Collaborative Research: Investigating the Detachment Fault Cycle at the Mid-Cayman Spreading Center

在海洋中心不断铺设新的海底是塑造地球表面的基本过程之一。在板块分裂相对较快的地方，随着熔岩上升到地表，形成新的地壳，然后冷却形成固体地壳。板块分开的速度越慢，填补缺口的熔岩就越少，相反，板块分离被称为拆离的长寿断层上的运动所占据。人们对在这些千米级断层上滑动而形成新的大洋海底知之甚少，并与提供富含金属的流体的热液喷口系统有关，这些热液喷口系统创造了矿藏，支持了蓬勃发展的深海生态系统。了解这些断层行为的最好方法之一就是研究它们所产生的地震。该项目将使用由海底地震仪网络记录的地震数据，该网络部署在加勒比海中开曼扩张中心的两个板块分开的分离断层系统上。这一结果将有助于我们通过监测断层活动、岩浆作用和地下热液流动，了解大洋拆离断层生命周期的最后阶段。该项目支持培训加州大学圣地亚哥分校的一名研究生和伍兹霍尔海洋研究所的一名博士后研究员。它还通过参加远洋考察和暑期项目来支持本科生的培训。这个项目的总体目标是了解支配支队断层生命周期后期阶段的过程，特别是放弃断层系统的过程。海洋分离经历了一个持续数百万年的滑动和遗弃的生命周期，通常暴露在被称为海洋核心杂岩的千米级穹顶中的海底上地幔岩石。尽管它们形成于岩浆贫乏的环境中，但拆离体往往拥有高温热液系统，热液喷口与超镁铁质岩石之间的相互作用产生了具有不同成分的流体。滑脱断层与构造、岩浆和热液作用之间的微妙相互作用有关，但这种相互作用如何在~2Myr生命周期内演化存在争议。这个项目将使用当地的微震调查。在中开曼扩张中心凹陷地块，以限制与生命周期后期阶段相关的构造-岩浆作用。一个海底地震仪网络将部署6-12个月来检测微震到达，将用于生成震源和震源机制目录，并测试用于检测和定位震源的新的全波形方法。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Continuous paving of new seafloor at the center of the oceans is one the fundamental processes that shape Earth’s surface. Where plates spread apart relatively quickly, new crust is formed as molten rock rises to the surface, and cools to form solid crust. Where the plates move apart more slowly less molten rock fills the gap, and instead, plate separation is taken up by motion on long-lived faults called detachments. Creation of new oceanic seafloor by slip on these kilometer-scale faults is poorly understood, and is associated with hydrothermal vent systems that provide metal-rich fluids, which create ore deposits and support thriving deep-sea ecosystems. One of the best ways to understand the behavior of these faults is to study the earthquakes that they generate. This project will use earthquake data recorded by a network of seafloor seismometers, deployed on a detachment fault system where two plates are spreading apart in the Caribbean Sea, at the Mid-Cayman Spreading Center. The results will help us understand the final stages of the ‘life cycle’ of an oceanic detachment fault, by monitoring the faulting, magmatism, and hydrothermal fluid flow in the subsurface. This project supports the training of a graduate student at the University of California San Diego, and a postdoctoral investigator at Woods Hole Oceanographic Institution. It also supports the training of undergraduate students, through participation in a sea-going research expedition and summer programs.The overarching goal of this project is to understand the processes that govern the late stages of the detachment faulting life cycle, and the processes by which the fault system is abandoned, in particular. Oceanic detachments undergo a life cycle of slip and abandonment that lasts millions of years, and commonly expose upper mantle rocks on the seafloor in kilometer-scale domes called oceanic core complexes. Although they form in magma-poor settings, detachments often host high-temperature hydrothermal systems, and interactions between hydrothermal vents and ultramafic rocks generate fluids with distinct compositions. Detachment faults are associated with a delicate interplay between tectonic, magmatic, and hydrothermal processes, but how such interactions evolve over the ~2 Myr life cycle are controversial. This project will use a local microearthquake survey of the Mt. Dent massif on the Mid-Cayman Spreading Center, to constrain the tectono-magmatic processes associated with the late stage of the life cycle. A network of ocean bottom seismographs will be deployed for 6–12 months to detect microearthquake arrivals, which will be used to generate hypocenter and focal mechanism catalogs, and also to test new full-waveform methods for detecting and locating hypocenters.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.