The deep structure of the South Atlantic Kwanza Basin - Insights from 3D structural and gravimetric modelling

We present results from 3D gravimetric modelling of the Kwanza Basin offshore Angola accomplished to investigate the deep crustal structure beneath the basin and discuss our findings with respect to their implications for the opening of the Central South Atlantic. The Kwanza basin is located in the southern part of the Central South Atlantic. Although the post-rift evolution of the Kwanza Basin is well studied, little is known about the basin's early history. This is mainly due to the missing knowledge of its crustal structure owing to the masking effect of an up to 4 km thick salt layer, which seismically obscures the underlying basement. To get an insight into the deeper structure of this part of the Angolan margin we combined 3D structural, isostatic and gravimetric modelling. 2D seismic reflection data was used to determine the structural setting and the configuration of the stratigraphic units in the sedimentary part of the basin, whereas its crustal structure was constrained by isostatic and gravity modelling. Our modelling results indicate that high density lower crustal bodies, similar to ones found in the Northern part of the central segment, are present in the Southern part, and thus seem to be a general feature of the crust of the Central South Atlantic. Thinning of the crust occurs gradually rather than in an abrupt manner and block faulting seems to have played a significant role during rifting as is indicated by a strongly structured upper crust. In contrast, we find little evidence for ductile thinning or exhumation of the deeper lithosphere as previously suggested for the northern segment of the central South Atlantic. In its Southern segment it appears more likely that magmatic intrusions prevented mantle exhumation by sealing crustal detachment faults and giving the margin a distinct magmatic signature. (C) 2013 Elsevier B.V. All rights reserved.