Longevity of fluorine-bearing tremolite on Venus |
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| Authors: | Natasha M Johnson Bruce Fegley Jr |
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| Institution: | a Planetary Chemistry Laboratory, Department of Earth and Planetary Sciences, Washington University, Campus Box 1169, St. Louis, MO 63130, USA
b NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Code 691, Greenbelt, MD 20771, USA |
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| Abstract: | There is a general belief that hydrous minerals cannot exist on Venus under current surface conditions. This view was challenged when Johnson and Fegley (2000, Icarus 146, 301-306) showed that tremolite (Ca2Mg5Si8O22(OH)2), a hydrous mineral, is stable against thermal decomposition at current Venus surface temperatures, e.g., 50% decomposition in 4 Ga at 740 K. To further explore hydrous mineral thermal stability on Venus, we experimentally determined the thermal decomposition kinetics of fluorine-bearing tremolite. Fluor-tremolite is thermodynamically more stable than OH-tremolite and should decompose more slowly. However how much slower was unknown. We measured the decomposition rate of fluorine-bearing tremolite and show that its decomposition is several times to greater than ten times slower than that of OH-tremolite. We also show that F-bearing tremolite is depleted in fluorine after decomposition and that fluorine is lost as a volatile species such as HF gas. If tremolite ever formed on Venus, it would probably also contain fluorine. The exceptional stability of F-bearing tremolite strengthens our conclusions that if hydrous minerals ever formed on Venus, they could still be there today. |
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| Keywords: | Venus Venus surface Tremolite Fluorine Mineralogy |
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