Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon

Journal Article · Fri Feb 01 00:00:00 EST 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90004-O· OSTI ID:5551818

La Tourrette, T Z; Burnett, D S ^[1]; Bacon, C R ^[2]

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1. California Inst. of Tech., Pasadena (USA)
2. Geological Survey, Menlo Park, CA (USA)

Crystal-liquid partitioning in Fe-Ti oxides and zircon was studied in partially melted granodiorite blocks ejected during the climactic eruption of Mt. Mazama (Crater Lake), Oregon. The blocks, which contain up to 33% rhyolite glass (75 wt% SiO{sub 2}), are interpreted to be portions of the magma chamber walls that were torn off during eruption. The glass is clear and well homogenized for all measured elements except Zr. Results for Fe-Ti oxides give D{sub U}{sup oxide/liq} {approx} 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are modestly well equilibrated with the melt for many of the minor elements, while those that are inclusions in relict plagioclase are not. Uranium and ytterbium inhomogeneities in zircons indicate that the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons have only partially equilibrated with the melt and that uranium appears to have been diffusing out of the zircons faster that the zircons were dissolving. Based on the authors measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractional during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in the authors samples. This demonstrates an actual case of nonequilibrium source retention of accessory phases, which in general could be an important trace element fractionation mechanism. Their results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites.

• OSTI ID: 5551818
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Vol. 55:2; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GRANODIORITES
GEOCHEMISTRY
PETROGENESIS
THORIUM
FRACTIONATION
URANIUM
CHEMICAL COMPOSITION
CRATERS
CRYSTALLIZATION
ERUPTION
GEOLOGIC HISTORY
GLASS
INCLUSIONS
IRON OXIDES
MAGMA
MINERALOGY
OREGON
ROCK-FLUID INTERACTIONS
TITANIUM OXIDES
VOLCANOES
ZIRCON
ACTINIDES
CAVITIES
CHALCOGENIDES
CHEMISTRY
DEVELOPED COUNTRIES
ELEMENTS
FEDERAL REGION X
GRANITES
IGNEOUS ROCKS
IRON COMPOUNDS
METALS
MINERALS
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
SEPARATION PROCESSES
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
ZIRCONIUM COMPOUNDS
ZIRCONIUM SILICATES
580000* - Geosciences