Post pan-african thermo-tectonic evolution of the north Mozambican basement and its implication for the Gondwana rifting. Inferences from 40Ar/ 39Ar hornblende, biotite and titanite fission-track dating

This research paper investigates the thermo-tectonic history of the north Mozambican basement subsequent to the Pan-African metamorphism. Six 40Ar/ 39Ar hornblende, three 40Ar/ 39Ar biotite and 25 titanite fission-track data place new constraints on the earliest timing of rifting in the central sector of Gondwana, and demonstrate a close linkage between the geometric rift configuration and the ductile metamorphic basement fabrics during the initial dispersal of the supercontinent. The 40Ar/ 39Ar hornblende and biotite ages range from c. 542 to 456 Ma and from c. 448 to 428 Ma, respectively. These data record slow basement cooling after the latest Pan-African meta, morphism at rates of c.7-11°C Ma -1 between Early and Late Ordovician times. Locally, syn, to post-tectonic granitoid emplacements around 500-450 Ma delayed basement cooling to Late Ordovician-Early Silurian times. The titanite fission-track (TFT) ages fall into two age groups of c. 378-327 Ma and c. 284-219 Ma. The older TFT ages record very slow cooling from the Late Ordovician-Early Silurian to below 275 ± 25 °C in the Late Devonian-Early Carboniferous at slow rates of less than 1 °C Ma -1. This slow cooling is related to decreasing denudation in association with the establishment of pre-Karoo peneplains in central Gondwana. The younger TFT ages record denudation due to rift flank uplift in the context of initial Gondwana disintegration in the Mozambican sector. Corresponding Early-Late Permian crustal extension proceeded obliquely to a NW-SE tensional palaeo-stress field and was associated with a brittle reactivation of easterly trending ductile basement fabrics. In total, up to ≤9-12 km of denudation is deduced from the TFT results since Permo-Carboniferous times. © Geological Society of London 2009.