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Origin of the Eocene Gyeongju A-type Granite, SE Korea: Implication for the High Fluorine Contents
에오세 경주 A-형 화강암의 기원: 높은 불소 함량에 대한 고찰
Econ. Environ. Geol. 2018 Oct;51(5):439-53
Published online October 31, 2018;  https://doi.org/10.9719/EEG.2018.51.5.439
Copyright © 2018 the Korean society of economic and environmental gelology.

Bora Myeong1,2, Jung-Hoon Kim3, Hyeong-Dong Woo4 and Yun Deuk Jang2*
명보라1,2 ·김정훈3 ·우현동4 ·장윤득2*

1Deep-sea and Seabed Resources Research Center, Korea Institute of Ocean Science & Technology (KIOST),Busan 49111, South Korea
2Department of Geology, Kyungpook National University, Daegu 41566, South Korea
3Division of Environment Policy, Gyeongsangbuk-Do, Andong, 36759, South Korea
4Department of Structural System and Site Safety Evaluation, Korea Institute of Nuclear Safety (KINS), Daejeon 34142, South Korea
1한국해양과학기술원 심해저광물자원연구센터, 2경북대학교 지질학과
3경상북도청 환경정책과, 4한국원자력안전기술원 구조·부지평가실
Received July 30, 2018; Revised October 20, 2018; Accepted October 27, 2018.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
The Eocene Gyeongju granitoids in SE Korea are alkali feldspar granite (AGR), biotite granite (BTGR), and hornblende biotite granodiorite (HBGD) along Yangsan fault and Ulsan fault. According to their geochemical characteristics, these granitoids are classified as A-type (AGR) and I-type (BTGR and HBGD) granitoids, and regarded that were derived from same parental magma in upper mantle. The hornblende and biotite of AGR as an interstitial phase indicate that influx of F-rich fluid during the crystallization of AGR magma. AGR is enriched LILE (except Sr and Ba) and LREE that indicate the influences for subduction released fluids. The highest HFSE contents and zircon saturation temperature of AGR among the Eocene Gyeongju granitoids may indicate that it was affected by partial melting rather than magma fractionation. These characteristics may represent that the high F contents of AGR was affected by F-rich fluid derived from the subducted slab and partial melting. It corresponds with the results of the REE modeling and the dehydrated fluid component (Ba/Th) modeling showing that AGR (A-type) was formed by the partial melting of BTGR (I-type) with the continual influx of F-rich fluid derived from the subducted slab.
Keywords : A-type granite, fluorine, partial melting, F-rich fluid, dehydrated fluid components

 

October 2018, 51 (5)