Detrital zircon U-Pb and Hf isotopic constraints on the crustal evolution of North Korea

The crustal evolution of North Korea is poorly constrained. This study utilises detrital zircon U-Pb and Lu-Hf isotopic data, obtained from sands at the mouths of the Taedong, Chongchon and Songchon Rivers, in order to sample the Rangnim massif. These data are then used to constrain the magmatic age spectrum and crustal growth history of this massif. Zircon U-Pb analyses indicate that the Rangnim Massif, previously considered to be an Archean block, is characterized by ∼1.8 Ga magmatism, with subsequent peaks at 220 and 110 Ma. Archean magmatism appears to be limited, which is in marked contrast to the nearby North China Craton in terms of the timing of Precambrian events although the oldest age obtained is ∼3.4 Ga, indicating the existence of some Mesoarchean material in North Korea. In situ zircon Hf isotopic data show that some zircons have Hf model ages up to 4.0 Ga, suggesting a more ancient crustal history. The Hf isotopic data also indicate that the ∼1.8 Ga zircons have Archean Hf model ages, suggesting derivation from recycled Archean material. Phanerozoic zircons are less abundant than those of Precambrian age, however, the limited data indicate that Phanerozoic magmatism mostly occurred in the Mesozoic, accompanied by significant juvenile crustal growth. The similarities of the crustal formation ages and ∼1.8 Ga thermal event between the Rangnim Massif and the North China Craton indicate that they were probably a coherent block since Archean time.