Mineralogy of the Martian Surface Bethany Ehlmann and Christopher Edwards

 Using the emissivity spectrum from a pure material it is easy to identify its composition.  Emissivity spectra from the individual components of a mixture add together in a linear fashion.  Rock spectra must first be unmixed or deconvolved by comparing the features of the spectrum to those of the endmemer spectra from a library.  Individual components of the mixture are identified by matching its spectrum to those in the library.  Using this technique we are also able to determine the relative amounts present

Surface age

Figure 2 a) Global olivine distribution from TES and OMEGA. The purple to green tones are the total olivine abundances for all compositions derived from TES deconvolution results. Yellow to red tones are olivine spectral indicies, correlated with 1-um absorption band strength and derived from OMEGA data for locations where olivine was detected

Primary Igneous Mineralogy  TIR and VNIR of dust free southern highlands indicates a basaltic crust  Local variation is present due to fractional crystallization and crustal assimilation  Surface can be grouped into distinctive types based on mineral proportions (olivine, Cpx, Opx, feldspars, etc.)  Plag. And Cpx are the dominant minerals of most of the southern highlands  Northern plains have the lowest Pyx abundance and highest concentration of silica phases.

Figure 3. a) Location of the Nili Patera caldera on a topographic hillshade map. (b) Yellow tones identify a late-stage dacite lava flow (white arrow), likely formed by differentiation of magmas. Magenta/ purple tones identify olivine-bearing deposits. (c) Small deposits of hydrated silica ( yellow arrows) identified by CRISM on and around the volcanic cone formed during the Hesperian or later from alteration by volcanic vapors and/or waters (Skok et al. 2010).

Sands and Soils  Product of local bedrock compositions  Local variation in sands and soils are found throughout mars.  Generally regolith material appears olivine depleted  Olivine rich sands in Nili Fosse  Course Olivine sands in Columbia hills  Hematite grains sands are derived from weathering in Meridiani  Rock-water interactions has produced gypsum dunes in the northern lowlands  Mars dust appears to be an alteration product  VNIR data shows a strong Fe3+ absorption  VNIR and TIR data show that dusty surfaces are hydrated silicates  Using TES lofted dust has been sampled and is dominantly Plag, and hydrated silicates, with lesser amounts of olivine, Pyx, and sulfates Collectively this data show that the dust is a product of weathering of primary rocks along with oxidation and limited exposure to liquid water

Secondary Alteration of the Crust

Hydration and Alteration of the crust  Global widespread occurrence of hydrated silicates  High resolution orbital data has shown exposures are small but widespread. We have observed phylosilicates…  In stratigraphic units possible due to in-situ alteration  Associated with impact craters (central peaks, walls, ejecta)  As deposits in sedimentary basins

 CRISM data overlain HiRISE image  Aluminum phyllosilicates overlie nontronite-bearing sediments at Mawrth Vallis.  Outcrops similar to this have been observed in Nili Fosse, Vallis Marineris, and in numerous small outcrops across the southern highlands.  These may be the result of acid alteration and/or leaching later in Mars history. Scale bar indicates 200m

 Impact craters have provided exposure of the deep Noachian crust.  Fe/Mg smectites are common throughout many craters  Some also contain chlorite minerals as well prehnite and illite.  This assemblage indicates a high temperature hydrothermal system  The location of these minerals throughout the crater as well as in the central peak and ejecta blanket indicate that the hydrothermal alteration preceded the impact

Paleolakes

Groundwater, Sulfates, and Ferric Oxides  Clear relationship between predicted groundwater upwelling & orbital detections of sulfate minerals.  Hesperian sedimentary rocks with hematite and hydrated sulfates overlie Noachian units with phylosilicates.  Vugs and spherical nodules of hematite are evidence of multiple episodes of groundwater upwelling and precipitation.  The presence of Jarosite and alunite in some of these basins indicates acidic waters with a ph<4

Secondary Alteration of the Crust

Carbonates  CRISM image  Upper capping rock unit (purple) is sitting atop olvine bearing units (yellow) and clays (blue). Where olivine units have greenish coloration is indicative of carbonate formation within the olivine stratigraphy. Image Credit: NASA/JPL/JHUAPL /MSSS/Brown University 20 KM

Conclusions  Oldest Noachian crust is basaltic, it is unknown if any examples of the Primary crust have survived till today  Extensive examples of phyllosilicates and aqueous altered minerals present in much of the older Noachian crust.  Some aqueous alteration seen into the Hesperian, evidence for a more acid environment.  Paleolakes existed in the late Noachian to early Hesperian. Some basins host sedimentary clay and precipitated salts.  Ground water played an important role in formation of clay minerals. Upwelling of groundwater has produced large deposits of sulfates, and hematite.  Amazonian units do not have crystalline alteration minerals, implying substantially less water

References  Ehlmann, B. L., & Edwards, C. S. (2014). Mineralogy of the Martian Surface. Annual Review of Earth and Planetary Sciences, 42(1), 291–  watery-environment php