Geological correlation of southwest Japan and Korean Peninsula-tectonics for spreading of active continental margin-.

项目题目为《日本西南部与朝鲜半岛的地质对比——活动大陆边缘扩张的构造学》。部分项目组成员访问了龙月地区，对龙月煤田的Pamuchi混岩单元进行了地质考察，发现了以下地质事件；1)晚二叠世Pamuchi古海的伸展发育，以中二叠世晚期至晚二叠世早期硅质岩与下二叠世泻湖相灰岩互层为代表；2)晚二叠世至三叠纪Pamuchi盆地的封闭导致Pamuchi混杂岩单元的形成。后者与日本西南部晚二叠世舞津和超坦巴地区的事件有明显的重合，并根据砂岩岩石学资料进行了详细的研究。其他组员留在了韩国东南部，对白垩纪-第三纪火成岩和沉积岩进行了实地考察。朝鲜东南部白垩系—古近系侵入岩与日本西南部三仁地区的花岗质岩石相似，多为i型磁铁矿系。这些岩石显示出较低的初始Sr同位素比率，可与日本西南部三仁带的岩石相比较。两个具有代表性的岩体显示Rb-Sr全岩等时线年龄分别为53和58 Ma。这些资料表明，朝鲜东南部花岗岩类岩石的年龄多为古近系，其岩浆来源与三隐带下的花岗岩类岩石相似。全岩及角闪岩K-Ar年龄测定结果表明，中新世火山岩年龄与山仁地区相近，但火山活动最强烈的时期在韩国东南部略早于日本西南部。与日本西南部山仁地区不同，韩国东南部的碱性岩系火山活动始于白垩纪。这是考虑伴随日本海开放而来的大陆边缘岩浆和构造演化的重要因素。

The title of the project is geological correlation of southwest Japan and Korean Peninsula-tectonics for spreading of active continental margin-. Some members of the project visited Yongwol area and examined geologically the Pamuchi melange unit in the Yongwol coal field, and revealed following geologic events ; 1) extensional development of the Late Permian Pamuchi paleo-sea represented by the occurrence of the late Middle to early Late Permian siliceous rocks interbedded with the Lower Permian lagoonal facies limestones, 2) Closure of the Pamuchi basin in Latest Permian to Triassic which resulted to the formation of the Pamuchi melange unit. The latter event coincides significantly to that of the Late Permian Maizuru and Ultra-Tanba Terrains of SW Japan which was investigated in detail on the basis of petrographical data of sandstones. Other members of the project stayed in southeastern part of Korea to do field work for Cretaceous-Miocne igneous and sedimentary rocks. Similar to the granitoid rocks in the San'in Zone, SW Japan, most Cretaceous-Paleogene intrusive rocks in SE Korea are I-type magnetite-series. These rocks show low initial Sr isotope ratios comparable to those in the San'in Belt, SW Japan. Two repesentative plutons show Rb-Sr whole rock isochron ages of 53 and 58 Ma. These data may suggest that the most granitoid rocks in SE Korea are Paleogene in age, and their magmas were derived from similar source materials to those beneath the San'in Belt. Whole rock and hornblende K-Ar age determination revealed that Miocene volcanic rocks have similar ages to those in the San'in district, but the period of the most intensive volcanism was slightly older in SE Korea than in SW Japan. In contrast with San'in district, southwest Japan, volcanism of alkaline rock series initiated in the Cretaceous in SE Korea. This is an important factor to consider magmatic and tectonic evolution of the continental margin accompanied by the opening of Japan Sea.