HR: 1340h
AN: T33B-1347    [Abstracts]
TI: From Basalt to Dacite: Examining Magmatic Evolution at the 9° 03'N Overlapping Spreading Center, East Pacific Rise
AU: * Wanless, D
EM: dorseyw@ufl.edu
AF: Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, United States
AU: Perfit, M
EM: perfit@geology.ufl.edu
AF: Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, United States
AU: Ridley, W I
EM: iridley@usgs.gov
AF: U.S.G.S., Denver Federal Center Box 25046, MS 973, Denver, CO 80225, United States
AU: Klein, E
EM: ek4@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AU: Zaino, A
EM: ajz20@duke.edu
AF: Nicholas School of the Environment and Earth Sciences, Duke University, Box 90328, Durham, NC 27708, United States
AB: Over 280 rock samples were collected in the spring of 2007 from the 9°03' N Overlapping Spreading Center (OSC) using the ROV Jason II. This was done in combination with an extensive DSL 120A side-scan sonar survey, providing one of the most detailed sampling suites from an OSC. The site was also the focus of past geophysical studies that indicated the presence of an extensive magma lens in the region. Lava geochemistry at 9°03' N covers a wide range of compositions (Mg# from 17 to 56), including evolved MORB, FeTi basalts, andesites, and dacites (~67 wt% SiO₂). The diversity in composition at the OSC appears to be related to geologic setting of the erupted lavas, shallow magma chamber processes, and variations in magma supply. The 9°03' N OSC can be divided into three main sections: the eastern limb propagating southward, the western receding limb, and an overlap basin separating the two limbs. Lavas erupted within the neovolcanic zone on the eastern limb span the range of compositions erupted at the OSC (7.29 to 0.67 wt% MgO), while those erupted over the northern portion of the overlap basin are more limited in composition (6.47 to 7.23 wt% MgO). Preliminary results suggest that the on-axis major element variations may be due to mixing of evolved MORB and a silica-rich melt beneath eastern limb axis. Magma mixing is also supported by petrographic and macroscopic textural observations. Eruptions on the southern tip of the east limb, which is propagating into cold crust, are more primitive in composition and contain large phenocrysts suggesting that both thermal conditions in the crust and low magma supply may be important factors in the magmatic evolution. The phenocryst abundance and composition of lavas erupted on the dying western limb may also be related to similar factors.
DE: 1036 Magma chamber processes (3618)
DE: 1065 Major and trace element geochemistry
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 3075 Submarine tectonics and volcanism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting