AGE AND PETROGENESIS OF EARLY PROTEROZOIC DIORITES FROM DYKES OF
THE BAIKAL UPLIFT OF THE SIBERIAN CRATON
T.V. Donskaya1, D.P. Gladkochub1, A.B. Kotov2, E.B. Salnikova2, E.E. Badashkova1, A.M. Mazukabzov1, V.P. Kovach2, U.S. Efremova1
1Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia
2Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, Russia
Keywords: Diorites, U-Pb age, geochemistry, Early Proterozoic, Siberian craton
Abstract
A detailed geological, geochronological, geochemical and isotopic study of diorites from a dyke located in the central part of the Baikal uplift of the Siberian craton was carried out. Moreover, a comparison of geochemical and isotopic data obtained for diorites of the studied intrusion with coeval mafic and intermediate igneous rocks of the southern part of the Siberian craton was carried out. The U-Pb (ID-TIMS) baddeleyite age of 1862±7 Ma was obtained for diorite from a dyke located in the area of the Onguren village. The obtained data is the first reliable age determination for the Early Proterozoic mafic and intermediate igneous rocks of the Baikal uplift, which are part of the South Siberian post-collisional magmatic belt. The dyke has a northeast strike. The dyke rocks correspond to diorites in chemical composition and are highly differentiated varieties (mg# = 36.5–37.4). There were no significant variations in the composition of diorites in the marginal and central parts of the dyke. The rocks are characterized by low contents of TiO2, P2O5,
Nb, high concentrations of Th, Zr, Ba, light rare earth elements and exhibit low
negative values εNd(t) = -5.9...-6.2. It is assumed that the source of diorites was the enriched
subcontinental lithospheric mantle. Analysis of geochemical and isotopic data
obtained for Early Proterozoic mafic and intermediate igneous rocks of the South
Siberian post-collisional magmatic belt within the Aldan
shield, the Baikal uplift and the Irkut block of the Sharyzhalgay uplift showed
that most rocks showed similar negative values of εNd(t) in range from
-4.3 to -11.6 and geochemical characteristics corresponding to rocks, the
formation of which is associated with the melting of subduction-modified
lithospheric mantle sources in a post-collisional extension environment at the
final stage of formation of the Siberian craton in the Early Proterozoic.
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