TECTONICS OF ARTEMIS-CHASMA - A VENUSIAN PLATE BOUNDARY

Artemis Chasma, an similar to 2600-km-diameter arcuate trough located in southwestern Aphrodite Terra, Venus, has been the site of <250 km o f regionally coherent, southeast-directed, lithospheric convergence an d strike-slip displacement. This study examines the tectonics of the i nterior platform encircled by Artemis, the annulus of deformation coin ciding with the trench, and the exterior region. A prominent northeast -trending interior deformation belt experienced phases of both shorten ing and extension that likely predate the formation of the chasma. Ext erior 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 displace ments on the northeast segment. Displacements of similar to 50-250 km are inferred from distortion of a graben in the southeast fold-and-thr ust belt and the left-lateral offset of an intersecting deformation be lt at the northeast strike-slip boundary. The trench-outer rise system results from flexural processes, and is analogous to the topography a t terrestrial subduction zones. These observations support limited sou theast-vergent overthrusting of the entire interior plateau over the e xterior plains. The tectonics of Artemis are not explained by an under lying mantle plume, as evidenced by the unidirectional-not radial-conv ergence and the greater age of the interior volcanism and tectonism re lative to the annulus. However, early plume activity may have produced a block of thickened crust-now manifested by the interior plateau-whi ch 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 t hat is favored for terrestrial subduction. (C) 1995 Academic Press, In c.