Long time-span for crystallization of final residual melt in Martian magma ocean: A potential consequence of dense early Martian atmosphere

A previous work predicted the persistence of a KREEP-like silica-rich primitive crust on Mars， which provides a possible explanation for the enriched andesitic-like reservoir of the zircons discovered in NWA 7034. Accordingly， the crystallization of the final residual melt on the top of the Martian magma ocean (MMO) would have begun before ∼4.547 Ga and sustained until ∼4.45-4.40 Ga according to the Sm-Nd data of shergottites. Such a long time-span of ∼100-150 Myrs for the crystallization of the final residual melt may imply a thermally insulating layer above the MMO， perhaps associated with a dense atmosphere formed by the vigorous outgassing of the MMO. Correspondingly， the Martian climate would be considerably warm by the end of the MMO phase， but cools down rapidly until ∼3.9 Ga owing to the thermal escape of hydrogen and carbon driven by the strong EUV radiation of the early Sun.