Hot lherzolite exhumation,UHT migmatite formation,and acid volcanism driven by Miocene rollback of the Banda Arc,eastern Indonesia |
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| Institution: | 1. SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, United Kingdom;2. Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia;1. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering/South China Sea Bioresource Exploitation and Utilization Collaborative Innovation Center, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510006, China;2. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Guangdong Ocean University, Zhanjiang 524088, China;1. Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, USA;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, PR China;3. Department of Earth Sciences, The University of Adelaide, Adelaide, SA 5005, Australia;4. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea;1. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3, Koptyug ave., Novosibirsk 630090, Russia;2. Novosibirsk State University, 2, Pirogova str., Novosibirsk 630090, Russia;3. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, 3, Koptyug ave., Novosibirsk 630090, Russia;4. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1А Favorsky str., Irkutsk 664033, Russia;1. School of Geography, Geology & Environment, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK;2. Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9FE, UK;3. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK;4. Department of Earth and Planetary Sciences, Birkbeck College, Gower Street, London WC1E 7HX, UK |
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| Abstract: | The northern Banda Arc, eastern Indonesia, exposes upper mantle/lower crustal complexes comprising lherzolites and granulite facies migmatites of the ‘Kobipoto Complex’. Residual garnet–sillimanite granulites, which contain spinel + quartz inclusions within garnet, experienced ultrahigh-temperature (UHT; > 900 °C) conditions at 16 Ma due to heat supplied by lherzolites exhumed during slab rollback in the Banda Arc. Here, we present U–Pb zircon ages and new whole-rock geochemical analyses that document a protracted history of high-T metamorphism, melting, and acid magmatism of a common sedimentary protolith. Detrital zircons from the Kobipoto Complex migmatites, with ages between 3.4 Ga and 216 Ma, show that their protolith was derived from both West Papua and the Archean of Western Australia, and that metamorphism of these rocks on Seram could not have occurred until the Late Triassic. Zircons within the granulites then experienced three subsequent episodes of growth – at 215–173 Ma, 25–20 Ma, and at c. 16 Ma. The population of zircon rims with ages between 215 and 173 Ma document significant metamorphic (± partial melting) events that we attribute to subduction beneath the Bird's Head peninsula and Sula Spur, which occurred until the Banda and Argo continental blocks were rifted from the NW Australian margin of Gondwana in the Late Jurassic (from c. 160 Ma). Late Oligocene-Early Miocene collision between Australia (the Sula Spur) and SE Asia (northern Sulawesi) was then recorded by crystallisation of several 25–20 Ma zircon rims. Thereafter, a large population of c. 16 Ma zircon rims grew during subsequent and extensive Middle Miocene metamorphism and melting of the Kobipoto complex rocks beneath Seram under high- to ultrahigh-temperature (HT–UHT) conditions. Lherzolites located adjacent to the granulite-facies migmatites in central Seram equilibrated at 1280–1300 °C upon their exhumation to 1 GPa (~ 37 km) depth, whereupon they supplied sufficient heat to have metamorphosed adjacent Kobipoto Complex migmatites under UHT conditions at 16 Ma. Calculations suggesting slight (~ 10 vol%) mantle melting are consistent with observations of minor gabbroic intrusions and scarce harzburgites. Subsequent extension during continued slab rollback exhumed both the lherzolites and adjacent granulite-facies migmatites beneath extensional detachment faults in western Seram at 6.0–5.5 Ma, and on Ambon at 3.5 Ma, as recorded by subsequent zircon growth and 40Ar/39Ar ages in these regions. Ambonites, cordierite- and garnet-bearing dacites sourced predominantly from melts generated in the Kobipoto Complex migmatites, were later erupted on Ambon from 3.0 to 1.9 Ma. |
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