Neoproterozoic (∼600 Ma) aggregation of Western Gondwana: a tentative scenario

Abstract

Gondwana resulted from accretion of fragments of the Rodinia supercontinent. However, precise times and circumstances of individual accretions are still disputed. Aggregation of Western Gondwana occurred at ca 600 Ma or somewhat earlier, with the orogeny closing the old, long-lived Pan-African-Brasiliano tectonic cycle (1000-900 to 600 Ma). It resulted mainly from a submeridional collision between the huge West Africa-Amazon-Rio de la Plata mega-continent, recently broken off the eastern border of Laurentia, and two smaller continents: the joined Congo-São Francisco-Northeast Brazil-Central West Africa continent and the Kalahari continent. Basins related to the second young, and short-lived tectonic cycle opened at ca 600 Ma, or slightly later, and were deformed and metamorphosed around the Early-Middle Cambrian boundary at ca 520 Ma. There are various types: intramontane grabens and foreland molasse basins individualized into or at the margins of belts of the old, long-lived orogenic cycle; impactogen-type grabens developed far away inside the cratons. Most of them were ensialic and did not succeed in breaking up the newly aggregated Neoproterozoic West Gondwana supercontinent. Their rifting was contemporaneous with that of the large Palaeozoic basins such as the Appalachians. Their filling started with gravitationally reworked glacial deposits roughly of Vendian to early Cambrian age.