Tectonics of Artemis Chasma: A Venusian "Plate" Boundary

Abstract

Artemis Chasma, an ∼2600-km-diameter arcuate trough located in southwestern Aphrodite Terra, Venus, has been the site of <250 km of regionally coherent, southeast-directed, lithospheric convergence and strike-slip displacement. This study examines the tectonics of the interior platform encircled by Artemis, the annulus of deformation coinciding with the trench, and the exterior region. A prominent northeast-trending interior deformation belt experienced phases of both shortening and extension that likely predate the formation of the chasma. Exterior tectonics are characterized by rift zones that are both younger and older than Artemis. The annulus displays substantial shortening on its southwest, south, and southeast margins, a transition to oblique convergence in the east annulus, and left-lateral strike-slip displacements on the northeast segment. Displacements of ∼50-250 km are inferred from distortion of a graben in the southeast fold-and-thrust belt and the left-lateral offset of an intersecting deformation belt at the northeast strike-slip boundary. The trench-outer rise system results from flexural processes, and is analogous to the topography at terrestrial subduction zones. These observations support limited southeast-vergent overthrusting of the entire interior plateau over the exterior plains. The tectonics of Artemis are not explained by an underlying mantle plume, as evidenced by the unidirectional—not radial—convergence and the greater age of the interior volcanism and tectonism relative to the annulus. However, early plume activity may have produced a block of thickened crust—now manifested by the interior plateau— which later served to localize deformation on its periphery, forming the annulus. The driving forces responsible for lithospheric underthrusing at Artemis Chasma are probably quite unlike the slab-pull mechanism that is favored for terrestrial subduction.