PRE-CENOZOIC TECTONIC DEFORMATION PHASES IN THE MUONG XEN AREA, NGHE AN PROVINCE

Abstract

The Ca River fault zone, located in the north- Central region, is one of the deformation zones having a complex structure, high level of folding and deformation, but producing very low grade metamorphism. Studies of deformation conducted in the Muong Xen area, northwest of the Ca River fault zone, show that, the Ca River fault zone had undergone at least three deformation phases before the Cenozoic. The first (oldest) deformation phase is characterized by plane, reversed and overthrust folds NW-SE direction. The second deformation phase is characterized by large Z-shaped tilted folds, deformed those structures formed in the first deformation phase. Age of these two deformation phases is marked by a pre-Late Triassic clino-unconformable plane. The third deformation phase formed structures, which altered much of the previous stage’s structures, having form and feature almost similar to those of the first folding phase. These three deforming-phase structures were subsequently effected by tectonic activities during the Cenozoic.

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