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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]

Shihuiyao Rb–Nb–Ta-rich granites from the Late Jurassic period are newly discovered rare-metal-bearing granites found in the southern Great Xing'an Range, NE China. Further research of these granites may contribute to better understanding the petrogenesis of rare-metal granites and their associated mineralization mechanisms. The granites are high-silica (SiO2 = 73.66–77.08 wt%), alkali-rich (K2O + Na2O = 8.18–9.49 wt%) and weakly to mildly peraluminous with A/CNK values (molar ratios of Al2O3/(CaO + Na2O + K2O)) ranging from 1.06 to 1.16. High differentiation indexes (DI = 95–97) and low P2O5 contents demonstrate that Shihuiyao rocks are low-P and peraluminous rare-metal granites. Mineral chemistry and whole-rock geochemistry can be used to obtain the following lithological sequence: zinnwaldite granite, muscovite–zinnwaldite granite, amazonite-bearing granite and amazonite pegmatite. The effect of the rare-earth element tetrad; low K/Rb (18.98–32.82), Nb/Ta (2.41–4.64) and Zr/Hf (5.99–8.80) ratios; and the occurrence of snowball-textured quartz suggest that extreme magmatic fractionation might be the key factor that causes Rb–Nb–Ta enrichment. [ABSTRACT FROM AUTHOR]

The super-large Baerzhe Be–Nb–Zr–REE deposit in NE China is hosted in the Early Cretaceous peralkaline granites. In this work, the newly discovered granitic dikes developed around the Baerzhe deposit were studied for the first time, focusing on their genesis and genetic relationships with the Baerzhe peralkaline granites. Zircon U-Pb dating of these granitic rocks (including the granite porphyry, rhyolite and miarolitic granite) yielded Early Cretaceous ages of 125–121 Ma. Their mineral assemblages and geochemical features suggest that they share similar features with the peralkaline A-type granites. Their geochemical data and zircon Hf isotopic compositions (εHf(t) = +3.4 to +10.5) indicate that the peralkaline granitic rocks were formed by the partial melting of dehydrated charnockite with extensive plagioclase crystal fractionation, which resulted in a peralkaline affinity. There are two types of distinct zircons in the studied samples: the type I zircon with a bright rim and dark core, which may represent a cumulate mineral phase captured together with aggregates during eruption, and the type II zircon with a higher evolution degree crystallized in the residual melts. Combined with the simulation results using whole-rock trace elements, we proposed that the peralkaline granitic dikes represent more evolved interstitial melts than the Baerzhe granitic magma. In the Early Cretaceous extensional tectonic settings, mantle-derived magma upwelled, which induced the melting of the lower crust and prolonged the evolutionary process of the magma crystal mush. [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]

The Ordovician plutons in the Erguna Block, NE China, can be classified into two groups: Early Ordovician diorites with zircon U-Pb ages ranging from 486 to 485 Ma and Middle Ordovician gabbros and granites with zircon U-Pb ages ranging from 466 to 463 Ma. The diorites are calc-alkaline in nature and are characterized by weak to moderate enrichments of large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to high field strength elements (HFSE) and heavy rare earth elements (HREE). The gabbros and granites have high total alkali contents, and all samples are enriched in LREE and LILE and depleted in HFSE such as Nb, Ta, and Ti. Isotopically, Early Ordovician diorites display values that are less radiogenic [εHf(t) = + 9.9-+16.8] compared to those of Middle Ordovician gabbros [εHf(t) = − 3.0-+5.0]. Middle Ordovician granites have positive εHf(t) values of +1.4 to +4.3 and two-stage Hf model ages (TDM2) of 1167 to 1356 Ma. These data indicate that the diorites may have been generated by the partial melting of a recently metasomatized mantle source, whereas the gabbros and granites may have been formed by the partial melting of enriched lithospheric mantle and Mesoproterozoic crust, respectively. Our results, combined with other regional results, suggest that Early Ordovician magmatism was likely associated with the northward subduction of the Heihe-Xilinhot oceanic plate beneath the Erguna-Xing'an Block, whereas the Middle Ordovician gabbros and granites were most likely formed in an extensional setting controlled by the rollback of this subducted oceanic plate. [ABSTRACT FROM AUTHOR]

• A Late Jurassic porphyry Cu-Mo deposit in the Erguna Block is reported. • Ore-bearing rocks were derived from the partial melting of the oceanic slab. • Petrogenesis of ore-related rocks related to a flat-slab subduction. The genesis of igneous rocks associated with the newly discovered Xiaokele porphyry Cu-Mo deposit, located in the eastern Erguna Block, NE China, can give insights into the regional geodynamic evolution during the Late Mesozoic. Several ore-bodies have been identified in a granodiorite porphyry stock, which intruded the rhyolite and was subsequently intruded by diorite porphyry and granite porphyry. The U–Pb ages of zircons from rhyolite, mineralized granodiorite porphyry, diorite porphyry and granite porphyry associated with the Xiaokele deposit are 152.5 ± 1.7, 150.0 ± 1.6, 147.9 ± 1.3, and 123.2 ± 1.7 Ma, respectively. The rhyolite and granite porphyry have high SiO 2 and low MgO, Cr, Co, and Ni contents. Their isotopic data show negative ε Nd (t) values of −4.76 to −0.87, initial 87Sr/86Sr ratios of 0.7066 to 0.7134 and positive zircon ε Hf (t) values of 0.33–5.56, indicating that they were derived from a basaltic lower continental crust. The mineralized granodiorite porphyry is characterized by high Sr/Y values and low Y (3.7–8.0) contents, showing adakite affinity. The low K 2 O/Na 2 O (0.51–0.7) ratios, high CaO contents, weakly negative ε Nd (t) (−1.17 to −0.27), and low zircon ε Hf (t) (1.49–5.4) values from the adakitic samples indicate that they were derived from the partial melting of an altered oceanic slab together with assimilation of mantle peridotite and crustal materials. The 148 Ma diorite porphyry has high Mg# (51–58), weakly negative and positive ε Nd (t) (−0.09 to 0.01) values, and lower (87Sr/86Sr) i (0.7055–0.7057) ratios, suggesting an enriched mantle wedge source. Considering the late Mesozoic regional tectonic evolution of the Erguna Block and adjacent area, we propose that the formation of the Xiaokele deposit is linked to the southward flat-slab subduction of the Mongol–Okhotsk oceanic plate during the Later Jurassic-Early Cretaceous. [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]

• 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 petrogenesis and geodynamic implications of the early Paleozoic adakitic rocks in the North Qilian orogenic belt remain topics of debate. In this study, petrology, zircon U–Pb age and Lu–Hf isotopic composition, whole-rock geochemistry and Sr–Nd isotopes were carried on both low-Mg and high-Mg adakitic rocks from the North Qilian orogenic belt. These results will provide significant constraints on the evolution of the North Qilian orogenic belt. In general, the low-Mg adakitic granites mainly consist of plagioclase (50–55%), alkali feldspar (20–25%), quartz (20–25%) and biotite (5%). In contrast, the high-Mg adakitic granodiorites are generally composed of alkali feldspar (30–35%), plagioclase (30–45%), quartz (20–25%) and amphibole (∼10%). The low-Mg adakitic granitoids (446–457 Ma) are characterized by high SiO 2 (69–72 wt.%), low Mg # (39–42) and low Cr and Ni contents. However, the high-Mg adakitic granitoids (430–431 Ma) have relatively lower SiO 2 (65–66 wt.%), higher Mg # (50–59) and higher Cr and Ni contents. The low-Mg adakitic rocks have high initial 87 Sr/ 86 Sr ratios (0.7068–0.7080), negative ε Nd ( t ) (−2.3 to −3.3) and ε Hf ( t ) values (−6.8 to 1.9) with old zircon Hf model ages (1.2–1.6 Ga). However, the high-Mg adakitic rocks show lower initial 87 Sr/ 86 Sr ratios (0.7044–0.7066), higher ε Nd ( t ) (−1.8 to 3.0) and positive ε Hf ( t ) values (2.3–7.7) with younger zircon Hf model ages (0.9–1.1 Ga). These results suggest that the low-Mg rocks were generated by partial melting of thickened crust, whereas the high-Mg rocks were derived from anatexis of delaminated lower crust, which subsequently interacted with mantle magma upon ascent. The data obtained in this study provide significant information about the geological and tectonic processes after the closure of the Qilian Ocean. The continent–continent collision and thickening probably occurred during 440–467 Ma with formation of low-Mg adakitic rocks; and the transition of the tectonic regime from compression to extension probably occurred at ∼430 Ma with formation of high-Mg adakitic rocks. [ABSTRACT FROM AUTHOR]

The article focuses on the study with the relationship between metamorphism, anatexis, deformation and exhumation mechanism of ultra high-pressure (UHP) metamorphic rocks in collisional orogen. It mentions microscopic evidence for in situ partial melting, as well as the geochemistry, zircon and isotopic results of migmatite from the North Qaidam. It also mentions zircon crystallization from anatectic melt for petrogenesis and the dynamic mechanism of anatexis.