Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43d..07m&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P43D-07
Other
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5220 Hydrothermal Systems And Weathering On Other Planets, 5410 Composition (1060, 3672), 5464 Remote Sensing, 6225 Mars
Scientific paper
The regional mineralogy from OMEGA and high-resolution mineralogy from CRISM are showing that the Noachian crust contains a diverse suite of hydrated minerals resulting from the alteration of the primary igneous and volcanic crust. Nevertheless, the most common phyllosilicates dating from this era are Mg/Fe smectite clays indicating moderate to low temperature (<200 C) formation. In contrast, mineral assemblages indicative of high temperature metamorphism or extensive hydrothermal systems are absent or rare. The precise characterization of the potentially habitable environments represented by these mineral deposits is hindered by the complex stratigraphy resulting from impacts, up to basin-forming. Megabreccia has been observed in a number of Noachian terrains and may date from this period of heavy bombardment. Preserved in the megabreccia are blocks that retain layered sequences suggesting that sedimentary processes were widely present in the Noachian. During the waning stages of the Noachian, extensive valley network formation and chains of crater lakes are the possible last stages of processes that dominated the surface during the Noachian. In the Nili Fossae region this period of transition is well preserved and provides a window into the Noachian habitable environments. The Noachan crust is well exposed showing megabreccia containing layered blocks rich in phyllosilicate as well as blocks of unaltered rock. These units are the window to the period of abundant phyllosilicate formation to determine if phyllosilicate formation was driven by weathering near or at the surface, or was dominantly due to alteration by hydrothermal processes in the shallow crust. Following the formation of the Isidis basin, widespread gradation facilitated by water transported abundant material to topographic lows, filling craters and graben. Valley network formation followed, resulting in the transport and deposition of phyllosilicate minerals in the crater lake delta in Jezero Crater. Concurrent with this era of valley network activity is the formation of a near-surface deposit rich in kaolinite accompanied perhaps by the the formation of a thin carbonate unit. By the time of the emplacement of the Hesperian Syrtis Major lavas, processes of alteration were either absent or declining. Thus this region of Mars captures critical components of the Noachian crust relevant to habitability: unaltered, altered and layered blocks in megabreccia; water-borne deposits filling the floors of craters and graben; valley networks and a crater lake with deltas; and regional deposits of kaolinite and carbonate. Ongoing work will further refine these relationships and seek to extend these analyses to other regions.
R. C.
Ehlmann Bethany
Mangold Nicolas
McEwen Alfred
Milliken Ralph
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