2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 50-6
Presentation Time: 9:00 AM-5:30 PM


KANG, Ji-Hoon1, LEE, Deok-Seon1, NOH, Sin Young1, JEONG, Jin-Woo1, KOH, Sang-Mo2 and HAYASAKA, Yasutaka3, (1)Department of Earth and Environmental Sciences, Andong National University, 1375 Gyeongdong-ro, Andong-si, Gyeongsangbuk-do, 760-749, South Korea, (2)Mineral Resources Research Division, Korea Institute of Geoscience and Mineral Resources, 124, Gwahak-ro Yuseong-gu, Daejeon, 305-350, South Korea, (3)Department of Earth and Planetary Systems Science, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-Hiroshima, 739-8526, Japan, jhkang@anu.ac.kr

The rare earth element (REE) mineralized zone with bimodal-type volcano-plutonic rocks involved in Neoproterozoic rifting has been reported in the Ogcheon metamorphic rock (OMR) of Chungju-Goesan area, Northwestern Ogcheon Rift Basin, Korea. We drew up detailed geological map by lithofacies classification, and analyzed SHRIMP zircon U-Pb age of acidic rock, radioactivity value (RV) of each lithofacies, structural characteristics in each deformational phase to understand the source and relative age of REE mineralization in this area. The results show that the Neoproterozoic OMR is composed of plutonic acidic, porphyric, conglomerate, volcanic acidic, basic, carbonate, psammitic, pelitic rocks, (iron-bearing) quartzite. The Mesozoic igneous rocks, which intruded the OMR, consist of hornblende foliated granite, biotite granite, gabbro, diorite, pegmatite. The SHRIMP zircon U-Pb analyses from a coarse-grained type plutonic acidic rock show that the upper and lower intercept ages of 870 ± 66 Ma and 194 ± 18 Ma which reflect a Neoproterozoic magmatism by the rifting of original Gyeonggi Massif and a contact metamorphism by the intrusion of Mesozoic igneous rocks, respectively. The basic-bearing type plutonic acidic rock (MPAR-B) shows the highest RV, and the lithofacies distribution of MPAR-B agrees with the REE mineralized zone. It indicates that the MPAR-B was a source rock of REE ore body. The geological structures were formed at least through 4 times of deformation phase [F1 sheath, "A" type folds and S1 mylonite foliation, (E)NE trending F2 isoclinal, intrafolial folds and S1-2 composite foliation, E-W trending F3a open, kink folds and F3b recumbent fold, N-S trending F4 kink folds]. The (E)NE trend of D2 phase also agrees with the regional foliation and the lithofacies distribution of OMR and the trend of the high-density distribution of RV. It also indicates that the D2 was the most dominant deformation and the REE mineralization occurred before F3 folding.