TY - JOUR T1 - Imaging proto-oceanic crust off the Brazilian Continental Margin A1 - Klingelhoefer,Frauke A1 - Evain,Mikael A1 - Afilhado,A. A1 - Rigoti,Caesar A1 - Loureiro,Afonso A1 - Alves,D. A1 - Lepretre,Angelique A1 - Moulin,Maryline A1 - Schnurle,Philippe A1 - Benabdellouahed,Massinissa A1 - Baltzer,Agnes A1 - Rabineau,Marina A1 - Feld,Aurelie A1 - Viana,A. A1 - Aslanian,Daniel AD - IFREMER, Dept Marine Geosci, ZI Pointe Diable, F-29280 Plouzane, France. AD - Univ Lisbon, Fac Ciencias, IDL, P-1749016 Lisbon, Portugal. AD - Petrobras SA, Petrobras Res Ctr, Rio De Janeiro, Brazil. AD - Univ Nantes, Inst Geog & Amenagement Reg, LETG UMR CNRS 6554, Geolittomer, F-44312 Nantes 3, France. AD - Inst Univ Europeen Mer, UMR6538, F-29280 Plouzane, France. AD - IFREMER, Ctr Brest, DEC QAE, Genavir,ZI Pointe Diable, F-29280 Plouzane, France. UR - https://archimer.ifremer.fr/doc/00242/35296/ DO - 10.1093/gji/ggu387 KW - Controlled source seismology KW - Seismic tomography KW - Mid-ocean ridge processes KW - Continental margins: divergent KW - Continental tectonics: extensional KW - Crustal structure KW - South America N2 - During the Sanba (Santos basin seismic transect) experiment in 2010–2011, a 380-km-long combined wide-angle and reflection seismic profile has been acquired using 30 ocean-bottom seismometers, a 4.5 km seismic streamer and a 8900 in.3 airgun array. The Sanba 3 profile crosses the southern flank of the Sao Paulo Plateau, the Sao Paulo Ridge and the easternmost Santos Basin in an east–west direction. Its eastern end is located on undisturbed oceanic crust. Tomographic and forward modelling of the wide-angle seismic data reveals that the sedimentary thickness is variable with only 1–2 km on top of the ridge and thickening to 4–5 km in the basin. Crustal thickness at the ridge is about 18 km and the relative layer thickness and velocity gradients indicate a continental origin of this ridge. The eastern Santos Basin is underlain by crust of only 5 km thickness, characterized by high seismic velocities between 6.20 km s–1 in the upper crust and 7.40 km s–1 in the lower crust. Three hypotheses for the nature of the crust in this region are tested here: (i) thinned continental crust, (ii) serpentinized upper mantle material, (iii) thin oceanic crust. As seismic velocity gradients seem to rule out a continental origin of this region, and clear Moho reflections argue against serpentinized upper mantle, we propose that the crust underlying the easternmost Santos Basin is of oceanic origin. Deviations from normal oceanic crustal velocities in the lower crust (6.70–7.00 km s–1) can be explained by accretion at slow spreading rates leading to the inclusion of serpentinite into the lower crust at the onset of organized seafloor spreading. Y1 - 2015/01 PB - Oxford Univ Press JF - Geophysical Journal International SN - 0956-540X VL - 200 IS - 1 SP - 471 EP - 488 ID - 35296 ER -