HR: 0800h
AN: T41C-1210    [Abstracts]
TI: Microplate rotation leads to rapid exhumation of a subduction complex in eastern Papua New Guinea
AU: * Baldwin, S L
EM: sbaldwin@syr.edu
AF: Dept of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AU: Finn, C A
AF: U.S. Geological Survey, P.O. Box 25046, MS 964, Denver, CO 80225 United States
AU: Webb, L E
AF: Dept of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AU: Fitzgerald, P G
AF: Dept of Earth Sciences, Syracuse University, Syracuse, NY 13244 United States
AU: Little, T
AF: School of Earth Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, 6000 New Zealand
AU: Anderson, E
AF: U.S. Geological Survey, P.O. Box 25046, MS 964, Denver, CO 80225 United States
AB: The Solomon Sea microplate (SSM) formed in response to oblique Australian (AUS)-Pacific convergence. Since the latest Miocene counterclockwise rotation of the SSM has led to rifting, metamorphic core complex (mcc) formation, eclogite exhumation at plate tectonic rates, and seafloor spreading along the SSM-AUS boundary. Aeromagnetic data provide additional constraints on the nature of this plate boundary. The Papuan Peninsula north of the Owen Stanley Fault (OSF) is characterized by low frequency magnetic lows associated with outcrops of mafic and ultramafic rocks of the Papuan Ultramafic belt (PUB). The magnetic signature of the OSF is a sharp contact separating the low frequency magnetic lows of the PUB from the high frequency magnetic highs associated with greenschist grade AUS metasediments and basalts. A similar aeromagnetic pattern is found on the Fergusson and Goodenough Island mccs. Low frequency magnetic lows occur on the north sides of the islands where mafic and serpentinized ultramafic rocks occur in the upper plates. The lower plates consist of gneisses, migmatites and eclogites, bounded by mylonitic shear zones, and intruded by magnetic granodiorites and volcanic rocks; these are characterized in general by high frequency magnetic highs. Reconstructions based on magnetic anomalies in the western Woodlark Basin agree with GPS crustal motion studies and predict sinistral motion along the OSF on the Papuan peninsula and extension in the D'Entrecasteaux Islands from the Pliocene to the Present. We interpret the southward decrease in metamorphic grade of AUS metasediments and basalts (i.e., eclogite to prehnite-pumpellyite facies) as regional isograds and infer that rifting has reactivated structures within a primary plate boundary. Major extensional shear zones exhumed previously subducted AUS crust from beneath mafic and ultramafic rocks of the PUB. This was accompanied by ascent of migmatitic crust, intrusion of granodiorite plutons and rift-related volcanism that variably reset mineral assemblages and thermochronometers as the Woodlark Basin spreading center rift tip propagated westward.
DE: 8109 Continental tectonics--extensional (0905)
DE: 8150 Plate boundary--general (3040)
DE: 8158 Plate motions--present and recent (3040)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 1517 Magnetic anomaly modeling
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting