Abstract DGP2026-90

Reconstructing Venus’ paleoenvironment is challenging due to its geologically young surface. Whether Venus had a temperate surface and liquid water until <1 Ga (Way et al., 2016) or instead surface water never condensed (Turbet et al., 2021) and had a surface possibly warmer than today (Noack et al., 2012; Gillmann & Tackley, 2014) may hold the key to understanding the divergent evolution of Earth and Venus. Surface temperature is linked to volcanic outgassing and volatile content, but whether Venus’ interior is dry (Constantinou et al.,2024) or significant volatiles remain in the lower mantle (Smrekar & Sotin,2012) is debated. Therefore, the question of early surface conditions is inseparable from Venus magmatic evolution.

Venus’ geodynamic regime is debated (Rolf et al., 2022). Recent evidence of ongoing volcanic activity (Herrick & Hensley, 2023) suggests magmatism plays a key role today. Early geodynamic models considered extrusive magmatism, known as the heat-pipe regime (Moore & Webb, 2013). Recent studies explored scenarios dominated by magmatic intrusions, known as the plutonic-squishy regime (Lourenco et al., 2020). Although current surface and lithospheric conditions suggest a highly intrusive magmatic style (Maia et al., 2025), the relative roles of intrusive and extrusive magmatism in mantle cooling across surface temperatures and rheologies remain unexplored.

We study the effects of surface temperature and mantle viscosity on Venus’ long-term cooling using the geodynamic code GAIA in 2D spherical annulus geometry (Hüttig et al., 2013; Fleury et al., 2024). We assume a temperature- and depth-dependent viscosity (Hirth & Kohlstedt,2003), pressure- and temperature-dependent thermal conductivity and expansivity (Tosi et al., 2013), radiogenic heat decay, core cooling, and melting curves from thermodynamic models (Stixrude et al., 2009; Jennings et al., 2025).

We find that surface temperature and mantle viscosity are key factors in determining the efficiency of planetary cooling for different magmatic styles (intrusive or extrusive). Hot surface conditions, like present-day Venus, enable more efficient mantle cooling when intrusive magmatism dominates, whereas cooler surfaces (~500 K) promote stronger mantle cooling in extrusive-dominated scenarios. Mantle viscosity modulates this behavior: lower viscosities (~10^20 Pa s) allow planets with cold surfaces to cool more efficiently if intrusions are present, while higher viscosities (~10^22 Pa s) with hot surfaces cool more efficiently if eruptions dominate.

Our results highlight surface-mantle feedbacks as a key control on magmatic and cooling history, which may be reflected in the surface composition as well as shape the evolution of the deep interior. We show that intrusive magmatism efficiently cools a planet when the surface temperature and mantle viscosity promote lithospheric recycling. Such recycling 1) influences crustal and lithospheric conditions, which are determinant for the onset of plate tectonics; 2) affects volatile redistribution in the mantle, lowering the solidus and sustaining long-lasting magmatism; 3) boosts melt production, which impacts outgassing and atmospheric composition; and 4) enhances the core-mantle boundary cooling, which is relevant for the onset and sustainability of a thermal dynamo. Our study provides insights on the differences in the cooling pathways of early Earth vs. Venus and gives perspectives for potential habitability of exo-Venuses.