Chemtob, Steven M. and Jolliff, Bradley L. and Rossman, George R. and Eiler, John M. and Arvidson, Raymond E. (2010) Silica coatings in the Ka’u Desert, Hawaii, a Mars analog terrain: A micromorphological, spectral, chemical, and isotopic study. Journal of Geophysical Research E, 115 . Art. No. E04001. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20100520-142022744
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High-silica materials have been observed on Mars, both from orbit by the CRISM spectrometer and in situ by the Spirit rover at Gusev Crater. These observations potentially imply a wet, geologically active Martian surface. To understand silica formation on Mars, it is useful to study analogous terrestrial silica deposits. We studied silica coatings that occur on the 1974 Kilauea flow in the Ka'u Desert, Hawaii. These coatings are typically composed of two layers: a ~10 μm layer of amorphous silica, capped by a ~1 μm layer of Fe-Ti oxide. The oxide coating is composed of ~100 nm spherules, suggesting formation by chemical deposition. Raman spectroscopy indicates altered silica glass as the dominant phase in the silica coating and anatase and rutile as dominant phases in the Fe-Ti coating; jarosite also occurs within the coatings. Oxygen isotopic contents of the coatings were determined by secondary ion mass spectrometry (Cameca 7f and NanoSIMS). The measured values, δ^(18)O_(Fe-Ti) = 14.6 ± 2.1‰, and δ^(18)O_(silica) = 12.1 ± 2.2‰ (relative to SMOW), are enriched in ^(18)O relative to the basalt substrate. The observations presented are consistent with a residual formation mechanism for the silica coating. Acid-sulfate solutions leached away divalent and trivalent cations, leaving a silica-enriched layer behind. Micrometer-scale dissolution and reprecipitation may have also occurred within the coatings. Chemical similarities between the Hawaiian samples and the high-silica deposits at Gusev suggest that the Martian deposits are the product of extended periods of similar acid-sulfate leaching.
|Additional Information:||© 2010 American Geophysical Union. Received 27 July 2009; accepted 2 November 2009; published 1 April 2010. This work was supported by funding from NASA grants NAG5–12684 to B. Jolliff and NNX06AB20G to G. Rossman as well as Gordon and Betty Moore Foundation funding for the Caltech Center for Microanalysis to J. Eiler. The manuscript was significantly improved by the input of Kim Seelos and an anonymous reviewer. We thank Chi Ma for assistance with collection of SEM imagery, Naomi Levin for assistance with laser fluorination measurements, and Yunbin Guan for assistance in the use of the NanoSIMS and Cameca 7f.|
|Subject Keywords:||silica, Mars analog|
|Official Citation:||Chemtob, S. M., B. L. Jolliff, G. R. Rossman, J. M. Eiler, and R. E. Arvidson (2010), Silica coatings in the Ka’u Desert, Hawaii, a Mars analog terrain: A micromorphological, spectral, chemical, and isotopic study, J. Geophys. Res., 115, E04001, doi:10.1029/2009JE003473.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||24 Jun 2010 20:49|
|Last Modified:||26 Dec 2012 12:03|
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