LA-ICP-MS zircon U-Pb dating from granitoids in southern basement of Songliao basin: Constraints on ages of the basin basement

摘要

Seven LA-ICP-MS zircon U-Pb datings from granitoids in the southern basement of the Songliao basin were done in order to constrain the ages of the basin basement. The cathodoluminescence (CL) images of the zircons from seven granitoids indicate that they are euhedral-subhedral ones with striped absorption and obvious oscillatory zoning rims. The dating results show that a weighted mean ~(206)Pb/~(238)U age is 236±3 Ma for quartz diorite (sample No.T6-1) located in the western slope of the basin, that weighted mean ~(206)Pb/~(238)U ages are 319 ± 1 Ma (2126 m) and 361 ± 2 Ma (1994 m) for diorite (sample No.YC1-1) and granite (sample No.YC1-2) located in northern part of southeastern uplift of the basin, respectively, and that weighted mean ~(206)Pb/~(238)U ages are 161 ± 5 Ma, 165 ± 2 Ma, 165±1 Ma and 161 ±4 Ma for samples Q2-1, SN121, SN122, and SN72 granitoids located in southern part of southeastern uplift of the basin, respectively. The statistical results of ages suggest that the middle Jurassic granitoids constitute the main part of basement granitoids, and that the Hercynian and Indo-Sino magmatisms also occur in the basin basement. It is implied that the Songliao basin should be a rift one formed in the intracontinent or active continental margin settings in the late Mesozoic after the Middle Jurassic orogeny took place.