A preliminary study of the sedimentary petrography of coarse clastic deposits in the Da Nang-Khe Sanh shear zone, central Vietnam
The ductile deformation belt in the Da Nang-Khe Sanh shear zone is the one of the NW-trending fault zone developing in the central Vietnam. This belt mainly comprises undeformed Jurassic sedimentary rocks, granite, gneissose metamorphic rocks, serpentine, and schistose rocks originated from the Paleozoic with extensive faulting. The A Lin Formation comprising undeformed conglomerate, sandstone, andesite, felsic tuff, and tuffaceous mudstone is distributed in the Da Nang-Khe Sanh shear zone and is designated to the Upper Permian formation. Its distribution is narrow and restricted to the NNW-trending shear zone, wherein the sedimentary mode is considered as a fault-bounded basin fill. The preliminary study of the clastic composition of the A Lin Formation reveals the derivation from volcanic and metamorphic terranes comprising andesite, rhyolite, psamitic schist, quartz mica schist and mylonite. This suggests that the provenance of the A Lin Formation is correlated to the metamorphic rocks contiguous to the depositional basin. The petrographic characteristics of the metamorphic rock fragments in the sandstone are consistent with the gneissose granitic complex, which is adjacent to the basin and was dated as early Triassic with subordinate Jurassic-Cretaceous metamorphic age. These results lead to the inference that the A Lin Formation was deposited following the early Triassic metamorphic event. The deposition might be correctable to the Jurassic-Cretaceous tectonic movement, i.e., andesitic volcanism and reactivation of the shear zone. Although sufficient information on post-collisional crustal deformation of the Indochina Block during Mesozoic is not available, sedimentation in the NW-trending fault zone leading to the A Lin Formation provides significant information for a crustal deformation the in post-collisional stage.
Journal of the Faculty of Science Shinshu University. 39:25-38(2005)
- Journal of the Faculty of Science Shinshu University
Journal of the Faculty of Science Shinshu University 39 25-38, 2005-03-30
Faculty of Science, Shinshu University