Apatite thermochronology of the Bole-Nangodi Shear Zone (northern Ghana): insights into the thermal history of equatorial Atlantic rifting

Abstract

The Bole-Nangodi (BN) shear zone is located in northern Ghana and is thought to represent the continental extension of an equatorial Atlantic transform fault. This study applies low temperature thermochronology to constrain the thermal history of the BN shear zone with relation to Gondwana break-up during the Mesozoic. Apatite fission track (AFT) data obtained from the Ghanese Paleo-proterozoic basement along the primary NE-SW structural trend of the BN shear zone suggests a complex two phase cooling history. (1) Heating of the crust in the late Triassic – early Jurassic, related with the emplacement of the Central Atlantic Magmatic Province (CAMP); (2) Cooling associated with rift shoulder exhumation during early Cretaceous rifting of Africa from Brazil. Cooling ages obtained across the structural architecture furthermore constrain differential exposure of the thermal history, preserving older (CAMP) signatures to the south and younger (rifting) signatures to the north of the BN shear zone respectively. This indicates that the BN shear zone has been reactivated during the Cretaceous as a result of the build-up of strain being generated by the Central and South Atlantic rift margins. The results obtained in this work indicate the extent to which CAMP-related heat flow that has affected the upper crust within the West African Craton can at least be constrained to northern Ghana. Furthermore, Cretaceous intra-continental strike-slip faulting of the West African continental crust was likely induced along Paleo-proterozoic shear zones acting as zones of weakened crust where deformation and rifting were localised and may have ultimately controlled the orientation of fracture zones within the Equatorial Atlantic.