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.

Palaeomagnetic studies in the Malani Igneous Suite (ca. 770–750 Ma) of the Marwar Crustal Block, NW India, provide essential constraints on palaeogeographic reconstructions of the Rodinia Supercontinent. The Malani Igneous Suite is intrusive into megacrystic granite and granite-gneissic enclaves of the Marwar Crustal Block. A crustal-scale NE–SW ductile transpressional shear zone with a southeasterly dip known as the Phulad Shear Zone (820–810 Ma) separates this Marwar Crustal Block from the rocks farther east. The pre-shearing tectonic evolution of the Marwar Crustal Block is poorly understood. Three phases of ductile deformations (D1, D2, and D3, with associated fabrics S1, S2, and S3) were identified in the Marwar Crustal Block. The D1 deformation is restricted to enclave gneisses. The megacrystic granite was emplaced syn-tectonically during D2 deformation. The S2 magmatic foliation (NNW–SSE) in the megacrystic granite is oblique to the Phulad Shear Zone. The D3 deformation in the megacrystic granite is synchronous with the Phulad Shear Zone mylonites. Another porphyritic granite (Phulad granite, ca. 820 Ma) emplaced syn-tectonically during D3 deformation along and across the Phulad Shear Zone. U-Pb zircon dates in the Marwar Crustal Block document ca. 890 Ma and ca. 860 Ma magmatic dates. U-Pb-Th monazite dates in the Marwar Crustal Block show a strong peak at ca. 820 Ma. By integrating critical field relations, deformational patterns, and geochronology, we argue that the Marwar Crustal Block shows distinct geological evolution prior to its accretion with the remaining parts of India. We propose that the accretion of the Marwar Crustal Block must be younger than ca. 860 Ma and culminate during ca. 820–810 Ma to form the Greater India landmass along the Phulad Shear Zone.

Meta-granites of the South Delhi Fold Belt, northwestern India, contain spectacular reaction textures formed during the metamorphic replacement of primary minerals. Textural relationships imply that amphibole was replaced sequentially in two stages. Epidote + titanite + quartz symplectite formed syn-tectonically on amphibole grain boundaries/fractures, followed by post-deformational growth of euhedral garnet overprinting amphibole grains. Besides occurring as symplectite grown during deformation, titanite in this rock also developed as a post-tectonic corona around magnetite. Parent magnetite contains exsolutions of ilmenite and/or ultrafine lamellae of Ti-rich oxide (Ti-oxd). Textures involving coronal titanite suggest their formation through a magnetite + ilmenite(/Ti-oxd) + plagioclase → titanite reaction. Compositional attributes and the calculation of the gain versus loss of components during the reaction suggest that the Mn2+ for garnet (XSpss = 0.23–0.29) that grew replacing amphibole was supplied by ilmenite (Mn2+ is 0.118–0.128 apfu) as it disintegrated to form coronal titanite. The redistribution of components between the metamorphic reaction sites connects the texturally unrelated domains and suggests that these zones were in chemical equilibrium during metamorphism. We estimated the P–T conditions of metamorphism for these post-tectonic assemblages as ∼650–700 °C from pseudosection modelling and conventional thermometry. Zircon data from this study suggest that the granitic rock crystallized at 988.8 ± 8.8 Ma. We propose that the metamorphic phases replaced the primary minerals during the mid Neoproterozoic tectonic activity reported from this terrane. The syn-tectonic symplectitic assemblage formed as the temperature increased during prograde metamorphism, and the post-tectonic minerals developed at peak conditions following the cessation of deformation.

<p>In the northwestern Indian shield, the northeast-southwest trending South Delhi Fold Belt (SDFB) is a multiply folded and poly-metamorphosed rock of the Proterozoic age. Phulad Shear Zone (PSZ) is described as a terrane boundary shear zone that separates the SDFB to the east and Marwar craton to the west. This shear zone is defined by steep easterly dipping mylonitic foliation and strong downdip stretching lineation. The PSZ has developed a ductile transpressive regime with a top-to-the-north-north-west reverse sense of movement during 810Ma. The PSZ shows regional NE-SW trends with small bends of N-S orientation. The present study deals with a variably deformed porphyritic granite named Phulad granite that occurs about 200 by 6 km along and across the PSZ.</p> <p> </p> <p>The Phulad granite is characterized by a bi-modal grain size population with prominent euhedral grains of feldspar clasts (2-6 cm long) in a fine-grained (< 3 mm) mosaic of recrystallized feldspar and quartz aggregates. It consists of phenocrysts of k-feldspar that show characteristic features of magmatic origin. Microstructural study reveals a series of magmatic, sub-magmatic, high-temperature and solid-state deformation structures in this granite. Mesoscopic field relations show evidence of magmatic fabric in the studied granite. The granite also preserves tectonic foliation parallel to this magmatic fabric. Strong foliation developments with mean attitude 24˚/85˚E and prominent stretching lineation have been developed in the granitic rock. A detailed study of structural elements of Phulad granite and PSZ demonstrates a similarity in geometry and style, signifying that the deformation in both units is synchronous, and this granite is emplaced during the regional deformation prior to its complete crystallization. The N-S orientation of the PSZ acted as releasing bends and provided the space required for the emplacement of the granite in a transpressional ductile regime. Monazite chemical age data and conventional zircon age data suggest a magmatic age of 819.1 ± 4 and 818 ± 18 Ma, respectively. Integrating micro-meso and macro scale structures along with geochronology of Phulad granite we suggest that the Phulad granite acted as a stitching pluton at the time of suturing around 810-820Ma.</p>