Tectonics of Mars

Like the Earth, the crustal properties and structure of the surface of Mars are thought to have evolved through time; in other words, as on Earth, tectonic processes have shaped the planet. However, both the ways this change has happened and the properties of the planet's lithosphere are very different when compared to the Earth. Today, Mars is believed to be largely tectonically inactive. However, observational evidence and its interpretation suggests that this was not the case further back in Mars's geological history.

At the scale of the whole planet, two large scale physiographic features are apparent on the surface. The first is that the northern hemisphere of the planet is much lower than the southern, and has been more recently resurfaced – also implying that the crustal thickness beneath the surface is distinctly bimodal. This feature is referred to as the "hemispheric dichotomy". The second is the Tharsis rise, a massive volcanic province that has had major tectonic influences both on a regional and global scale in Mars's past. On this basis, the surface of Mars is often divided into three major physiographic provinces, each with different geological and tectonic characteristics: the northern plains, the southern highlands, and the Tharsis plateau. Much tectonic study of Mars seeks to explain the processes that led to the planet's division into these three provinces, and how their differing characteristics arose. Hypotheses proposed to explain how the two primary tectonic events may have occurred are usually divided into endogenic (arising from the planet itself) and exogenic (foreign to the planet, e.g., meteorite impact) processes.^[2] This distinction occurs throughout the study of tectonics on Mars.

In general, Mars lacks unambiguous evidence that terrestrial-style plate tectonics has shaped its surface.^[3] However, in some places magnetic anomalies in the Martian crust that are linear in shape and of alternating polarity have been detected by orbiting satellites. Some authors have argued that these share an origin with similar stripes found on Earth's seafloor, which have been attributed to gradual production of new crust at spreading mid-ocean ridges.^[4] Other authors have argued that large-scale strike-slip fault zones can be identified on the surface of Mars (e.g., in the Valles Marineris trough), which can be likened to plate-bounding transform faults on Earth such as the San Andreas and Dead Sea faults. These observations provide some indication that at least some parts of Mars may have undergone plate tectonics deep in its geological past.^[5]