HR: 1330h
AN: T32A-0902    [PDF]
TI: Detailed analysis of the spreading history of the Parece Vela and Shikoku Basins: Implications for Philippine Plate Rotation
AU: * Roest, W R
EM: wroest@ifremer.fr
AF: Department of Marine Geosciences IFREMER, BP 70, Plouzane, 29280 France
AU: Sdrolias, M
EM: marias@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science University of Sydney, Edgeworth David Building F05, Sydney, NSW 2006 Australia
AU: Mueller, R D
EM: dietmar@geosci.usyd.edu.au
AF: University of Sydney Institute of Marine Science University of Sydney, Edgeworth David Building F05, Sydney, NSW 2006 Australia
AB: The Philippine plate, located between the Pacific and Eurasian plates, is the world's largest marginal basin plate. Its motion history is poorly understood as it is almost entirely surrounded by subduction zones. Hence, the rotation of the Philippine plate through time has only been constrained by palaeomagnetic data, and estimated to be 34 degree clockwise between 25 and 5 Ma . Here, we present a comprehensive analysis of geophysical data from two Oligocene to Miocene back-arc basins, the Parece Vela and the Shikoku Basin, located along the eastern margin of the Philippine Plate. By means of their seafloor spreading record, these basins provide independent constraints on the rotational history of the Philippine Plate. Our detailed plate model is based on a joint analysis of all available magnetic, gravity and bathymetric data in the region. Subduction occurred along the proto-Izu-Bonin-Mariana trench and led to trench roll-back, arc rupture and back-arc rifting in the Parece Vela and Shikoku Basins at ~30 Ma. A northward and southward propagating rift developed from the extremities of the basin inward, and seafloor spreading in both basins developed by chron 9 (28 Ma) and possibly by chron 10 (29 Ma). The spreading orientation in the Parece Vela Basin was initially E-W, as opposed to ENE-WSW spreading in the Shikoku Basin. The ridges joined by chron 6B (23 Ma) and formed a R-R-R triple junction to accommodate the difference in spreading orientations in both basins. At approximately 20 Ma, the direction of spreading in both basins changed dramatically, from E-W to NE-SW in the Parece Vela Basin and from ENE-WSW to NE-SW in the Shikoku Basin. This change was accompanied by a marked decrease in spreading rate. Cessation of back-arc opening occurred at ~15 Ma, a time of regional plate reorganisation. The dramatic change in spreading rate and direction at ~20 Ma is interpreted to be an expression of Philippine plate rotation, a rotation which was previously thought to have occurred at 25 Ma as a result of a global change in plate motions. Our results suggest that the Philippine Plate rotated clockwise by about 4 degrees between 20-15 Ma about a pole located 35oN, 84oE. This implies that most of the 34 degree clockwise rotation inferred from paleomagnetic data to have occurred between 25 and 5 Ma may have been confined to the period between 15 and 5 Ma. The mechanisms that drive this rotation remain uncertain, but we speculate that changing boundary conditions result in edge driven rotation.
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8155 Plate motions--general
DE: 9355 Pacific Ocean
SC: Tectonophysics [T]
MN: 2003 Fall Meeting