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].