Complex thermal histories in the Banggai-Sula Microcontinent, Indonesia: Evidence from monazite U-Th-Pb geochronology

<p>Continental fragments with Australian or Gondwanan affinities are widely distributed in eastern Indonesia. Metamorphic rocks intruded by Permo-Triassic granitoids have long been considered remnants of Paleozoic basement. However, recent geochronological studies in eastern Indonesia have revealed Mesozoic metamorphism with Cenozoic overprints, challenging previous interpretations. The Banggai-Sula microcontinent (BSM), a prominent continental fragment at the eastern tip of Sulawesi, preserves such Paleozoic basement rocks. Although the sedimentary cover sequences of the BSM are well studied, the metamorphic history of its Paleozoic basement remains underexplored. This study integrates petrography and monazite U-Th-Pb geochronology to investigate the metamorphic evolution of the BSM. In contrast to the Cenozoic resetting observed in neighboring continental fragments, this study reveals multiple tectonothermal episodes from the Mesoproterozoic to the Permian. Garnet-sillimanite-biotite gneiss records the earliest metamorphism at ∼ 1500 and 1400 Ma, consistent with major tectonothermal events in the North Australian Craton, suggesting a Gondwanan affinity. Regional Ordovician-Silurian metamorphism (∼ 460-433 Ma) occurred under medium P-T conditions. This metamorphism is linked to the eastern continuation of the Proto-Tethyan oceanic subduction zone from south of the Tarim Block along the northern Gondwana margin. Devonian-Carboniferous metamorphism (∼ 360 Ma) correlates with the evolution of the Tasman Orogen in eastern Australia, followed by Permian-Triassic granitic intrusion (∼ 260 Ma) representing an extension of continental arc magmatism from eastern Australia into New Guinea and the Sula Spur. Comparable tectonothermal histories in the Bird’s Head region of New Guinea indicate a shared tectonic history since at least the Devonian. These results establish the BSM as a fragment of the North Australian Craton crust that underwent significant reworking during the Paleozoic-Triassic evolution of the Gondwana margin.</p>