collisional tectonics of microcontinents derived from the northern parts of Gondwaqna in Thailand and Laos

本研究的目的主要是阐明西默利亚大陆的斯布玛苏与南中国地块碰撞时的构造和古地理。在三年的时间里，我们在泰国和老挝进行了十次实地考察。其结果是：研究了南-乌特拉迪特缝合带(以前解释为西布马苏和印度支那之间的缝合带)的北部延伸，并对其进行了新的推断。这条缝合线没有延伸到老挝，可能会绕过国家边界向北转。否则，这种缝合可能会在泰国南城以北结束。其次，证明了洛伊缝合不是缝合，而是与蛇绿岩相对应。即确定了蛇纹岩、玄武岩和硅质岩自东向西的北向展布。再次，认识到构造差异，即西侧为板岩带，东侧为逆冲褶皱带，为美洪逊断裂的边界。第四，对硅质岩的沉积环境作出了新的解释。关于硅质岩是作为远洋沉积物沉积在深海的认识已经被广泛接受，但这项研究证明，锡布马苏的硅质岩沉积更多地是在较浅的环境中沉积的。

The purpose of this study is mainly to elucidate of tectonics and paleogeography at the time of collision between Sibumasu, a part of Cimmerian continent, and Indochina united with South China block. We carried out ten times field trips in Thailand and Laos during three years. As results, the following are clarified ;The northern extension of the Nan-Uttradit Suture (formerly interpreted as a suture between Sibumasu and Indochina) was examined and newly inferred. This suture does not extend into Laos, and probably turns northward around the national border. Otherwise, this suture may be ended north of Nan city in Thailand. Secondly, it is proved that the Loei Suture is not a suture, but corresponds to ophiolite. Namely, the north extending distribution of serpnetinite, basalt and chert, from east to west, was confirmed. Thirdly, the structural difference, that is, slate belt on the western side and thrust and fold belt on the eastern as a border of the Mae Hong Son fault is recognized. Fourthly, the new interpretation concerning the sedimentary environment of chert was obtained. The knowledge that chert was deposited in deep sea as pelagic sediments has been widely accepted, but this study proves that chert sedimentation on Sibumasu was rather deposited in shallower environments.