EVIDENCE FOR THE PRESERVATION OF MULTIPLE STRESS ORIENTATIONS WITHIN THE DIANA-DALI RIFT SYSTEM IN THE MAHUEA THOLUS (V-49) QUADRANGLE, VENUS

The Mahuea Tholus quadrangle (V-49) is a 25° latitude by 30° longitude quadrangle in Venus’ southern hemisphere centered at 37.5° S, 180° E. One of its most notable features is the Diana-Dali Chasmata system, which cuts across the northwest corner of the quadrangle as it extends from near Artemis Corona in V-48 to the west to Atla Regio (V-26) to the northeast. This rift is ~500 km wide here and has an overall NE-SW trend that parallels the lowlands that dominate the rest of the map area. Mapping of tectonic structures within the rift zone reveal that, in addition to the dominant NE-SW fracture trend, there are at least three other suites of fracture trends: 1) an E-W-trending suite; 2) a NW-SE-trending suite; and 3) fractures that radiate from a tectono-magmatic center (e.g., a corona) within the rift. Based on cross-cutting relations, these four suites of structures suggest changing stress orientations within the rift through time. The E-W and NW-SE trending suites appear to be the earliest preserved fractures within the rift here, but the timing between these two suites is indeterminable and it is possible they formed synchronously. They are best preserved as two southeast trending arms that extend a few hundred kilometers out from the main portion of the rift and wrap around two quasi-circular crustal blocks (centered at ~25.7° S, 162.5° E and 29.2° S, 159.5° E) that appear to represent mechanically strong portions of lithosphere. The E-W-trending suite does contain pit chains that crosscut the NW-SE suite and parallel apparent trends of small shields within the crustal block at ~29.2° S, 159.5° E, which suggests that activity within the E-W suite extended past the timing of the NW-SE suite and likely fed eruptions of the small shields. The cause of these two earliest suites is not clear, but it is possible they are associated with formation of earlier-formed tectono-magmatic centers within Diana-Dali. The NE-SW suite of fractures that largely characterize Diana-Dali overprint both the E-W and NW-SE suites, which is in turn cut by suites of radial fractures that can be traced to specific coronae. When taken together, these four fracture suites suggest that formation and evolution of the Diana-Dali rift zone is the result of complex and evolving centers of stress and unravelling its history requires careful mapping and interpretation of its tectonic structures.