SOUTHWARD SUBDUCTION HISTORY OF THE MONGOL-OKHOTSK OCEANIC PLATE BENEATH THE ERGUNA MASSIF: EVIDENCE FROM IGNEOUS ROCKS IN NE CHINA

New zircon U–Pb dating, Hf isotope, major and trace elements, and Sr–Nd isotope data for Early Triassic-Early Jurassic intrusive rocks in the Erguna Massif of NE China are reported, to constrain the tectonic evolution of the southward subduction of the Mongol–Okhotsk oceanic plate and its influence on NE China. Zircon U–Pb dating indicates that Early Triassic–Early Jurassic magmatisms in the Erguna Massif can be subdivided into four stages: ~246 Ma, ~225 Ma, ~205 Ma, and ~185 Ma. The ~246 Ma intrusive rocks comprise a suite of high-K calc-alkaline diorites, quartz-diorites, granodiorites, monzogranites, and syenogranites. They formed in an active continental margin setting related to the southwards subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Massif. The ~225 Ma intrusive rocks consist of gabbro–diorites and granitoids, displaying a typical bimodality. They formed under an extensional environment during the intermission of subduction of the Mongol–Okhotsk oceanic plate. The ~205 Ma intrusive rocks are dominated by the granitoids, with subordinate intermediate and mafic rocks. The ~205 Ma intrusive rocks formed in an active continental margin setting with regional extension related to the southwards subduction of the Mongol–Okhotsk oceanic plate. The ~185 magmatic event is composed mainly of basalt-basaltic andesite-andesite belonging chemically to calc-alkaline series as well as monzogranite. These igneous rocks, together with coeval porphyry-type ore deposits, formed under an active continental margin setting. Taking all this into account, we conclude that (1) the southwards subduction of the Mongol–Okhotsk oceanic plate beneath the Erguna Massif took place in three times (~246 Ma, ~205 Ma, and ~185 Ma) during Early Triassic–Early Jurassic; and (2) the subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif not only caused the intense magmatism, but also was favorable for the formation of porphyry-type ore deposits.