A Jurassic Metamorphic-Anatectic Event in the Jiaodong Peninsula, Eastern China: Zircon and Titanite U-Pb Ages of Migmatites and Their Implications

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Migmatite, generated from anatexis or partial melting, links metamorphism with magmatism and can be used to investigate the source of magmas. Zircon and titanite, as refractory minerals in migmatite, can illuminate both the conditions of partial melting and the sources of associated granites. Mesozoic granitoids in the Jiaodong Peninsula, eastern China, have been studied extensively for their origins as partial melts of the lower continental crust. However, Jurassic metamorphism and partial melting of their hypothesized parent rocks have rarely been reported and discussed. In this study, we investigated the morphology, interior structure, U-Pb geochronology, and trace element compositions of zircon and titanite from diverse migmatites in the Yantai-Rushan area of the Jiaodong Peninsula. For leucosomes, inherited metamorphic and magmatic (or anatectic) zircon cores yield Paleoproterozoic ages, indicating a North China affinity; in contrast, anatectic zircon domains with high rare earth element concentrations show Jurassic ages of 160–154 Ma. For mafic melanosomes, metamorphic zircon and titanite yield ages of 154–149 Ma and c. 150 Ma, respectively; in contrast, two inherited metamorphic zircons record Triassic ages, suggesting an affinity with the ultrahigh-pressure rocks in the Sulu orogen. For granites, the oldest age of anatectic zircons is 175 Ma. Altogether, these data demonstrate a long-lived (c. 25 Myr), Jurassic, metamorphic-anatectic event in the Jiaodong Peninsula. These new findings prove that three lithotectonic units—the Jiaobei terrane, Sulu orogen, and preexisting granites in the Jiaodong Peninsula—were all sources for protracted Jurassic partial melting. This study deepens our understanding of the links between metamorphism and magmatism in demonstrating the diverse rock types that simultaneously source granites.