Anorthosites in Layered Mafic Intrusions

Layered mafic intrusions (LMI) may be defined here, with due caution, as differentiated bodies of igneous rock, having broadly gabbroic, noritic, or troctolitic bulk compositions and well developed layering, that have been emplaced into continental crust.4 There is usually a substantial volume of ultramafic rocks, in addition to plagioclase-bearing cumulates, including anorthosite. This definition is meant to effectively distinguish the “stratiform” anorthosites of these intrusions from those of Proterozoic massifs (Chap. 3), although problems remain with several intrusions that have features common to both (Sects. 3.1.3, 3.12).