HR: 11:05h
AN: P12A-04    [Abstracts]
TI: Mineralogic Diversity and Geomorphology of CRISM-detected Phyllosilicate Bearing Materials in Nili Fossae, Mars: Implications for Aqueous Alteration
AU: * Ehlmann, B L
EM: bethany_ehlmann@brown.edu
AF: Geological Sciences, Brown Univ., Providence, RI 02912,
AU: Mustard, J F
EM: john_mustard@brown.edu
AF: Geological Sciences, Brown Univ., Providence, RI 02912,
AU: Swayze, G A
EM: gswayze@usgs.gov
AF: U.S., Geological Survey, Denver, 80225,
AU: Griffes, J L
EM: GriffesJ@si.edu
AF: CEPS, Smithsonian Inst., Washington, 20013,
AU: Bishop, J L
EM: jbishop@arc.nasa.gov
AF: SETI, Inst., Mtn View, 94043,
AU: Milliken, R E
EM: Ralph.Milliken@jpl.nasa.gov
AF: JPL, Caltech, Pasadena, 91109,
AU: Clark, R N
EM: rclark@usgs.gov
AF: U.S., Geological Survey, Denver, 80225,
AU: Bibring, J P
EM: bibring@ias.u-psud.fr
AF: IAS, Universite Paris-Sud, Orsay, 91405,
AU: Poulet, F
EM: francois.poulet@ias.u-psud.fr
AF: IAS, Universite Paris-Sud, Orsay, 91405,
AU: Murchie, S L
EM: Scott.Murchie@jhuapl.edu
AF: JHU, APL, MD, 20723,
AU: Seelos, F P
EM: Frank.Seelos@jhuapl.edu
AF: JHU, APL, MD, 20723,
AU: Humm, D
EM: David.Humm@jhuapl.edu
AF: JHU, APL, MD, 20723,
AB: The Noachian crust of Nili Fossae, northwest of the Isidis basin, is of substantial interest because of km-scale exposures of Fe,Mg-rich phyllosilicates (Bibring et al, 2005; Poulet et al, 2005), the largest spatial exposure of olivine on Mars (Hoefen et al, 2003; Hamilton and Christensen, 2005; Mustard et al, 2005), and stratigraphic relationships with the comparatively well-dated Isidis impact structure (early Noachian) and Syrtis Major lava flows (middle Hesperian) which provide temporal constraints on regional aqueous alteration. MRO-CRISM has identified diverse alteration minerals including nontronite, saponite, kaolinite, chlorite, illite/muscovite and hydrated silica-rich glass (Mustard et al, Nature, submitted). Zeolite is also a potential match to material in craters near 19 N, 65 E. We present the geologic setting of alteration minerals in this region through analyses of CRISM, HiRISE, and CTX data. Mineralogic and geomorphologic data are assessed relative to hydrothermal, near-surface pedogenic, deep crustal, and lacustrine modes of phyllosilicate formation. Based on the spatial distribution of assemblages of the alteration minerals, three distinct provinces are tentatively identified: (1) Western: Chlorite, smectite, hydrated glass, and potentially zeolite are found. In two cases, these minerals are associated with crater central peaks, identified by Bandfield et al (2004) as having quartzofeldspathic material. (2) Central: Phyllosilicates are associated with small eroded knobs and ridges in heavily cratered terrain. Chlorite dominates over smectites and illite/muscovite. (3) Eastern: Smectites and kaolinite underlie a cap of spectrally neutral mesa-forming material in erosional terrain. Fe,Mg-smectite, the dominant alteration mineral, usually occurs as a ridged or polygonally fractured bright unit. In Jezero crater (Fassett and Head, 2005), phyllosilicates have been transported from within a regional watershed and deposited in a delta fan during erosion by surface water flow. Distinct provinces suggest that the nature of aqueous activity varied in space and time across Nili Fossae. Smectites within the Eastern province are cut by the fossae and exposed as the lowermost stratigraphic unit in images sampling over 200,000 km2 of terrain. The great spatial extent of this unit seems to exclude hydrothermal or lacustrine processes as the primary mechanism for smectite formation, and instead favors near surface alteration or deep crustal processes. However, the existence of small-scale exposures of kaolinite within this province indicates that, locally, more intense weathering may have occurred due to enhanced throughflow of water or hydrothermal alteration. Further, a post-smectite formation episode of fluvial activity (e.g. Mangold et al, 2007) is indicated by transported phyllosilicates in Jezero crater. Greater mineral diversity in the Central and Western provinces may have been generated in small-scale hydrothermal systems related to impact events or may reflect changes in underlying regional crustal materials westward from the Isidis basin. Units underlying phyllosilicates (if exposed) are key in determining formation processes and are being sought in CRISM targeted observations.
DE: 3672 Planetary mineralogy and petrology (5410)
DE: 5220 Hydrothermal systems and weathering on other planets
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting