HR: 08:30h
AN: T51A-01    [Abstracts]
TI: Non-volcanic rifting: New processes and new materials
AU: * Sawyer, D S
EM: dale@rice.edu
AF: Rice University, 6100 Main St., Houston, TX 77005 United States
AB: The study of non-volcanic rifting of continental lithosphere to form new oceans is encountering a number of new processes and new materials. It is now well established that upper mantle peridotite has been exposed at the seafloor during rifting. This exposure seems to have occurred by processes similar to the exposure of middle and lower crustal rocks in metamorphic core complexes and the exposure of upper mantle rocks, "oceanic megamullions," at slow spreading mid-ocean ridges. The serpentinization of this peridotite, both where it is exposed and where it underlies extending continental crust, creates a "slippery" surface for possible low-angle normal faults to operate. The serpentinized material may also behave in a diapiric fashion to create ridges and other seafloor topography. These new materials, beyond the "normal oceanic crust" and "normal continental crust" that we used to talk about, make the task of identifying an "ocean-continent" boundary increasingly difficult, and probably irrelevant. Rifting seems to create a continuum of oceanic and continental processes, whose details no doubt vary from margin to margin. Our effort needs to focus on understanding these processes. Non-volcanic rifted margins are potential laboratories for studying progressive rifting of continental crust. We see clear examples of tilted fault blocks that have been cut by a second generation of faults. The earlier generation of faults created larger tilted fault blocks with the bounding faults soling in the middle crust. The next generation of faults cut to the crust mantle boundary and bound smaller fault blocks. Unraveling the history of faulting and deformation in these environments awaits the availability of modern 3D seismic reflection data. These data will give us the capability to correlate stratigraphy from basin to basin around the ends of the tilted fault blocks, and hence to get relative dates on the formation of the individual faults. These data will give us 3D constraint on the shape of the faults and fault bounded blocks. Palinspastic restoration of these will help us understand the large scale deformation of the margin.
DE: 8109 Continental tectonics--extensional (0905)
SC: Tectonophysics [T]
MN: 2005 Joint Assembly