A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

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Serval ID
serval:BIB_F8E029D98F94
Type
Article: article from journal or magazin.
Collection
Publications
Institution
Title
A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)
Journal
Contributions to Mineralogy and Petrology
Author(s)
Dessimoz M., Muntener O., Ulmer P.
ISSN-L
0010-7999
Publication state
Published
Issued date
2012
Peer-reviewed
Oui
Volume
163
Pages
567-576
Language
english
Abstract
Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U. S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of similar to 1.0 GPa followed by isobaric cooling to 700 degrees C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite.
Open Access
Yes
Create date
28/09/2012 22:41
Last modification date
01/10/2019 7:20
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