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

俯冲带海洋岩石圈的下沉驱动着地球板块构造的基本过程。为了了解板块构造，了解新的俯冲带是如何形成的是很重要的。该项目将使用一艘研究船和一个能够在3英里深的水下工作的系绳遥控潜水器（ROV），研究西太平洋挑战者深海和美国关岛附近俯冲开始的新例子。在为期23天的考察中，调查人员将研究9个地点。收集的样品将进行几次实验室测试。由年轻和资深地球科学家组成的团队将为新的海洋地球科学家提供重要的培训，而异常强大的互联网连接将使残疾的地球科学家能够参与远征科学。新的俯冲带如何形成是地球科学研究的一个关键课题，需要识别和研究活跃的例子。本研究的研究人员将对西太平洋新近认识到的俯冲起始的活跃例子进行一项新的跨学科海洋地质研究。他们将研究位于关岛西南马里亚纳海沟内海沟壁的挑战者深前弧段（CDFS）。ROV Jason/Medea将用于研究分布在水深6500米以上的CDFS 220公里处的9个地点。他们将在为期23天的海洋探险中取样并检查海洋地壳和上地幔岩石的完整横截面。在过去5 Ma左右的时间里，与马里亚纳海槽弧后盆地的张开有关的伸展形成了CDFS，表明伸展速率为~40mm/y。在前弧中如此强烈的伸展是非常不寻常的，它提供了一个机会来研究广泛的重要构造和岩浆过程，这些过程将促进对水在岩石圈伸展中的作用以及新的俯冲带如何形成的理解，同时探索莫霍暴露和前弧渗漏和喷口群落的新区域。研究人员推测，由于CDFS东部的俯冲比西部更早，因此地幔、下地壳和上地壳的含水量、微量元素组成、岩石组构、热史和氧逸度的沿走向变化将是可测量的，可能还有弧前喷口的分布。他们预计将收集大约450个年轻玄武岩、始新世地壳和上地幔的样品，并将从岩石学、矿物丰度和组成、主要元素和微量元素组成、辐射年龄、地幔结构、地幔和年轻新鲜玄武岩玻璃中的水浓度等方面对这些样品进行研究。由年轻和资深地球科学家组成的团队将为新的海洋地球科学家提供重要的培训，而异常强大的互联网连接将使残疾的地球科学家能够参与远征科学。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。

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.