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The crustal dichotomy on Mars

Robinson, Cordula Astrid; (1991) The crustal dichotomy on Mars. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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The crustal dichotomy is the term used for the surface division of Mars into a lightly-cratered third of the planet, in the middle to upper latitudes of the northern hemisphere, and a remaining heavily-cratered two-thirds. The lightly-cratered third stands approximately 3 km lower than the heavily-cratered surface. Established explanations for the crustal dichotomy consider it a stable feature that originated early in the planet's history either by endogenic means (in the form of catastrophic overturn of the mantle, probably associated with core formation) or by exogenic means (either in the form of a giant single impact or the focusing of several large impacts). A review of the processes acting on the surface of Mars, combined with detailed geological mapping studies, shows that five conditions must be met by any explanation for crustal dichotomy formation. They are: 1. That fretted terrain formation occurred between the late Noachian to early Hesperian, and small-scale structural adjustment occurred subsequently; 2. The subsurface thermal activity leading to surface volcanism between the late Noachian and early Hesperian needs to be accounted for; 3. The existence of a faulted southern-hemisphere-type surface beneath the northern plains needs to be accounted for; 4. The origins of the three highland-lowland boundary provinces (namely the Tharsis Province, the chaotic terrain and the fretted terrain) need to be compatible with the proposed explanation; 5. The topography and isostatic equilibrium of the northern lowlands needs to be accounted for. None of the explanations so far put forward for the crustal dichotomy on Mars are consistent with these conditions. The conditions support an endogenic mechanism for crustal dichotomy formation, and as an alternative I suggest that Mars constitutes a single plate planet that was at the threshold of developing more than one plate between the late Noachian and early Hesperian. This resulted in crustal dichotomy formation whereby the Tharsis Province represents the site of continental rifting, and the northern lowlands a corresponding region of subsidence that formed in order to maintain isostatic equilibrium and to accommodate the stretching involved in the formation of the Tharsis Province and the fretted terrain.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The crustal dichotomy on Mars
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Earth sciences; Martian surface
URI: https://discovery.ucl.ac.uk/id/eprint/10124974
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