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Garnet-clinopyroxenite from the Red Mountain pluton, Alaska

February 1, 1974

Several lens-shaped and irregular masses of garnet-clinopyroxenite occur along the north margin of the Red Mountain pluton, near Seldovia, Alaska. The pluton is composed of intercalated dunite, clinopyroxenite, and banded chromite layers. The chromite layers appear to dip toward the center of the mass, but they have been deformed, and in some places display isoclinal overturned folds. The garnet-clinopyroxenite bodies are compositionally layered and appear to have been deformed along with the host peridotite.

The garnet-clinopyroxenite bodies have whole-rock compositions analogous to alkali-poor anorthite gabbro or mafic anorthosite. Garnet compositions are dominated by the pyrope, grossularite, and almandine components, and the clinopyroxene bodies are rich in Ca-Tschermaks molecule (CaAl2SiO6).

Although crystallization from the liquidus is a possibility, textures, structures, and the chemical composition of the constituent mineral phases indicate that the garnet-clinopyroxenite has equilibrated in the solid state at pressures of 15 to 25 kb and temperatures of 1100°C to 1300°C. Such P-T parameters suggest an upper-mantle origin for the garnet-clinopyroxenite and the enclosing pluton.

Publication Year 1974
Title Garnet-clinopyroxenite from the Red Mountain pluton, Alaska
DOI 10.1130/0016-7606(1974)85%3C285:GFTRMP%3E2.0.CO;2
Authors R. B. Forbes, R. C. Swainbank
Publication Type Article
Publication Subtype Journal Article
Series Title GSA Bulletin
Index ID 70247297
Record Source USGS Publications Warehouse