HR: 16:00h
AN: T44C-01 INVITED    [Abstracts]
TI: Geochemical studies of the Izu-Bonin-Mariana subduction system: highlights, progress and future directions
AU: * Shaw, A M
EM: ashaw@whoi.edu
AF: Geology and Geophysics Dept., WHOI, Woods Hole, MA 02543, United States
AU: Hauri, E H
EM: hauri@dtm.ciw.edu
AF: DTM, Carnegie Institution of Washington, Washington, DC 20015, United States
AU: Fischer, T P
EM: fischer@unm.edu
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, United States
AU: Hilton, D R
EM: drhilton@ucsd.edu
AF: SIO, UCSD, La Jolla, CA 92039, United States
AU: Stern, R J
EM: rjstern@utdallas.edu
AF: Dept. of Geosciences, University of Texas at Dallas, Richardson, TX 75083, United States
AB: Significant progress has been made over the last few years in understanding the source of subduction-related melts and the efficiency of recycling processes at both the Central American and Izu-Bonin-Mariana (IBM) margins. These arc systems have distinct physical and geochemical characteristics, which influences how slab- derived components are fluxed through their respective subduction factories. Here we report results from our recent and ongoing melt inclusion studies in the IBM system. However, our presentation will also highlight geochemical studies presented at this year's joint NSF-MARGINS and IFREE IBM workshop. We present volatile, major and trace element data for olivine-hosted melt inclusions from several subaerial and submarine volcanoes within the Izu-Bonin-Mariana subduction zone system. The aim of this work is to quantitatively assess how volatiles are cycled through the IBM subduction system and evaluate their relationship to physical subduction parameters and geochemical slab tracers. Our results show significantly higher CO₂ contents in the cross chain samples (i.e., from volcanoes located behind the volcanic front and trending across the arc) as compared to the arc front samples, suggesting either enhanced decarbonation at depth, or that the cross chain samples have experienced less degassing. We find large variations in water contents along the arc system from 0.2 wt% at Maug volcano up to close to 6 wt% at NW Rota, Agrigan and Nijima volcanoes. Ongoing studies examining the dehydration process across the arc show that high water contents in the cross chain samples show similar values to the arc-front samples, suggesting that volatile release is a continuous process across the arc. This finding is consistent with experimental results ¹ and melt inclusion studies across the Central American arc ². Intriguingly, our data set shows a strong decoupling of water and slab fluid tracers such as Ba/La and B contents. The highest water contents are not found in samples with the highest Ba/La or B contents. The IBM system is therefore distinctly different from the Central American system where these simple relationships seem to hold ³; this implies that either the source of IBM fluids is different or there are key differences in the dehydration/melting regime in IBM as compared to Central America. ¹Schmidt and Poli (1998) EPSL 163, 361–379 ²Walker et al. (2003) Contrib. Mineral. Petrol. 146, 62-77 ³Wade et al., in prep.
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting