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岩石学报 1988
CHARACTERISTICS OF LEAD ISOTOPE COMPOSITION OF TWO-TYPES OF GRANITES IN SOUTH CHINA
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Abstract:
This paper discusses the characteristics of lead isotope composition of transformation-type and syntexis-type granites proposed by Xu Keqin or S-type and I-type granites proposed by Chappell and White. In the paper, eleven granitoids in South China, whose genetic types are known, are studied and twenty-four lead isotopic data are obtained. Based on the study of lead isotope compositions of eleven granitoids, it can be seen that these two types of granites possess different lead isotope compositions. The transformation-type (or S-type) granites is relatively richer in radiogenic lead, with higher lead isotope ratios, Pb~*/~(204)Pb>72 (Pb~*=~(206)Pb+~(207)Pb+~(208)Pb). Moreover, it is richer in uraniumgenic lead but poorer in thoriumgenic lead, ~(208)Pb/~(206)Pb<2.1. The syntexis-type (or I-type) granites is poorer in radiogenic lead, with lower lead ratios Pb~*/~(204)Pb<72. In addition, it is poorer in uraniumgenic lead but richer in thoriumgenic lead, ~(208)Pb/~(206)Pb>2.1. Some diagrams of lead isotopes are used in the paper. By these diagrams, genetic types of granites can be discriminated effectively. Through above-listed studies it is stated that the char-acteristics of lead isotope composition of granites could give the information about resources of their rock-foirming material and therefore, could be used to divde different types of granites.