Single-zircon Pb-evaporation and 40Ar/39Ar dating of the metamorphic and granitic rocks in north-west Spitsbergen |
| |
| Authors: | Yoshihide Ohta Alexander N. Larionov Alexander M. Tebenkov Claude Lepvrier Henri Maluski Michael Lange Barbara Hellebrandt |
| |
| Affiliation: | Y. Ohta, Norwegian Polar Insitute, c/o NGU, Box 5348, Majorstua, N-0304 Oslo, Norway;A. N. Larionov, Laboratory for Isotope Geology, Swedish Museum of Natural History, Box 50 007, SE-104 05 Stockholm, Sweden;A. M. Tebenkov, Polar Marine Geological Expedition, ul. Pobedy 24, 189510 Lomonosov-St. Petersburg, Russia;C. Lepvrier, Dept. of Geotectonics, P. &M. Curie University, 4 Place Jussieu, F-75252 Paris Cedex 05, France;H. Maluski, Laboratory of Tectonics and Geochronology, University of Montpellier, Place E. Bathillon, 34000 Montpellier, France;M. Lange &B. Hellebrandt, German Aerospace Centre, Koenigswinterer Str. 522-524, D-53227 Bonn, Germany. |
| |
| 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. |
| |
| Keywords: | |
|
|
