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Abstract ▼ AI-Helper

U-Pb age determination was performed on the zircon fractions separated from the metamorphic rocks of three locations of the Gyeonggi Massif. The ages obtained from the upper and lower intersections between concordia curve and discordia lines made of the zircon fractions separated from the rocks of e...

U-Pb age determination was performed on the zircon fractions separated from the metamorphic rocks of three locations of the Gyeonggi Massif. The ages obtained from the upper and lower intersections between concordia curve and discordia lines made of the zircon fractions separated from the rocks of each locality we: $2168\pm$24 Ma and $1227\pm$40 Ma for the Yongduri Gneiss Complex, $1955\pm$22 Ma and $493\pm$32 Ma for the Euiam Group, and $3712\pm$244 Ma and $1613\pm$51 Ma for the Yongmunsan Group (2$\sigma$ errors). The upper intercept ages from the Yongduri Gneiss Complex and the Euiam Group of Gyeonggi massif are very similar to those obtained from the granitic gneisses and the porphyroblastic gneisses of Yeongnam massif respectively. Such similarities suggest that Gyeonggi and Yeongnam massifs might situate under the similar tectonic and geographic environment during ca. 2.2-1.9 Ga. The upper intercept age of Youngmunsan Formation (3.7 Ga) shows large error, because most of the zircon fractions are plotted very close to the lower intersection. It is necessary to investigate further to confirm this age. However, It may suggest the possibility of occurrence of the oldest crust of the northeast Asia similar to the one reported recently from the northeast China. The lower intercept age of the Yongmunsan Group is interpreted to indicate strong metamorphism. Such age postdates the 1.85-1.7 Ga metamorphism and igneous activities occurred in the Yeongnam massif, which might record the late Paleoproterozoic tectonic activities simultaneously occurred in both massifs.

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