Petrology and geochemistry of metapelites and basic granulites from Sonapahar region of Shillong Meghalaya gneissic complex, North East India

摘要

The geochemistry of the metapelites and basic granulite of Sonapahar has been studied in order to assess the nature of the protolith and their likely tectonic environment. Metapelites contains SiO2 (av. 62.16wt %), K2O+Na2O (av. 4.57 wt%), Al2O3 (av. 16.69 wt%), MgO (av. 5.31 wt%), Mg# av. 0.60 and low TiO2 (av. 0.68 wt%) with low Y (av. 23.48 ppm) and Yb (av. 1.6 ppm) which point to their derivation from andesite source. Metapelites show prominent negative europium anomaly (EuN/Eu* = 0.38–0.54) and fractionated LREE to HREE pattern (LaN/LuN) 17.23 to 56.69. Basic granulites demonstrate low content of SiO2 (av50.95 wt%), Al2O3 (av13.67 wt%), K2O (av 0.58 wt%) and enriched in Fe2O3 t (av 11.42 wt%), MgO (av 7.29 wt%), CaO (av 10.60 wt %), Na2O (av 2.26 wt%), Mg# av. 0.56 and range from calc-alkaline to tholeiitic in nature. The geochemistry of the metapelites and basic granulites advocate that metapelites are derived from arc related andesitic source due to subduction whereas protoliths of basic granulites was originated in rift related volcanism through diapiric movement of hot rising mantle derived basaltic magmas.