Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p31c1716r&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P31C-1716
Other
[1039] Geochemistry / Alteration And Weathering Processes, [5415] Planetary Sciences: Solid Surface Planets / Erosion And Weathering, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The detection of clay minerals and other secondary silicates in light-toned surfaces at Mawrth Vallis from near-infrared (NIR) spectroscopy indicates that this surface experienced aqueous alteration. The types of alteration products can help constrain past aqueous environments to assess habitability. NIR data from OMEGA and CRISM show a Fe/Mg-smectite layer stratigraphically below a layer containing a variety of secondary silicates, including kaolinite, montmorillonite, beidellite, and amorphous silica (Bishop et al., 2010). Detections of Fe/Mg-smectites at Mawrth Vallis suggest that the lower layer experienced aqueous alteration at alkaline pH, while detections of kaolinite and amorphous silica suggest that the upper layer experienced intense acidic alteration (Bibring et al., 2006; Bishop et al., 2008). Thermal-infrared (TIR) spectroscopy is an essential tool for identifying both primary and secondary silicate minerals. Previous models of Thermal Emission Spectrometer (TES) data from Mawrth indicate clays are present in dark surfaces, while amorphous silica is present in light-toned surfaces (Michalski and Fergason, 2009). However, spectral libraries have heretofore lacked nano-crystalline weathering products, such as allophane, that are important constituents of terrestrial soils. Their identification at Mawrth can help further understand alteration environments and soil formation processes. We synthesized allophanes and gels with a range of Si/Al ratios and measured their TIR emission and NIR reflectance spectra. TES data from dark- and light-toned surfaces at Mawrth were modeled using a spectral library containing allophanes and other secondary silicates. Models of dark-toned surfaces identify 20 vol.% allophane, 10% phyllosilicates and zeolites, and 45% basaltic igneous minerals. Models of bright-toned surfaces identify up to 30% allophane, 25% montmorillonite, and 30-35% basaltic igneous minerals. The identification of allophane in bright-toned surfaces is consistent with the detection of amorphous silica from CRISM data because silica and allophane have similar NIR spectra. On Earth, allophanes are found in basalt weathering rinds and in well-drained ash and tephra deposits that have been weathered at low temperatures and near-neutral pH (Colman, 1982; Wada, 1989). The detection of allophanes in dark-toned Mawrth surfaces with low clay and high igneous mineral abundances suggests these surfaces are weakly weathered basalts. The detection of allophanes and montmorillonite in bright-toned surfaces suggests this unit experienced multiple aqueous conditions. Allophane indicates formation in well-drained environments at near-neutral conditions and low water-to-rock ratios, while montmorillonite indicates formation in poorly-drained environments and higher water-to-rock ratios. Additionally, bright-toned deposits are layered on meter to decimeter scales and drape topography (Michalski and Noe Dobrea, 2007; Bishop et al., 2008). The morphology of these units and the detection of allophane from TIR and NIR spectroscopy indicate these units are weakly to moderately altered volcanic ash deposits and may not have experienced intense acidic alteration.
Kraft Michael David
Rampe E. B.
Sharp Thomas G.
No associations
LandOfFree
Allophane at Mawrth Vallis: Implications for Aqueous Alteration History does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Allophane at Mawrth Vallis: Implications for Aqueous Alteration History, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Allophane at Mawrth Vallis: Implications for Aqueous Alteration History will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-870264