Cretaceous rifting of the Ghana transform margin - Evidence from on shore apatite fission track data and optimum thermal history models

Abstract

The rock samples of the granitoid at the marginal ridge of the Ghanaian shelf within La Côte d’ Ivoire continental transform margin, have been studied using fission tracks in apatite. The ages of the apatite fission track (AFT), which are mainly metamorphosed igneous rocks, range from 130 to 415 Ma. Apatite fission track measurements demonstrate that the rocks were cooled from temperatures >110 oC to temperatures below 60 oC during the early Cretaceous. Quantitative thermal histories, derived from rock data from southern Ghana, indicate two stages of cooling and two stages of denudation during Devonian-Permian times, and in the Cretaceous. The denudation was the result of faults and landslides produced by increases in bathymetric step between the continental margin and the oceanic crust. The latter cooling stage commencing at 130 Ma
represents the 2.5–5.5 km of basement denudation which is related to intra-continental transform faulting between West Africa and Brazil. The AFT data of La Cote d’ Ivoire-Ghana marginal ridge reveal similar times of
cooling, thus, ruling out provenance-related AFT ages of the meta igneous rocks. Instead, cooling of ODP samples from the offshore marginal ridge is the consequence of coeval hydrothermal circulation within intracontinental
fault acting between African and Brazilian basements.