First results of the U-Pb isotopic (LA-ICP-MS) dating of detrital zircons from the lower paleozoic of spitsbergen

This work presents the first results of dating of detrital zircons (dZrs) from the Lower Paleozoic ter- rigenous-carbonate rocks of the Cambrian Blåstertoppen (samples 08-137 and 08-142, south of the Wedel Jarlsberg Land) and Ordovician Wiederfjellet (sample K06-17, north of the Land) sequences, which are wide- spread to the north and south of the Hornsund Fjord, on the southwestern coast of Spitsbergen Island. Against the background of sporadic values of 1-3 Ga, samples K06-17 and 08-142 showed similar spectra of the age distribution of dZrs with dominant compact numerous age groups of ∼1.8-1.9 Ga and peaks of the maximum of the probability density of 1850 and 1862 Ma, respectively. The only noticeable difference in these spectra is the presence of a young grain of 541 Ma in sample 08-142 (with a very good value of concordance), which is close to the suggested Cambrian age of formation of the Blåstertoppen sequence. The distribution of the dZr ages in sample 08-137 is significantly distinct. First, the general age range is narrower: 1.15-1.95 Ga (no Archean ages). Second, the age of 1.8-2.0 Ga dominant in the other two samples corresponds to only one grain. Thus, although samples 08-137 and 08-142 were taken from closely located levels of the section of the Cambrian Blåstertoppen sequence (in the same interception), the age spectra of dZrs from these samples differ cardinally. The statistical Kolmogorov-Smirnov test quantitatively supports the visual similarity of age spectra of dZrs from samples K06-17 and 08-142 (p = 0.913) and the distinction of those from samples 08-142 and 08-137 (p = 0). Thus, the provenance areas, which supplied the clastic material to the sedimentary basin, whose remnants are presently located in the southwestern part of Spitsbergen, abruptly changed in the Cambrian. The basal levels of the Cambrian section of this basin (sample 08-137) were mostly formed due to accumulation of the erosion products of the local (Spitsbergen) sources: metarocks of the Eimfjellet Group located in the south of the Wedel Jarlsberg Land and of the Smerenburgfjord Group abundant on the Albert I Land. The dZrs age spectrum is a print of the ages of the Late Paleoprotero- zoic-Mesoproterozoic (pre-Grenville) basement unaffected by assemblage of Rodinia. Then the conditions changed and the basin became to accumulate the material from the remote regions, significant parts of which were the areas of ancient cratons, including Archean blocks. The general sedimentation conditions did not change considerably, because the rock type remained the same. © Pleiades Publishing, Ltd., 2014.