Sources of Sediment Clasts and Depositional Environment of Sedimentary Rocks of the Daur Series of the Argun Continental Massif

• Published in: Russian journal of Pacific geology 2022-02, Vol.16 (1), p.11-28
• Main Authors: Smirnova, Yu. N., Ovchinnikov, R. O., Smirnov, Yu. V., Dril, S. I.
• Format: Article
• Language: English
• Subjects: Conglomerates; Earth and Environmental Science; Earth Sciences; Geochemistry; Geology; Igneous rocks; Isotope studies; Isotopes; Metamorphic rocks; Mineral composition; Precambrian; Sedimentary rocks; Subduction; Trace elements; Volcanic rocks
• ISSN: 1819-7140; 1819-7159
• DOI: 10.1134/S1819714022010092

This paper presents the results of geochemical and isotope-geochemical (Sm–Nd) studies of the Upper Riphean (?) (in the Stratigraphic Scale of Russia) sedimentary rocks of the Urulungui and Dyrbylkei formations of the Daur Series in the Argun continental massif, as well as U–Th–Pb and Lu–Hf isotope studies of detrital zircons from these formations. Rocks of the Urulungui and Dyrbylkei formations differ significantly in their mineral composition and major-element composition, which is probably related to the degree of chemical weathering of source rocks. Analysis of the trace-element concentrations in the sedimentary rocks of the Urulungui and Dyrbylkei formations enabled us to establish that they were formed in a subduction-related setting. The presence of conglobreccias, conglomerates, gravelstones, fragments of igneous and volcanic rocks, the low level of roundness of clastic material, as well as the abundant Neoproterozoic detrital zircons in the formations, are evidence for tectonic and igneous activities in the region during sedimentation. Sedimentary rocks of the Urulungui and Dyrbylkei formations have two-stage Nd model ages of TNd (DM2)  = 2.0–2.1 Ga and 1.6–1.8 Ga, respectively. The abundant Neoproterozoic zircons in sandstones of the Urulungui and Dyrbylkei formations suggest that Neoproterozoic igneous rocks that were widely developed within the western Argun continental massif were the main source of clastic materials. At the same time, the presence of Early Precambrian detrital zircons indicates that Early Precambrian rocks were also present in the source area. However, reliably dated Early Precambrian igneous and metamorphic rock associations have not yet been found within the Argun continental massif. Thus, it is possible that the rocks of the Daur Series form an “exotic block” involved in the Argun massif.