ON THE MESOARCHEAN AGE OF DETRITAL ZIRCONS FROM META-TERRIGENOUS ROCKS OF THE SKELYUVATKA AND SAKSAGAN SUITES OF THE KRYVYI RIH STRUCTURE, ACCORDING TO THE RESULTS OF U-Pb DATING

Convincing geochronological data regarding the time of accumulation of deposits that fill the Kryvyi Rih structure, Ukraine, are still lacking, and in the current Chronostratigraphic chart they are attributed to the Paleoproterozoic. Thus, dating of detrital minerals that allows determination of the maximum age of sedimentation, is especially important. The paper presents results of the U-Pb LA-ICP-MS dating of zircons from two quartzite and two phyllite samples from the Kryvyi Rih structure. Three of these samples are from metaterrigenous sediments of the Skelyuvatka Suite, whereas one sample was collected from the Saksagan Suite. The study was carried out applying LA-ICP-MS method. Most of the obtained results are highly discordant due to the high degree of metamictization caused by high concentrations of Th and U. Only results of U-Pb dating with the degree of concordance higher than 80% were further considered. Zircons from all four samples yielded ages that fall within a narrow interval of 2.9-3.3 Ga that corresponds to the age of the basement rocks of the Middle Dnieper Domain that underlies the Kryvyi Rih structure. The youngest measured age of ca. 2.9 Ga corresponds to the maximum sedimentation age of the Saksagan and Skelyuvatka Suites. Within error this age also corresponds to the age of detrital monazite (2.85 Ga) found earlier in sandstones of the Skelyuvatka Suite. It is somewhat younger than the age of meta-morphosed basalts of the New Kryvyi Rih Suite (2.96 Ga), whose outpouring indicated initial formation of the Kryvyi Rih structure. The earlyer defined age of granites of the Hannivka massif (2.68 Ga) that cut through deposits of the New Kryvyi Rih and Saksagan suites, also confirms their at least Neoarchean age. Currently available geochronological data indicate Meso-to Neoarchean deposition age of the New Kryvyi Rih, Skelyuvatka and Saksagan suites.