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Abstract The Alaska Peninsula has a long history of plate subduction with along‐arc variations in volcanic eruption styles and geochemistry. However, the sub‐arc melting processes that feed these volcanoes are unclear. The Alaska slab morphology below 200 km depth remains debated due to limited seismic data and thus low tomography resolution in this region. Here we utilize the newly available regional and teleseismic data to build 3‐D high‐resolutionVPandVSmodels to 660 km depth. We find that the high‐velocity Pacific Plate subducts to the bottom of the mantle transition zone (MTZ) with complex deformation and gaps. In the southwest, we observe a wide gap in the high‐velocity slab at 200–500 km depths. Toward the northeast, the slab becomes more continuous extending to the MTZ with a few holes below 200 km. We interpret these gaps as a slab tear that coincides with the subducted ancient Kula‐Pacific Ridge. We also invert for 3‐DVPandVP/VSmodels to 200 km depth with higher resolution and find strong along‐strike changes in slab dehydration and sub‐arc melting, indicated by lowVPand highVP/VSanomalies. Slab dehydration and sub‐arc melting are most extensive below the Pavlof and Shumagin segments in the southwest, becoming limited below the Chignik and Chirikof segments in the northeast, and extensive again beneath the Kodiak segment further to the northeast. We propose that the variations of slab hydration at the outer rise significantly influence slab dehydration at greater depths and further control sub‐arc melting beneath the Alaska Peninsula.
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Genesis of Intermediate‐Depth and Deep Intraslab Earthquakes beneath Japan Constrained by Seismic Tomography, Seismicity, and Thermal Modeling
Abstract The distribution of intermediate‐depth and deep intraslab earthquakes with respect to subducting slabs offers a unique insight into seismogenesis at high pressures and temperatures that should inhibit brittle failure. This study constrains the surface of the subducting Pacific Plate beneath Japan at depths between 100 and 380 km based on a previous continental‐scale adjoint tomography model. Earthquake distributions relative to the slab surface reveal double seismic zones located within the top 60 km of the Pacific Plate. Thermal modeling suggests that the lower‐plane seismicity corresponds to temperatures between 400 and 900 °C. The seismogenic pressure and temperature conditions correlate approximately with the conditions of dehydration reactions of several hydrous minerals, that is, antigorite (serpentine) and chlorite at depths between 100 and 200 km and phase A at greater depths between 200 and 380 km. These correlations indicate that at these depths water released from dehydration processes may facilitate triggering slab mantle earthquakes.
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- PAR ID:
- 10461490
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 4
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- p. 2025-2036
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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