[S-MP24] Supercontinents and Crustal Evolution

[SMP24-P06] Microtextural, fluid inclusion and C-O stable isotope studies of sparry magnesite of Deoban group of Kumaun Lesser Himalayas

*Prakash Chandra Arya¹, Sajeev Krishnan¹, Kiran S^2,3, Satish Kumar², Claude Nambaje¹ (1.Centre for Earth Science, Indian Institute of Science, Bangalore, India, 2.Department of Geology, Faculty of Science, Niigata University, Niigata, Japan, 3.Graduate School of Science and Technology, Niigata University, Niigata, Japan)

Keywords:Microtexture, Fluid Inclusion, Sparry magnesite (Pinolite), Stable isotopes

Carbonate-hosted voluminous sparry magnesite (Pinolite) occurrence are known from Deoban group of Kumaun Lesser Himalayas. The origin of the sparry magnesite is still not fully understood and is still a matter of debate. Several models have been proposed for their origin such as evaporative, diagenetic, hydrothermal, metamorphic, metasomatic, and biogenic. In the Kumaun region, the field evidence suggests a close association of stromatolites with the magnesite-bearing beds (10-120 mts). The sparry magnesite's microtextural and fluid inclusion studies are investigated to understand the magnesite formation and trapping temperatures of fluids during magnesite crystallization. The color of the sparry magnesite of Kumaun Himalayas varies from yellow to white-off white, grey, and muck colored. The grain size of magnesite crystal varies from few millimeters to 2 to 3 cm, with deformed rhombohedral cleavage. Fluid inclusion results suggest, presence of low density bi-phase primary and bi-phase pseudo secondary fluids. Three fluids populations were classified based on the homogenization temperature (T_h) and final ice melting (T_f). The first category (T_f ~ -18 to -23 ^oC with T_h ~160 to 200 ^oC), the second (T_f ~ -7 to -12 ^oC with T_h ~150 to 320 ^oC), and the third (T_f ~ 0 to -5 ^oC with T_h ~160 to 280 ^oC). The maximum homogenization temperature of fluids ~320 ^oC. These observations suggest that the magnesites hosting in the Deoban group were subjected to a minimum temperature of 320 ^oC. Preliminary carbon and oxygen stable isotope results indicate that magnesite have a relatively constant carbon isotopic composition comparable to marine carbonates, however with large variations in oxygen isotopic composition. Further studies are ongoing and we present a comprehensive discussion on the origin of sparry magnesite.