Clinopyroxenes from the Upper Layered Series

SUMMARY. Chemical compositions, unit-cell contents, and optical properties of six clinopyroxenes from the Upper Layered Series are presented. There is a gradual enrichment i iron upwards in the intrusion although there is no measurable effect on the optical properties, possibly because of Cr varia-tion and exsolution of Fe and Ti as oxides. The chemistry of the clinopyroxenes is consistent with crystallization from a water-rich magma of transitional nature between tholeiite and alkali-olivine basalt. X-ray oscillation photographs of single crystals reveal the presence ofsub-microscopic exsolu-tion lamellae of pigeonite, a feature consistent with the transitional nature of the parent magma. Exsolution lamellae of titanomagnetite ar ubiquitous and were formed at subsolidus temperatures in response to high buffered oxygen fugacity. Comparisons are made between the properties of clino-pyroxenes from the Lower, Middle, and Upper Layered Series, and the conditions of crystallization f each series. THE Kap Edvard Holm complex, consisting of layered gabbros and later quartz-bearing syenites, is situated on the west side of Kangerdlugssuaq Fjord, East Green-land. From an analysis of the structure of the gabbros, a Lower, Middle, and Upper Layered Series can be distinguished (Elsdon, t969). The clinopyroxenes of the Lowe