Mangerite magmatism associated with a probable Late-Permian to Triassic Hongseong-odesan collision belt in South Korea

摘要

The Odesan area in the eastern Gyeonggi Massif, South Korea, consists principally of migmatitic and porphyroblastic gneisses intruded by mangerite. Mafic mangerites with SiO2 contents from 52.40 to 54.20 wt.% have higher FeO*+MgO (14.98-18.28 wt.%) and CaO contents (5.80-7.84 wt.%) but lower total alkali contents (4.74 < Na2O+K2O < 5.80 wt.%) than felsic mangerites (55.9 < SiO2 < 60.61 wt.%, 9.51 < FeO*+MgO < 11.62 wt.%, 3.28 < CaO < 5.68 wt.%, 6.72 < Na2O+K2O < 8.05 wt.%). Fe-numbers (FeO*/[MgO+FeO*]) are 0.44-0.47 for mafic mangerites and 0.38-0.42 for felsic mangerites. The mangerites show calc-alkaline affinities in an AFM plot and resemble high-Ba-Sr granitoids with low Rb/Sr ratios of 0.25-0.10. Their MORB-normalized compositions show enrichment in LILE (decoupled LIL/HFS pattern) and negative anomalies in Ti-Nb-Ta. Their geochemical characters are consistent with their formation by partial melting of a basaltic source at temperatures higher than 1025 degrees C. The mangerites of the present study differ from mangerite formed in a typical within-plate tectonic setting in their high mg# and Sr concentrations and negative Nb and Ta anomalies. Their LILE enrichment and negative Ti-Nb-Ta anomalies could well have been inherited from a pre-collision subduction event. A mean U-Pb zircon age of 257 Ma for the mangerite demonstrates that the tectonic belt connecting the Hongseong and Odesan areas represents a probable extension of the late Permian-Triassic collision belt between the North China and South China blocks into South Korea, with collision occurred earlier in South Korea. (c) 2005 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.