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

尽管厚大陆岩石圈伸展并最终破裂的概念已经被接受了50多年，但发生这种情况所需的条件以及控制裂谷样式、构造分段的形成和维持以及岩浆作用的启动的最重要因素仍然存在争议。对于伸展的早期阶段尤其如此，部分原因是大多数研究集中于成功的裂谷边缘和成熟的裂谷，其中广泛的伸展、裂谷后和裂谷后的岩浆作用以及裂解后的沉积作用覆盖和埋葬了早期伸展的记录。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谷过程中首先形成和演化的，对于更广泛地理解板块分歧是至关重要的。该项目的主要科学目标是研究所有不同板块边界的两个基本特征的出现和早期演化：岩浆作用和分割。在大多数大洋中脊和晚期裂谷，岩浆作用适应了相当大比例的板块分离。同样，转换断层划分了大洋中脊的离散扩张段，这些中脊的大致特征是中心的岩浆活动比边缘的岩浆活动更强劲。在晚期裂谷和新洋盆中也观察到了发育良好的岩浆作用和构造分段性，但对年轻裂谷中岩浆作用的发生和发展以及分割性的控制知之甚少。具体地说，绩效指标旨在解决以下问题：？岩浆作用何时、何地和为什么在裂谷中开始，它在适应伸展方面起到什么作用？是什么控制了早期裂谷中构造分段的发展？它是如何在岩浆作用和变形的4D模式中表现出来的。该项目包括对东非裂谷系统中的马拉维湖北部地区进行的综合地球物理、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所需材料的地方之一。主动和被动地震数据以及大地电磁测深数据将在不同的长度尺度上揭示地壳和岩石圈的三维结构，从边界断裂和调节带的结构到地幔岩石圈中的变形和岩浆(如果存在)的分布。地表变形、地震活动和裂谷地层学，以及火山岩的地质年代学、温压测量和地球化学，将对岩浆活动的起源以及变形和岩浆作用在一系列时间尺度上的演化产生制约，包括可能来自岩石圈以下来源和岩石圈来源的不同贡献。活动形变模式和累积形变模式的比较将使人们能够评估幕式、地震活动和岩浆作用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过程中分段和岩浆作用的启动产生独特的见解。

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.