Assessing the relationship between strain localization and magmatism during rift evolution

地球表面的大部分被海洋覆盖，海洋下面的岩石构成了海洋地壳。地球上的大陆可能会持续数十亿年，而海洋地壳却在不断地被破坏和创造。这些动力过程导致海洋盆地的打开和关闭，甚至导致大陆的分裂。大陆裂谷表现为大陆上一系列相互连接的线状到弧形的山谷，是大陆分裂和新海洋形成过程的表现。因此，对新海洋形成的洞察取决于大陆裂谷中活跃的过程。这个项目的重点是大陆裂谷中大量熔岩的产生。这些熔岩形成了后来海洋地壳的基础，但岩浆产生的机制目前尚不清楚。该项目关注东非裂谷——现代大陆裂谷的首要例子，并研究岩浆如何在地幔中产生，在地壳中演化，并最终在这个裂谷中爆发。该项目的最终目标之一是了解为什么在某些时期大量熔岩涌入裂谷表面，而在其他时期熔岩被限制为线性带。这项工作可以为不断发展的模型提供依据，这些模型试图将地壳的结构限制在裂谷和新生的海洋盆地中。从东非获得的见解对于理解全球裂谷边缘，以及地壳和沿这些边缘的近海盆地如何发展具有广泛的意义。通过检查在东非暴露的岩石，我们可以产生更好的概念模型，这些岩石可能被几公里长的沉积物（例如，美国东海岸）所掩埋。更广泛的影响包括本科研究经验。本文将获得东非裂谷熔岩的新的地球化学和岩石学约束。重点将放在熔岩场上，这些熔岩场代表了火山喷发风格的末端成员——大型熔岩流、孤立的盾和较小的熔岩锥。东非拟议的研究区域如下：(i)阿法尔，一个研究人员激烈争论海洋地壳是否已经形成的地区；（ii）图尔卡纳，一个早期的裂谷事件使地壳比预期的薄。本建议所进行的工作将围绕四个相互关联的问题进行安排：(A)不同熔岩场的岩浆产生机制是什么？(B)哪些地幔源有助于这些熔岩场中的岩浆形成？(C)岩浆生成/源贡献如何随时间变化？(D)在不同的熔岩场之间，地壳内岩浆演化的条件有区别吗？本项目重点关注的地区涵盖了《地球地质信息系统实施计划》阐明的两个目标。图尔卡纳位于“重点调查的主要地区”，而阿法尔位于“合作目标”地区。因此，这项研究的结果可以与同一地区正在进行的其他由nsf赞助的科学研究进行比对，以实现地质科学目标。结合起来，这些数据将用于解决科学问题：“在整个岩石圈中，应变是如何调节和划分的，以及控制应变定位和迁移的因素是什么？”这项工作的结果将对与东非上地幔深部物质分布有关的其他科学问题产生进一步的影响。这些问题目前正在通过其他跨学科研究加以解决，拟议的工作将对最近熔岩中记录的裂谷过程的限制因素增加一个关键组成部分。总的来说，这些研究旨在突破裂谷如何开始、演变和过渡到海洋扩张的现有知识的界限。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The majority of Earth's surface is covered in oceans, below which lie rocks that constitute the oceanic crust. Unlike Earth's continents, which may persist for billions of years, the oceanic crust is continually destroyed and created. These dynamic processes lead to the opening and closure of ocean basins, and even the breaking apart of continents. Continental rifts, which manifest as a series of interconnected linear to arcuate valleys on continents, are the manifestation of the process by which continents may split and new oceans form. Insights into the creation of new oceans thus depends on the processes active within continental rifts. This project focuses on the generation of large volumes of lavas within continental rifts. These lavas form the basis of later oceanic crust, but the mechanism of magma generation is currently unclear. The project focuses on the East African rift - the premier example of a modern continental rift, and examines how magmas are generated in the mantle, evolve in the crust, and eventually erupt in this rift. One of the eventual aims of this project is to develop an understanding as to why large-volumes of lavas flood onto the surface of the rift during certain periods, while during other periods the lavas are restricted to linear belts. This work can feed into evolving models that seek to constrain the architecture of the crust within rifts and nascent ocean basins. Insights gained from East Africa have broad implications in understanding rifted margins globally, and how the crust and offshore basins along these margins develop. By examining rocks that are exposed in East Africa, we may generate better conceptual models of regions where these rocks may be buried by kilometers of sediments (e.g., Eastern U.S. seaboard). Broader Impacts include undergraduate research experience.In this proposal new geochemical and petrographic constraints on lavas from the East African rift will be obtained. The focus will be on lava fields that represent end members in eruption style - large lava flows, isolated shields, and smaller lava cones. The proposed study regions in East Africa are the following: (i) Afar, a region where researchers vigorously debate if ocean crust is already being formed, and (ii) Turkana, a region where an earlier rifting event has made the crust thinner than would be anticipated. The work being undertaken in this proposal will be arranged around four interlinked questions: (A) What is the mechanism of magma generation for the different lavas fields? (B) What mantle sources contribute to magma creation within these lavas fields? (C) How does magma generation/ source contribution change over time? (D) Is there a difference in the conditions of magma evolution within the crust between the different lava fields? The region this project focuses on spans two of the targets elucidated by the GeoPRISMS Implementation Plan. Turkana lies within the "Primary area for focused investigations", while Afar lies within the "collaborative target" region. Thus, the results of this study can be collated with other NSF-sponsored science being undertaken in the same region to address GeoPRISMS science goals. When combined, these data will be used to address the science question: "How is strain accommodated and partitioned throughout the lithosphere, and what are the controls on strain localization and migration?" The results of this work will have further impact upon other science questions related to the distribution of deep mantle material in the East African upper mantle. These questions are currently being addressed through other interdisciplinary studies and the proposed work would add a critical component to the the constraints on the rifting process that is recorded in the recent lavas. When considered in aggregate, these studies aim to push the boundaries of current knowledge as to how rifting initiates, evolves, and transitions to oceanic spreading.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.