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。当板块相对较快地分开时，随着熔岩上升到地表，新的地壳形成，并冷却形成固体地壳。在板块分离较慢的地方，较少的熔融岩石填充空隙，相反，板块分离被长期存在的断层运动所取代，称为分离。人们对这些千米级断层上的滑动形成新的海洋海底知之甚少，这与热液喷口系统有关，热液喷口系统提供富含金属的流体，这些流体产生矿床，支持繁荣的深海生态系统。了解这些断层行为的最好方法之一是研究它们产生的地震。该项目将使用海底地震仪网络记录的地震数据，该网络部署在加勒比海两个板块分开的分离断层系统上，位于中开曼扩散中心。通过监测断裂、岩浆活动和地下热液流动，这些结果将帮助我们了解海洋剥离断层“生命周期”的最后阶段。该项目支持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的培训。它还通过参加海上研究考察和暑期项目来支持本科生的培训。该项目的首要目标是了解控制分离断层生命周期后期阶段的过程，特别是断层系统被放弃的过程。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，通常会在海底暴露上地幔岩石，形成千米规模的圆顶，称为海洋核复合体。尽管它们形成于岩浆缺乏的环境中，但分离体通常拥有高温热液系统，热液喷口与超镁铁质岩石之间的相互作用产生了具有独特成分的流体。拆离断层与构造、岩浆和热液过程之间的微妙相互作用有关，但这种相互作用如何在~2 Myr生命周期中演变是有争议的。该项目将利用对中开曼扩张中心登特山地块的局部微地震调查，来约束与生命周期晚期相关的构造-岩浆过程。海底地震仪网络将部署6-12个月来探测微地震的到来，这将用于生成震源和震源机制目录，并测试用于探测和定位震源的新的全波形方法。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。

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.