HR: 1340h
AN: V13A-1448    [Abstracts]
TI: The Role of Water in Arc Magmatism in Nicaragua and Costa Rica.
AU: * Sadofsky, S J
EM: ssadofsky@ifm-geomar.de
AF: SFB 574, University of Kiel and Leibniz Institute for Marine Sciences/IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: Hoernle, K
EM: khoernle@ifm-geomar.de
AF: SFB 574, University of Kiel and Leibniz Institute for Marine Sciences/IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148 Germany
AU: van den Bogaard, P
EM: pbogaard@ifm-geomar.de
AF: SFB 574, University of Kiel and Leibniz Institute for Marine Sciences/IFM-GEOMAR, Wischhofstr. 1-3, Kiel, D-24148 Germany
AB: The Central American Volcanic Arc provides an excellent opportunity to study the effect of varying subduction parameters on arc magma geochemistry. Here we examine melt inclusions trapped in olivine phenocrysts in young mafic tephras from the active arc segments in Nicaragua and Costa Rica. These segments of the subduction zone provide starkly contrasting situations with differing oceanic crustal input (East Pacific Rise vs. oceanic crust overprinted by the Galapagos hot spot) and slab dip ($\sim70\deg$ vs. $\sim30\deg$) in Nicaragua and Costa Rica respectively. We collected major-, trace-, and volatile-element concentration data from olivine-hosted (Fo$_{68-87})$ melt inclusions from volcanoes Cerro Negro, Nejapa, Masaya, and Mombacho along the volcanic front in central Nicaragua and Irazu and Arenal in Costa Rica. In Nicaragua H$_{2}$O shows a general increase with decreasing Fo of the host olivine, reflecting incompatible behavior during differentiation from 1-3 wt. $%$ in samples from Fo$_{>85}$ to $\sim 5%$ in some of the slightly more evolved, yet still relatively undegassed, samples. This is best illustrated by samples from Mombacho and Cerro Negro. Comparison of the major element data with experimental melting studies indicates that the Nicaraguan melts with higher FeO and lower SiO$_{2}$ (at similar MgO contents) could have formed at greater depths and temperatures in the presence of less water than the Costa Rican melts with higher SiO$_{2}$ and lower FeO. The most primitive samples from Irazu (host olivine Fo$_{84-89)}$ are extremely rich in H$_{2}$O (3-5 wt. $%$). H$_{2}$O enrichment correlates with enrichment of some LILE, LREE (i.e., Ba, La, K), relative to HFSE for most samples from the Nicaraguan volcanoes. S/Nb and Cl/Nb also show some correlation with H$_{2}$O/Nb in Nicaraguan samples, with some exceptions possibly related to volatile loss is the less primitive samples. These correlations are generally not present in the Costa Rican samples, thus suggesting that despite apparent larger initial water contents in Costa Rican magmas, many Nicaraguan trace element enrichments are derived mainly through input of hydrous fluids whereas Costa Rican trace element budgets may require additional processes.
DE: 3640 Igneous petrology
DE: 3655 Major element composition
DE: 3670 Minor and trace element composition
DE: 1030 Geochemical cycles (0330)
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting