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

合作研究：早期裂谷期间的构造和岩浆过程：非洲马拉维湖北部的综合研究

• 批准号: 1109512
• 负责人: Matthew Pritchard
• 金额: $ 7.93万
• 依托单位: Cornell University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-04-15 至 2018-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1109512&HistoricalAwards=false
• 关键词: Collaborative; Research; Tectonic; Magmatic; Processes

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.

尽管厚大陆岩石圈延伸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以及控制裂谷类型、构造分段的形成和维持以及岩浆作用启动的最重要因素仍然存在争议。对于伸展的最早阶段尤其如此，部分原因是大多数研究都集中在成功裂谷的边缘和成熟的裂谷上，其中广泛的伸展、同裂谷和裂谷后的岩浆作用以及破碎后的沉积覆盖和掩埋了早期伸展的记录。了解大洋中脊和裂谷特征在早期裂谷过程中如何、为何以及何时首次形成和演化对于更广泛地了解板块分歧至关重要。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。岩浆作用在大多数洋中脊和晚期裂谷处容纳了很大比例的板块分离。同样，转换断层划分了大洋中脊中离散的扩张段，这些断层的总体特征是其中心的岩浆活动比其边缘的岩浆作用更强烈。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割作用，但对于年轻裂谷岩浆作用和分割作用的起始和发展的控制机制知之甚少。具体而言，PI 寻求解决以下问题： ?岩浆作用何时、何地、为何在裂谷中开始，它在容纳扩张方面的作用是什么？ ？是什么控制着早期裂谷构造分段的发展？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 (EARS) 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。这是世界上为数不多的拥有全面研究早期裂谷所需所有要素的地方之一。主动和被动地震数据以及大地电磁数据将揭示地壳和岩石圈在各种长度尺度上的3D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、地震活动和裂谷地层学，以及火山岩的地质年代学、热压测量和地球化学，将对岩浆作用的起源以及一系列时间尺度上的变形和岩浆作用的演化产生限制，包括来自岩石圈下与岩石圈来源的可能的可变贡献。活动和累积变形模式的比较将能够评估幕式活动、地震活动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结合将对大陆裂谷期间分段和岩浆作用的启动产生独特的见解。