SUMMARY

On the activities of neotectonic fault zones in West Bắc Bộ, Việt Nam

Nguyễn Văn Hùng, Hoàng Quang Vinh

Neotectonic fault systems of West Bắc Bộ are composed of: Lai Châu - Điện Biên, Sa Pa - Văn Bàn, Phong Thổ - Than Uyên, Nghĩa Lộ - Ninh Bình, Mường La - Chợ Bờ, Sông Đà, Sơn La - Bỉm Sơn, Luân Châu - Pắc Nậm etc, fault systems. Most of them have NW-SE direction, apart from the Lai Châu - Điện Biên fault zone, which has the submeridional direction in the northern part, NE-SW direction in the southern part, and the Luân Châu - Pắc Nậm fault zone which has the submeridional form.

These fault zones were activated with lateral movement during Cenozoic and their activities may be divided in two phases:

In the first phase (Paleogene-Miocene), the NW-SE fault systems had the left-lateral movement, sometime with reverse component; meanwhile the Lai Châu - Điện Biên fault zone has right-lateral movement, sometime with reverse component. This phase has main role in the reconstruction of the main features of neotectonic plan of the region.

In the second phase (Pliocene-Present), the NW-SE fault zones have been operating with right strike-slip or normal slip, but many submeridional sections are of normal slip; particularly, the Lai Châu - Điện Biên fault zone is of left strike-slip. In this phase some parts of the structural plan inherited the former plan with the formation of series of normal faults and tectonic basins of different  sizes.

Ngày nhận bài: 30-7-2004

Người biên tập: Nguyễn Trọng Yêm