wAbstract
@The secondary mineral budget on Earth is dominated by clay minerals,
Al-hydroxides, and Fe-oxides, which are formed under the moderate
pH, high water-to-rock ratio conditions typical of Earth's near-surface
environment. In contrast, geochemical analyses of rocks and soils
from landed missions to Mars indicate that secondary mineralogy
is dominated by Mg (}Fe, Ca)-sulfates and Fe-oxides. This discrepancy
can be explained as resulting from differences in the chemical
weathering environment of Earth and Mars. We suggest that chemical
weathering processes on Mars are dominated by: (1) a low-pH, sulfuric
acid-rich environment in which the stoichiometric dissolution
of labile mineral phases such as olivine and apatite (}Fe-Ti oxides)
is promoted; and (2) relatively low water-to-rock ratio, such
that other silicate phases with slower dissolution rates (e.g.,
plagioclase, pyroxene) do not contribute substantially to the
secondary mineral budget at the Martian surface. Under these conditions,
Al-mobilization is limited, and the formation of significant Al-bearing
secondary phases (e.g., clays, Al-hydroxides, Al-sulfates) is
inhibited. The antiquity of rock samples analyzed in-situ
on Mars suggest that water-limited acidic weathering conditions
have more than likely been the defining characteristic of the
Martian aqueous environment for billions of years.
Keywords: Mars; weathering; rates; aluminum; clays; APXSx
1. Introduction
2. Data sources and sample collection site conditions
3. Discussion
@3.1. Major element chemistry of weathered rocks on Earth
@3.2. Major element chemistry of weathered rocks and soils on
Mars
@3.3. Weathering in acidic environments: examples from Mars and
the laboratory
@3.4. Aluminum mobility and implications for water-to-rock ratio
@3.5. Implications for long-term Martian climate
Acknowledgements
References