Abstract
This study reports the results about the petrography and geochemical characteristics of the Cretaceous volcanic rocks distributed in the vicinity of the Namhae island composed of basaltic, through andesitic rocks, dacitic welded tuff, and rhyolitic rocks in ascending order. Sedimentary rock is the basement in the study area covered with volcanic rocks. Andesitic rocks compose of pyroclastic volcanic breccia, lithic lapilli tuff and cryptocrystalline lava-flow. Most dacitic rocks are lapilli ash-flow welded tuff. Rhyolitic rocks consist of rhyolite tuff and rhyolite lava-flow. Rhyolite tuff are lithic crystal ash-flow tuff and crystal vitric ash-flow tuff with somewhat accidental fragments of andesitic and sedimentary rocks. Aeidic dyke inwdes in to andesitic, dacitic and rhyolitic rocks. The variation of major and trace element of the volcanic rocks shows that contents of Al₂O₃, FeO, CaO, MgO, TiO₂ decrease with increasing of SiO₂. On the basis of variation diagrams such as Al₂O₃ vs. CaO, Th/Yb vs. Ta/Yb, and Ce_N/Yb_N vs. Ce_N, these rocks represent mainly differentiation trend of calc-alkaline rock series. On the discriminant diagrams such as Ba/La and La/Th ratio, Rb vs. Y+Nb, the volcanic rocks in the study area belong to high-K orogenic suites. According to the tectonic discriminant diagram by Wood, these rock falls into the destructive continental margin. Volcanic rocks in the study area show well correlation to the Yucheon Group in terms of rock age dating and geochemical data, and derived from andesitic cale-alkaline magma