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- How should charnockitic rocks be named?
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How should charnockitic rocks be named?
Abstract
The IUGS Subcommission on the Systematics of Igneous Rocks, at its meeting of Montreal, agreed to Recommendations (1972) for plutonic rocks, which were published in various reviews. Charnockitic rocks were not included, as their nomenclature was still under review by a special working group. This paper outlines the results reached at present.
Charnockitic rocks are classified and named according to their positions in the QAP diagram. General and special names may be used in an optional manner. Definitions of special names are given. Only special names of current usage are recommended: charnockite, opdalite (or charno-ederbite), enderbite, mangerite, jotunite; the use of farsundite is debated. A classification scheme of charnockitic rocks is presented.
The attribution of perthitic felspar to alkali feldspar or plagioclase is discussed. It is recommended that perthitic feldspars are distributed over A and P according to the actual (modal) content of their K-feldspar and plagioclase phases. As albite is considered as an alkali feldspar, perthites are attributed to A.
It is suggested that the terms anorthosite, norite (including leuconorite), and monzonorite be used for rocks of any An content.
A list of terms which should be abandoned is annexed.