Study of deformation patterns of erinpura granites from parts of Rajasthan and its implications

Abstract

The Marwar Craton is located in the west of Delhi Fold Belt (DFB). The Delhi Fold Belt (DFB) of northeast southwest trending, multiply folded and poly-metamorphosed rock of Proterozoic age. The western margin of the SDFB is demarcated by Phulad Shear Zone (PSZ) of mid-Proterozoic age (810 Ma), defining a contact between DFB and Marwar Craton. The PSZ is characterized by northeasterly striking ductile shear zone with a well developed mylonitic foliation and a down-dip stretching lineation. The Marwar Craton is dominated by a number of granites and granite gneisses and among them Erinpura granites are present in the vicinity of PSZ. The present study deals with the systematic study of these granites to understand its deformation pattern in relation to Phulad Shear Zone (PSZ). The granite is a coarse grained, white to grey coloured and slightly to strongly deformed. The granite shows crude foliations to prominent well developed foliations with attitudes varying from NNW-SSE to NE-SW. The less deformed granites are present at places far away from PSZ and are showing crude tectonic foliations which are oriented parallel to the magmatic foliation defined by oriented euhedral phenocrysts. The highly deformed granites are showing highly deformed phenocrysts with asymmetric tail. These highly deformed granites are present at vicinity of PSZ where they are ultimately transforming into remobilized belt comprising of ultramylonite oriented parallel to PSZ. The granites present in between are showing characteristic oriented euhedral phenocrysts and deformed phenocrysts with asymmetric tails, both oriented in NNW-SSE and NE-SW repectively. Systematic study of mesoscopic structures of these granites and the shear zone rocks demonstrate similarity in geometry and style. This indicates that the deformation in the granite and the shear zone is broadly synchronous