An Ocean-Bottom View of Mantle Convection Beneath the Pacific Basin
The Pacific basin provides an outstanding natural laboratory to study a range of tectonic and upper-mantle dynamic processes, including seafloor spreading, midplate volcanism, and multiscale thermal convection. Historically, geophysical insights into these processes were limited to low-resolution, long-wavelength imaging due to the restriction of instrumentation to continents and islands. Recent advances in ocean-bottom seismometry have now enabled high-resolution investigation of these processes using localized (few 100s-km aperture) broadband arrays. We present emerging results from the ORCA (OBS Research into Convecting Asthenosphere) project, comprising two 12-month seismic arrays in the central and southwest Pacific. ORCA was designed to image upper-mantle wavespeeds in two regions where satellite-derived gravity variations display linear structures suggestive of small-scale upper-mantle convection, one at intermediate plate age (30-40 Ma), and one at old plate age (90 Ma+). At the younger site, we find linear blobs of fast and slow material (~250–300 km wavelength), parallel to the gravity features, that we infer to represent cold sinking and warmer rising material beneath the plate. Preliminary results from the older site show similar velocity heterogeneity, but perhaps less linear structure and longer wavelength (>400 km). Both regions are characterized by a narrow (50–75 km), low-velocity (~4.2 km/s), low-Q (~25–35) asthenosphere, suggesting grain-size reduction combined with a small amount of partial melt (<0.3%) play an important role in controlling rheology. Seismic anisotropy varies strongly within and between regions, with distinctive variations with depth that suggest regional differences in the scale and strength of deformation controlled by seafloor spreading, lithosphere-asthenosphere coupling, and pressure- and temperature-driven asthenospheric flow. By combining these results with previous analyses from across the Pacific, we are gaining an improved understanding of the processes controlling the formation and evolution of the ocean plates and the highly dynamic convective system beneath them.
Session: Seismology in the Oceans: Pacific Hemisphere and Beyond - II
Type: Oral
Room: Tubughnenq’ 3
Date: 5/2/2024
Presentation Time: 11:00 AM (local time)
Presenting Author: James Gaherty
Student Presenter: No
Additional Authors
James Gaherty Presenting Author Corresponding Author james.gaherty@nau.edu Northern Arizona University |
Zachary Eilon eilon@geol.ucsb.edu University of California, Santa Barbara |
Joshua Russell jbrussel@syr.edu Syracuse University |
Joseph Phillips jp2888@nau.edu Northern Arizona University |
Anant Hariharan ahariharan@ucsb.edu University of California, Santa Barbara |
Colleen Dalton colleen_dalton@brown.edu Brown University |
Donald Forsyth donald_forsyth@brown.edu Brown University |
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An Ocean-Bottom View of Mantle Convection Beneath the Pacific Basin
Category
Seismology in the Oceans: Pacific Hemisphere and Beyond
Description