[S-MP25] Supercontinents and Crustal Evolution

[SMP25-04] Metamorphic evolution of Mall Johar region of the central sector of the Himalaays

*Prakash Chandra Arya¹、K Sajeev¹、M Satish-Kumar²、V Kiso¹ (1.Centre for Earth Sciences, Indian Institute of Science, Bangalore, India、2.Department of Geology, Niigata University, Ikarashi, Nishi-ku, Niigata, Japan)

キーワード：Himalayas, Metamorphism, Microcomputed tomography

Orogenic belts are a result of colliding continents and thus provide an excellent opportunity to enhance our understanding of plate dynamics. Although re-equilibrium largely wipes out early metamorphic information but garnet zoning with pseudosection modelling is useful in re-establishing it. Traditionally, the bulk composition is estimated from XRF and EPMA database but estimating the bulk composition is challenging for coarse-grained heterogeneous rock. Here, we have used the above two techniques along with a relatively new microcomputed tomography to calculate the bulk chemistry of texturally heterogeneous Malla Johar metapelite, i.e., exposed Vaikrita group at the highest structural level in an unexplored region of the central Himalayan sector. Garnet inclusions within staurolite were visible only in microcomputed tomography and were not visible in any thin section. The mineral assemblage of Johar Valley metapelite is reflected in the pseudosections generated from EPMA (~ 500-600 ^oC, at 2-7 kbar) and microcomputed tomography (~500-600 ^oC, at 4.8-3.5 Kbar). The same could not be modelled through XRF data, suggesting phase diagrams are very sensitive to bulk compositions. The textural and phase equilibrium results show that the staurolite was formed after garnet formation, during prograde metamorphism. These features are consistent with the observed textural analysis using microCT and the generated phase diagrams.