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Keewook Yi,조문섭 한국지질과학협의회 2009 Geosciences Journal Vol.13 No.3
Reaction textures, mineral chemistry, and U–Pb SHRIMP geochronology of monazite from the Hwacheon granulite complex were investigated to delineate the timing of granulite-to-amphibolite transition. Reaction textures of apatite and allanite surrounding partially-dissolved monazites in the transition zone (HY-23) are similar to those of symplectic hornblende and garnet corona around pyroxenes in mafic granulite at the same outcrop. The texture and chemistry of retrograde rare earth element-bearing minerals indicate that disequilibrium in metasomatic reactions and the availability of fluid during the amphibolitization contributed to the variable degrees of transition. The U–Pb age of dissolved monazite was dated at 1861 ± 20 Ma, which is indistinguishable from 1873 ± 17 Ma of unaltered monazite. On the other hand, the crystallization age of symplectic allanite is interpreted to be either Devonian or Triassic, based on Th–Pb and U–Pb ages, respectively. Thus, the synchroneity between accessory mineral growth and its microstructure such as corona or symplectite needs to be carefully assessed for unraveling the nature of tectonometamorphic events.
Yi, Sang-Bong,Oh, Chang Whan,Lee, Seung-Yeol,Choi, Seon-Gyu,Kim, Taesung,Yi, Keewook Elsevier 2016 Lithos Vol.246 No.-
<P><B>Abstract</B></P> <P>Triassic coeval mafic and intermediate magmatism occurred in the area suggested to be the southern margin of the North China Craton (NCC) in the Gyeonggi Massif (GM) of the Korean Peninsula. This study investigates aspects of the mafic and intermediate magmatism using SHRIMP zircon ages and whole-rock chemical and isotopic Sr–Nd data. The mafic and intermediate rocks intruded into a basement paragneiss in three areas (Yangpyeong, Odesan and Yangyang) within the GM at ca. 230Ma. The paragneiss was metamorphosed in both the Paleoproterozoic and Triassic. Gabbros (hornblende gabbro and pyroxene–mica gabbro) from the study areas exhibit strong light REE (LREE) enrichment relative to chondrite (La<SUB>N</SUB>/Yb<SUB>N</SUB> =11.1–30.6) and a high LILE/HFSE pattern, Ta–Nb–P–Ti troughs and positive Ba–K–Pb–Sr spikes on the N-MORB-normalized multi-element variation diagram. These features are typical characteristics of arc-related gabbros. The gabbros also show strongly enriched initial isotopic compositions (<SUP>87</SUP>Sr/<SUP>86</SUP>Sr<SUB>(i)</SUB> =0.7100–0.7137; ε<SUB>Nd</SUB>(t)=−13.1 to −19.7). The coeval intermediate intrusive rocks also exhibit whole-rock chemical and isotopic features (<SUP>87</SUP>Sr/<SUP>86</SUP>Sr<SUB>(i)</SUB> =0.7099–0.7143; ε<SUB>Nd</SUB>(t)=−10.8 to −18.6) similar to those of the gabbros. The mafic and intermediate intrusive rocks plot in the within-plate and/or post-collisional fields on tectonic discrimination diagrams. These data indicate that the mafic and intermediate magmatism in the study areas occurred during the Triassic post-collisional relaxation period via partial melting of sub-continental lithospheric mantle (SCLM) that was enriched in a subduction environment prior to (or during) the Permo-Triassic continental collision between the NCC and the South China Craton (SCC). The highly enriched mantle signatures revealed by the gabbros from the study areas are matched to the enriched features identified in Cretaceous mafic igneous rocks (ca. 130Ma) on the southern margin of the NCC. Thus, this study suggests that the lithospheric mantle beneath the Yangpyeong, Odesan and Yangyang areas are comparable to the SCLM of the NCC southern margin. The highly enriched nature of mafic and intermediate rocks from the study areas indicates that their source is the SCLM that was metasomatized by Permian to early Triassic subduction–continental collision processes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mafic and intermediate magmatism may have occurred during post-collisional setting. </LI> <LI> The magma source of these rocks appears to be the enriched sub-continental lithospheric mantle (SCLM). </LI> <LI> This lithospheric mantle is comparable to the SCLM of the southern margin of the North China Craton. </LI> </UL> </P>
화석 외 지질유산의 보호·조사·관리방안의 국내 현황 및 개선안
이기욱(Keewook Yi) 대한지질학회 2021 대한지질학회 학술대회 Vol.2021 No.10
‘매장문화재 보호 및 조사에 관한 법률’은 천연동굴과 화석 외에도 지표·지중·수중 등에 생성·퇴적되어 있는 지질학적 가치가 큰 지질유산을 매장문화재의 한 종류로 정의하고 있다. 그리고 동법 시행령 별표1에 지질구조·지질경계선·퇴적구조·지형 중 지질학적 가치가 큰 기준을 15가지 이상의 분류로 규정하고 있다. 그러나, 이 법은 기본적으로 고고유물 문화재 중심으로 매장문화재의 보호·조사·관리에 관한 사항을 규정하고 있어서, 지질유산을 다루는 전문 학문분야와의 현장교육 및 연구 활동과는 상당히 동떨어진 내용을 포함하고 있으며, 특히, 화석 외 지질유산은 별도의 판단과 검증을 통해 지질학적 가치를 결정해야 하므로 더욱더 많은 문제가 발생되고 있다. 우선 시행령 별표1의 규정이 상당히 모호하여 이를 구체적으로 적용하여 화석 외 지질유산을 보호·조사·관리하는 것이 매우 힘들다. 또한, 화석 외 지질유산의 잠재적 후보 대상물이 시행령 별표 1에서 규정한 ‘지질학적 가치가 큰’ 매장문화재인지를 판단할 수 있는 주체 및 절차가 준비되어 있지 않다. 이를 위해 1) 매장문화재법 취지에 맞는 화석 외 지질유산의 보호·조사·관리를 위해 관련전문가 의견수렴을 거쳐 시행령 별표 1을 현실에 맞게 개정하는 것이 필요하며, 2) 대한지질학회를 중심으로 관련 전문가들이 화석 외 지질유산의 가치를 판단하고 자문하는 국가적 공공검증 절차가 마련되어야 한다. 나아가 화석 외 지질유산의 현황 파악 및 관리하는 지질유산 국가 포탈 시스템이 장기적으로 구축되어야 한다.