Traces of the Transscandinavian Igneous Belt in the central Scandinavian Caledonides: U-Pb zircon dating and geochemistry of crystalline basement rocks in the Middle Allochthon. (2nd April 2016)

• Record Type: Journal Article
• Authors: Grimmer, J.C.; Hellström, F.A.; Greiling, R.O.
• Is Part Of: GFF. Volume 138:Number 2(2016)
• Page Start: 320
• Page End: 335
• Publication Date: 2016-04-02
• Subjects: Geology -- Scandinavia -- Periodicals; Geology -- Periodicals; 554.8
• DOI: 10.1080/11035897.2015.1063537
• Languages: English
• ISSNs: 1103-5897

Abstract

Abstract : Basement-slices are frequent components in the lower nappes of the central Scandinavian Caledonides. New geochronological and geochemical data provide evidence that three of these basement-slices in the Middle Allochthon are derived from the Transscandinavian Igneous Belt. Dated samples in this study comprise a quartz monzonite from the Stalon Nappe Complex and a quartz monzodiorite and a monzonite from the Ammarnäs Nappe Complex. A Ce/Yb-Ta/Yb-plot of the mafic rocks from the Ammarnäs Nappe Complex suggests a calc-alkaline to shoshonitic geochemical character. Low Ni- and Cr-contents and low Mg# indicate that the mafic rocks originated from an already evolved magma. Enrichment of Fe-Ti oxides and V>200 ppm indicate presence of cumulus phases to various degrees. These basement-derived rocks in the Middle Allochthon yielded concordant U-Pb zircon SIMS ages of 1799 ± 10 Ma, 1787 ± 6 Ma and 1797 ± 5 Ma. They are therefore interpreted to represent rocks detached from the Palaeoproterozoic Transscandinavian Igneous Belt and incorporated in the Middle Allochthon during Scandian orogeny.