Depositional age and source analysis of the Changcheng System in the Licheng area, Shanxi Province: Evidence from U-Pb geochronology and Lu-Hf isotope of detrital zircons

The Changcheng System is the oldest sedimentary cover after the formation of the unified crystalline basement in the North China Craton (NCC). The analysis for the U-Pb geochronology and Hf isotopes of the detrital zircons from the Changcheng System is of great significance for exploring the formation age and source characteristics of this strata as well as the basement evolution. This study conducted a detailed analysis upon the U-Pb ages and Hf isotopes of the detrital zircons from the lower segment of the Changcheng System in the Licheng area of the central part of NCC. The results demonstrate the U-Pb ages of detrital zircons exhibit three main age peaks of 2.55 similar to 2.45Ga, 2.15 similar to 2.0Ga and similar to 1.92Ga, as well as two minor ones of 3.5 similar to 3.1Ga and 2.9 similar to 2.7Ga, respectively. The Pb-207/Pb-206 weighted average age of the youngest detrital zircons constrain the Changcheng System to be deposited after 1.76Ga in this area. The age distributions and Hf isotope characteristics from the detrital zircons are highly similar to the geological events recorded by the basements in the central and southern parts of the NCC. In addition, the strong comparability of the Changcheng System between the Licheng and the southern Xiong'er areas suggests that the extension of the southern Xiong'er rift basin should reach the southern areas of Taihang Mountains after 1.76Ga, and their sedimentary materials were mainly derived from the central and southern parts of NCC. The 3.5 similar to 3.4Ga old detrital zircons yielded epsilon(Hf)(t) values from -8.6 to -4.6, likely indicating the presence of Paleoarchean crustal material in the central and southern NCC. The epsilon(Hf)(t) values of 2.9 similar to 2.7Ga zircons in the Early Neoarchaean period are mainly positive (accounting for 85%), and their tDMC ranges from 3190Ma to 2774Ma, which are the same or close to their crystallization ages, indicating there was an important juvenile crustal growth at the Early Neoarchean in the southern NCC. The zircons within the 2.55 similar to 2.45Ga peak in the Late Neoarchean period are also dominated by positive epsilon(Hf)(t) values (69% of the total), while zircons of the 2.15 similar to 2.0Ga peak mostly have negative epsilon(Hf)(t) values (56% of the total), suggesting the gradual transition from the crustal growth accompanied by some crustal reworking in the Late Neoarchean to the crustal reworking with minor juvenile crustal accretion around the Middle Paleoproterozoic in the southern NCC. The detrital zircons of the similar to 1.92Ga age peak are characterized by a wide range of epsilon(Hf)(t)(-11.9 similar to +2.0), demonstrating the reworking of early continental materials is very strong during the end of the Paleoproterozoic.