Archean crustal evolution in the southeastern North China Craton: New data from the Huoqiu Complex

The southeastern margin of the North China Craton (NCC) is characterized by zircon ages of dominantly >2.6Ga and differs significantly from most other regions in the NCC with mostly ~2.5Ga zircons. In order to better understand the Precambrian crustal evolution of the NCC, we conducted a study of in situ zircon U-Pb dating, trace element and Hf isotope analyses as well as whole-rock geochemistry on a comprehensive set of core samples from three drilling holes intersecting the basement rocks of the Huoqiu area at the southeastern margin of the NCC. Our data reveal three magmatic events at ~3.02Ga, ~2.77Ga and ~2.71Ga. In addition, seven analyses of possibly inherited zircon cores plot along a discordant line with an upper intercept age of 3262±35Ma, indicating possible existence of a Paleoarchean crystalline basement. The ~3.02Ga zircons have positive ε_Hf(t) values close to the depleted mantle growth curve and their U-Pb ages are only slightly younger than the T_DM1 model ages, hence recording a Mesoarchean crust-forming event. The ~2.77Ga zircons also register a period of crustal growth, but probably with some involvement of older crust. The ~2.71Ga zircons have lower ε_Hf(t) values and older T_DM1 model ages than the ~2.77Ga zircons, suggesting that the former were mainly derived from older continental crust, in contrast to the traditional idea that ~2.7Ga was a major period of crustal growth in the NCC.