Origin of the Anorthosite-Mangerite Rocks in

Rocks of the anorthosite-mangerite suite were intruded in many places in the southern part of the Grenville province of the Canadian Shield. These rocks, known as the Morin series in southern Quebec, are described from two contrasted areas, one in which there has been intense deformation during the emplacement of these rocks and in the other only mild deformation. Differences in the mineralogy and chemistry of these rocks in the two areas can be related to the degree of deformation. Although many of the rocks of the series still retain their igneous textures, others, especially the mangerites, are largely recrystallized and commonly exhibit a gneissic foliation. The feld-spars and pyroxenes which are by far the most abundant minerals of the Morin series are dealt with in detail. From a study of the coexisting pyroxenes and the amount of iron in the plagioclases, evidence is given for a difference in the degree of metamorphism between the two areas. All of the pyroxenes from the more highly deformed area contain considerably more alumina than those from the other area. Coexisting lime-rich and lime-poor pyroxenes are characteristic of almost all of the rocks of the series. The coexistence of subcalcic ferro