PROVENANCE AND TECTONIC IMPLICATIONS OF PALAEOPROTEROZOIC (C. 1740 MA) QUARTZ PORPHYRY CLASTS IN THE BASAL OLD RED SANDSTONE (LILLJEBORGFJELLET CONGLOMERATE FORMATION) OF NORTHWESTERN SVALBARD'S CALEDONIDES

Abstract

The Lilljeborgfjellet Conglomerate Formation composes the lower part of the alluvial Siktefjellet Group of northwestern Spitsbergen's Old Red Sandstone succession. Siktefjellet strata are of late Silurian or early Devonian age, but lack precise age-diagnostic fossils. They are unconformably overlain by conglomerates and sandstones of the Red Bay Group, which contain a well established fish fauna of Lochkovian age. The Lilljeborgfjellet Conglomerate rests with a major unconformity on high-grade (with eclogites) schists and gneisses, with associated corona gabbros and granitic gneisses. Previous isotope-age studies have shown that these igneous rocks yield U/Pb ages of c. 950 Ma, and that the eclogite facies metamorphism may be of Caledonian or late Neoproterozoic age. The high P/high T rocks are intercalated with and overlain by schists affected only by Caledonian amphibolite facies metamorphism, recorded by 40Ar/39Ar and Rb/Sr cooling ages of 400–430 Ma.