Lithospheric Elastic Thickness Beneath the Caloris Basin: Implications for the Thermal Structure of Mercury

Abstract

AbstractThe elastic thickness of a planet's lithosphere is essential to the investigation of its thermal evolution. Our work focuses on the largest visible impact basin on Mercury, Caloris, which has undergone complex magma‐tectonic deformation after its formation. Using a flexural lithosphere model with the initial mantle plug loading, we estimated the elastic thickness in the Caloris region to be 18.0  4.4 km. The successful application of the mantle loading model and the small load ratio indicates that major load in the Caloris region is the mantle plug rather than the lateral density anomaly. The 18 km effective elastic thickness indicates the lithospheric temperature at the time of loading. The current heat production rate in Mercury mantle is estimated as 2.2–4.2 × 10−12 W/kg. Comparison between the effective elastic thickness predicted from the thermal model and loading model suggests that the megaregolith in the Caloris basin region has a certain thickness (>3 km) to ensure the formation of a lithosphere with 18 km elastic thickness. The temperature model results also indicate that the mantle heat production rate at 3.6 Ga is closer to that calculated based on a model with heat‐producing elements abundance close to CI chondrite‐like primitive silicate portion of Mercury. The surface heat flow in the Caloris region is consistent with other megaregolith‐covered regions.