HR: 14:35h
AN: V33F-04    [Abstracts]
TI: Simple Models of Melting and Trace Element Transport in Subduction Zones
AU: * Cagnioncle, A
EM: amandine@brown.edu
AF: Brown University, Dept. Geological Sciences Brown University 324 Brook St, Providence, RI 02912, United States
AU: Parmentier, E
EM: em_parmentier@brown.edu
AF: Brown University, Dept. Geological Sciences Brown University 324 Brook St, Providence, RI 02912, United States
AU: Saal, A
EM: alberto_saal@brown.edu
AF: Brown University, Dept. Geological Sciences Brown University 324 Brook St, Providence, RI 02912, United States
AU: Kelemen, P
EM: peterk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, PO Box 1000 61 Route 9W, Palisades, NY 10964, United States
AB: Melting at subduction zones has been recognized as a combination of dry decompression melting and wet melting. This study focuses on 2D models in which hydrous fluids released by slab dehydration reactions rise into the wedge by porous flow to provoke melting following the numerical models of Cagnioncle et al. [2007]. In these models, melting is parameterized according to MELTS [Hirschmann et al., 1999] and therefore depends on pressure, temperature, water fraction and degree of depletion. Depletion is in turn influenced by solid flow which dictates the rate at which fertile material is brought into the melting region. Solid flow thereby plays an important role in determining both melt production rates and the extent of melting. Transitions from an oceanic-oceanic to an oceanic-continental subduction are good locations to investigate the influence of solid flow on melting because they significantly alter solid flow: indeed, the increase in crustal lid thicknesses associated with the presence of a continent may reduce solid flow relative to the amount of water released by the slab and influence the relative contributions of flux and decompression melting. Trace elements concentrations in arc lavas provide a good indication of melting behavior in the wedge and have long been used to help understand the respective contributions from the slab, sediments and the mantle. However, in the past, models used to interpret trace element patterns have focused on melting processes (batch melting, fractional melting, or hybrid models of these two end members) and have not taken into account the fluid dynamics of melt transport. This study therefore also investigates the influence of melting and melt migration on stable trace element geochemistry in an open system. We vary the lid thickness in our temperature-dependent viscosity thermal models and examine the variations both in the degree of melting and trace element concentrations. Two end-member trace element transport behaviors are studied: equilibrium transport in which the melt completely equilibrates with the solid as it percolates from its source and which is therefore equivalent to batch melting; and disequilibrium transport in which melt is locally in equilibrium with the matrix and is thereby similar to fractional melting. We concentrate on the contribution from the solid source to trace element patterns and compare the resulting trace element concentrations of the aggregated melt to those of subduction zones which transition from an oceanic to a continental setting (e.g. Aleutians/Alaska Peninsula, Tonga).
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1065 Major and trace element geochemistry
DE: 3060 Subduction zone processes (1031, 3613, 8170, 8413)
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting