Petrochemistry and Sr, Pb and Nd isotopic geochemistry of the paleoproterozoic kuandian complex, the eastern liaoning province, china

Abstract

A geochemical and isotopic study has been carried out on the Paleoproterozoic Kuandian Complex and some associated granitoids in the eastern Liaoning Province, China. The Kuandian amphibolite and granite give an imprecise 1.9±0.4 Ga (all errors are 2σ) Rb-Sr “errorchron” with ( 87 Sr / 86 Sr ) o = 0.711 ± 0.006 , a 2.11 ± 0.06 Ga PbPb isochron with a first-stage growth μ = 8.43, and a 2.31 ± 0.10 Ga SmNd isochron with ( 143 Nd / 144 Nd ) o =0.50970±0.00009 or ϵ nd (T) =1 ± 1. Nd-depleted mantle model dates (TDM) of amphibolite are 2.75 to 2.46 Ga, those of granite are 2.53 to 2.36 Ga. Zircons from the Kuandian granite give a minimum 2.14±0.05 Ga upper intercept date. The Kuandian amphibolite is chemically similar to the high-Mg member of Columbia River basalts, and the Kuandian granite is an anorogenic granite. They are genetically related and formed 2.4 to 2.3 Ga ago. Fractional crystallization of olivine, pyroxene and plagioclase from precursor magma of the Kuandian amphibolite can produce magma with composition of the Kuandian granite. The Paleoproterozoic mantle source in the eastern Liaoning Province is less depleted than that inferred from the average mantle evolution curve, in contrast with the Archean mantle in the Sino-Korean craton, which is more depleted than the average. This study also reveals that the Lishan granite of the eastern Liaoning Province is older than 3 Ga and that some granites and dykes previously mapped as Proterozoic are of Mesozoic age.