HR: 08:15h
AN: V51G-02    [Abstracts]
TI: Trace element constraints on the origin of subduction components in the Eastern Lau Back- arc Spreading Center
AU: * Bezos, A
EM: antoine.bezos@univ-nantes.fr
AF: Harvard University, Earth and Planetary Sciences, 20 oxford street, Cambridge, MA 02139, United States
AU: * Bezos, A
EM: antoine.bezos@univ-nantes.fr
AF: Universite de Nantes, LPGN, 2 rue de la houssiniere, Nantes, 44322, France
AU: Escrig, S
AF: Harvard University, Earth and Planetary Sciences, 20 oxford street, Cambridge, MA 02139, United States
AU: Langmuir, C H
AF: Harvard University, Earth and Planetary Sciences, 20 oxford street, Cambridge, MA 02139, United States
AU: Michael, P J
AF: University of Tulsa, Department of Geosciences, 600 S.College Ave., Tulsa, OK 74104, United States
AU: Asimow, P D
AF: Caltech, Geological & Planetary Sciences, Passadena, CA 91125, United States
AB: Back-arc basin basalts display a unique and wide spectrum of chemical compositions ranging from depleted to enriched mid-oceanic ridge basalts to island arc basalts. The general explanation has been to relate the arc component to the "subduction input" and mantle enrichments as observed in mid-oceanic ridges (E-MORB) to old, pre-existing mantle compositions that flow into the mantle wedge. Melting has also generally been evaluated using the assumption of immobility of high field strength elements (HFSE) in subduction components, from which mobile elements systematics have been evaluated. A new and comprehensive geochemical data set on closely spaced samples from the Eastern Lau Spreading Center (ESLC) provides new perspectives on these issues. Here we emphasize the northern ELSC, where samples with a large range of water contents and factor of five variations in trace element abundances occur over a along a single ridge segment. Based on the trace elements systematics, there are two well-defined enriched components that occupy two distinct portions of the segment along-axis. The southern magmatic province is influenced by a water-rich component (wet component) that has strong affinities with island arc-like volcanism. The most enriched and depleted samples occur on a single segment within hundreds of meters of each other, requiring their generation from a single melting regime. The northern magmatic province is influenced by a component that has intermediate water content (damp component) and geochemical affinities with both E-MORB and island arc basalts. Trace elements inversion from the wet component samples indicates that the water-rich subduction fluids significantly mobilize HFSE, light rare earth elements (REE) and Y. The least affected elements are the heavy REE, and lutetium provides the best estimates of extent of melting to evaluate source component compositions. Using the observed linear correlations of water vs. other elements in the source, chemical compositions of both damp and wet components can be determined assuming the water content. The chemical variations and modeling suggest systematic and coupled relationships between a water-rich subduction fluid and a low-degree melt component that is consistent with melting of recycled eclogite or mantle peridotite. Mixing processes between these two components account well for the chemical diversity of the subduction components (wet and damp) observed in N-ELSC. We propose a model where mixing processes occur at depth in the subduction zone and where both components are derived from the subduction process and added to the back arc region via mantle diapirism. This model may apply generally in back-arc settings, and explain the common occurrence of "E-MORB" like components in this environment.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting