ABSTRACT

A detailed geochemical and isotopic study was performed on the Ogcheon amphibolites from the central Ogcheon Belt, Korea, to investigate the source characteristics and petrogenesis. Major and trace element data indicate that the parental rocks of the amphibolites are mostly transitional basalts, except for a few tholeiitic basalts. The tholeiitic basalts are less enriched in incompatible elements than transitional basalts and are geochemically close to primary magmas. Some transitional basalts with low SiO₂ (<45 wt%) and high Fe₂O₃ (>16 wt%) are clearly distinguished from others and are believed to be derived from a ferro-basaltic magma. On the basis of several contamination parameters (e.g., La/Nb ratio, Nb/Th ratio, Nb and Ta anomaly), we suggest that crustal contamination has not significantly influenced the chemistry of the amphibolites. All amphibolite samples are moderately enriched in incompatible elements and plot in within-plate fields on a number of tectonic discriminant diagrams, and are consistent with previous works. The parental magmas of the amphibolites were derived from a heterogenous mantle source. Sm-Nd isotope whole rock data define a poor linear array. Considering variations in incompatible elements and Nd isotopes, the linear array may be not a true isochron but rather a mixing pseudoisochron due to source heterogeneity.