Petrochemistry and P–T path for garnet mica schists from Patharkhola, Almora

This study presents petrographic, geochemical and thermobarometric analyses of garnet mica schists from Patharkhola area to understand their petrogenesis, protolith characteristics and pressure–temperature evolution. The schists occur in folded outcrop patterns within the southern limb of the Dudhatoli syncline and are characterized by fragile, powdery textures with well-developed schistosity defined by preferred orientation of phyllosilicate minerals. Petrographic analysis reveals two distinct mineral assemblages: Garnet-Biotite-Muscovite-Chlorite-Plagioclase-Quartz and Garnet-Biotite-Muscovite-Plagioclase-Quartz. Geochemical analysis of major oxides reveals SiO₂ content ranging from 64.74% to 75.78% while Al₂O₃ from 10.53% to 19.88%. The K₂O/Al₂O₃ versus Na₂O/Al₂O₃ discrimination plot confirms sedimentary protolith origin, while Herron’s classification indicates derivation from silty-to-silty clay sediments in a shale-dominated environment. Rare earth element patterns show gentle LREE enrichment with average La/Eu ratio of 24.19 and flat to slightly enriched HREE patterns. Thermobarometric calculations using garnet-biotite thermometry and GASP barometry reveal P–T variations between garnet core and rim. Garnet cores yield average conditions of 519 °C and 4.2 kbar, while rims indicate 574 °C and 9.8 kbar, documenting a steep prograde metamorphic path. The dramatic decrease in Mn content from core (0.752) to rim (0.078) in garnets suggests substantial crustal burial during prograde metamorphism which is again validated by calculated P–T path plotted on the KFMASH system demonstrating typical clockwise evolution characteristic of collisional orogenic belts.