Geochemical study of peridotites from the Manipur Ophiolite Complex, Northeast India with special reference to their PGE concentration

摘要

The peridotites of the Manipur Ophiolite Complex (MOC) have been examined based on mineral chemistry, major elements and PGE contents. They represent high-magnesian cumulates with Mg# 0.90 (Mg/Mg+Fe) in olivine and Cr# 0.12 (Cr/Cr+Al) in spinel. High Mg* contents of the olivine show that these rocks are most likely derived from partial melting of the residual upper mantle. The peridotites contain higher concentration of Palladium Group PGE (PPGE) (Rh=4.4−6.6ppb; Pd=336−458ppb and Pt=14.6−36.4ppb) than the Iridium Group PGE (IPGE) (Os=2.4−5.8ppb; Ir=3.2−4.16ppb and Ru=5.2−7ppb). These are characterized by overall enrichment of PGE concentration (σPGE=365.8 − 516.6 ppb) and high ratio of (Pt+Pd)/(Os+Ir+Ru). This suggests that the rocks are formed by partial melting and crystal fractionation of olivine-rich (picritic) magma.