Abstract
We investigate the evolution of olivine crystal preferred orientation (CPO) and its effect on local shear wave splitting (SWS) in the mantle wedge of oblique subduction zones. Based on model-predicted 3-D mantle wedge flow fields, we compute the A-type and E-type olivine CPO distribution for a range of subduction obliquity. The results show that the seismically fast axis does not necessarily align with the flow direction. To model the local SWS parameter distribution for oblique subduction zones, we apply a full range of initial polarization to multilayer models that approximate the model-predicted CPO distributions. These models result in a bimodal SWS parameter distribution, which relaxes as subduction obliquity increases. Unlike non-oblique subduction models, these models indicate considerable variations in the SWS parameters with subduction obliquity and initial polarization and also among the forearc, arc, and backarc regions. Because of this variability, a single SWS measurement cannot constrain the CPO distribution, and shear waves with a range of initial polarization are required to interpret the SWS parameters in oblique subduction zones. Our results indicate that 3-D mantle wedge flow due to oblique subduction cannot explain commonly observed margin-parallel fast direction in the forearc region but can explain margin-normal fast directions that are observed in the arc and backarc regions of oblique subduction zones.
| Original language | English (US) |
|---|---|
| Article number | e2021JB022752 |
| Journal | Journal of Geophysical Research: Solid Earth |
| Volume | 127 |
| Issue number | 4 |
| DOIs | |
| State | Published - Apr 2022 |
| Externally published | Yes |
Bibliographical note
Funding Information:We thank Phil Skemer and an anonymous reviewer for their constructive comments that helped to improve the manuscript. We thank Maximiliano Bezada, Neala Creasy, Karen Fischer, Lars Hansen, and Zachary Michel, for discussions during the early phase of this research. This research was partially funded by the National Science Foundation through Grant EAR‐1620604 to I.W. and the University of Minnesota—Twin Cities through startup funds. The details of the model and additional modeling results that are discussed in this article are found in Supporting Information, and the modified version of D‐Rex and the SWS calculation code are available on Zenodo. Figures were generated using the Generic Mapping Tool and MSAT.
Funding Information:
We thank Phil Skemer and an anonymous reviewer for their constructive comments that helped to improve the manuscript. We thank Maximiliano Bezada, Neala Creasy, Karen Fischer, Lars Hansen, and Zachary Michel, for discussions during the early phase of this research. This research was partially funded by the National Science Foundation through Grant EAR-1620604 to I.W. and the University of Minnesota—Twin Cities through startup funds. The details of the model and additional modeling results that are discussed in this article are found in Supporting Information, and the modified version of D-Rex and the SWS calculation code are available on Zenodo. Figures were generated using the Generic Mapping Tool and MSAT.
Publisher Copyright:
© 2022. American Geophysical Union. All Rights Reserved.
Keywords
- crystal preferred orientation
- mantle wedge flow
- mantle wedge seismic anisotropy
- oblique subduction
- shear wave splitting