K-Ar age-dating results of some major faults in the gyeongsang basin: Spatio-temporal variability of fault activations during the cenozoic era

We present the K-Ar age-dating results of the bulk and the less than 0.1 µm fraction of the fault gouges collected from some major faults in the Gyeongsang basin. We try to determine the timings of fault activation based on the mineralogical characteristics, and to interpret the spatio-temporal variability of the major fault events during the Cenozoic Era by considering together with the previous results. We propose at least the 3-times of major fault events at about 50 Ma, and just after 30 Ma and 20 Ma in the Gyeongsang basin, which were inferred from the combined approach of the K-Ar ages and the clay mineralogy of the bulk fault gouges and the <0.1 µm fractions. The fault activation timings of the Yangsan fault tend to be younger in the northern part than in the southern part. In particular, the inferred fault events just after 30 Ma and 20 Ma are mainly detected in the Ocheon fault and the related faults, and the fault in the Gyeongju area. The fault activation timings of the major faults can be revised accurately by using illite-age-analysis(IAA) method. These geochronological determinations of the multiple events of the major faults in the Gyeongsang basin are crucial to establish the tectonic evolution in the southeastern part of the Korean Peninsula during the Cenozoic Era.