Multiple thrust systems from the Southern Granulite Terrane, India: Insights on Precambrian convergent margin tectonics

Abstract

• Field relationships as shown in structural cross sections indicate thrust-nappe tectonics. • Multiple thrusting and associated features reveal that the granulitic units are allochthonous in nature. • The charnockite massifs represent nappes of volcanic arcs and/or microcontinents. • The Neoproterozoic-Cambrian evolution of the SGT involved the closure of the Mozambique Ocean. The geological and structural complexities of the Southern Granulite Terrane (SGT) of India, a key Gondwana collisional orogenic belt, are increasingly recognized and our understanding is still evolving despite several multidisciplinary efforts. Six important structural cross sections along some critical geological corridors have been reconstructed covering the entire stretch of SGT. We propose subduction related multiple thrust systems for the evolution of the SGT, based on the salient features derived from the structural cross sections and the currently available geoscientific data sets. The presence of tectonic windows and klippe structures in Madurai block and unusual occurrence of high strain zones on top of some of the highly elevated quartzite hills support the thrust-nappe tectonic model for the SGT implying possible allochthonous nature of many of the supracrustals and granulitic units involving multiphases of thrusting. The evolution of the SGT involves converging accretionary processes of island arc magmatic intrusives, thrust stacking, crustal coupling, granitic emplacement and the obduction of ophiolite complexes indicating a complete range of geological processes encountered in modern orogenic belts. These features could thus be representative of multiple thrusting related to south directed subduction processes followed by wide scale collision of Gondwana fragments during the end Precambrian.