Coupled substitution of H and minor elements in rutile and the implications of high OH contents in Nb- and Cr-rich rutile from the upper mantle
Abstract
Infrared absorption spectra of rutile crystals from a variety of geological environments (carbonatite, hydrothermal vein, kyanite + rutile + lazulite association, xenoliths that are kimberlite hosted and dominated by Nb- and Cr-rich rutile) exhibit strong absorption in the 3300-cm^(-1) region due to interstitial protons bonded to structure O. In general the proton is located at sites slightly displaced from 1/21/20 of the unit cell, although some samples show evidence of additional protons at tetrahedral interstitial sites. H contents of rutile range up to 0.8 wt% H_2O, the highest concentrations occurring in mantle-derived Nb- and Cr-rich rutile of metasomatic origin. The role of H in rutile was examined, particularly with respect to its relations to other impurities. Protons are present in the rutile structure to compensate for trivalent substitutional cations (Cr Fe V AI) which are only partly compensated by pentavalent ions (Nb, Ta). The possibility of using the H content of rutile as a geohygrometer is illustrated for the case of coexisting hematite and rutile.
Additional Information
© 1993 Mineralogical Society of America. Manuscript Received November 2, 1992. Manuscript accepted July 18, 1993. We would like to extend our appreciation to Ulrich Klabunde (E.I. du Pont de Nemours and Company, Inc.) for providing the synthetic samples and stimulating discussions and to J.L Rosenfeld for a natural sample (R-8). We also thank Jill Banfield (University of Wisconsin, Madison) for her interest in this study and for access to data prior to publication, Glenn Waychunas (Stanford University) for contributions from XAS that significantly constrained our interpretations, and David Bell for performing the microprobe analyses and discussions. Helpful comments were provided by Harry Green and Alison Pawley. The research was funded in part by NSF grants EAR-91-04059 to G.R.R. and EAR-91-16551 to S.E.H. Division contribution no. 5284Additional details
- Eprint ID
- 44401
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- CaltechAUTHORS:20140319-151358635
- EAR-91-04059
- NSF
- EAR-91-16551
- NSF
- Created
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2014-03-19Created from EPrint's datestamp field
- Updated
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2019-10-03Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences
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- Caltech Division of Geological and Planetary Sciences
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- 5284