An overview and tectonic synthesis of the pre‐Tertiary very‐high‐pressure metamorphic and associated rocks of Java, Sulawesi and Kalimantan, Indonesia

Abstract

High‐pressure metamorphic rocks are widely distributed in Cretaceous accretionary complexes throughout Java, Sulawesi (formerly Celebes) and southeast Kalimantan (Indonesian Borneo). Many of these rocks occur as imbricate slices of carbonate, quartzose and pelitic schists of shallow marine or continental margin parentage, interthrust with subordinate basic schists and serpentinite. They are predominantly of low‐to‐intermediate metamorphic grade (300 < T < 550 °C; 4 < P < 12 kbar) and yield mica K–Ar radiometric ages of 110–120 Ma. Metamorphic rocks that exhibit evidence of exhumation from much greater depths (> 60 km), however, are sporadically exposed, usually as tectonic blocks, throughout the Cretaceous accretionary complexes. They include eclogite, garnet–glaucophane rock (P = 18–24 kbar, T = 580–620 °C), and jadeite–garnet–quartz (?coesite) rock (?P > 27 kbar, T = 720–760 °C) in Bantimala, southwest Sulawesi; eclogite and garnet granulite in west central Sulawesi; eclogite and jadeite‐glaucophane‐quartz rock (P ∼ 22 kbar, T ∼ 530 °C) in Luk Ulo, Central Java; and Mg–chloritoid‐bearing whiteschists (P ∼ ?18 kbar) in the Meratus Mountains, southeast Kalimantan. Garnet lherzolites from depths of > 60 km are also associated with schists in east central Sulawesi (P = 22–28 kbar, T = 1000–1100 °C), west central Sulawesi (P = 16–20 kbar, T = 1050–1100 °C); and garnet pyroxenite (P ∼ 20 kbar, T ∼ 850 °C) occurs as blocks with pyrope–kyanite amphibolite, eclogite and blueschist, within Miocene conglomerate in Sabah, northeast Borneo. Many of the metamorphic rocks were probably recrystallized in a north‐dipping subduction zone at the margin of the Sundaland craton in the Early Cretaceous. Exhumation may have been facilitated by the collision of a Gondwanan continental fragment with the Sundaland margin at ca 120–115 Ma.