HR: 17:00h
AN: T44C-05 INVITED    [Abstracts]
TI: An Overview of Volatile and Isotopic Variations Along the Central American Volcanic Front
AU: * Hoernle, K
EM: khoernle@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: * Hoernle, K
EM: khoernle@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Insitute of Marine Sciences, Kiel, 24148, Germany
AU: Portnyagin, M
EM: mportnyagin@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Insitute of Marine Sciences, Kiel, 24148, Germany
AU: Wehrmann, H
EM: hwehrman@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Heydolph, K
EM: kheydolph@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Kutterolf, S
EM: skutterolf@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Freundt, A
EM: afreundt@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Freundt, A
EM: afreundt@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Insitute of Marine Sciences, Kiel, 24148, Germany
AU: Abt, D
EM: DavidAbt@brown.edu
AF: Dept. of Geological Sciences, Brown Univ., Providence, RI 02906, United States
AU: Fischer, K
EM: KarenFischer@brown.edu
AF: Dept. of Geological Sciences, Brown Univ., Providence, RI 02906, United States
AU: Grevemeyer, I
EM: igreveme@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Grevemeyer, I
EM: igreveme@ifm-geomar.de
AF: IFM-GEOMAR, Leibniz Insitute of Marine Sciences, Kiel, 24148, Germany
AU: Ivandic, M
EM: mivandic@ifm-geomar.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Rabbel, W
EM: rabbel@geophysik.uni-kiel.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Thorwart, M
EM: thorwart@geophysik.uni-kiel.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AU: Dinc-Akdogan, N
EM: nilay@geophysik.uni-kiel.de
AF: Collaborative Research Center (SFB574), Christian Albrechts Univ., Kiel, 24148, Germany
AB: An overview of the volatile (H2O, CO2, S, halogens) and isotopic (Sr-Nd-Pb-Hf) variations along the Central American volcanic front and preferred explanations of their origin will be presented. Volatile data from 1200 melt inclusions in olivine, pyroxene and feldspar phenocrysts from Central American mafic through felsic rocks provide an unprecedented picture of volatile cycling through subduction zones. In primitive olivine-hosted melt inclusions from Central America, H2O and CO2 show maxima and S, Cl and F minima in Nicaraguan samples. In evolved melt inclusions in pyroxene and feldspar, F shows a maxima in Nicaragua and Cl shows a systemic decrease from Costa Rica to Guatemala. As suggested by previous studies, the high water contents in Nicaraguan magmas are likely to reflect the greatest dehydration of serpentinite where the downgoing slab is deepest beneath the volcanic front. Seismic data indicate that serpentinite is indeed present in the incoming plate outboard of Nicaragua and that the mantle beneath Nicaragua may contain more water-rich melts than beneath Costa Rica. High CO2 content in primitive melt inclusions from Nicaragua and the rear arc (Walker et al., 2003, CMP, 146:62-77) may reflect greater decarbonation with increasing depth of the subducting slab and/or greater degassing of volcanic front melts from Costa Rica and Guatemala. Volatile fluxes estimated for mafic Central American melts are similar to global arc averages (Wallace, 2005, JVGR 140:217- 240). Systematic variations in isotope geochemistry occur along the volcanic front in Central America from Costa Rica to Guatemala: Sr, Nd and Hf isotope ratios display maxima and Pb isotopes a minima in Nicaragua. Highest Sr isotope ratios in Nicaragua may be related to the dehydration of serpentinites in the subducting plate beneath Nicaragua. The systematic variation in isotope ratios from central Costa Rica to NW Nicaragua and the lead isotope geochemistry of Costa Rica volcanic rocks can be explained through addition of fluids/melts from the subducting seamount province of the Galapagos hotspot track to the mantle wedge beneath central Costa Rica and flow of this mantle beneath NW Nicaragua. Seismic velocity anisotropy provides additional support for an arc- parallel component of flow in the mantle wedge beneath the Costa Rican and Nicaraguan volcanic fronts. A decrease in Nd and Hf isotopic composition in the volcanic front from NW Nicaragua to NW Guatemala cannot be explained by addition of sediment melts to the source or crustal assimilation and therefore most likely reflect the increasing contribution of an enriched component located in the mantle wedge (possibly lithospheric mantle) to the melts.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1040 Radiogenic isotope geochemistry
DE: 1043 Fluid and melt inclusion geochemistry
SC: Tectonophysics [T]
MN: 2007 Fall Meeting