南大西洋的开放模式。以中生代构造为参照系，将检验冈瓦那西南部的裂解是否遵循先前存在的较老的岩石圈结构。看来可能出现几种不同的构造情形：(1)南大西洋沿着在冈瓦那拼装期间在南部非洲大陆克拉通块体和南美洲里约热拉普拉塔克拉通之间形成的泛非缝合带打开，即在以前的俯冲和大陆碰撞带内；(2)可能是沿着沿卡拉哈里古大陆西缘的前弧后沿一个热和流变软化的壳域开始的解体；或(3)可能是继承的岩石圈各向异性对中生代大陆裂谷的启动和位置没有起到任何重要作用。为了实现既定的目标，首先需要确定与南大西洋开放有关的中生代构造的运动学演化。这将作为与裂谷前构造的结构运动学历史进行比较的参照系，而裂谷前构造的历史需要从实地观察中推断出来。这项拟议的研究的整体内容是推断产生中生代和前中生代构造的古应力场的方向(及其变化)。这将通过PI开发的一种算法来完成，该算法使用稳健的回归技术，能够检测离群值，从现场数据计算具有地质意义的古应力方向(即折合应力张量)。这项构造运动学研究将通过对选定的样品进行岩石学和地球化学调查而得到加强。此外，拟议的研究应证明前中生代构造是否影响了与裂谷有关的岩浆侵位。此外，还将努力利用Rb-Sr和Ar-Ar同位素系统直接测定沿主要断裂和剪切带的运动年龄。