Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids

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Serval ID
serval:BIB_88E7FF344237
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids
Journal
Contributions to Mineralogy and Petrology
Author(s)
Alonso-Perez R., Muntener O., Ulmer P.
ISSN-L
0010-7999
Publication state
Published
Issued date
2009
Peer-reviewed
Oui
Volume
157
Pages
541-558
Language
english
Abstract
To evaluate the role of garnet and amphibole fractionation at conditions relevant for the crystallization of magmas in the roots of island arcs, a series of experiments were performed on a synthetic andesite at conditions ranging from 0.8 to 1.2 GPa, 800-1,000 degrees C and variable H2O contents. At water undersaturated conditions and fO(2) established around QFM, garnet has a wide stability field. At 1.2 GPa garnet ? amphibole are the high-temperature liquidus phases followed by plagioclase at lower temperature. Clinopyroxene reaches its maximal stability at H2O-contents <= 9 wt% at 950 degrees C and is replaced by amphibole at lower temperature. The slopes of the plagioclase-in boundaries are moderately negative in T-XH2O space. At 0.8 GPa, garnet is stable at magmatic H2O contents exceeding 8 wt% and is replaced by spinel at decreasing dissolved H2O. The liquids formed by crystallization evolve through continuous silica increase from andesite to dacite and rhyolite for the 1.2 GPa series, but show substantial enrichment in FeO/MgO for the 0.8 GPa series related to the contrasting roles of garnet and amphibole in fractionating Fe-Mg in derivative liquids. Our experiments indicate that the stability of igneous garnet increases with increasing dissolved H2O in silicate liquids and is thus likely to affect trace element compositions of H2O-rich derivative arc volcanic rocks by fractionation. Garnet-controlled trace element ratios cannot be used as a proxy
Open Access
Yes
Create date
18/04/2009 0:56
Last modification date
01/10/2019 7:18
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