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。 在板块相对快速地分开的地方，新的地壳随着熔融的岩石上升到表面而形成，并冷却形成固体地壳。 在板块分离较慢的地方，填充差距的熔融岩石较少，相反，板块分离是通过被称为断层的长期存在的断层上的运动来进行的。 人们对这些大型断层滑动产生新海底的情况知之甚少，这种情况与提供富金属流体的热液喷口系统有关，这些热液喷口系统产生矿床并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，该地震仪网络部署在开曼群岛中部扩展中心加勒比海两个板块正在扩展的分离断层系统上。 通过监测地下的断层活动、岩浆活动和热液流动，这些结果将有助于我们了解大洋拆离断层“生命周期”的最后阶段。 该项目支持培训加州圣地亚哥大学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。 它还支持本科生的培训，通过参加航海研究考察和暑期课程。该项目的总体目标是了解控制剥离断层生命周期后期阶段的过程，特别是断层系统被遗弃的过程。 海洋碎屑岩经历了一个持续数百万年的滑动和废弃的生命周期，通常在海底暴露出上地幔岩石，形成更大规模的圆顶，称为海洋核复合体。虽然它们形成于岩浆贫乏的环境中，但碎屑岩往往是高温热液系统的宿主，热液喷口和超镁铁岩之间的相互作用产生了具有不同成分的流体。拆离断层与构造、岩浆和热液过程之间微妙的相互作用有关，但这种相互作用如何在200万年的生命周期中演化仍有争议。 该项目将使用当地的微震调查山。开曼群岛中部扩展中心的Dent Baglif，以限制与生命周期后期阶段相关的构造岩浆过程。一个海底地震仪网络将被部署6-12个月，以探测微地震到达，这将被用来生成震源和震源机制目录，并测试新的全波形方法来探测和定位震源。这个奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的智力价值和更广泛的影响审查标准。

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.