Mars, The First Billion Years Warm and Wet vs. Cold and Icy?

Transcription

1 Mars, The First Billion Years Warm and Wet vs. Cold and Icy? Bethany L. Ehlmann 1,2 1 GPS-Caltech, 2 JPL-Caltech 8 th International Mars Conference July 15, 2014

2 Mineralogy & Chemistry this presentation Early Martian Habitats(?)/ Environments Geomorphology Climate Modeling

3 Aqueous Minerals on Mars (circa 6 th Mars Conf., 2003) Hematite (Fe 2 O 3 ) Terra Meridiani Christensen et al., J. Geophys. Res. 2000; 2001

4 Aqueous Minerals on Mars (circa 7 th Mars Conf., 2007) sulfates phyllosilicates hydrated material Bibring et al., 2006

5 (release of volatiles, including S) Wet, circum neutral ph Drying, acidic ph Bibring et al., 2006 If phyllosilicates had formed in the subsurface, the Mars environment might have always been tenuous, cold, and dry, except for transient episodes. If instead phyllosilicates formed at or close to the surface, this would require the Mars early atmosphere to be dense. The global change to an acidic environment would then have been coupled to a rapid drop in atmospheric pressure.

6 Distribution of Aqueous Minerals on Mars (circa 8 th Mars conf., 2014) Ehlmann & Edwards, Ann. Rev. Earth Plan. Sci., 2014 (influence of latitude-dependent mantle) (influence of latitude-dependent mantle) Ehlmann et al., 2011, Nature Carter et al., 2013, JGR Osterloo et al., 2010, JGR Niles et al., 2013, Space Sci Rev

7 Secondary Minerals Observed to Date on Mars (circa 8 th Mars conf., 2014) Oxides Phyllosilicates (Clay minerals) Other hydrated silicates Carbonates Sulfates Chlorides Perchlorates Ehlmann & Edwards, Ann. Rev. Earth Plan. Sci., 2014 Hematite Goethite Akaganeite Fe,Mg smectites (e.g., nontronite, saponite) Al-smectite (e.g. montmorillonite, beidellite) Kaolin group minerals (e.g. kaolinite, halloysite) Chlorite Serpentine High charge Al,K phyllosilicate (e.g. illite) Prehnite Analcime Opaline silica, quartz (n=0) Mg, Ca, Fe carbonates (solid solutions) Fe,Mg mono- and poly-hydrated sulfates Gypsum (n=2), bassanite (n=0.5), anhydrite (n=0) Alunite Jarosite Fe 3+ SO 4 (OH) [not a named mineral] chlorides perchlorates

8 A Conceptual Framework

9 Chemical & Mineralogical Styles of Alteration Diagram after Nesbitt &Wilson, 1992; Hurowitz & McLennan, EPSL, 2007 see Ehlmann et al., 2011, Nature

10 Low, W:R, open system (acidic) atmosphere Mineralogy: no clay, Fe oxides, salts, amorphous silica coatings contact with a little (acidic) water

11 e.g. Kau Desert, Hawaii, Seelos et al., JGR, 2010 Sulfate salts Silica coatings

12 Low, W:R, open system (acidic) atmosphere contact with a little (acidic) water

13 Styles of Alteration to form Clays Open system, high W:R Mineralogy of residue : Al-clays, Fe-oxides atmosphere water-dominated, extensive thru-flow in contact w/ atm. loss (transport) K +, Na +, Ca 2+, Mg 2+. SALTS (elsewhere) composition -SO 4, -Cl, -CO 3, depends on atmosphere

14 Fe-oxides (e.g. hematite, Fe 2 O 3 ; goethite FeOOH) Al clays ( e.g. kaolinite Al 2 Si2O 5 (OH) 4) Salts, e.g. gypsum CaSO 4 2H 2 O; halite NaCl; jarosite, KFe 3+ 3(OH) 6 (SO 4 ) 2 Fe-oxides (e.g. hematite, Fe 2 O 3 ; goethite FeOOH) 5 m Parana, Brazil W. Australia

15 Closed System, low W:R Low W:R, closed system Mineralogy of residue : bulk: Fe/Mg-clays pores: w/ zeolites (Ca, Na), other hydrated silicates (silica, prehnite) almost no loss (transport), chemically similar to basalt not in contact w/ atm. little water thru-flow, rock-dominated TEMPERATURE, PARENT ROCK COMPOSITION are the key controls on mineralogy

16 e.g. groundwater systems in Iceland, Newfoundland basalts

17 Closed System, low W:R Low W:R, closed system Mineralogy of residue : bulk: Fe/Mg-clays pores: w/ zeolites (Ca, Na), other hydrated silicates (silica, prehnite) almost no loss (transport), chemically similar to basalt not in contact w/ atm. little water thru-flow, rock-dominated TEMPERATURE, PARENT ROCK COMPOSITION are the key controls on mineralogy

18 Conceptual Framework Ehlmann et al., 2011, Nature

19 Returning to the Data

20 Distribution of Aqueous Minerals on Mars (circa 2014) Ehlmann & Edwards, Ann. Rev. Earth Plan. Sci., 2014 (influence of latitude-dependent mantle) (influence of latitude-dependent mantle) Ehlmann et al., 2011, Nature Carter et al., 2013, JGR Osterloo et al., 2010, JGR Phyllosilicates are in the most ancient terrains Salts vary across space and time Niles et al., 2013, Space Sci Rev

21 Widespread Clay Formation in Noachian terrains hydrated silicate new detections, L. Pan, poster yesterday Carter et al., 2013

22 but mostly divorced from valley networks Carter et al., 2013

23 Multiple Settings with Evidence for the Importance of Groundwaters Meridiani Valles Marineris Crustal Clay Mineral Assemblages

24 Layered sedimentary sulfates e.g. Meridiani Planum McLennan et al.,; Grotzinger et al., 2005, EPSL (Squyres et al., 2004;Grotzinger 1cm et al., McLennan et al., 2005; Arvidson et al., 200

25 Valles Marineris & Meridiani Layered Sulfate Deposits Color bar: thickness of modeled evaporites Yellow: locations of VM ILDs Murchie et al., 2009, JGR Andrews-Hanna et al., 2010, JGR Sulfate-bearing deposits also occur in etched terrain in Terra Meridiani, craters in Arabia, and in Aram Chaos, areas of predicted groundwater discharge Buried Many of the predicted locations of groundwater discharge are buried by younger units or dust, so sulfates are hidden if they occur in those locations Aram Chaos Meridiani etched deposits

26 Phyllosilicates: Indicators of A Warmer, Wetter Subsurface Example 1: Prehnite Prehnite/Chlorite-bearing rocks Ca 2 (Al,Fe 3+ ) 4 (Si,Al) 8 (OH) 2 (Mg, Fe 2+ ) 5 Al(Si 3 Al)O 10 (OH) 8 10 km Illite/Muscovite-bearing rocks KAl 2 AlSi 3 O 10 (OH) 2 Ehlmann et al., 2009, JGR; Ehlmann et al., 2011; Clays & Clay Min.

27 Phyllosilicates: Indicators of A Warmer, Wetter Subsurface Example 1: Prehnite Ehlmann et al., 2011; after Robinson and Bevins, 1999 Prehnite/Chlorite-bearing rocks Ca 2 (Al,Fe 3+ ) 4 (Si,Al) 8 (OH) 2 (Mg, Fe 2+ ) 5 Al(Si 3 Al)O 10 (OH) 8 10 km Illite/Muscovite-bearing rocks KAl 2 AlSi 3 O 10 (OH) 2

28 Phyllosilicates: Indicators of A Warmer, Wetter Subsurface Example 2: Serpentine requires reducing conditions Valles Marineris Serpentine melange terrain [Ehlmann et al., 2010, GRL; Viviano et al., 2014, LPSC] Claritas Fossae

29 Phyllosilicates: Indicators of A Warmer, Wetter Subsurface Global Statistics Ehlmann et al., 2011 Carter et al., 2013 ~10-25% of images with phyllosilicates contain prehnite Therefore, there was subsurface hydrothermalism/metamorphism on early Mars

30 Crustal Clays: Evidence of Elevated Temperature Alteration Mineral assemblages are consistent with low W:R ratio formation by Subsurface (hydrothermal) alteration Diagenesis/Low-grade metamorphism Deuteric formation (e.g. lava cooling) [Meunier et al., 2012, Nat. Geosci.] Key Indicator Minerals Prehnite Chlorite Illite/Muscovite Serpentine Zeolites GLOBAL CLAY MINERALOGY (in %) Ehlmann et al., Nature, 2011 & Clays & Clay Minerals, 2011; McSween et al., MAPS, 2014

31 But what about the other minerals? Carter et al., 2013 Ehlmann et al Difficult because mere presence of Fe/Mg smectites is not an indicator Do indicate higher W:R, possibly open system

32 Layered Al over Fe/Mg Phyllosilicates Type Locality: Mawrth Vallis Al-clays (+ silica?) The largest exposures of clays on Mars (Mawrth Vallis, Nili Fossae, Valles Marineris) show distinctive stratigraphic compositional variation: Al-clays above Fe/Mgclays nontronite (Fe-clay) 200 m

33 Buczkowski et al., JGR Bishop et al., 2008, Science; Loizeau et al., 2007, JGR; 2010, Icarus; Wray et al. 2008, GRL; Michalski et al., 2010, Astrobio. Wiseman et al., 2010, JGR Mustard & Ehlmann, 2012, GRL Ehlmann et al., Nature, 2011 Murchie et al., 2009, JGR Milliken et al., 2010, GRL

34 Timing of Valley Network Formation Fassett & Head, 2008, Icarus 34

35 Mars Clays and Fluvial/Lacustrine Deposits JEZERO EBERSWALDE, HOLDEN TERRA SIRENUM BASINS COLUMBUS, CROSS Open-basin Fe/Mg clay, Mg carbonate Open?-basin Fe/Mg clay Closed?-basin Chloride salts overlying, Fe/Mg clays Closed-basin Al (, Fe/Mg) clays and sulfates (incl. jarosite, alunite) Alkaline Acidic Diversity in alteration products, settings implies diversity in water chemistry BUT the timing of all of these is similar*: Late-Noachian to Early-Hesperian *=but possibly not identical; time correlation of sediments in basins is challenging

36 Adapted from Murchie et al., JGR, 2009 with mineralogic epochs from Bibring et al., 2006 Proposed Chemical Environments phyllosian theiikian siderikian clays sulfates anhydrous ferric oxides Deep phyllosilicates Carbonate deposits Layered phyllosilicates Phyllosilicate in fans Plains sediments?? Intracrater claysulfates?? The oldest preserved clay forming environments do not require extensive amounts of surface water Meridiani layered S-rich alteration lavas Middle period with more surface water? How episodic vs. continuous? Sourced from melting? Valles layered Siliceous layered? Curiosity Gale Crater Opportunity Meridiani, Planum? Gypsum plains? Noachian Hesperian Geologic Eras Amazonian

37 Ehlmann, this conf.

38 Environments Change Through Time avail. liquid water enviros. valleys Fassett & Head, 2008 outflow channels Tanaka, Gyr 3.7 Gyr 3.1 Gyr Ehlmann, et al., Nature, 2011

39 A Hypothesis: Warmer, Wetter (esp. in subsurface) But always relatively cold and dry Early atmosphere does not need to be thick, nor surface warm Episodic, transient liquid waters (e.g. volcanic-gas release: Johnson et al., 2008; Phillips et al., 2001) Crustal hydrothermal environments may be the oldest, most stable, and longest aqueous (habitable) environments on Mars Ehlmann et al., 2011, Nature

40 Five Key Questions about Early Mars Environments What is the Noachian crust? Altered lavas, ashes, or sediments? relative prevalence of early sedimentary (fluvial?) vs. igneous processes What was the mechanism(s) of the oldest Fe/Mg phyllosilicate formation? Were waters deuteric, hydrothermal, diagenetic, or weathering? Timing of clay mineral formation: Noachian or later? Atmospheric chemistry or rock chemistry? What controls the spatial discretization of salt deposits? Atmospheric chemistry or rock chemistry? Why so little carbonate? Not global acidity. Local acidity? Most alteration in the subsurface?

41 Measurement Needs Petrology Time (Age/Exposure Dating) More Type Environments Explored In Situ Understanding the globally widespread clays requires sub mm-scale

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