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

该项目的题目是日本西南部和朝鲜半岛的地质对比-活动大陆边缘扩张的构造-。该项目部分成员走访了永无山地区，并对永吾尔煤田的帕木池混杂岩单元进行了地质考察，发现了以下地质事件：1)晚二叠世帕木池古海的伸展发展，表现为晚二叠世晚期、中晚期至晚二叠世早期硅质岩与下二叠世泻湖相灰岩的互层；2)帕木池盆地在晚二叠世至三叠纪闭合，形成帕木齐混杂岩单元。后者与日本西南部晚二叠世Maizuru和Ultra-Tanba地体的事件显著重合，后者是根据砂岩的岩石学数据进行详细调查的。该项目的其他成员留在韩国东南部，为白垩纪-中新世火成岩和沉积岩做野外工作。韩国东南部白垩纪-古近纪侵入岩多为I型磁铁矿系列，与日本西南部三连带的花岗岩相似。这些岩石的初始锶同位素比值很低，可与日本西南部桑宁带的岩石相媲美。两个蚀变岩体的Rb-Sr全岩等时线年龄分别为53 Ma和58 Ma。这些数据可能表明，韩国东南部大多数花岗岩类岩石的年龄为古近纪，它们的岩浆来源与山银带下的物质来源相似。全岩和角闪石K-Ar年龄测定结果表明，中新世火山岩的年龄与三宁地区的火山岩年龄相似，但朝鲜东南部的火山活动最强烈时期略早于日本西南部。与日本西南部的三连地区不同，碱性岩系火山作用始于韩国东南部的白垩纪。这是考虑伴随日本海开放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.