Low-grade, M1 metamorphism of the Douglas Island Volcanics, western metamorphic belt near Juneau, Alaska

GSA Special Papers
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Abstract

The western metamorphic belt is part of the Coast plutonic-metamorphic complex of western Canada and southeastern Alaska that developed during collision of the Alexander terrane and Gravina assemblage on the west against the Yukon Prong and Stikine terranes to the east. Deformation, metamorphism, and plutonism range from about 120 to 50 Ma. Subgreenschist to lower greenschist facies metabasalts exposed along the west end of the western metamorphic belt near Juneau, Alaska, record the earliest metamorphic event (M1). The protolith of the M1, low-grade metamorphic mineral assemblages is mostly arc-affinity basaltic rocks of the Douglas Island Volcanics. The most common metamorphic mineral assemblages are chlorite-epidote-actinolite with or without pumpellyite and stilpnomelane. There is no systematic distribution of metamorphic mineral assemblages in the study area, and all assemblages are in the pumpellyite-actinolite facies near the transition to the lower greenschist facies. Different low variance assemblages can be attributed to minor differences in pressure (P), temperature (T), or X CO2 . Mineral chemistry and phase equilibria suggest that thermal peak metamorphism of pumpellyite-bearing assemblages occurred at about 325 °C and 2 to 4.8 kbar.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Low-grade, M1 metamorphism of the Douglas Island Volcanics, western metamorphic belt near Juneau, Alaska
Series title GSA Special Papers
DOI 10.1130/SPE296-p51
Volume 51
Issue 66
Year Published 1995
Language English
Publisher GSA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center
Description 16 p.
First page 51
Last page 66
Country United States
State Alaska
City Juneau
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