Volcanic-Tectonic Interactions of the Tharsis Region, Mars

The Tharsis region of Mars is characterized by large volcanic and tectonic centers with distinct sets of graben systems that extend radially for distances of hundreds to thousands of kilometers. Formation of these grabens has been attributed to magmatic dike intrusion and used to interpret underlying dikes and dike swarms in the Tharsis region, which has implications for both the magmatic and tectonic history of Mars and potential astrobiological research sites. Research to date on Martian dike propagation has almost exclusively relied on boundary element models to predict surface deformation and none has provided observational evidence from Earth analog sites.

In this project, the extent to which igneous activity can create and/or reactivate faults and fractures was examined through a series of interrelated tasks, including Martian data analyses, field investigations, discrete element modeling, and physical analog experiments. Neither the discrete element models nor the physical analog experiments of dike injection produced the simple graben morphology characteristic of the Tharsis grabens. The primary result of both modeling approaches was surface deformation in the form of contractional folds producing uplift at the surface (i.e., bounding anticlines with a synclinal trough ) rather than extensional faults over the dike tip producing subsidence (i.e., bounded by normal faults with a down dropped floor). Field investigations of dike intrusion did not find large-scale extensional features surrounding dikes in rock outcrop. Together, these investigations suggest a more passive role in dike emplacement, rather than the more active, graben-producing, hypothesis. This suggests that the Tharsis-radial grabens were not formed primarily in response to magmatic dike intrusion, but instead dike emplacement occurred along pre-existing faults. It is likely that many of the grabens in the Tharsis region are underlain (filled) as dikes; however, absent additional evidence (e.g., lava flows, fissure ramparts, cinder cones), the grabens alone are not evidence of an underlying dike.