The tectonic record of Mars is well preserved in the Martian crust and tells us about the history of the planet. The Martian surface is characterized by tectonic fractures of various sizes and styles comprising extensional structures like rifts and long and narrow simple grabens as well contractional features like wrinkle ridges and lobate scarps. Also, some structural features point towards lateral motion and strike-slip faults. Tectonic deformation of the crust is the surface expression of interior processes and the Martian tectonic record is therefore intimately liked to its interior structure and evolution. The style and extent of tectonic deformation tells us about the structure and composition of the Martian lithosphere and the combined study of interior rocesses and surface deformation will therefore greatly further our understanding of the red planet.
Current seismic activity is driven by lithospheric shrinking and therefore a direct indicator of the thermal evolution of the planet. Since the arrival of global-scale topography data of uniform quality in the years following the Mars Global Surveyor mission, global studies of Martian tectonic features have been embarked upon (Fig. 1). These studies will allow us to reconstruct the sequence and spatial distribution of tectonic events and the calculation of seismic moment release from fault offsets can be used to link the planetary thermal evolution to the seismic record of Mars. In particular, we will be able to address the questions of whether the activity was continuously distributed in time or episodic, and how activity declined during Martian history. Also, we will learn about the spatial distribution of tectonic centers and if the tectonic activity was connected to only a few centers or more globally distributed.
The global history of tectonic events is linked to the style of heat transfer in the Martian mantle. Currently, there are three leading hypothesis when considering the history of the heat transport. The first assumes an early episode of plate tectonics followed by an epoch of stagnant lid convection. The second assumes an initially stably layered mantle as a result of a magma ocean overturn. Heat transport in this regime proceeds by heat conduction and this episode may have been followed by convective heat transport in the stagnant lid regime later on. Finally, the third approach assumes stagnant lid convection throughout the entire evolution of the planet. These different approaches lead to distinct thermal histories and the tectonic record may help to discriminate between them.
Other large-scale processes that directly influence the tectonic record are connected to the formation of the crustal dichotomy and the emplacement of the Tharsis bulge. These events have left distinct tectonic signatures (e.g., Fig. 2) on the Martian surface and an interpretation of these features greatly benefits from a combined approach considering both the interior processes responsible for their formation and their tectonic surface expressions. In particular, the question of whether Tharsis and/or the dichotomy are connected to large-scale mantle flow like, e.g., plumes is central to the understanding of these features. An investigation of the associated stress fields will therefore teach us about the mechanisms responsible for their formation.
One way to approach these questions is to employ comparisons of Martian and terrestrial tectonism. Structural similarities and dissimilarities may be used to infer the formation processes of the corresponding tectonic features and the characteristics of the resulting fault sets may be directly compared to terrestrial measurements. Furthermore, fault characteristics may be linked to the rheological properties of the crust and its water content in particular. Therefore, the strength of bounding faults and the relationship of fault lengths to displacements need to be investigated.
Last update: 31/05/2010 15:59
