Search

Geochronological (LA–ICP–MS) U–Th–Pb studies of detrital zircon of the Late Cenozoic sand deposits on Ol'khon Island have been performed. It has been shown that their main source is represented by Early Paleozoic igneous and metamorphic complexes of the Ol'khon Terrane of the Central-Asian Mobile belt and Late Carboniferous–Early Permian granitoids of the Angara–Vitim batholite. Sands from the source were transported over a distance of no less than 100 km. It is supposed that it was effectuated by strong air flows, over the ice on the Lake Baikal in particular. [ABSTRACT FROM AUTHOR]

The basement of the Zheltav sialic massif (Southern Kazakhstan) is composed of different metamorphic rocks united into the Anrakhai Complex. In the southeastern part of the massif, these rocks form a large antiform with the core represented by amphibole and clinopyroxene gneissic granite varieties. By their chemical composition, dominant amphibole (hastingsite) gneissic granites correspond to subalkaline granites, while their petroand geochemical properties make them close to A-type granites. The U-Pb geochronological study of accessory zircons yielded an age of 1841 ± 6 Ma, which corresponds to the crystallization age of melts parental for protoliths of amphibole gneissic granites of the Zheltav Massif. Thus, the structural-geological and geochronological data make it possible to define the Paleoproterozoic (Staterian) stage of anorogenic magmatism in the Precambrian history of the Zheltav Massif. The combined Sm-Nd isotopic-geochronological data and age estimates obtained for detrital zircons indicate the significant role of the Paleoproterozoic tectono-magmatic stage in the formation of the Precambrian continental crust of sialic massifs in Kazakhstan and northern Tien Shan. [ABSTRACT FROM AUTHOR]

U-Pb (LA-ICPMS) geochronological studies established the minimum age of detrital zircons from metasedimentary rocks of the Uril Formation of the Amur Group of ∼240 Ma, which approximately corresponds to the lower age boundary of formation of their protoliths. The upper boundary of accumulation of sedimentary rocks of this formation is governed by the age of superimposed structural-metamorphic transformations (220-210 Ma). It follows that the age of protoliths of metasedimentary rocks of the Uril Formation is Triassic in contrast to the previously suggested Early Precambrian age. At the same time, previous estimations of the Nd model age of metasedimentary rocks of the Tulovchikha Formation of the Amur Group and intruding gabbroic rocks are 1.7 and 0.5 Ga, respectively. In other words, the age of this formation is 1.7-0.5 Ga. All of this indicates a combination of sedimentary and volcanic rocks of different ages in the section of the Amur Group. Judging from the Lu-Hf isotopic-geochemical studies of zircons, the major sources of protoliths for metasedimentary rocks of the Uril Formation are Neoproterozoic igneous rocks and also Early and Late Paleozoic and Early Mesozoic igneous rocks, the formation of which was related to the reworking of the Neo- and Mesoproterozoic continental crust. [ABSTRACT FROM AUTHOR]