Pressure–temperature conditions and retrograde paths of eclogites, garnet–glaucophane rocks and schists from South Sulawesi, Indonesia

Abstract

High‐pressure metamorphic rocks exposed in the Bantimala area, c . 40 km north‐east of Ujung Pandang, were formed as a Cretaceous subduction complex with fault‐bounded slices of melange, chert, basalt, turbidite, shallow‐marine sedimentary rocks and ultrabasic rocks. Eclogites, garnet–glaucophane rocks and schists of the Bantimala complex have estimated peak temperatures of T =580–630 °C at 18 kbar and T =590–640 °C at 24 kbar, using the garnet–clinopyroxene geothermometer. The garnet–omphacite–phengite equilibrium is used to estimate pressures. The distribution coefficient K D1 =[( X pyr ) 3 ( X grs ) 6 /( X di ) 6 ]/[(Al/Mg) M2,wm (Al/Si) T2,wm ] 3 among omphacite, garnet and phengite is a good index for metamorphic pressures. The K D1 values of the Bantimala eclogites were compared with those of eclogites with reliable P–T estimates. This comparison suggests that peak pressures of the Bantimala eclogites were P =18–24 kbar at T =580–640 °C. These results are consistent with the P–T range calculated using garnet–rutile–epidote–quartz and lawsonite–omphacite–glaucophane–epidote equilibria.