Trace and rare earth element geochemistry of granitic rocks, southern part of the Kyongsang Basin, Korea

Abstract

This article presents geochemical characteristics of trace and rare earth elements in the late Cretaceous granitic plutons, southern part of the Kyongsang Basin, and discusses related magmatic processes and possible source materials. The granitic rocks in the study area were formed in volcanic-arc environments, and can be divided into four plutons (Masan, Jinhae, Kimhae, and Busan plutons). According to LILE/HFSE and initial Sr ratios, the plutons are grouped into the western, HFSE-depleted (Masan/Jinhae) and the eastern, HFSE-enriched (Kimhae/Busan) suites. In each suite, the younger plutons (Jinhae and Busan plutons) are chemically more felsic, and occur as smaller bodies. Plagioclase, apatite, and Fe-Ti oxides have been fractionated in all plutons. Zircon fractionation is recognized in the Masan pluton, whereas small amounts of allanite fractionations are detected in the Jinhae, Kimhae, and Busan plutons. The primary compositions of the plutons were probably LREE-enriched with almost unfractionated HREE and negative Eu anomalies. The plutons were, therefore, likely to be generated from abundant-plagioclase source materials. Taking into account the critical melt fraction which controls magma segregation, the intermediate Masan and Kimhae plutons formed earlier in each suite seem to have been derived directly from the gabbroic lower crust. The later, felsic Jinhae and Busan plutons appear to have been formed by remelting of modified protoliths which were chemically very similar to the Masan and Kimhae plutons, respectively. This reworking process may have occurred during comparatively short period of time (< 30 m.y.).