Late Neoproterozoic Amphibolite-Facies Metamorphism of a Pre-Caledonian Basement Block in Southwest Wedel Jarlsberg Land, Spitsbergen: New Evidence from U-Th-Pb Dating of Monazite

Jaroslaw Majka, AGH, University of Science and Technology
Stanislaw Mazur, University of Wroclaw
Maciej Manecki, AGH, University of Science and Technology
Jerzy Czerny, AGH, University of Science and Technology
Daniel Holm, Kent State University - Kent Campus

© 2008, Cambridge University Press. The original published version is available at .

Abstract

Southwest Spitsbergen, Wedel Jarlsberg Land, consists of two Proterozoic crustal blocks with differing metamorphic histories. Both blocks experienced Caledonian greenschist-facies metamorphism, but only the southern block records an earlier pervasive M1 amphibolite-facies metamorphism and strong deformational fabric. In situ EMPA total-Pb monazite geochronology from both matrix and porphyroblast inclusion results indicate that the older M1 metamorphism occurred at 643 ± 9 Ma, consistent with published cooling ages of c. 620 Ma (hornblende) and 580 Ma (mica) obtained from these same rocks. This region thus contains a lithostratigraphic profile and metamorphic history which are unique within the Svalbard Archipelago. Documentation of a pervasive late Neoproterozoic Barrovian metamorphism is difficult to reconcile with a quiescent non-tectonic regime typically inferred for this region, based on the occurrence of rift-drift sequences on the Baltic and Laurentian passive margins. Instead, our new metamorphic age implies an exotic origin of the pre-Devonian basement exposed in SW Spitsbergen and supports models of terrane assembly postulated for the Svalbard Archipelago.