HR: 0830h
AN: T51F-0220    [PDF]
TI: Back-arc Basins: Spreading and Convergence History
AU: M\"{u}ller, R
EM: dietmar@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science, Building F05 University of Sydney, Sydney, NSW 2006 Australia
AU: * Sdrolias, M
EM: marias@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science, Building F05 University of Sydney, Sydney, NSW 2006 Australia
AB: Back-arc basins are regions of extension between the active and remnant volcanic arc in a subduction zone setting. Although subduction is a necessary condition for the formation of back-arc basins, not all subduction zones have an associated back-arc basin at all times. A relationship between the presence/absence of back-arc spreading and the motion of the downgoing plate has previously been proposed but this relationship has not been tested in light of new plate reconstruction constraints. We present global plate reconstructions for the past 60 m.y as a series of palaeo-agegrids based upon an updated global isochron and rotation file. Our reconstructions include a revised absolute plate motion model based on moving hotspots, an improved convergence history at the circum-Pacific subduction zones due to the inclusion of East-West Antarctica motion in the global plate circuit and a globally consistent set of magnetic anomaly identifications in back-arc basins. The palaeo-agegrids also provide a reconstructed age distribution of the subducted oceanic lithosphere. The spreading history in back-arc basins is examined together with the absolute plate motion of the downgoing and over-riding plates to compute the roll-back of the subduction hinge. Our results from the seafloor spreading record in back-arc basins suggests that: (1)Spreading is episodic. There are gaps of several million years between the cessation of spreading in one back-arc basin and initiation of the next. (2)There is a high ratio of spreading centres to surface area in each back-arc basin with numerous examples of triple junctions and ridge jumps. (3)Spreading in the back-arcs record changes in regional plate configurations. Changes in the spreading directions and cessation of spreading in back-arc basins, as well as changes in convergence vectors, can be correlated with regional changes in plate motions. Further work on integrating absolute plate motion models and subduction hinge roll-back with mantle convection models will improve our knowledge on the mechanisms behind back-arc basin formation.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8150 Plate boundary--general (3040)
DE: 8157 Plate motions--past (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting