The petrology of the Harkerbreen Group, Ny Friesland, Svalbard: protoliths and tectonic significance

• Published in: Geological Magazine
• Main Author: Manby, G. M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1990
• Subjects: Billefjorden; Ny Friesland; Svalbard
• Online Access: http://dx.doi.org/10.1017/s0016756800013820; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0016756800013820

Abstract The late Precambrian–early Palaeozoic rocks of Ny Friesland, which have been subjected to Caledonian deformation and metamorphism, constitute part of the Eastern Province or Terrane of Svalbard. The Harkerbreen group and other divisions of the Stubendorffbreen supergroup form a high-grade and intensely deformed core complex to this terrane which is bounded to the west by the Billefjorden Fault Zone and to the east by a major north–south shear zone. The Stubendorffbreen rocks exhibit two gneissic foliations, one axial planar to a large scale, F 1 fold nappe closing to the east and the other axial planar to kilometre-scale upright F 2 folds subsidiary to the Atomfjella Arch. Metamorphism in the mid-amphibolite facies range coincided with generation of these folds, and F 3 .crenulation folding was accompanied by waning P–T conditions. A significant proportion of the gneisses within the Harkerbreen group display silica–major element covariation patterns consistent with their position in the granodiorite field on the AFM plot. Incompatible, immobile element ratios Zr/Ti v. Nb/Y indicate affinities with rhyolites to rhyodacites which is also suggested by their REE profiles. Normalized multi-element plots of the gneisses are similar to those of granites from attenuated within-plate settings such as Mull and Skaergaard. The amphibolites which were intruded in the D 1 –D 2 interval appear to be derivatives of fractionated basalts. They plot across the calk-alkaline tholeiite boundary on the AFM diagram, and the calc-alkaline character of some of the amphibolites is further suggested by their Yb-normalized Ce-Ta abundances. Zr-Ti-Y and REE abundances would support their derivation from a related suite of fractionated basalt liquids. On the Zr/Y v. Zr discrimination diagram the amphibolites appear to have compositions transitional between Mid Ocean Ridge and Within-Plate basalts whilst the Zr-Nb-Ta plot indicates Volcanic Arc Basalt affinities. Th-Hf-Ta and multi-element plots, however, indicate a marginal to ...