Topographic Comparisons of Uplift Features on Venus and Earth: Implications for Venus Tectonics

Introduction: Earth and Venus have many similar features, yet their tectonic histories are quite different. Like the Earth, Venus has a global rift system, which has been cited as evidence of tectonic activity, despite the apparent lack of Earth-style plate tectonics. Both systems are marked by large ridges, usually with central grabens. On Earth, the topography of the rifts can be modeled well by a cooling half-space and the spreading of two divergent plates. The origin of the topographic signature on Venus, however, remains enigmatic. Venus' rift zones (termed "chasmata") can be fit by four great circle arcs extending 1000s of kilometers. This chasmata system measures 54,464 km [1], which when corrected for the smaller size of Ve-nus, nearly matches the 59,200-km total length of the spreading ridges determined for Earth [2]. Venus and Earth also both have large regions of apparent upwell-ing – hotspots on Earth, and regiones on Venus [3]. These are marked by broad topographic and geoid highs as well as evidence of volcanic activity. We use topographic profiles to look for well-understood terrestrial analogs to Venusian features. Specifically, we cross-correlate average profiles for terrestrial rifts (slow and fast) and hotspots (oceanic and continental) with those for Venusian chasmata and regiones, and draw inferences as to the processes responsible for shaping Venus' surface. Procedure: Using Magellan topography data for Venus, and ETOP05 for Earth, and techniques described more fully in Jurdy and Stoddard [4], we analyze profiles for the Africa/South America portion of the slow-spreading Mid-Atlantic Ridge and the Pa-cific/Nazca portion of the fast-spreading East Pacific Rise for comparison with profiles for Ganis Chasma on Atla Regio and Devana Chasma, which extends from Beta Regio to Phoebe Regio [5]. These rifts are among the most recently active on Venus [6] with profuse volcanism as documented by the nature of crater-ing. For upwelling regions, we consider the oceanic Hawaii and Iceland hotspots and Yellowstone, a hot-spot beneath a continent on Earth. On Venus, broad topographic and geoid highs are called regiones [3]. Venus has approximately a dozen, and we examine Atla, Beta, and W. Eistla regiones. For ridge features, we take profiles perpendicular to the ridge trend every half-degree or so. For uplift features, we take 36 radial profiles through the center