A Morphometric Investigation of Large‐Scale Crustal Shortening on Mars

Abstract

AbstractMars' surface exhibits abundant topographic expressions of large thrust fault‐related folds that have been attributed to global planetary contraction. Morphometric analyses of such structures provide insight into their growth history. With global THEMIS imagery and HRSC–MOLA topographic data, 49 thrusts with lengths between 35 and 544 km were mapped across Mars' surface. Assuming planar fault geometries with dips of 30°, the average maximum displacement‐length ratio (Dmax/L) of these structures is 6.1 × 10−3 ± 1.4 × 10−3, with smaller ratios observed for faults within the northern lowlands (2.9 × 10−3 ± 0.9 × 10−3) compared to the southern highlands (9.2 × 10−3 ± 1.9 × 10−3). However, these differences may be accounted for if mechanical layering in the northern lowland crust promotes either a shallowing of the fault dip angle relative to the southern highlands or the development of ramp‐flat geometries such that the topographic scarp height may under‐estimate the total fault displacement or a combination of these two scenarios together. Alternatively, these Dmax/L patterns may reflect hemispheric differences in the brittle‐ductile transition (BDT) depth; however, the observed pattern is stratigraphically inconsistent with the Martian crustal dichotomy, whereby the northern lowlands have thinner (or denser) crust and therefore presumably a deeper BDT than the southern highlands. Fault displacement‐length profiles are commonly asymmetric, with multiple local minima observed along their lengths. Spectral analysis of these profiles, using Fourier‐ and S‐Transforms, indicates power at a range of spatial frequencies, reflecting complex growth and linkage histories, with peak spectral frequency, or number of segments, being negatively correlated with the Dmax/L ratios.