Petrogenesis of three Cretaceous granites in the Okcheon Metamorphic Belt, South Korea: Geochemical and Nd–Sr–Pb isotopic constraints

Abstract

The Sokrisan, Weolaksan and Muamsa granites in the Okcheon Metamorphic Belt (OMB), Korea are among the representative Cretaceous granites in the Korean Peninsula. Major and trace elements, and Sr–Nd isotopic data for the three granites are reported for evaluating the source characteristics and petrogenesis. The Sokrisan and Weolaksan granites are complexes of batholith type, most of which consists of biotite granite, whereas the eastern part of the body consists of hornblende–biotite granite. The Muamsa granite is a biotite granite of stock type. The three granites all have miarolitic texture suggesting that they belong to shallow intrusive type. The Muamsa granite has a Rb–Sr whole-rock age of 88.2 ± 1.7 Ma (2 σ) with an initial Sr isotopic ratio of 0.7139 ± 0.0041 (2 σ), whereas the Weolaksan granite has 89.6 ± 2.2 Ma (2 σ) with an initial Sr isotopic ratio of 0.7132 ± 0.0014 (2 σ). Recalculated Rb–Sr whole-rock age of the Sokrisan granite is 94.8 ± 3.6 Ma (2 σ) with an initial Sr isotopic ratio of 0.7084 ± 0.0029 (2 σ). The three granites have high SiO 2, FeO t/MgO, K 2O + Na 2O, and LREE contents and Rb. They are mostly depleted in Ba, Sr, P 2O 5 and TiO 2 with strongly negative Eu anomalies. The geochemical characteristics of the granites suggest mixed type of A-type and highly fractionated granite. The ε Nd( T) of the granites ranges from − 13.3 to − 15.8. The Rb–Sr whole-rock age, consistent negative values of ε Nd( T), trace element variations and consistent REE patterns from the three granites indicate that they might have been derived from a chemically similar crustal source. In tectonic discrimination diagrams, the granites fall in the range of syn-collisional to within-plate granites. The chondrite-normalized REE patterns and spider diagrams normalized by primitive mantle are similar to those of anorogenic A-type granites which were produced during the Late Yanshanian orogeny in SE China. However, negative initial ε Nd( T) values reveal that source material of the three Cretaceous granites in the OMB should be different from those of SE China.