Characteristics of clay minerals in gouges of the Red River fault, Vietnam

Abstract

Earthquake is currently one of the biggest concerns in Vietnam, especially, when a number of earthquakes recorded by seismometers in recent years imply the danger of earthquake in the country. In Vietnam, the recorded earthquakes were pinpointed as the consequence of stratigraphic movements along active fault zones. Identifying of the activities of fault is mainly based on tectonics, geomorphology and observation techniques utilizing geophysical methods with data on seismic waves of earthquakes. However, determining the active fault intervals is generally a difficult task which is of the interest of many domestic and worldwide scientists. One of the methods of identifying the active intervals of faults that has been applied in many countries is studying authigenetic clay mineral forming in fault planes and cataclasites due to fault activities. The movement of fault surface will create fault gouges formed at low temperature, the typical of which is illite mineral. In order to date active phases of faults, K-Ar dating of illite mineral is now proved to be an effective method. Based on the successful studies on modern fault activities using the method of K-Ar dating of authigeneticillite, and with the goal of having a general view on the activities of Red Rive Fault, Vietnam and more information on earthquakes caused by this fault, the authors have conducted a study on characteristics of the authigenetic clay minerals formed by fault activities, accordingly identifying their formation periods using K-Ar dating method. Based on the recorded ages, we hope to be able to explain the active fault intervals and its relationship with earthquake activity in the surround areas. In this paper, we are presenting the initial results about characteristics of clay minerals in gouges of the Red River fault zone, Vietnam. Several gouges amples were collected from the Red River fault zone. Then, they were separated into four grain-size fractions (<0.1, 0.1 - 0.4, 0.4 - 1.0, and 1-2µm) using standard gravitational settling and high-speed centrifuging techniques based on a preliminary analysis. The samples after separating were characterized by using FTIR spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The results indicated that authigenetic clay minerals forming in fault planes due to fault activities such as illite, illite/smectite is in samples with significant amounts. These are important results in defining modern active time of Red River fault zone using method of K-Ar dating for authigenetic clay minerals.