HR: 11:05h
AN: V52A-04    [Abstracts]
TI: Melts, Minerals and Inclusions: Unpacking Magmatism in the Sulu Ranges, New Britain Arc.
AU: * Edwards, L
EM: l.edwards4@pgrad.unimelb.edu.au
AF: School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia
AU: Danyushevsky, L
EM: l.dan@utas.edu.au
AF: Centre for Ore Deposit Research, University of Tasmania, Hobart, TAS 7001, Australia
AU: Hergt, J
EM: jhergt@unimelb.edu.au
AF: School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia
AU: Woodhead, J
EM: jdwood@unimelb.edu.au
AF: School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia
AB: The New Britain Arc, lying off the eastern coast of mainland Papua, New Guinea, offers a unique insight into the 3D chemical structure of an island arc. In addition to typical arc-front and limited rear-arc ranges observed in other convergent margin settings, sub-aerial volcanism in New Britain extends to 500km above the subducting slab. Previous studies of this unique record of Quaternary volcanism have revealed striking chemical trends related to the distance to the Benioff zone; however, these data are restricted to whole-rock analyses of a small "representative" sample set taken from across the whole arc. To further investigate these remarkable across arc trends, a detailed study of individual volcanoes in the New Britain Arc is required. The Sulu Ranges comprise a group of arc front volcanoes on the central north coast of New Britain. The suite of rocks analysed spans the compositional range from basalt through to rhyolite and samples are highly phyric (30- 40 percent phenocrysts by volume). Clinopyroxene and plagioclase feldspar phenocrysts are ubiquitous whereas olivine and orthopyroxene are observed in the most and least mafic samples, respectively. The Sulu Ranges therefore provide an unparalleled opportunity to investigate the effects of differentiation and accumulation on whole-rock chemistry in the New Britain Arc. Olivine-hosted melt inclusions, as well as olivine, pyroxene and plagioclase feldspar phenocrysts from the most primitive Sulu Ranges sample were analysed for major and trace element contents. Large variations in olivine, clinopyroxene and plagioclase feldspar compositions together with dissolution textures present throughout indicate that the observed phases cannot represent an equilibrium assemblage. The data arrays defined by bulk rock compositions cannot be explained by liquid lines of descent resulting from simple fractional crystallisation. Estimates of groundmass compositions are used to test the extent to which whole-rock compositions may be used as proxies for melt compositions, and how melt inclusions are related to macro-scale magmatic reservoirs.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 1065 Major and trace element geochemistry
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting