Abstract
Shear zones of the Paleoproterozoic Eburnean accretionary Orogen (West African craton) are investigated by means of large-scale structural mapping. Regional scale (10-100 km) mapping was based on the aeromagnetic survey of Burkina Faso and craton-scale (1000 km) mapping on a compilation of fabric data. At both scales, shear zones are arranged as an anastomosed transpressional network that accommodated distributed shortening and lateral flow of the orogenic lithosphere between the converging Kénéma-Man and Congo Archean provinces. Structural interference patterns at both scales were due to three-dimensional partitioning of progressive transpressional deformation and interactions among shear zones that absorbed heterogeneities in the regional flow patterns while maintaining the connectivity of the shear zone network. Such orogen-scale kinematic patterns call for caution in using the deformation phase approach without considering the “bigger structural picture” and interpreting displacement history of individual shear zones in terms of plate kinematics. The West African shear zone pattern is linked to that of the Guiana shield through a new transatlantic correlation to produce an integrated kinematic model of the Eburnean-Transamazonian orogen.
Highlights
The record and geodynamic meaning of tectonic strain in Precambrian accretionary orogens are matters of renewed interest and debate
We address the relationships among deformation, shear zone patterns and kinematic boundary conditions of Precambrian accretionary orogens from the regional (100 km) to the orogen (1000 km) scale
Our results show how regional shear zone patterns can be used as a gauge of orogen-scale deformation
Summary
The record and geodynamic meaning of tectonic strain in Precambrian accretionary orogens are matters of renewed interest and debate. In absence of crustal-scale thrusts such as those documented in modern collision belts, the ubiquitous transpressive shear zones of Precambrian accretionary orogens (Cagnard et al, 2006a; Chardon et al, 2009; Duguet et al, 2009) are central to the debate. Whether they record large displacement or could be tight to a far-field kinematic framework or to a kind of plate kinematics is not straightforward (Treloar and Blenkinsop, 1995; Hanmer et al, 1997; Gapais et al, 2005; Chardon et al, 2008; Harris and Bédard, 2014). Our results show how regional shear zone patterns can be used as a gauge of orogen-scale deformation
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