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Abstract

Recently analyzed orthopyroxenes, clinopyroxenes, and garnets from charnockites and granulites are plotted on a triangular diagram expressing total amounts of Fe, Mg, and Ca. Trends of all compositional tie lines formed by coexisting orthopyroxenes and clinopyroxenes from these rocks intersect the Mg-Ca join. The intersection values seem to differ according to the metamorphic history of the host rock and may be of value in assessing temperatures of formation of the minerals.

Relations of tie lines between garnet and host rock are plotted on a triangular net whose corners are CaO, MgO, and FeO + MnO. Most garnets have higher ratios of FeO + MnO and FeO + MgO than do their host rocks. Garnets of acid granulites do not show pronounced systematic variations in composition relative to compositions of host rocks. The minerals of these garnetiferous granulites probably are not equilibrium assemblages.

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