| Popis: |
Basalt magmas, derived by the partial melting of planetary interiors, have compositions that reflect the pre-accretionary history of the material from which the planet formed, the planets, subsequent evolutionary history, the chemistry and mineralogy of the source regions, and the intensive thermodynamic parameters operating at the source and emplacement sites. Studies of basalt suites from the Earth, its Moon, and the eucrite parent body reveal compositional differences intrinsic to their source regions which are, in turn, a characteristic of the planet and its formational and evolutionary history. Major interplanetary differences are observed in iron, Mg(Mg + Fe2+), TiO2, Al2O3, Na2O, Cr, Ni, and in volatile element abundances. The most primitive mare basalts have Mg#s ∼ 0.6, on the Earth they are 0.70–0.72 for mid-ocean ridge basalts (MORBs) and up to 0.9 for Archean peridotitic komatiites. Eucrites have Mg#s approaching 0.5 (excepting Binda). These differences reflect inherent differences in Mg(Mg + Fe2+) of their sources. Striking differences in the TiO2 abundances of the planetary basalts reflect both inter- and intra-planetary variations in source chemistry. Primitive MORBs and primitive oceanic intraplate tholeiites have a factor of 2–3 difference in TiO2 at comparable Mg# (0.7–1.2 vs 2–3 wt.% respectively). Three major titania groups are recognized in the mare suite; high TiO2 (8–13 wt.%), low TiO2 (2–5 wt.%) and very low TiO2 ( |
