Contrasting Episodes of Regional Granulite-Facies Metamorphism in Enclaves and Host Gneisses from the Aravalli Delhi Mobile Belt, NW India

The Aravalli–Delhi Mobile Belt in the northwestern partof India demonstrates how granulite enclaves and their hostgneisses can be utilized to unravel multistage metamorphic historiesof orogenic belts, using three suites of metamorphic rocks:(1) an enclave of pelitic migmatite gneiss–leptynite gneiss;(2) metamorphosed megacrystic granitoids, intrusive into theenclave; (3) host tonalite–trondhjemite–granodiorite(TTG) gneisses associated with an interlayered sequence of garnetiferousmetabasite and psammo-pelitic schist, locally migmatitic. Basedon integrated structural, petrographic, mineral compositional,geothermobarometric studies and P–T pseudosection modellingin the systems NCKFMASH and NCFMASH, we record three distincttectonothermal events: an older, medium-pressure granulite-faciesmetamorphic event (M₁) in the sillimanite stability field, whichis registered only in the enclave, a younger, kyanite-gradehigh-pressure granulite-facies event (M₂), common to all thethree litho-associations, and a terminal amphibolite-faciesmetamorphic overprint (M₃). The high-P granulite facies eventhas a clockwise P–T loop with a well-constrained prograde,peak (M₂, P 12–15 kbar, T 815°C) and retrograde (M_2R,6·1 kbar, T 625°C) metamorphic history. M₃ is recordedparticularly in late shear zones. When collated with availablegeochronological data, the metamorphic P–T conditionsprovide the first constraint of crustal thickening in this belt,leading to the amalgamation of two crustal blocks during a collisionalorogeny of possible Early Mesoproterozoic age. M₃ reactivationis inferred to be of Grenvillian age. KEY WORDS: Northwestern India; polycyclic granulite enclave; pseudosection; high-pressure metamorphism; P–T path