[PPS05-P12] Phobos: A Sample of Mars and Its Primordial Environmental Conditions?
Keywords:Mars, Phobos, primordial crust, anorthosite, Habitable Trinity, ocean-atmosphere
Dynamic primordial Mars, updated and abbreviated from that theorized by , included the following stages generally through time: 1 - shortly after accretion, dry Mars differentiates from a magma ocean, which includes the formation of a primordial crust with composition that includes anorthosite, KREEP, and komatiite layers ; 2 - Mars is impacted by asteroids and comets which deliver an ocean-atmosphere system to its system, perturbs the solid lid of the solidified magma ocean, and initiates plate tectonic activity around 4.37 Ga to 4.2 Ga in accordance with the ABEL model proposed by ; in addition the dynamo initiates sometime during Stages 1-2; 3 – accretion of thickened, continental crust and subduction of hydrated oceanic crust to the lower mantle of Mars occurs, including the development of the felsic Martian supercontinent (i.e., the southern highlands); 4 - the core dynamo terminates with continued, waning plate tectonic activity; and 5 – large basin-forming impacts result in Hellas, Chryse, Isidis, and Argyre, with the later phase of development of the Martian supercontinent including the termination of plate tectonic activity (estimated to have occurred between the Hellas and Argyre impact events, ~between 4.0 and 3.93 Ga) with significant anorthosite-rich primordial crust preserved due to size  contrasting with Earth that destroyed its primordial continental crust [2,6], and Tharsis superplume initiates (also see a summarized Mars evolution by ).
Return samples from Phobos will inform on its origin and evolution, as well as possible primordial Martian environmental conditions recorded in both the blue and red units.
References:  Craddock, R. A., 1994, Abstracts of the 25th LPSC, p. 2.  Dohm JM et al, 2017, Geos. Front., DOI: 10.1016/j.gsf.2016.12.003.  Baker VR et al., 2007, In Superplumes: Beyond plate tectonics: Springer, 507–523.  Dohm, J.M. Maruyama, S., 2014, Geos. Front. 6, 95-101.  Kikuchi, H., Miyamoto, H., 2017, this meeting.  Maruyama S., Ebisuzaki T., 2017, Geos. Front., http://dx.doi.org/10.1016/j.gsf.2016.10.005.  Dohm, J.M., 2017, abstracts of the 48th LPSC, Abstract #1962.