Artemis: Surface expression of a deep mantle plume on Venus
Artemis, a unique 2600-km-diameter circular feature on Venus, defies geomorphic classification as a corona, crustal plateau, or volcanic rise. Artemis is similar in size to plateaus and rises, yet topographically resembles a corona. Geologic mapping using correlated digital remote data sets including NASA Magellan C1-, C2-, and F-scale synthetic aperture radar (SAR) imagery, altimetry, and synthetic stereo has led to a determination of the geologic history of Artemis. Artemis comprises a large topographic welt that includes a paired circular ∼1-km-deep trough (Artemis Chasma) and ∼1-km-high outer rise; thus, Artemis is divisible into chasma (trough), interior region, and exterior region. The chasma hosts trough-normal faults and folds. The interior includes five ∼350-km-diameter coronae (quasi-circular features marked by radial and/or concentric fractures) that record rich tectono-volcanic histories; radial extension fractures and trough-concentric wrinkle ridges dominate the exterior tectonic fabric. Artemis formed as a coherent entity; the coronae, chasma, chasma structures, radial fractures, and wrinkle ridges are all consistent with a deep plume model for Artemis formation. Rising and flattening of the plume head led to early uplift, doming, and radial fracturing as the plume head collapsed vertically and spread laterally, likely causing outward migration of the trough, as well as fracturing and wrinkle-ridge formation outboard of the trough. Within the trough, material was pulled downward, forming normal faults and folds. The plume continued to spread laterally outboard of the trough, resulting in continued radial fracturing and wrinkle-ridge formation. Small-scale interior convection cells or compositional diapirs resulted in coronae with radial fractures, and/or concentric fractures and/or folds, and associated volcanism. Artemis is akin in its formation to crustal plateaus and volcanic rises and likely formed during the transition from globally thin to thick lithosphere.