@phdthesis{oai:niigata-u.repo.nii.ac.jp:02000448, author = {Ha, Youngji}, month = {2022-05-10, 2022-05-10}, note = {The Okcheon Metamorphic Belt, located in the middle of the Korean Peninsula, is a key to understand the tectonic evolution of East Asia. This belt is mainly composed of the pelitic and psammitic schists, phyllites, and sparsely distributed meta-carbonate rocks. Despite its importance, the depositional timing of the protoliths of the Okcheon Metamorphic Belt has been debatable last few decades. Recently, U-Pb zircon age dating attempts have been made on various constituents of the Okcheon Metamorphic Belt. Such U-Pb zircon geochronology data facilitate a better understanding of the evolutionary history of the Okcheon Metamorphic Belt. However, it has been concentrated in clastic metasedimentary sequences. Because it is tough to find proper absolute dating methods applicable to carbonate rocks. This thesis aims to constrain the age of carbonate sequence, especially Hyangsanni Dolomite, by adopting chemostratigraphy. The age-unknown Hyangsanni Dolomite is distributed in the northeastern part of the Okcheon Metamorphic Belt. It has been claimed as Early to Middle Cambrian because of the misidentified Archaeocyatha fossil in the past, but the time of sedimentation has not yet been confirmed. In order to clarify this, I performed elemental and isotopic analyses for the Hyangsanni Dolomite. Several geochemical parameters suggest that the Hyangsanni Dolomite was deposited in a rift basin connected to the ocean rather than in the passive continental margin, considering the occurrence of magmatism related to continental rifting within the Okcheon Metamorphic Belt. The isotope results concur with the proposal that Hyangsanni Formation is not the Phanerozoic strata but Neoproterozoic strata. The consistent high δ^<13>C values (mostly > 5‰) and minimum value of ^<87>Sr/^<86>Sr ratio (present value, 0.7074) obtained from the Hyangsanni Formation refer to Neoproterozoic. The shale-normalized REE+Y signatures for the Hyangsanni Dolomite are generally flat and negative cerium anomaly is commonly negligible to the extent that it display solely weakly in some samples. Y/Ho ratios ranges from 29 to 43, which is quite lower than that of typical modern seawater. It indicates that the Hyangsanni Dolomite might have been influenced by terrigenous materials. All metacarbonate samples from the Hyangsanni Dolomite were analyzed for carbon and oxygen isotopic compositions. To avoid recrystallized calcite, the analysis was carried out on dolomite powders scraped off from polished surfaces which are unstrained with Alizarin-Red-S. The Hyangsanni Dolomite has δ^<13>C_<(V-PDB)> and δ^<18>O_<(V-SMOW)> values ranging from +2.9‰ to + 6.2‰ and from +11.3‰ to + 24.5‰, respectively. These δ^<13>C values are significantly higher than those in the Cambro-Ordovician, and it is coinciding of the Neoproterozoic values. The minimum ^<87>Sr/^<86>Sr ratio acquired from the Hyangsanni Dolomite pertain to Neoproterozoic, not Phanerozoic as well. Taken together, I suggest that the Hyangsanni Dolomite is the Neoproterozoic sedimentary sequence in accordance with other sedimentary sequences of the northeastern Okcheon Metamorphic Belt. Thus, the isotope results concur with the proposal that Hyangsanni Formation is not the Phanerozoic strata but Neoproterozoic strata. The consistently high δ^<13>C values (mostly > 5‰) and minimum value of ^<87>Sr/^<86>Sr ratio obtained from the Hyangsanni Formation refer to Neoproterozoic. In addition, this thesis reports the zircon U-Pb data of other constituents, metasedimentary sequences, of the Okcheon Metamorphic Belt as well. These include the Daehyangsan Quartzite, Bugnori Formation, Hwanggangni Formation, Seochangni Formation, and Changni Formations. Daehyangsan Quartzite has largely occurred in association with the Hyangsanni Dolomite along Lake Chungju. The stratigraphic relationship between this formation and Hyangsanni Dolomite has been suggested to be conformable, but, still debatable. Because recently reported reliable zircon U-Pb age of the Daehyangsan Quartzite is Paleozoic (ca. 420 Ma). This study also identified that the Daehyangsan Quartzite belongs to the Paleozoic. The Bugnori and Hwanggangni Formations, pebble-bearing phyllitic sequences, are considered as composing of glaciogenic sediments. The detrital zircon age of Hwanggangni Formation it is dominated by ca. 1870 Ma and 750 Ma even though differs from region to region. While in the case of Bugnori Formation, the Mesoproterozoic component is predominant. The Seochangni and Changni Formations, phyllitic sequences, are considered equivalent to each other. However, opinions differ on this matter depending on the researcher. The ages of Late Paleoproterozoic to Mesoproterozoic are dominant and reveal the age component of Neoproterozoic as well. The geochronology data from these two formations are similar, and such results lend weight to the possibility for correlation of these two strata. The presence of Mesoproterozoic detrital zircons found in the metasedimentary sequences of the Okcheon Metamorphic Belt is also the same as the Neoproterozoic sedimentary sequences in the southern margin of North China Craton. Taken together, I suggest that the correlation of the Okcheon Metamorphic Belt, at least in part, with the southern margin of the North China Craton, provides important clues in interpreting crustal evolution and tectonics on the Korean Peninsula., 新大院博(理)第470号}, school = {新潟大学, Niigata University}, title = {Isotopic and trace element geochemistry of the Hyangsanni Dolomite and its implications on the evolution of the Okcheon Metamorphic Belt, Korean Peninsula}, year = {} }