Zircon U-Pb age and geochemical studies on the petrogenesis of the Chugongnyeong pluton of the Hwacheon granite

The Jurassic Hwacheon granite located in the area of Hwacheon and Chuncheon in central Gyeonggi massif consists of Yonghwasan pluton and Chugongnyeong pluton. The Chugongnyeong pluton is composed of a major porphyritic biotite granite and a minor equigranular biotite granite. 185.3 +/- 0.6 Ma of zircon U-Pb age dating result of the porphyritic biotite granite indicates that an early Jurassic Pliensbachian igneous activity occurred in the Hwacheon and Chuncheon area of the central Gyeonggi massif. The Chugongnyeong pluton is peraluminious and it is inferred that the pluton was derived from partial melting of meta-psammite protolith such as clay -poor meta-graywackes or their igneous counterparts. The difference in lithology and rare earth element pattern between the porphyritic biotite granite and the equigranular biotite granite suggests that two different rocks were generated through distinct melting event from similar protoliths. The enriched values of lithophile element of Cs, Rb, Ba, and negative trough of Nb, Ti, P on the spider diagram suggest that the Chugongnyeong pluton formed in subduction tectonic environment. Whole -rock zircon saturation thermometer indicates that porphyritic biotite granite and equigranular biotite granite of the Chugongnyeong pluton were melted over 696-813 C (mean value: 755 C ) and 710-840 C (mean value: 764 C ), respectively.