Curiosity Rover Mars Hand Lens Imager (MAHLI) Grain-Scale Observations of Silica-Enriched Fracture-Associated Halos in Stimson Formation Sandstones, Gale Crater, Mars
Abstract
The Stimson formation is an erosion-resistant, dark gray rock unit dominated by a cross-bedded eolian sandstone facies exposed on the lower northern slope of Aeolis Mons (Mt. Sharp) in Gale crater, Mars. The Stimson formation overlies mudstone lithologies of the less-resistant Murray formation; they are in contact along an undulating erosional unconformity that cuts across tens of meters of Murray strata. The eolian sandstone consists of well-sorted, well-rounded, medium to coarse mafic sand; its cross beds are cross-cut by linear fractures occurring in dozens of locations along the Mars Science Laboratory Curiosity rover traverse. The sandstone is light gray to white for several to tens of cm on both sides of these fractures, essentially appearing as a "halo" that parallels each fracture. Geochemical and mineralogical observations of these halos, investigated using the rover's instrument suite, showed them to be enriched in silica relative to the host rock. Here, we use 16-100 microns/pixel MAHLI images to compare and contrast grain-scale characteristics of these sandstones as viewed in naturally weathered outcrops, on brushed surfaces, in drilled holes, on rocks broken and dislodged by rover wheels, and on surfaces damaged by the ChemCam laser. The images show that there is little to no visible porosity in the host rock, indicating that the sands were well cemented before they were fractured. Relative to the host rock, the intergranular cement in the lighter-toned fracture-associated halos is light gray to white, no visible difference in porosity is observed, and the sand grains typically have a dark gray center partially enveloped by a lighter gray to white rim. The halo surfaces exhibit variations in resistance to erosion relative to the host rock at scales of tens of microns to millimeters (some less resistant, some more). In some cases the observations suggest that preceding, white mineral veins inhibited fluid flow associated with halo-forming processes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.P11B1859E
- Keywords:
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- 5220 Hydrothermal systems and weathering on other planets;
- PLANETARY SCIENCES: ASTROBIOLOGYDE: 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 5419 Hydrology and fluvial processes;
- PLANETARY SCIENCES: SOLID SURFACE PLANETSDE: 5470 Surface materials and properties;
- PLANETARY SCIENCES: SOLID SURFACE PLANETS