OCE-PRF: Quantifying Magmatic Influences on the Longevity of Segmented Transform Fault Systems

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。该项目将使用数值模拟来研究控制海洋转换断层几何形状的过程。海洋转换断层是遍布全球洋中脊系统的大型断层。变换断层被认为是分裂、分段，并产生新的火山扩张中心。这些变化可以改变海底可能发生地震的位置。本文拟重点研究岩浆供给对转换断层寿命和几何形状的影响。将开发新的二维和三维模型，并将结果与地壳厚度的观测结果进行比较。项目结果将提高对中洋脊上新洋壳形成的控制和对海底地震驱动过程的理解。该项目将支持一名早期职业科学家（PI/博士后）。它还将通过一个介绍性系列研讨会，向两个主办机构的本科生介绍海洋地球科学研究，帮助扩大代表性不足的科学家对海洋地球科学的参与。本文假设在分段变换系统中，对变换内扩展中心的岩浆供应是扩展中心寿命的主要控制因素。当岩浆供应减弱时，变形区内的扩张将停止，先前分段的走滑断层将统一起来，无论由于板块运动变化而施加的构造压缩或伸展。该假设将通过一系列有限差分、单元内标记、二维和三维数值构造模型进行研究，并受海底测深和重力异常观测的约束。在案例研究中（Clarion FZ、St. Paul TF和Gofar TF），将通过断层和海底结构测量，结合重力异常观测得出的地壳厚度估算，估算非活动断裂带和活动转换断层沿洋中脊扩张的岩浆比例变化。数值模拟中的岩浆供应将根据观测条件随时间有系统地减少，并记录变换断层形态的相应变化。变化的参数包括扩展速率、原始转换断层偏移的长度以及转换区内岩浆扩张与构造调节扩张的比例。这项工作产生的三维模型将公开供其他研究人员使用，以扩展这项工作。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。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).The project will use numerical modeling to study the processes that control the geometry of oceanic transform faults. Oceanic transform faults are large faults that occur throughout the global mid oceanic ridge system. Transform faults are known to split, segment, and give rise to new volcanic spreading centers. These shifts can alter the locations where earthquakes are likely to occur on the seafloor. The proposed study will focus on the influence of magma supply on the longevity and geometry of transform faults. New 2-D and 3-D models will be developed, and results compared with observations of crustal thickness. Project results will improve the understanding of the controls on formation of new ocean crust on mid ocean ridges, and on the processes that drive seafloor earthquakes. The project will support an early career scientist (the PI/postdoc). It will also help broaden participation by underrepresented scientists in marine geosciences through an introductory seminar series that will introduce marine geoscience research to undergraduates at both host institutions.The proposed work hypothesizes that magmatic supply to an intra-transform spreading center is the primary control on spreading center longevity in a segmented transform system. As magmatic supply wanes, spreading in the intra-transform region will cease, and previously-segmented strike slip faults will unify, regardless of imposed tectonic compression or extension due to changing plate motions. The hypothesis will be investigated with a series of finite difference, marker-in-cell, 2-D and 3-D numerical tectonic models, constrained byseafloor bathymetry soundings and gravity anomaly observations. Changing magmatic proportions of spreading at both inactive fracture zones and active transform faults along mid-oceanic ridges in the case studies (Clarion FZ, St. Paul TF, and Gofar TF) will be estimated from fault and seafloor fabric measurements, coupled with crustal thickness estimates derived from gravity anomaly observations. Magmatic supply in the numerical simulations will be systematically decreased over time according to observational constraints and the responding changes in transform fault morphology will be recorded. Parameters varied will include the spreading rate, length of original transform fault offset, and the proportion of magmatic to tectonically-accommodated spreading within the intra-transform region. The 3-D model produced by this work will be publicly available for use by other researchers to expand upon this work.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.