Tectonic evolution of the Red river basin and adjacent area (Vietnam) in Cenozoic era

Abstract

Basing on the structural and tectonophysic analysis of data collected from outcrops around Tonkin Gulf and the results of analysis of seismic setions of the Red river basin, the fourmain successivetectonic phases with specific paleostress fields since beginning of Cenozoic era have been established. The first middle Eocene-early Miocene (45-15.97 my) tectonic phase, with sub-latitudinal compression and sub-longitudinal extension, was accompanied by large scale sinistral displacement of the Red river fault, the extension centers of the Red river basin andseafloor spreading of East Vietnam Sea. The second 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 late Miocene (~7.25-5.33 my BP) tectonic phase, with NE-SWcompression, has caused strongest inversion in the Red river basin with strong uplift of some blocks and significant shrinkage of the RRB up to 15–20%. The fourth Quaternary-to-Recent tectonic phase, with NW-SE compression and NE-SW extension, is appeared in form of existing of the recent grabens of NW-SE direction, earthquakes and GPS data. Formation and development of the Red river basin was controlled by the tectonic activities and closely connected to NW-SE trending fault system of regional scale such as the Red river fault, Chay river fault, Lo river faults as well the local faults such as Ca river fault, Rao Nay river fault, Thakhek-Da Nang fault. Some spectacular examples for tectonic activity can be seen in form of geographic features of Vietnam, Laos and Thailand, in particular the mountain ranges, such as Truong Son (or Viet-Laos) belt. The Red river fault when comes to the sea becomes less active, while the other faults of the RRFS like Chay river and Lo river had played the main role in development of the Red river basin.