LATE PRECAMBRIAN SEQUENCES OF MANA TROUGH (northwestern Eastern Sayan): ISOTOPE CHEMOSTRATIGRAPHY AND DETRITAL ZIRCON GEOCHRONOLOGY
B.B. Kochnev1,2, N.I. Vetrova2, A.I. Proshenkin2
1Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia
2Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk,Russia
Keywords: Mana Trough, East Sayan, Late Precambrian, carbonaceous sediments geochemistry, C-isotope chemostratigraphy, detrital zircon geochronology, sedimentation settings
Abstract
The chemical and isotope (C and O) composition of carbonate deposits and the age distribution of detrital zircon grains from the Late Precambrian sequences of the Mana Trough from Sayan Segment of the Central-Asian Mobile Belt (CAMB) were studied. Limestones of volcanic-sedimentary Kuvai Group (Mana and Bakhta Formations) formed in open-ocean conditions have highly positive δ13C values and, with another data, allow to limit their age as Late Riphean, оr Late Tonian. Angaloy Horizon strata have near-zero or slightly positive δ13C values, and minimal detrital zircon ages about 580 Ma, allowing to resemble it to Upper Vendian (or Upper Ediacaran). In the upper part of the Anastas’ino Horizon, two pronounced positive δ13C excursions was found, contrasting to sub-zero values, and marking the base of the Cambrian Tommotian Stage. Detrital zircon age spectra from the Angaloy and lower Anastas’ino Horizons demonstrate two Neoproterozoic populations with 710 and 630 Ma peaks. Possible sources for these zircons ages are volcanic and granitoid complexes coming from Sayan segment of the CAMB. Judging from occurrence of Paleoproterozoic zircon age population in the studied sequences, complete accretion of sedimentary basin of the Mana Trough to Siberian Craton was completed at Early Cambrian. These conclusions verified by geochemical indicators of sedimentation settings and by geodynamic reconstructions from the adjacent regions.
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