A Morphometric Investigation of Large‐Scale Crustal Shortening on Mars

• Published in: Journal of geophysical research. Planets 2022-05, Vol.127 (5), p.n/a
• Main Authors: Atkins, R. M., Byrne, P. K., Bohnenstiehl, D. R., Wegmann, K. W.
• Format: Article
• Language: English
• Subjects: Asymmetry; Crustal shortening; Displacement; displacement profile; Ductile-brittle transition; Faults; Geological faults; Highlands; Landforms; Layering; lobate scarp; Lowlands; Mars; Mars surface; Planetary interiors; Segments; Spectral analysis; Spectrum analysis; Stratigraphy; thrust fault; Topography
• ISSN: 2169-9097; 2169-9100
• DOI: 10.1029/2021JE007110

Mars' 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. Plain Language Summary Long curvilinear features that exhibit substantial topographic relief are globally distributed across the surface of Mars. Based on similar Earth features, those on Mars are believed to be produced by thrust faults likely resulting from global contraction as the planet's interior cooled through time. Examination of how topography varies over the length of these structures allows for an interpretation of how the underlying thrust faults behave. This study investigated 49 features globally distributed Mars to allow for comparisons of fault behavior at a large scale. An analysis of topographic profile variability along the length of each structure revealed that fault displacemen