Juxtaposition of allochthonous terranes in the central Korean Peninsula: Evidence from zircon U-Pb ages and O-Hf isotopes in Jurassic granitoids

• Published in: Chemical geology Vol. 484; pp. 136 - 147
• Main Authors: Jo, Hui Je, Cheong, Albert Chang-sik, Yi, Keewook, Li, Xian-Hua
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-05-2018
• Subjects: Age pattern; Collisional orogeny; Hf isotope; Inherited zircon; Korean Peninsula; O isotope; Inherited zircon; Age pattern; Collisional orogeny; Hf isotope; O isotope; Korean Peninsula
• ISSN: 0009-2541; 1872-6836
• DOI: 10.1016/j.chemgeo.2017.10.006

The eventual docking of an exotic continental mass over the course of a Wilson cycle is marked by intracontinental sites of prograde metamorphism, contractional deformation, and syn- or post-collisional magmatism. This study shows that inherited premagmatic zircon in subsequently emplaced granitoid rocks provides another line of evidence for the collisional orogeny. Following the continental collision between the North and South China Cratons, Jurassic granitoids intruded widely throughout the central Korean Peninsula in association with the subduction of the Paleo-Pacific plate. The latest Early to Middle Jurassic (177–167Ma) granitoids occur throughout the cratonic Gyeonggi Massif, whereas Early Jurassic (194–184Ma) granitoids occur locally along the Okcheon Metamorphic Belt to the southeast of the massif. These two spatiotemporal groups differ profoundly in their age patterns and O-Hf isotopic signatures of inherited zircon. The younger group yields a typically North China-like Archean-Paleoproterozoic (mostly 2.5–1.8Ga) zircon inheritance. In contrast, inherited zircons from the older group exhibit exclusively Neoproterozoic (ca. 0.9–0.7Ga) and Paleozoic (ca. 0.4Ga) cluster along with Archean-Paleoproterozoic populations. The exotic feature of the protolith of the older group is further indicated by significantly lower δ18O (−0.9 to +4.9‰) and positive εHf (+3 to +15) values of the Cryogenian zircon cores. The results of zircon analysis demonstrate that South and North China-like terranes were juxtaposed infracrustally along the southeastern margin of the Gyeonggi Massif during the pre-Jurassic collisional orogeny, and then selectively provided major source material to the older and younger Jurassic granitoids, respectively.
•Zircons extracted from Jurassic granitoids in the central Korean Peninsula were analyzed.•The younger and older granitoid groups show contrasting age patterns of zircon inheritance.•Distinctly low δ18O and positive εHf of the Cryogenian zircon cores from the older group indicate a South China affinity.•These features support the juxtaposition between the allochthonous terranes along the SE margin of the Gyeonggi Massif.