Hydrogen Incorporation in Natural Mantle Olivines
Abstract
Constraints on water storage capacity and actual content in the mantle must be derived not only from experimental studies, but also from investigation of natural samples. Olivine is one of the best-studied, OH-bearing "nominally anhydrous" minerals, yet there remain multiple hypotheses for the incorporation mechanism of hydrogen in this phase. Moreover, there is still debate as to whether the mechanism is the same in natural samples vs. experimental studies, where concentrations can reach very high values (up to ~0.6 wt% H_2O) at high pressures and temperatures. We present new observations and review IR and TEM data from the literature that bear on this question. Hydrogen incorporation in natural olivine clearly occurs by multiple mechanisms, but in contrast to some previous assertions we find that there are strong similarities between the IR signatures of experimentally annealed olivines and most natural samples. At low pressures (lower than ~2 GPa) in both experiments and natural olivines, hydrogen incorporation might be dominated by a humite-type defect, but the nature of the defect may vary even within a single sample; possibilities include point defects, planar defects and optically detectable inclusions. IR bands between 3300 and 3400 cm^(-1), ascribed previously to the influence of silica activity, are apparently related instead to increased oxygen fugacity. At higher pressures in experiments, the IR band structure changes and hydrogen is probably associated with disordered point defects. Similar IR spectra are seen in olivines from xenoliths derived from deeper parts of the mantle (below South Africa and the Colorado Plateau) as well as in olivines from the ultra-high pressure metamorphic province of the Western Gneiss Region in Norway.
Additional Information
© 2006 by the American Geophysical Union. Published Online: 19 Mar. 2013. Financial support for this work was provided by NSF grants OCE-0095294 and OCE-0241716 to PDA, EAR-0337816 to GRR, and EAR-0208419 to TGS. Several of the Buell Park samples came from the thesis collection repository of David Bell at Caltech. Doug Smith graciously provided samples, enlightening discussion and encouragement. Erik Hauri provided a preprint and went beyond the call of duty discussing it. We also thank Maarten Broekmans, Bradley Hacker, Stephen Mackwell, Gordon Medaris, Michael Roden, and Michael Terry for helpful discussions and information about localities. Chi Ma assisted with electron microprobe analyses. Thorough reviews by Andrew Berry, Steven Jacobsen and an anonymous reviewer helped us refine the manuscript. Finally, we once again thank all of the original donors who provided samples for the study of Miller et al. [1987], and especially Masao Kitamura, for continuing use of his samples from Buell Park.Attached Files
Published - Mosenfelder_2006p45.pdf
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Additional details
- Eprint ID
- 38340
- Resolver ID
- CaltechAUTHORS:20130508-075922683
- OCE-0095294
- NSF
- OCE-0241716
- NSF
- EAR-0337816
- NSF
- EAR-0208419
- NSF
- Created
-
2013-05-30Created from EPrint's datestamp field
- Updated
-
2021-11-09Created from EPrint's last_modified field
- Caltech groups
- Division of Geological and Planetary Sciences
- Series Name
- Geophysical Monograph
- Series Volume or Issue Number
- 168