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Subsurface water and clay mineral formation during the early history of…
Subsurface water and clay mineral
formation during the early history of Mars
Controls on Clay Mineralogy
Open System
Nearer to the surface
fluids are in contact with the Martian atmosphere
Water to rock ratios:
Higher (W/R > 1)
More ion transport = changes element amounts/composition
Residual rock (Rock that is not transported) is aluminium rich
Transported rock generate Fe/Mg smectite, jarosite & silica formation
Low (W/R < 1)
Olivine is mostly what dissolves
Depleting the abundances of Fe/Mg smectite formation
amorphous products & salt form coatings
Closed System
Occur in subsurface waters
Closed =Water is closed off from the Martian afmosphere
Typically low water-rock ratio (W/R <1)
Ion transport is minimal, so elemental amounts remain constant
Products: Iron(ii)/Magnesium smectits, chlorite and serpentine
CLAY MINEROLOGY
Can be used to model hydrothermal systems during Noachian/Hesperian periods
Through clay formation/diversity, we can understand the Martian hydrosphere
Clay Distribution and Diversity
Figure 1
Map of clay distribution and diversity on Mars
Highlights the 3 different types of clays superposed on a map of Mars
Crustal Clays
Fe/Mg smectite and chlorite make up 78% and 39% (respectively) of crustal clays
Associated with craters
Either the result of crater impact (heat initiate hydrothermal systems)
These materials placed as crater 'ejecta' are found ~5-10km deep in the craters
Or were pre-existing, but were excavated by crater impact
Sedimentary Clays
Clays detected in fluvial basins & lakes
Unlike crustal clays, hydrated silicates have not been detected
sedimentary clay composition varies depending on the fluvial system
it is not possible to determine whether sedimentary clays were transported to their current location (allocthonous) or formed there (autochthonous)
Clays in Stratigraphies
Occur in high-standing topography
Cannot be explicitly defind as crustal or sedimentary
Eg: Al clays that overly Fe and Mg clays
Timelines for Martian environments (Figure 4)
a. Presence of a Pre-noachian era magnetic field
b. large impact craters through the Noachian era
d. Changes in aqueous environments (that influence weathering and precipitation)
f. formations of various clays (w/ different compositions) during various time periods (owing to the processes above)
c. Volcanism through the Noachian & Hesperian eras
e. Valley networks & outflow channels that are responsible for sedimentary clay formation
Conclusions + Connections to previous papers
The physiochemical conditions on Mars that led to Fe and Mg clay formation imply the presence of Hydrothermal systems, direct precipitation, and subserface liquid waters throughout Mars' history
This links to the Baker paper, which explored Martian landforms due to the presence of water during various (Noachian, Hesperian and Amazonian eras)
This, in tandem with the Christiansen paper, paints a vivid picture of the Martian landscape with respect to Mineralogy
