Evidence for ～ 1.8 Ga extension of the Eastern Block of the North China Craton from SHRIMP U-Pb dating of mafic dyke swarms in Shandong Province

摘要

A large mafic dyke from the NNW-trending dyke swarms in the Eastern Block of the North China Craton was dated by SHRIMP U-Pb age analysis. This dyke occurs near Mt. Taishan in Shandong Province; it cuts Neoarchean tonalite, adamellite and diorite plutons. Two types of zircons were found in the dyke. Type 1 zircons were inherited from the host rocks and gave a SHRIMP U-Pb age of 2544 ± 24 Ma with a weighted mean ~(207)Pb/~(206)Pb age of 2523 ± 18 Ma. Type 2 zircons were crystallized from the dyke magma and yielded a concordant SHRIMP U-Pb age of 1830 ± 17 Ma with a weighted mean ~(207)Pb/~(206)Pb age of 1837 ± 18 Ma, indicating that the large dyke at Taishan was emplaced at ～ 1830 Ma. The mafic dyke swarm provides evidence of a phase of extension in the Eastern Block of the North China Craton at ～ 1.8 Ga. This dyke has a similar age to dyke swarms in the Western Block and in the Central Orogen Belt of the North China Craton. This lithospheric extension, led to the opening of the Yanliao and Zhongtiao aulacogens. The similar ages and orientations of ～1.8Ga dyke swarms throughout the North China Craton demonstrate that at that time the Eastern and Western blocks were united and that the amalgamated craton experienced widespread extension.