The oldest (~ 1.9 Ga) metadolerites of the southern Siberian craton: age, petrogenesis, and tectonic setting

Geological, geochronological, and isotope-geochemical studies of the metadolerites of the Angaul complex, widespread in the Urik-Iya graben of the southern Siberian craton, were carried out. The metadolerites forming separate conformal bodies (sills) among the metasandstones of the Ingash Formation were studied in detail. U-Pb zircon (SHRIMP) dating of metadolerites yielded an age of 1913 ± 24 Ma, and U-Pb baddeleyite (ID-TIMS) dating of these rocks yielded an age of 1914.0 ± 1.7 Ma. Thus, the date of 1914 ± 2 Ma can be taken as the most precise age estimate for the studied rocks. The metadolerites of the Angaul complex correspond in chemical composition to the normal-alkaline tholeiitic basalts. Metadolerites are differentiated rocks with mg# of 36 to 58. They show fractionated REE patterns: (La/Yb)n = 1.2-3.5. All metadolerites, independently of their mg# value, have low contents of Nb (1.6-10.2 ppm) and show well-pronounced negative Nb-Ta anomalies in multielement patterns (Nb/Nb* = 0.19-0.54). The metadolerites are characterized by positive eNd(T) values ranging from 0.4 to 5.2, which correlate well with their SiO2 content and mg# value. The isotope-geochemical parameters of the metadolerites of the Angaul complex indicate that fractional crystallization, along with the assimilation of the host rocks (AFC), might have been the main process during the formation of the most differentiated metadolerites. The geochemical characteristics of metadolerites with the maximum mg# values of 57-58 and eNd(T) = 5.2 suggest that the parental mantle source of the metadolerites resulted from mixing of predominant depleted mantle material with the subcontinental-lithosphere material. Intrusion of the dolerites of the Angaul complex, as well as the deposition of the sedimentary strata of the Ingash Group, took place at the Paleoproterozoic stage of intracontinental extension caused by the collapse of the orogen resulted from the collision of the Biryusa block with the Tunguska superterrane in the southern Siberian craton

Early evolution of the Paleoasian ocean: LA-ICP-MS dating of detrital zircon from Late Precambrian sequences of the southern margin of the Siberian craton

We present U–Pb (LA-ICP-MS) data on detrital zircon from the Late Precambrian terrigenous rocks of the Baikal Group and Ushakovka Formation, western Cisbaikalia (southern flank of the Siberian craton). The sources of clastic material for the studied sediments are interpreted. The youngest group of detrital zircon grains from the upper Baikal Group and Ushakovka Formation permits assigning these sediments to the Vendian. The lack of Mesoproterozoic detrital zircon in most of the analyzed samples confirms the hypothesis of a global (~1 Gyr) break in endogenic activity within the southern flank of the Siberian craton through the Precambrian. The abundance of Neoproterozoic zircon in sandstones from the upper horizons of the Baikal Group and the Ushakovka Formation might be due to the shrinkage of the ocean basin as a result of the convergence of the craton with the microcontinents and island arcs within the Paleoasian ocean

U-Pb detrital zircon geochronology and provenance of Neoproterozoic sedimentary rocks in southern Siberia: New insights into breakup of Rodinia and opening of Paleo-Asian Ocean

© 2018 International Association for Gondwana Research We present the synthesis of new data on detrital zircon geochronology of the Neoproterozoic strata of the southern part of the Siberian craton as well as a comprehensive analysis of previously published stratigraphic, sedimentological and geochronological (LA-ICP-MS) data obtained for key sections in this area that allows us to trace the process of birth and early stages of development of the Paleo-Asian Ocean (PAO). Before the break-up of Rodinia and opening of PAO, Tonian – Cryogenian intracontinental sedimentary basin existed between southern Siberia and northern Laurentia. The detachment of the southern flank of the Siberian craton from northern Laurentia and opening of the PAO between these cratons took place in Cryogenian. The detrital zircon ages from lower parts of Neoproterozoic successions suggest the Siberian craton as the sole provenance area right after the opening of the PAO. The age constraints on the lower parts of the studied Neoproterozoic successions, which are based on correlation of their tillite horizons with the Marinoan glaciation, suggest the late Cryogenian age for these sedimentary rocks. A clear change in the age spectra of detrital zircons from “unimodal” (Early Precambrian only) in older sedimentary rocks to “bimodal” (Early Precambrian as well as Neoproterozoic) in younger sequences of the studied successions marks the next stage of the PAO evolution. The abundance of youngest (630–610 Ma) detrital zircons in the upper parts of the studied sequences reflects a shrinkage of the oceanic basin as a result of the convergence of the craton with the microcontinents and island arcs within the Paleo-Asian Ocean. We suggest that a passive oceanic margin along the southern margin of the Siberian craton has been transformed into a series of foreland basins at ~610 Ma