A Study on the Time Relations Between Movements, Metamorphism and Granite Emplacement in the Middle Proterozoic Delhi Supergroup Rocks of Rajasthan

Abstract

The Delhi Supergroup rocks, an important tectonic-stratigraphic unit of the Aravalli Mountains, are affected by multiple folding and polyphase metamorphism. Three generations of deformational structures have been recognized in these rocks (DFI, DF2 and DF3). DFI structures which include a set of isoclinal folds with penetrative axial planar schistosity, were deformed successively by DF2 and DF3 folding movements. Microtcxtural studies of rocks yielded evidence for two metamorphic events-a progressive metamorphism (M1) rising upto epidote amphibolite facies, followed by a retrogressive phase (M3) under greenschist facies condition. Field and microscopic studies indicate that both DF1 and DF2 structures were formed during Ml phase, and DF3 structures were formed during the retrogressive phase (M2). The metamorphic climax of M1 phase was during the early phase of DF2, and the granites emplaced coevally with this event indicated ca. 1450 Ma Rb/Sr isochron age. No definite relationship could be established for the 850-700 Ma secondary (mineral) ages with DF3 deformation and M2 metamorphism.