Journal
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS
Volume 14, Issue 8, Pages 3192-3209Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/ggge.20213
Keywords
three-dimensional magnetotelluric inversion; slab window; Nazca flat slab subduction
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Funding
- U.S. National Science Foundation (NSF) [EAR9909390, EAR0310113, EAR0739116]
- U.S. Department of Energy Office of Basic Energy Sciences [DE-FG03-99ER14976]
- NSF [EAR9616421, EAR0236538]
- Agencia Nacional de Promocion Cientifica y Tecnologica PICT [38253]
- Seattle Chapter of the ARCS Foundation
- Department of Earth and Space Sciences, University of Washington
- National Science Foundation
- GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation [EAR-0552316]
- National Science Foundation EarthScope Program [EAR-0733069]
- Directorate For Geosciences
- Division Of Earth Sciences [739116] Funding Source: National Science Foundation
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We present a three-dimensional (3-D) interpretation of 117 long period (20-4096 s) magnetotelluric (MT) sites between 31 degrees S and 35 degrees S in western Argentina. They cover the most horizontal part of the Pampean shallow angle subduction of the Nazca Plate and extend south into the more steeply dipping region. Sixty-two 3-D inversions using various smoothing parameters and data misfit goals were done with a nonlinear conjugate gradient (NLCG) algorithm. A dominant feature of the mantle structure east of the horizontal slab is a conductive plume rising from near the top of the mantle transition zone at 410 km to the probable base of the lithosphere at 100 km depth. The subducted slab is known to descend to 190 km just west of the plume, but the Wadati-Benioff zone cannot be traced deeper. If the slab is extrapolated downdip it slices through the plume at 250 km depth. Removal of portions of the plume or blocking vertical current flow at 250 km depth significantly changes the predicted responses. This argues that the plume is not an artifact and that it is continuous. The simplest explanation is that there is a wedge-shaped slab window that has torn laterally and opens down to the east with its apex at the plume location. Stress within the slab and seismic tomography support this shape. Its northern edge likely explains why there is no deep seismicity south of 29 degrees S.
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