Onset of the neogene-quaternary continental southern Malawi Rift and linkage to the Late Carboniferous-Early Jurassic Shire Rift

Abstract

Previous thermal history models have supported Miocene aged rift initiation in northern Malawi Rift without the thermal history of southern Malawi Rift (which is believed to have initiated at a later time) and its interactions with the relic of an older rift system along the Shire Rift just south of it. New thermal history models, derived from new apatite fission-track data from this study, outline three distinct cooling episodes in the Cretaceous, Eocene-Oligocene and Miocene-Pliocene that suggest the southern Malawi Rift has been accommodating strain along their border faults since the Miocene just as the northern Malawi Rift. Our thermal modelling approach combines thermochronology and previous published geochronology with the Monte Carlo approach of the HeFTy software.

The timing and rate of rock uplift were further constrained through application of remote sensing fracture strain analyses. These results, when combined with our thermal history modeling results, yield inferred deformation strain rates that support linkage between the two rift systems. Exhumation histories show the southern Malawi Rift has likely been uplifting since the Early Miocene just as the northern Malawi Rift and its growth and evolution has caused linkage and transfer of strain between southern Malawi Rift and the older Shire Rift which appears to have been reactivated and accommodating strain since Pliocene. These results provide evidence of coeval extension across the Western Branch of the East African Rift System which has implications for the tectonic evolution of the East African Rift system.