Himalayan-type indenter-escape tectonics model for the southern part of the late Neoproterozoic–early Paleozoic East African– Antarctic orogen

Abstract

The East African–Antarctic orogen is one of the largest orogenic \nbelts on the planet. It resulted from the collision of various parts of \nproto–East and West Gondwana during late Neoproterozoic–early \nPaleozoic time (between 650 and 500 Ma). We propose that the \nsouthern part of this Himalayan-type orogen can be interpreted in \nterms of a lateral-escape tectonic model. Modern Gondwana reconstructions \nshow that the southern part of the East African– \nAntarctic orogen can best be reassembled when a number of microplates \n(the Falkland, Ellsworth-Haag, and Filchner blocks) are \npositioned between southern Africa and East Antarctica. This microplate \nassemblage is unusual. The microplates probably represent \nshear-zone–bounded blocks, produced by tectonic translation \nduring lateral escape, similar to those currently evolving in Southeast \nAsia. One of the escape-related shear zones is exposed as the \n20-km-wide Heimefront transpression zone in western Dronning \nMaud Land. Coats Land, a crustal block within the orogen, probably \nrepresents a block of older crust that was not subjected to \ntectonometamorphic reworking ca. 500 Ma by lateral tectonic escape. \nThe southern part of the orogen is also typified by very large \nvolumes of late-tectonic A2-type granitoids, intruded ca. 530–490 \nMa, probably as a consequence of delamination of the orogenic \nroot and the subsequent influx of hot asthenospheric mantle during \ntectonic escape. Erosional unroofing of the orogen is documented \nby the remnants of originally massive areas covered by Cambrian– \nOrdovician molasse-type sedimentary rocks throughout Africa, \nArabia, and Antarctica, testifying to the past extent and size of this \nlargest of orogens.