Collaborative Research: Magmatic and Mechanical Extension of the Challenger Deep Forearc Segment: Insights into Subduction Initiation

俯冲带中大洋岩石圈的下沉驱动了板块构造的基本地球过程。要了解板块构造，重要的是要了解新的俯冲带是如何形成的。该项目将研究在西太平洋挑战者深海和美国关岛附近发起俯冲的新例子，使用一艘考察船和一艘能够工作到3英里深的系泊遥控潜水器(ROV)。调查人员将在为期23天的探险中研究9个地点。收集的样本将接受几项实验室测试。年轻的和资深的地球科学家团队将为新的海洋地球科学家提供重要的培训，异常强大的互联网连接将使残疾的地球科学家能够参与探险科学。如何形成新的俯冲带是地球科学研究的一个关键课题，需要确定和研究活跃的例子。这项研究的研究人员将对新发现的西太平洋俯冲启动的活跃实例进行一项新的跨学科海洋地质学研究。他们将研究位于关岛西南部马里亚纳海沟内海沟墙内的挑战者深弧段(CDF)。水下机器人Jason/Medea将用于研究沿6500米水深以上220公里的CDF分布的9个地点。在为期23天的海洋探险中，他们将对洋壳和上地幔岩石的全横截面进行采样和检查。过去5 Ma左右，马里亚纳海槽弧后盆地的拉张形成了CDF，其伸展速率约为40 mm/年。弧前如此强烈的伸展是非常罕见的，它提供了一个研究广泛的重要构造和岩浆过程的机会，这将促进对水在岩石圈伸展中的作用以及新俯冲带形成的理解，同时探索莫霍面暴露、弧前渗漏和喷口群落的新区域。研究人员推测，由于东部CDF的俯冲作用比西部更先进，因此来自地幔、下地壳和上地壳的岩石中的水含量、微量元素组成、岩石组构、热史和氧逸度将发生可测量的沿走向的变化，可能还有弧前喷发的分布。他们预计将采集约450个年轻玄武岩、始新世地壳和上地幔的样本，并将从岩石学角度研究其中的一部分，包括矿物丰度和组成、常量元素和微量元素组成、放射性年龄、地幔组构以及地幔和年轻新鲜玄武岩玻璃中的水浓度。年轻和资深的地球科学家团队将为新的海洋地球科学家提供重要的培训，异常强大的互联网连接将允许残疾地球科学家参与探险科学。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。

The sinking of oceanic lithosphere in subduction zones drives the fundamental Earth process of plate tectonics. To understand plate tectonics, it is important to understand how new subduction zones form. This project will study a new example of subduction initiation in the Western Pacific near the Challenger Deep and Guam USA using a research vessel and a tethered remotely-operated vehicle (ROV) capable of working down to 3 miles deep. Investigators will study 9 sites during a 23-day expedition. Collected samples will be subjected to several laboratory tests. The team of young and senior geoscientists will provide important training of new marine geoscientists and an unusually strong internet connectivity will allow a handicapped geoscientist to participate in expeditionary science.How new subduction zones form is a key topic of geoscientific research that requires identifying and studying active examples. Investigators in this study will conduct a novel interdisciplinary marine geologic study of a newly recognized active example of subduction initiation in the Western Pacific. They will study the Challenger Deep Forearc Segment (CDFS) located in the inner trench wall of the Mariana Trench SW of Guam. ROV Jason/Medea will be used to study 9 sites distributed along 220 km of the CDFS above 6500m water depth. They will sample and examine a full cross-section of oceanic crust and upper mantle rocks during a 23-day marine expedition. The CDFS formed by extension associated with opening of the Mariana Trough backarc basin over the past 5 Ma or so, suggesting an extension rate of ~40mm/y. Such strong extension in a forearc is very unusual and provides an opportunity to investigate a wide range of important tectonic and magmatic processes that will advance understanding of the role of water in lithospheric extension and how new subduction zones form, at the same time explore a new region for Moho exposures and forearc seeps and vent communities. The investigators hypothesize that, because subduction is more advanced in the eastern CDFS than in the west, there will be measurable along-strike changes in water contents, trace element compositions, rock fabrics, thermal histories, and oxygen fugacity in rocks from the mantle, lower crust, and upper crust and perhaps the distribution of forearc venting. They expect to collect ~450 samples of young basalts, Eocene crust, and upper mantle and will study a subset of these petrographically, for mineral abundances and compositions, for major and trace element compositions, for radiometric ages, for mantle fabrics, and for water concentrations in mantle and young fresh basaltic glass. The team of young and senior geoscientists will provide important training of new marine geoscientists and an unusually strong internet connectivity will allow a handicapped geoscientist to participate in expeditionary science.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.