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Home , Carbonates on Mars, Coprates Chasma

46th Lunar and Planetary Science Conference (2015) 2112.pdf

Carbonates and phyllosilicates detections in Coprates , , . B. Bultel1, C. Quantin1, J. Flahaut2 and M. Andréani1 1Laboratoire de Géologie de Lyon, Université Lyon 1, ENS Lyon, CNRS UMR 5271 (Laboratoire de Géologie de Lyon, Bâtiment Géode 2 Rue Raphael DUBOIS 69622 VILLEURBANNE CEDEX). [email protected] ,

Introduction: Valles Marineris is a unique place on Mars Spectroscopic study: where deep crust is exposed at its original place [1]. We use CRISM data that we pre-process with The primitive crust is observed at the base of Coprates CAT [5]. Because the signal to noise ratio in CRISM Chasma as well as in the eastern parts of Valles - data is low, we use a personal noise removal pipeline neris [1]. Elsewhere on Mars, several authors [2 and describe in [6]. The ratio used is the median by column references therein] reported detections of ratio describe in [6]. We discriminate our detections by associated with phyllosilicates in crustal outcrops the study of the combination of the position of center thanks to CRISM (Compact Reconnaissance Imaging of absorption near 2.3 and 2.5 µm after continuum re- Spectrometer for Mars) data. is a moval [7 and 8]. The carbonates are detected by these proposed landing site for Mars 2020 mission and is so combinations of absorption in addition to a strong ab- intensely covered by CRISM data. It allows us to in- sorption before 3.45µm and to the presence of the drop vestigate the alteration signs of the primitive crust. We near 3.8 µm. All the carbonates signatures reported describe here the study of 3 CRISM FRT observations here present the characteristic of a mixture with a hy- on the wall of Valles Marineris in Coprates Chasma drated phase or a weathering of the carbonates (pres- and on a remnant horst in middle of the canyon seeking ence of absorptions near 1.4 and/or 1.9 µm, shoulder for alteration minerals. near 2.27 µm and drop of the reflectance after 2.2µm) . [9]. Geological context: We detected the carbonates signatures on the two According to [1 and 3], the walls of Coprates CRISM observations on the walls of Coprates Chasma Chasma exposes both the primitive Low Calcium Py- while similar signature are absent of the CRISM obser- roxene rich crust and the lava stack vation on the floor of the chasma studied here. [1 and 3]. The sharp crustal boundary between the two The absorptions of the Fe/Mg-rich phyllosilicates on types of crust would occur around our study area [1, 3]. #244FE are close to 2.3µm rather than 2.33-2.35µm as A part of the observation #194CA is a 24 km crater for the #249DA and #194CA observations (Figure 2). lying down the floor of the canyon. A part of the ob- This suggests a better match with chlorite for the ob- servation #244FE is on the central horst of the canyon servations on the walls and a better match with smectite (Figure 1). for the observation on the horst.

Figure 1: Geological context. CRISM observations footprints are shown in blue. The Detected mineralogy from CRISM study is reported with the following symbol: blue for chlorite, yellow for smectite, red star for carbonates, orange for sulfates, light blue for LCP and for olivine. The back ground color map is from CRISM multispectral analyze of the area from [4] 46th Lunar and Planetary Science Conference (2015) 2112.pdf

Geologic interpretation: Carbonates are so observed in the crater walls at the level of the southern wall as well as in the north wall. The central horst shows only phyllosilicates. A relationship between the presence of the crater and the presence of carbonates is likely to be exclude because of the same detections made on the facing side of the wall of the chasma. This may suggest an extended layer of carbonated crust. The absence of carbonates signa- ture on the central horst of the chasma can be either because the carbonated layer is not exposed in the cen- tral horst or that the carbonation process is a spatially localized process.

Conclusion: Hydrothermal signatures have already been reported in this area [i. e.: 3 and 10] suggesting hydro- thermal processes at a large scale in the region of Val- les Marineris. Our detection of carbonates associated to phyllosilicates implies carbonation and hydration pro- cess of the crust exposed in the deepest part of Valles Figure 2: Marineris. a: Spectra from RELAB library. b: Spectra detected: Implication for exobiological perspectives will be pre- from #249DA (red: X:345 Y:357 [10x10 AVG]) and sented. #194CA (orange: X:224 Y:281 [30x30 AVG]) without our pipeline in color, with our pipeline in black. References: [1] Flahaut, J., Mustard, J. F., Quantin, C., Clenet, H., Allemand, P., & Thomas, P. (2011). Geophysical Research Letters,38(15). [2] Niles, P. B., Catling, D. C., Berger, G., Chassefière, E., Ehlmann, B. L., Michalski, J. R., ... & Sutter, B. (2013). Geochemistry of : implications for climate history and nature of aqueous environments. Space Science Reviews, 174(1-4), 301-328. [3] Quantin, C., Flahaut, J., Clenet, H., Allemand, P., & Thomas, P. (2012). Icarus, 221(1), 436-452. [4] C. Quantin, J. Flahaut, H. Clenet and P. Allemand, First Landing Site Workshop/NASA and ESA Joint Rover Mission, Wahington D.C., 2012 [5] Parente, M., 2008, LPSC 39. [6] Bultel, B., Quantin, C. and L. Lozac’h, JSTARS (under review). [7] Gaffey S. J. (1987). Jour- nal of Geophysical Research. 92 (B2).753 1429–1440. [8] Hunt, G. R., & Salisbury, J. W. (1971), Modern Geology, 2, 23-30. [9] Gaffey S. J. (1984), Doctoral dissertation. [10] Viviano-Beck, C. E., & Murchie, S. L. (2014), Lunar and Planetary Institute Science Con- ference Abstracts (Vol. 45, p. 1963).

Figure 3: Aknowledgement : a: Spectra from RELAB library. b: Spectra detected: The research leading to these results has received from #194CA (X:238 Y:261 [5x5 AVG]), #244FE funding from the European Research Council under the (X:151 Y:354 [5x5 AVG]) and #249DA (X:235 Y:356 European Union's Seventh Framework Program [5x5 AVG]) (FP7/2007-2013)/ERC Grant agreement n° 280168.