No abstract

North‐west Spitsbergen consists of a complex of Caledonian and Grenvillian crystalline rocks, situated at the north‐west corner of the Barents Shelf. The aim of this study is to understand the extent of pre‐Caledonian basement rocks and their protoliths. Micas and zircon grains from six rocks from north‐west Spitsbergen have been dated by the 40Ar/39Ar and single‐zircon Pb‐evaporation methods. Two grey granites yielded Late Caledonian mica 40Ar/39Ar and zircon ages of ca. 420‐430 My, with inherited zircon grains as old as 1725 My. Zircon grains from a gneissose granite xenolith in a grey granites gave crystallization ages of ca. 960 My; some grains from a migmatite neosome show similar ages. Zircon grains yielding Archean and late Palaeoproterozoic ages (1600‐1800 My) are interpreted as xenocrysts of detrital origin. The youngest ages obtained from detrital zircon grains from a greenschist facies quartzite of the Signehamna unit are ca. 1800 My. Similar schists are included as xenoliths in the 960 My old gneissose granite; therefore, the sedimentary protoliths of the unit are Mesoproterozoic. The dating results suggest a significant tectonothermal event during Grenvillian time; subsequent Caledonian events had less extensive thermal effects. However, it is still a matter of debate whether Grenvillian or Caledonian metamorphism produced the majority of the migmatites. A large population of zircon grains with Late Palaeoproterozoic ages suggests a wide surface exposure of rocks of this age in the source area, with some Archean zircons.

No abstract

No abstract

No abstract