Ordovician and Silurian Magmatism in the Upper Nappe, Uppermost Allochthon, Helgeland Nappe Complex, North-Central Norway
Date
2011
Authors
Barnes, Calvin G.
Reid, Kristin
Frost, Carol D.
Barnes, Melanie
Allen, Charlotte M
Yoshinobu, Aaron S
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Geological Society Norway
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.
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Keywords: allochthon; batholith; dehydration; depositional sequence; emplacement; gneiss; magmatism; migmatization; nappe; Ordovician; shear zone; Silurian; zircon; Helgeland; Nordland; Norway
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Norsk Geologisk Tidskrift - Norwegian Journal of Geology
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Journal article
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2037-12-31
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