Rifting Venus: Insights From Numerical Modeling

Abstract

Venus is a terrestrial planet with dimensions similar to the Earth, but a vastly different geodynamic evolution, with recent studies debating the occurrence and extent of tectonic‐like processes happening on the planet. The precious direct data that we have for Venus is very little, and there are only few numerical modeling studies concerning lithospheric‐scale processes. However, the use of numerical models has proven crucial for our understanding of large‐scale geodynamic processes of the Earth. Therefore, here we adapt 2D thermomechanical numerical models of rifting on Earth to Venus to study how the observed rifting structures on the Venusian surface could have been formed. More specifically, we aim to investigate how rifting evolves under the Venusian surface conditions and the proposed lithospheric structure. Our results show that a strong crustal rheology such as diabase is needed to localize strain and to develop a rift under the high surface temperature and pressure of Venus. The evolution of the rift formation is predominantly controlled by the crustal thickness, with a 25 km‐thick diabase crust required to produce mantle upwelling and melting. The surface topography produced by our models fits well with the topography profiles of the Ganis and Devana Chasmata for different crustal thicknesses. We therefore speculate that the difference in these rift features on Venus could be due to different crustal thicknesses. Based on the estimated heat flux of Venus, our models indicate that a crust with a global average lower than 35 km is the most likely crustal thickness on Venus.

Estimates on the Possible Annual Seismicity of Venus

“…The rifts on Venus are scaled with continental rift seismicity on Earth in the lower bound estimate for an active Venus. This is also a reasonable assumption, with many studies pointing to the morphological and geological similarities between the rift zones on Venus and continental rifts on Earth such as the Eastern African rift zone (Basilevsky & McGill, 2007;Foster & Nimmo, 1996;Graff et al, 2018;Kiefer & Swafford, 2006;Regorda et al, 2023;Solomon, 1993;Stoddard & Jurdy, 2012). For our upper bound, we scale the rift zones of Venus with mid-oceanic ridge seismicity since it is also an extensional setting and the higher temperatures at the mid-oceanic ridges and the corresponding different slope of the size-frequency distribution on Earth might be a better fit for rift seismicity under Venus' high surface temperature.…”

“…Modeling studies also indicate that continental rifting is a plausible mechanism to generate the rifting morphologies observed on Venus (Regorda et al., 2023). It is clear, however, that the difference in surface conditions between Venus and Earth plays a role in the rift mechanism as well (Regorda et al., 2023).…”

Plume‐Induced Delamination Initiated at Rift Zones on Venus

“…We assume a weak crustal rheology (Arkani‐Hamed, 1993; Buck, 1992; R. Ghail, 2015; Tian et al., 2023; Zuber, 1987) consistent with the effects of Peierls creep of a plagioclase rheology at the brittle‐ductile transition (Azuma et al., 2014; Katayama, 2021). Yet in addition to experimental data supporting a relatively strong (yet weak compared to olivine) crustal rheology (Mackwell et al., 1998), numerical models of rift formation on Venus may also require a strong crust (Regorda et al., 2023). Though the PBD mechanism as we have modeled is reliant on the existence of a weak crustal layer ( C 0 = 10 MPa), delamination events on Earth are thought to result from a variety of mechanisms other than crustal yielding, including melting and thermal weakening near the crust‐mantle boundary (Faccenda et al., 2009; Ueda et al., 2012).…”