- © 2001 Geological Society of South Africa
This paper discusses the question as to whether or not the high-grade metamorphic rocks exposed in the Mozambique belt (MB) of East Africa and Madagascar have played any role in the formation and dispersal of the supercontinent Rodinia, believed to have existed between ~1000 and ~750 Ma. First, there is little evidence for the production of significant volumes of ~1300 to ~1000 Ma (Kibaran- or Grenvillian-age) continental crust in the MB, except, perhaps, in parts of northern Mozambique. This crust cannot be related conclusively to either magmatic accretion processes along the active margin(s) of Rodinia, or to a collision event during continental collision and accretion leading to amalgamation of the supercontinent. Madagascar is totally devoid of rocks in this age bracket. Second, there is no conclusive evidence for a ~1000 Ma high-grade metamorphic event in the MB, although such metamorphism has been recorded in the presumed continuation of the MB in East Antarctica. Third, there is also no evidence for post-1000 Ma sedimentary sequences that could have been deposited on the passive margin(s) of Rodinia. In contrast, extensive structural reworking and metamorphic overprinting of Archaean rocks, particularly in Tanzania and Madagascar, characterize the MB of East Africa and Madagascar, and these rocks either constitute marginal parts of cratonic domains or represent crustal blocks (terranes or microcontinents?) of unknown derivation. Furthermore, there is evidence for extensive granitoid magmatism in the time period ~840 to <600 Ma, whose predominant calc-alkaline chemistry suggests subduction-related active margin processes. If this were related to the breakup and dispersal of Rodinia, this breakup must have begun prior to ~840 Ma. Peak metamorphic events during the Pan-African accretion and amalgamation process leading to formation of the supercontinent Gondwana are diachronous across the MB and occurred between ~640 and ~550 Ma. This suggests that the MB did not form by simple collision of East and West Gondwana, but represents a terrane collage resulting from accretion of crustal blocks whose dimensions and origins remain to be defined.