A Preliminary View of Metamorphic Rocks from Schwaner Mountains – West Kalimantan and Bantimala Complex – South Sulawesi, Indonesia
Annual Meeting of the Geological Society of Japan
Indonesian archipelago formed by reassembly of fragment derived from Gondwana that arrived at the Eurasian subduction margin. A Cretaceous active margin is interpreted along Sumatra into western Java continued through southeastern Kalimantan into western Sulawesi, as suggested by the distribution of subduction related high-pressure -lowtemperature metamorphic rocks. Present-day, geology of Indonesia is the result of Cenozoic subduction and collision and situated at the boundaries of Eurasia,
... o-Australia, and Pacific-Philippine Sea plate (Hall, et al., 2009). Williams, et al. (1988 divided the geology of West Kalimantan into three geological domains, which are Schwaner Mountains consists of granitic and metamorphic rocks, northwest Kalimantan domain consists of schist and deformed granite, and mélange associated with accretionary deposits on the north. K-Ar ages of granitoids from Schwaner Mountains yield Early Cretaceous (129 Ma) to Late Cretaceous (87 Ma). On the other hand, metamorphic rocks from NW Kalimantan domain yield Permian (320 Ma) to Late Triassic (204 Ma). High-pressure metamorphic rocks are distributed on the South Sulawesi. K-Ar ages of phengite on garnet-glaucophane rock from South Sulawesi yields 132 ± 7 Ma and 113 ± 6 Ma, 124 ± 6 Ma on mica rich intercalated with garnet-glaucophane rock, 114 ± 6 Ma and 115 ± 6 Ma for mica-quartz schist intercalated with hematite bearing glaucophane schist (Wakita, et al., 1994). Purpose of this study is to understanding in detailed Indonesia tectonic regime from the study of metamorphic rocks. In this preliminary view, metatonalite (84MS89A) from Schwaner Mountains -West Kalimantan taken by Geological Research and Development Centre of Indonesia have been observed petrographically, analyzed with EPMA, XRF and determined age dating by zircon LA-ICPMS. XRF analysis indicating that these rocks are derived from volcanic arc granitic with the tholeiitic affinities. Age determination by zircon LA -ICP-MS on the metatonalite is yields 233 ± 3 Ma for igneous domains. This indicating that metamorphism on metatonalite suggests simultaneous syn-metamorphic igneous activity and the same group with NW Kalimantan metamorphic rocks. During fieldwork on the Bantimala Complex -South Sulawesi, highpressure metamorphic rocks are found along the Pangkajene, Pateteang, Cempaga and Batupute River. These high-pressure metamorphic rocks are eclogite, jadeite-garnet-quartz rock, and garnet-blueschist have been observed petrographically and analyzed by EPMA. EPMA and chemical mapping analysis on jadeite-garnet-quartz rock shows that garnet grain has chemical zoning by increasing of spessartine (Mn) content in the core (~ 48 mol%) and decreasing of almandine (Fe) in the core (~ 25 mol%). Suggests that this rock passed through Jd+Qz stability field during metamorphic evolution. Detailed laboratorium observation of all samples from Bantimala Complex -South Sulawesi and Central Java with EPMA, bulk chemical analyses and age determinations are needed to understanding in details geological evidence constrain from metamorphic petrology on the Indonesia region.