HR: 1330h
AN: T53A-12    [Abstracts]
TI: The rifting to spreading transition in the Central Mariana Trough
AU: * Faerber, R D
EM: faerb001@bama.ua.edu
AF: Department of Geological Sciences, University of Alabama,
AU: Goodliffe, A M
AF: Department of Geological Sciences, University of Alabama,
AU: Taylor, B
AF: SOEST, University of Hawaii,
AU: Klemperer, S L
AF: Department of Geophysics, Stanford University,
AB: The Mariana backarc basin is an actively opening basin in the western Pacific formed by the rifting of an earlier arc massif at about 6 Ma and subsequent seafloor spreading beginning at about 3-4 Ma. Bordered to the east by the active Mariana Arc and to the west by the remnant Mariana Ridge, the basin is 250 km wide at its widest at 18⁰ north. In 2002, a marine geophysical survey on the R/V Maurice Ewing (EW0202 and EW0203) to study the MARGINS subduction factory in the area between 14-19⁰ north and 141-149⁰ east, included a portion of the conjugate backarc margins. Concurrent multi-channel seismic reflection, gravity, magnetics, and multibeam bathymetry data were collected during the cruises. The objective of this study is to create an image of the seafloor and sub-seafloor in order to characterize the location and describe the nature of the transition between rifted arc crust and newly accreted oceanic crust. Seismic profiles across the western margin of the basin, where sediment cover is thin, show an abrupt transition from rifting to seafloor spreading. This transition appears to take place over as little as one (shallow angle) normal fault spanning a distance of about 3 km. On the eastern margin, where sediment from the active arc blankets the seafloor, the nature of the transition is less clear in the seismic data, but it is apparent that it takes place over a much greater distance. Magnetic and isostatically balanced gravity models provide insights into the crustal structure and first order compositional changes across both margins. Magnetic modeling differentiates the highly magnetized oceanic crust from relatively poorly magnetized rifted arc crust. We present detailed cross-sectional models across both the eastern and western margins. Combining these geophysical methods provides a powerful tool for locating the transition from rifted arc crust to seafloor spreading.
DE: 3025 Marine seismics (0935)
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 8105 Continental margins and sedimentary basins
DE: 8109 Continental tectonics--extensional (0905)
DE: 9355 Pacific Ocean
SC: Tectonophysics [T]
MN: 2005 Joint Assembly