Subsurface Architecture of Coronae, Venus

Despite sharing a broadly similar interior structure and composition with Earth, Venus exhibits a starkly contrasting geodynamic regime. On Venus, the coronae, large quasi-circular volcano-tectonic structures, represent very prominent surface expressions of mantle plume activity thus providing important clues for the understanding the tectonic evolution of the planet [1, 2]. They are commonly interpreted as forming in response to crustal stresses induced by an upwelling mantle plume, followed by gravitational relaxation or collapse associated with magma withdrawal [3].

Our findings allow to transition from reliance on numerical modeling to the direct investigation of coronae subsurface architecture using an observation-based geological dataset. This study examines fractures associated with seven coronae, spanning diameters from 115 km to 1070 km, capturing the coronae size variability: Atahensik, Demeter, Didilia, Heng-O, Kamui-Huci, Ninkarraka, and Pavlova. Fractal analyses of mapped fractures were performed to estimate the thickness of the fractured medium, with each fracture family comprising hundreds to thousands of features to ensure robust statistical significance. The results reveal distinct behaviors between fractures confined to the corona annulus and those extending beyond it, highlighting fundamental differences in their formation and evolution processes.

For coronae with diameters ≤320 km, fracturing systems within and along the annulus are confined to the crustal thickness [4,5] while maintaining a scaling relationship with the coronae diameter. This pattern suggests a unified formation mechanism operating across the entire volcano-tectonic structure. Such behavior is consistent with the hypothesis that diking driven by a mantle plume facilitates magma emplacement within the crust, resulting in the formation of shallower magma chambers. Magma withdrawal from these reservoirs, spanning from initial evolution to collapse, appears to govern the surface fracturing observed [6]. In contrast, larger coronae exhibit a thicker fractured medium beneath their central regions, indicating mechanical coupling between the crust and upper mantle. This coupling likely arises due to elevated strain rates, which may result either from interactions between the plume and lithosphere (i) during active plume uplift, where magma advection generates high strain rates, or (ii) during later stages of evolution, when the cooling of underplated magma drives rapid subsidence of the lithospheric block. The mechanical interplay between the crust and shallow mantle thus spans multiple evolutionary phases, facilitating the development of deep fracture systems similar to those observed on Venus. These findings align with the coexistence of both active and inactive coronae [7] identified within the dataset.

 

[1] Ghail, R. C., et al., Space Sci-ence Reviews 220.4 (2024): 36. [2] Phillips, R. J., J. Geophys. Res. 95, 1301–1316 (1990). [3] Janes, D. M., S. W. et al., J. Geophys. Res., 97(E10), 16,055– 16,067, (1992) [4] James, P.B., et al., 118, 859–875, (2013). [5] Ji-ménez-Díaz, A., et al., Icarus 260 (2015): 215-231. [6] Lang, N.P., and López, I., Geological Society, London, Special Pub-lications 401.1 (2015): 77-95. [7] Gülcher, A.J.P., et al., Nat. Geo. 13.8 (2020): 547-554.

Acknowledgement: This research was supported by the European Union NextGenerationEU pro-gramme and the 2023 STARS Grants@Unipd pro-gramme “HECATE”.