Physics
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004natur.429..399b&link_type=abstract
Nature, Volume 429, Issue 6990, pp. 399-403 (2004).
Physics
21
Scientific paper
Beneath much of the Andes, oceanic lithosphere descends eastward into the mantle at an angle of about 30° (ref. 1). A partially molten region is thought to form in a wedge between this descending slab and the overlying continental lithosphere as volatiles given off by the slab lower the melting temperature of mantle material. This wedge is the ultimate source for magma erupted at the active volcanoes that characterize the Andean margin. But between 28° and 33° S the subducted Nazca plate appears to be anomalously buoyant, as it levels out at about 100km depth and extends nearly horizontally under the continent. Above this `flat slab', volcanic activity in the main Andean Cordillera terminated about 9 million years ago as the flattening slab presumably squeezed out the mantle wedge. But it is unknown where slab volatiles go once this happens, and why the flat slab finally rolls over to descend steeply into the mantle 600km further eastward. Here we present results from a magnetotelluric profile in central Argentina, from which we infer enhanced electrical conductivity along the eastern side of the plunging slab, indicative of the presence of partial melt. This conductivity structure may imply that partial melting occurs to at least 250km and perhaps to more than 400km depth, or that melt is supplied from the 410km discontinuity, consistent with the transition-zone `water-filter' model of Bercovici and Karato.
Booker John R.
Favetto Alicia
Pomposiello Cristina M.
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