The Mesozoic tectonic architecture of the Korean peninsula is largely governed by the continental collision between the North and South China blocks. Zircon Hf isotopic compositions presented in this study and whole-rock geochemical and SrNd isotope data in the literature collectively suggest that the lithophile-elements-enriched signature of the Late Triassic post-collisional plutons from the Gyeonggi massif in central Korea is a primary feature inherited from the metasomatized mantle lithosphere. Highly negative zircon e Hf (t) values (À23 to À19) of plutons from the middle and eastern parts of the massif indicate an ancient metasomatism of their mantle source. Distinctly higher zircon e Hf (t) values (À15 to À12) from the southwestern plutons are ascribed to a contribution from an accreted component of the South China-like block. The involvement of asthenospheric mantle is not recognized in zircons from either group. The implications of these isotopic features are discussed in the context of Mesozoic collisional tectonics.

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Zircon oxygen-hafnium and biotite magnesium isotopic compositions of Late Cretaceous to Oligocene (88-27 Ma) granitoids from the Gyeongsang continental arc, southeastern Korea, collectively provide a new insight into shallow magma petrogenesis. Zircon crystals extracted from eight calc-alkaline or alkaline plutons commonly contain xenocrystic cores and typically show magmatic cathodoluminescence zonings and sharp Raman spectra. Most zircons have positive e Hf values plotting below the mid-ocean-ridge basalt evolution path, indicating that the arc magmatism was dominated by the recycling of juvenile crustal materials. Zircon d 18 O values shifted upward or downward from the mantle range attest to the O isotopic exchange of crustal protoliths with surface waters at various temperature conditions. Small (<1‰) but discernable core-to-rim decreases of d 18 O values are recognized selectively in magmatic zircon grains from four plutons possessing biotite d 26 Mg values (-0.07‰ to +2.32‰) distinctly higher than the mantle range. Such a concomitant O-Mg isotopic variation provides compelling evidence for a series of self-induced hydrothermal alteration and assimilation processes (i.e ., "crustal self-cannibalization"). This study shows that the supracrustal input to magmas in a young and juvenile orogen can be traced effectively by the combination of stable isotope records from the plutonic root.