Elastic thickness estimates for the northern lowlands of Mars

The northern lowlands cover approximately one-third of Marsʹ surface and are a fundamental part of the geologic evolution of Mars. We examine the admittance signature, the ratio of gravity to topography data in the spectral domain, for four regions in the northern lowlands that are both well resolved in the gravity data and have well constrained lithospheric parameters. These regions also have topographic power spectra similar to many highlands regions. A Cartesian multitaper method is used to calculate admittance. We compare the observed admittance signatures to those predicted from models of lithospheric flexure. On the basis of these comparisons, we estimate the thickness of the Martian elastic lithosphere (Te) required to support the observed topographic load since the time of loading. We use both top and bottom loading models to derive values of elastic thickness and crustal thickness or apparent depth of compensation although all four regions are best fit by bottom loading models. We obtain best fit elastic thickness estimates between 10 and 25 km with an acceptable error range of 0 to 45 km. These low elastic thickness estimates are consistent with the formation in the Noachian, when heat flow was high. The consistency in Te estimates between the Noachian highlands and lowlands basement suggests that both regions of the crust formed at similar times. The paucity of crustal magnetization in the lowlands is thus more likely a result of demagnetization than formation following shut down of the dynamo.