Structural Mapping of Devana Chasma Venus: Implications for rift development in the Beta-Atla-Themis Region

The surface geologic structure of Venus is both complex and highly variable, as illuminated through Magellan Synthetic Aperture Radar (SAR) that can pierce the thick cloud cover. Extensive analysis of radar images has led to the distinction of many terrains and their subsequent geologic interpretations. Of particular interest to this study are coronae, circular volcano-tectonic features unique to Venus and chasmata, which have been interpreted to represent extensional rift zones (Stofan et al., 1997). A major portion of the surface of Venus, which possesses a large population of both features, is the Beta-Atla-Themis Region (the BAT) (Figure 1), an area of anomalously high volcanic and tectonic landforms (Crumpler et al., 1997), demarcated by the three major volcanic centers of Beta, Alta, and Themis Regiones. Connecting the three volcanic centers are three extensive topographic and highly deformed troughs (Parga, Hecate, and Devana Chasmata). The study area for this analysis is Devana Chasma, a north-south trending deformation belt along the eastern BAT that starts north of Beta Regio, extends south through Phoebe Regio, and ends near the northern edge of Themis Regio (Fig. 1). In this study, Devana Chasma and its surroundings are analyzed to better constrain its detailed structural character, including the locations and structural density of major fault systems, the distribution of coronae (a small population). ArcGIS mapping at a scale of 1:1,000,000 attributed features such as normal faults, lineaments, scarps, depressions, channels, and crater rims. The mapped linear features allow for a qualitative assessment of the relative timing and history of rift development recently studied by Keifer and Swafford (2006). Keifer and Swafford proposed that Devana was a discontinuous rift through gravity and lithospheric extension measurements. The slight bend seen along the study section in the rift (Figure 1) was selected as an offset region connecting two distinct rift arms from the north and the south respectively. In this study, three possible scenarios of formation of Devana were proposed: the two legs where either synchronous; the northern leg formed first; or the southern leg formed first. Mapping of Devana Chasma supported the first hypothesis of rift development. Forty-two topographic profiles along the length of the study area were constructed using the location of mapped linear features in conjunction with Magellan altimetry data. These sections were analyzed for structural density asymmetry and topographic asymmetry. The 42 profiles are further categorized into 4 discrete sections along the length of Devana Chasma in order to further understand the structural nature in the proposed northern and southern legs Devana, as well as the offset region (Keifer and Swafford, 2006). The distinct character of the northern and southern rifts of Devana, along with a paucity of normal faults in the offset region (hinting to little extension) further support the conclusion of Keifer and Swafford (2006). Structural mapping also included locating pseudocoronae along Devana Chasma. Psuedocoronae are arcuate landforms and / or structure belts that appear to be the result of partial corona development that never matured into fully circular coronae (Bleamaster and Hansen, 2004). By identifying these features we expand the criteria for recognizing volcano-tectonic interactions along chasmata. Only 4 areas of pseudocoronae development were located and catalogued. The merging of 2-D mapping of radar data with 3-D altimetry from Magellan proves to be an invaluable method for understanding the nature of rifting on Venus and the complex nature of Devana Chasma