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.

俯冲是板块构造的一个基本组成部分，其中一个板块向下俯冲到另一个板块下方，并在上面的板块上产生火山弧。然而，人们对俯冲如何开始知之甚少，很大程度上是因为目前还没有观察到这一过程的发生。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和亨特海沟沿线的俯冲作用才刚刚开始。该项目将进行两次前往马修-亨特俯冲带的科学巡航，以部署和恢复海底地震仪，并收集海洋地球物理数据集。地震数据将用于对火山下方的下降板块和岩浆源区域进行成像。这些巡航还将绘制海底地图并进行重力和磁力测量，这将提供有关构造结构、火山活动、地壳变形和俯冲起始过程年龄的证据。该项目将与来自法国和新喀里多尼亚的科学家合作进行。俯冲起始可能是陆地地球动力学中最持久的问题。大多数有关俯冲起始的知识来自对过去起始事件的研究，其中一些火山产物被保存下来。目前缺乏包括弧前岩浆作用的经典序列在内的俯冲起始实例，限制了对这些过程如何发生的理解。然而，最近的研究表明，俯冲起始和伴随的岩浆活动正在沿着新赫布里底海沟和斐济地台之间的马修和亨特海沟发生。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，但其先进程度足以产生岩浆产物。该项目将部署由 25 台被动海底地震仪组成的阵列（20 台美国地震仪和 5 台法国地震仪），并进行海洋地球物理调查，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。地震仪将沿着由法国合作巡航进行拍摄的线路部署，以利用浅层结构的限制，该阵列的设计目的是对弧前、火山猎人岭和外延蒙齐尔裂谷的结构进行成像。将使用来自环境噪声和地震的瑞利波层析成像、体波层析成像和剪切波分裂来分析地震数据。此外，还将进行广泛的多波束测深、声学反向散射图像、重力和磁力勘测，以确定构造结构、近期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，以完整绘制弧前区域并在与主要地震仪部署相同的区域进行三维地球物理反演。近地表和更深的地壳和地幔成像的结合将为理解俯冲起始提供强大的约束。该项目将与来自 IFREMER 和新喀里多尼亚的研究人员合作开展，他们提出了目前正在等待安排的法国巡航，以收集主动源地震数据以及热流和流体样本。该奖项反映了 NSF 的法定使命，并已被视为值得通过使用基金会的智力优点和更广泛的影响审查标准进行评估来支持。