An outline of the petrology, structure and age of the Pompangeo Schist Complex of central Sulawesi, Indonesia

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Abstract
Variably dismembered and metamorphosed accretionary complexes constitute the basement of much of the Indonesian island of Sulawesi. The most extensive of these is the Pompangeo Schist Complex, which crops out over ∼ 5000 km2 in central Sulawesi, and is predominantly composed of interbanded phyllitic marble, calcareous phyllite, graphitic schist and quartzite; rocks of terrigenous to shallow marine origin. Along the eastern margin of the complex, schists are interthrust with unmetamorphosed Jurassic sandstone, which may represent parental material of the complex. The schists are unconformably overlain by pelagic sediments with an Albian–Cenomanian biostratigraphy. Synmetamorphic progressive deformation of the Pompangeo Schist Complex has resulted in repeated isoclinal folding and a strong transposition foliation striking north‐northwest/south‐southeast and dipping west, subparallel to the compositional banding of the complex; microstructural fabrics indicate a top‐to‐east sense of shear. On a regional scale the Pompangeo Schist Complex is lithostratigraphically coherent and an east‐to‐west metamorphic field gradient is recognizable, which, if continuous, represents a relatively low thermal gradient of ∼ 15 °C/km. K–Ar dating yielded ages of ca 111 Ma. Correlative metamorphic rocks appear to underlie the entire Neogene magmatic province, since they occur sporadically throughout western Sulawesi, including the Bantimala region of the South Arm. The Pompangeo schist metamorphism cannot be correlated with arc magmatism in western Sulawesi, which is of Neogene age. The Pompangeo and Bantimala schists, as well as other accretionary complexes in western Sulawesi, were probably generated in the same subduction system that was responsible for the extensive Mesozoic continental arc in central Kalimantan, at the eastern margin of Sundaland.