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

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，将检验冈瓦纳西南部的断裂是否遵循先前存在的较古老的岩石圈构造。几种不同的构造情景似乎是可能的：（i）南大西洋沿着泛非缝合带打开，该缝合带是在冈瓦纳大陆拼合期间在南部非洲大陆板块和南美洲拉普拉塔河板块之间形成的，即在前俯冲和大陆碰撞带内，（ii）断裂可能是沿着卡拉哈里古大陆西缘的前弧后，沿着热软化和流变软化的地壳域开始的，或者，（3）继承性岩石圈各向异性对中生代大陆裂谷作用的发生和定位没有明显作用。为了实现既定目标，首先需要确定与南大西洋开口有关的中生代构造的运动学演化。这将作为一个参考框架，用于与裂谷前构造的构造-运动学历史进行比较，而裂谷前构造的构造-运动学历史需要从实地观测中推断出来。所提出的研究的一个组成部分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开发的算法来完成，该算法使用能够检测异常值的稳健回归技术，以根据现场数据计算具有地质意义的古应力方向（即约化应力张量）。对选定的样品进行岩石学和地球化学调查，将加强这种构造运动学研究。此外，拟议的研究应证明前中生代构造是否影响与裂谷有关的岩浆侵位。此外，还将利用Rb-Sr和Ar-Ar同位素系统直接测定沿着主要断裂和剪切带的运动年龄。

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.