HR: 17:30h
AN: T34B-07    [Abstracts]
TI: Structure of the upper mantle and crust beneath the Amazonian Craton and the Southern Andes
AU: * van der Lee, S
EM: suzan@earth.northwestern.edu
AF: Northwestern University, Dept. EPS 1850 Campus Dr., Evanston, IL 60208, United States
AU: Lloyd, S
EM: simon@earth.northwestern.edu
AF: Northwestern University, Dept. EPS 1850 Campus Dr., Evanston, IL 60208, United States
AU: Feng, M
EM: anmeijian@yahoo.com.cn
AF: Chinese Academy of Geological Sciences, Inst. of Geomechanics, Beijing, 100081, China
AU: Assumpcao, M
EM: marcelo@iag.usp.br
AF: University of Sao Paulo, Dept. of Geophysics, Sao Paulo, 05508-900, Brazil
AU: Russo, R
EM: rrusso@ufl.edu
AF: University of Florida, Dept. of Geological Sciences P.O. Box 112120, Gainesville, FL 32611, United States
AB: The structure of the upper mantle and crust beneath South America has been inhomogeneously resolved because of the particularly heterogeneous distribution of earthquakes and seismic stations in the continent. We recently improved resolving power for northeastern Brazil, which contains the oldest geology of South America, through the BLSP02 seismic project. We incorporated BLSP02 data in a joint inversion of about 5700 Rayleigh wave group velocity dispersion curves, 1537 regional S and Rayleigh wave trains, and 58 receiver functions. The new model shows no significant difference in crustal thickness between Archean and Proterozoic regions in South America, with the Moho roughly at a depth of 42 km depth. Imaged Moho depth ranges from 30 km in the central Chaco basin to 45-70 km beneath the orogenic Andean belt. The imaged S-velocity indicates an average lithosphere thickness of around 160 km for the Amazonian craton. Extremely low average velocities are imaged for the mantle wedge beneath the Andes and appear to be strongest in regions of normal-dip subduction. However, upper mantle structure beneath the southern portion of the continent, including for the mantle wedge beneath the southern Andes, remains poorly resolved. To investigate spatial variations in the low velocity mantle wedge along the southern Andes, we incorporate regional waveform data from the Chile Ridge Subduction Experiment, which provides path coverage as far south as the triple junction between the South American, Nazca, and Antarctic plates. Comparing the S velocities beneath the Andes above the slab window near the triple junction where the Chile Ridge meets the trench, to those beneath the Andes north of the triple junction in regions of normal- and small-dip subduction, will facilitate assessing the relative roles of wet and hot mantle in the Andean mantle wedge.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 9360 South America
SC: Tectonophysics [T]
MN: 2007 Fall Meeting