Geologic Development of the Truong Son Fold Belt In Central Vietnam - Study on the Evolution of Asian Continent (IGCP-411) -

该项目的目的是阐明亚洲大陆的构造演化，它是由冈瓦兰岛的分散开始的复杂过程与日本群岛的发展关系而形成的。人们认为，澄清越南造山带的构造是实现这一目标的关键。该项目的日本成员在越南地质学家的协助下进行了以下地区的地质调查：孙马缝合带的花岗岩构造分析和取样以确定年龄，红河断裂两侧的取样以进行古地磁研究(2000年)，张子褶带的沉积岩石学研究和越南北部的古生物学和构造研究(2001年)，以及越南印度支那地块与邻近地块之间关系的构造分析。地质调查结果如下：1)越南红河断裂北侧分为两个bl…缝合带是中国地块南部的南延伸段，有更多的岩块。(2)长城褶皱带南侧由大洋板块物质堆积杂岩组成的带，其边缘朝东北方向。3)越南境内不存在印度支那地块的东南边界，对上述地区采集的样品进行了古地磁、生物地层学、年代学和沉积岩石学研究。到目前为止，有以下几点是明确的：1)红河断裂两侧白垩纪对应的两极在统计上彼此难以区分。2)孙马缝合带南侧的增生杂岩产生泥盆纪的牙形刺，使孙马缝合带北侧的大陆碎片至少在泥盆纪从冈瓦瓦兰漂移。3)包括斜长花岗岩在内的三个花岗岩样品的年龄。中三叠世为238.9±1.80 Ma，早二叠世为280.7±3.9Ma，中二叠世为256.1±1.2Ma。4)越南东北部华夏地块与扬子地块之间的缝合带也含有泥盆纪牙形刺。4)在砂岩岩石学和地球化学研究的基础上，长孙褶皱带中上古生界的物源揭示了未成熟岩浆弧的形成，物源的明显变化是越南北部及邻区古生代构造发育的重要方案。1)张子褶皱带是印度支那陆块与南中国陆块之间的缝合带。2)长孙缝合带的北界为孙马缝合带，其南界可能对应于岘港断裂。3)长孙缝合带包括洋板残留物和岛弧残留物。4)越南中国南部陆块由扬策地块和华夏地块组成。较少

The purpose of this project is to clarify the tectonic evolution of Asian Continent that was formed by the complicated process started from the dispersion of Gondwanaland in the relation with the development of Japanese Islands. It is considered that the clarification of the tectonics of the orogenic belts in Vietnam is a key to this purpose. Japanese member of the project did the geological survey in the following areas by the assistance of Vietnam geologists; structural analysis and sampling of granitic rocks for age determination in the Son Ma Suture Zone, and sampling for paleomagnetic study in both sides of the Red River Fault (2000), sedimentary petrological study in the Truong Son Fold Belt and paleontological and structural study in northern Vietnam (2001), and tectonic analysis of the relationship between Indochina Block and adjacent blocks in Vietnam. The results of the geological survey are as follows; 1) Northern side of the red River Fault in Vietnam is divided into two bl … More ocks by the suture zone which is a southern extension from the South China Block. 2) Zone consisting of accretionary complex of ocean plate materials are recognized southern side of the Truong Son Fold Belt and its vergence is toward northeast. 3) Southeastern boundary of the Indochina Block does not exist inside Vietnam.Paleomagnetic, biostratigraphic and chronological, and sedimentary petrological studies are going on concerning samples collected from the areas mentioned above. Until now, the following points are made clear, 1) The corresponding poles in Cretaceous at two localities in the both sides of the Red River Fault are statistically indistinguishable from each other. 2) Accretionary Complex in the southern side of the Son Ma Suture Zone yields Devonian conodonts so that the continental fragment in the northern side of the Son Ma Suture Zone drifted from the Gondwanaland at least in Devonian. 3) Age of three granitic sample including plagiogranites (?) from the Son Ma Suture Zone is 238.9+/-1.8 Ma (Middle Triassic), 280.7+/-3.9 Ma (Early Permian) and 256.1+/-1.2 Ma (Middle Permian). 4) Suture zone between the Cathaysia and Yantze blocks in northeastern Vietnam is also contains Devonian conodonts. 4) On the basis of the sandstone petrography and geochemistry, the provenance in the Middle-Upper Paleozoic sequence in the Truong Son Fold Belt reveals the formation of the immature magmatic arc and distinct change of the provenance is considered as important scheme of Paleozoic tectonic development in northern Vietnam and adjacent terranes.From above-mentioned results of the study, we could indicate the following points at this stage. 1) The Truong Son Fold Belt is a suture zone between the Indochina and South China Continental Blocks. 2) Northern boundary of the Truong Son Suture Zone is the Son Ma Suture Zone and its southern boundary may be correspond to the Danang Fault. 3) Truong Son Suture Zone includes relicts of ocean-plate and island arc. 4) South China Continental Block in Vietnam is composed of Yantze and Cathaysia Blocks. Less