47th Lunar and Planetary Science Conference (2016) 2165.pdf

A SERPENTINIZATION ORIGIN FOR JEZERO CRATER CARBONATES. A. J. Brown1, C.E. Viviano- Beck2, J.L. Bishop1, N.A. Cabrol1, D. Andersen1, P. Sobron1, J.Moersch3, A.S. Templeton4, M.J. Russell5. 1SETI Insti- tute, 189 N. Bernardo Ave, Mountain View, CA ([email protected]) 2Johns Hopkins Applied Physics Laboratory, 3University of Tennessee, 4University of Colorado, Boulder, 5Jet Propulsion Laboratory, Pasadena, CA.

Figure 1 – (left) CRISM image FRT47A3 and HRL40FF, CAR browse product, overlain on CTX image D14_032794_1989_XN_18N282W in Jezero crater. Green regions show strong carbonate signatures, with associated 2.38μm band. Light/dark blue shows north/south fan as delin- eated by Goudge et al. [9]. Note 2.38μm feature appears strongly in west part of north fan. The east part of the northern fan is spectrally feature- less. (right) Example of spectra from point A in the right image, showing 2.31, 2.38 and 2.54μm bands.

Introduction: The Nili Fossae region is the site of used this spectral feature to map the locations and con- a number of proposed Landing Sites for the Mars 2020 fine the talc findings to eastern Nili Fossae. Rover. A distinguishing feature of all of these sites is Methods: The so-called “talc-carbonate” hypothe- the access to large amounts of carbonate deposits [1] sis rests on the presence of a 2.38μm absorption band and smaller carbonate deposits have been found else- that is almost always present when carbonate absorp- where on Mars [2]. Serpentinization has been proposed tion bands are detected. It is hypothesized that because as a formation mechanism of the Nili Fossae carbon- the carbonate 2.54μm feature is so often accompanied ates, including carbonated [3-5] and low temperature, by a 2.38μm band, there must be a genetic link be- near surface serpentinization [3,6]. tween the Mg-phyllosilicate causing the 2.38μm band Serpentinization: The presence of talc following and the accompanying Mg-carbonate [3-4]. Figures 1 carbonated serpentinization has been linked to Earth and 2 show example of such spectra. These spectra analogs in terrestrial greenstone belts such as the Pil- have been extracted from the CRISM MTRDR product bara in Western Australia, where talc-bearing komatiite [8]. No ratioing has been conducted on these spectra. cumulate units of the Dresser Formation overlie the A recent compelling study of the Jezero crater delta siliceous, stromatolite-bearing Strelley Pool Chert unit network suggested there are large amounts of carbon- [7]. If a similar relationships exists on Mars, investiga- ate with no accompanying 2.38μm band [9]. We have tions of rocks stratigraphically beneath the talc-bearing therefore conducted a detailed search of the north and units at Nili Fossae may provide the best chance to ex- western delta fan deposits and parts of the northern fan amine well preserved, siliceous organics. This hypoth- watershed to determine whether any carbonate signa- esis is testable at any of the remaining Nili Fossae tures with accompanying 2.38μm band are present. sites, but here we examine the case of Jezero Crater. Take-away message: In fact, our mapping of the Talc-carbonate hypothesis: Two recent studies watershed region and the Jezero delta has revealed sev- have uncovered corroborating spectral evidence for eral key regions (Figures 1-2) that show evidence of talc in association with the carbonate at Nili Fossae us- stratigraphic relations between carbonate and 2.38μm ing the CRISM spectrometer on MRO. Motivated by bearing material. fieldwork in the Pilbara region of Western Australia Results: We have used CRISM image browse [7], Brown et al. [3] suggested talc was present in products and spectral feature fitting to discriminate be- some locations at Nili Fossae. Viviano et al. [4] then tween 2.38μm-bearing material and Mg-carbonate that identified a spectral signature for talc vs. saponite lacks the 2.38μm band. Figure 1 shows two CRISM which identified the presence of a talc component and images overlaying a CTX image of Jezero crater, and 47th Lunar and Planetary Science Conference (2016) 2165.pdf

shows the north and western fans as mapped by Astrobiological Implications: Following the over- Goudge et al. [9]. The CAR browse image are green in turn of their respective magma oceans and creation of the presence of a 2.54μm band [10]. A large expanse of their primordial seas [11], life began on Earth and may green is shown to the west of the western fan, and have emerged on Mars in an ocean-floor setting [12]. some green appears on the western fan itself. However, The presence of talc-carbonate is consistent with hy- there is also a region of green shown in the west part of drothermal alteration of ultramafic rocks in an ocean- the northern fan. We extracted spectra from all of these floor setting [3] and may therefore be an indicator of units (including the western fan), and a representative an astrobiologically-rich environment at Nili Fossae. spectrum from Point A is shown on the right of Figure Talc-dominated terrestrial hydrothermal sys- 1. This demonstrates that the 2.38μm band accompa- tem. The recent discovery of talc-dominated hydro- nies the carbonate 2.54μm band in these regions. The thermal systems in a modern terrestrial seafloor setting location with the weakest (absent?) 2.38μm band is the [13] provides another potential mechanism for talc-for- western fan outliers at Point B, but this may just be due mation that may be of relevance to early Mars. The to the weakness of the overall spectra. Figure 2 con- formation and detection of large amounts of talc in this sists of two images (FRT 23370 and FRT 97E2) from setting is a timely reminder that our understanding of the watershed region for the northern fan, and a spec- talc formation is still in its nascent stages [14]. trum showing that they also possess an accompanying Acknowledgements: This work was sponsored by 2.38μm band. the NASA Astrobiology Institute. Implications for Carbonate Formation condi- References: [1] Ehlmann B.L. et al. (2008) Sci- tions: This first mapping of 2.38μm material in most ence 322 1828 [2] Morris, R. et al. (2010) Science sci- of the Jezero basin, particularly in the northern fan, is ence.1189667, Carter, J. and Poulet, F. (2012) Icarus key to linking these carbonate occurrences to the other 219 250, Bishop, J.L. et al. (2013) LPSC 44 #2555 [3] Nili Fossae carbonates. We would hypothesize that Brown, A. J., et al. (2010) EPSL 297 174 [4] Viviano, since the 2.38μm material is present in both the water- C.E., et al. (2013) JGR 118 1858 [5] McSween, H.Y.. shed and deltaic fan of Jezero crater, these Mg-phyl- et al. (2014) MAPS 50 1 [6] Ehlmann, B.L. et al. losilicate-carbonate bearing materials would most (2009) JGR 114 10 [7] Brown, A.J. et al. (2005) AJES likely have been transported to Jezero from the water- 52 353 [8] Seelos, F. P. et al. (2016) this meeting [9] shed, and thus the Jezero delta material likely shares an G o u d g e , T. A . e t a l . ( 2 0 1 5 ) JGR Planets (carbonated serpentinization [3,4]) origin in common 10.1002/2014JE004782 [10] Viviano-Beck et al. with the remainder of the Nili Fossae carbonate expo- (2014) JGR doi:10.1002/2014JE004627 [11] Elkins- sures. This hypothesis can be tested by in situ investi- T a n t o n , L . T . , e t a l . ( 2 0 0 5 ) E 1 2 S 0 1 gations by Mars2020 if it lands at Jezero crater. 10.1029/2005JE002480. [12] Russell, M.J. et al. Testing with the Mars2020 payload. As part of (2014) Astrobiology 14 308 [13] Hodgkinson M. et al. the SETI Institute NAI team project, this summer we Nature Comms 10150 10.1038/ncomms10150 [14] Vi- are conducting fieldwork in the north western Pilbara viano-Beck, C.E. et al. (2016) this meeting region of Australia with a Raman SuperCam analog in- strument suite in order to test the ability of the Figure 2 - (left) CRISM FRT23370 and FRT 97E2 overlain on Mars2020 rover suite to discriminate Mg-phyllosili- CTX image G20_025990_1993_XN_19N283W. The CAR browse cates such as saponite and talc. We will report on labo- product shows carbonate in green tones. These carb locations all have accompanying 2.38μm bands as seen for example on (right) ratory preparations for this fieldwork at the meeting. spectra from FRT 23370 showing 2.31 and 2.38μm bands with a broad 2.54μm band due to Mg-carbonate.