HR: 1340h
AN: P33A-0232    [Abstracts]
TI: Temperature-Dependent Geochronometry of the Surface of Venus
AU: * Bullock, M A
EM: bullock@boulder.swri.edu
AF: Southwest Research Institute, 1050 Walnut St., Suite 400, Boulder, CO 80302 United States
AU: Grinspoon, D H
EM: david@boulder.swri.edu
AF: Southwest Research Institute, 1050 Walnut St., Suite 400, Boulder, CO 80302 United States
AU: Head, J W
EM: James_Head_III@Brown.edu
AF: Brown University, POB 1846 Lincoln Field Bldg Department of Geological Sciences, Providence, RI 02912 United States
AB: Most amphiboles and micas are not thermodynamically stable at the surface of Venus [Zolotov et al. 1997]. However, Johnson and Fegley [2000] found in laboratory experiments that tremolite is metastable on Venus, decomposing on timescales of billions of years. It is possible therefore that geochemical tracers of past climate change currently exist at the Venus surface. Because of the large range of temperatures from lowlands to highlands on Venus (~100 K), measurements of differential tremolite abundance can constrain the time a particular lithologic unit formed, the average surface temperature since its emplacement, or both. Past episodes of high temperatures may have left their imprint on differential abundances of other minerals, such as other amphiboles, halogen-bearing minerals, or even carbonates. In situ measurements at different altitudes can yield age and/or time-averaged surface temperature. Alternatively, remote sensing measurements (from below the clouds) of the 2.7 micron OH stretch could map tremolite or other hydrated minerals, and hence surface age and temperature history. The variation of atmospheric water vapor with time and altitude will affect tremolite stability, as will possibly other trace species and total atmospheric pressure. Nevertheless, determining ages and possibly averaged or maximum surface temperatures over some time period is of utmost for understanding the history of Venus. The development and testing of this scheme, including its predictive possibilities and its weaknesses and limitations, will be discussed. This work was supported by NASA Planetary Atmospheres Grant NASG511039, and NASA Planetary Geology and Geophysics Grant NAG510330. Johnson, N.M., and B. Fegley, Water on Venus: New insights from tremolite decomposition, Icarus, 146, 301-306, 2000. Zolotov, M.Y., B. Fegley, and K. Lodders, Hydrous silicates and water on Venus, Icarus, 130, 475-494, 1997.
DE: 5410 Composition (1060, 3672)
DE: 6295 Venus
SC: Planetary Sciences [P]
MN: Fall Meeting 2005