Dilational fault slip and pit chain formation on Mars

Abstract

Pit crater chains that are parallel or collinear with normal faults are common on Mars, but only rarely observed on Earth. We explore the origin of pit crater chains using recent high-resolution imagery from Mars, laboratory simulation of pit chains, investigation of recent pit chains formed in response to seismic fault slip in Iceland, and assessment of rock failure criteria and the Martian crustal stress field to develop a deeper understanding of the relationship between pit chain formation and fault activity. Based on these analyses, we conclude that pit chains form in response to dilational fault slip. Because gravitational acceleration on Earth (9.81 m/s2) is higher than on Mars (3.72 m/s2), stress within Earth is greater than that of Mars for any given depth. Consequently, steep fault segments are likely to extend to about 5 km depth on Mars compared with about 2 km depth on Earth. Dilation of these steep segments associated with fault slip on Mars could result in large volume increase in the uppermost crust, influencing groundwater flow and discharge and mineralization. Based on crosscutting relationships, pristine pit morphologies, and lack of evidence of sediment accumulation in the bottoms of pits, we interpret that some pit craters may be actively forming in response to dilational fault slip. Figure 1. (A) Composite Viking imagery of normal fault scarps defining horsts and grabens in the southeast part of Alba Patera, Mars. Fault segmentation and en echelon arrangement of faults and grabens are common. Scale bar is 50 km. (B) THEMIS visible spectrum image shows detail of normal faults and pit chain (Phlegethon Catena) shown in A. Scale bar is 5 km. (C) Mars Orbital Camera image shows clear association of pit chains with normal fault scarps within graben on the southeast flank of Alba Patera. Scale bar is 1 km.