Abstract

KD Mg/Fe for garnet-biotite pairs in calcium-rich metamorphic rocks from New Hampshire of the garnet to kyanite zones is significantly lower (0.10±0.01) than that in isogradic pelitic schists (0.16 ± 0.02). Sillimanite zone pelitic rocks show a wide range of KD (0.16 ± .03), but much lower values than those in the enclosed Kinsman Quartz Mon-zonite (Ko= 0.28 + .03), which has been variously described as a magmatic, granitized, or metamorphic rock. The Kinsman and the enclosing pelitic rocks have closely similar chemical compositions and mineral assemblages, and formed under high load pressure (>5 kbar), low to intermediate oxygen fugacity, and (probably) similar H2O fugacity. Thus the higher KD of the Kinsman rocks is taken as evidence of higher temperature of formation, and of probable magmatic origin.

In these rocks CaO and MnO in garnet is not directly related to metamorphic grade, as several investigators have proposed in other areas.

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