The role of variable slab dip in driving mantle flow at the eastern edge of the Alaskan subduction margin: insights from SKS shear-wave splitting
File(s)
Author(s)
Venereau, Clothilde
Robert, Martin-Short
Bastow, Ian
Richard, Allen
Kounoudis, Rita
Type
Journal Article
Abstract
Alaska provides an ideal tectonic setting for investigating the interaction between subduction and asthenospheric flow. Within the span of a few hundred kilometers along strike, the geometry of the subducting Pacific plate varies significantly and terminates in a sharp edge. Furthermore, the region documents a transition from subduction along the Aleutian Arc to strike‐slip faulting along the Pacific Northwest. To better understand mantle interactions within this subduction zone, we conduct an SKS shear‐wave splitting analysis on passive‐source seismic data collected between 2011 and 2018 at 239 broadband seismometers, including those from the Transportable Array. Anisotropic fast directions in the east of our study area parallel the Queen Charlotte and Fairweather transform faults, suggesting that the ongoing development of lithospheric anisotropy dominates the results there. However, our observed delay times (δt = 1–1.5 s) obtained across the study region may also imply an asthenospheric contribution to the splitting pattern. Our splitting observations exhibit slab‐parallel fast directions northwest of the trench and a rotation of fast directions around the northeastern slab edge. These observations suggest the presence of toroidal asthenospheric flow around the edge of the downgoing Pacific plate. We suggest that Wrangell Volcanic Field volcanism might be caused by mantle upwelling associated with this flow. Splitting observations closer to the trench can be explained by fossil anisotropy within the downgoing Pacific‐Yakutat plate combined with entrained subslab mantle. The geometry of the slab, including its variable dip and its abrupt eastern edge, thus plays an important role in governing mantle flow beneath Alaska.
Date Issued
2019-05-27
Date Acceptance
2019-04-11
Citation
Geochemistry, Geophysics, Geosystems, 2019, 20 (5), pp.2433-2448
ISSN
1525-2027
Publisher
American Geophysical Union
Start Page
2433
End Page
2448
Journal / Book Title
Geochemistry, Geophysics, Geosystems
Volume
20
Issue
5
Copyright Statement
©2019. American Geophysical Union. All Rights Reserved.
Subjects
Science & Technology
Physical Sciences
Geochemistry & Geophysics
subduction
Alaska
anisotropy
asthenosphere
WRANGELL VOLCANIC FIELD
WESTERN UNITED-STATES
SEISMIC ANISOTROPY
DEFORMATION
BENEATH
CONSTRAINTS
ORIGIN
COMPLEX
ORIENTATION
MAGMATISM
Geochemistry & Geophysics
04 Earth Sciences
02 Physical Sciences
Publication Status
Published
Date Publish Online
2019-04-18