Publication Date:
2014-11-26
Description:
We have discovered relatively fresh exposures of a hydrated, amorphous material along the wallrock slopes in Coprates Chasma, Mars. Visible and near-infrared reflectance spectra extracted from the deposits exhibit broad absorptions at 1.42, 1.94, and ~2.25 µm that are most consistent with laboratory spectra of nanophase hydrated Fe-rich allophane and Fe-rich opal. The three absorptions, especially the 1.4 µm band, have the strongest hydration signatures yet detected on Mars by orbital data, suggesting high water content that is relatively fresh and has not altered or lost water since its formation or exposure. Age dating from crater size-frequency distributions of the Fe-rich allophane/opal deposits yields ages of ~50-100 My, consistent with a young exposure time and minimal time for dehydration. Either the Fe-allophane/opal represents an older material already contained within the wallrock that has been more recently exposed, or it represents a younger material formed during more recent aqueous activity.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
Permalink