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Nd and Sr isotopic signatures of mesozoic granitoids in South Korea
- Nd and Sr isotopic signatures of mesozoic granitoids in South Korea
- Na C.K.; Kim K.H.; Park S.S.
- Ewha Authors
- SCOPUS Author ID
- Issue Date
- Journal Title
- Resource Geology
- Resource Geology vol. 46, no. 4, pp. 215 - 226
- SCIE; SCOPUS
- Document Type
- Mesozoic granitic plutons in the Korean peninsula have εNd values ranging from -14.9 to +0.4 and initial 87Sr/86Sr ratios from 0.704 to 0.717 ( εSr = -2.5 ∼ 183.7). The Nd and Sr isotopic variations in the granitic rocks are inversely correlated and are clearly divided into two distinct groups namely: a mantle type as in the Mesozoic Kyongsang basin and a crust type as in the Precambrian terranes, based on geologic and geographic differences. Cretaceous granitic rocks in the Kyongsang sedimentary basin have εNd of -4.4 to +0.4 and initial 87Sr/86Sr ratios of 0.704 to 0.706 (εSr = -2.5 ∼ 33.5), indicating derivatives of the mantle source. While, andesitic rocks in the basin have Nd-Sr isotopic compositions (εNd = -12.6 ∼ -0.8, (87Sr/86Sr)i = 0.705 ∼ 0.707, εSr = 9.4 ∼ 38.9) similar with those of the Cretaceous plutonic rocks, implying cogenetic sources of the magma. On the other hand, Jurassic plutons from outside of the basin, including some Cretaceous granites in the Okehon geosynclinal zone, have much lower εNd of -21.0 to -13.6 and higher initial 87Sr/86Sr ratios of 0.711 to 0.717 (εSr = 97.3∼183.7) than the Cretaceous plutons in the Kyongsang basin, which suggests a significant crustal assimilation or contamination of the granitic magma. The two stage model ages of the Cretaceous and Jurassic granite plutons were calculated to be 0.5 to 1.1 Ga and 1.6 to 2.2 Ga, respectively. This data suggests that the source materials of these Mesozoic plutons in the Korean peninsula have evolved considerably since mid - Proterozoic times.
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