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A late Caledonian tectono-thermal event in the Gaissa Nappe Complex, Arctic Norway: evidence from fine-fraction K?Ar dating and illite crystallinity from the Digermulen Peninsula

A late Caledonian tectono-thermal event in the Gaissa Nappe Complex, Arctic Norway: evidence from fine-fraction K?Ar dating and illite crystallinity from the Digermulen Peninsula Thumbnail


Abstract

Fine-fraction K?Ar dating and illite crystallinity determination were applied on a peculiar pale olive green shale sample from the upper Ediacaran Indreelva Member (Stáhpogieddi Formation, Vestertana Group, Gaissa Nappe Complex) of the Digermulen Peninsula in Finnmark, Arctic Norway, to constrain the age and metamorphic conditions of tectono-thermal overprint. The <2 µm and <0.2 µm grain-size fractions are almost purely illite and yielded an illite crystallinity (expressed as the Kübler index) of 0.215 ?° 2T and 0.228 ?° 2T and K?Ar ages of 403.9 ± 4.2 Ma and 391.5 ± 4.0 Ma, respectively. The K?Ar ages are interpreted to present late-stage thermal overprint under low epizonal conditions along a localized shear zone, likely post-dating the peak of metamorphism and cleavage generation on the Digermulen Peninsula. Thus, a later tectono-metamorphic event related to the late stage of the Scandian orogeny is locally recorded in the Gaissa Nappe Complex of the Caledonides of Finnmark. This late Scandian event was probably caused by orogenic extensional collapse and appears to have extended at least into Mid-Devonian time.

Acceptance Date Feb 8, 2019
Publication Date Oct 3, 2019
Publicly Available Date Mar 28, 2024
Journal GFF
Print ISSN 1103-5897
Publisher Taylor and Francis
Pages 289-294
DOI https://doi.org/10.1080/11035897.2019.1583685
Keywords Caledonides, Scandian orogeny, Finnmark, K?Ar geochronology, Ediacaran, Devonian
Publisher URL https://doi.org/10.1080/11035897.2019.1583685

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