Caledonian and precambrian history in Svalbard: a review, and an implication of escape tectonics

Abstract

This article contains two parts, a review of geochronological data of the Svalbard basement, and a hypothetical application of the concept of escape tectonics on the Caledonian-Franklinian mobile belts of the Arctic. All Caledonian and older isotopic ages obtained from Svalbard are compiled and synthesized into a sequence of events from Proterozoic to middle Paleozoic times. The areal distribution of the rocks of various ages are considered in conjunction with the present understanding of the lithostratigraphy of the archipelago. Caledonian tectonothermal events in the Middle Silurian and Middle Ordovician are well defined by isotopic age determinations and stratigraphie evidence. An oceanic suture zone represents the early Caledonian subduction event. The Late Proterozoic-Early Ordovician low-grade metasediments occupy ca. 60% of the pre-Devonian basement of Svalbard. Early Paleozoic and latest Proterozoic isotopic age groups have no clear geological correlatives, however, they may reflect regional geological events recognized in other parts of Arctic margins. The Grenvillian and Svecofennian events have been well documented by the isotope systems and these data have made it possible to distinguish Late, Middle and Early Proterozoic rock units in Svalbard. The Middle and Early Proterozoic rocks occupy ca. 40% of the whole basement, and most of the crystalline basement has been formed essentially during these two tectonothermal events. These basement rocks are separated into three orogen-parallel structural units by steeply dipping faults in Svalbard. In the second part of this article, these faults and other orogen-parallel faults in the western part of the Arctic Caledonian-Franklinian mobile belts are summarized and considered in the context of “escape tectonics”.