Epidote-and Plumose Quartz-bearing Granodiorites of the Hayuliang Granitoids, Arunachal Pradesh, India: Mineral Chemistry and Petrogenetic implications

Hayuliang granitoids are the products of felsic/acidic magmatism in and around Hayuliang locality (study area). It is a part of the Lohit Plutonic Complex (also known as Mishmi massif) which is located at the Trans-Himalayan belt of Arunachal Himalayas. Granodiorites containing magmatic epidotes and plumose quartz provide critical constraints on magma oxidation state and depth of emplacement. The Hayuliang granitoids of Arunachal Pradesh, NE India represent a distinctive suite of calc-alkaline granodiorites characterized by the stable coexistence of epidote and plumose quartz. Petrographic study of granodiorites reveals characteristic plumose extensional fracture patterns and radiating feather-like growths developed on healed microfractures. EPMA spot analyses of multiple plumose domains in granodiorites show high silica contents (SiO2 93-100 wt%), consistent with nearly pure quartz overgrowth. Plumose overgrowths indicate multiple pulses of metasomatism and episodic fluid flow contemporaneous with late-stage cooling and emplacement related stress release. These findings highlight the role of brittle-hydrothermal processes in modifying granitoid textures and provide a micro-structural framework for interpreting episodic fluids activity in shallow magmatic system. EPMA data indicates moderate pistacite contents (Ps 20 -30%), low Ti and Mn, and systematic Fe3+-Al substitution in epidote, consistent with a primary to late magmatic origin. Discrimination diagrams based on epidote mineral chemistry and whole-rock tectonic plots collectively suggest crystallization from oxidize, water-rich I-type magmas emplaced at mid-crustal depths in a convergent margin tectonic settings. Major oxides, trace elements, rare earth elements (REEs), CIPW norms and elemental ratios are used to constrain magma type, petrogenesis and tectonic setting. The aim of the present study is to analyse the petrography, whole rock geochemistry and mineral chemistry of epidote- and plumose quartz- bearing granodiorites by using petrological microscope, XRF and ICPMS to arrive the possible petrogenesis of Hayuliang granitoids.