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

本研究的主要目的是阐明西布马苏（西布马苏大陆的一部分）与印度支那与华南地块合并碰撞时期的构造和古地理。三年中，我们在泰国和老挝进行了十次实地考察。结果，澄清如下：对南乌特拉特缝合线（以前解释为西布马苏和印度支那之间的缝合线）的北延进行了考察和新的推断。这条缝合线并没有延伸到老挝境内，可能是绕着国境线向北转。否则，这条缝合线可能在泰国南城以北结束。其次，证明了Loei缝合线不是一条缝合线，而是与蛇绿岩相对应。确定了蛇长岩、玄武岩和燧石的北展分布，由东向西。第三，认识到梅红山断裂的构造差异，即西侧为板岩带，东侧为逆冲褶皱带。第四，对燧石沉积环境进行了新的解释。硅质岩作为中上层沉积物沉积于深海的认识已被广泛接受，但本研究证明，西布马苏的硅质岩沉积在较浅的环境中。

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.