HR: 15:25h
AN: V43E-08    [Abstracts]
TI: Geochemical study of lavas and sub-arc xenoliths from TLTF island chain, SW Pacific Ocean: deciphering magma sources in an island arc environment
AU: * Kamenov, G D
EM: kamenov@ufl.edu
AF: University of Florida, Dept. of Geol. Sciences, Gainesville, FL 32611 United States
AU: Perfit, M R
EM: perfit@geology.ufl.edu
AF: University of Florida, Dept. of Geol. Sciences, Gainesville, FL 32611 United States
AU: Mueller, P A
EM: mueller@gelogy.ufl.edu
AF: University of Florida, Dept. of Geol. Sciences, Gainesville, FL 32611 United States
AU: Jonassson, I R
EM: IJonasso@NRCan.gc.ca
AF: Geol. Survey of Canada, 601 Booth St., Ottawa, ON K1A OE8 Canada
AB: Numerous xenoliths recovered from TUBAF seamount in the Tabar-Lihir-Tanga-Feni (TLTF) island chain (SW Pacific) provide a unique view of the elemental and isotopic composition of the crust and mantle beneath the arc and its relationship to arc magmatism. The isotopic compositions of these xenoliths suggest at least 3 distinct geochemical components in the sub-arc mantle. Two of the components can be identified as Pacific oceanic mantle and Pacific sediments and the third component appears to be either Indian Ocean-type mantle or Australian subcontinental lithospheric mantle. Overall, these xenoliths exhibit a wide range of isotopic compositions compared to the the TLTF lavas suggesting that the underlying crust and metasomatized part of the mantle represented by the xenoliths did not play a major role in determining the trace element and isotopic characteristics of the magmas. The alkaline character of the lavas, their very high Sr content coupled with low 87Sr/86Sr, and their Pb isotopic signature suggest that the magmas were derived from a source similar to altered Pacific oceanic crust with a possible minor subducted sediment contribution. Tectonic considerations indicate the presence of a previoulsy subducted slab (probably Cretaceous) that stalled beneath the TLTF chain around 10 Ma ago. Thermal conditions suitable for melting of that slab now exist and melt inclusions provide direct evidence for slab-melts. Dilution of the slab melt with small amount of depleted peridotitic component from the mantle wedge, followed by crystal fractionation will result in magmas with similar chemical characteristics to the TLTF lavas. In this scenario a major part of the arc edifice is constructed from the slab-melts.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 8185 Volcanic arcs
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005