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- Title
Seismic Constraints on Crustal and Uppermost Mantle Structure Beneath the Hawaiian Swell: Implications for Plume‐Lithosphere Interactions.
- Authors
Le, Ba Manh; Yang, Ting; Morgan, Jason P.
- Abstract
We infer the lithospheric structure beneath the Hawaiian Swell based on a joint inversion of ambient noise and teleseismic Rayleigh waves collected during the PLUME experiment. These combined datasets let us use Rayleigh waves with a period range of 8–50 s that provides imaging resolution for the shallow lithosphere and constrains interactions between the upwelling plume and migrating plate. We find an elongated low‐velocity anomaly beneath the lithosphere along the island chain that connects to the plume conduit, consistent with the melting region associated with a restite hotspot swell root that has mechanically eroded the base of its overlying lithosphere. It could also be consistent with a plume refracted by the overriding plate motion if the plume could manage to deeply erode the lithospheric base, as only a more viscous restite root is seen to do in thermomechanical experiments. There is also a low‐velocity body beneath the North Arch that coincides with the location of recent off‐chain volcanic fields discovered there. Its location relative to the Molokai Fracture Zone (MFZ) supports the concept that swell‐root material has preferentially spread beneath the younger side of the MFZ. We also find a clear low‐velocity anomaly associated with the uppermost ∼50 km of the fracture zone lithosphere. The relatively well‐resolved shallow lithospheric structure determined here allows us to estimate the volumes of underplating and the total flux of the rising plume material that is added beneath the Hawaiian lithosphere, which we constrain to be in the range of 0.5–0.6 km3/yr. Plain Language Summary: The Hawaiian island chain is believed to be formed by magma rising from a mantle plume source. How the rising magma interacts with the overriding plate is still poorly understood. In particular, why does the Hawaiian Swell, a large area of ∼1 km uplifted seabed near islands, exist? How does a Fracture Zone on the overriding plate affect the magma distribution as it passes over the plume‐related melts? How much magma came from the deep mantle to generate the island chain? Answers to these questions require high‐resolution images of the shallow lithosphere. To improve seismic imaging of shallow lithosphere, in addition to earthquake signals, we carefully measured useful waves from the background noise between every pair of seismic stations. These waves provide the short‐period signals needed to image the shallow structure. As a result, the Fracture Zone on the overriding plate is better imaged in this study. The relative locations of this fault and deeper slow wavespeed zones indicate that the Fracture Zone helped to re‐distribute magma emplacement, and was also associated with the formation of the North Arch Volcanic Field. The magma emplacement volume associated with Hawaii is also more accurately estimated than in previous studies. Key Points: Low‐velocity body beneath the North Arch suggests swell‐root material preferentially spreads beneath the younger side of the Molokai FZA clear low‐velocity anomaly in the uppermost lithosphere is associated with the Molokai FZThe volumes of underplating and the total flux of the rising plume beneath Hawaii are more accurately estimated than in previous studies
- Subjects
HAWAII; RAYLEIGH waves; MICROSEISMS; ARCHIPELAGOES; VOLCANIC fields; IMAGING systems in seismology; MANTLE plumes; LITHOSPHERE
- Publication
Journal of Geophysical Research. Solid Earth, 2022, Vol 127, Issue 11, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB023822