『Abstract
We investigated the mineralogy of basalt weathering rinds and
fresh basaltic rocks using visible/near-infrared (VNIR) (λ= 0.4-2.5μm)
and thermal emission (λ= 6-30μm) spectroscopy to 1) constrain
the effects of chemical weathering on rock spectra, and 2) further
understand the context of infrared spectra of Mars, which may
contain evidence for weathered rocks and particulates derived
from them. VNIR spectra of weathered rock surfaces are generally
redder and brighter than fresh surfaces. Thermal infrared spectra
of weathered basalts show evidence for aluminous opal and clay
minerals (or clay precursor mineraloids) in natural surfaces.
Supporting VNIR observations generally do not show the same evidence
for neoformed clays or silica because of their textural occurrence
as thin coatings and microfracture-fill, and possibly due to poor
crystallinity of the aluminosilicate weathering products in this
context. Spectral trends observed at Mars, such as the detection
of low to moderate (10-25%) abundances of silica and clay that
are observed in the thermal infrared but not in the VNIR, are
therefore consistent with trends observed for natural rock surfaces
in the laboratory. The combined use of thermal infrared and VNIR
suggest that vast areas of martian dark regions contain sandy-rocky
basaltic materials with weathering rinds and thin coatings that
could have formed in conditions of relatively low water/rock ratios.
Keywords: Mars; weathering; spectroscopy; Mineralogy; alteration』
1. Introduction and background
2. Methods
3. Spectra of fresh basalt surfaces
4. Spectra of weathered basalt surfaces
5. Discussion
6. Conclusions Acknowledgements
References