Clinopyroxenes of the Gabbro Cumulates of the Kap Edvard Holm Complex, East Greenland

W. A. Deer and D. Abbott1
Department of Mineralogy and Petrology, Cambridge
1Present address: Research and Productivity Council, Fredericton, Canada.

Summary: The major part of the Kap Edvard Holm complex consists of two series of conspicuously banded gabbroic rocks. The primary minerals of both lower and upper layered series show a progressive change in composition, from higher to lower temperature phases, with increasing height in the complex. Minor fluctuations in the differentiation of the two series occur but the division of the layered rocks into the lower and upper series is based on abrupt and major changes in the compositions of the pyroxenes, olivine and plagioclase. This break is correlated with the injection of a large volume of undifferentiated magma which occurred after much of the lower layered series had consolidated, and from which the rocks of the upper layered series were formed. Twelve pyroxenes, five from the lower and seven from the upper layered series have been analysed; the relationships between their optical properties and chemical composition, and between the cell parameters and composition are considered. The crystallization trend of the pyroxenes is compared with that of the Skaergaard calcium-rich pyroxenes; it is suggested that the restricted enrichment in iron shown by the Kap Edvard Holm pyroxenes may be related to the higher water-vapour pressures which prevailed during much of the period of crystallization.

Mineralogical Magazine; 1965 v. 34; no. 268; p. 177-193; DOI: 10.1180/minmag.1965.034.268.14
© 1965, The Mineralogical Society
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