SUMMARY

Features of tectonic deformation stages of the Sông Cả Fault Zone

Nguyễn Bá Minh, Nguyễn Văn Vượng, Vũ Văn Tích

Located in the north of Trường Sơn Belt, the Sông Cả Fault Zone is one of the most complicated deformation zones in Việt Nam. The degree of deformation folding is very strong while the metamorphism is less. The topography and relief are so differentiated that the structural study faces to many difficulties. The recently obtained results of deformation studies have been evidencing the existence of at least three folding phases occuring before Cenozoic. The first phase is characterized by recumbent folds and overturned fold having the NW-SE axis and axial plan. The second folding phase produces the Z shape folding from outcropt to regional scales. The age of these two folding phases is marked by an angular unconformity and the folds were covered by Upper Triasic coal-bearing beds. The third folding phase coincides geometrically with the first folding phase and deformed all older folds. During Cenozoic, the Sông Cả Fault Zone was affected by a rotational stress field with 4 distinctive states. The firt stress field is characterized by strike slip with nearly horizontal sigma 1 in E-W direction while sigma 3 in N-S direction. The second stress field coresponds also to strike slip regime with horizontal sigma 1 in N-S and horizontal sigma 3 in E-W direction respectively. This stress field rotates about 20 to 30⁰ to produce the third stress field. The last one is characterized by an extensional stress field with sigma 3 oriented
NE-SW.

Người biên tập: GS.TS Trần Văn Trị.