Crustal-scale transcurrent shearing in the Paleoproterozoic Sefwi-Sunyani-Comoé region, West Africa

The Paleoproterozoic Sefwi-Sunyani-Comoé region that straddles the Ghana-Ivory Coast border in West Africa has been characterised as resulting from a combination of compression and simple shear with leucogranite intrusion either being prior to the compression or synchronous with late shearing. The analysis of regional magnetic datasets combined with field observations allows us to better define the geometry of the major lithostratigraphic packages and their structural contacts in this region. This analysis reveals a series of elongate rounded leucogranite intrusions enveloped by deformed metasediments. Recent finite element modelling of two-phase aggregates has shown that we can analyse the geometry of these systems both in terms of their finite deformation and their mechanical contrast. We interpret the geometries we see in the Sefwi-Sunyani-Comoé region as reflecting the activity of a major crustal deformation zone which was dominated by simple shear. The comparison with our modelling suggests a finite shear strain of approximately 5 gamma, which in turn implies a lateral displacement of 400. km parallel the Sefwi Greenstone Belt, which places Southern Ghana (EoGhana?) near eastern Burkina Faso prior to deformation. Our analysis also suggests that the leucogranites were already acting as more rigid bodies during the shearing, suggesting that their emplacement was predominantly pre-kinematic.