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Hot lherzolite exhumation, UHT migmatite formation, and acid volcanism driven by Miocene rollback of the Banda Arc, eastern Indonesia

Pownall, Jonathan M.; Hall, Robert; Armstrong, Richard A.

Authors

Jonathan M. Pownall

Robert Hall

Richard A. Armstrong



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.

Citation

Pownall, J. M., Hall, R., & Armstrong, R. A. (2017). Hot lherzolite exhumation, UHT migmatite formation, and acid volcanism driven by Miocene rollback of the Banda Arc, eastern Indonesia. Gondwana Research, 51, 92-117. https://doi.org/10.1016/j.gr.2017.07.003

Journal Article Type Article
Acceptance Date Jul 9, 2017
Online Publication Date Jul 25, 2017
Publication Date 2017-11
Deposit Date Sep 3, 2019
Publicly Available Date Mar 29, 2024
Journal Gondwana Research
Print ISSN 1342-937X
Electronic ISSN 1878-0571
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 51
Pages 92-117
DOI https://doi.org/10.1016/j.gr.2017.07.003
Public URL https://hull-repository.worktribe.com/output/2598038
Publisher URL https://www.sciencedirect.com/science/article/pii/S1342937X16304816
Additional Information ©2019, Elsevier. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

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