Geochronometry of the Middle Paleozoic volcanics of the Omolon Massif in Northeast Asia: A comparison of the K-Ar, Rb-Sr, and U-Pb data and their geological interpretation
Tóm tắt
The results of the K-Ar, Rb-Sr, and U-Pb (SHRIMP zircon method) dating of the Middle Paleozoic volcanogenic rocks of the Omolon Massif are summarized. It was concluded that they are principally consistent with each other, as well as with the geological data. The formation of the Kedon Group, which makes up the main volume of the Middle Paleozoic volcanics, began at the Early-Middle Devonian boundary about 400 Ma ago (U-Pb dates of 400.5 ± 4.4 and 387 ± 6.4; Rb-Sr isochron age of 402 ± 6 Ma). The isotopic age of the upper boundary of the Kedon Group remains unclear due to disagreements concerning its stratigraphic assignment. The histogram based on the 111 K-Ar dates of the volcanic rocks from the Kedon Group gives a polymodal distribution, which indicates that the K-Ar isotopic system was disturbed by thermal events, which occurred 310–290 (terminal Carboniferous—beginning of the Permian) and 240–220 (Middle-beginning of the Late Triassic) Ma ago. Both thermal events were associated with mantle (ultrabasic-basic) magmatism, which spanned a significantly wider territory than the distribution area of the Kedon Group
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