HR: 17:15h
AN: U34A-06    [Abstracts]
TI: Izanagi-Pacific Ridge Subduction and its Geodynamic Consequences
AU: * Müller, R D
EM: dietmar@geosci.usyd.edu.au
AF: EarthByte Group, School of Geosciences, University of Sydney, Building H11, Codrington Street, University of Sydney, NSW 2006, Australia
AU: Whittaker, J M
EM: j.whittaker@geosci.usyd.edu.au
AF: EarthByte Group, School of Geosciences, University of Sydney, Building H11, Codrington Street, University of Sydney, NSW 2006, Australia
AU: Sdrolias, M
EM: marias@geosci.usyd.edu.au
AF: EarthByte Group, School of Geosciences, University of Sydney, Building H11, Codrington Street, University of Sydney, NSW 2006, Australia
AB: As part of a global plate tectonic model for 140 Ma to the present we present a revised plate reconstruction for the western Pacific and investigate its geodynamic consequences. In our plate model, mid-ocean ridge subduction beneath southern Japan occurs at 60-55 Ma, 20 million years later than proposed for Kula-Pacific or Farallon- Izanagi ridge subduction. The difference arises because Izanagi-Pacific (I-P) spreading ceases in previous models after 110 Ma while our model incorporates continued spreading until the I-P ridge subducts beneath eastern Asia at 60-55 Ma. We regard cessation of spreading at the I-P ridge between 110 and 80 Ma as unlikely as the Izanagi plate was undergoing rapid motion, driven by net slab-pull force, from the north-northwest, immediately prior to the proposed spreading cessation. Metamorphism of the Ryoke Belt in southern Japan has previously been attributed to Kula-Pacific ridge subduction at 85 Ma, but the high-T/low-P Ryoke Belt cannot be uniquely linked to a ridge subduction event. We propose that sub-parallel subduction of the I-P mid-ocean ridge beneath Japan at 60-55 Ma resulted in nearly simultaneous slab break-off along the length of the Japanese trench (approximately 2700 km). Geological evidence for this model includes cessation of a major accretion phase in the late Cretaceous, emplacement of the Okitsu Melange due to subduction of hot, buoyant material at 55 Ma, and cross-cutting fault fabrics that indicate a counter-clockwise rotation in relative plate motions between Eurasia and the I-P plate, consistent with palaeothermal and palaeopressure data, some time between 55 and 34 Ma. Rapid subduction of the I-P ridge, over a vast distance, may have triggered a chain reaction of tectonic plate reorganizations. With complete subduction of the I-P ridge at 55 Ma, forces acting on the western edge of the Pacific Plate would have changed from ridge-push to slab pull, changing Pacific absolute plate motions from northwest to west. A combination of Australian and Pacific plate motion changes between 53 Ma and 50 Ma then initiated both the Tonga-Kermadec subduction system and the Izu-Bonin-Marianas subduction systems around 50Ma, likely due to convergence across a fracture zone caused by the Pacific plate motion change. We suggest that the observed slowdown of sub-Pacific mantle flow at 47 Ma was due to progressive impediment of lateral sub-Pacific mantle flow by the descending slabs of the Izu-Bonin-Marianas and Tonga-Kermadec subduction zones.
DE: 1532 Reference fields: regional, global
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8157 Plate motions: past (3040)
SC: Union [U]
MN: 2007 Fall Meeting