| 37922 |
abstract |
Impact-generated hydrothermal systems have been previously linked to the alteration
of Mars’ crust and the production of secondary mineral assemblages seen from orbit.
The sensitivity of the resultant assemblages has not yet been evaluated as a function
of precursor primary rock compositions. In this work, we use thermochemical modeling
to explore the variety of minerals that could be produced by altering several known
lithologies based on martian meteorite compositions. For a basaltic host rock lithology
(Dhofar 378, Humphrey) the main alteration phases are feldspar, zeolite, pyroxene,
chlorite, clay (nontronite, kaolinite), and hematite; for a lherzolithic host rock
lithology (LEW 88516) the main alteration phases are amphibole, serpentine, chlorite,
clay (nontronite, kaolinite), and hematite; and for an ultramafic host rock lithology
(Chassigny) the main minerals are secondary olivine, serpentine, magnetite, quartz,
and hematite. These assemblages and proportions of phases in each of those cases depend
on W/R and temperature. Integrating geologic, hydrologic and alteration mineral evidence,
we have developed a model to illustrate the distribution of alteration assemblages
that occur in different levels of an impact structure. At the surface, hot, hydrous
alteration affects the ejecta and melt sheet producing clay and chlorite. Deeper in
the subsurface and depending on the permeability of the rock, a variety of minerals
– smectite, chlorite, serpentine, amphiboles and hematite – are produced in a circulating
hydrothermal system. These modeled mineral distributions should assist with interpretation
of orbital observations and help guide surface exploration by rovers and sample return
assets. |