Garnet peridotite and associated high-grade rocks from Sulawesi, Indonesia

Abstract

The effects of collision between three major plates define the geological development of eastern Indonesia. Garnet peridotite and associated granulite-facies contact rocks are described from two sites within the valley of the active Palu-Koro left-lateral, strike-slip fault crossing central Sulawesi. Disrupted parts of a medium- to low-grade metamorphic complex intruded by Neogene granite occur on both sides of the fault. Thermobarometry on minerals and fluids in the garnet peridotite reveals a re-equilibration path from a depth of 60 km upward. Chemistry points to metasomatic effects — isolated trace-element enrichment — by a CO 2-rich liquid and fluid in a peridotite of oceanic affiliation. The granulite shows an increase in T and incipient melting at the arrival of peridotite. The sequence of fluid inclusions of an evolving CO 2CH 4(N 2)H 2O-bearing fluid defines a concave decompression path suggesting rapid uplift. Trace element chemistry of granulite with basaltic to peraluminious rhyolitic composition indicates island-arc affinity. The described history may well reflect the processes beneath a mantled gneiss dome, present as a coeval metamorphic aureole around the garnet peridotite outcrops.