Crystallization of some lunar mafic magmas and generation of rhyolitic liquid.

ABSTRACT

During crystallization of lunar crystalline rocks 10022 and 10024, augite changes in composition almost continuously from titanaugite (Ca(36)Mg(47) Fe, (17) with TiO(2) 3 percent) to a very iron-rich variety (Ca(9)Mg(5)Fe(86)), pigeonite changes from Ca(9)Mg(66)Fe(25) to Ca(1O)Mg(51)Fe(39), and olivine changes (in 10022) from Mg(71)Fe(29) to Mg(41)Fe(59), whereas plagioclase stays as bytownite. These compositional variations, as well as the textural relations, may be explained by rapid crystallization of undercooled magmas. The residual liquids found as mesostasis are rhyolitic, which suggests that fractional crystallization of some lunar mafic magmas can generate rhyolitic magmas. Melting experiments were made on crystalline rocks to determine liquidus temperatures and crystallizing phases.