Tectonic evolution of the Red river basin and adjacent areas of Vietnam in the Cenozoic era

Abstract

Based on the structural and tectonic-physical analysis of data collected from outcrops around Tonkin Gulf and the seismic results of the Red river basin, the four main successive tectonic phases with specific paleo-stress fields since the beginning of the Cenozoic era have been established. Firstly, the middle Eocene-early Miocene (45-15.97 my) tectonic phase, with sub-latitudinal compression and sub-longitudinal extension, was accompanied by a large-scale sinistral displacement of the Red river fault, and the extension centers of the Red river basin and seafloor spreading of East Vietnam Sea. Secondly, the middle-late of middle Miocene (13, 82-7, 25 my) tectonic phase, with sub-longitudinal compression and sub-latitudinal extension, has created a local depocenter N-S orientation, right-lateral strike-slip of the Red river fault and first inversion of the basin. The third tectonic phase started by the late Miocene (~7.25-5.33 my BP), with NE-SW compression, causing the most potent inversion in the Red river basin with substantial uplift of some blocks and significant shrinkage of the RRB up to 15–20%. The fourth tectonic phase was from the Quaternary-to-Recent, with NW-SE compression and NE-SW extension, and appeared in the form of existing recent grabens of NW-SE direction, earthquakes, and GPS data. The formation and development of the Red river basin were controlled by tectonic activities and closely connected to NW-SE trending fault systems of regional scale, such as the Red river fault, Chay river fault, Lo river faults, as well as the local faults, such as Ca river fault, Rao Nay river fault, Thakhek-Da Nang fault. Some spectacular examples of tectonic activity can be seen in the geographic features of Vietnam, Laos, and Thailand, particularly the mountain ranges, such as the Truong Son (or Viet-Laos) belt. When it comes to the sea, the Red river fault becomes less active, while the other faults of the RRFS, like the Chay river and Lo river, play the leading role in developing the Red river basin.