Author(s): Batista, Luís ; Hubscher, Christian ; Terrinha, Pedro ; Matias, Luís ; Afilhado, Alexandra ; Ludmann, Thomas
Date: 2017
Persistent ID: http://hdl.handle.net/10400.21/9775
Origin: Repositório Científico do Instituto Politécnico de Lisboa
Subject(s): Composition of the oceanic crust; Transform faults; Oceanic transform and fracture zone processes; Crustal structure; Atlantic Ocean; Composição da crosta oceânica; Transformar falhas; Estrutura crustal
The oceanic crustal and uppermost lithospheric mantle structure across the Gloria Fault (GF) transcurrent plate boundary between Africa and Eurasia in the Northeast Atlantic is investigated based on seismic reflection, seismic refraction and wide-angle reflection data. This experiment used 18 ocean bottom stations along an N-S 150 km long traverse together with acquisition of a multichannel seismic reflection profile. Modeling of P and S seismic waves and gravimetric anomalies allowed estimation of P- and S-wave velocities, density, Poisson's ratio and discussion of a compositional model. A five-layer model is proposed in which layers 1-3 correspond to normal sediments through typical oceanic crust layers 2 and 3. Layer 5 yielded mantle velocities above 7.9 km s(-1). Layer 4 with 4 km of thickness has Vp velocities between 7.1 and 7.4 km s(-1) and is clearly separated from typical oceanic crust and mantle layers. Comparison with natural analogues and published lab measurements suggest that layer 4 can be a mix of lithologies that comply with the estimated P and S velocities and computed Poisson's ratio and densities, such as, olivine cumulates, peridotite, gabbro and hydrated mantle. We favour the tectonic process that produces secondary porosity from which results serpentinization due to sea water circulation in fractures. Structural and seismic stratigraphic interpretation of the reflection profile shows that Neogene to recent tectonic deformation on this segment of the plate boundary concentrated on the southern side of the GF, that is, the Africa plate.
