Ordovician and Silurian magmatism in the Upper Nappe, Uppermost Allochthon, Helgeland Nappe Complex, north-central Norway

Calvin Barnes, Kristin Reid, Carol D Frost, Melanie Barnes, Charlotte M Allen, Aaron Yoshinobu

Research output: Contribution to journalArticle

Abstract

The structurally lowest parts of the Upper Nappe of the Helgeland Nappe Complex consist primarily of migmatitic quartzofeldspathic gneiss with intercalated calc-silicate gneiss. Detrital zircons in the gneiss indicate an Ordovician depositional age. Migmatization via biotite dehydration reactions occurred at ~480 Ma at pressures of ~700 MPa; some migmatites were mobilized into cross-cutting diatexites. Diverse gabbroic to granitic plutons and dikes of the Bindal Batholith were emplaced from 448–424 Ma. They range from calc-alkaline to alkalic and most have initial 87Sr/86Sr <0.707 and εNd from 0 to -4. Pressures of emplacement were ca. 300 MPa. Shear zones with reverse shear sense cut 437 Ma intrusions, suggesting that contraction accompanied magmatism.
Original languageEnglish
Pages (from-to)121-136
JournalNorwegian Journal of Geology
StatePublished - 2011

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