HR: 0830h
AN: GP11A-0254    [PDF]
TI: Crustal Structures of Cenozoic Pantanal Wetland (SW Brazil) From MT and Gravity Studies: Geophysical Evidence of a Buried Neoproterozoic-Cambrian Suture Zone
AU: * Fisseha, S
EM: shimeles@dge.inpe.br
AF: Departamento de Geofisica do Instituto Astronomico e Geofisico da Universidade de Sao Paulo, Rua do Matao, 1226, Sao Paulo, SP 05508-900 Brazil
AU: Ussami, N
EM: naomi@iag.usp.br
AF: Departamento de Geofisica do Instituto Astronomico e Geofisico da Universidade de Sao Paulo, Rua do Matao, 1226, Sao Paulo, SP 05508-900 Brazil
AU: Padilha, A L
EM: padilha@dge.inpe.br
AF: Instituto Nacional de Pesquisas Espaciais (INPE-MCT), Av. dos Astronautas, Sao Jose dos Campos, SP 12100 Brazil
AU: Vitorello, I
EM: icaro@dge.inpe.br
AF: Instituto Nacional de Pesquisas Espaciais (INPE-MCT), Av. dos Astronautas, Sao Jose dos Campos, SP 12100 Brazil
AB: The Paraguay fold belt and the actual positions of the Amazonian/Parana cratonic borders under the vast Cenozoic sedimentary cover of the Pantanal Wetland are still unresolved and constitute a major problem in understanding the geological and tectonic evolution of the central and southern South American Platform. In order to provide further geophysical constraints to help solving these geological uncertainties, we carried out a high resolution magnetotelluric (MT/AMT) study within the Pantanal basin and over the exposed northern segment of the Paraguay fold belt. MT data in the broadband frequencies of 1000 Hz to 0.006 Hz were collected and analyzed along a 350 km long NE - SW profile between the towns of Corumba and Coxim and along a WNW-ESE profile between the towns of Barra dos Bugres and Poxoreo. The analyses of the broadband MT data, including dimensionality studies and 2D inversion, have indicated the presence of a prominent electrical resistivity anomaly($<$ 50 Ohm.m) and strong electrical anisotropy in central Pantanal basin at depths beyond 6 km. Variations in the local geomagnetic transfer function, shown as induction vectors, have further strengthened the presence of these mid-crustal conductors. In a joint interpretation with gravity data, these crustal conductors are attributed to a suture zone related to graphitized metasediments and/or circulation of mineralized fluids in mid crustal fractures whereas the gravity anomaly is thought to be caused either by remnants of squeezed magmatic-arc terranes and/or by an overthrusted lower crust, along a collisional boundary between two petrophysically distinct crustal blocks. Within the framework of the regional geology, the western and eastern blocks are attributed to the Rio Apa Craton and the Parana block, respectively. The deeper geophysical signature of this collisional boundary may be the evidence of the previously postulated northward continuation of the Pampean belt (as Paraguay orogenic belt) under the Pantanal sedimentary cover.
DE: 1599 General or miscellaneous
DE: 8102 Continental contractional orogenic belts
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting