Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Detached Micros-Continents Offshore Southern Brazil: Crustal Thickness from Gravity Inversion and Plate Reconstructions
(1) Badley Geoscience Ltd, Hundelby, Spilsby, United Kingdom.
(2) Department of Earth & Ocean Sciences, University of Liverpool, Liverpool, United Kingdom.
Crustal thickness and ocean-continent transition mapping, using satellite gravity inversion incorporating a lithosphere thermal gravity anomaly correction, has been applied to the South Atlantic and its rifted continental margins. Results delineate the distribution and thickness of thinned continental crust under the Sao Paulo Plateau contiguous with the southern Brazilian margin and the Namibia Ridge on its conjugate African margin. To the south of the Florianopolis Fracture Zone, crustal thickness mapping using gravity inversion shows crustal thicknesses under the Rio Grande High and Walvis Ridge of the order of 30 km, and also regions of crust substantially thicker than oceanic crust between the Pelotas Basin margin and the Rio Grande High which we interpret as being continental fragments. New plate reconstructions have been used to explore the progression of continental breakup on the Campos, Santo and Pelotas margins, their African conjugates, and the formation of micro-continents south of the Florianopolis Fracture Zone. We propose that the Rio Grande High, locally underlain by crust 30 km thick, is of continental origin and when restored to its pre-breakup location, along with other micro-continental fragments, creates a continuous continental crustal barrier between South America to Africa until late Albian or younger. The gravity inversion technique used to determine Moho depth, crustal thickness and continental thinning factor is carried out in the 3D spectral domain. Input data used in this study is public domain satellite free-air gravity data, digital bathymetry and NOAA-NGDC sediment thickness. Crustal basement thicknesses and continental lithosphere thinning factors from gravity inversion provide estimates of ocean-continent transition (OCT) location independent of magnetic isochron data. The resulting maps of crustal basement thickness and continental lithosphere thinning factor have been corrected for variations in reference crustal thickness caused by dynamic topography.