METASEDIMENTARY DEPOSITS OF THE GUTARA-TUMANSHET TROUGH (SOUTHWESTERN OF THE SIBERIAN CRATON): NEOPROTEROZOIC SEDIMENTATION AND PROVENANCE OF DETRIDAL ZIRCONS
O.M. Turkina1, A.D. Nozhkin1, T.V. Donskaya2, U.S. Efremova2
1Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, Russia
2Institute of the Earth's Crust, SB RAS, Irkutsk, Russia
Keywords: metasedimentary rocks, Neroi Group, detrital zircon, Neoproterozoic, Gutara-Tumanshet Trough, Siberian platform
Abstract
A Paleoproterozoic age was inferred for metasedimentary rocks of the Neroi Group in the Gutara-Tumanshet Trough, allowing their correlation with metasedimentary deposits of Urik-Iya and Elash grabens in the southwestern Siberian Craton. This paper presents the first zircon age data for garnet-biotite gneisses, garnet-two-mica schists, and quartzites of the Alkhadyr and Tumanshet formations of the Neroi Group. Age spectra of detrital zircons demonstrate dominant Neoproterozoic (1100-600 Ma) and subordinate Paleoproterozoic and Archean data. The upper sedimentation boundary is determined by the age of the Malkhan granite and gabbroids of the Tartai massif, which intruded into the Neroi Group deposits at 740-712 Ma. The lower boundary of sedimentation is marked by the youngest zircon grains, aged 745-765 Ma, and exhibiting oscillatory zoning characteristic of magmatic zircon, which constrains the deposition of the Neroi Group to the Cryogenian. Growth of unzoned zircons with an age of ca. 600 Ma and extremely low Th/U (<0.1) in the rocks of Alkhadyr formation was resulted from Vendian metamorphism, widely manifested in the folded belts of the southern framing of the Siberian Craton. The age of detrital zircons, combined with the model Nd ages of gneisses and schists (2.7-1.9 Ga), indicate that the source province contains Early Precambrian magmatic/metamorphic complexes and dominant Neoproterozoic magmatic associations, formed by remelting of older, Paleoproterozoic crust. These conditions are satisfied by the Early Precambrian rock complexes of the Sharyzhalgai, Birusa and Angara-Kan blocks of the southwestern Siberian Craton and the Neoproterozoic granitoids of the Trans-Angara part of the Yenisei Ridge, respectively. It is assumed that formation of Gutara-Tumanshet Trough in the late Neoproterozoic occurred on the Early Precambrian basement in an intracontinental setting.
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