Some Chemical Characteristics of Anorthositic Suites and their Significance
Spirited discussion continues about the nature of the relationship of rocks of anorthositic composition to intermediate and silicic rocks comprising so-called mangerites, charnockites, adamellites, etc. Because of close spatial association, all of these rocks may be considered to constitute an 'anorthosite suite' without prejudgement as to genetic implications.About 700 rock analyses, largely from the literature but supplemented by previously unpublished analyses from the Michikamau and Morin intrusions have been used to examine some of the chemical characteristics of the anorthosite suites. The suites are commonly high in iron relative to magnesium and alkalies, high in alumina, and have high K2O/SiO2 ratios over a wide range of SiO2 concentrations. The chemical data together with the physical characteristics of the anorthosite suites are interpreted to mean that the magmas are orogenically generated but emplaced on the flanks of orogenic belts in 'anorogenic' environments. Rapakivi granitic suites are c...