A synopsis of events related to the assembly of eastern Gondwana

Abstract

The assembly of the eastern part of Gondwana (eastern Africa, Arabian–Nubian shield (ANS), Seychelles, India, Madagascar, Sri Lanka, East Antarctica and Australia) resulted from a complex series of orogenic events spanning the interval from ∼750 to ∼530 Ma. Although the assembly of Gondwana is generally discussed in terms of the suturing of east and west Gondwana, such a view oversimplifies the true nature of this spectacular event. A detailed examination of the geochronologic database from key cratonic elements in eastern Gondwana suggests a multiphase assembly. The model outlined in this paper precludes the notion of a united east Gondwana and strongly suggests that its assembly paralleled the final assembly of greater Gondwana. It is possible to identify at least two main periods of orogenesis within eastern Gondwana. The older orogen resulted from the amalgamation of arc terranes in the Arabian–Nubian shield region and oblique continent–continent collision between eastern Africa (Kenya–Tanzania and points northward) with an, as of yet, ill-defined collage of continental blocks including parts of Madagascar, Sri Lanka, Seychelles, India and East Antarctica during the interval from ∼750 to 620 Ma. This is referred to as the East Africa Orogen (EAO) in keeping with both the terminology and the focus of the paper by Stern [Annu. Rev. Earth Planet. Sci. 22 (1994) 319]. The second major episode of orogenesis took place between 570 and 530 Ma and resulted from the oblique collision between Australia plus an unknown portion of East Antarctica with the elements previously assembled during the East African Orogen. This episode is referred to as the Kuunga Orogeny following the suggestion of Meert et al. [Precambrian Res. 74 (1995) 225]. Paleomagnetic data are currently too few to provide a rigorous test of this proposal, but the extant data do not conflict with the notion of a polyphase assembly of eastern Gondwana. The major conclusion of this paper is that east Gondwana did not exist until its Cambrian assembly.