Geochemistry of the late Proterozoic Kapp Hansteen igneous rocks of Nordaustlandet, Svalbard

Abstract

Proterozoic igneous rocks occur in three areas in Nordaustlandet, Svalbard, and are found in the upper part of the Lower Hecla Hoek succession, the Botniahalveya Supergroup. The rocks have been called porphyrites in Botniahalveya. metadiabases in Prins Oscars Land and quartz porphyries in both areas as well as in the Sabinebukta area. All rocks have been metamorphosed under the greenschist facies conditions. The porphyrites are calc-alkaline acid andesites and dacites of medium to high K20 type, possibly showing a transition to tholeiitic series. The quartz porphyries are calc-alkaline rhyolites of high K20 type. The metadiabases are subdivided into two: the basic dykes of low K20 type and relatively high Fe tholeiite series, while the main bodies are acid andesites of medium to high K2O and low Fe tholeiite series. The basic dykes fall in the oceanic rock field of the Ti02-K20-P205 diagram, and are most likely belonging to the island arc type vo!canism. The metadiabases of main bodies and the porphyrites, and possibly the quartz porphyries, are chemically continuous. The medium to high K2O contents, and their Ti02-K20- P205 ratios suggest that these three rock groups are non-oceanic and resemble the rock associations of the areas having thick continental crust. This conclusion agrees with the reported high initial SrH7Mra tios and the existence of a distinct unconformity at the basc of this volcanogenic succession.