The ancient martian lithospheric structure at Isidis Planitia

The elastic thickness plays an important role in constraining the thermal evolution of the Mars. There was no definite elastic thickness at Isidis Planitia. To further explore the flexure parameter at Isidis, we introduced an updated load model to admittance between gravity and topographical data from recent Mars missions. To validate our model, we firstly studied the localized parameters at Olympus and Elysium Mons. We found a large elastic thickness (T-e > 88 km) at Olympus, but a small value (< 28 km) at Elysium. Our results are consistent with previous studies, indicating the feasibility and rationality of our approach. Then, we studied the elastic parameter at Isidis Planita, and found the local lithospheric formerly adjusted to the initial topographic depression depth. Considering the depression depth in our load model, the estimated parameters are constrained within 2 sigma(STD,) which is the first time to successfully take an admittance analysis for this region. It is found that a large density anomaly (even close to 300 kg.m(-3)) were ever intruded into the crust and two likely values of T-e existed: the large one around 110 km and the other one surrounding 55 km. The large value of Te corresponds to a large crustal density (> 2900 kg.m(-3).), while the small one corresponds to an unconstrained density around 2665 kg.m(-3). Considering the large free-air gravity anomaly at Isidis, its main contribution probably comes from the large density intrusion. Taking into account the small crustal density around Isidis Planitia and the volcanism during the secondary episode, the small elastic thickness is likely a mirror of the strength of the lithosphere during this basin formation.