Sm Nd isotope age and its geological significance of epimetamorphic rock series in the Qinglong area, eastern Hebei province

The epimetamorphic rock series exposed in the Qinglong area, eastern Hebei province, consists mainly of hornblende biotite leptynite （granulitite）, metamorphosed basic acid volcanic rocks, leucoleptynite and quartz biotite muscovite schist. Seven samples of amphibolite collected from the upper and lower layers of the conglomerate in Yaojiagou village have been determined for the Sm Nd isotopic compositions, and give an isochron age of （2 696±185） Ma （2σ）, with I Nd = 0.909 23±16 （2σ） and ε Nd （t） = +1.8±1.5, and their model ages t DM range from 2 890 to 2 955 Ma. Ten samples of amphibolite collected from Xihangou village yield an isochron age of （ 2 793 ±69） Ma （2σ）, with I Nd = 0.509 194±67 （2σ） and ε Nd （t） = +2.0. An average model age of 2 844 Ma has been calculated from seven samples with similar model age in Xihangou village.The similar Nd isotopic composition and identical Nd model ages of the upper and lower amphibolites of the conglomerate in Yaojiagou village show that the Yaojiagou conglomerate may be a volcanic interlayer conglomerate or a structure conglomerate. So the upper and lower amphibolites in the conglomerate formed at the same time. The isochron ages of 2 696 Ma and （2 793±69） Ma of the amphibolite samples from Yaojiagou and Xihangou villages indicate that the epimetamorphic rock series in the Qinglong area belongs to the Archean.