Cross faults in extensional settings: Stress triggering, displacement localization, and implications for the origin of blunt troughs at Valles Marineris, Mars

Abstract

[1] Motivated by conflicting interpretations concerning the origin of blunt terminations of troughs at Valles Marineris, Mars, we investigate the reactivation of preexisting cross faults in response to stress changes associated with slippage along a major, basin-bounding normal fault (i.e., border fault). Coulomb stress changes indicate that cross fault reactivation is possible in both the footwalls and hanging walls of border faults, although this is dependent on the distance between the border and cross faults. Cross faults accommodate dip-slip normal motion for most border fault geometries and conditions we tested, but strike-slip motions are predicted when preexisting cross faults are vertical. Furthermore, although lateral extensions of the border fault (LEBFs) may nucleate within cross fault footwalls at all stages of border fault development, they are favored to develop when border faults and cross fault tip lines are proximal. Observations from the Valles Marineris extensional province, Mars, are consistent with (1) normal displacements along cross faults, (2) numerous examples of pit-chains, interpreted to represent surface expressions of lateral extensions to the border fault (LEBF), (3) the lack of well-developed cross faults in the footwall of border faults, and (4) the inference that tapered trough ends formed in areas that lacked cross faults prior to the main phase of extension at Valles Marineris. We suggest a new sequence of deformation that accounts for the formation of blunt-trough terminations during the major phase of Valles Marineris extension: coeval and locally bidirectional extension, that results from local stress field changes associated with border fault growth in a dominantly unidirectional remote (extensional) strain field. By implication, many of the irregular closed troughs such as Hebes Chasma are better interpreted as grabens rather than collapse depressions.

Strength of Faults on Mars from MOLA Topography

“…The areas enclosed by dashed lines represent the regions of parameter space which are likely to be appropriate for the features in question; the ranges of λ are as given in Sections 2.1 and 3.2 and the ranges of T e reflect the values discussed in Sections 2.2 and 3.1. the large Tharsis volcanic center (Blasius et al 1977, Banerdt et al 1982, Sharp 1973, Frey 1979, Tanaka and Golombek 1989, review by Lucchitta et al 1992), were probably responsible for the formation of the narrow rectangular troughs (Schultz 1998). This hypothesis is in agreement with the crustal thinning observed under VM by Zuber et al (2000) and with the existence of fault-like features visible in images of the valley walls (e.g., Wilkins and Schultz, 2000). The tectonic grabens were probably superimposed on a series of older basins, produced by crustal collapse, resulting in the large width of the central section of VM (Melas Chasma) (Schultz 1998).…”

Modeling the collapse of Hebes Chasma, Valles Marineris, Mars

“…1B). (1) The elliptical planform, abrupt scalloped margins, blunt ends, and roughly uniform depth of chasma are atypical of rifts (although Wilkins and Schultz [2003] explained the blunt ends by inferred reactivated cross faults, using criteria that can equally be explained by karstic subsidence).…”

“…(3) Only a thin mantle of dust covers the chasma rim, though wind could have carried and deposited the dust elsewhere on the planet. So although surface erosion by water or McCauley et al (1972); Sharp (1973); Lucchitta (1979) Collapse by removal of water or magma Sharp (1973); Courtillot et al (1975); Schonfeld (1979); Tanaka and Golombek (1989); Spencer and Fanale (1990); Schultz (1998); Schultz and Lin (2001); Fueten et al (2005); Rodriguez et al (2006); Rossi et al (2008) Tectonic rifting Sharp (1973); Blasius et al (1977); Frey (1979); Masson (1977Masson ( , 1985; Schonfeld (1979); Anderson and Grimm (1998); Schultz (1991Schultz ( , 1995; Chadwick and Lucchitta (1993); Peulvast and Masson (1993); Mége and Masson (1996); Peulvast et al (2001); Wilkins and Schultz (2003); Bleamaster (2009) Combination of mechanisms Lucchitta et al (1992); Tanaka (1997); Schultz (1998); Lucchitta and Chapman (2002); Montgomery and Gillespie (2005); Montgomery et al (2009) wind was undoubtedly important in other canyons (Table 1), it is unlikely to be the main agent that formed Hebes Chasma. The tectonic rifting hypothesis invokes an origin by north-south tectonic extension, forming Hebes Chasma as a graben (Fig.…”

Planetary structural mapping

“…Such large grabens are characterized by multiply faulted borders and floors (e.g., Plescia and Saunders, 1982;Dohm and Tanaka, 1999;Wilkins et al, 2002;Wilkins and Schultz, 2003) and resemble complex terrestrial rift systems (Schultz, 1991(Schultz, , 1995Banerdt et al, 1992;Hauber and Kronberg, 2005). Other extensional structures include the Valles Marineris troughs (e.g., Blasius et ai., 1977;Lucchitta et ai., 1992;Mege and Masson, 1996;Schultz, 1991Schultz, , 1995Schultz, , 1998Schultz, , 2000bWilkins and Schultz, 2003), structurally controlled sapping channels (e.g., Davis et ai., 1995), and troughs of polygonal patterned ground (e.g., Pechmann, 1980;McGill, 1986;McGill and Hills, 1992;Buczkowski and McGill, 2002) . Wrinkle ridges occur across the Martian surface (e.g., Chicarro et al, 1985;Watters and Maxwell, 1986;Watters, 1988;Schultz, 2000a;Goudy et ai., 2005) and formed in association with impact basins, as on the Moon, and voIcanotectonic provinces such as Tharsis, Thaumasia, and Elysium.…”

“…The Mars Orbiter Laser Altimeter (MOLA), in contrast, has returned some of the highest vertical and spatial (460 m to lIS mJpixel near the poles) resolution interpolated digital elevation models for any of the terrestrial planets thus far (Smith et al, 1999(Smith et al, ,2001Zuber et al, 2000; . The high-resolution MOLA data were used to study Martian tectonic structures in unprecedented detail (e.g., Golombek et al, 2001;Schultz and Lin, 200 I;Schultz and Watters, 2001;Wilkins and Schultz, 2003;Okubo and Schultz, 2003, 2004Schultz et al, 2006;Golombek and Phillips, Chapter 4). These data have also revealed a previously undetected population of subdued wrinkle ridges in the northern lowlands of Mars, partly buried by sedimentary material (Withers and Neumann, 200 I;Head et al, 2002) or formed in weak materials (Tanaka et ai., 2003).…”