Sources of Sediment Clasts and Depositional Environment of the Upper Paleozoic Shazagaitui and Zhipkhoshi Formations of the Chiron Basin, Eastern Transbaikalia

Abstract

The article presents the results of comprehensive geological and geochemical study of the sedimentary rocks of the Upper Paleozoic Shazagaitui and Zhipkhoshi formations filling the upper part of the Chiron Basin, as well as U–Pb geochronological and Lu–Hf isotopic studies of zircons from these formations. The geochemical features of the terrigenous rocks of the Shazagaitui and Zhipkhoshi formations indicate that they were formed in a subduction zone environment. The presence of conglomerates and gravelstones and the predominance of unrounded and subrounded fragments in the rocks of the Shazagaitui and Zhipkhoshi formations also indicate their sedimentation in tectonically active zones. The abundant detrital zircons of Paleoproterozoic age, as well as the Paleoproterozoic and Archean Hf model ages of most of the zircons in the sandstones of the Shazagaitui and Zhipkhoshi formations, suggest that the main source of sediment clasts for these formations are the magmatic and metamorphic rocks of the southern surrounding of the North Asian Craton. However, the presence of Devonian–Carboniferous zircons with relatively young (mostly Neoproterozoic) Hf model ages is evidence that these zircons in the sedimentation basin were derived through erosion of mature (?) island arcs, but the contribution of this source is minor. The obtained results in combination with our regional geological data from previous studies suggest that the sediments of the Shazagaitui and Zhipkhoshi formations were accumulated in a basin setting on the southern framing of the North Asian Craton facing the Paleozoic Ocean.