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| Titel |
P-rich olivines in a melt vein of a composite mantle xenolith: implications for crystal growth and kinetics |
| VerfasserIn |
Ioannis Baziotis, Paul D. Asimow, Theodoros Ntaflos, Antonios Koroneos, Diego Perugini, Edward M. Stolper |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091280
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| Publikation (Nr.) |
 EGU/EGU2014-5564.pdf |
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| Zusammenfassung |
| The mineral chemistry of mantle xenoliths, and in particular the presence of phosphorus (P)
— a moderately incompatible and slowly diffusing element — may preserve the history of
mineral growth and constrain timescales of pre-eruption petrogenetic processes
(Boesenberg & Hewins 2010). P-rich zones in olivine may reflect incorporation of P in
excess of equilibrium partitioning during rapid growth, in which case zoning patterns
primarily record crystal growth rate variations (Milman-Barris et al. 2008; Stolper et al.
2009).
We investigated using EMP analyses and X-ray maps a composite amphibole-bearing,
mantle xenolith (sample: Ci-1-196) from Cima Volcanic Field (California, USA) that contains
second generation P-rich olivines. The xenolith contains multiple lherzolite, websterite, and
dunite layers. The host magma (not preserved in our hand-specimen) is thought to be a
hawaiite (Wilshire et al. 1988).
A thin (average ~200 μm width), dark layer is present along the contact between
lherzolite and websterite. Interpreted as a rapidly crystallized melt, this layer consists of
olivine + glass + plagioclase + spinel + clinopyroxene + apatite + ilmenite. The layer contains
olivines (Fo83-89.3) with 0.03-0.52 wt.% P2O5; the P-rich olivines (P2O5 >0.1 wt.%) are
Fo85 to Fo89.3. Apatite inclusions are present near the rim of P-rich olivine (Fo85)
and in plagioclase (An54).Glass is widespread (~15 vol.%) in the layer, having
variable composition with P2O5 up to 1.2 wt.%. Plagioclase occurs as prismatic,
flow-oriented crystals, parallel to the elongation of the layer or intergranular crystals
between olivine and/or clinopyroxene. Clinopyroxene formed either as crystallized
products within the melt layer or by reaction at the interface between melt and matrix
olivine. Spinel occurs as inclusions in the olivine or associated with plagioclase and
glass, showing anhedral shape and linear edges; spinel composition varies from
chromite to Ti-chromite from core to rim, with an outer rim rich in ulvöspinel.
Ilmenite occurs as idiomorphic crystals within the layer or as thin rims ( |
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