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Year 3 Geologic Mapping of Eastern Coprates Chasma (Mtm -15057), Mars

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Year 3 Geologic Mapping of Eastern Coprates Chasma (Mtm -15057), Mars 3rd Planetary Data Workshop 2017 (LPI Contrib. No. 1986) 7104.pdf YEAR 3 GEOLOGIC MAPPING OF EASTERN COPRATES CHASMA (MTM -15057), MARS. M. Chojnacki1, B. M. Hynek2-3, S. R. Black2-3, R. Thomas2, R. Hoover2, and J. R. Martin2. 1Lunar and Planetary Lab, University of Arizona, Tucson, AZ, 85721([email protected]); 2Laboratory for Atmospheric and Space Physics & 3Dept. of Geological Sciences, University of Colorado-Boulder, Campus Box 600 UCB, Boulder, CO 80303. Introduction: The eastern part of the Valles detected among central wall units [8] – our ongoing Marineris and Coprates chasma, is fundamentally analysis will attempt to correlate their occurrences important to our understanding of crustal formation with lithologic map units. Canyon Interior Units: and modification processes as there is more crust Mapping of the interior has revealed a diversity of exposed here (>11 km) than perhaps anywhere on units not resolved by previous efforts at coarser Mars [1, 2]. These exposures are relatively scales [3] (see [9-10]). Fine-scale map areas: unobscured, partially due to the lack of interior Additionally, we have initiated three 1:25,000-scale layered deposits that elsewhere mask wall contacts. region of interest maps (Fig. 2). These sub-area maps The primary objective of this 2013 PGG-funded provide fine scale details of key areas that can then study is to produce a geologic map of the Coprates be applied to the larger map region and are described chasma quadrangle (MTM-15057) at the 1:500,000- in further detail with prior presentations [9–11]. In scale that will be submitted for peer-review and summary, the detailed mapping is revealing a long publication by the USGS. and complex history for the formation and evolution Datasets: A 6 m/pix visible wavelength CTX of the Coprates chasma. Full results will be presented mosaic was used for the basemap. We supplemented at the meeting. with 100 m/pix daytime and nighttime IR data from Acknowledgements: Funding for this work came from THEMIS for morphology and thermophysical NASA PGG grant NNX14AN36G and ongoing support is properties, respectively. HiRISE coverage (Fig. 1; 25 provided by the USGS mapping group. Students and staff at the UA HiRISE Photogrammetry Lab are gratefully cm/pix) exists for roughly 12% of the map region and acknowledged. twelve HiRISE DTMs (1 m/post) are located in key References: [1] McEwen A.S. et al. (1999) Nature, 397, locales. HRSC stereo-derived DTMs (50 m/pix) 584–586. [2] Beyer R.A et al. (2005) Icarus, 179, 1–23. [3] provide additional topographic information. Finally, Tanaka K.L. et al. (2014) Plan. and Space Sci., 95, 11–24. CRISM hyper- and multi-spectral cubes were [4] Weitz C. et al. (2014) Geophys. Res. Lett., 41, 8744– consulted for compositional information. 8751. [5] Murchie S.L. et al. (2009) JGR-Plan., 114, E00D06. [6] Flahaut J. et al. (2012) Icarus, 221, 420–435. Mapping update: To date, we have drafted a [7] Chojnacki M. et al. (2014) Icarus, 232, 187–219. [8] preliminary 1:500,000-scale geologic map (Fig. 2). Chojnacki M. et al. (2016) JGR-Plan., 121, 1204–1231. [9] Plateau Units: Our plateau units above the canyon Hynek B. et al. (2015) Ann. Plan. Map. Meeting, Univ. of rim are fairly consistent with unit boundaries defined Hawaii. [10] Chojnacki M. et al. (2016) Ann. Plan. Map. by Tanaka et al. [3] in the recent global map. The Meeting, Flagstaff, AZ. [11] Martin J. et al. (2016) LPSC, oldest terrain occurs in the southwest/southcentral abs. # 2625. area of the map and includes a portion of an ancient volcanic edifice and degraded and structurally- deformed highlands. These are superposed by Late Noachian highlands exhibiting terrain of mottled albedo and varied topography. In places, fluviolacustrine processes have modified this surface, some of which show phyllosilicate signatures in CRISM data [4]. The youngest plateau units are smooth, lightly cratered terrains and are interpreted as Hesperian-aged lava flows. Canyon Wall Units: Mapping of canyon walls was initiated with the construction of more than a dozen HiRISE- based stratigraphic columns supplemented by CRISM analysis. In these, units show several classes of Figure 1. HiRISE close-up views of Coprates map units. mafic- and phyllosilicate-bearing surfaces [5–7]. a) RSL along Nectaris Montes massive spur units. b) Also, the intriguing phenomena of recurring slope Canyon floor layered terrain, lower bedded units, and lineae (RSL) or potential salty water seeps have been mantling units. c) Upper bedded units along the N wall. d) Noachian-aged light-toned plains intersecting older plains 1 units. See Fig. 2 for locations. 3rd Planetary Data Workshop 2017 (LPI Contrib. No. 1986) 7104.pdf Figure 2. Geologic map of Coprates chasma MTM -15057. Three 1:25,000-scale region of interest maps are indicated with red boxes (see [11-13]). Plateau Units: Three highlands units are present with variable albedo and degrees of sedimentary dissection and erosion. A single volcanic edifice exists in the southwest map area. Two smooth, low-relief plains units are interpreted to be ancient lava flows with variable modification histories. Younger dark and light toned plains units superpose the before aforementioned units. Several appearances of catena units are located in the southwest, which may have smaller interior units of variable origin. Craters and their ejecta occur across the map area. Catena Units: Numerous small units occur in Coprates Catena and are described in [11]. Canyon Wall Units: Laterally continuous sequences occur with the upper bedded unit north and south wall units. Bellow these are the massive spur units and occasional stretches of smooth wall units dominate wall sections to the north, south, and those of Nectaris Montes. Isolated occurrences of an undivided wall unit may also occur. These all override lower bedded units that are in contact with canyon interior units. Canyon Interior Units: Interior units include: (1) rough canyon floors with hummocky textures and a sparse crater distribution (> 1 km diameter); (2) smooth canyon floors with fractures, polygonal terrain, often heavily cratered; (3) rough mounds or blocks, possessing spurs, talus, and occasional fine-layering; (4) flat mounds with a smooth table-like morphology; (5) crater and ejecta materials; (6) crater interior deposits consisting of hummocky materials; (7) volcanic edifices with small cone like structures; (8) layered terrain which are light in tone, patchy, and distributed on canyon floors and walls; (9) landslide deposits of rugged, sometimes lineated materials and varying runout distances; (10) aeolian dune deposits of low-albedo sand forming slip faces and masking lower-lying units; (11) aeolian sand sheets of mid-toned fine materials without prominent duneforms; (12) resistant mantling units of dark-toned, relatively thick (>5 m) flat deposits that retain small craters; (13) blocky deposits of concentrated, small (<500 m) blocks or mounds. .
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