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Volatile loss during homogenization of lunar melt inclusions

Ni, Peng and Zhang, Youxue and Guan, Yunbin (2017) Volatile loss during homogenization of lunar melt inclusions. Earth and Planetary Science Letters, 478 . pp. 214-224. ISSN 0012-821X. http://resolver.caltech.edu/CaltechAUTHORS:20170926-143414146

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Abstract

Volatile abundances in lunar mantle are critical factors to consider for constraining the model of Moon formation. Recently, the earlier understanding of a “dry” Moon has shifted to a fairly “wet” Moon due to the detection of measurable amount of H_2O in lunar volcanic glass beads, mineral grains, and olivine-hosted melt inclusions. The ongoing debate on a “dry” or “wet” Moon requires further studies on lunar melt inclusions to obtain a broader understanding of volatile abundances in the lunar mantle. One important uncertainty for lunar melt inclusion studies, however, is whether the homogenization of melt inclusions would cause volatile loss. In this study, a series of homogenization experiments were conducted on olivine-hosted melt inclusions from the sample 74220 to evaluate the possible loss of volatiles during homogenization of lunar melt inclusions. Our results suggest that significant loss of H_2O could occur even during minutes of homogenization, while F, Cl and S in the inclusions remain unaffected. We model the trend of H_2O loss in homogenized melt inclusions by a diffusive hydrogen loss model. The model can reconcile the observed experimental data well, with a best-fit H diffusivity in accordance with diffusion data explained by the “slow” mechanism for hydrogen diffusion in olivine. Surprisingly, no significant effect for the low oxygen fugacity on the Moon is observed on the diffusive loss of hydrogen during homogenization of lunar melt inclusions under reducing conditions. Our experimental and modeling results show that diffusive H loss is negligible for melt inclusions of >25 μm radius. As our results mitigate the concern of H_2O loss during homogenization for crystalline lunar melt inclusions, we found that H_2O/Ce ratios in melt inclusions from different lunar samples vary with degree of crystallization. Such a variation is more likely due to H_2O loss on the lunar surface, while heterogeneity in their lunar mantle source is also a possibility. A similar size-dependence trend of H_2O concentrations was also observed in natural unheated melt inclusions in 74220. By comparing the trend of diffusive H loss in the natural MIs and in our homogenized MIs, the cooling rate for 74220 was estimated to be ∼1 °C/s or slower.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2017.09.010DOIArticle
http://www.sciencedirect.com/science/article/pii/S0012821X17305058PublisherArticle
Additional Information:© 2017 Elsevier B.V. Received 15 April 2017, Revised 26 July 2017, Accepted 7 September 2017, Available online 26 September 2017. We would like to thank two anomalous reviewers for their suggestions that greatly improved our manuscript. We thank NASA CAPTEM for providing the lunar samples, and K.P. Jochum for providing the MPI-DING glass standards. This research is supported by NASA grant NNX15AH37G.
Funders:
Funding AgencyGrant Number
NASANNX15AH37G
Subject Keywords:Moon; melt inclusions; volatiles; water loss; homogenization; cooling rate
Record Number:CaltechAUTHORS:20170926-143414146
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170926-143414146
Official Citation:Peng Ni, Youxue Zhang, Yunbin Guan, Volatile loss during homogenization of lunar melt inclusions, Earth and Planetary Science Letters, Volume 478, 15 November 2017, Pages 214-224, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2017.09.010. (http://www.sciencedirect.com/science/article/pii/S0012821X17305058)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:81847
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:26 Sep 2017 22:46
Last Modified:26 Sep 2017 22:46

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