HR: 0830h
AN: V11E-0538    [PDF]
TI: A Geochemical Investigation of the Woodlark Spreading Center-Solomon Islands Arc Triple Junction
AU: Grimm, C
EM: siliciclaire@yahoo.com
AF: Idaho State University, Dept. of Geosciences, Pocatello, ID 83209 United States
AU: * Chadwick, J
EM: chadjohn@isu.edu
AF: Idaho State University, Dept. of Geosciences, Pocatello, ID 83209 United States
AU: Perfit, M
EM: perfit@geology.ufl.edu
AF: University of Florida, Dept. of Geological Sciences, Gainesville, FL 32611 United States
AB: The triple junction formed by the subduction of the Woodlark spreading ridge beneath the Solomon Islands arc (New Britain and San Cristobal trenches) is an area of tectonic, volcanic, and geochemical complexity. Anomalous volcanism along the Simbo and Ghizo ridges and the presence of numerous arcuate faults near the triple junction suggest the area is under extreme tectonic stress, and the absence of a deep trench or strong Benioff zone beneath the New Georgia Group (NGG) of the Solomon Islands suggests that subduction is being stifled by the impingement of the high-standing ridge on the trench. The tectonic effects of the ridge collision may have also led to NGG volcanic activity, including the currently active Kavachi volcano, which is anomalously close to the trench (30 - 90 km) in what would normally be considered the forearc region. A previous episode of Pacific Plate subduction, prior to the current subduction of the Australian Plate, may have geochemically enriched the mantle beneath the triple junction. To identify the source(s) of enrichment for the arc-like lavas in the study area, major and trace element concentrations and radiogenic isotopic ratios for rocks from the NGG and Woodlark Ridge have been analyzed. NGG lavas are generally more enriched in LILE and LREE relative to Woodlark lavas for a given silica content, and Woodlark Basin lavas become progressively less enriched with distance from the triple junction. Different trends in correlations between Sr and Nd isotopic ratios with trace element concentrations suggest that NGG and Woodlark Basin magmas were enriched by different sources. NGG enrichments may have been supplemented by partial melts from the subducting Australian Plate, as they exhibit enrichments in HFSE and depletions in HREE and Y. The subducting Australian Plate is young ($<$6 my) and hot, which may allow it to partially melt at relatively shallow depths.
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
DE: 8434 Magma migration
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting