Hydration of eclogite, Pam Peninsula, New Caledonia

Abstract

Garnet glaucophanite and greenschist facies assemblages were formed by the recrystallization of barroisite‐bearing eclogite facies metabasites in northern New Caledonia. The mineralogical evolution can be modelled by calculated P–T and P–X H2O diagrams for appropriate bulk rock compositions in the model system CaO–Na 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O. The eclogites, having developed in a clockwise P–T path that reached P ≈19 kbar and T ≈590 °C, underwent decompression with the consumption of free H 2 O as the volume of hydrous minerals increased. Eclogite is preserved in domains that experienced no fluid influx following the loss of this fluid. Garnet glaucophanite formed at P ≈16 kbar during semi‐pervasive fluid influx. Fluid influx, after further isothermal decompression, was focused in shear zones, and resulted in chlorite–albite‐bearing greenschist facies mineral assemblages that reflect P ≈9 kbar.