Pan-African rejuvenation of the c. 1.1 Ga Natal Metamorphic Province(South Africa):K–Ar muscovite and titanite fission track evidence

Abstract

K–Ar muscovite and titanite fission track analyses were obtained from selected lithologies from the Grenville-aged ( c. 1.1 Ga) Natal Metamorphic Province, SE Africa in order to constrain the low temperature cooling history of this critical part of Gondwana. The data revealed two periods of basement rejuvenation and exhumation at c. 900 Ma and c. 530 Ma respectively. Over large areas of the Natal Metamorphic Province, late-stage skeletal muscovite, dated at c. 900 Ma. has overgrown the regional Mesoproterozoic fabrics. This indicates that, after magmatism and tectonics ceased at c. 1000 Ma. The Natal Metamorphic Province underwent an early Neoproterozoic thermal/hydration event. Titanite fission track dates from the southern Natal Metamorphic Province scatter around 530Ma. showing that the basement finally cooled fairly rapidly through the300°C isotherm during Pan-African times. Since the Natal Metamorphic Province is unconformably overlain by clastic sedimentary rocks dated at c. 490 Ma. The basement must have been uplifted and exhumed by c. 6–10km during the Pan-African event.Two possible uplift processes might best account for this Pan-African exhumation: Pan-African crustal thickening and subsequent uplift during the collision of east-and west-Protogondwana or magmatic underplating from hot mantle plumes. Although a combined collision-plume model cannot be discounted for western Dronning Maud Land, the Natal data favour the collision model, so it is proposed that the wider ‘Mozambique Belt’ of East Africa and East Antarctica generally resulted from classical Wison-cycle processes.