Charnockitic and Related Cordierite-Bearing Rocks from Dangin, Western Australia

Abstract

VI. SummaryA series of charnockitic rocks and associated cordierite-bearing rocks from Western Australia has been described and compared with charnockitic rocks from other localities. This charnockitic suite is considered to be a series of basic intrusions into an older series of paraschists. It has, in places, been considerably contaminated by assimilation of the aluminous metasediments and in such cases is now represented by cordierite-bearing rocks. The basic charnockitic rocks and their contaminated equivalents have been subsequently invaded, under deep-seated conditions by granitic magma or emanations, and now appear as recrystallized remnants of the original masses. They have suffered extensive granitization which has yielded the acid charnockites (hypersthene-alkali felspar gneisses) in which the hypersthene is considered to have been derived from the older hypersthene-bearing basic charnockites. In view of the similarity to the Indian and Antarctic charnockites it appears possible that the charnockitic rocks of these areas are of similar origin, and that charnockite (hypersthene granite) rather than being the result of crystallization from a magma, is due to the granitization of older hypersthene-bearing rocks. If charnockite is of magmatic origin then it is most probable that this magma was of palingenetic origin and that the hypersthene is a relict from the earlier rocks and not the product of crystallization of the charnockite magma. Dunn (1942, p. 23) considers that the evidence afforded by Indian rocks is not opposed to the view that the hypersthene gneisses (charnockites) are the product of partial or complete palingenesis of very deep-seated rocks which had lost their water content.