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

大洋岩石圈在俯冲带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。该项目将使用一艘研究船和一个能够在3英里深的水下作业的系留遥控潜水器，研究在美国挑战者深海和关岛附近西太平洋发生俯冲的新实例。调查人员将在为期23天的考察中研究9个地点。采集的样本将接受多项实验室检测。 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，异常强大的互联网连接将使残疾地球科学家能够参与探险科学。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。这项研究的调查人员将对西太平洋一个新发现的俯冲活动实例进行一项新的跨学科海洋地质研究。 他们将研究位于关岛马里亚纳海沟西南部海沟内壁的挑战者深前弧段（CDFS）。Jason/Medea将用于研究分布在水深6500 m以上的CDFS的沿着220 km的9个地点。 他们将在为期23天的海洋考察中对大洋地壳和上地幔岩石的完整横截面进行取样和检查。CDFS是在过去5 Ma左右与马里亚纳海槽弧后盆地张开有关的伸展作用形成的，表明伸展速率约为40 mm/y。 这种强烈的扩张在弧前是非常不寻常的，并提供了一个机会，调查范围广泛的重要的构造和岩浆过程，将推进水在岩石圈扩张的作用和新的俯冲带的形成，同时探索一个新的区域莫霍面暴露和弧前渗漏和喷口社区的理解。 研究人员假设，由于俯冲是更先进的东部CDFS比在西部，将有可测量的沿走向的变化，水含量，微量元素成分，岩石组构，热历史，和氧逸度的岩石从地幔，下地壳，上地壳，也许弧前排气的分布。 他们预计将收集约450个年轻的玄武岩，始新世地壳和上地幔样品，并将研究这些岩石学的子集，矿物丰度和成分，主要和微量元素成分，放射性年龄，地幔结构，以及地幔和年轻的新鲜玄武岩玻璃中的水浓度。这个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，并且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。这个奖项反映了NSF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.