Petrogenesis and Tectonic Implications of Anorogenic Acid Plutonic Rocks of Southwestern Haryana of Northwestern Peninsular India

This paper discusses the petrological and geochemical characteristics of the acid plutonic rocks (mainly granites of different colors) exposed in Khanak and Devsar areas of Neoproterozoic Malani Igneous Suite (MIS) to understand their magmatic evolution processes, petrogenetic history and tectonic regimes. Petrographically, granites of both areas show porphyritic, hypidiomorphic, granophyric, perthitic and micro-granophyric textures. Geochemically, these acidic rocks having peraluminous nature are enriched in SiO2, Na2O + K2O, Fe/Mg, Rb, Zr, Y, Th, U, REE and depleted in MgO, CaO, Sr, P, Ti, Ni, Cr, V & Eu abundances, which have affinity with A-type granites in extensional environment. The enrichment of trace elements and negative anomalies of Sr, Eu, P & Eu in the multi-element spider diagrams suggest that the emplacement of these granites were controlled by fractional crystallization and crustal contamination of protolith magma. Elemental geochemistry also attests that they are of rare-metal bearing with high heat production (HHP) nature and represent a genetically related post-collisional A2-type granitic intrusions. Petrogenetic modeling (batch melt related) suggests that the early phase (grey and grayish green colored granites) might have been generated from a gabbroic source by partial melting (5%) leaving a residue with 25% alkali feldspar, 20% quartz, 35% plagioclase, 10% biotite, 8% hornblende, 1% orthopyroxene and 1% clinopyroxene whereas late phase (pink colored granites) might have been generated from a metavolcanic source by partial melting of 2% leaving a residue with 30% alkali feldspar, 15% quartz, 45% plagioclase, 2% biotite, 2% hornblende, 3% orthopyroxene and 3% clinopyroxene. Hence, the petrology and geochemistry of these acid plutonic rocks are consistent with their formation in a plume related rift-magmatic tectonic setting and exhibit complex post magmatic chemical variations.