ROLE OF PLANETARY SIZE ON THE PRESERVATION OF PRIMORDIAL ANORTHOSITE-ENRICHED CONTINENTAL CRUST AND HABITABILITY

The Moon has primordial continental crustal materials consisting of anorthosite. Anorthosite has also been observed on Mars, with occurrence possibly extensive similar to the lunar-like global anorthosite crust [1]. We propose that Mars retains a primordial anorthosite-enriched continental crust which includes andesite and granite. Conglomeratic alluvial-fan materials of Peace Vallis in Gale crater, for example, have been interpreted to be representative of an ancient felsic crust [2] of Terra Cimmeria exposed by the Gale impact [3]. Terra Cimmeria is an ancient geological province, dated to be > 4.0 Ga based on impact crater statistics, stratigraphy, and magnetic data; it records ancient major magmatic-tectonic activity (including a mobile lithosphere), similar to other ancient provinces. In the case of the Earth, the occurrence of anorthosite is observed to be limited in the geological record. However, lunar and Martian surface geology indicates that anorthosite was likely more universal on the Earth as a primordial continent during the first 600 million years after its formation. We theorize that whether a rocky planetary body retains its primordial continent is due to its size. For example, the reason why the primordial continent of the Earth disappeared can be explained by the strength and duration of mantle convection and plate tectonics. On the other hand, a theorized early phase of plate tectonics on Mars shut down prior to ~3.93 Ga due to its relatively small mass and rapid cooling [4], preserving its primordial crust. In addition, Mars recorded ancient hydrological cycling among the proposed primordial crust, ocean, and relatively thick atmosphere, Habitable-Trinity conditions important for life [5]. At this conference, we will discuss the significance of planetary size on both the preservation of primordial anorthosite-enriched continental crusts on rocky planetary bodies and habitability potential such as super-Earths and their rapid destruction of nutrient-enriched primordial crust.

References: [1] Carter, J, Poulet, F (2013) Nat Geosci 6, 1008-1012. [2] Sautter, V et al (2015) Nat Geosci, 605–609. [3] Anderson, RC et al (2015) GSA Ann Meet, Pap # 203-11. [4] Baker, VR et al (2007) In Super-plumes: Beyond plate tectonics, Springer, 507–523. [5] Dohm JM, Maruyama S (2014) J Geosci Front 6:95-101.