JUVENILE MAGMATISM AND CRUSTAL RECYCLING AT THE END OF THE NEOARCHEAN IN WESTERN SHANDONG PROVINCE, NORTH CHINA CRATON: EVIDENCE FROM SHRIMP ZIRCON DATING

Western Shangdong Province experienced major crustal growth as a result of 2.75 to 2.50 Ga tectonothermal events, different from other Archean areas in the North China Craton. Besides early Neoarchean tonalite-trondhjemite-granodiorite (TTG) and supracrustal assemblages, there are large volumes of late Neoarchean gabbroic, dioritic and granitic rocks in western Shandong. SHRIMP zircon dating of thirty-one samples of different rock types from late Neoarchean rocks yielded a narrow age range from 2560 to 2490 Ma. Based on these data and previously published results, the following conclusions can be drawn: 1) the Archean basement can be divided into three belts: a Late Neoarchean (2525-2490 Ma) crustally-derived granite belt in the northeast, an Early Neoarchean (2.75-2.60 Ga) rock belt in the center, and a Late Neoarchean (2550-2500 Ma) belt of juvenile rocks in the southwest; 2) the tectonic regime in western Shandong Province probably changed from compressional to extensional at around 2525 Ma (between 2530 and 2520 Ma); 3) crustal recycling with addition from the mantle occurred at the end of the Neoarchean; 4) the late Archean magmatic rocks were probably formed in an arc environment.