Toroidal mantle flow through the western U.S. slab window
Abstract
The circular pattern of anisotropic fast-axis orientations ofsplit SKS arrivals observed in the western U.S. cannot be attributedreasonably to either preexisting lithospheric fabric or to asthenosphericstrain related to global-scale plate motion. A plume originfor this pattern accounts more successfully for the anisotropyfield, but little evidence exists for an active plume beneathcentral Nevada. We suggest that mantle flow around the edgeof the sinking Gorda-Juan de Fuca slab is responsiblefor creating the observed anisotropy. Seismic images and kinematicreconstructions of Gorda-Juan de Fuca plate subductionhave the southern edge of this plate extending from the Mendocinotriple junction to beneath central Nevada, and flow models ofnarrow subducted slabs produce a strong toroidal flow fieldaround the edge of the slab, consistent with the observed patternof anisotropy. This flow may enhance uplift, extension, andmagmatism of the northern Basin and Range while inhibiting extensionof the southern Basin and Range.
- Publication:
-
Geology
- Pub Date:
- April 2008
- DOI:
- 10.1130/G24611A.1
- Bibcode:
- 2008Geo....36..295Z