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Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration

Porter, Ryan and Gilbert, Hersh and Zandt, George and Beck, Susan and Warren, Linda and Calkins, Josh and Alvarado, Patricia and Anderson, Megan (2012) Shear wave velocities in the Pampean flat-slab region from Rayleigh wave tomography: Implications for slab and upper mantle hydration. Journal of Geophysical Research-Solid Earth, 117 (B11301). ISSN 0148-0227


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Publisher’s or external URL: http://dx.doi.org/10.1029/2012jb009350


The Pampean flat-slab region, located in central Argentina and Chile between 29° and 34°S, is considered a modern analog for Laramide flat-slab subduction within western North America. Regionally, flat-slab subduction is characterized by the Nazca slab descending to ∼100 km depth, flattening out for ∼300 km laterally before resuming a more “normal” angle of subduction. Flat-slab subduction correlates spatially with the track of the Juan Fernandez Ridge, and is associated with the inboard migration of deformation and the cessation of volcanism within the region. To better understand flat-slab subduction we combine ambient-noise tomography and earthquake-generated surface wave measurements to calculate a regional 3D shear velocity model for the region. Shear wave velocity variations largely relate to changes in lithology within the crust, with basins and bedrock exposures clearly defined as low- and high-velocity regions, respectively. We argue that subduction-related hydration plays a significant role in controlling shear wave velocities within the upper mantle. In the southern part of the study area, where normal-angle subduction is occurring, the slab is visible as a high-velocity body with a low-velocity mantle wedge above it, extending eastward from the active arc. Where flat-slab subduction is occurring, slab velocities increase to the east while velocities in the overlying lithosphere decrease, consistent with the slab dewatering and gradually hydrating the overlying mantle. The hydration of the slab may be contributing to the excess buoyancy of the subducting oceanic lithosphere, helping to drive flat-slab subduction.

Item Type: Article
Publisher’s Statement: ©2012. American Geophysical Union. All rights reserved.
ID number or DOI: 10.1029/2012JB009350
Keywords: flat-slab; subduction; tectonic plates; slab mantle; shear velocity inversion
Subjects: Q Science > QE Geology
NAU Depositing Author Academic Status: Faculty/Staff
Department/Unit: College of Engineering, Forestry, and Natural Science > School of Earth Sciences and Environmental Sustainability
Date Deposited: 18 Oct 2015 19:41
URI: http://openknowledge.nau.edu/id/eprint/932

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