10:45 〜 12:15
[PPS07-P13] Lithospheric elastic thickness beneath the Caloris basin: Implications for the thermal structure of Mercury
キーワード：Elastic thickness, Thermal evolution, Gravity
Elastic thickness of the planetary lithosphere is essential to the investigation of planetary thermal evolution. Our work focuses on the youngest and largest visible impact basin on Mercury, Caloris, which has undergone complex magma-tectonic deformation after its formation. Using a flexural lithosphere model with initial mantle loading, we use a Monte Carlo sampling method to estimate the lithospheric elastic thickness. The elastic thickness and load ratio are estimated as 18.5 3.9 km and -0.026 0.019, respectively. The successful application of the mantle loading model and the small load ratio indicates that the main sub-surface load at the Caloris region is the mantle plug rather than the lateral density anomaly. We investigate the implication of the obtained lithospheric elastic thickness to the temperature structure of Mercury by estimating heat production and its decay in the mantle. Under two composition assumptions about the silicate portion of Mercury (CI chondrite and Earth primitive mantle), the current heat production rate in Mercury mantle is estimated as 2.41 to 4.19 ×10-12 W/kg. The mantle heat production rate at 3.7 Ga is also inferred, and our thermal model is constructed based on it. Comparison between elastic thickness from the thermal model and loading model suggests that the primitive silicate portion of Mercury component is closer to that of CI chondrite rather than Earth primitive mantle. The estimated surface heat flow at ~3.7 Ga at the Caloris region is lower than that estimated for the other megaregolith-covered regions, indicating the heterogeneity of heat flow at Mercury surface.