Within the Western slope of the Southern Urals, there are plenty of basite dyke complexes of Riphean to Vendian among Precambrian terrigenous-carbonate formations. In metamorphic formations of the Taratash complex (Archean to Early Proterozoic, the northern closure of the Bashkirian meganticlinorium) there was observed the andesitic dyke with isotopic age of 71±1 Ma (U-Pb SHRIMP II on zircons) and near Bakal two bodies of gabbroids with zircons of similar ages were found. These are the first evidence of possible Mezozoic magmatism in this region.
Carbonate formations of the Cambro-Ordovician Period occur in the Taebaek and Jeongseon areas, located in the central–eastern part of the Korean Peninsula. This study analyzed the rare earth element (REE) contents and Sr–Nd isotope ratios in these carbonates to elucidate their depositional environment and diagenetic history. The CI chondrite-normalized REE patterns of the carbonates showed negative Eu anomalies (EuN/(SmN × GdN)1/2 = 0.50 to 0.81), but no Ce anomaly (Ce/Ce* = CeN/(LaN2 × NdN)1/3 = 1.01 ± 0.06). The plot of log (Ce/Ce*) against sea water depth indicates that the carbonates were deposited in a shallow-marine environment such as a platform margin. The 87Sr/86Sr ratios in both Taebaek and Jeongseon carbonates were higher than those in the seawater at the corresponding geological time. The 87Sr/86Sr ratios and the values of (La/Yb)N and (La/Sm)N suggest that the carbonates in the areas experienced diagenetic processes several times. Their 143Nd/144Nd ratios varied from 0.511841 to 0.511980. The low εNd values and high 87Sr/86Sr ratios in the carbonates may have resulted from the interaction with the hydrothermal fluid derived from the intrusive granite during the Cretaceous Period.
REE and Sr–Nd Isotope Characteristics of Cambrian–Ordovician Carbonate in Taebaek and Jeongseon Area, Korea
