One of the big news items out of the #AGU11 meeting was confirmation that Mars rover Opportunity had recently discovered the most unambiguous evidence yet of water on Mars. The evidence? A vein of gypsum, nicknamed “Homestake”. The vein takes its name from the Homestake Gold Mine in the Black Hills of South Dakota, where an open pit beautifully exposes some Tertiary felsic dikes crosscutting Precambrian metavolcanic rocks. Although the “Homestake” gypsum vein on Mars (below) is unlikely to contain significant quantities of elemental gold, it was a nonetheless a metaphorical bonanza because it is the best evidence yet that water once flowed underground on Mars in ways very similar to well understood processes here on Earth.
“This color view of a mineral vein called “Homestake” comes from the panoramic camera (Pancam) on NASA’s Mars Exploration Rover Opportunity. The vein is about the width of a thumb and about 18 inches (45 centimeters) long. Opportunity examined it in November 2011 and found it to be rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum.” –NASA
Image Credit: NASA/JPL-Caltech/Cornell/ASU
Back here on Earth you may be more familiar with veins filled with quartz or calcite. But make no mistake, if you find an environment on Earth that resembles Mars, you can find plenty of gypsum veins here, too. I had the good fortune to GigaPan just such an area on the south side of the San Rafael Swell two summers ago. The GigaPan below (and subsequent photographs) illustrate a variety of gypsum veins, as well as some nice faults, crosscutting the Jurassic Summerville Formation (itself composed mostly of shale and bedded gypsum evaporites).
Gypsum Veins, Summerville Cliff
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Large Gypsum Vein and Smaller Veinlets, Jurassic Summerville Formation, Southern San Rafael Swell, Utah
This post also serves as my Tuesday entry in Evelyn Mervine’s “GeoPicture Week” geomeme.