Collaborative Research: Tectonic and Magmatic Processes during Early-Stage Rifting: an Integrated Study of Northern Lake Malawi, Africa

尽管厚的大陆岩石圈伸展并最终破裂的概念已被接受了50多年，但发生这种情况所需的条件和控制裂谷样式的最重要因素，构造分割的形成和维持以及岩浆活动的开始仍然存在争议。对于最早的伸展阶段尤其如此，部分原因是大多数研究集中在成功的裂陷边缘和成熟的裂谷上，在这些地方，广泛的拉伸、裂陷前后的岩浆作用和破碎后的沉积作用覆盖并掩盖了早期的伸展记录。了解大洋中脊和裂谷的特征是如何、为什么以及何时在早期裂陷中形成和演化的，对于更广泛地理解板块分裂是至关重要的。该项目的主要科学目标是研究所有发散板块边界的两个基本特征的出现和早期演化：岩浆作用和分段作用。岩浆作用在大多数洋中脊和晚期裂谷中容纳了很大比例的板块分离。同样地，转换断层在洋中脊上划分出离散的扩展段，其普遍特征是中心的岩浆活动比边缘的岩浆活动更强烈。在晚期裂谷和新洋盆中也观察到发育良好的岩浆作用和构造分割作用，但对年轻裂谷中岩浆作用和分割作用的发生和发展的控制因素知之甚少。具体来说，这些计划寻求解决以下问题：？岩浆活动何时、何地、为何在裂谷中开始，它在适应伸展方面起什么作用？？ 是什么控制了早期裂陷构造分段的发展？它如何在岩浆活动和变形的四维模式中表现出来？该项目包括对东非裂谷系统马拉维湖北部地区进行综合地球物理、地球化学和地质研究，以解决这些问题。这是世界上少数几个拥有全面研究早期裂谷作用所需的所有成分的地方之一。主动和被动地震数据以及MT数据将揭示地壳和岩石圈在各种长度尺度上的三维结构，从边界断层和调节带的结构到地幔岩石圈中变形和岩浆（如果存在）的分布。地表变形、地震活动性和裂谷地层学，以及地质年代学、热气压学和火山岩的地球化学，将对岩浆活动的起源以及在一定时间尺度上的变形和岩浆活动的演化产生限制，包括岩石圈下和岩石圈源可能产生的不同贡献。活动变形模式和累积变形模式的比较将有助于评价偶发性、地震活动性和岩浆活动在适应伸展方面的重要性，以及它们与分段的关系。这种时间和空间约束的强大组合将对大陆裂谷期间的分段和岩浆活动的起源产生独特的见解。

Although the concept that thick continental lithosphere extends and ultimately ruptures has been accepted for over 50 years, the conditions required for this to occur and the factors that are most important in controlling the style of rifting, the formation and maintenance of tectonic segmentation and the initiation of magmatism remain contentious. This is especially true of the earliest stages of extension, in part because most studies focus on successfully rifted margins and mature rifts, where extensive stretching, syn- and post-rift magmatism, and post-breakup sedimentation overwrite and bury the record of incipient extension. Understanding how, why and when features that are characteristic of mid-ocean ridges and rifts first form and evolve during early rifting is essential for a broader understanding of plate divergence. The primary scientific goal of this project is to examine the emergence and early evolution of two fundamental features of all divergent plate boundaries: magmatism and segmentation. Magmatism accommodates a significant percentage of plate separation at most mid-ocean ridges and late-stage rifts. Likewise, transform faults demarcate discrete spreading segments in mid-ocean ridges, which are broadly characterized by more robust magmatism at their centers than at their edges. Well-developed magmatic and tectonic segmentation is also observed in late-stage rifts and new ocean basins However,little is known about the controls on the initiation and development of magmatism and segmentation in young rifts. Specifically, th PIs seek to address the following questions: ? When, where and why does magmatism initiate in rifts, and what is its role in accommodating extension? ? What controls the development of tectonic segmentation in early-stage rifts? How is it manifested in 4D patterns of magmatism and deformation. The project consists of an integrated geophysical, geochemical and geological study of the northern Lake Malawi region in the East African Rift System (EARS) to address these questions. This is one of the few places in the world that has all of the ingredients necessary for a comprehensive study of early rifting. Active and passive seismic data and MT data will reveal the 3D structure of the crust and lithosphere at a variety of length scales, from the architecture of border faults and accommodation zones to the distribution of deformation and magma (if present) in the mantle lithosphere. Surface deformation, seismicity, and rift stratigraphy, as well as geochronology, thermobarometry and geochemistry of volcanic rocks, will yield constraints on the origin of magmatism and the evolution of deformation and magmatism at a range of time scales, including possibly variable contributions from sub-lithospheric versus lithospheric sources. Comparisons of active and cumulative deformation patterns will enable the evaluation of the importance of episodicity, seismicity and magmatism in accommodating extension and how they relate to segmentation. This powerful combination of temporal and spatial constraints will produce unique insights into the initiation of segmentation and magmatism during continental rifting.