The Ocean-Continent Transition along the Northeast Brazilian Rifted Margin

New and established analytical methodologies were applied in a workflow to the identification of the ocean-continent transition (OCT) and to the location of the continent-ocean crustal and lithosphere boundaries (COCB and COLB) at the Northeast Brazilian rifted margin. The workflow was applied to six cross-sections located in the segments Almada-Jequitinhonha, Jacui¬pe, Sergipe, Alagoas and Pernambuco. The OCT of the Northeast Brazilian rifted margin is complex due to variable extrusive and intrusive magmatism and antithetic tectonics. The workflow comprises: 1) determination of sediment-corrected basement depth profiles, 2) analysis of the residual depth anomalies of the oceanic crust, 3) gravity inversion of the Moho with crustal thinning determination and 4) inversion of lithosphere thinning using subsidence analysis. The position of the COCB constrains the distribution of syn-rift source rocks. The inversion of crustal and lithosphere thinning from geologic and geophysical data are determine the petroleum systems thermal evolution. The calibration of the gravity inversion to the residual depth anomaly in unequivocal oceanic crust is a new approach to determine the reference Moho depth in areas without seismic refraction data. A new lithosphere thinning inversion was developed, constrained by the continental lithosphere thickness and by the adjacent oceanic crust thickness, controlled by magmatic addition. Minor differences between the crustal and lithosphere thinning profiles have been identified and the predicted COCB and COLB locations for each cross-section were similar. The Almada-Jequitinhonha OCT is dominated by antithetic faulting and low free-air gravity anomaly, while Jacui¬pe OCT is a region of seaward-dipping reflectors, but with normal magmatic addition, associated to a relatively high free-air gravity anomaly. The Sergipe margin OCT corresponds to a region of continental crust thinner than the adjacent oceanic crust, with antithetic faulting and a stable free-air gravity anomaly. Both Alagoas and Pernambuco margins OCTs correspond to regions of synthetic and antithetic faulting with low free-air gravity anomaly. The rifted margin ranges from 110 to 130 km between Almada-Jequitinhonha and Sergipe to around 170 km between Alagoas and Pernambuco. The Northeastern Brazil margin changes from magma-poor in the Almada-Jequitinhonha region to slightly magma-rich in Sergipe and Pernambuco, both probably affected by the Santa Helena Hot Spot.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California