Fluid inclusions evidence for differential exhumation of ultrahigh pressure metamorphic rocks in the Sulu terrane

Abstract

Differential exhumation was petrologically recognized in ultrahigh pressure metamorphic rocks from the southern and northern parts of the Sulu terrane. While a normal exhumation occurred for eclogites and gneisses in south Sulu, granulite-facies overprinting of ultrahigh pressure metamorphic rocks took place with high retrograde temperatures in north Sulu. A study of fluid inclusions reveals trapping of five type fluid inclusions in high and ultrahigh pressure eclogite minerals and vein quartz in the Sulu terrane. These are A-type N2±CO2 inclusion trapped at high and ultra-high pressure eclogite-facies metamorphic condition, B-type pure-CO2 liquid phase inclusion with higher density trapped during granulite-facies overprinting metamorphism of eclogites, C-type CO2−H2O inclusion and D-type hypersaline inclusion trapped in high pressure eclogite-facies re-crystallization stage, and E-type low salinity H2O inclusion trapped in the latest stage of ultrahigh pressure exhumation (amphibolite-facies retrogression). Identification of crowded-distributing pure-CO2 liquid inclusions with higher density trapped in garnet of eclogites provides an evidence for granulite-facies overprinting metamorphism in the north Sulu terrane.