INTERPRETING THE ORIGIN AND STRUCTURES OF RIDGE BELTS ON VENUS WITH AN INTRACONTINENTAL OROGENY ANALOGUE ON EARTH

Ridge belts are a type of tectonic landform on Venus, manifest as linear-to-arcuate bands of densely packed, parallel ridges interpreted to accommodate crustal shortening via folding and faulting. However, the dimensions, topographic signatures, structural complexity, and spatial context of ridge belts remain to be fully characterized. We test the hypothesis that ridge belts represent intracontinental-like orogenies controlled spatially and structurally by mantle sutures or scars by comparing select ridge belts on Venus with observations of the Ouachita Mountains in western Arkansas/southeastern Oklahoma. The Ouachita Mountains formed after north-oriented compressive stresses reactivated a south-dipping mantle scar—an extinct subduction zone—pushing a crustal block and its overlying sedimentary cover against the North American craton. We evaluate evidence from our field observations and existing literature that allow us to recognize the effects of this style of scar-assisted mountain building, observing: (1) geophysical indicators of the indenting crustal block (comprising parts of Louisiana, Mississippi, and Arkansas); (2) a limited geographical extent, especially in length, of the collisional orogeny; (3) local, strong crust in association with the orogeny with minimal crustal shortening (relative to the Appalachians) and little crustal root; and (4) asymmetrical, condensed topography with diverse shortening structures localized near the projected upper tip of the suture. We next compare ratios of length to width, relief to length, and foreland and hinterland slopes between the Ouachitas (suture-controlled uplift), the Appalachians (non-suture-controlled uplift), and select ridge belts. We find that a mantle scar formed by downwelling or delamination may localize deformation and produce the structural geometries we observe at Venus under local, horizontally compressive stress regimes. Moreover, with topographic and structural reconstructions of the uneroded orogenic surface of the Ouachita orogeny, we show that subsurface structures accommodate greater shortening strains than those estimated from topography alone.