Seismic evidence for melt-rich lithosphere-asthenosphere boundary beneath young slab at Cascadia
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1.
California Institute of Technology
Abstract
The Lithosphere-Asthenosphere Boundary (LAB) beneath oceanic plates is generally imaged as a sharp seismic velocity reduction, suggesting the presence of partial melts. However, the fate of a melt-rich LAB is unclear after these plates descend into the mantle at subduction zones. Recent geophysical studies suggest its persistence with down-going old and cold slabs, but whether or not it is commonly present remains unclear, especially for young and warm slabs such as in the Cascadia subduction zone. Here we provide evidence for its presence at Cascadia in the form of a large (9.8±1.5%) decrease in shear-wave velocity over a very small (<3 km) depth interval. Similarly large and sharp seismic velocity reduction at the bottom of both old and young slabs, as well as along the base of oceanic plates before subduction, possibly represents widespread presence of melts. The melt-rich sub-slab LAB may strongly influence subduction dynamics and viscoelastic earthquake cycles.
Copyright and License
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Acknowledgement
We thank the Incorporated Research Institutions for Seismology Data Management Center for providing seismological data. This study was supported by the National Key R&D Program of China grant 2022YFF0802600 (X.W.), National Natural Science Foundation of China grants 91958209 (Q-F.C.) and 42288201 (L.C.), National Science Foundation grant 1722879 (Z.Z.), the Young Elite Scientists Sponsorship Program by CAST grant 2020QNRC001 (X.W.), the Key Research Program of the Institute of Geology and Geophysics, Chinese Academy of Sciences No. IGGCAS-201904 (X.W.).
Contributions
X.W. designed the project, conducted the seismic analyses. X.W., L.C., K.W., Q-F.C., Z.Z. and J.Y. contributed to the interpretation of results. X.W. drafted the paper with substantial input from K.W. and L.C. and additional input from all co-authors.
Data Availability
The seismic data used in this study are archived by the Incorporated Research Institutions for Seismology Data Management Center (IRIS DMC, network name: XZ_1993 and ZO_2017). All the seismic data used in this study are publicly available from the IRIS DMC. The subsurface structures obtained in this study, along with the scripts used to generate the figures, can be downloaded at https://doi.org/10.6084/m9.figshare.25434769.v1.
Code Availability
The codes used in this study are available to interested researchers upon request. Requests for material should be addressed to Ling Chen (lchen@mail.iggcas.ac.cn) or Xin Wang (wangxin@mail.iggcas.ac.cn).
Conflict of Interest
The authors declare no competing interests.
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Additional details
- PMCID
- PMC11045719
- Ministry of Science and Technology of the People's Republic of China
- 2022YFF0802600
- National Natural Science Foundation of China
- 91958209
- National Natural Science Foundation of China
- 42288201
- National Science Foundation
- EAR-1722879
- Chinese Academy of Sciences
- 2020QNRC001
- Institute of Geology and Geophysics
- IGGCAS-201904
- Caltech groups
- Division of Geological and Planetary Sciences, Seismological Laboratory