Pressure–temperature conditions and retrograde paths of eclogites, garnet–glaucophane rocks and schists from South Sulawesi, Indonesia |
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| Authors: | K MIYAZAKI I ZULKARNAIN J SOPAHELUWAKAN & K WAKITA |
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| Institution: | Geological Survey of Japan, 1–1-3 Higashi, Tsukuba, Ibaraki 305, Japan,;Research and Development Centre for Geotechnology, Jl. Cisitu, 21/154D, Bandung, 40135 Indonesia |
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| 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 D1values 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. |
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| Keywords: | eclogite high-pressure metamorphism Indonesia P–T conditions retrograde metamorphism |
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