Mid‐Neoproterozoic Tectonics of Northwestern India: Evidence of Stitching Pluton along 810 Ma Phulad Shear Zone

Abstract

AbstractIn northwestern India, Phulad Shear Zone (PSZ, ~810 Ma) demarcates the boundary between South Delhi Fold Belt to the east and Marwar craton to the west. This shear zone has regional NE‐SW trend with small bends of N‐S orientations. PSZ is characterized by steep southeasterly dipping mylonitic foliation with steep oblique stretching lineation. The PSZ has developed in a ductile transpression with top‐to‐the‐NNW reverse sense of movement associated with a component of sinistral‐slip movement on horizontal section. The 200 by 6 km porphyritic Phulad granite occurs along and across the PSZ, and it is variably deformed. Phulad granite shows evidence of magmatic foliation with preservation of parallel alignment of euhedral feldspars phenocrysts and microgranitoid enclaves. The feldspar phenocrysts show simple twin interfaces parallel to the direction of elongation. This granite also shows development of solid‐state foliation parallel to this magmatic foliation. Detailed study of structural elements suggests that Phulad granite has formed during the regional deformation in the country rock shear zone prior to its complete crystallization. Our data indicate that the releasing bends of N‐S orientation within the PSZ have provided the space required for emplacement of Phulad granite in a transpressional regime. EPMA U‐Pb‐Th monazite and U‐Pb LA‐ICP‐MS zircon ages in Phulad granite indicate a magmatic age of 819.1 ± 4 and 818 ± 18 Ma, respectively. PSZ represents the suture along which Marwar craton accreted with remaining India to form the Greater India landmass. The present study suggests that Phulad granite acted as a stitching pluton during this suturing along PSZ at 810–820 Ma.