Magmatic complexity on early Mars as seen through a combination of orbital, in-situ and meteorite data

Violaine Sautter (1) , Michael Toplis (2) , Pierre Beck (3) , Nicolas Mangold (4) , Roger Wiens (5) , Patrick Pinet (6) , Agnès Cousin (2) , Sylvestre Maurice (2) , Laetitia Ledeit (4) , Roger Hewins (7) , Olivier Gasnault (2) , Cathy Quantin (8) , Olivier Forni (2) , Horton Newsom (9) , Pierre-Yves Meslin (2) , James Wray (10) , Nathan Bridges (11) , Valérie Payré (12) , William Rapin (2) , Stéphane Le Mouélic (4)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 IRAP - Institut de recherche en astrophysique et planétologie
3 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
4 LPG - Laboratoire de Planétologie et Géodynamique [UMR 6112]
5 LANL - Los Alamos National Laboratory
6 ECOMAR - Laboratoire d'Ecologie Marine
7 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
8 LGL-TPE - Laboratoire de Géologie de Lyon - Terre, Planètes, Environnement
9 IOM - Institute of Meteoritics [Albuquerque]
10 School of Earth and Atmospheric Sciences [Atlanta]
11 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
12 Rice University [Houston]

Until recently, Mars was considered a basalt-covered world, but this vision is evolving thanks to new orbital, in situ and meteorite observations, in particular of rocks of the ancient Noachian period. In this contribution we summarise newly recognised compositional and mineralogical differences between older and more recent rocks, and explore the geodynamic implications of these new findings. For example the MSL rover has discovered abundant felsic rocks close to the landing site coming from the wall of Gale crater ranging from alkali basalt to trachyte. In addition, the recently discovered Martian regolith breccia NWA 7034 (and paired samples) contain many coarse-grained noritic-monzonitic clasts demonstrably Noachian in age, and even some clasts that plot in the mugearite field. Olivine is also conspicuously lacking in these ancient samples, in contrast to later Hesperian rocks. The alkali-suite requires low-degree melting of the Martian mantle at low pressure, whereas the later Hesperian magmatism would appear to be produced by higher mantle temperatures. Various scenarios are proposed to explain these observations, including different styles of magmatic activity (i.e. passive upwelling vs. hotspots). A second petrological suite of increasing interest involves quartzo-feldspathic materials that were first inferred from orbit, in local patches in the southern highlands and in the lower units of Valles Marineris. However, identification of felsic rocks from orbit is limited by the low detectability of feldspar in the near infrared. On the other hand, the MSL rover has described the texture, mineralogy and composition of felsic rocks in Gale crater that are granodiorite-like samples akin to terrestrial TTG (Tonalite-Trondhjemite-Granodiorite suites). These observations, and the low average density of the highlands crust, suggest the early formation of `continental' crust on Mars, although the details of the geodynamic scenario and the importance of volatiles in their generation are aspects that require further work. (c) 2016 Elsevier B.V. All rights reserved.

Mots clés: Alkaline suite, Crust, Mars, Martian meteorites, Orbital spectroscopy, Rover observations

Domaines: Planète et Univers [physics]

Violaine Sautter, Michael Toplis, Pierre Beck, Nicolas Mangold, Roger Wiens, et al.. Magmatic complexity on early Mars as seen through a combination of orbital, in-situ and meteorite data. Lithos, 2016, 254-255, pp.36-52. ⟨10.1016/j.lithos.2016.02.023⟩. ⟨hal-02373373⟩