Fig. 3: Evolutionary pathways of magmatic water in CE6 mare basalt. | Nature

Fig. 3: Evolutionary pathways of magmatic water in CE6 mare basalt.

From: Water abundance in the lunar farside mantle

Fig. 3

a, CE6 mare basalt was derived from the partial melting of lunar mantle rocks. The melt aggregates at depth in networks to form the source magma and intrudes upwards into shallow depths. The ambient rocks are much colder than the hot melt, resulting in fractional crystallization of the source magma. In certain circumstances, the residual melt (parent magma of CE6) from the source magma flowed up to the lunar surface, forming the rocks of CE6 mare basalt. The water abundances and hydrogen isotopic compositions measured on melt inclusions and apatite from the CE6 mare basalt depict an evolutionary pathway for water in the parent melt. b, Rare MgO-rich olivine (Fo 45–62 atom%; Supplementary Table 3) in CE6 mare basalt should crystallize much earlier than the main constituent phases (pyroxene and plagioclase) in the crystallization processes of the parent melt, characterized by a low water abundance and a lunar-mantle-like δD value (Fig. 2) in the melt trapped in the olivine grains, as well as a notably high MgO content of the melt (Extended Data Table 2 and Extended Data Fig. 5, Supplementary Table 3). c, Onset of ilmenite formation in low-Ti mare basalts occurred at a late crystallization stage of the parent melt28 accompanying enrichment of water in the residual melt followed by degassing of water when the ambient pressure is inadequate to trap the water dissolving in the melt. Thus, ilmenite-hosted melt inclusions exhibit variability in both water concentration and δD (Fig. 2). d, Apatite is one of the last-crystallized minerals in CE6 basalts, recording notable higher δD values than olivine-hosted melt inclusions. Some residual melt from which apatite crystallized may have been trapped by late-crystallized ilmenite (Fig. 2). Ol, olivine; Pl, plagioclase; Px, pyroxene; Ilm, ilmenite; and Ap, apatite.

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