Assembly and breakup of Gondwana - seismological signatures in the lithosphere/asthenosphere system of Southern Madagascar (SELASOMA)

威尔逊旋回中超大陆的组装和破坏是理解超越海底磁性线理所记录的时间的板块构造历史的决定性范例之一。在这种情况下，问题产生了，在多大程度上，分裂的位置和方式受到早期旋回形成的古代组构的控制。与这个问题相辅相成的问题是，缝合或裂开在多大程度上覆盖了早期的织物，以及这些早期的事件如何影响最近的运动学。虽然这些问题已经通过地质调查得到了广泛的解决，但这些过程的动力学很可能受到中下地壳和岩石圈地幔部分的流变性的强烈影响，而地震学调查最能体现这一点。马达加斯加在冈瓦瓦兰的集结和多阶段分裂中占据了一个关键地区(斯特恩，1994年)，冈瓦瓦兰本身就是超级大陆泛古大陆的一部分。马达加斯加由几个不同的构造单元组成的混合大陆物质组成，最古老的岩石为太古代(3.2Ga)。主要地质界线通常遵循反映该岛地理方向的N-S趋势。其元古界-早古生代组构以横跨数百公里的剪切带网络为特征，部分分支与N-S走向成斜行，特别是在岛的南部。最近在新近纪期间，岛的中部和北部发生了中等程度的火山活动，有迹象表明，在过去10 Ma期间，整个马达加斯加东部都有隆起(Roberts等人)。2012年)。尽管马达加斯加位于非洲板块内部，远离主要板块边界，但其地震活动表明正在发生一些形变。基于大地测量数据和地震矩张量的现代运动学模型确定了一个弥漫的N-S方向的次要边界，该边界分隔两个微板块，似乎穿过马达加斯加(Stamps等人。2008年)。由于它在冈瓦那会议中的关键作用，在马达加斯加进行了大量的地质调查。然而，对地下结构的了解相对较少，因为在马达加斯加进行的集中地震学研究很少。在这项提案中，我们的目标是使用被动地震实验的数据来描述马达加斯加南部的岩石圈结构，该实验是从2012年5月到2014年5月进行的。这项实验包括一个大致面向东西方向的全岛宽带站概况(运行两年)，以及一个区域阵列的短周期站(运行一年)。该剖面横跨所有主要地质省份，短周期阵列将用于绘制当地地震活动图，并对岩石圈/软流圈系统的三维结构提供额外控制。

The assembly and destruction of supercontinents in the Wilson cycle is one of the defining paradigms for understanding the plate tectonic history beyond the time recorded by seafloor magnetic lineations. In this context the question arises to what extent the location and mode of breakup is controlled by ancient fabric formed during earlier cycles. Complementary to this issue is the question to what extent major episodes of suturing or rifting overprint earlier fabric, and how these earlier events influence recent kinematics. Whereas these questions have been addressed extensively by geological investigations, the dynamics of these processes are likely to be strongly influenced by the rheology of the mid- and lower crust and the mantle part of the lithosphere, best characterised by seismological investigations. The island of Madagascar occupied a key region in both the assembly and the multi-stage breakup of Gondwanaland (Stern 1994), itself part of the super-continent Pangaea. Madagascar consists of amalgamated continental material comprising several distinct tectonic units, with the oldest rocks being of Archaean age (3.2 Ga). Major geological boundaries generally follow a N-S trend mirroring the geographic orientation of the island. Its Proterozoic to early Paleozoic fabric is characterised by a shear-zone network spanning hundreds of kilometers, with some of the branches running oblique to the N-S trend, in particular in the south of the island. More recently during the Neogene, moderate volcanism has occurred in the Central and Northern part of the island, and there are indications of uplift throughout Eastern Madagascar over the last 10 Ma (Roberts et al. 2012). Although Madagascar is located within the interior of the African plate and far away from major plate boundaries, its seismic activity indicates that some deformation is taking place. Present-day kinematic models based on geodetic data and earthquake moment tensors identify a diffuse N-S-oriented minor boundary separating two microplates, which appears to pass through Madagascar (Stamps et al. 2008). Because of its key role in the assembly of Gondwana, numerous geological investigations have been carried out in Madagascar. However, comparatively little is known about the sub-surface structure as few focused seismological studies have been carried out in Madagascar. In this proposal we aim to characterise the lithospheric structure of southern Madagascar using data from a passive seismic experiment, which we carried out from May 2012 to May 2014. This experiment included an approximately E-W oriented profile of broadband stations across the island (operating for two years), and an areal array of short-period stations (operated for one year). The profile crosses all major geologic provinces and the short-period array will be used to map local seismicity and provide additional control on the 3-dimensional structure of the lithosphere/asthenosphere system.