Subsetting a Global Morphologic Map of Tesserae on Venus: Irregularly-shaped Tessera Deposits

Stratigraphically the oldest units on the surface of Venus, tesserae exhibit a range of morphologies influenced by syn- and post-emplacement tectonic deformation, as well as other surface modification processes such as flood lava embayment. A better understanding of the composition and tectonic deformation of tesserae, currently poorly constrained, would inform the climatic and tectonic past of Venus. Geologic interpretation of morphologic units can inform the deformational history of tesserae based on the presence of features such as ridges and valleys (compression) or graben (extension). Previously mapped tesserae include Aphrodite Terra (Ovda Regio, Manatum Tessera, and Thetis Regio) and Alpha Regio, all of which exhibit a near-circular, concentrated shape expected from a formational mechanism in which tesserae are accretionary terrains coalescing around downwelling centers. Here we present a subset of a completed global morphologic map of tesserae, focusing on those which diverge from the regularly-shaped tesserae described above. In this study, mapped tesserae are geographically dispersed units which do not have the condensed, near-circular shape of many larger tessera and include those in Beta and Phoebe Regio, as well as smaller tesserae (<1x106 km2) like Cocomama, Snotra, and Bathkol. The Magellan SAR Left-Look Mosaic dataset (75m/pixel) is the basemap on which morphologic units within the tesserae were identified at a mapping scale of 1:750,000. No identified morphologic units are unique to a single tessera and all tesserae contain some subset of identified units. Units range from sets of parallel, linear features spaced ~5 km apart to broader (10s of kms) polygonal highs surrounded by topographic lows, both of which may have sub-textures, such as smaller scale lineations. Mapped units are compared to the Magellan topography dataset and backscatter coefficient maps derived from the Magellan Left-Look mosaic. Initial results indicate morphologic units do not correlate with topography at the available dataset resolution. The use of globally defined morphologic units will facilitate comparison of tesserae, whose broad characteristics may differ due to a number of variables during emplacement, such as material availability or downwelling length.