THE CONTRIBUTION OF SMALL SHIELD VOLCANOES TO THE VOLCANIC RESURFACING OF THE MAHUEA THOLUS QUADRANGLE [V-49], VENUS

Small shield volcanoes are a common type of edifice on Venus (Guest et al., 1992). Given their abundance, they likely play a significant role in the volcanic resurfacing of the planet. Here, we help constrain their role in resurfacing Venus by identifying their areal extent in the Mahuea Tholus quadrangle (V-49). We used Magellan radar images with a resolution of ~100 m/pxl in ArcGIS 10.3 to map small volcanic edifices in the quadrangle. We differentiate between four types: shields, flats, cones, and domes. Shields are identified by a change in backscatter, shallow slope, and a diameter ≤ 20 km. Flats are identified as circular edifies with little topographic expression, diameter of ≤ 20 km, and contrasting radar dark/bright backscatter. Cones are identified by radar brightness, steep slope, and a diameter of ≤ 15 km. Domes are identified by their very circular form, flat tops, and diameter of 20-30km. In V-49, a total of 637 small shield volcanoes are present. Of that 637, 277 are shields (~43%), 209 are cones (~33%), 149 are flats (~23%), and 2 are domes (<<1%). The four types of shields show a range of average diameters; domes: ~36 km (Standard Deviation [SD] of ~0.5 km), flats: ~11km (SD of ~4 km), shields: ~4 km (SD of ~2 km), and cones: ~3 km (SD of ~1 km). The areas of highest density of volcanic edifices (7 to 9 x 10¯⁴ shields/km²) are found in the NW (near 158° E, 30° S) and SW (near 162° E, 49° S). These two sites are associated with Puaulinka crater and Nortia Tesserae. The lowest density of volcanic edifices (0 - 2 x 10¯⁴ shields/km²) can be found in the central area of the quadrangle (near 162° E, 37° S) where shield occurrences are associated with Mahuea Tholus and Urd Tesserae. Shields in V-49 often occur in tight clusters known as shield fields (Crumpler et al., 1997). There are four shield fields identified in the quadrangle located at the following coordinates: (158° E, 30° S) (154° E, 48° S) (161° E, 49° S) (171° E, 39° S). Small volcanic edifices resurfaced ~25,000 km² (.38%) of the 6,500,000 km² quadrangle. Our results suggest that small shields have not played a significant role in large-scale volcanic resurfacing of V-49; instead, volcanic resurfacing here may be related to larger sources (e.g., Diana-Dali and associated features).