Mars Exploration Rover Opportunity traversed 7.9 km and 27 degrees of arc along the rim of the 22 km-diameter Noachian "Endeavour" impact crater since its arrival 1200 sols ago. Areas of aqueous and low-grade thermal alteration, and changes in structure, attitude, and macroscopic texture of outcrops are notable across several discontinuities between segments of the crater rim. The discontinuities and other post-impact joints and fractures coincide with sites of apparent deep fluid circulation processes responsible for thermal and chemical alteration of local outcrops

Arvidson, R. E.

Crumpler, L. S.

Farrand, W. H.

Golombek, M. P.

Grant, J. A.

Ming, D. W.

Mittlefehldt, D. W.

Parker, T. J.

NASA Technical Reports Server

OPPORTUNITY IN SITU GEOLOGIC CONTEXT OF AQUEOUS ALTERATION ALONG OFFSETS IN 
THE RIM OF ENDEAVOUR CRATER. L. S. Crumpler1, R. E. Arvidson2, W. H. Farrand3, M. P. Golombek4, J. 
A. Grant5, D. W. Ming6, D. W. Mittlefehldt6, T. J. Parker4, 1New Mexico Museum of Natural History & Science, 
1801 Mountain Rd NW Albuquerque, NM, 87104, USA, larry.crumpler@state.nm.us, 2Washington University in St 
Louis, St. Louis, MO, USA, 3Space Science Institute, Boulder, CO, USA, 4Jet Propulsion Laboratory, Caltech, 4800 
Oak Grove Drive, Pasadena, CA 91109, 5Smithsonian Institution, NASM CEPS, 6th at Independence SW, Wash-
ington, DC, 20560, 6NASA Johnson Space Center, Houston, TX, United States, 77058, USA 
 
   Introduction: Mars Exploration Rover Opportunity 
traversed 7.9 km and 27 degrees of arc along the rim of 
the 22 km-diameter Noachian "Endeavour" impact cra-
ter since its arrival 1200 sols ago. Areas of aqueous and 
low-grade thermal alteration, and changes in structure, 
attitude, and macroscopic texture of outcrops are nota-
ble across several discontinuities between segments of 
the crater rim. The discontinuities and other post-impact 
joints and fractures coincide with sites of apparent deep 
fluid circulation processes responsible for thermal and 
chemical alteration of local outcrops. 
   In Situ Geology of Rim: Opportunity determined the 
elemental, spectral, and petrographic character of dis-
tinctive outcrop lithologies along the crater rim [cf. 1, 2, 
3, 4]. The petrologic results, contacts, attitudes of bed-
ding, and structures have been mapped along a swath 
determined by the limit of Navcam detection, empiri-
cally defined at ~20 m distance from the rover [4]. Out-
crops examined along the rim crest and upper slopes at 
Cape York and south at Murray Ridge consist of impact 
breccias ("Shoemaker formation") from >> 5 m thick 
overlying smectite bearing [1] fine-grained pre-impact 
materials ("Matijevic formation") (>>3 m thick), both 
laced with thin (1-2 mm) CaSO4 veins [1]. An overlying 
unit ("Grasberg formation") (<1m thick) drapes in un-
conformable contact over the deeply eroded Shoemaker 
breccias. The eroded and weathered upper surface of the 
moderately dipping (~10°) Grasberg fm is in turn over-
lain by the sulfate-rich sands of the "Burns formation" 
(>100m thick) constituting most of the surface of Me-
ridiani Planum and partially burying and filling En-
deavour crater. 
Mapping has continued south of Cape York along the 
western margin of Endeavour crater (Fig. 1). A consis-
tent stratigraphy determined from correlation of results 
from site to site, along with determination of attitude of 
contacts [4], outlines the geologic history and sequence 
of alteration events. The recognition of an azimuthally 
segmented structural fabric of the rim correlates with 
distinct sites of identified petrologic differences and 
intensities of aqueous alteration. 
   Segmented Structural Regimes: Segmentation of the 
crater rim occurs as azimuthal discontinuities in relief 
Figure 1. A. In situ mapping along Opportunity's traverse. 
Dashed lines denote boundaries between left and right-
stepping rim segments, across which structure, outcrop 
characteristics, and elemental abundances differ. B-F. Sites 
of in situ measurements discussed in the text (white dots). 
 
https://ntrs.nasa.gov/search.jsp?R=20150002839 2019-08-31T13:49:32+00:00Z
and patterns of surface roughness. In situ detection of 
differences in geologic character and disparities in struc-
tural grain across these segments are apparent along the 
rim from Murray Ridge and southward to Cape Tribula-
tion. Alteration is pervasive at outcrops throughout the 
rim, but it is at or near the boundaries between segments 
where the most intense alteration [5] has been observed.  
   General Rim Structure: The crater rim consists of 
right and left-stepping segments and low and narrow 
segments that are sinuous. The western slopes are planed 
along uniform grades of ~10° while bedding/laminations 
of outcrops exceed the slope angle (~10°). But planar 
features east of the rim consistently dip shallowly east-
ward, as do outcrops observed along-strike in the vicin-
ity of segment offsets. The origin of a uniform sloping 
pediment-like planation of the western slopes across the 
dipping beds remains unclear. 
Solander Point (Fig 1b): The geologic sequence here 
is consistent with that noted 1500 m to the north at Cape 
York in which the Burns fm is in unconformable contact 
with the dipping weathered carapace of the Grasberg fm. 
Structural contours on the contact between the Burns-
Grasberg fms and the Noachian rim breccias ascends 
from east to west around Solander Point implying a thin-
ning of the late sulfate sands inboard of the crater rim. 
Laminations or layering of the Shoemaker fm breccias 
dip westward (~20°) along a ridgeline ("Murray Ridge") 
that continues south 800 m.  
   Cook Haven (Fig 1c): Observations during the 5th 
winter were conducted at "Cook Haven", where Murray 
Ridge steps left and there is a change in relief, outcrop 
habit, and plunge of the ridge crest. Fractures in the 
plains to the west are coincident with the strike (N69W) 
of the discontinuity in ridge characteristics, denoting a 
possible relationship with a deep-seated fracture. Un-
usual exposures in the outcrop here have oxidized coat-
ings enriched in Mn deposited on sulfates suggesting 
enhanced low-grade oxidizing, and possible thermal, 
aqueous deposition [5, 8]. 
   "Al-OH Region" (Fig 1d): 400m south of Cook Ha-
ven Murray ridge steps left. This segment is notable in 
that CRISM spectra detected the presence of aluminous 
smectite [6]. Also, near the crest and on the western 
slope near the step "Pillinger Point", CaSO4 veins are 
more prominent in rim outcrops than elsewhere. Both 
observations indicate that in addition to acting as zones 
of enhanced alteration, the discontinuities are also 
boundaries on segments with different prevailing altera-
tion histories. 
   Wdowiak Ridge (Fig 1e): Dark, fine-grained rocks 
occur at two locations, 80 m south of Cook Haven and at 
Wdowiak Ridge, an unusual ridge aligned with the north 
margin of the right-stepping Cape Tribulation rim seg-
ment. The rocks capping Wdowiak Ridge are a dense 20 
m x 200 m mass several meters thick of irregularly frac-
tured dark blocks perched several meters above the sur-
roundings and represent yet another manifestation of 
segment boundaries. The dark rocks are compositionally 
distinct from the Shoemaker formation breccias of the 
crater rim [6]. Given the deep erosion of the crater rim 
[7] and similar rocks elsewhere along the crest of the 
crater rim, inversion of topography representing former 
trough aligned along the segment boundary appears 
likely. Either the dark rocks were emplaced as massive 
deposits (impact melt?) or fragmented, mobilized, and 
collected in the trough.  
   "The Fracture" (Fig 1f): Outcrops are sparse on the 
tilted planar slopes of the ridge leading up to Cape 
Tribulation summit. Tangential and radial fractures oc-
cur here not seen elsewhere in Noachian outcrops along 
the rim. Opportunity examined outcrops exposed in a ra-
dially oriented example, a simple 2-3 m wide graben, 
"The Fracture". Higher Cl and S concentrations in these 
outcrops highlight the potential for any vertical disconti-
nuity to enhance localized fluid flow.  
   Interpretation: Discontinuities in the rim are consis-
tent with development of transverse faults as the upward 
and radial compression of the upper crust during crater 
formation is accommodated by a series of discontinuous 
oblique thrust faults along discreet blocks. The relative 
motion between blocks would require accommodation 
by vertical dip, oblique slip scissor faults or lateral ramp 
structures. Inspection of MRO/HiRISE image data along 
the rim of Santa Fe crater, in Chryse Planitia (19.5°N 
48.0°W), a similar size (21 km), but much younger 
(Amazonian) complex crater, suggests that the fault 
zones may re-activate as oblique slip zones accommo-
dating inboard extension within crustal blocks during 
post-impact modification. Mylonization and fault-line 
brecciation along the bounding deep crustal faults serve 
as major vertical discontinuities and high permeability 
pathways along the rim. Both post-impact hydrothermal 
circulation [8] and regional groundwater much later 
would preferentially follow these zones during the proc-
esses associated with subsequent aqueous alteration. 
   Conclusions: Rim segmentation by transverse faults 
enhanced aqueous chemical alteration in specific loca-
tions along the rim of Endeavour crater. Fracture con-
trolled alteration may be another origin for hydrated 
minerals detected along the rims of many Noachian 
craters [9]. Combined with the apparent exposure of pre-
impact lithologies, as noted in the rim at Endeavour [4], 
impact crater rims also favor retention of physical and 
chemical evidence of past complex aqueous environ-
ments and chemistries. 
References Cited: [1] Squyres et al, (2012). Science 336, 
570; [2] Arvidson et al., (2013). Science; [3] Ferrand et al., 
(2014), JGR, in press; [4] Crumpler et al., (2014), JGR, in revi-
sion; [5] Arvidson et al., (2015), this conference; [6] Mittle-
fehldt et al., (2015), this volume [7] Grant et al., (2015), this 
volume; [8] Newsom et al., (1986), JGR, 1981, [8] Ming et al, 
(2015), this conference; [9] Fairen et al, (2010). Proc.Nat'l 
A.S., 107. 12095-12100. 


Opportunity In Situ Geologic Context of Aqueous Alteration Along Offsets in the Rim of Endeavour Crater

Opportunity In Situ Geologic Context of Aqueous Alteration Along Offsets in the Rim of Endeavour Crater

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