Reactivation of an obliquely rifted margin, Campos and Santos basins, southeastern Brazil

We interpret and document Late Cretaceous and Cenozoic reactivation of olde r structures on the obliquely rifted margin of southeastern Brazil, attribu ting them to the combined effects of far-field stresses and hot-spot activi ty. Our conclusions are based on current seismicity, digital topography, fi ssion-track ages, gravity data, regional reflection seismic profiles, and w ell data. Our results have important implications for risk factors associat ed with deep-water exploration plays, especially the prolific Early Cretace ous lacustrine petroleum system of the Campos and Santos basins. Onshore, widespread crustal seismicity indicates a current transpressional stress regime. The Moho is 37-42 km. deep, and neotectonic fault-block tilt ing has resulted in mountain ranges up to 2700 m high and extensive river c apture. Based on fission-track data, the mountains were exhumed in the Cret aceous and Eocene. A series of Tertiary continental pull-apart basins, deve loped during Paleogene right-lateral transtension, became inverted during N eogene right-lateral transpression. Late Cretaceous-Paleogene alkaline intr usions, attributable to the Trindade hot spot, were emplaced along reactiva ted Neocomian strike-slip faults and transfer zones. Offshore, current seismicity is widespread across the continental margin. T he locus of clastic fan deposition shifted during the Late Cretaceous and T ertiary because of onshore block faulting and drainage reorganization. Cret aceous sedimentary rocks were folded, tilted, eroded, and unconformably onl apped above an inferred Neocomian Moho uplift to produce an accentuated nea rshore hinge line. Neocomian transfer zones were reactivated during ongoing sedimentation, accompanied by abundant volcanism and deep-seated folds att ributed to lithospheric buckling. In the Campos area, a coastal salient was uplifted and turbidites were redeposited. In general, regional tilting res ulted in thin-skinned deformation above Aptian salt.