HR: 1340h
AN: T33D-0585    [Abstracts]
TI: Geochemical Variability of Dikes and Lavas Exposed in the Pito Deep
AU: * Pollock, M A
EM: map16@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708 United States
AU: Klein, E M
EM: ek4@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708 United States
AU: Karson, J A
EM: jkarson@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708 United States
AU: 2005 Scientific Party, P
T33D-0585 AF: Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708 United States
AB: The Pito Deep Rift (PD), located near the NE boundary of the Easter microplate, exposes vertical sections of ~3 Ma crust generated along the superfast-spreading (>140 mm/yr) East Pacific Rise. During the Pito Deep 2005 cruise, which investigated two major escarpments within the PD, detailed sampling along vertical and lateral transects through the lava and dike units were made with the Jason II ROV and Alvin submersible. The traverses, which were spaced <700 m apart and covered vertical distances up to 1400 m, recovered 131 samples in the lava sequence and 193 samples in the dike unit. The known geologic context of the extensive sample suite allows us to examine chemical variations across small (meter) and large (kilometer) spatial scales as well as explore possible relationships between chemical composition and physical characteristics, such as dike width and orientation. Initial geochemical analyses of a small subset of samples (39 dikes and 5 lavas) from one escarpment reveal that the dikes and lavas are normal mid-ocean ridge basalt (N-MORB; Zr/Y 2.3 to 3.5). As a whole, the samples show a wide range in compositional variability, particularly in terms of differentiation, extending from primitive to moderately evolved compositions (6.6 to 9.2 wt% MgO). Compared to dikes collected in the Hess Deep Rift (HD), a tectonic window in the eastern equatorial Pacific which exposes fast-spread (110 mm/yr) crust, the PD dikes are restricted to more primitive compositions (HD dikes range from 4.5 to 8.2 wt% MgO; Stewart et al., 2003). Closely spaced dikes, separated by short distances (<1m - 20 m), encompass much of the range of compositional variability shown by the entire sample suite; this finding is similar to the chemical relationships observed in the HD dikes, which led to an understanding of the significance of lateral dike propagation and along-axis transport of magma on fast-spreading ridges (Stewart et al., 2003). Additional analyses will provide further insights into processes of crustal accretion that generated this superfast-spread crust.
DE: 1021 Composition of the oceanic crust
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1065 Major and trace element geochemistry
DE: 3035 Midocean ridge processes
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
SC: Tectonophysics [T]
MN: Fall Meeting 2005