Paleomagnetic study of Remagnetization by a Dike in the Gyeongsang Supergroup

경북 고령지역에 분포하는 경상누층군의 관입암류에 의한 재자화작용에 관한 고지자기 연구

Paleomagnetic study is carried out to investigate the possibility of remagnetization by dikes in the Cretaceous Gyeongsang Basin. We selected a site for a contact test as a preliminary study, and collected 41 core samples (7 from andesitic dike, 17 from sedimentary rock on the left side of dike and 17 from sedimentary rock on the right side). Magnetite was responsible for the remagnetization based on microscopic observation and demagnetization analysis. Although the increasement of magnetic susceptibility appears on both sides about 100 cm from the dike, the increment of NRM intensity was obtained from the specimens on the left side only. This is interpreted that the size of magnetite newly formed is dominated by superparamagnetic grains in the right side, but by larger than single-domain grains in the left. Reversed polarity component remagnetized by intrusion of dike was also found only for core samples from 116 cm left side of dike but abscent from right side indicating the remagnetization by the dike depends on the geometric shape and width of the dike, which is supported by field observations. The content of epidote is well correlated with remagnetization, and indicates the hydrothermal alteration/metameorphism was activated by the intrusion. We concluded that the above evidences in this study further support thermally-activated chemical origin of the remagnetization with meager contribution of contact metamorphism, and that any significant evidence of regional-scaled remagnetization was not found in the study area.