HR: 14:15h
AN: GP23A-02    [Abstracts]
TI: Revisiting the Meso-Neoproterozoic dykes of Bahia, Brazil
AU: * Catelani, E L
EM: edcatelani@gmail.com
AF: Departamento de Geofisica, Universidade de Sao Paulo, Rua do Matao, 1226, Sao Paulo, 05508-090, Brazil
AU: Evans, D A
EM: dai.evans@yale.edu
AF: Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, 06520-8109, United States
AU: Smirnov, A V
EM: aleksey.smirnov@yale.edu
AF: Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, 06520-8109, United States
AU: Trindade, R I
EM: rtrindad@iag.usp.br
AF: Departamento de Geofisica, Universidade de Sao Paulo, Rua do Matao, 1226, Sao Paulo, 05508-090, Brazil
AU: D'Agrella-Filho, M S
EM: dagrella@iag.usp.br
AF: Departamento de Geofisica, Universidade de Sao Paulo, Rua do Matao, 1226, Sao Paulo, 05508-090, Brazil
AU: Heaman, L M
EM: Larry.Heaman@ualberta.ca
AF: Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Edmonton, T6G 2E3, Canada
AB: Mafic dykes exposed along the Bahia coastline of Brazil have yielded paleomagnetic and geochronological results that are important for Rodinia reconstructions and Precambrian geodynamo behavior. Previously published data have been interpreted in terms of four paleomagnetic components residing within these dykes: a south-down "C" direction associated with a U-Pb baddeleyite age of ca. 924 Ma, an east-up "B" direction of unknown age, and two nearly antipodal "A" components that are associated with Ar/Ar ages of ca.1080 Ma (the east-steeply up "A-reversed" direction) and ca.1020-1010 Ma (the northwest-steeply down "A-normal" direction). Literal reading of these data, particularly the high-latitude positions inferred for the 1080-1010 Ma interval, have supported exclusion of the Sao Francisco - Congo craton from Rodinia. However, an additional U-Pb baddeleyite age of ca. 920 Ma, on a dyke with "A-normal" direction in Salvador, has prompted our return to Bahia with the goal of obtaining precise U-Pb ages for each of the paleomagnetic components, thus testing the reliability of the Ar/Ar ages. Following a sampling trip in September, 2006, we have completed the paleomagnetic analyses and confirmed the published directions for the "A-normal" dykes at Ilheus, both the "A-normal" and "A-reversed" dykes at Olivenca, and the "B" and "C" dykes in Salvador. Our new direction for the ca.920-Ma "A-normal" dyke in Salvador differs slightly from the published direction, but it does not resolve the large discrepancy between that direction and the coeval (ca. 924 Ma) "C" component. We are currently processing samples for U-Pb geochronology, from Ilheus "A-normal", Olivenca "A-normal", and Salvador "B" dykes. To complement our study of Rodinian paleogeography, we are also beginning a paleointensity study of these dykes in order to characterize mid-Proterozoic geomagnetic field variations.
DE: 1525 Paleomagnetism applied to tectonics: regional, global
DE: 1527 Paleomagnetism applied to geologic processes
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly