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

Magmatic response to the interplay of collisional and accretionary orogenies in the Korean Peninsula: Geochronological, geochemical, and O-Hf isotopic perspectives from Triassic plutons

“…In this study, we found inherited zircon cores from five granitoid samples (Seosan and Namyang granites from the western Gyeonggi Massif, Yangpyeong monzonite from the central Gyeonggi Massif, and Hamyang granodiorite and Sangju granite from the Yeongnam Massif). Their age patterns are shown in Figure 9, together with those of the inherited zircon cores from the Jurassic granitoids in the Gyeonggi Massif and the Okcheon Belt (Jo et al, 2018). As shown in this figure, the age pattern of the zircon inheritance differs profoundly between the western Gyeonggi Massif and the Yeongnam Massif.…”

“…This range cannot be explained by the evolution of the North China crust, which has a zircon Hf model age typically between 3.4 and 2.7 Ga (Geng et al, 2012;Kim et al, 2014), but is most strongly correlated with ε Hf (t) values of the Neoproterozoic (780-750 Ma) rocks in the northern and western margins of the Yangtze Block in South China (~11-2; Liu et al, 2009;Zheng et al, 2007). Jo et al (2018) suggested that mixing between this Neoproterozoic component with near chondritic ε Hf (t = Jurassic), and the Archean-Paleoproterozoic component with significantly negative ε Hf (t = Jurassic) resulted in a diverse range of Hf isotopic compositions of the magmatic zircons in the Early Jurassic granitoids. In summary, the inherited zircon data of the Triassic and Jurassic granitoids collectively indicate that the infracrustal basements of the interior Gyeonggi and Yeongnam massifs and the marginal parts of the Gyeonggi Massif (the western Gyeonggi Massif and the Okcheon Belt) were composed of North Chinaand Yangtze-like terranes, respectively.…”

“…The exotic feature of the protolith of the Early Jurassic granitoids was further highlighted by the significantly low δ 18 O values 4.9 to -0.9‰) of Cryogenian (ca. 750-700 Ma) zircon cores (Jo et al, 2018). Neoproterozoic rocks and zircons from South China, especially from the northern margin of the Yangtze Block, commonly have δ 18 O values substantially lower than the normal mantle range (5.3 ± 0.3‰; Valley et al, 1998), possibly resulting from the hightemperature reaction of their source rocks with glacial water (Zheng et al, 2008, and references therein).…”

“…Neoproterozoic rocks and zircons from South China, especially from the northern margin of the Yangtze Block, commonly have δ 18 O values substantially lower than the normal mantle range (5.3 ± 0.3‰; Valley et al, 1998), possibly resulting from the hightemperature reaction of their source rocks with glacial water (Zheng et al, 2008, and references therein). Jo et al (2018) therefore interpreted that the geochronological and oxygen isotopic contrasts of inherited zircon cores observed between the Early and Middle Jurassic granitoids resulted from selective contributions from South and North China-like terranes that had been juxtaposed infracrustally along the margin of the Gyeonggi Massif during the prior collisional orogeny.…”

“…The zircon ε Hf (t) and δ 18 O values of the Triassic plutons are plotted against their corresponding crystallization ages in Figure 10. In this figure, O and Hf isotope data for the inherited zircon cores from the Jurassic granitoids (Jo et al, 2018) are also shown for reference. Although the Cryogenian oxygen isotopic feature was not observed in the Neoproterozoic zircon cores from the Triassic Seosan and Namyang granites (δ 18 O = 8.4-6.9‰), zircon Hf isotopes reveal the fundamental difference in the evolutionary history of the crustal source between granitoid rocks in the western Gyeonggi Massif and the Okcheon Belt, and those in the interior Gyeonggi and Yeongnam massifs.…”