SHRIMP U-Pb ages and Hf isotopic composition of the detrital zircons from the Myogok Formation, SE Korea: development of terrestrial basin and igneous activity during the early Cretaceous

Abstract

To constrain sedimentation age of the Myogok Formation and timing of the last episode of the Daebo orogeny, SHRIMP U-Pb age determination and Hf isotopic studies were carried out for the zircon separates. The detrital zircon U-Pb ages of the Myogok Formation show a wide range from Archean to Cretaceous and yield four main clusters at age intervals of 130–150 Ma, 170–220 Ma, 221–320 Ma and Paleoproterozoic. Such age clusters indicate that the main provenance rock types during the sedimentation were basement rocks of the Yeongnam massif and the Mesozoic granitoids distributed around the Myogok Formation. The concordia age of the youngest population is 138.6 ± 2.1 Ma (n = 7), indicating the possible maximum deposition age for the Myogok Formation. Considering the suggestion of probable deposition of Nakdong Formation during the Barremian (Lee et al., 2012), the Valanginian or Hauterivian seems to be the most appropriate timing for the deposition of the Myogok Formation. The last activity of the Daebo orogeny might be constrained to Hauterivian or Barremian considering some time lag needed for basin closure and deformation that followed. The measured eHf(t) values from the detrital zircons of the Myogok Formation vary from −25.7 to 4.8. However, most of the zircons, even those with Mesozoic ages, show negative values except a few, implying dominant influence of old continental crusts in the generation of their igneous protoliths.