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To determine the emplacement age, petrogenesis, and geodynamic setting of the Xizhelimu diorite in Keyouzhongqi, Inner Mongolia of northeastern China, a detailed study of the petrography, geochronology, and whole-rock geochemistry has been conducted. Geological and petrographic studies show that the Xizhelimu diorite is zoned: the central lithofacies zone is composed of medium-fine-grained monzodiorite and quartz diorite, and the marginal lithofacies zone is fine-grained diorite. The zircon U–Pb dating results show that the ages of the central and marginal facies are 133.5 ± 1.9 and 133.4 ± 1.4 Ma, respectively. The whole-rock rare earth and trace element characteristics of the Xizhelimu diorite show an O-type adakite affinity. Combining the analysis of zircon Hf isotope composition (εHf(t) values of +7.7 to +10.0), the geochemical features of whole rock, and the results of partial melting modeling, we suggest that the parental magma of the Xizhelimu diorite was derived from the partial melting of altered oceanic crust mixing with subducting sediments at shallow depths. In the early stage of early Cretaceous, the Xizhelimu diorite originated in an extensional setting, mainly related to the closure of the western part of the Mongol–Okhotsk Ocean. The upwelling asthenospheric flow in this extensional setting induced partial melting of the paleo-oceanic crust to form the parental magma of the Xizhelimu diorite. [ABSTRACT FROM AUTHOR]

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]

• Xinlin ophiolitie indicates an ocean between Erguna and Xing'an blocks. • Zircon U–Pb age of 669 Ma for gabbro pegmatite constrains the age of Xinlin ophiolite. • Xinlin ophiolite was accreted onto the Erguna Block due to westward subduction. The Xinlin ophiolite in northeastern China marks the Xinlin–Xiguitu branch of the Paleo-Asian Ocean (PAO), and provides an opportunity to reconstruct the evolution of the Xing'an–Mongolian orogenic belt (XMOB). The main ophiolitic body is composed of mantle peridotites, mafic and ultramafic cumulates, isotropic gabbros, diabase dykes, and massive basaltic lava flows, from base to top. The uppermost pelagic sediment cover is missing and was presumably eroded. The cumulate gabbro yields a concordant zircon U–Pb age of 669 ± 8 Ma and has positive zircon ε Hf (t) values (+10.7 to +15.6). The mafic rocks of the ophiolite have rare earth element (REE) patterns that plot between the compositions of normal (N-) and enriched (E-) mid-ocean ridge basalt (MORB). The monzogranite that intruded into the Xinlin ophiolite yields a narrow age range (574–571 Ma), and is enriched in light REE and depleted in high field strength elements (HFSE). Zircon grains from the monzogranite have negative ε Hf (t) values (−5.6 to −10.0), suggesting the monzogranite was formed by partial melting of the Erguna continental crust, rather than oceanic crust. The geochemical characteristics of the ophiolite and spatially associated younger arc granites show that the Xinlin ophiolite developed at a mid-ocean ridge setting, and was subsequently accreted onto the Erguna continental margin before amalgamation with the Xing'an Block. [ABSTRACT FROM AUTHOR]

The subduction processes and geodynamic scenarios of the late-stage southward subduction of the Mongol–Okhotsk oceanic slab since the Early Jurassic are subjects of great debate. This contribution presents new U–Pb zircon dating, trace element geochemistry, Ti-in zircon geothermometry, and Lu–Hf isotopes of zircon, as well as bulk-rock geochemical data for Early–Middle Jurassic intrusive rocks in the Erguna Block, NE China. Approximately 181–198 Ma monzogranites and ca. 162–174 Ma quartz monzonites were identified in the block. The Early Jurassic monzogranites are high-K calc-alkaline I-type granites, which display moderately concave-upward rare earth element (REE) patterns with slightly negative Eu anomalies, and low zircon crystallization temperatures. The Middle Jurassic quartz monzonites have low Yb and Y concentrations, high Sr/Y ratios, and strong high field strength elements (HFSEs) depletions, that are in excellent agreement with adakitic rocks. They exhibit right-sloping REE patterns with negligible Eu anomalies, and a wide range of zircon crystallization temperatures. The intrusions yield εHf(t) values between −4.1 to +4.8 and juvenile two-stage model (TDM2) ages varying from 918–1488 Ma. The geochemical and isotopic signatures suggest that the monzogranites were likely derived by the partial melting of K-rich meta-basalts within the lower part of a juvenile crust that had medium-thickness (≤40 km), with the involvement of minor mantle materials. Whereas, the quartz monzonites were possibly produced by partial melting of a thickened continental lower crust (≥50 km). The Mongol–Okhotsk tectonic regime played a dominant role in accounting for their formation. An Andean-type continental arc setting was developed during the Early–Middle Jurassic, with gradual thickening of the continental crust. The significant crustal thickening may reach its ultimate stage at ca. 162–174 Ma, which marks the tectonic transition from compression to extension. The southward subduction beneath the Erguna Block was continuous and stable during the Early Jurassic. Rollback of the subducted slab occurred at ca. 174–177 Ma, followed by moderate magmatic activities represented by adakitic rocks. [ABSTRACT FROM AUTHOR]

Highlights • Grenvillian orogeny of Rodinia in Oulongbuluke Block systematically investigated. • Metabasite, augen granitic gneiss, paragneiss ages of 1132 ± 33, 1118 ± 9, 1124 ± 12 Ma. • Peak metamorphic P-T conditions of 4.8–5.8 kbar and 652–700 °C. • Metabasites resemble the geochemical characteristics of Andean arc magmatism. • Oulongbuluke Block likely temporarily connected to Qilian Block and Tarim Craton. Abstract A systematic petrologic, geochemical, and zircon U-Pb and Lu-Hf isotopic investigation of an ∼1.1 Ga arc magmatism and metamorphism was studied to evaluate the Grenvillian orogeny and assembly of Rodinia in the Oulongbuluke Block in NW China. The peak metamorphic P-T conditions of the paragneiss were restricted to 4.8–5.8 kbar and 652–700 °C based on P-T pseudosection and conventional geothermobarometry. Zircon U-Pb ages of 1132 ± 33 Ma, 1118 ± 9 Ma, and 1124 ± 12 Ma were determined for the metabasite, augen granitic gneiss, and paragneiss, respectively, indicating magmatic intrusion and a metamorphism event in the late Mesoproterozoic. The metabasites exhibited enrichment of light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) and depletion of heavy rare earth elements (HREEs) and high-field-strength elements (HFSEs), resembling the geochemical characteristics of Andean arc magmatism. The whole-rock geochemistry and in-situ zircon ε Hf (t) values of 4.3 and 11.2 suggested that the protolithic mafic magma originated from a subduction-modified lithospheric mantle. The low zircon ε Hf (t) values of −5.2 and −0.5 also suggested that the calc-alkaline augen granitic gneisses were derived from the partial melting of a late Paleoproterozoic crustal source. The ∼1.1 Ga arc-related magmatism and metamorphism in the Oulongbuluke Block indicated the occurence of a tectonic-thermal event in an Andean-type active continental margin in the late Mesoproterozoic. In this regard, the Oulongbuluke Block was likely temporarily connected to the Qilian Block and Tarim Craton, forming a single continuous block with similar Grenville age during the late Mesoproterozoic to early Neoproterozoic (1.1–0.9 Ga). [ABSTRACT FROM AUTHOR]