Age, provenance and tectonostratigraphic status of the Mesoproterozoic Blefjell Quartzite, Telemark sector, Southern Norway
Andersen, T.; Laajoki, K.; Saeed, A.
Precambrian Research 135(3): 217-244
The Blefjell quartzite is ca. 40X6-10 km gneissic metasupracrustal occurrence deposited on a 1159+ or -8 Ma old felsic volcanite. It is part of a mature beach--shallow shelf complex deposited between ca. 1155 and 1145 Ma. LAM-ICPMS U-Pb ages of single, detrital zircons range from 1.40 to 2.07 Ga, with frequency maxima in the age-range 1.65-1.90 Ga. Younger zircons (1.53-1.64 and 1.40-1.50 Ga are less abundant. Present-day (super 176) Hf/ (super 177) Hf ranges from 0.2814 to 0.2822, corresponding to epsilon (sub Hf) (t) between -8 and +14. The minor and trace element distribution of the zircons suggest derivation from a range of mafic to granitic protosources, characterized by distinct, relative LREE enrichment or HREE depletion. The data confirm the presence of important 1.7-1.9 Ga protosources for Precambrian sediments in S Norway, indistinguishable in age and crustal history from rocks of the Transscandinavian Igneous Belt. This lends further support to regional tectonic models in which southern Norway west of the Oslo Rift has been an integral part of the Baltic Shield since the formation of the regional protolith in the Paleoprotoerozoic.