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Assessing fault-controlled volatile migration in sedimentary rock Assessing fault-controlled volatile migration in sedimentary rock
Chris H. Okubo
chriso@lpl.arizona.edu
Lunar and Planetary Laboratory
University of Arizona
Tucson, AZ 85721
Terrestrial observations show that sedimentary deposits are productive host rocks for
volatile reservoirs because of their high porosities and permeabilities. Within these reservoirs,
faults play an important role in controlling the pathways along which volatiles tend to migrate;
this is because faults can act as either barriers or conduits to fluid flow. Faults are thereby
important volatile concentrators, which means that evidence of geochemical, hydrologic and
biologic processes are likely concentrated near faults as well.
Recent observations have revealed that exposures of layered sedimentary deposits are
common on the surface of Mars. These deposits are in places deeply eroded and faulted.
Therefore past faultcontrolled volatile reservoirs may now be exposed at the surface of Mars
within the layered sedimentary deposits. Since faults act as volatile concentrators, these exhumed
faults are potentially fruitful sites for surface exploration.
Field observations and laboratory analyses of layered sedimentary rocks and soils on
Earth show that volatile migration pathways around faults are systematic and predictable (Okubo
& Schultz 2005, J. Geol. Soc. London). The distribution of these pathways around faults are
known to be a function of the stress state that caused the fault to slip and the geometry of the
fault. These principals of softrock deformation, initially developed for terrestrial reservoir
analysis, are now being used to assess the distribution volatile migration pathways within layered
sedimentary deposits on Mars.
The framework for understanding the mechanics of faultcontrolled volatile migration on
Mars is based on studies of exhumed, faultcontrolled reservoirs on Earth, such as those within
the Grand StaircaseEscalante National Monument region of Utah. Analyses of fault
displacements within the layered sedimentary deposits (to retrieve the causative stress state and
fault geometry) on Mars is ongoing, but is currently limited by the resolution and availability of
MOC, HRSC and MOLA data. Finer spatial resolutions in image and topographic data provided
by the HiRISE instrument on board the Mars Reconnaissance Orbiter will allow for predictions of
volatile migration pathways with meter to 10meterscale resolutions; scales that are useful for
evaluating future landing sites.