Ages and sources of detrital zircons from the Early Mesozoic metasedimentary rocks of the Un’ya-Bom terrane of the Mongol-Okhotsk fold belt: results of U-Th-Pb and Lu-Hf isotope studies

Abstract

The U-Pb and Lu-Hf isotope studies have been performed to investigate detrital zircons from metaterrigenous deposits (Nel, Kurnal and Amkan f ormations) of the Un’ya-Bom terrane of the eastern part of the Mongol-Okhotsk fold belt. T he concordant age s of the youngest zircon in the metasiltstone of the studied formations are as follows: 213±3.6 Ma – N el , 194±4.4 Ma – K urnal , and 202±2.5 Ma – A mkan. The new data suggest that a previously assumed (Middle Jurassic) age of the A mkan f ormation is uncertain . Most likely, the Kurnal and Amkan formations are of the same ( E arly Jurassic) age. In any case, a relationship between these formation s needs to be clarified . I n co mbination with the data from previous studies of the Tukuringra t errane, our study results show that the E arly Mesozoic sedimentary rocks in the structure of the eastern part of the Mongol-Okhotsk fold belt are more abundant than it is currently assumed . Our study results suggest that during the accumulation of the Nel, Kurnal and Amkan formation s , the materials were supplied from different provinces, especially from the Amur s uperterrane ( i.e. from the south , in modern coordinates) , as well as from the fram e of the North Asian craton ( i.e from the north , in modern coordinates), although the contribution of the craton source was insignificant.