Detailed Mineralogy of Eberswalde Crater
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42nd Lunar and Planetary Science Conference (2011) 2450.pdf DETAILED MINERALOGY OF EBERSWALDE CRATER. Nancy K. McKeown1 and Melissa S. Rice2, 1Grant MacEwan University (Physical Sciences, Edmonton, AB, T5J 4S2, [email protected]), 2Cornell Uni- versity (Department of Astronomy, Ithaca, NY 14853, [email protected]). Introduction: Eberswalde Crater has been select- µm, 1.9 µm, and 1.4 µm [14]. Fe/Mg phyllosilicate ed as one of four candidate landing site for the Mars signatures have been identified in both Holden ejecta Science Laboratory (MSL) mission based on the pres- and in several layers of the delta sediments [15]. The ence of a fan-shaped deposit interpreted as a delta strength of the signatures within the delta vary between [1,2]. This feature is strong evidence for persistent layers and some layers also contain HCP in addition to fluvial processes and a standing body of water on the the Fe/Mg phyllosilicates (figs. 4,5). Unfortunately, in surface of Mars [3-5]. Elsewhere in Eberswalde Crater, many cases the mineral spectra are too weak to identify inverted channels and plateaus of layered rocks suggest which Fe/Mg phyllosilicate is present. Additionally, a complex history of fluvial activity and deposition in the 2.3 µm absorption is frequently very weak and the basin [6,7]. therefore not visible at the scale of figure 4. Phyllosilicate minerals have previously been de- Hydrated minerals. In several locations, outcrops tected in the putative Eberswalde delta in observations with a hydrated mineral signature are observed. These from the Compact Reconnaissance Imaging Spectrom- spectra present a 1.9 µm absorption feature due to eter for Mars (CRISM) [8]. In this work, we use overtones of the stretching and bending modes of H2O CRISM data to study the mineralogic stratigraphy of within the mineral structure (fig. 3) [14]. No other the putative delta and to characterize the mineralogy of absorption features are present in these spectra. other units in the Eberswalde basin. By examining the Conclusions: Mineralogically distinct layers are mineralogy in detail, we may be able to better charac- present within the delta in Eberswalde Crater, suggest- terize the past geologic environment. ing changes in the mineralogy of the source region. Methods: TRR3 data from CRISM—produced to None of the phyllosilicate signatures are very strong, aid the Mars Science Laboratory landing site selection however, implying they are present in low quantities or process—were used in this study after atmospheric and covered with dust. No phyllosilicates have yet been cos-i correction (fig. 1) [9]. Spectra of interest are identified on the crater floor, only olivine and the ratioed to a spectrally unremarkable region in the same ubiquitous HCP. This implies that any possible phyl- column to reduce systematic noise [9, 10]. All spectra losilicate-bearing lake sediments have been eroded are single-pixel spectra rather than averages due to the away, are covered with sand/dust, or are present in morphology of outcrops in the images. Parameter small quantities below CRISM’s spatial resolution. maps [11] were generated to aid identification of re- gions of interest (fig. 2). Results: Olivine, high calcium pyroxene (HCP), and Fe/Mg phyllosilicates, and a hydrated phase have been identified within Eberswalde crater. Olivine. Olivine spectra are characterized by three overlapping absorptions near 1.0 µm that appear as one broad asymmetric absorption with a strong positive slope from 1.0-1.8 µm (fig. 3) [12]. Olivine has been identified on the crater floor and in blocks interpreted as ejecta from Holden Crater [6,7]. The olivine on the crater floor appears smooth in CRISM and HiRISE data and seems to directly underlie the sand/dust that covers the crater floor. It is possible these olivine ex- posures are also Holden Crater ejecta. HCP. The spectrum of HCP is characterized by two broad absorpstions centered near 1.0 and 2.0 µm (fig. 3) [13]. HCP has been identified throughout Eberswalde crater, perhaps in dust or sand on the sur- Figure 1. False-colour IR CRISM image face. In some cases, however, it appears to be mixed FRT000060DD of the edge of the putative Eberswalde with Fe/Mg phyllosilicates in layers of the delta. delta, basin floor material, and possible Holden ejecta. Fe/Mg Phyllosilicate. Spectra of Fe/Mg phyllosili- R: 2.56 µm, G: 1.8 µm, B: 1.05 µm. Blues are hydrat- cates are characterized by sharp absorptions at ~2.3 ed Fe/Mg phyllos and reds are olivine. 42nd Lunar and Planetary Science Conference (2011) 2450.pdf Figure 2. Parameter map for FRT000060DD R: D2300 (stretched -0.006 to -0.002), G: HCPINDEX (0.146 to 0.187), B: BD1900R (-0.002 to 0.001). White box indicates the location of figs. 4, 5. Figure 4. Zoom from fig. 1 showing layers in the delta with different mineral compositions. Figure 3. Spectra from FRT000060DD (top four spectra) with CRISM library spectra (bottom three). References: [1] Malin M. and Edgett K. (2003) Science, 302, 1931-1934. [2] Moore et al. (2003) GRL, 30. [3] Wood L. (2008) GSA Bulletin, 118. [4] Pondrelli M. et al. (2008) Icarus, 197. [5] Lewis K. and Aharonson O. (2006) JGR, 111. [6] Schieber J. (2008) 39th LPSC, abs. no. 1391. [7] Rice M. and J.F. Bell III (2010) 41st LPSC, abs. no. 2524. [8] Milliken R.E. et al. (2006) 7th Interna- tional Conf. on Mars, abs. no. 3282. [9] Murchie S. L. et al. (2009) JGR, 114, doi:10.1029/2009JE003344. [10] McKeown N.K. et al. (2009) JGR, 114, doi:10.1029/2008JE003301. [11] Pelkey S.M. et al. (2007) JGR, 112, doi:10.1029/ 2006JE002831. [12] Sunshine Figure 5. Zoom from fig. 2 in the same location as J.M. and Pieters C.M (1998) JGR, 103, no. E6. [13] Burns R.G. fig. 4. The yellow layer is a mixture of 2.3 µm and (1970) Mineralogical Applications to Crystal Field Theory, Camb. HCP, white is 2.3 µm, 1.9 µm, and HCP (Fe/Mg phyl- Uni. Press. [14] Bishop J.L. et al. (2008), Clay Miner., 43(1). [15] lo+HCP), and green is HCP. Milliken R.E. and Bish D.L. (2010), Phil. Mag. .