Formation age and provenance of the Iman group in the Khanka Massif: Evidence from U-Pb geochronology of detrital and magmatic zircons

In this paper, we present the zircon LA-ICP-MS U-Pb ages and Hf isotope compositions of detrital and magmatic zircons from the metasedimentary rocks and intrusive rocks within the Iman Group in the southern Khanka Massif to constrain the formation age range of ages of 555 ∼ 1322Ma. The main age populations are 555Ma, 612Ma, 700Ma, 739Ma, 769Ma, 839Ma and 936Ma. Their ϵHf(t) values and two-stage model ages (tDM2) of 533Ma vary from -4. 1 to + 3 and from 1305Ma to 1755Ma, respectively. Thelr ϵHf(t) values and two-stage model ages (tDM2) of 700 ∼839Ma vary from -3. 7 to +7. 8 and from 1246Ma to 1907Ma, respectively. The zircons from the muscovite monzogranite that intruded into the Iman Group yield a weighted mean 206Pb/238U age of 443 ± 3Ma, its ϵHf(t) values and two-stage model ages (tDM2) range from -17. 6 to -4. 2 and 1688Ma to 2529Ma, respectively. Combined with the youngest age of the two-mica quartz schist and the formation time of the intruding muscovite monzogranite in the Iman Group, we conclude that the Iman Group was formed between 443 ∼ 555Ma, i. e., the Late Neo-Proterozoic to Late Ordovician. The age populations of the two-mica quartz schist, together with the regional magmatic events, indicate that the provenance of the Iman Group mainly come from the Neo-Proterozoic igneous rocks in the Songnen and Jiamusi massifs. Additionally, the muscovite monzogramtes exhibit a geochemical affinity to adakitic rock, suggesting that its primary magma could be derived from partial melting of a thickened lower crustal material, which implies that the continental crust thickening might occur in the study area in the Late Ordovician. © 2020 Science Press. All rights reserved.