[S-MP24] Supercontinents and Crustal Evolution

[SMP24-10] Evidence of carbonic crustal fluid during deep to shallow crustal evolution of the interior of Eastern Ghats Belt India: Grenvillian to Kuunga orogenies

*Kaushik Das^1,6、Sankar Bose^2,6、Junji Torimoto³、Yasutaka Hayasaka^1,6、Daniel Dunkley^4,5 (1.Hiroshima University、2.Presidency University、3.JAMSTEC, Yokotsuka、4.NIPR, Tokyo、5.IG-PAS, Poland、6.HiPeR, Japan)

キーワード：Eastern Ghats Province, UHT metamorphic rocks, Zircon and monazite age dating, C-O-H fluid

We report an occurrence of aluminous granulite and associated gneiss metamorphosed in ultra-high temperature conditions at the continental deep crust at the Eastern Ghats Belt (EGB), India. The detailed pressure-temperature-time-fluid history is retrieved from this suite of aluminous granulite and associated gneisses from a single exposure, which were injected by granitic aplite veins at a high angle at a ductile depth of the host gneissic rocks. The sapphirine-spinel-quartz-bearing aluminous granulite reveals a peak metamorphic condition of ~1000 °C at ~8 kbar at ~990 Ma (U-Pb zircon SHRIMP age). Porphyroblastic garnet and quartz in the peak assemblage have mono-phase, high-density, CO₂-rich primary fluid inclusions (~1 g/cm³). Secondary fluid inclusions in quartz grains of the retrograde cooled and/or decompressed assemblages of the same aluminous granulite have the signature of bi-phase CO₂-H₂O fluids with a comparatively low estimated density (0.8 g/cm³). The CO₂ isochore plots suggest a pressure drop from 7-8 kbar to 4-5 kbar (simultaneous or after the cooling from 1000 ºC to 800 ºC). While the late aplite dykes were emplaced at an high angle with asymmetrically bent foliation of the surrounding gneiss at 492+3 Ma (monazite U-Th-total Pb EPMA age). This aplite dyke also contain numerous primary and pseudosecondary fluid inclusions in the quartz grains (CO₂ monophase to biphase at room temperature). The calculated density is in the range of 0.71-0.82 g/cm³, suggesting the entrapment of this stage at < 3 kbar. This is the only occurrence known so far from the "orogenic interior" of the EGB that preserves the evidence of carbonic fluid presence during the evolution of UHT metamorphosed deep crust till its exhumation to shallow crust in a period encompassing the Grenvillian orogeny and the Kuunga orogeny, the later one being the age of the final cratonization of the EGB.