GEOCHEMICAL AND GEOCHRONOLOGICAL STUDY ON THE TAISHAN NEOARCHEAN GRANITOIDS AND IMPLICATIONS ON THE CRUSTAL GROWTH OF THE EASTERN NORTH CHINA CRATON

In the past decades, the tectonic evolution and final amalgamation of the North China Craton (NCC) has become a hot topic of the International Precambrian Research. Of which, the crustal growth and its formation mechanism of the cratonic basement is a key into understanding this issue. The Taishan area of the eastern NCC contains a successive Neoarchean rock assemblage and therefore represents a promising area for studying the crustal evolution. To achieve this goal, we present the detailed geochronological, lithological and geochemical data for the typical rock assemblage formed at different time period (i.e. ~2.7 Ga, 2.6 Ga and 2.5 Ga). Geochemical data show that the representative granitoid gneisses in the Taishan area have high Na₂O (3.81-4.50 wt%), low Mg# (40–56), with Sr (292-508 ppm) , Sr/Y (35.6-66.6) and Nb/Ta (10.1-15.9), which are obviously lower than the value of high pressure granitoids. They were probably derived from partial melting of hydrate mafic rocks in lower crust, with a certain amount of hornblende and plagioclase in the residue. Zircon U–Pb age dating results and Lu-Hf isotopic analyses revealed that these granitoids were emplaced at 2700–2550 Ma and exhibit commonly positive εHf(t) values of +2.2 to +6.1. The calculated Hf model ages are between 2949 and 2665Ma, suggesting that the Taishan Neoarchean granitoids were mainly derived from the juvenile crust that was extracted from the depleted mantle since Mesoarchean to Neoarchean. The new data of this study, combined with the recently published data of the adjacent areas, lead us to reconstruct an integrated evolutionary history for the continental basement of the eastern North China Craton.