HR: 11:20h
AN: V41D-05    [PDF]
TI: A Plate Tectonic Scenario for the Formation of Intra-oceanic Magmatic Arcs and Associated Back-arc Basins
AU: * Sdrolias, M
EM: marias@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science, Building F05 Univeristy of Sydney, Sydney, NSW 2006 Australia
AU: M\"{u}ller, R
EM: dietmar@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science, Building F05 Univeristy of Sydney, Sydney, NSW 2006 Australia
AB: During prolonged periods of Mariana-type intra-oceanic subduction, a series of island arc and back-arc basins are formed on the over-riding plate. The remnant arc-back-arc-active arc sequence is particularly prevalent in the marginal seas of the Western Pacific, Scotia and Mediterranean Seas. The initiation, location and development of intra-oceanic island arcs are dependent, among other things, on the behaviour of the subduction zone (shape, orientation, roll-back) and on the properties of the subducted slab (age, dip, composition). We present reconstructions of the age distribution of the oceanic crust (including subducted oceanic crust) using a revised absolute plate motion model based on moving hotspots and including the motion between East and West Antarctica in the global plate circuit. Our plate reconstructions allow us to identify the tectonic conditions prior to, during and after subduction initiation and the subsequent development of the island arc and back-arc basin. Palaeo-agegrids provide valuable time-dependent information regarding the age of the subducting slab, the orientation of the MOR relative to the subduction hinge and the convergence rates and directions of the down-going plate. Our preliminary results on the intra-oceanic convergent margins of the SW Pacific, Philippine Sea and Scotia Sea suggest that: (1)The age of the downgoing slab when a back-arc basin is formed is never younger than 30 m.y. This provides an important constraint on the location of the Benioff zone through time. (2)The MOR and seafloor spreading isochrons on the downgoing plate are orthogonal to the strike of the subduction zone. (3)Changes in convergence rates between the downgoing and over-riding plates influence the spreading in the back-arc basin and as a result must influence island arc development. Linking geophysical observations and plate reconstructions with the volcanic history of island arcs will not only provide better constraints on the factors influencing magmatic arc formation but also on the entire remnant arc-back-arc-active arc sequence.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8150 Plate boundary--general (3040)
DE: 8157 Plate motions--past (3040)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting