Imaging early oceanic crust spreading in the Equatorial Atlantic Ocean: Insights from the MAGIC wide-angle experiment
|Author(s)||Moulin Maryline1, Schnurle Philippe1, Afilhado Alexandra2, 3, Gallais Flora1, Dias Nuno2, 3, Evain Mikael1, Soares José4, Fuck Reinhardt4, Da Cruz Pessoa Neto Otaviano5, Viana Adriano5, Aslanian Daniel1, 2, 3, 4, 5, 6, 7, 8|
|Affiliation(s)||1 : Ifremer, Department of Marine Geosciences, BP 70, 29280, Plouzané, France
2 : ISEL - Instituto Superior de Engenharia de Lisboa, Lisboa, Portugal
3 : IDL – Instituto Dom Luis, Lisboa, Faculdade das Ciências da Universidade de Lisboa, 1749-016, Lisboa, Portugal
4 : Instituto de Geociências – Lablithos, Universidade de Brasilia, Campus Darcy Ribeiro, 70910-900, Brasilia, Brazil
5 : Petrobras S.A., Research Center, CENPES, PROFEX, Rio de Janeiro, Brazil
6 : LETG-Nantes Geolittomer, Université de Nantes, Campus Tertre, BP 81227, 44312, Nantes Cedex 3, France
7 : IUEM, Domaines Océaniques, CNRS, 29280, Plouzané, France
8 : Departemento de Geofisica, Universidade Federal de Pampa, Campus Caçapava do Sul, 96570000, Caçapava do Sul, RS, Brazil
|Source||Journal Of South American Earth Sciences (0895-9811) (Elsevier BV), 2021-11 , Vol. 111 , P. 103493 (20p.)|
|WOS© Times Cited||1|
|Keyword(s)||Equatorial Atlantic Ocean, Brazil, Para-Maranhao-Barreirinhas-Ceara basins, Wide-angle seismic, Oceanic crust, Intermediate domain|
During the MAGIC (Margins of brAzil, Ghana, and Ivory Coast) experiment, five combined wide-angle, and reflection seismic profiles were acquired in the Pará-Maranhão/Barreirinhas/Ceará basins northern Brazil. This is a pull-apart passive margin, with two strike-slip borders. The equipment deployed includes 143 sea-bottom seismometers (OBS), a 4.5-km seismic streamer, and a 7587-in3 airgun array. In this paper, we focus on the distal parts of three profiles, and one entire transverse NW-SE profile, located on the presumed Cretaceous oceanic crust.
Forward modelling of these wide-angle data sets reveals an E-W lateral evolution of the oceanic crust spreading initiation with: 1) just after the so-called intermediate domain, 60 km-wide domain that consists of a 5-km-thick crystalline crust. The basement presents two layers characterized by high acoustic velocity. This domain is bounded to the NW by a NW-SE volcanic line (Volcano Alignment), and 2) a 5-km-thick oceanic crust consisting of two layers characterized by “normal velocities” spanning between the two main fracture zones that fringe the Pará-Maranhão-Barreirinhas-Ceará segment. Despite a similar thickness, these two sub-domains present different velocity distribution in their two layers. They are both overlain by 5.5 km of sedimentary deposits. Forward wide-angle modelling confirms that the seafloor spreading process was progressive, with firstly the emplacement of a proto-oceanic crust, and then a thin oceanic crust. The “proto-oceanic” crust presents a similar seismic velocity with the intermediate domain interpreted as exhumed lower continental crust except for the lower part where the intruded lower crust gives place to a very sharp Moho at the base of the proto-oceanic domain. By contrast, the thin oceanic crust domain has a lower velocity structure in its upper layer, that is interpreted as basalt and is absent in the proto-oceanic crust. This eastward evolution, as also observed in the Provençal Basin, and the Santos Basin, suggests the involvement of the lower continental crust in the first steps of seafloor spreading.