Age of Detritic Zircon and Composition of Cambrian-Ordovician Terrigenous-Carbonate Deposits in the Middle Reach of the Vilyui River (South of the Siberian Platform)

The article presents result of lithological and mineralogical studies of Upper Cambrian and Lower Ordovician terrigenous-carbonate deposits within the Vilyui syneclise (the middle reaches of the Vilyui River, south of the Siberian platform). The composition of detritic zircon, garnet, tourmaline and chromium spinels were carried out in a sample from the Upper Cambrian Kholomolokh Formation and two samples from the Balyktakh Formation (Upper Cambrian-Lower Ordovician). Predominant sources of the detritic minerals were igneous and metamorphic rocks of the Archean-Paleoproterozoic basement of the Siberian platform: rocks of acidic and intermediate compositions, amphibolite-facies metasediments and granulite- and amphibolite-facies mafic-ultramafic complexes. Results of U-Th-Pb dating of zircon from the Kholomolokh and Balyktakh Formations of the middle reaches of the Vilyui River showed a noticeable difference in the demolition sources of terrigenous matter in the Late Cambrian and Ordovician times. The sample from the Upper Cambrian Kholomolokh Formation contains the youngest zircon with a predominance of Neoproterozoic ages (peak ages of 550 and 845 Ma) indicating the main source of demolition in the Late Cambrian time were Neoproterozoic terranes rocks which are widespread along the southern margin of the Siberian craton. The Early Ordovician rocks of the Balyktakh Formation contain the main zircon population (~70%) f Paleoproterozoic (1880-1890 Ma) age. The Early Ordovician the most probable source of matter for the Vilyui syneclise was an uplift of the Archean-Paleoproterozoic basement in the Siberian platform central part that represented an eroded land during the Ordovician. The almost complete absence of younger zircon (~500-900 million years) in the Balyktakh deposits indicates a weak influence of the demolition source from the southeastern margin of the Siberian platform in the Ordovician time.