Imaging proto-oceanic crust off the Brazilian Continental Margin

Type Article
Date 2015-01
Language English
Author(s) Klingelhoefer FraukeORCID1, Evain MikaelORCID1, Afilhado A.1, 2, Rigoti Caesar3, Loureiro Afonso2, Alves D.2, Lepretre Angelique1, Moulin MarylineORCID1, Schnurle Philippe1, Benabdellouahed Massinissa1, Baltzer Agnes4, Rabineau MarinaORCID5, Feld Aurelie6, Viana A.3, Aslanian DanielORCID1
Affiliation(s) 1 : IFREMER, Dept Marine Geosci, ZI Pointe Diable, F-29280 Plouzane, France.
2 : Univ Lisbon, Fac Ciencias, IDL, P-1749016 Lisbon, Portugal.
3 : Petrobras SA, Petrobras Res Ctr, Rio De Janeiro, Brazil.
4 : Univ Nantes, Inst Geog & Amenagement Reg, LETG UMR CNRS 6554, Geolittomer, F-44312 Nantes 3, France.
5 : Inst Univ Europeen Mer, UMR6538, F-29280 Plouzane, France.
6 : IFREMER, Ctr Brest, DEC QAE, Genavir,ZI Pointe Diable, F-29280 Plouzane, France.
Source Geophysical Journal International (0956-540X) (Oxford Univ Press), 2015-01 , Vol. 200 , N. 1 , P. 471-488
DOI 10.1093/gji/ggu387
WOS© Times Cited 16
Keyword(s) Controlled source seismology, Seismic tomography, Mid-ocean ridge processes, Continental margins: divergent, Continental tectonics: extensional, Crustal structure, South America
Abstract 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.
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Klingelhoefer Frauke, Evain Mikael, Afilhado A., Rigoti Caesar, Loureiro Afonso, Alves D., Lepretre Angelique, Moulin Maryline, Schnurle Philippe, Benabdellouahed Massinissa, Baltzer Agnes, Rabineau Marina, Feld Aurelie, Viana A., Aslanian Daniel (2015). Imaging proto-oceanic crust off the Brazilian Continental Margin. Geophysical Journal International, 200(1), 471-488. Publisher's official version : https://doi.org/10.1093/gji/ggu387 , Open Access version : https://archimer.ifremer.fr/doc/00242/35296/