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New zircon U-Pb age data, Hf isotopes, whole-rock major and trace elements, and Sr-Nd isotopic data for Early-Middle Triassic intrusive rocks from the Jiawula and Tsagenbulagen area in the southern part of the Erguna Massif provide valuable constraints on the southward subduction of the Mongolia-Okhostk Ocean lithosphere. The Jiawula-Tsagenbulagen granitoids mainly consist of granodiorite, quartz monzonite, and biotite granite. These granitoids, long believed to be mainly Late Jurassic-Early Cretaceous (ca. 150-139 Ma) and minor Permian (ca. 278 Ma and 254-253 Ma), are newly found to contain a latest Early Triassic to Middle Triassic generation (zircon U-Pb age: ca. 248-244 Ma). Geochemically, the Early to Middle Triassic granitoids are characterized by high SiO 2 (74-77 wt.%) and Al 2 O 3 (12.2-15.95 wt.%), low Mg # values (12.98-37.32), and variable Na 2 O/K 2 O ratios (0.62-1.75). They are metaluminous to peraluminous and belong to the high-K calcalkaline series. Moreover, they show enrichment in light rare earth elements and large-ion lithophile elements and depletion in heavy rare earth elements and highfield-strength elements (e.g., Nb, Ta, and Ti). They have an increased amount of SiO 2 /Al 2 O 3 but lower V/Th ratios and negative correlations between V/Th and SiO 2 / Al 2 O 3 ratios, indicating that the magmas experienced various degrees of biotite and/or plagioclase fractional crystallization. Their whole-rock ε Nd (t) and zircon ε Hf (t)values ranged from +1.07 to +4.15 and from +0.5 to +2.9, respectively, indicating that the primary magmas were probably generated by partial melting of juvenile crustal material with the help of mantle-derived mafic magmas. These magmas subsequently underwent fractional crystallization, magma mixing, and a small amount of crustal contamination during their emplacement. The geochemical characteristics of these Early-MiddleTriassic intrusive rocks have affinities with intrusive rocks from active continental margin settings. Therefore, we conclude that the Early-Middle Triassic magmatism in the Erguna Massif was generated within an Andean-type arc setting related to the southwards subduction of the Mongol-Okhotsk oceanic plate beneath the Erguna Massif. We summarized previous age data of the Early to Late Triassic magmatic rocks from Erguna and Central Mongolia and identified arc setting granites and post-orogenic granites. Thus, a tectonic evolutionary model was proposed for the geological observations in the Erguna and Central Mongolia massifs, involving the Triassic continuous

The microgranular enclaves (MEs) and their host granitoids contain vital information on the genesis and evolution of the magma, especially for those which have close relationship with mineralization, yet remains a hot debate on their origin. Here, we investigate the MEs and their host granitoids in the Shuangjianzishan (SJZ) deposits, southern Great Hinggan Range, NE China, using ziron U-Pb dating and Hf isotopes, along with a systematic analysis of whole-rock geochemical and Sr-Nd isotopic compositions. The SJZ MEs mainly consist of monzonites and quartz monzonites, and the SJZ granitoids comprise a suite of fine-grained syenogranites and coarse-grained monzogranites. The zircon U-Pb dating results suggest that the SJZ granitoids and the SJZ MEs were emplaced at approximately 143-141 Ma. Geochemical features and isotopic compositions of the SJZ granitoids indicate that they are mainly generated by partial melting of juvenile lower-crustal basaltic rocks. The fine-grained syenogranites and the coarsegrained monzogranites have a gradual contact relationship, similar crystallization age, Sr-, Nd-, and Hf-isotopic compositions, suggesting that they were derived from a similar silicic magma reservoir. According to the geochemical compositions and petrographic characteristics (aggregates of coarse-grained euhedral plagioclase crystals) of the SJZ granitoids, we infer that the monzogranites (SiO 2 = 69.24-74.95 wt%) are regarded as the residual cumulate and the fine-grained syenogranites (SiO 2 = 74.83-77.97 wt%) are high silica melts segregated from a crystal mush. The SJZ MEs are characterised by low SiO 2 (50.03-64.20 wt%) and MgO (1.08-2.63 wt%) contents, high P 2 O 5 contents and contain acicular apatite, which are consistent with the products of intermediate magma.Combining with the MEs have comparable crystallization age, mineral assemblage, whole-rock Sr-Nd and zircon Hf-isotopic compositions with their host granitoids, implying the MEs were autoliths related to their host monzogranites. Collectively, we infer that the SJZ MEs were generated by the rapid cooling and crystallization of the hot ascending intermediate magmas contacted with the cooler wall rocks, then those subsolid fine-grained crystal-rich margins were fragmented and injected into the progressive evolved mush chamber, leading to the extraction and upward percolation of high silicic melts from the compacting crystal-rich mush in the shallow crust.

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