The development of dual volcanic chains, parallel to the trnd of the sucduction trench, is observed in the souythern part of Korea. Elsewhere on the Earth volcaniv arcs dominantly consist of two such chains. In the southern part of Korea, two volcanic chains within a single volcanic arc was developed. Kyongsand basin, where the first volcanic chain located, and Youngdong-Kwangju depression zone where the second volcanic zone located. showed sub-parallel volcanic rock distributed areas. Concentrations of incompatible elements in the southern part of Korea samples show clear across-arc variations, with lavas from the first volcanic chain being most depleted in these elements, all incompatible element concentraions towards the second volcanic chain. The above across-arc variation may be caused by the difference in solid phases coexsting with the fluid phases during the dehydration processes. The concentraions of incompatible elements, Zr/Y ratios, and Rb/K ratios indicate that the second volcanic chain (Youngdong-Kwangju depression zone) was generated by low degree of partial melting at the deeper depth compared to the conditions of the first volcanic chain (Kyongsang basin) and residual garnet probably attributed to the their partial melting.
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