Abstract:

Recently a graniteporphyry dike has been recognized near the Dalongmen Village in the north of the Shachang Town, Miyun County, Beijing. The dike emplaced into the Neoarchean Miyun Group amphiboleplagiogneiss. Both the dike and the wall rock gneiss were unconformably overlain by the conglomerate and sandstone of the Changzhougou Formation. By means of LAMCICPMS zircon UPb dating, the emplacement age 1673±10 Ma of the graniteporphyry dike has been obtained. This dating result indicates that the base age of the Changzhougou Formation, i.e. the base age of the Changchengian System at the northern North China Craton (NCC) should be younger than 1670 Ma, probably close to 1650 Ma, at least ~150 Ma younger than the conventionally adopted age 1800 Ma. This is the most direct and precise age constraint for the base of the Changchengian System at the northern NCC to date. Combining with the available age results of the overlying Dahongyu and Gaoyuzhuang formations, the duration of the newlyrevised Changchengian System can be limited in the time interval from 1650 Ma to 1600 Ma, comparable with the latest of the Statherian Period (18001600 Ma). Moreover, this new achievement suggests that the base age of the Meso and Neoproterozoic succession at the northern NCC is almost identical with that of the Riphean at the Siberia and the Vindhyan at the northern India, which probably implies that the NCC and the abovementioned paleocontinents have close affinity relationships during the assemblage and breakup of the Columbia Supercontinent.

Key words:  North China Craton, base age of Changchengian System, 1670 Ma graniteporphyry dike, zircon LAMCICPMS dating, Statherian Period, Columbia Supercontinent.