ASSESSING FAULT-CONTROLLED VOLATILE MIGRATION IN SEDIMENTARY ROCK

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 fault–controlled 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 soft–rock 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 fault–controlled volatile migration on Mars is based on studies of exhumed, fault–controlled reservoirs on Earth, such as those within the Grand Staircase–Escalante 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 on–going, 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 10–meter–scale resolutions; scales that are useful for evaluating future landing sites.