| Summary: | The Precambrian basement of Lithuania and NE Poland, much of which is metasedimentary paragneiss, can be accessed only by cores from deep borcholes. Ion microprobe dating of detrital zircons from samples of these metasediments and the geochemical signatures of the rocks provide new insights into their age and provenance. Detrital zircons from metasediments from Jastrzebna and Monki have Pb isotopic ages in the ranges 3.14-1.83 and 3.53-1.82 Ga, respectively. Similar results have been obtained from the Lithuanian Lazdijai and Bliudziai paragneisses. About 30% of the analysed Polish detrital zircon cores are of Late Archaean age (2.90-2.60 Ga) and about 70% are Palaeoproterozoic (2.10-1.90 Ga), similar to the age distributions of detrital zircon from Svecofennian metasediments exposed in Central Sweden and Southern Finland. The youngest detrital zircon sub-groups indicate maximum deposition ages of about 1.86 Ga, similar to the ages of exposed Svecofennian sedimentary basins. Possible source rocks of comparable ages and affinities can be found within Fennoscandia, Greenland and Sarmatia.
|
|---|