HR: 1340h
AN: T33D-0588    [Abstracts]
TI: Internal Structure of Basaltic Lavas and Sheeted Dikes in 3 Ma Super-Fast EPR Crust Exposed at Pito Deep
AU: * Morgan, L A
EM: lindsay.morgan@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, NC 27708
AU: Karson, J A
EM: jkarson@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, NC 27708
AU: Hayman, N W
EM: hayman@duke.edu
AF: Division of Earth and Ocean Sciences, Duke University, Durham, NC 27708
AU: Varga, R J
EM: rvarga@wooster.edu
AF: Department of Geology, College of Wooster, Wooster, OH 44691
AU: Hurst, S D
EM: shurst@uiuc.edu
AF: Department of Geology, University of Illinois, Urbana, IL 61801
AB: Oceanic crust exposed by rifting near Pito Deep (Easter Microplate) was created at the EPR about 3 Ma ago at a super-fast spreading rate of 144 mm/yr. Direct observations, imaging and sampling with the submersible Alvin and ROV Jason II document the architecture of lavas and sheeted dikes and have important implications for crustal accretion processes at fast spreading ridges. Upslope transects spaced at about 300 m apart in two study areas show that the basaltic lavas range from about 300 to 500 m thick and are composed dominantly of pillow and lobate morphologies. Sheet flows are most voluminous in the lower part of the section but constitute about 20% of the lava pile. Near the top of the lava unit, flattening surfaces and interspersed sheet flows have inconsistent dips, generally less than 10°. Downward, lavas dip more persistently "inward" toward the EPR spreading axis at about 20°. The transition between lavas and dikes is typically 100 to 250 m thick and areas of tilted sheet flows and tilted dikes can be difficult to distinguish in this interval. The sheeted dike complex is spectacularly exposed both vertically and laterally and is typically 700 to 1000 m thick. The dikes are generally steeply dipping, in the range of 65° to 80°. Most dikes dip "outward" away from the EPR axis. Tilt domains in the lavas and dikes suggest a complex pattern of tilting resulting in vertical subsidence. Near vertical, crosscutting dikes strongly suggest that tilting and related subsidence occurred near the spreading center. The documented structure contrasts strongly with the much more complexly tilted and intensely fractured upper crustal structures found in other tectonic windows and deep drill holes in the Pacific region, most of which formed at significantly slower spreading rates. We interpret the upper crustal structure at Pito Deep to be the result of a high magma budget related to the super-fast spreading rate.
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
DE: 3641 Extrusive structures and rocks
DE: 3642 Intrusive structures and rocks
DE: 8012 High strain deformation zones
SC: Tectonophysics [T]
MN: Fall Meeting 2005