HR: 08:00h
AN: T31F-01    [Abstracts]
TI: The Effect of Sedimentation on Extensional Style: Applications to the Gulf of California
AU: * Bialas, R W
EM: rbialas@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, United States
AU: Buck, W R
EM: buck@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, United States
AB: We examine the effect of deposition of large amounts of non-locally derived sediment on extensional style. Our model differs from previous work with sedimentation and extension as it does not erode material off of rift flanks but deposits material from a third, lateral dimension, in the manner of a prograding delta, making this what is sometimes referred to as a 2.5 dimensional model. Depending on initial model conditions the onset of rifting in thick continental crust occurs in either the narrow rifting, wide rifting, or core complex mode. With continued extension, all cases eventually transition to a narrow rifting mode. We proposed that the weight of the sediments reduces the crustal buoyancy effect caused by local crustal thinning, allowing the system to extend more easily in a narrow rift mode. Two dimensional, regional scale numerical experiments of extending a plateau, represented in the models as an area of thick continental crust surrounded by areas of crust with normal thickness, are used to test this hypothesis. During extension the sediments depress the extended crust and reduce the amount of crustal flow from the still thick edges. Simultaneously, the sediments thicken the thinned area, allowing for further extension. For a system in wide or core complex mode, sedimentation would shorten the time needed to transition to a narrow rift. Sedimentation rate, extension rate, the concentration of radiogenic elements, plateau width, plateau thickness, and sediment density were varied across a suite of models to examine under what conditions sedimentation can influence the mode of extension in this way. Results indicate that sedimentation must keep up with crustal thinning at a site of concentrated extension in order to shut down the lower crustal flow and transition to a narrow rift earlier than if no sedimentation were present. A comparison is made between the numerical and analytical results to seismic data from and the geological history of the Gulf of California, where a similar system may be unfolding today.
DE: 0545 Modeling (4255)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 8109 Continental tectonics: extensional (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting