Paleoproterozoic Metavolcanosedimentary Sequences of the Yenisei Metamorphic Complex, Southwestern Siberian Craton (Angara-Kan Block): Subdivision, Composition, and U-Pb Zircon Age

摘要

The results of this study reveal the chemical heterogeneity of the Yenisei metamorphic complex, which is a series of blocks within the Yenisei Fault of the southern Yenisei Ridge (Angara Kan block). The Yenisei complex is composed of four metamorphic sequences: amphibolite-marble-paragneiss (volcanic-carbonate-terrigenous), amphibolite-orthogneiss (volcanic), marble-paragneiss (carbonate-terrigenous), and paragneiss (terrigenous). Study of the nature of the protoliths of metamorphic rocks shows that gneisses and schists of Sequences I and IV correspond to polymict or arkose sandstones and siltstonc-mudstones and can be classified as first-cycle sediments. Garnet-two-mica schists of Sequence III correspond in composition to mudstones and show evidence of recycling. Metavolcanic sequence II is composed of andesite-dacite-trachyrhyodacite, leucobasalt-basalt, and basalt-basaltic-andesite-trachyandesite formations. The metasedimentaty rocks are 1.2-1.4 times richer in REE and Th than the average PAAS. The high-alumina varieties have high contents of K, Rb, HFSE, Fe, Cr, Ni, and Co. The total similarity of the average trace-element contents in the rocks of the two complexes suggests that the composition of the Kan granulites was inherited by metasedimentary rocks of the Yenisei complex. The U-Pb zircon dates for granite veins cutting gneisses of amphibolite-marble-paragneiss Sequence I limit the deposition age to 1.84-1.85 Ga and indicate that these rocks were deposited before the emplacement of postcoilisional granites of the Taraka massif and thus predate the major orogenic events within the Angara-Kan block. Therefore, these rocks can be correlated with the lower part of the Urik-Iya graben section. The metamorphic rocks from the lower parts of the sections of the Yenisei complex and the Subluk Group formed during the same rifling phase of sedimentation. The amphibolite-orthogneiss (volcanic) sequence formed in the Angara-Kan block of the Yenisei Ridge during the second stage (1.74 Ga). The volcanic rocks formed in an extension setting and thus can be correlated with the emplacement of within-plate granites of the Taraka massif. In the Sayan area, tenigenous sediments and volcanic rocks of various compositions accumulated at the second stage (1.75-1.70 Ga) during the intracontinental extension. Therefore, there is a good correlation between the ages and geodynamic settings of deposition of late Paleoproterozoic volcanic and volcanosedimentary complexes of the Yenisei Ridge and the Sayan region.