Structural Analysis of Ogygis Rupes Lobate Scarp on Mars.

Ogygis Rupes is a 200 kilometers long lobate scarp, striking N30ºE, with approximately 2km of maximum structural relief. It is located in Aonia Terra, in the southern hemisphere of Mars near the northeast margin of Argyre impact basin. Similar to other large lobate scarps on Mercury or Mars, it shows a roughly arcuate to linear form, and an asymmetric cross section with a steeply rising scarp face and a gently declining back scarp. This asymmetry suggests that Ogygis Rupes is the topographic expression of a ESE-vergent thrust fault. By using the Mars Orbiter Laser Altimeter data and the Mars imagery available we have measure the horizontal shortening on impact craters cross-cut by this lobate scarp to obtain a minimum value for the horizontal offset of the underling fault. Two complementary methods were used to estimate fault geometry parameters as fault displacement, dip angle and depth of faulting: (i) analyzing topographic profiles together with the horizontal shortening estimations from cross-cut craters to create balanced cross sections on the basis of the thrust fault propagation folding [1]; (ii) using a forward mechanical dislocation method [2], which predicts fault geometry by comparing model outputs with real topography. The significant size of the fault underlying this lobate scarp suggests that its detachment is located at a main rheological change, for which we have obtained a preliminary depth value of around 30 kilometers by the methods listed above. Estimates of the depth of faulting in similar lobate scarps [3] have been associated to the depth of the brittle-ductile transition. [1] Suppe (1983), Am. J. Sci., 283, 648-721; Seeber and Sorlien (2000), Geol. Soc. Am. Bull., 112, 1067-1079. [2] Toda et al. (1998) JGR, 103, 24543-24565. [3] i.e. Schultz and Watters (2001) Geophys. Res. Lett., 28, 4659-4662; Ruiz et al. (2008) EPSL, 270, 1-12; Egea-Gonzalez et al. (2012) PSS, 60, 193-198; Mueller et al. (2014) EPSL, 408, 100-109.