Print this pageTectono-stratigraphic Evolution of South Atlantic Extensional Rifted Margins: Constraints from Sandbox Analogue Modelling
Cappelletti, Alessio 1; Salvi, Francesca 1;
Meda, Marco 2; Cavozzi, Cristian 3; Chowdhury, Baishali
Roy 3; Nestola, Yago 3; Argnani, Andrea 4;
Tsikalas, Filippos 1; Magistroni, Corrado 2; Dalla,
Stefano 1; Roveri, Marco 3; Bevilacqua, Nicola 2
(1) GEOLAB, eni E&P, San Donato Milanese - Milano, Italy. (2) GEBA, eni
E&P, San Donato Milanese - Milano, Italy. (3) Earth Science Department,
Univeristy of Parma, Parma, Italy. (4) ISMAR, CNR, Bologna, Italy.
A series of 3D sandbox analogue models, with the support of 2D structural restoration on selected regional transects, were used to analyse the pre-salt tectono-stratigraphic evolution of the Central segment of the South Atlantic Ocean. Seafloor spreading in the study area occurred at the Aptian-Albian boundary, and the margin segment (conjugate West Africa and Brazil rifted continental margins), is classified as a “magma-poor” margin characterized by the presence of an intermediate/transitional crust between the continental and the oceanic crust. The extensional sandbox analogue models were performed at full lithospheric-scale: a 4-layers setup (upper and lower crust/mantle) with alternating layers of sand and silicone putty, representing different rheological layering (strength-depth functions) with their inferred initial thicknesses and alternating brittle and ductile rheologies; the entire pre-salt sedimentary succession (pre, syn-rift, and late syn-rift). The layer-cake has been set so as to freely deform above a glucose solution, that represents the asthenosphere, and the density of modelling materials has been appropriately scaled to reproduce a realistic lithosphere/asthenosphere system. Lateral anisotropy in the viscosity of the lower crust has been introduced in some sandbox models. In order to reproduce a realistic geodynamic evolution, various stretching factors were tested. The analogue modelling results show a pure shear affecting the ductile mantle lithosphere, in the initial stages, and the breakup of the brittle mantle, which is subsequently followed by a necking of the ductile lithospheric mantle and lower crust that join together. A simple shear deformation, typically dominated by one major extensional fault that soles out into the underlying ductile unit, characterizes the upper layers. Typically, some degree of asymmetry in the fault system and in the sedimentary basin is observed in the brittle upper layer. Limited portions of weaker brittle mantle appear quite effective in localizing the main ductile mantle deformation, imposing the large-scale geometry of the rift system. Lateral heterogeneity in the viscosity of the lower crust affects the faulting of the overlying brittle layer, and may promote some degree of asymmetry in the rift fault patterns. The study elucidates the structural elements and features reflecting the syn-rift basin evolution and the processes that governed the pre-breakup lithospheric extension at a rifted margin.
AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.