1. The Mawrth Vallis Phyllosilicates Within a Regional Context: Extent, stratigraphy, and mineralogy of Phyllosilicates around Mawrth Vallis and Western Arabia Terra E. Z. Noe Dobrea, J.L. Bishop, N.K. McKeown, R. Fu, C. Rossi, G. Swayze, J.R. Michalski, F. Poulet, J.-P. Bibring, J.F. Mustard; R. Arvidson, R.V. Morris, S. Murchie, A.S. McEwen, E. Malaret, C. Hash, and the CRISM Team.

2. Outline Introduction, Purpose Introduction, Purpose Spectroscopic/Morphological evidence for regional-scale aqueous activity Spectroscopic/Morphological evidence for regional-scale aqueous activity Formation hypotheses Formation hypotheses

3. The two largest phyllosilicate exposures The two largest phyllosilicate exposures 1. plains around Mawrth Vallis 2. region around Nili Fossae Smaller exposures also identified throughout the highlands Smaller exposures also identified throughout the highlands Numerous hypothesis have been suggested regarding their formation Numerous hypothesis have been suggested regarding their formation Hydrothermal, lacustrine, diagenetic Hydrothermal, lacustrine, diagenetic one thread of observation that appears to be common: one thread of observation that appears to be common: all appear to have been exhumed or excavated from under dark, practically unaltered (possibly mafic) material. all appear to have been exhumed or excavated from under dark, practically unaltered (possibly mafic) material. coupled to the global distribution of the observed phyllosilicates, this suggests that aqueous alteration was a globally-active process early in Martian history. coupled to the global distribution of the observed phyllosilicates, this suggests that aqueous alteration was a globally-active process early in Martian history. Point of talk is to: Point of talk is to: place the detailed observations made at Mawrth Vallis into a large regional context place the detailed observations made at Mawrth Vallis into a large regional context Evaluate the possible formation hypotheses from this regional perspective Evaluate the possible formation hypotheses from this regional perspective

4. OMEGA Mineralogy 50 m layers

5. Important questions Extent of layered hydrated units (is this the tip of the iceberg)? Geologic origin of light-toned and dark units? Impact Impact Volcaniclastic Volcaniclastic Sedimentary Sedimentary Aeolian Aeolian Lacustrine / marine deposition Lacustrine / marine deposition Origin of hydrated material? Aqueous deposition in a lacustrine system Aqueous deposition in a lacustrine system Diagenesis Diagenesis Hydrothermal Hydrothermal

8. Unit 1 (bottom)

9. Chlorite + Nontronite CRISM

10. Unit 2 (middle)

11. Unit 2 Mineralogical mixtures

12. FRT00008438

14. Mawrth Vallis Al-phyllosilicates KaoliniteMontmorillonite Yellow - Kaolinite, Magenta - Montmorillonite

15. 1. Extent A) Hydrated phyllosilicates are identified everywhere that deeper layers have been exhumed: extending up to ~1000 km x ~1000 km extending up to ~1000 km x ~1000 km B) Mineralogical stratigraphy is same throughout region: Fe/Mg phyllo. underlies Al-phyllo and/or hydrated silica, which underlies cap unit, regardless of elevation (~2000 m. vertical change).  regional process 2. Hydrates occur under a dark, boulder-shedding, highly cratered, and unaltered cap unit, which is uncomformably overlain on layered hydrated units  transition from altered to less-altered units 3. Presence of kaolinite and other leaching products suggests leaching  significant amounts of water in a warm climate 4.We see geomorphic evidence for fluvial activity preserved in the geologic record in the form of channels.  Extensive fluvial activity during and/or after the deposition of now hydrated units, but before the emplacement of cap unit. Summary of observations

16. Al/Si-OH Observations: Observations: 1. Finely layered 2. Stronger (cliff-former) 3. ~20-40 m thick 4. Contains Al-smectites mixed w/ kaolinite, hydrated silica, and possibly other products Hypotheses: Hypotheses: 1. Deposition in a lacustrine system 2. Diagenetic alteration of volcanic ash 3. Pedogenesis Origin of hydrated units Fe/Mg - OH Observations: Observations: 1. Finely layered 2. Weak (slope-former) 3. >200 m thick 4. Contains Fe/Mg smectites mixed w/ Chlorites Hypotheses: Hypotheses: 1. Deposition in a lacustrine system + metamorphism 2. Diagenetic alteration of volcanic ash + metamorphism 3. Alteration of impact ejecta

17. Geological Scenarios Deposition of sequence of hydrates (lacustrine) Deposition of sequence of primaries (mafic  felsic) Deposition of mafic primaries Aqueous alteration  Al/Si-OH from felsic  Fe/Mg smectites from mafic Alteration to Fe/Mg smectites Low-T metamorphism at depth  chlorites Leaching of upper layers  Al/Si-OH

18. 2.19 2.28 1.37 1.42 Madejova’ et al., 2008

19. Conclusions: Mineralogical relationships observed near Mawrth Vallis are repeated everywhere that we have observed capping unit to be eroded away (up to ~1000 km from Mawrth Vallis), suggesting a regional process in their formation. Mineralogical relationships observed near Mawrth Vallis are repeated everywhere that we have observed capping unit to be eroded away (up to ~1000 km from Mawrth Vallis), suggesting a regional process in their formation. Mineralogic sequence is the same over a wide range in elevations and locations Mineralogic sequence is the same over a wide range in elevations and locations  The clays of Mawrth Vallis are common, and representative  mineralogical transitions are representative of a regional, if not global, process The most likely alternatives for the formation of hydrated materials include diagenesis of primary minerals to form hydrated phyllosilicates, possibly followed by pedogenesis, and low-grade metamorphism. The most likely alternatives for the formation of hydrated materials include diagenesis of primary minerals to form hydrated phyllosilicates, possibly followed by pedogenesis, and low-grade metamorphism. Morphological evidence suggests that water flowed on the surface of Mars during and/or after the deposition of the clay-bearing units, but before the deposition of the cap unit. Morphological evidence suggests that water flowed on the surface of Mars during and/or after the deposition of the clay-bearing units, but before the deposition of the cap unit. Cap unit is relatively unaltered, and it overlies altered bedrock Cap unit is relatively unaltered, and it overlies altered bedrock  possibly representative of a transition period