130-6 Post-metamorphic Peak Shortening of a Granulite Terrane: Evidence for Post-UHT Shortening and Thickening in the Eastern Ghats Province, India

Session: Evolution of Orogenic Belts Through Time: Insights from Sedimentation, Deformation, Magmatism, and Metamorphism, Part II

Presenting Author:

Anuj Ghosh

Authors:

Ghosh, Anuj¹, Samantaray, Suvankar², Gupta, Saibal³

(1) Geology and Geophysics, Indian Inst of Techn-Kharagp, KHARAGPUR, INDIA, India, (2) Geology and Geophysics, Indian Institute of Technology, Kharagpur, Kharagpur, India, India, (3) Geology and Geophysics, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India,

Abstract:

The Eastern Ghats Province (EGP) is a well-known granulite facies terrane in India that retains evidence of ultra-high temperature (UHT) metamorphism. The formation of the EGP and the associated UHT metamorphism is generally correlated with the assembly of supercontinent Rodinia. However, the tectonic setting leading to such elevated thermal conditions remains subject to ongoing debate. Reconstruction of such evolution of high-grade terranes have traditionally relied on pressure-temperature (P-T) pseudosections. In this study, the technique has been applied to study rock samples collected from the Angul domain present in the northernmost parts of EGP. The P-T pseudosections were generated using PERPLE_X (v.7.1.3) by determining the effective bulk compositions of selected domains within specific rock samples. A. domain selected within a garnet-cordierite metapelite preserves the peak conditions at 850-1000°C and 5.5-7.5 kbar which may lie within the UHT regime. Based on the presence of garnet overgrowing the peak garnet rims, sillimanites rimming around cordierite, and the stabilization of biotite in presence of melt, a cooling associated with loading is the most plausible post-peak trajectory. An augen gneiss sample was also selected for the same study but since the rock is texturally homogeneous, the bulk rock chemistry was obtained using whole rock X-ray fluorescence (XRF) data based on which a P-T pseudosection was obtained, which yields peak conditions at 750-850°C and >6kbar (which also corresponds to the P-T conditions at which the precursor granite intruded) signifying that this rock never truly attained thermal conditions as high as the former. Within the same sample, isoclinal folds and penetrative S₁/S₂ fabrics defined by biotite suggest that the rock underwent strain due to a shortening event that took place after the stabilization of the assemblage biotite+plagioclase+quartz while the rock was cooling. While UHT metamorphism reported across the globe is commonly linked with continental collision, this study emphasizes on the suggests that shortening deformation possibly related to terrane amalgamation may occur well after high grade metamorphism (may be UHT) of a terrane.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4572

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