Coronae and Large Volcanoes on Venus with Unusual Emissivity Signatures in Virtis- Venus Express Data

Recent Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) images from the Ve-nus Express mission found emissivity variations on the venusian surface that correlate with some volcanic edifices and coronae [1-3]. Increased emissivity was noted near Quet-zalpetlatl Coronae, Atete Corona, Mertseger Mons, Shiwanokia and Shulamite Coronae in Themis Regio, Idunn Mons, Hathor Mons and Ininni Mons. Hathor and Ininni Montes are located on Dione Regio, Idunn Mons on Imdr Regio, and Mertseger Mons is adjacent to Parga Chasma and Themis Regio, and Atete Corona is on Parga Chasma. Mueller et al. [2] note that Themis, Imdr and Phoebe Regiones were classified as active hotspots by [4]. These results are consistent with either unusual compositions or young, unweathered surfaces. Mueller et al. [2] note that the high flux anomaly at young lava flows would support the hypothesis of komatiite or picrite volcanism predicted by [5] as a consequence of chemical differentiation of the upper mantle during the resurfacing event. Smrekar et al. [3] noted that gravitational instability of the lithosphere on a one-plate planet like Ve-nus can create a wide range of melt compositions as the sinking lithosphere may either devolatilize, enriching the upper mantle, or melt itself [6]. In order to explore whether unusual compositions and/or young, unweathered surfaces are causing the emissivity signals, we are assessing some of these sites, focusing first on the features in Themis Regio, as well as Idunn Mons in Imdr Regio. We are evaluating morphologies of volcanism that would indicate more evolved or non-basaltic compositions , and the stratigraphic history of each feature. Through mapping, we are in the process of defining whether young volcanism at the features is potentially present, and/or identify specific volcanic morphologies that might indicate unusual compositions. These morphologies would include channels (e.g., 7), steep-sided domes (e.g., 8, 9), or flows with unusual surface properties (e.g., ridges, high roughness, high reflectivity). As we have limited knowledge of the composition of the surface, we must rely on morphology. However , factors besides composition can control the morphology of volcanic features, including eruption rate, gas content and cooling rate (e.g., 10-12). Therefore, we will interpret unusual volcanic morphologies with caution. Our initial analysis has focused on Shi-wanokia and Shulamite Coronae (Figure 1), expanding our mapping and analysis from the V53 Quadrangle [13]. Shiwanokia Corona is a 500 km diameter concentric corona on the Themis rise. It has two main flow units, which we …