RECONNAISSANCE 1:5M SCALE GEOLOGIC MAPPING OF THE MAHUEA THOLUS (V-49) QUADRANGLE, VENUS

The Mahuea Tholus quadrangle (V-49) extends from 25° to 50° S to 150° to 180° E and encompasses 6,500,000 km² of the Venusian surface. The NE-trending Diana-Dali Chasma characterizes the NW-edge of the quadrangle, whereas topographically lower plains comprise the rest of the map area. Diana-Dali is ~1,800 km wide and is dotted with four coronae in V-49 that are ~50-100 km in diameter. Outpourings of flow material from Diana-Dali and associated coronae (including Flidais Corona in V-37 [Hansen and DeShon, 2003]) extend south, flooding the topographic basin; these materials overlap with, and in many cases are indivisible from, locally sourced flows from small shields and Mahuea Tholus (MT; 37.5° S, 165° E) – a 356 km x 765 km central vent volcano. Flow material sourced from the MT edifice ranges from older and extensive radar-dark materials (low-viscosity flow material?) to younger, radar-bright, thick, high-viscosity materials that comprise the edifice (see also Moore et al., 1992). NE-trending wrinkle ridges ~190 km long with wavelengths from ~10 to 70 km that cut through the topographic basin appear to deform the oldest MT materials (as well as Diana-Dali-sourced materials), but are covered by the youngest flows suggesting MT erupted over a protracted period. Seven E-W trending channels occur along the northern and southern edges of the basin. Channel sources are indeterminable, but formation of the northern channels was likely associated with Diana-Dali-sourced flows; longitudinal profiles suggest all channels have been deformed by long-wavelength warping since formation. The east side of V-49 hosts basement materials associated with Urd Tessera, which outcrop as part of a broad, N-trending warp. 13 impact craters occur within the quadrangle and range from 12-100 km in diameter. All craters are associated with ejecta blankets, but two craters also host fluidized ejecta materials. Seven craters also exhibit radar-dark floors. Our initial mapping is consistent with relations identified in surrounding quads and indicates a geologic history for V-49 punctuated by multiple, overlapping periods of volcanism and tectonism that occurred at both large and small scales and seemingly erased much of the earlier history for this part of Venus. Future mapping here should further constrain the relative timing of these events.