SR ISOTOPE AND RARE EARTH ELEMENT GEOCHEMISTRY IN HIGH TEMPERATURE HOT SPRINGS IN KOREA: GEOCHEMICAL CONSTRAINTS FOR THE ORIGIN OF THERMAL WATERS

Despite non-volcanic area, there are a number of high temperature hot springs with more than 40°C in the Korean Peninsula. Most of these hot springs are related with the Mesozoic granite. The Mesozoic granites at the southern part of the Korean Peninsula are divided into two groups, Jurassic Daebo-granite and Cretaceous Bulguksa granite.

In order to clarify the source of hot springs in South Korea, we carried out a geochemical study for the high temperature hot springs. The samples were collected on four occasions from February 2004 till March 2006. Based on the geochemical characteristics of Sr isotope and REE geochemistry, we discuss some relationships between the distribution of granites in the Korean Peninsula and high temperature hot springs.

The hot springs in the area of the Jurassic Daebo-granite are mainly of Na-HCO₃ type, whereas those of the Cretaceous Bulguksa granite are Na-Cl (-SO₄) type. In PASS-normalized REE patterns, the hot-spring waters in the Jurassic granite area show LREE-depleted and HREE-flattened pattern with negative (-) or no Eu anomaly. However, hot-spring waters in the Cretaceous granite area have characteristics of PAAS-normalized flattened REE patterns with strong positive Eu or Ce anomaly. The ⁸⁷Sr/⁸⁶Sr ratio of the hot springs in the Jurassic Daebo granite area ranges from 0.710 to 0.730, whereas that in the Cretaceous Bulguksa granites ranges from 0.700 to 0.710. Such Sr values of hot springs correspond well to the range of initial Sr values of the Jurassic Daebo granite and Cretaceous Bulguksa granites. In addition, the ⁸⁷Sr/⁸⁶Sr ratio of the hot springs also divided into three groups according to geographical classification such as eastern, western and southern part. The correspondence between ⁸⁷Sr/⁸⁶Sr ratio in hot springs and the initial ⁸⁷Sr/⁸⁶Sr ratio of the hot spring-bearing granite suggests strongly that the high temperature hot springs in South Korea may be derived from the heat source related with the Mesozoic granite.