NSF Org:	OCE Division Of Ocean Sciences
Recipient:	WASHINGTON UNIVERSITY, THE
Initial Amendment Date:	June 5, 2020
Latest Amendment Date:	June 6, 2023
Award Number:	1928914
Award Instrument:	Continuing Grant
Program Manager:	Gail Christeson gchriste@nsf.gov  (703)292-2952 OCE  Division Of Ocean Sciences GEO  Directorate for Geosciences
Start Date:	September 1, 2020
End Date:	August 31, 2026 (Estimated)
Total Intended Award Amount:	$252,964.00
Total Awarded Amount to Date:	$252,964.00
Funds Obligated to Date:	FY 2020 = $53,632.00 FY 2021 = $53,977.00 FY 2022 = $89,153.00 FY 2023 = $56,202.00
History of Investigator:	Douglas Wiens (Principal Investigator) doug@wustl.edu
Recipient Sponsored Research Office:	Washington University 1 BROOKINGS DR SAINT LOUIS MO  US  63130-4862 (314)747-4134
Sponsor Congressional District:	01
Primary Place of Performance:	Washington University MO  US  63130-4899
Primary Place of Performance Congressional District:	01
Unique Entity Identifier (UEI):	L6NFUM28LQM5
Parent UEI:
NSF Program(s):	Marine Geology and Geophysics
Primary Program Source:	01002021DB NSF RESEARCH & RELATED ACTIVIT 01002122DB NSF RESEARCH & RELATED ACTIVIT 01002324DB NSF RESEARCH & RELATED ACTIVIT 01002223DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s):
Program Element Code(s):	162000
Award Agency Code:	4900
Fund Agency Code:	4900
Assistance Listing Number(s):	47.050

ABSTRACT

A fundamental goal of solid earth science is to improve our understanding of the Earth?s interior evolution, which is driven by mantle convection. There are three primary components of the mantle convection system: 1) subduction where one tectonic plate (slab) descends into the Earth?s interior along an oceanic trench, 2) plate spreading at mid-ocean ridges where the majority of seafloor is created, and 3) buoyant upwelling, or mantle plumes, where hot and less dense materials rise from the deep earth to the surface to create volcanoes like the Hawaiian islands. Locations where these three systems interact?including the Tonga oceanic trench, Lau back-arc spreading centers, and Samoa volcanic islands?provide unique opportunities to investigate these competing mechanisms. In this study, the juxtaposition of the Samoan plume and the northern edge of the Tonga-Lau subduction system is used to investigate mantle flow in a slab-plume setting, and to understand how the distinctive compositional and thermal characteristics of plume materials are distributed. The project provides training for graduate and undergraduate students and a postdoctoral investigator.

An interdisciplinary project, consisting of seismic imaging, geochemical analysis of submarine lavas, and geodynamic modeling, is used to investigate the Tonga-Lau-Samoa system. Seismic observations will be obtained from an 18-month deployment of 30 Ocean Bottom Seismographs (OBSs) and 5 land seismometers (including 3 permanent stations) in the northern Tonga-Lau and Samoa regions. Several different seismic imaging techniques will provide 3-D velocity models of the upper mantle, precise earthquake locations will image the slab tear and associated deformation, and the variation of seismic velocity with direction will provide constraints on mantle flow. Lava samples will be dredged at 10 seamount locations east of the Tonga Trench to better understand subduction inputs into the northern Tonga Trench with the goal of understanding the distribution of enriched mantle material in the Lau Basin. The samples will be analyzed for isotopic compositions allowing identification of possible sources of non-Samoan hotspot materials in the Lau Basin, which is critical for geochemical interpretations of mantle flow. A series of geodynamic models will simulate slab-plume interactions with a variety of possible configurations. Using the integrated history of time-dependent mantle flow in the models, the predicted thermal structure and mantle textures can be directly compared with seismic and geochemical observations.

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.

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