Density Variations as a Function of Compostion in the Venusian Crust: Implications for Tesserae Formation

Baker, Aedan; Semprich, Julia; Schwenzer, Susanne; Greenwood, Richard C. and Filiberto, Justin (2022). Density Variations as a Function of Compostion in the Venusian Crust: Implications for Tesserae Formation. In: 53rd Lunar and Planetary Science Conference, 7-11 Mar 2022, Houston, TX.



The Venusian surface plains are thought to be predominantly basaltic, while tesserae occupy ~ 7 % and are potentially the oldest units preserved. They consist of layered, folded, and eroded rocks, potentially giving an insight into what tectonic regimes were present during Venus’ history. Studies of the tesserae have noted lower emissivity measurements compared to the surrounding plains. Several explanations for these lower emissivity values have been proposed, including a more felsic composition for the tesserae, that the lower emissivity could be a result of a difference in mineralogy caused by chemical weathering facilitated between the rocks and atmosphere by the lower temperatures at the higher elevations of tesserae. Alternatively, the morphology of some features on tesserae, such as the Ovda Fluctus, are more consistent with a basaltic composition.
The presence of significant amounts of felsic igneous compositions could either imply partial melting of hydrous material and hence a higher water content in early Venus, or differentiation of basaltic melts. Further, tesserae composition influences the density of the crust with major implications for the stability of crustal roots.
Here, we use thermodynamic modeling to compute phase diagrams and extract rock densities for two end-member compositions: a basalt and a granite. We discuss major phase and density changes for each composition and describe the effect of compositional variations along geothermal gradients with implications for the stability of crustal roots with the aim to provide constraints on the composition of tesserae.

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