HR: 1340h
AN: T13B-1357    [Abstracts]
TI: Structure of the Upper Crust Exposed at Endeavor Deep: Implications for Crustal Accretion at Ultra-Fast Spreading Rates
AU: * Popham, C T
EM: pophamc@gso.uri.edu
AF: Graduate School of Oceanography, Univeristy of Rhode Island, Box 200 S. Ferry Rd., Narragansett, RI 02882 United States
AU: Pockalny, R A
EM: robp@gso.uri.edu
AF: Graduate School of Oceanography, Univeristy of Rhode Island, Box 200 S. Ferry Rd., Narragansett, RI 02882 United States
AU: Larson, R L
EM: rlar@gso.uri.edu
AF: Graduate School of Oceanography, Univeristy of Rhode Island, Box 200 S. Ferry Rd., Narragansett, RI 02882 United States
AB: Endeavor Deep lies at the tip of the propagating spreading center defining the Juan Fernandez/Nazca plate boundary. This 3 km-deep, amagmatic basin,which rifted into ultra-fast spread 3Myr old Nazca Plate crust, was recently surveyed and sampled with Simrad EM300, DSL-120 and ROV Jason II. Over 140 structural orientations measured from Jason II video of the south rift wall show that flows in extrusive layer 2a strike north-south and dip shallowly to the west, while dikes in intrusive layer 2b strike east-west and dip steeply to the south. Using a general model for crustal accretion in which dikes are emplaced vertically and extrusives horizontally, a rotational history is determined for the 3 Myr old crust exposed in the walls of the deep. Multiple rotations are necessary with two-fold intent, first to return structure to the original off-axis orientation prior to tectonic reorganization; second to account for rotations involved in the process of accretion. Tectonic events are first addressed with a 10-25 degree rotation about a horizontal rift parallel axis to account for flexural uplift. Next a 65-degree rotation applied about a vertical axis to return magnetic lineation 2a to its proposed paleo-off axis orientation. After rotation, intrusive and extrusive populations are strike parallel (N5E). In this orientation, dikes average 65-degree dip away from and extrusives 25-degree dip towards the ridge axis. This generally conforms to observations at Hess deep, Blanco FZ, and ODP hole 801C. The second goal of rotation is to account for off axis adjustments during crustal accretion; a 25-degree rotation about a ridge parallel, horizontal axis returns the average dike inclination to vertical and the extrusive dip to horizontal.
DE: 8015 Local crustal structure
DE: 8020 Mechanics
DE: 3040 Plate tectonics (8150, 8155, 8157, 8158)
DE: 3045 Seafloor morphology and bottom photography
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting