Rifting, volcanism, and neotectonic processes in Madagascar: understanding the mechanism of breakup of old, stable continental lithosphere

大陆撕裂或裂谷作用是地球上最重要的板块构造过程之一，但人们对裂谷作用的成因和机制知之甚少。了解大陆裂谷如何开始，传播和最终形成海洋盆地是我们了解地球动力学的基础，以及构造过程如何塑造地球表面。此外，大陆裂谷带往往与地震和火山有关，因此了解其成因和演变对减轻火山和地震灾害至关重要。 北美大陆（克拉通）内的大多数裂谷系统是古老的，通常被厚的沉积物掩埋和/或受到许多裂谷后变形事件的影响，因此，阻碍了对裂谷过程的直接研究。另一方面，马达加斯加为研究大陆裂谷带的诞生和早期发展提供了机会，因为它正在经历与东非裂谷系（EARS）南部臂（也称为索马里-非洲扩散板块边界）可能扩展有关的积极延伸。该岛的关键位置是揭示EARS的重要特征：（1）裂谷相关断层系统的性质和几何形状;（2）裂谷在时间和空间上的演化;（3）构造结构和裂谷岩浆活动之间的关系。 拟议的研究计划将集中在马达加斯加两个地震、构造和火山活动最活跃的地区，Itasy-Ankaratra（中部）和Nosy Be-Anivorano（北方）：（1）进一步研究该岛活动裂谷系的性质、几何形态、成因和演化及其形态表现，（2）建立构造与火山位置的几何关系;以及（3）进一步记录和评估这些地区近期火山活动的普遍性。这项研究将包括系统的地质填图、构造野外研究、遥感分析、年龄测定以及岩石学和地球化学的综合方案。此外，这项研究还将整合其他地球物理数据，如地震、重力和电磁数据。这项研究计划将导致在大陆岩石圈裂谷过程中断层系统和岩浆相互作用的新模型，可以作为基准，以老的和年轻的裂谷影响小或大的大陆（如北美大陆）。它还将导致对EARS南部分支和马达加斯加第四纪火山区的几何学、运动学、年龄和结构演变的新认识，在马达加斯加，对EARS的演变和起源的不同观点正在出现。该计划将涉及加拿大和马达加斯加的专业同事之间的合作，并允许加拿大和马达加斯加在实地和实验室研究中的参与和培训。

Continental tearing or rifting is one of the most important plate tectonic processes on Earth, yet the cause and mechanism of rift are poorly understood. Understanding how continental rifting starts, propagates and eventually forms oceanic basins are fundamental to our understanding of the dynamics of the Earth, and how tectonic processes shape the Earth's surface. In addition, continental rift zones are often associated with earthquakes and volcanoes, as such understanding their cause and evolution are crucial for volcanic and earthquake hazards mitigation. Most rift systems within the North American continent (craton) are old, often buried by thick sediments and/or have been affected by numerous post-rifting deformation events, thus, preventing direct study of the rifting processes. Madagascar, on the other hand, provides an opportunity to investigate the birth and early development of continental rift zones, as it is undergoing active extension related to the possible propagation of the southern arm of the East African Rift System (EARS), also known as the Somalian-African diffuse plate boundary. The island is critically positioned to reveal important features of the EARS: (1) the nature and geometry of rift-related fault system; (2) the rift evolution through time and space, and (3) the relationships between tectonic structures and rift magmatism. The proposed research program will focus on the two most seismically, tectonically, and volcanically active regions of Madagascar, Itasy-Ankaratra (central) and Nosy Be-Anivorano (northern) to: (1) further investigate the nature, geometry, origin and evolution of the active rift system in the Island and its morphological expressions; (2) establish the geometric relationship between tectonic structures and volcano locations; and (3) further document and evaluate the prevalence of recent volcanism in these regions. This research will involve an integrated program of systematic geological mapping, structural field study, remote sensing analysis, age dating, as well as petrology and geochemistry. In addition, the study will integrate other geophysical data such as seismic, gravity and electromagnetic data when available. This research program will result in a new model of fault system and magmatic interactions during the rifting of continental lithosphere that can serve as benchmark to both old and younger rifts affecting small or large continents (e.g. North American Craton). It will also lead to a new understanding of geometry, kinematics, age and structural evolution of the southern branch of the EARS and the Quaternary volcanic fields in Madagascar where divergent views of its evolution and origin are emerging. The program will involve collaboration between professional colleagues in Canada and Madagascar, and allow for the participation and training of Canadian and Malagasy in field-and laboratory-based research.