Dynamics of Venusian rifts and their interactions with plumes and intrusions

Abstract

The surface of Venus features extensive rift zones, known as chasmata, up to 10,000 km in length. Many of Venus' rifts exhibit intersecting branches, multiple troughs, and associations with coronae, which are often interpreted as small-scale mantle upwellings. With no Earth-like plate tectonics, the driving forces and rates of extension and lithospheric structure are poorly constrained. Here, we present the first 3D numerical models of rift tectonics under Venus-like conditions. We investigate the impact of crustal rheology (wet vs. dry diabase) and the thickness of the crust and lithosphere on rift geometry, topography, and surface fracturing. We further explore interactions between evolving rift structures and thermal upwellings (plumes) and magmatic intrusions – key components of Venus' global geodynamics. We find that rift morphology is highly sensitive to crustal rheology and lithospheric properties, with five modes of rift morphologies predicted: (1) narrow, (2) multiple, (3) wide-troughs, (4) wide-valley, and (5) branching; the multiple, wide-troughs, and branching modes align most closely with Venus observations. Underplated thermal plumes induce lower-crustal intrusions and cause localized lithospheric weakening, narrowing the rift regionally. Many coronae located within chasmata display arcuate trenches and may require alternative mechanisms or conditions to explain their rift morphology. Lateral offsets of rift valleys, branching from a single rift into multiple, and multiple parallel rift valleys are promoted by a relatively weak crust (wet diabase) or a strong crust (dry diabase) combined with a thin, warm lithosphere. If Venus' crust follows a dry diabase rheology, a significantly warm and thin lithosphere is required to reproduce observed rift characteristics. Some first-order differences in rift morphology across Venus may result from spatial or temporal variations in crustal and lithospheric properties.