Imaging the hydrous Tonga slab in the fastest and coldest subduction zone

GSTDTAP

项目编号	1842989
	Imaging the hydrous Tonga slab in the fastest and coldest subduction zone
	Songqiao Wei (Principal Investigator)
主持机构	Michigan State University
项目开始年	2019
	2019-04-15
项目结束日期	2021-03-31
资助机构	US-NSF
项目类别	Standard Grant
项目经费	179426(USD)
国家	美国
语种	英语
英文摘要	When a tectonic plate descends into Earth's mantle along an oceanic trench - a process called subduction - both solid rocks and water stored in major hydrous minerals are carried into the deep earth. Most of the water will return to the surface of Earth through volcanism when the minerals hosting the water break down (dehydration) because of the high pressure and temperature encountered as they descend deeper. Trace amounts of water stored in so called anhydrous minerals may be preserved in the descending plate (subducting slab) to greater depths and get involved in whole mantle convection. This process is called Earth's deep-water cycle, which controls the water flux in Earth's interior. After decades of seismic observations, numerical simulations, and petrological/mineralogical experiments, it is generally agreed that slab dehydration takes place at a few hundred kilometers depth below the seafloor. However, a fundamental question remains unsolved: How deep can major hydrous minerals be subducted? Hydrous minerals presumably can be preserved to greater depths in a colder slab because dehydration reactions are controlled by temperature and pressure. The Tonga slab, which is the Pacific Plate that descends along the Tonga Trench, is believed to the fastest moving and coldest slab on Earth. Therefore, imaging hydrous minerals and determining their maximum depths in the Tonga slab, as an extreme case study, are critical to understanding the water flux in subduction zones and estimating Earth's water budget. This project will provide research opportunities for both graduate and undergraduate students. In this study, the Tonga slab crust and uppermost mantle will be imaged by analyzing converted and guided seismic waves from local earthquakes because these waves are most sensitive to slab interface and internal structure. The data were collected from a local broadband seismic array deployed in 2009-2010 in the Tonga-Lau-Fiji region, and provide unprecedented constraints on local seismicity and mantle structure of this subduction zone. The Tonga slab surface (upper interface) position and relative locations of intermediate-depth earthquakes at depths of 50-200 km will be refined. The high-resolution seismic structure of the Tonga slab interior at depths of 50-300 km will be constrained by PS and guided P waves, providing insights into the distribution of the subducted hydrous minerals in this coldest slab. The results will help to test the hypothesis that the Tonga slab, along with other similarly cold slabs in the history of Earth, can carry hydrous minerals to depths greater than 250 km, or even to the mantle transition zone. Verifying this hypothesis will have important impacts on our understanding of the Earth's deep-water cycle because direct evidence of a significant amount of water being subducted into the mantle transition zone is still lacking. 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.
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/213035
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Songqiao Wei .Imaging the hydrous Tonga slab in the fastest and coldest subduction zone.2019.