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

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 oc...

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Bibliographic Details
Main Authors: Barnes, Calvin, Reid, Kristin, Frost, Carol, Barnes, Melanie, Allen, Charlotte, Yoshinobu, Aaron
Format: Article in Journal/Newspaper
Language:unknown
Published: Geological Society of Norway 2011
Subjects:
Helgeland
Norway
Bindal
Online Access:https://eprints.qut.edu.au/108703/
Description
Summary: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 87 Sr/ 86 Sr <0.707 and ε Nd 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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