The Peculiar Case of Extensional Tectonics on Venus: Modes of RIfting and Activity

Venus’ geological history holds critical insights into why Venus and Earth, despite their similarities, have followed such divergent evolutionary paths. Recent discoveries have transformed the perception of Venus from a geologically inactive planet to a one characterized by active and diverse geological processes. Mantle convection, lithospheric delamination, and plume-lithosphere (have) create(d) a surface rich with tectonic and volcanic structures, despite the absence of plate tectonics today. Among the most striking tectonic features on Venus are the expansive extensional rift structures, or "chasmata", which can span up to 10,000 km in length and show both unique and familiar features relative to Earth’s extensional tectonics. Many of Venus' rifts exhibit intersecting branches, multiple troughs, and associations with coronae, which are often interpreted as small-scale mantle upwellings.Here, we present the first 3D geodynamic models of rift tectonics on Venus. With models of uniformly, slowly extending lithosphere, we investigate the impact of crustal rheology (wet vs. dry diabase, i.e., weaker vs. stronger crust) and the thickness of the crust and lithosphere on rift geometry, topography, surface fracturing, and heat flow. We further explore interactions between evolving rift structures and thermal upwellings (plumes) and magmatic intrusions – considered key components of Venus’ geodynamic regime.We find that rift morphology is highly sensitive to crustal rheology and lithospheric properties, with five modes of rift morphologies predicted: (1) narrow, (2) wide-valley, (3) wide-troughs, (4) multiple, and (5) branching; of which the latter three (see Figure) align most closely with Venus observations. We find that a dry diabase crust -- often assumed likely for Venus -- favors Venus-like rift patterns only when combined with a thin, warm lithosphere, leading to focused faulting and branching rift structures. In contrast, a weaker wet diabase crustal rheology results in broader, less pronounced deformation zones. Underplated thermal plumes induce lower-crustal intrusions and cause localized lithospheric weakening, narrowing the rift regionally.Importantly, the results show that along-axis rift geometry variations, like multiple offsets and branching, can emerge even in symmetric, uni-axial extension settings. Moreover, the models indicate that if Venus' crust follows a dry diabase rheology, a significantly warm and thin lithosphere is required to reproduce observed rift characteristics. Through comparison to observations, we find that Venus rift morphologies are reproduced by various activity stages of model evolution, commonly under conditions of a thin lithosphere, which supports the possibility that Venus rifts are currently active.This research was partially conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract (80NM0018D0004) with the National Aeronautics and Space Administration.