Collaborative Research: Geophysical Study of Ongoing Subduction Initiation Along the Matthew-Hunter Trench

合作研究：沿马修-亨特海沟持续俯冲起始的地球物理研究

• 批准号: 2228414
• 负责人: Fernando Martinez
• 金额: $ 41.8万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-11-15 至 2027-10-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2228414&HistoricalAwards=false
• 关键词: Collaborative; Research; Geophysical; Study; Ongoing

Subduction, where one plate plunges downward beneath another plate and produces a volcanic arc on the overriding plate, is a fundamental component of plate tectonics. However, there is little understanding of how subduction begins, largely because there have been no observations of this process happening at the present time. Recent studies show that subduction is just beginning along the Matthew and Hunter Trench, between Vanuatu, New Caledonia, and Fiji in the South Pacific. This project will conduct a pair of scientific cruises to the Matthew-Hunter Subduction Zone to deploy and recover ocean bottom seismographs, as well as gather marine geophysical datasets. The seismic data will be used to image the downgoing plate and magma source regions beneath volcanoes. The cruises will also map the seafloor and make gravity and magnetic measurements that will provide evidence concerning tectonic structures, volcanism, crustal deformation, and ages of subduction initiation processes. This project will be carried out in collaboration with scientists from France and New Caledonia. Subduction initiation may be the most enduring question in terrestrial geodynamics. Most knowledge of subduction initiation comes from the study of past initiation events where some of the volcanic products have been preserved. The lack of present-day examples of subduction initiation that include the classic sequence of forearc magmatism limits the understanding of how these processes occur. However, recent studies show that subduction initiation with accompanying magmatic activity is occurring along the Matthew and Hunter Trench between the New Hebrides Trench and the Fiji Platform. The Matthew-Hunter Subduction Zone thus offers a unique opportunity to study a young subduction zone in the process of formation but sufficiently advanced to create magmatic products. This project will deploy an array of 25 passive ocean bottom seismographs (20 US and 5 French) and carry out a marine geophysical survey to define the slab geometry, seismicity, structure, and mantle flow patterns associated with this developing subduction zone. The seismographs will be deployed along lines to be shot by a collaborative French cruise to take advantage of shallow structure constraints, and the array is designed to image the structure of the forearc, the volcanic Hunter Ridge, and the extensional Monzier Rift. Seismic data will be analyzed using Rayleigh wave tomography from ambient noise and earthquakes, body wave tomography, and shear wave splitting. In addition, an extensive multibeam bathymetric, acoustic backscatter imagery, gravity and magnetic survey will be carried out to identify tectonic structures, regions of recent seafloor volcanism, and magnetic isochrons. Geophysical track spacing will be sufficiently dense to fully map the forearc area and carry out three-dimensional geophysical inversions over the same regions as the main seismograph deployment. This combination of near surface and coincident deeper crustal and mantle imaging will provide powerful constraints for understanding subduction initiation. This project will be carried out in collaboration with investigators from IFREMER and New Caledonia, who have proposed a French cruise currently awaiting scheduling to collect active source seismic data as well as heat flow and fluid samples.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.

俯冲作用是指一个板块向下俯冲到另一个板块下方，并在覆盖的板块上形成火山弧，这是板块构造的基本组成部分。然而，人们对俯冲是如何开始的知之甚少，这主要是因为目前还没有观察到这一过程发生。最近的研究表明，南太平洋瓦努阿图、新喀里多尼亚和斐济之间的马修海沟和亨特海沟才刚刚开始俯冲。该项目将对马修-亨特俯冲区进行两次科学巡航，以部署和回收海底地震仪，并收集海洋地球物理数据集。地震数据将被用于对火山下方的板块和岩浆源区进行成像。巡航还将绘制海底地图，并进行重磁测量，以提供关于构造结构、火山活动、地壳变形和俯冲开始过程的年龄的证据。该项目将与法国和新喀里多尼亚的科学家合作开展。俯冲的启动可能是地球动力学中最持久的问题。有关俯冲启动的大部分知识来自对过去启动事件的研究，其中一些火山产品已被保存下来。目前缺乏包括经典的弧前岩浆作用序列在内的俯冲开始的例子，限制了人们对这些过程如何发生的理解。然而，最近的研究表明，伴随着岩浆活动的俯冲开始发生在新赫布里底海沟和斐济地台之间的马修海沟和亨特海沟。因此，马修-亨特俯冲带提供了一个独特的机会来研究正在形成过程中的年轻俯冲带，但足够先进，可以产生岩浆产物。该项目将部署一组25台被动海底地震仪(20台美国地震仪和5台法国地震仪)，并进行一次海洋地球物理调查，以确定与这一发展中的俯冲带相关的板块几何形状、地震活动、结构和地幔流动模式。地震仪将沿线部署，由一艘合作的法国邮轮拍摄，以利用浅层结构限制，阵列旨在成像前弧形、火山猎人山脊和伸展的Monzier裂谷的结构。地震数据将使用环境噪声和地震的瑞利波层析成像、体波层析成像和横波分裂进行分析。此外，还将进行广泛的多波束测深、声学后向散射成像、重力和磁力测量，以查明构造结构、最近海底火山活动区域和磁等时线。地球物理轨道间距将足够密集，以充分绘制弧前区域的地图，并在与主地震仪部署相同的区域进行三维地球物理反演。这种近地表和重合的深部地壳和地幔成像的结合，将为理解俯冲开始提供强有力的约束。该项目将与IFREMER和新喀里多尼亚的研究人员合作进行，他们提议目前正在等待日程安排的法国邮轮收集活动震源地震数据以及热流和流体样本。这一奖励反映了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。