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

Abstract

In 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.

Petrological implications of element redistribution during metamorphism: insights from meta-granite of the South Delhi Fold Belt, Rajasthan, India

“…Correlation of the results of this study with published literature suggests that the metamorphic mineral growth was presumably related to the event that developed the regional fabric of the SDFB along the western margin of the belt (Heron, 1953;Gupta et al 1980Gupta et al , 1995Gupta et al , 1997Roy & Jakhar, 2002;Chatterjee et al 2017Chatterjee et al , 2020. Retainment of the delicate micro-textural imprints like corona and symplectite in the meta-granite suggests that the rock is unlikely to have witnessed any significant deformation after the textures formed during metamorphism (Wayte et al 1989;Lang & Gilotti, 2001).…”

“…The PSZ mylonitic foliation has a northeasterly strike and a steep easterly dip with a very strong down-dip stretching lineation. Detailed structural studies indicate that the PSZ developed in a ductile transpressional regime (Ghosh et al 1999;Roy Choudhury et al 2016; with a top-to-the-NNW reverse sense of movement (Ghosh et al 1999;Chatterjee et al 2017Chatterjee et al , 2020. The meta-granite of the present study area belongs to the SDFB and is situated on the hanging wall side of the PSZ, nearly a kilometre east of the proper shear zone (Fig.…”

“…Retainment of the delicate micro-textural imprints like corona and symplectite in the meta-granite suggests that the rock is unlikely to have witnessed any significant deformation after the textures formed during metamorphism (Wayte et al 1989;Lang & Gilotti, 2001). From the study area, Chatterjee et al (2017Chatterjee et al ( , 2020 reported ~820-810 Ma metamorphism, and they suggested that the pervasive fabric in the western part of the SDFB had formed during reverse shearing of the PSZ. The studied meta-granites occur in close association with the metapelites examined by Chatterjee et al (2017).…”

“…The SDFB consists mainly of calc-silicate rocks inter-layered with mica schists, granites, and mafic and ultramafic rocks (Heron, 1953;Gupta et al 1980Gupta et al , 1995Gupta et al , 1997Roy & Jakhar, 2002;Chatterjee et al 2016). The western margin of the SDFB is demarcated by a crustal-scale shear zone known as the Phulad Shear Zone (PSZ) (Gupta et al 1980;Sinha-Roy, 1988;Golani et al 1998;Ghosh et al 1999;Chatterjee et al 2017Chatterjee et al , 2020. The PSZ mylonitic foliation has a northeasterly strike and a steep easterly dip with a very strong down-dip stretching lineation.…”

“…Studies from Aravalli Mobile Belt suggest a Grenvillian-age collisional orogen between the North Indian Block to the east and Marwar craton to the west (Deb et al 2001;Pandit et al 2003;Bhowmik et al 2010). There is another view, where the suturing between the Marwar craton to the west and the remaining part of India took place along the PSZ during mid Neoproterozoic time (~820-810 Ma; Chatterjee et al 2017Chatterjee et al , 2020.…”