Abstract DGP2026-33

The geodynamic history of Mercury has been characterized by global contraction in response to planetary cooling. Such contraction has been recorded in tectonic landforms on Mercury’s surface. However, estimates substantially vary between < 2 km (Watters et al., 2021) and up to 7 km (Byrne et al., 2014), depending on whether wrinkle ridges are considered to contribute to global contraction. A recent study by Broquet and Andrews-Hanna (2025) revisited Mercury’s tectonic record and found global contraction values of 8.3±4.3 km, with a conservative range of 6.3±3.2 km when considering only primary tectonic landforms.

Here we use 3D geodynamic simulations to model Mercury’s thermal evolution and global contraction. Our geodynamic models build upon the work of Fleury et al. (2024) and use the mantle convection code GAIA (Hüttig et al., 2013). GAIA solves the conservation equations of mass, momentum and energy from 4.5 Ga to present day under the assumption of homogeneous mantle composition, Newtonian rheology, and negligible inertia. Our models employ surface temperature variations caused by the combined effects of Mercury’s low obliquity and its 3:2 spin-orbit resonance, as well as crustal thickness variations derived from gravity and topography data (Fleury et al., 2024). For the first time, we account for a laterally variable crustal thermal conductivity considering crustal porosity variations (Broquet et al., 2024). Additionally, we investigate the effects of melt extraction on regional contraction. While previous models (Peterson et al., 2021; Tosi et al., 2025) have considered only fully extrusive scenarios, where the entire amount of melt produced in the interior is instantaneously extracted at the surface, we test both intrusive and extrusive cases as well as different intrusive to extrusive ratios and depths for placing the magmatic intrusions. Predicted present-day global and local contraction are then compared to tectonic strain from Broquet and Andrews-Hanna (2025). 

Our models typically predict between 5-10 km of global contraction today. The average crustal thickness is found to have no substantial effect on global contraction estimates. When considering porosity and its effect on thermal conductivity, we find that regions covered by a thick, porous crust are warmer during the early evolution and experience a more pronounced cooling later on, which leads to substantially larger contractional strain compared to the rest of the planet. Assuming different megaregolith thicknesses up to 5 km, as well as a linear or exponential decrease of conductivity with increasing porosity (Henke et al., 2016), affects global contraction estimations by up to ± 10%. Similarly, magmatic intrusions, typically located at the crust-mantle boundary, provide a local heat source, keeping the lithosphere warm over prolonged time periods, and therefore affecting the record of planetary contraction on a regional scale. These analyses show that planetary contraction is far from isotropic, which has implications for our understanding of Mercury’s tectonic record. More detailed comparisons of our planetary contraction estimates with those inferred from shortening landforms will provide important insights into the interior processes and cooling history of Mercury.