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

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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