Bilateral Topographic Symmetry Patterns Across Aphrodite Terra, Venus

Western Aphrodite Terra, Venus, is characterized by a series of parallel linear structural discontinuities 2000-4000 km in length and 100-200 km wide, which strike at high angles to the general topographic trend of the Aphrodite Terra highlands. The broad characteristics of the cross-strike discontinuities (CSDs) are similar to both strike-slip fault zones and terrestrial oceanic fracture zones. In an effort to distinguish between these two hypotheses, topographic profiles were taken across Aphrodite Terra to test for bilateral symmetry of the type associated with thermal boundary layer topography at divergent plate boundaries on Earth. In addition to a broad bilateral symmetry at a range of angles across Aphrodite Terra, detailed bilateral symmetry is observed within domains between linear discontinuities in directions generally parallel to the strike of the discontinuities. In addition, within a domain the centers of symmetry of several profiles define a linear rise crest that is oriented normal to the bounding CSDs and terminates against them. Furthermore, linear rise crests are offset in a right-lateral sense along the CSDs between domains by 200-1200 km. If the discontinuities represent strike-slip movement, then retrodeformation of the axes of symmetry along the CSDs to form a straight line should form a broadly symmetrical topographic high. Instead, when the topography is retrodeformed, the edges of the highlands are characterized by distinctive misfits of topography at the edge of the rise where it intersects the CSDs. The nature and configuration of the CSDs, the characteristics of the topography and topographic patterns, including bilateral topographic symmetry generally parallel to CSDs within domains, the existence of linear rise crests defined by the axes of bilateral symmetry within domains, and the offsets of these linear rise crests between domains, all suggest hat western Aphrodite Terra on Venus is similar to terrestrial oceanic divergent plate boundary environments and that the cross-strike discontinuities are analogous to oceanic fracture zones rather than strike-slip faults.