REE and Sr-Nd Isotope Characteristics of Cambrian-Ordovician Carbonate in Taebaek and Jeongseon Area, Korea

초록

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 (Eu-N/(Sm-N x Gd-N)(1/2) = 0.50 to 0.81), but no Ce anomaly (Ce/Ce* = Ce-N/(La-N(2) x Nd-N)(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 Sr-87/Sr-86 ratios in both Taebaek and Jeongseon carbonates were higher than those in the seawater at the corresponding geological time. The Sr-87/Sr-86 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 Nd-143/Nd-144 ratios varied from 0.511841 to 0.511980. The low epsilon(Nd) values and high Sr-87/Sr-86 ratios in the carbonates may have resulted from the interaction with the hydrothermal fluid derived from the intrusive granite during the Cretaceous Period.

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