CONSTRAINTS ON THE ORIGIN OF MAHUEA THOLUS, VENUS: IS IT RELATED TO DIANA-DALI CHASMA?

Mahuea Tholus (37.5° S, 165° E) is a solitary, intermediate-sized volcano located in the center of the V-49 quadrangle, Venus. The edifice is ~100 km in diameter (with all flow materials, Mahuea is ~300 km in diameter), ~0.5 km in height with a ~4 km diameter flattish top, and an erupted volume of ~10³ km³. Mahuea is located within the center of a topographic basin in Zhibek Planitia ~1400 km SE of the main axis of Diana-Dali Chasma-related rifting. The occurrence of this seemingly isolated volcano is intriguing and here we describe our efforts of using NASA Magellan radar data to help constrain its origin. Geologic mapping in ArcGIS 10.3 of a ~10° x 10° area around Mahuea Tholus using Magellan imagery and altimetry has allowed us to place the volcanic construct into a regional perspective and shows that Mahuea Tholus resides at the eastern end of Annapurna Corona-related fractures (Naguchitsa Fossae) and overlies Annapurna-sourced flow material – material previously interpreted as possible pyroclastic deposits sourced from Mahuea Tholus (Moore et al., 1992); Annapurna-sourced flows were then subsequently deformed by NE-trending wrinkle ridges, which was then followed by formation of Mahuea Tholus. At least four eruptive events are recorded at Mahuea Tholus and each event is marked by a thick (~100 m), lobate, radar bright flow that records numerous pressure ridges and channel structures; the earliest recorded flow materials are the most extensive with the youngest flows being more localized. Based on mapped relations, we interpret that fractures within Naguchitsa Fossae facilitated eruption of Mahuea Tholus flow material and, therefore, magmatism at this volcano is likely related to magmatism at Diana-Dali Chasma as a whole. Perhaps the location of this volcano off the main axis of rifting caused stalling of magma ascent, which in turn could have facilitated either a slower effusion rate and/or evolution of magma chemistry resulting in the eruption of thick lava flows. Such a prediction may be testable through continued regional mapping of intermediate-sized Venusian volcanoes, in situ spectral analyses by Venusian landers, and further constraints on thickness variations of the Venusian crust.