CaltechAUTHORS
  A Caltech Library Service

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

La Tourrette, T. Z. and Burnett, D. S. and Bacon, Charles R. (1991) Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon. Geochimica et Cosmochimica Acta, 55 (2). pp. 457-469. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20150427-094750631

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20150427-094750631

Abstract

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_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 DU^(oxide/liq) ≈ 0.1. Partitioning of Mg, Mn, Al, Si, V, and Cr in Fe-Ti oxides indicates that grains surrounded by glass are moderately 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 faster than the zircons were dissolving. Minimum U, Y, and P concentrations in zircons give maximum DU^(zrc/liq) = 13,DY^(zrc/liq) = 23, and DP^(zrc/liq) = 1, but these are considerably lower than reported by other workers for U and Y. Based on our measurements and given their low abundances in most rocks, Fe-Ti oxides probably do not play a major role in U-Th fractionation during partial melting. The partial melts were undersaturated with zircon and apatite, but both phases are present in our samples. This demonstrates an actual case of non-equilibrium source retention of accessory phases, which in general could be an important trace-element fractionation mechanism. Our results do not support the hypothesis that liquid structure is the dominant factor controlling trace-element partitioning in high-silica rhyolites. Rough calculations based on Zr gradients in the glass indicate that the samples could have been partially molten for 800 to 8000 years.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/doi:10.1016/0016-7037(91)90004-ODOIArticle
http://www.sciencedirect.com/science/article/pii/001670379190004OPublisherArticle
Additional Information:© 1991 Pergamon Press. Received February 26, 1990; Accepted in revised form November 21, 1990. P. Carpenter and J. Armstrong assisted with the electron microprobe analyses. Neutron irradiations were carried out by T. Crofoot at the TRIGA reactor facility at U. C. Irvine. Reviews by M. Harrison, P. Henderson, M. Clynne, T. Sisson, and an anonymous reviewer and helpful discussions with S. Newman, G. Rossman, and L. Silver are greatly appreciated. This study was initiated while CRB was a visiting professor at Caltech.
Issue or Number:2
Record Number:CaltechAUTHORS:20150427-094750631
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20150427-094750631
Official Citation:Tourrette, T. Z. L., Burnett, D. S., & Bacon, C. R. (1991). Uranium and minor-element partitioning in Fe-Ti oxides and zircon from partially melted granodiorite, Crater Lake, Oregon. Geochimica et Cosmochimica Acta, 55(2), 457-469. doi: http://dx.doi.org/10.1016/0016-7037(91)90004-O
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56995
Collection:CaltechAUTHORS
Deposited By: Joanne McCole
Deposited On:27 Apr 2015 19:16
Last Modified:03 Oct 2019 08:19

Repository Staff Only: item control page