Caledonian terranes in Svalbard

Recent collaborative field, petrological, and geochronological studies have provided important new data that aid in the definition of Caledonian lithotectonic terranes in Svalbard. Several lower–middle Paleozoic tectonothermal events have been outlined in north-central (Biskayer Peninsula) and west-central (Motalafjella area) Spitsbergen. Although a younger (Middle Silurian) event was approximately synchronous in both areas, older events were different in character and timing. In the Biskayer Peninsula a tectonothermal event occurred during the Middle to Late Cambrian and resulted in formation of eclogite in tectonically thickened continental crust. In contrast, in the Motalafjella area, Early to Middle Ordovician subduction of oceanic crust resulted in development of an accretionary wedge and formation of a blueschist-eclogite complex. The polyphase Caledonian evolution of Spitsbergen is generally similar to that of the Pearyan terrane in northernmost Ellesmere Island where pre– and post–Upper Ordovician island-arc volcanic sequences suggest several regionally significant orogenic events. The western, northwestern, and north-central tectonic elements of Spitsbergen, therefore, are considered to have been initiated at a similar time as the Pearyan terrane and are termed the “West Svalbard terrane.” There is no record, so far known, of Middle to Late Cambrian tectonic activity in northeastern Svalbard (including Ny Friesland and Nordaustlandet). However, Early to Middle Ordovician tectonic instability is reflected by initiation of an extensive depositional hiatus. Northeastern Svalbard tectonic elements appear to represent a coherent terrane (East Svalbard terrane), which amalgamated with the West Svalbard terrane in Middle Ordovician time. Although the West and East Svalbard terranes were palinspastically separated prior to Middle Ordovician amalgamation, they share, in part, similar Precambrian elements, including constituents of Grenville-age basement and upper Proterozoic (Vendian?) tillites with possibly time-correlative magmatic rocks. These Precambrian elements appear to be common along the entire western margin of Iapetus, and suggest that the two Svalbard terranes originated proximal to East Greenland.