HR: 1340h
AN: T33D-0594    [Abstracts]
TI: Lithologic and structural observations at Endeavor Deep and their implications for the accretion process at fast to ultra-fast spreading rates.
AU: Larson, R L
EM: rlar@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Rd., Narragansett, RI 02882
AU: * Popham, C T
EM: pophamc@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Rd., Narragansett, RI 02882
AU: Pockalny, R A
EM: robp@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Box 200 South Ferry Rd., Narragansett, RI 02882
AB: The south wall of Endeavor Deep on the Juan Fernandez Microplate is a linear, 2-3km thick, steep-sided exposure of upper oceanic crust nearly 75km in length, and oriented roughly orthogonal to the original spreading direction. Recent investigation with the ROV Jason observed an intensely fractured extrusive section of extremely variable thickness (280-560m), overlying a 400-500 meter section where dikes and pillows/flows coexist, overlying an 100m section of sheeted dikes exposed amidst talus. This section is exposed across 4 vertical transects (and 2 following contour) covering 10 horizontal kilometers. The extreme variability of layer thicknesses along this outcrop hints at the variability of the fast to ultra-fast accretion process. The structural orientations of dikes and extrusives, when rotated back to an assumed paleo-ridge parallel orientation, are seen consistently rotated inward toward the ridge axis. The orientations of dikes are remarkably consistent within the limited exposure of the sheeted dike section and the more extensive exposure of the Transition Zone. Dikes are seen either individually or in swarms (<10 units) but are not generally seen in cross cutting relationships. Orientations from flows taken in the highly fractured extrusive section reveal mutually strike-parallel orientations with dikes, after removing subsequent flank uplift and vertical axis tectonic rotations. These findings agree with magnetic observations from the Blanco fracture zone and visual observations at Hess Deep of dipping polarity boundaries and rotated internal structures. These consistently rotated orientations of flows (dipping toward the ridge axis) and intrusives (dipping away from the ridge axis) appear to be an intrinsic property of the accretion process, where in a apparently fractured section of crust, a regular rotation pattern emerges within a state of controlled and consistent chaos.
DE: 8038 Regional crustal structure
DE: 8178 Tectonics and magmatism
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: Fall Meeting 2005