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This study presents new zircon LA-ICP-MS U–Pb ages, zircon Hf isotopes, and whole-rock geochemical compositions for Late Palaeozoic–Early Mesozoic intrusive rocks from the Erguna Massif, Northeast China. Zircon U–Pb dating results indicate that the intrusive rocks were emplaced during the Late Permian–Middle Triassic (ca. 256–234 Ma) and Late Triassic (ca. 210 Ma) in the western and eastern parts of the Erguna Massif, respectively. The Late Permian gabbros and quartz monzodiorites display enrichment in Rb and K, but are depleted in Nb, Ta, and Ti. Their εHf(t) values (+5.1 to +9.1 and −0.2 to +3.7, respectively) and one-stage Hf model ages (TDM1 = 544–704 Ma and 764–889 Ma, respectively) indicate that they might be derived from the reworking of the Neoproterozoic lithospheric mantle that was metasomatised by subduction-related fluids. The Late Permian–Early Middle Triassic quartz monzonites, monzogranites, and syenogranites display variable enrichment of rare earth elements (REEs) and large ion lithophile elements (LILEs). They have εHf(t) values varying from −5.7 to +2.7 with two-stage Hf model ages (TDM2) of 1.09–1.69 Ga, implying that they possibly originated from the Mesoproterozoic continental crust. The Late Triassic syenogranites show geochemical signatures of A2-type granites with various enrichment in LILEs and LREEs and depletion in Nb, Ta, and Ti. Combined with regional geological evidence, we conclude that Late Permian to Late Triassic igneous rocks on both sides of the Mongol–Okhotsk suture belt record an active continental margin environment associated with the ongoing bidirectional subduction of the Mongol–Okhotsk Ocean. The eastern Erguna Massif and Xing'an Massif were likely located in a back-arc setting at least since ca. 216 Ma, with long-term southward subduction of the Mongol–Okhotsk oceanic slab spanning from the Late Permian–Early Jurassic. [ABSTRACT FROM AUTHOR]

Abstract The tectonic setting and geodynamic processes of the large-scale Early Cretaceous volcanism in the Great Xing'an Range (GXAR) remain subjects of great debate. The aim of this review is to clarify these issues on the base of a study of previously published geochemical and isotopic data for this region. The compiled data show that the Early Cretaceous volcanic rocks were erupted from 145 to 106 Ma, with the main eruptive stage occurring from 130 to 122 Ma. The eruptions in the NE GXAR were generally later than those in the NW GXAR. The compiled geochemical and Sr-Nd-Pb isotopic data for the intermediate-basic volcanic rocks indicate a source in a mantle wedge that had been extensively metasomatized by fluids derived from an oceanic slab, whereas the acid rhyolitic rocks suggest multiple sources in a heterogeneous lower crust. Following our discussion of the possible geodynamic setting of this volcanism, we conclude that the large-scale Early Cretaceous volcanic event in the GXAR was dominated by the tectonic regime of the Mongol-Okhotsk oceanic plate, which broadly controlled the tectonic evolution of eastern Asia during the Mesozoic. We suggest that the rapid closure of the Mongol–Okhotsk Ocean during the Late Jurassic–Early Cretaceous resulted in the thickened continental lithosphere overriding at high velocity the cold subducting oceanic slab. These geological conditions, combined with the possible involvement of an oceanic plateau, might have resulted in the flat-slab subduction of the Mongol–Okhotsk oceanic plate beneath the Great Xing'an Range between ca. 150 and 140 Ma. Subsequent heating and dehydration of the oceanic slab, and its transition to the eclogite facies, led to the large-scale sinking of the slab and upwelling of the asthenosphere. This model not only explains the development of a broad (˜900-km-wide and ˜1700-km-long) intracontinental volcanic belt that erupted mainly between 130 and 122 Ma but also accounts for the chain of events that followed: a short and significant regional uplift between ca. 150 and 140 Ma, the contemporaneous foreland folding and thrusting, the basin-and-range-type extensional setting of NE China, and a magmatic gap in the northeastern part of the arc during the Early Cretaceous. [ABSTRACT FROM AUTHOR]