page_title: Tectonics of Mars
section_title: Endogenic origins
hierarchical_section_title: Tectonics of Mars / Hemispheric dichotomy / Endogenic origins
caption_attribution_description: English: Fig. 4. Single plume mantle convection generating new crust in southern hemisphere with alternating bands of normal and reversed remanent magnetism, adapted from Vita-Finzi &amp; Fortes, 2013.
context_page_description: 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 both 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' 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' past.
context_section_description: Endogenic hypotheses include the possibility of a very early plate tectonic phase on Mars. Such a scenario suggests that the northern hemispheric crust is a relic oceanic plate. In the preferred reconstruction, a spreading center extended north of Terra Cimmeria between Daedalia Planum and Isidis Planitia. As spreading progressed, the Boreal plate broke into the Acidalia plate with south-dipping subducting beneath Arabia Terra, and the Ulysses plate with east-dipping subducting beneath Tempe Terra and Tharsis Montes. According to this reconstruction, the northern plains would have been generated by a single spreading ridge, with Tharsis Montes qualifying as an island arc. However, subsequent investigations of this model show a general lack of evidence for tectonism and volcanism in areas where such activity was initially predicted.
  Another endogenic process used to explain the hemispheric dichotomy is that of primary crustal fractionation. This process would have been associated with the formation of the Martian core, which took place immediately after planetary accretion. Nevertheless, such an early origin of the hemispheric dichotomy is challenged by the fact that only minor magnetic anomalies have been detected in the northern plains.
  Single plume mantle convection has also been invoked to explain the hemispheric dichotomy. This process would have caused substantial melting and crustal production above a single rising mantle plume in the southern hemisphere, resulting in a thickened crust. It has also been suggested that the formation of a highly viscous melt layer beneath the thickened crust in the southern hemisphere could lead to lithospheric rotation. This may have resulted in the migration of volcanically active areas toward the dichotomy boundary, and the subsequent placement and formation of the Tharsis plateau. The single plume hypothesis is also used to explain the presence of magnetic anomalies in the southern hemisphere, and the lack thereof in the northern hemisphere.
caption: A model for a mantle plume origin for the hemispheric dichotomy. Single plume mantle convection generates new crust in southern hemisphere with alternating bands of normal and reversed remanent magnetism, adapted from Vita-Finzi & Fortes, 2013.[4]
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