Chronology and Geochemistry of Mesozoic Volcanic Rocks in the Linjiang Area,Jilin Province and their Tectonic Implications

Zircon U‐Pb ages and geochemical analytical results are presented for the volcanic rocks of the Naozhigou, Ergulazi, and Sidaogou Formations in the Linjiang area, southeastern Jilin Province to constrain the nature of magma source and their tectonic settings. The Naozhigou Formation is composed mainly of andesite and rhyolite and its weighted mean ²⁰⁶Pb/²³⁸U age for 13 zircon grains is 222±1 Ma. The Ergulazi Formation consists of basaltic andesite, basaltic trachyandesite, and andesite, and six grains give a weighted mean ²⁰⁶Pb/^Z38U age of 131±4 Ma. The Sidaogou Formation consists mainly of trachyandesite and rhyolite, and six zircon grains yield a weighted mean ²⁰⁶Pb/²³⁸U age of 113±4 Ma. The volcanic rocks have SiO₂= 60.24%–77.46%, MgO = 0.36%–1.29% (Mg^#= 0.32–0.40) for the Naozhigou Formation, SiO₂= 51.60%–59.32%, MgO = 3.70%–5.54% (Mg^#= 0.50–0.60) for the Ergulazi Formation, and SiO₂= 58.28%–76.32%, MgO = 0.07%–1.20% (Mg^#= 0.14–0.46) for the Sidaogou Formation. The trace element analytical results indicate that these volcanic rocks are characterized by enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), relative depletion in heavy rare earth elements (HREEs) and high field strength elements (HFSEs, Nb, Ta, and Ti), and negative Eu anomalies. Compared with the primitive mantle, the Mesozoic volcanic rocks in the Linjiang area have relatively high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7053–0.7083) and low ?_Nd(t) values (?8.38 to –2.43), and display an EMU trend. The late Triassic magma for the Naozhigou Formation could be derived from partial melting of a newly accretional crust with the minor involvement of the North China Craton basement and formed under an extensional environment after the collision of the Yangtze Craton and the North China Craton. The Early Cretaceous volcanic rocks for the Ergulazi and Sidaogou Formations could be formed under the tectonic setting of an active continental margin related to the westward subduction of the Izanagi plate.