ANORTHOSITES MARE BASALTS IMPACT BRECCIAS 15415 15016 67016 Basics: Basics: Basics: • Igneous (Volcanic) rocks • Igneous (Volcanic) rocks • Composite rocks made from a • Contain minerals such as feldspar • Contain dense minerals such as collection of rock and mineral which are less dense than olivine and olivine and pyroxene fragments all mixed together pyroxene • Mare basalts formed by remelting the • Formed by impact events • These less dense minerals floated in dense materials that sank out of the • Heat and pressure from impact events a layer of molten rock (magma) magma ocean. caused different rock fragments to forming an anorthosite crust. • Age of mare basalts range from ~3.9 fuse together • Age of anorthosites range from ~4.5 – 3.2 billion years old • Vary in age – 4.3 billion years old Characteristics: Characteristics: Characteristics: • Brighter/lighter in color than the mare • Dark gray to black in color • Mixture of both fine and coarse grains basalts • Fine grained (you cannot easily see • Combination of characteristics of • Very friable (easily breakable) individual minerals that make up the basalts and anorthosites • Generally coarse grained (can see rock) • Appear to have fragments (clasts) that individual minerals) • Usually include holes (vesicles) have been “cemented together” to created by gases that escaped before form the rock magma solidified into rock • Rough texture • Hard surface Lunar Magma Ocean Concept: When the Moon formed it was surrounded by a layer of molten rock (ocean of magma) hundreds of kilometers thick. As the magma crystallized, the minerals more dense than the magma sank while those less dense (such as feldspar) floated, forming the anorthosite crust. [This process is known as differentiation.] The dense minerals (olivine and pyroxene) later remelted to produce the basalts that compose the lunar maria..