College of Earth Sciences, Jilin University, Changchun 130061, China

The authors report zircon U-Pb geochronological, whole-rock geochemical and zircon Lu-Hf isotope data for the hornblende gabbro within the Khanka Massif, with the aim of constraining its formation time and petrogenesis. The zircon U-Pb dating shows that ²⁰⁶Pb/²³⁸Pb ages of zircons from the hornblende gabbro range from 120 to 129 Ma, yielding a weighted mean age of 123±2 Ma, i.e., the Early Cretaceous. The hornblende gabbro has SiO₂ of 44.77%-46.58% and belongs to the tholeiitic series on FeO^t/MgO-SiO₂ diagram. It displays a right-inclined REE pattern with (La/Yb)_N ratios of 3.44 to 4.42. The trace element spidergram shows that they are enriched in large ion lithophile elements (LILE) such as Rb, Th, U, K and Pb, and depleted in high field strength elements (HFSE) such as Nb, Ta, Ti and P, indicating an affinity to arc igneous rocks. The ε_Hf(t) values of zircons vary from -2.6 to +3.9 and Hf model ages (T_DM1) range from 622 to 883 Ma. These geochemical characteristics indicate that primary magma of the hornblende gabbro could be derived from partial melting of young mantle material accreted during the Neoproterozoic. Combined with the Early Cretaceous igneous rock assemblages in NE Asia. It is concluded that the hornblende gabbro formed in an active continental margin related to the westward subduction of the Paleo-Pacific Plate beneath the Khanka Massif.