Petrographic and Chemical Data for the Large Mesozoic and Cenozoic Plutonic Sills East of Juneau, Southeastern Alaska

摘要

Petrographic, chemical, and age data are presented for six plutonic sills of Late Cretaceous to early Tertiary age located east of Juneau, Alaska. Five of the sills--the Mount Juneau, Carlson Creek, Lemon Creek Glacier, Mendenhall Glacier, and Taku Cabin plutons--are mostly tonalite but range from quartz diorite to granodiorite; their mean color indexes range from 19 to 32. The more silicic Annex Lakes pluton is mostly granodiorite but has significant quartz monzodiorite and tonalite and a mean color index of 14. Although the six plutons are calc-alkaline and generally similar in average chemical and modal composition, they vary in form, mineralogy, texture, and petrographic and chemical characteristics. The Mount Juneau and Annex Lakes plutons exhibit the greatest internal differences, whereas the Taku Cabin and Mendenhall Glacier plutons are the most homogeneous. Plots on silica-oxide variation and AFM diagrams exhibit coherent trends with some scatter.