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Hydrous species in zircon

Woodhead, James A. and Rossman, George R. and Thomas, Andrew P. (1991) Hydrous species in zircon. American Mineralogist, 76 (9-10). pp. 1533-1546. ISSN 0003-004X.

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A survey of hydrous species in zircon from a number of localities with a range of occurrences and structural states was carried out using infrared spectroscopy and electron microprobe analysis. Stepwise heating experiments on a crystalline and a nearly metamict zircon were also performed. The region of IR spectra of OH-bearing crystalline zircon from 4000 to 2500 cm-^(1), exhibits anisotropic OH bands resulting from at least three OH sites, one at vacant tetrahedra and two that may be at Si-occupied tetrahedra. One site associated with Si-occupied tetrahedra is the most important, producing IR absorption bands at ~3420cm^(-1)(E‖c)and ~3385cm^(-1)(E⊥c). OH maybe introduced during crystal growth by a coupled substitution of the form [M^(3+) + H^4] ↔ [Zr^(4+)]. The sites at vacant tetrahedra account for considerably less OH, producing relatively weak IR absorption bands at ~3510 cm^(-1)(E‖c > E⊥c). OH may be introduced during crystal growth by the hydrogrossular substitution of the form [4(OH)-] ↔ [(SiO_4)^(4-). An additional OH band at ~3270 cm^(-1) appears to be associated with an occupied tetrahedron. Heating experiments produced two more OH environments and indicate that H can migrate among the sites at high temperatures. Some crystalline samples are entirely free of OH. IR spectra of metamict zircon exhibit broad, asymmetric, isotropic OH bands similar to H_2O bands, but the absence of the H_2O bending-mode band indicates that OH is the dominant hydrous species present. IR spectra of partially metamict zircon samples retain some anisotropy. The breadth of their OH bands is a function of degree of metamictizatron. The maximum OH observed in any metamict or partially metamict zircon sample was approximately 0.1wt%, expressed as H_2O. SuchO H is probably secondary. The maximum primary OH observed is ~0.05 wt% partially metamict zircon from a hydrothermal vug. Crystalline crustal zircon contains more than an order of magnitude less OH. The maximum OH content observed in crystalline zircon, ~0.01 wt%,i s in a mantle zircon sample from a kimberlite, suggesting high activity of H_2O in the mantle. Additional OH is present in some metamict and partially metamict zircon samples in the form of inclusions of hydrous silicates such as kaolinite. Fluid inclusions containing H_2O occur in some samples. This may be a partial explanation of the high H_2O contents reported for some radiation-damaged zircon based on loss-on-heating measurements.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1991 Mineralogical Society of America. Manuscript received September 24, 1990. Manuscript accepted May 23, 1991. This research was funded in part by the Earth Sciences Section, National Science Foundation, grant EAR-7919987 to G.R.R. and Leon T. Silver and grants EAR-8618200 and EAR-8916064 to G.R.R. Leon T. Silver's ongoing interest in the chemistry and behavior of zircon suites of different parageneses was the stimulus for this study. His insight has been highly valuable to us. We thank Armond Chase, Karl Francis, Ed Grew, Warren Hamilton, Anthony Jones, Peter Keller, Demethius Pohl, and Leon Silver for samples included in this work. We thank G. Cleve Solomon for conducting the heating experiment on the Reinbolt Hills zircon sample. Caltech contribution number 4927.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Caltech Division of Geological and Planetary Sciences4927
Issue or Number:9-10
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Official Citation:Hydrous species in zircon JAMES A. WOODHEAD, GEORGE R. ROSSMAN, ANDREW P. THOMAS 1533-1546
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44120
Deposited By: Ruth Sustaita
Deposited On:04 Mar 2014 19:04
Last Modified:03 Oct 2019 06:14

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