Figure 5 . A) Semi-curvilinear faults mapped on a CTX mosaic near 115oW, 38oS, in the southern-central sector of the Bathys Planum mapping area. Pink features represent sinistral strike-slip faults, yellow features represent dextral strike-slip faults, purple features represent compressional faults, and white features are possibly structural lineaments of an uncertain sense. Features are identified as left- or right- lateral based on the presence and relative orientations of strike-slip landforms to different fault segments; they are not assigned a fault type if no such landforms are observed, or if the sense of slip is indeterminate. Note that while the “stair-stepping” of graben in this area is indicative of structural control associated with the same trends as the mapped faults, these deflections are not mapped in (A) if they do not correspond to explicit transcurrent / strike-slip geomorphologies. Note that while all other features on the geologic map of Bathys Planum [Adrian et al., 2021] were mapped at a 1:250,000 scale, mapping of the structures in this figure was performed at a 1:24,000 scale on CTX.B) The semi-curvilinear faults with sense of slip for strike-slip landforms overlaid. 127 transpressional landforms (restraining bends, pop-up ridges, possible positive flower structures) are digitized as black squares and 48 transtensional landforms (releasing bends, pull-apart basins, possible negative flower structures) are digitized as red circles.
A total of 19 left-lateral strike-slip fault strands were mapped between two highland ridge-forming units (Noachian highlands Nh2 and Nh3) and an inter-ridge fill unit (middle-Noachian plains mNp), per Adrian et al., [2021], in the central part of the Bathys Planum map region near 115oW, 38oS (Figure 5). The faults generally strike east/northeast-west/southwest, although 6 right-lateral strike-slip fault strands were mapped in the northern-central section of the frame of Figure 5 and may represent conjugate features to the more dominant left-lateral trend. In general, the strike-slip faults are considerably more linear than the compressional faults in this section of Bathys Planum, which are observed to dip towards a central point (using the Golombek et al., [2001] model). In some locations, the strike-slip faults appear to be overridden by the east-west compressional faults, before continuing along the same east/northeast - west/southwest parallel trend farther down the compressional fault’s scarp. This suggests that the more curvilinear compressional faults preceded the emplacement of the strike-slip faults.
The Bathys strike-slip faults are relatively discontinuous with minimal lateral displacement. A distinct offset of approximately 1.6 km (Figure 3) occurs on one of the strands. Furthermore, they are associated with relatively small and shallow pull-apart basins not expected to exceed the depth of their bounding strike-slip faults [Aydin and Nur, 1985]. This suggests that the observed strike-slip faults are shallow features which do not directly represent tectonism in the deeper crust [Aydin and Nur, 1985; Christie-Blick and Biddle, 1985].
The possible strike-slip faults identified in this work notably differ from those proposed by Andrews-Hanna et al., [2008] in Terra Sirenum and Amazonis Planitia because the strike-slip morphology of the faults in Bathys Planum appear to be foremost characterized by the existence of transcurrent landforms (as opposed to linear ridges with asymmetrically tapering throws on each side of the fault). They also differ from models invoking accommodation of oblique slip in Tharsis-radial graben sets [e.g., Masson, 1980; Fernández and Ramírez-Caballero, 2019; Montgomery et al. 2009], and from regionally extensive invocations of strike-slip faulting which largely depend on offset as a kinematic indicator [Schultz, 1989; Yin, 2012]. Note that transcurrent/strike-slip landforms have also been reported on Europa [e.g., Sarid et al., 2002] and Venus [Koenig and Aydin, 1998].