A Timanian island-arc fragment in North Greenland: The Midtkap igneous suite

Abstract

The distribution of rocks with Timanian ages along the circum-arctic continental margins provides important information for the post-Rodinia palaeogeographic reconstruction of the Arctic. The Midtkap igneous suite in northern Peary Land, North Greenland, forms isolated outcrops (centres A–F) in early Palaeozoic deep-water sedimentary rocks of the Franklinian Basin. The suite is composed of intermediate and felsic intrusive rocks, serpentinite, and heterogeneous volcanic breccia. Timanian zircon ages of the intrusive rocks were previously reported from centres D, E, and F (628–570 Ma). Field observations, zircon U-Pb and biotite Ar–Ar dating, whole-rock geochemical and Sr–Nd isotope data allow greater insight into the composition of the suite and its genetic interpretation. A supra-subduction zone origin and a formation in an intra-oceanic volcanic arc is very likely for the whole suite. The intrusive rocks (monzonite, granitoids, gabbro, rodingite) were probably uplifted by serpentinite diapirism. The heterogeneous volcanic breccia (basalt/spilite mixed with arc-derived rocks) is interpreted as a mélange. Both serpentinite diapirs and mélanges indicate a forearc setting. A monzonite of centre B with a zircon 206Pb/238U age of 650 ± 3 Ma represents the oldest intrusion of the Timanian suite. 40Ar/39Ar biotite dating of a granite of centre A (∼535 Ma) points to a duration of the island-arc magmatism until the earliest Palaeozoic. Coeval volcaniclastic detritus derived from a Timanian island arc has also been found in the Pearya composite terrane at the north coast of the Canadian Ellesmere Island. The Timanian arc was possibly split and displaced during the Caledonian Orogeny.