Early stages of the tectonic and magmatic development of the Earth and Moon: Similarities and differences

The main peculiarity of the tectonic and magmatic development of the Moon i s its resemblance to the Paleoproterozoic stage of the Earth development. T he Moon shows no analogues of both the ancient (Archean) terrestrial magmat ism, which produced tonalite series granitoids and minor komatiite and basa lt, and Phanerozoic magmatism related to active plate boundaries. The earli est (4.45-4.25 Ga) highland magmatism of the Moon is represented by magnesi an series rocks cutting the primary anorthositic crust. These rocks are che mically similar to the terrestrial early Paleoproterozoic igneous rocks (2. 5-2.2 Ga) that compose the siliceous highly magnesian series (SHMS), but th e lunar melts are more reduced. Similar to the Earth, their intrusive analo gues form layered complexes of mafic and ultramafic rocks (ANT series). Sta rting from an age of 4.34 Ga, the magnesian series associated with rocks en riched in K, REE, and P (KREEP series) including potassium granites. The se cond stage (3.9-3.2 Ga) of the tectonic and magmatic development of the Moo n was characterized by extensive generation of mare basalts, which filled t he depressions of newly formed lunar maria. Similar to the oceanic and cont inental flood basalt provinces of the Earth, two varieties of mare basalts are: distinguished on the basis of chemical composition, low-titanium and h igh-titanium. The former are similar to MORE, and the latter are close to g eochemically enriched Fe-Ti picrites and basalts, which first appeared on t he Earth in considerable amounts only at 2.2-2.0 Ga, simultaneously with th e onset of plate tectonics. Similar to the Earth, the mare magmatism is bel ieved to be related to the ascent of mantle plumes of the second generation from the boundary between the liquid metallic core, which existed then, an d the silicate mantle. The spreading of plume heads was probably responsibl e for the formation of large mare depressions with reduced crust thickness. It is proposed that the formation of the Earth and Moon occurred simultane ously and proceeded in two stages: (1) the formation of their iron cores fr om a protoplanetary nebula around the Sun and (2) the subsequent accumulati on of silicate chondritic material. However, the proximity of the Earth, wh ich more efficiently "scavenged" volatile components (especially, H2O) from the surrounding space owing to its greater mass, resulted in the depletion of the Moon and especially its core in these components. The differences i n the evolution of tectonic and magmatic processes in the Earth and Moon ar e probably related to different energy capacities of these planetary bodies .