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岩石学报 1988
~(40)Ar/~(39)Ar AGE SPECTRUM OF QIANAN CHARNOCKITE
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Abstract:
The cbarnockite samples were collected from Sbuichang area of Qianan county, Hebei Province, China. Previously, they yielded a Rb/Sr whole rock age of 2.65Ga and an U/Pb zircon age of 2.73Ga. Some scholars thought that the charnockitcs belong to the migmatic bodies. The ~(40)Ar/~(39)Ar step heating experiment performed on biotite and hypersthene yielded two age spectra, and gave two ~(40)Ar preserved ages of 1.87Ga and 1.96Ga respectively. The two complex age spectra show that the charnockites underwent a thermal perturbation at low temperature interval. The diversified dates by different dating methods indicate that the charnockite slowly cooled down since emplacement. The charnockitc plutons had an uplift rate of 6.5m/Ma from 2.70Ga to 1.96Ga, while the uplift rate rose up to 111m/Ma from 1.96Ga to 1.87Ga. The orogeny of 1.96Ga had universal significance not only in Shuichang and eastern Hebei, but also for the whole North China Block.
