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The relationship between Sn–Ag mineralization and mantle magmatism is a topic of high interest in current ore deposit research. Here, we investigate porphyry-, skarn-, and cassiterite-sulfide type Sn-polymetallic deposits associated with granitoids and vein-type Ag–Pb–Zn deposits hosted in sub-volcanic rocks in the southern Great Xing'an Range (SGXR), northeast China, as a case example. We use He, Ar, and S isotopes and isotopic end-member simulation calculations to determine the contribution of mantle-derived fluids/melts to the ore mineralization. Our He–Ar isotope data demonstrate that the ore-forming fluids are mixtures of shallow crust-derived fluid containing radiogenic 4He but no radiogenic 40Ar and magmatic fluids with mantle-derived 3He and 40Ar. The Pb–Zn–Ag deposits have a higher contribution of magmatic volatiles than the Sn-polymetallic deposits. Sulfide δ34S values of − 2.7 to − 0.6‰ in the Pb–Zn–Ag deposits are consistent with a magmatic sulfur source, whereas sulfides with δ34S values of − 12.2 to − 0.15‰ in the Sn-polymetallic deposits signal a possibly bimodal source of sulfur, i.e., crustal light sulfur mixed with magmatic sulfur. The noble gas compositions of the ore fluids are controlled by crustal thickness, high 3He fluxes (24 to 404 at/s/cm2), and low residence time (1 to 18 Myr) of He in the asthenosphere below the SGXR. Non-equilibrium open-system magma degassing is evidenced by the range of elevated values of 4He/40Ar* ratios (4.8–127). The 3He/heat ratio of the ore fluids from the Sn and Pb–Zn–Ag deposits overlap (0.01–0.76 × 10−2 cm3 STP J−1 (cubic centimeter at standard temperature and pressure per joule) and 0.02–1.08 × 10−2 cm3 STP J−1, respectively), indicating a consequence of conduction of mantle-derived heat across the magma-hydrothermal interface. Furthermore, an increasing abundance of Sn reserves in the SGXR deposits can be equated with an increase in the mantle-derived He component in the ore fluids. These findings suggest that a continuous flux of mantle-derived fluids/melts plays an essential role in Sn–Ag–Pb–Zn mineralization. [ABSTRACT FROM AUTHOR]

Halogens and other volatiles are widely recycled into the deep mantle by subduction and are key components to metasomatize the sub-continental lithospheric mantle (SCLM). Lamprophyres are well known to be rich in volatiles and are important for understanding the halogen characteristics of the metasomatized SCLM and/or the mobilization of halogens during the ascent of such volatile-rich, low-degree partial melts. The North China Craton (NCC) hosts lamprophyre dikes coeval with extensive thinning of the eastern NCC in the Mesozoic and generated from lithosphere metasomatized by multiple-stage subduction components. Here we report bulk-rock heavy halogens (Cl, Br, and I) of 16 lamprophyres from the eastern NCC. The bulk-rock halogen concentrations are overall very low (Cl = 58–170 μg/g, Br = 285–559 ng/g, and I <5 ng/g), comparable with depleted Mid-Ocean ridge basalts (N-MORBs). Volatile-rich minerals (e.g., amphibole and biotite) are abundant (20–30 vol%) in these lamprophyres, however, electron probe microanalyses (EPMA) data indicate that amphiboles are mainly rich in OH and F but display very low Cl concentrations (0.01–0.04 wt%). The bulk rock and amphibole data consistently indicate low abundances of heavy halogens in the lamprophyres, which is dificult to reconcile with the remarkable enrichment of fluid-mobile large ion lithophile elements such as Ba, Rb, and K. Based on low Cl/Nb and Br/Nb but high Ba/Nb and K/Nb ratios, the low halogen concentrations likely resulted from extensive volatile loss (>90%) during melt ascent. The low Cl concentrations in early-stage amphiboles (Mg# 60–64) further indicate that such loss would have occurred before amphibole crystallization at a depth of ~15 km. We thus propose that crystallization of early olivines and pyroxenes and reaction with surrounding mantle rocks likely induced volatile saturation and exsolution, leading to strong partitioning of the halogens into the exsolved aqueous volatile phases and thus the extensive loss of halogens from the rising melt. These results reveal that significant volatile loss of halogens not only occurs during surficial low-pressure eruption but also at much deeper levels in the crust, as also identified for some kimberlites. Consequently, it would be dificult to constrain the primitive halogen components of the mantle sources via lamprophyres or similar magmas. [ABSTRACT FROM AUTHOR]

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Most porphyry Cu deposits are formed in magmatic arc settings, but some occur in non-arc environments, such as intracontinental settings. The petrogenesis of fertile magmas for porphyry Cu deposits formed in intracontinental settings is still ambiguous. To address this issue, we performed an integrated study of the late Mesozoic porphyry Cu deposits in the South Qinling Orogenic Belt. Zircon U–Pb ages indicate that these late Mesozoic porphyry Cu deposits were formed at 149–142 Ma, in a postcollisional intracontinental setting. εNd(t) (− 4.5 to − 2.7), initial 87Sr/86Sr (0.7046 to 0.7084), and zircon εHf(t) values (− 3.8 to + 2.2) of the late Mesozoic ore-forming and barren rocks suggest that both originate from Meso-Neoproterozoic juvenile lower crust. Whole-rock geochemical and isotopic characteristics indicate that the ore-forming rocks could be formed by the delamination of thickened juvenile lower crust or by the reaction of mantle with normal juvenile lower crust. The barren rocks could be formed by the partial melting of thickened or normal juvenile lower crust. Whole-rock petrochemistry and reversed anorthite contents and Sr isotope data of zoned plagioclase crystals indicate that the mafic magma was recharged into the ore-forming magma chamber. Due to the injection of mafic magma, the ore-forming rocks obtained higher oxygen fugacity, volatiles, water, sulfur, and Cu contents than the barren rocks. According to the regional tectonic evolution, the late Mesozoic porphyry Cu deposits in the South Qinling Orogenic Belt were formed in an extensional environment due to transformation of the tectonic regime. Large-scale lithospheric extension caused asthenospheric mantle upwelling and crust-mantle interaction, providing the crucial metallogenic conditions. Moreover, the injection of mantle-derived mafic magma into the normal magma is a key factor in the formation of the late Mesozoic porphyry Cu deposits in the SQB and similar porphyry systems in an intracontinental setting. [ABSTRACT FROM AUTHOR]

• Chemistry indicates that most Jiande peridotites were formed by mild to moderate degrees of mantle partial melting. • The South China Block crust and mantle were coupled during the Mesoproterozoic formation in the breakup of the Columbia supercontinent. • Minor early Paleoproterozoic mantle fragments are possibly linked to ancient crust-mantle differentiation events or asthenospheric mantle heterogeneities. Fresh mantle peridotite xenoliths entrained in the Eocene Jiande alkaline basalts from western Zhejiang Province, South China Block (SCB), offer an opportunity to elucidate the compositional and temporal relationships between the subcontinental lithospheric mantle (SCLM) and its overlying crust. The Jiande peridotites (20 lherzolites + one harzburgite) exhibit tightly correlated and relatively fertile whole-rock major element compositions (WR Mg#=89.0–90.8), indicating mild to moderate degrees (mostly ≤ 10 %) of mantle partial melting and limited metasomatism experienced by the Jiande SCLM. The above mantle processes are further underscored by: 1) the nearly unfractionated highly-siderophile-element (HSE) relative abundances ((Pd/Ir) N = 0.81–1.37, normalized to primitive-upper-mantle values); 2) the robust positive correlations observed between 187Os/188Os (0.1196–0.1283) and 187Re/188Os ratios (0.112–0.451; R2 = 0.79), and Al 2 O 3 contents (1.5–3.8 wt%; R2 = 0.85) across the majority of high-187Os/188Os samples. Both Re-Os (initial 187Os/188Os = 0.1172) and Al-Os isochrons (initial 187Os/188Os = 0.1181) also yield an age of ∼ 1.4 Ga for the predominant melt depletion event that shaped the formation of the Jiande SCLM, aligning well with the peak of two-stage depleted mantle Hf model ages of the SCB crustal rocks. This age-coupled crust-mantle differentiation event occurring in the Mesoproterozoic may have been controlled by tectonic-magmatic processes during the breakup of the Columbia supercontinent. In addition, two low-187Os/188Os (0.1108–0.1128) samples with ∼ 15–20 % melting degrees ((Pd/Ir) N = 0.15–0.30) show the oldest Re-depleted Os model ages (2.2 and 2.4 Ga) among all the reported SCB mantle peridotites. These older SCLM materials may represent remnants linked to earlier crust-forming events that were incompletely reworked or replaced. Alternatively, they could represent mantle heterogeneity inherited by the newly formed lithospheric mantle during the Mesoproterozoic era. [ABSTRACT FROM AUTHOR]

The North Qaidam subduction-collision zone is a typical Alpine-type ultra-high pressure (UHP) metamorphic zone due to the Early Palaeozoic subduction of the Qaidam Block beneath the Oulongbuluke Block, with an integrated record of oceanic subduction, continental subduction, collision, and exhumation to post-collisional extensional collapse. In this study, systemic petrology, zircon U-Pb geochronology, Hf isotopic data and whole-rock geochemical analyses have been carried out for granitoids in the North Qaidam UHP metamorphic units to determine their petrogenesis and further reveal the tectonic evolution of the continental collision orogen. Zircon U-Pb dating yields weighted mean ages of 433 ± 2 Ma, 351 ± 8 Ma, 416 ± 4 Ma, 389 ± 3 Ma and 383 ± 1 Ma, with the εHf(t) values of the latter three ages ranging from −2.4 to 3.3, −5.9 to 1.1 and −3.3 to 2.4, respectively. Based on field relationship, petrological, geochronological, and geochemical results, these granitoids could be divided three groups. The early group granodiorites (~433 Ma) show a marked chemical resemblance to adakites: (1) high La/Yb and Sr/Y ratios, with low Y and HREE values; (2) high Al2O3 and low Mg#, Cr, and Ni values with obvious positive Eu anomalies. Petrological and geochemical characters indicate that the early group adaktic granodiorites may be derived from partial melting of metabasite in a thickened mafic lower crust. The middle group granites (~416 Ma) have an affinity to I-type granitoids, characterized by high Na2O contents (>4.18 wt.%) and low A/CNK values, which were probably generated by partial melting of felsic gneiss of subducted continental crust. The late group granites (389 ~ 351 Ma) are also I-type granitoids, which were originated from partial melting of Mesoproterozoic crust, with minor mantle material input. According to a comprehensive study of these granitoids, along with regional geological background and HP-UHP metamorphism, a four-stage evolutionary process of the North Qaidam UHP metamorphic belt from oceanic subduction, continental subduction, collision to extensional collapse is proposed. After the final closure of the Proto-Tethys Ocean, the subducted continental crust experienced HP-UHP eclogite-faces metamorphism (460 ~ 430 Ma), and thickening of the lower crust lead to generation of adakites and S-type granites. Following break-off of the subducting oceanic slab (425 ~ 400 Ma), the reduction in negative buoyancy caused the exhumation of deeply subducted continental crust accompanied by associated anataxis and syn-collisional I-type granitoids, representing the transition in tectonic regime from compression to extension. Due to the tectonic transition, mantle-derived intrusions and post-collisional granitoids were emplaced during 400 ~ 350 Ma. Simultaneously, the pronounced decreasing in La/Yb and Sr/Y ratios of magmatic rocks (age of 460 ~ 350 Ma) suggested that the crustal thickness decreased gradually from syn-collisional to post-collisional stage. [ABSTRACT FROM AUTHOR]

Element geochemistry, Sr and Nd isotope, and LA-ICP-MS zircon U-Pb isotope data have been obtained for the granitoids of Dazesan pluton in the Jiaodong Peninsula, East China, and their intermediate microgranular dark enclaves so as to reveal their petrogenesis and tectonic implications. These granitoids have high SiO2 (68.25–71.56 wt.%), K2O (3.44–5.50 wt.%), total alkalis (K2O + Na2O = 7.29–9.00 wt.%), Sr (451–638 ppm), Ba (1157–2842 ppm) and light rare earth elements (LREEs) (131.57–210.08), with strong depletion both in heavy rare earth element (HREE) and high field strength element (HFSE) concentrations as well as unclearly Eu anomalies, showing typical signatures of high Ba-Sr granitoids. They possess high (La/Yb)N (32–50) and Sr/Y (50–79) values and low MgO (0.76–1.11 wt.%), Cr (9.9–19.6 ppm) and Ni (4.51–7.04 ppm) concentrations. All the above geochemical compositions are similar to those of late Early Cretaceous granitoids, in combination with zircon LA-ICP-MS U-Pb ages of 119.6 ± 1.3 to 120 ± 1 Ma for these granitoids obtained in this study, indicating c. 120 Ma probably represents the lower limit of ages when late Early Cretaceous granitoids emplaced in the Jiaodong Peninsula. The microgranular dark enclaves, forming a linear trend with their host granitoids on the oxide against SiO2 plots, display higher MgO contents of 3.05–4.39 wt.% at lower SiO2 concentrations of 54.25–56.84 wt.% and possess a zircon LA-ICP-MS U-Pb age of 119 ± 2 Ma, identical to those of these granitoids, indicating the acid magma and intermediate magma were coeval. Furthermore, dark enclaves and their host granitoids have indistinguishable (87Sr/86Sr)i values of 0.709523–0.70972 and 0.709361–0.709858, respectively, and plot within a two-liquid immiscible field on the Greig pseudoternary phase diagram. In addition, they have markedly parallel REE patterns, with the dark enclaves having much greater REE and HFSE abundances than those of their host granitoids. Therefore, it is suggested that liquid immiscibility is a viable model to explain the chemical compositional variations between the Dazeshan granitoids and their dark enclaves. Based on the element geochemistry, geochronology and Sr- and Nd-isotope of the Dazeshan granitoids and their dark enclaves, it is envisaged the crust-derived acid melts due to partial melting of ancient continental lower crust in the Jiaodong Peninsula (mainly Neoarchean-Palaeoproterozoic basement in the Jiaobei terrane) containing a subduction-related material, resulting from the addition of the enriched subcontinental lithospheric mantle-derived melts, assimilated the lithospheric mantle-derived basic melts and formed the homogeneous magma chamber at the crust base, then split into two immiscible liquids, with one granitic liquid producing the Dazeshan granitoids and the other intermediate one forming the dark enclave during its ascent. Combined with previous studies, the identification of a lithospheric mantle-derived material in the Dazeshan granitoids suggests a catastrophic lithospheric thinning at c. 120 Ma, reflecting an abrupt change in the direction of Palaeo-Pacific plate subducting and the corresponding regional tectonic transition from E–W extension to NW–SE extension. [ABSTRACT FROM AUTHOR]

The geochemistry of arc rocks provides a window to probe compositional variability in mantle wedge and slab-derived inputs. However, quantitative estimation of their contribution is a great challenge. Here we report an integrated study for determination of variable contributions to early Paleozoic arc plutons (the Mafan diorites and gabbros), from the northern Hong'an orogen, central China. Zircon grains from the diorites yielded crystallization age of 445 ± 3 Ma, whereas the gabbros have zircon U Pb age of 432 ± 3 Ma. Although both the two mafic rocks suites exhibit typical arc-like trace element distribution patterns, they show a series of differences in stable Li–Mo–O and radiogenic Sr–Nd–Hf isotope compositions, as well as major and trace element features. Geochemically, the diorites are medium-K calc-alkaline series with high and positive whole-rock ε Nd (t) (+3.8 to +4.5) and zircon ε Hf (t) values (+12.4 to +14.3), and normal mantle-like zircon δ18O values (5.1 ± 0.2 ‰). Contrarily, the gabbros are tholeiitic and have relatively low whole-rock ε Nd (t) (+ 2.3 to +3.1) and zircon ε Hf (t) (+5.0 to +8.5) values with normal mantle-like zircon δ18O values (5.4 ± 0.3 ‰). The diorites have δ98Mo values of −0.15 to −0.03 ‰, while the gabbros have δ98Mo values of −0.28 to −0.12 ‰. These values are slightly higher than those of the mid-ocean ridge basalts (MORB) (−0.20 ± 0.01 ‰). Whereas, δ7Li values of the studied diorites (2.15–4.49 ‰) and gabbros (2.89–5.33 ‰) are mostly consistent within the range of MORB. In combination with the above results, the primary magma of diorites was inferred to be derived from 1 to 5% partial melting of depleted lithospheric mantle metasomatized by slab-derived fluid with minor sediment-derived melts. While the gabbros were suggested to be generated by 5–10% partial melting of more depleted lithospheric mantle that had undergone perhaps extra 0.3% melt extraction, which had further been metasomatized by more subducted materials. In summary, both the slab-derived components and nature of the mantle wedge sources are quantitatively constrained for the mafic rocks in the Mafan plutons. Our new data suggest that the Mafan plutons exhibited the Mariana arc-affinity and represented products of an intra-oceanic subduction system in the northern Hong'an orogen. Combined with previously published data for the early Paleozoic mafic magmatic rocks along the Qinling-Tongbai-Hong'an orogenic belt, there exists an oceanic arc in the east (Hong'an orogen) and an Andean-type continental arc in the west (Qinling-Tongbai orogen). • The Mafan plutons are composed of diorites (ca. 445 Ma) and gabbros (ca. 432 Ma) with systematically geochemical variations. • Both more depleted mantle wedge and more slab-derived materials metasomatized are required for generating the Mafan gabbros. • The Mafan plutons represented products of an intra-oceanic subduction system. [ABSTRACT FROM AUTHOR]

Despite being volumetrically minor components, carbonate-rich ultramafic magmas like aillikites represent good candidates to investigate the compositional variations in plume and/or lithospheric mantle sources because they represent low-degree melts which preferentially sample highly fusible components including recycled crustal material. To gain new insights into the composition of the plume-related magmas and, more broadly, the petrogenesis of ultramafic lamprophyres, we have undertaken the first comprehensive study of bulk rock and mineral (olivine and Ti-magnetite) highly siderophile element (HSE) abundances and Re-Os isotopes combined with in situ major-, trace-element and Sr-Nd isotope analyses of apatite and perovskite from the Permian Wajilitag aillikites of the Tarim large igneous province, China. The Wajilitag aillikites have high PPGE (Pt and Pd) contents relative to IPGE (Os, Ir and Ru), which can be ascribed to low-degree partial melting and/or fractionation of olivine and laurite. Measured 187Os/188Os ratios are moderately to highly radiogenic (0.186–0.313) with age-corrected γOs values up to +113. In situ Sr and Nd isotope analyses of apatite phenocrysts (87Sr/86Sr (i) = 0.70349–0.70384; εNd (i) = +1.3 to +4.9) and fresh perovskite grains (87Sr/86Sr (i) = 0.70340–0.70390; εNd (i) = +1.3 to +3.8) exhibit limited variability both within and across samples from different aillikite dykes and the only volcanic pipe in the area. These Nd isotopic values resemble those from bulk-rock samples (εNd (i) = +1.9 to +5.2), whereas Sr in apatite and perovskite extends to marginally less radiogenic values than the bulk-rock compositions (87Sr/86Sr (i) = 0.70362–0.70432). The moderately depleted Sr-Nd isotope compositions of magmatic apatite and perovskite, and the previously reported mantle-like C isotope values of these samples suggest that the aillikites and their carbon probably derived from a sub-lithospheric (plume) source with minimal contribution of deeply subducted material. Conversely, the radiogenic Os isotope compositions of the Tarim aillikites and separated minerals require some contribution from recycled crustal material in the plume source. Mass balance calculations suggest that the radiogenic Os isotopes and moderately depleted Sr-Nd isotopes can be reproduced by less than one third of eclogite component addition to a moderately depleted mantle source. We conclude that the combination of complementary isotopic systems can enlighten contributions from different components to mantle-derived magmas and, in this case, clarifies the occurrence of carbon-free subducted oceanic crust in the Tarim plume. [ABSTRACT FROM AUTHOR]

Detrital zircon U–Pb ages and Lu–Hf isotopes of three metasandstone samples from the recently identified Caiziyuan‐Tongan accretionary complex (CTAC) in the southwestern Yangtze Block are presented. The detrital zircons are characterized by high Th/U ratios, oscillatory zoning, and nonabrasive crystal shapes, implying that these metasandstones in the CTAC were dominantly derived from proximal magmatic sources. The detrital zircon age spectrum shows three prominent intervals of 2.8–2.6 Ga, 2.5–2.2 Ga, and 2.1–1.7 Ga with minor dispersions between 3.8 and 2.9 Ga, matching well with those of the exposed magmatic rocks in the Yangtze Block. Two samples show consistent youngest age peaks at ~1.72 Ga, but the remaining sample has the youngest age peak at ~1.56 Ga, indicative of their differences in depositional ages. The Eoarchean zircons have negative εHf(t) values with Hadean depleted mantle two‐stage (TDM2) model ages, indicating the earliest crustal growth of the Yangtze Block in the Hadean. The Mesoarchean to Neoarchean zircons show both negative and positive εHf(t) values, suggesting a prolonged and complicated crustal reworking and growth process. By contrast, the Paleoproterozoic zircons have dominantly negative εHf(t) values, suggestive of extensive crustal reworking in response to the Nuna supercontinent assembly. Available detrital zircon TDM2 model ages from the southwestern Yangtze Block produce three prominent peaks at ~3.06 Ga, ~2.95 Ga, and ~2.84 Ga, suggesting significant crustal growth pulses in the Mesoarchean. Given that the ~1.38 Ga Caiziyuan SSZ‐type ophiolitic mélange and the complex tectonothermal evolution process, we deduce that the CTAC belt may represent a relict suture zone between micro‐blocks in the Yangtze Block and may have witnessed the Nuna breakup and subsequent Rodinia assembly. [ABSTRACT FROM AUTHOR]

Rare earth elements and Yttrium (REYs) are critical to the emerging high-tech and green-energy industries, generating tremendous REY demand in recent decades. Recently, many sedimentary phosphorites have been reported to have extraordinary REY enrichment (> 1000 ppm) and may become new REY resources. However, the controls of REY enrichment in phosphorites have not been well constrained. To better understand the discrepant REY enrichment in phosphorites, the early Cambrian high-REY Zhijin (ZJ) phosphorites (∼500–2000 ppm) and the relatively low-REY Meishucun (MSC, ∼200–400 ppm) and Xia'an (X'A, mostly < 200 ppm) phosphorites on the Yangtze Block of South China were investigated with mineralogy, bulk-rock elements, total organic carbon, in-situ elements, and Zn-Fe isotopes. The mineral characteristics, REY indexes, and in-situ REY mapping indicate that the X'A phosphorites may represent pristine phosphorites, whereas the ZJ and MSC phosphorites may have experienced intensive diagenetic alteration. Diagenetic alteration can only explain the REY enrichment in the MSC phosphorites compared to the pristine X'A phosphorites, but it does not sufficiently explain the extraordinary REY enrichment in the ZJ phosphorites. Additionally, the lower δ66Zn values of the ZJ and X'A phosphorites (δ66Zn average = 0.16‰ and 0.14‰, respectively) than those of the MSC phosphorites (δ66Zn average = 0.75‰) indicate higher productivity levels in the ZJ and X'A areas. However, the high-productivity X'A phosphorites yielded very low REY concentrations, indicating that the extraordinary REY enrichment in the ZJ phosphorites cannot be ascribed to high productivity levels. Notably, the ZJ phosphorites may have experienced more intensive Fe redox cycling under fluctuating oxic–suboxic deposition conditions (∼0.0‰–0.45‰ δ56Fe values in near-pure phosphorites) than the MSC and X'A phosphorites with completely oxic deposition conditions (∼0.0‰ δ56Fe values). Frequent Fe redox cycling can greatly enrich REYs in porewater, which can be subsequently transferred into francolites during its formation and early diagenesis. Therefore, frequent Fe redox cycling driven by fluctuating oxic–suboxic seawater conditions may be responsible for the extraordinary REY enrichment in the ZJ phosphorites. If this is the case, we propose that phosphorites deposited near the oxic–suboxic redox chemocline are favorable for extraordinary REY enrichment, such as the coeval near-slope phosphate concretions on the Yangtze Block and other phosphorites or phosphatic rocks formed in different basins at different geological times. [ABSTRACT FROM AUTHOR]

Alkaline basalts occur widely in intraplate settings and carbonate-bearing mantle sources such as carbonated peridotites are increasingly regarded to play a key role in their formation. Carbonated eclogites, most likely the products of subducted carbonate-bearing altered oceanic crust, are probable alternative ingredients in the mantle sources of many intraplate alkaline basalts, highlighting the importance of the subduction-driven deep carbon cycle. However, this widely proposed hypothesis remains enigmatic because the recognition of low-MgO primitive alkaline basalts predicted by experiments is scarce. Here we show that Cenozoic continental intraplate alkaline basalts occurring above the stagnant oceanic slab in the mantle transition zone beneath the Hannuoba region, eastern China, display geochemical features consistent with their origin as low-degree partial melts of carbonate-bearing eclogites. Their MgO contents correlate positively with CaO, Ba/Th and Ti/Eu, but negatively with Dy/Yb and ε Nd. Remarkably, the most primitive alkaline basalts are characterized by low MgO (<5.25 wt.%), low heavy rare earth elements and Sc contents, low CaO/Al 2 O 3 (<0.41), low Ti/Eu (<3380), but Dy/Yb (>7.1) higher than those of ocean island basalts (OIBs). These features cannot be ascribed to differentiation from high-MgO alkaline basalts because significant amounts of crystallization of clinopyroxene and garnet did not occur during ascent. Differentiation also cannot account for the correlations of time-integrated Sr-Nd isotopes with MgO, Dy/Yb and Ba/Th. Instead, the linear correlations mainly reflect strong interaction between ascending primitive alkaline melts and the lithospheric mantle. The compositions of primitive alkaline basalts reflect the key control of garnet and clinopyroxene in the mantle residue (eclogites), and the Ti, Zr and Hf anomalies further indicate the critical effect of carbonates in the eclogite source. Partial melting of the carbonate-bearing eclogites likely occurred in the uppermost asthenosphere. The production of alkaline basalts with low MgO contents by partial melting of carbonate-bearing eclogite below the peridotite solidus in an intraplate setting has been overlooked and the magmas were instead often considered to be highly evolved. Recycled altered oceanic crust thus may not only cause metasomatism of the deep mantle but may also serve as a direct source of mafic melts. These results on natural rocks support the experiment-based model for subducted altered oceanic crustal material and also indicate its diverse fate in the mantle. [ABSTRACT FROM AUTHOR]

The Neoproterozoic granites along the western margin of the Yangtze Block are crucial for understanding the evolution of the Rodinia supercontinent and crust–mantle interaction. Based on a regional geological survey, this study analyses the zircon U–Pb geochronology, Lu–Hf isotope, whole‐rock Sr–Nd isotopes, and geochemistry of the Maoniushan granites along the western margin of the Yangtze Block and discusses the Neoproterozoic tectonic evolution history of the Mianning–Maoniushan belt. The results show that the Maoniushan granites belong to calc‐alkaline weak peraluminous monzogranite. The granites are enriched in large‐ion lithophile elements (i.e., Rb, Sr, Cs, and Ba) but relatively depleted in high‐field‐ strength elements (i.e., Nb, Ta, U, and Th). The zircon saturation temperature (TZr) ranges from 628 to 766°C, and the weighted average 206Pb/238U ages of zircon range from 771 ± 30 to 759 ± 26 Ma. The εHf(t) values range from −2.0 to +7.2, with TDM2 model ages ranging from 1,797 to 1,208 Ma. The whole‐rock Sr–Nd isotopic data show (87Sr/86Sr)i ratios of 0.7039–0.7093, and the εNd(t) values range from +1.25 to +1.76 with TDM2 model ages ranging from 1,303 to 1,344 Ma. These findings indicate the presence of deep Mesoproterozoic crustal materials in the source area. The Maoniushan monzogranites belong to I‐type granite, which is formed by the partial melting of the basic rocks and pelites in the ancient lower crust due to the metasomatism of fluids from the subducted oceanic crust. The Maoniushan monzogranites may be formed in the process of transformation from regional thickening to thinning under the oceanic crust subduction setting. [ABSTRACT FROM AUTHOR]

The Permian mafic dykes of Santanghu Basin offer an opportunity to study the nature of mantle source and tectonic setting of the basin, as well as to provide the theoretical basis for structural transformation of East Junggar region. In this study, zircon U–Pb geochronology, mineral composition analysis, whole‐rock elemental, and Sr‐Nd isotopic geochemistry were conducted to explore the origin and evolution of the primitive magma. LA‐ICPMS zircon U–Pb dating yields ages at 269 Ma. The elemental geochemistry results suggest enrichments in Ba, Pb, and Sr but depletions in Nb, Ta, Zr, and Hf, which indicate that the magma source was influenced by fluid metasomatism. All samples show moderate initial Sr‐Nd isotope results ((87Sr/86Sr)I = 0.704299 to 0.704490 and εNd(t) = +6.16 to +6.83) and have high Sm/Yb ratios, which suggest that the diabases were derived from partial melting of 5%–7% spinel‐garnet Iherzolite lithospheric mantle. Combined with petrological, geochronological data, and the regional tectonic background, it is interpreted that the diabases from Santanghu Basin originated from lithospheric mantle metasomatized by subduction fluids under the background of intracontinental extension. [ABSTRACT FROM AUTHOR]

High‐K calc‐alkaline granitoids play a key role in understanding the formation and evolution of the continental crust. Herein, we present new laser ablation inductively coupled plasma mass spectrometry zircon U–Pb and Lu–Hf isotopic, whole‐rock geochemical and Sr–Nd isotopic data of early Jurassic high‐K calc‐alkaline granitoids in the Zhanggunagcai Range, NE China. In situ zircon U–Pb dating shows that the granodiorite‐monzogranite‐granite (GMG) suite was emplaced at ca. 192–187 Ma. They are high‐K calc‐alkaline and weakly peraluminous, similar to the geochemical characteristics of I‐type granites. The GMG suite has lower bulk‐rock initial 87Sr/86Sr ratios of 0.7037–0.7042, slightly positive εNd(t) values of +1.10 to +1.87 and highly positive zircon εHf(t) values of +5.3 to +10.9. This result suggests a major contribution of juvenile crust to the magma source. The tetrad rare earth element patterns and highly negative Eu anomalies of samples with high SiO2 contents indicate that fractional crystallization plays an important role in the genesis. Together with data in the literature, we infer that the early Jurassic granitic rocks have been formed by partial melting of juvenile arc crust associated with the westward subduction of the Paleo‐Pacific Plate. [ABSTRACT FROM AUTHOR]

The process of continental growth and closure of the Paleo‐Asian Ocean are controversial. To address this problem, we report new geochemical and geochronological data of granitic rocks along a N‐S corridor of the Dananhu arc. These rocks yield 401–270 Ma U‐Pb zircon ages. The arc‐related granites are enriched in the light rare earth elements (LREE), Rb, Ba, Th, Sr and Pb, but depleted in Nb and Ta, and have high zircons values of εHf(t) (+7.7−+19.6) and εNd(t) (+5.4−+7.2); they were possibly generated by partial melting of juvenile intermediate or mafic arc crust. A 356 Ma high‐K calc‐alkaline granite has high Ga/Al (3.28–3.37), low Mg# (14–16), and high zircon εHf(t) (+8.9−+12.0); it can be classified as A2‐type‐granite, suggesting it was a product of substantial fractional crystallization of a mantle‐derived arc‐related magma in an intra‐arc extensional setting. The youngest granite (254 Ma) is an adakite‐like granite which is characterized by high Sr/Y (26–38), depletion in heavy rare earth elements (HREE), and high εNd(t) (+7.0) and εHf(t) (+10.4 to +15.4) values, most likely it was derived from a subducted oceanic slab. Therefore, all the granitic rocks formed in subduction‐related settings. The granitic rocks are generally young southwards from the Kezier area (ca. 401–335 Ma) to the Tuwu area (334–315 Ma), and to the Kanguer area (ca. 280–254 Ma), indicating that the arc grew southwards, and the Paleo‐Asian Ocean closed possibly after 254 Ma. Therefore, our data provide a robust constraint on the prolonged growth of the Altaids. Plain Language Summary: The continental growth mechanism and closure time of the Paleo‐Asian Ocean in the Altaids are global research hotspots. The arcs (especially the intra‐oceanic type) in the Paleo‐Asian Ocean are the essential accretionary component in the Altaids, however, detailed knowledge of the growth processes of the arcs that generated the different types of magmatism is still insufficient. The voluminous, continuous, and well‐exposed granitic rocks in the Dananhu arc provide an ideal opportunity to study the complicated processes of subduction and evolution of the southern Altaids. We report geochemistry and geochronology of granitic rocks along a N‐S corridor of the Dananhu intra‐oceanic arc in the Eastern Tianshan (NW China), southern Altaids. These I‐type, A2‐type and adakite‐like subduction related granitic rocks were emplaced from Devonian (ca. 401 Ma) to Latest Permian (ca. 254 Ma) with a general younging southward, indicating a complex episodic switch of subduction processes from the Devonian to Late Permian. Our results suggest that the arc grew southwards by retreat and rollback of the Kanguer oceanic plates where overall compressional and extensional events alternated, and the closure time of the Paleo‐Asian Ocean was possibly after 254 Ma. Key Points: The subduction related granites are a general southward younging southward from Devonian (ca. 401 Ma) to Latest Permian (ca. 254 Ma)The arc grew southwards by retreat and rollback of the Kanguer oceanic plates where overall compressional and extensional events alternatedThe continental growth accompanied with volumes of granitic rocks and Paleo‐Asian Ocean possibly closed after 254 Ma in the southern Altaids [ABSTRACT FROM AUTHOR]

The uplift history of northeastern Asian continental margin has been the subject of much debate. The Sanjiang Basin is an ideal area to investigate the uplift history of this margin. We present new data from sandstone petrology, whole-rock geochemistry, U–Pb geochronology and Hf isotopy of detrital zircons to trace the provenance of the basin and to unravel the uplift history of the northeastern Asian continental margin. We investigated the chemical and plagioclase indices of alteration and index of compositional variability (CIA, PIA and ICV, respectively) in samples from two formations. The geochemical proxies indicate that source rocks were subjected to an intensified weathering process. Based on the high SiO2/Al2O3 values and low K2O, we infer that the two basinal strata experienced silicification and insignificant potassium metasomatism. Sandstone petrography is indicative of low degrees of sedimentary sorting, suggesting a proximal deposition. The provenance fingerprints of light rare earth, high-field-strength and transition metal elements indicate that parts of the provenance included recycled sediments, and that first-cycle sediments were derived mainly from felsic rocks with a minor contribution from intermediate and mafic rocks. The combined detrital zircon U–Pb ages and Hf isotopic results constrain the contributions of different source terranes over time. The provenance results, in combination with seismic profile interpretations from the Sanjiang Basin, suggest that the northeastern Asian continental margin experienced at least three stages of uplift, which were driven by subduction initiation of the Paleo-Pacific Ocean during the Jurassic Period, a plate motion change during the Early Cretaceous Epoch, and a shallowing of the slab dip angle during the Late Cretaceous Epoch. [ABSTRACT FROM AUTHOR]

The mechanisms and processes by which subducted slab interacted with mantle plume remain controversial, as direct observation of such interaction is difficult to impossible. Compositional heterogeneity of large igneous provinces (LIPs) additionally makes plume-slab interaction hard to detect. Oxygen isotopes are sensitive enough to trace the source of magmas. Here we provide evidence for plume-slab interaction mainly based on in situ zircon Hf-O isotope analyses, as well as whole-rock elemental and Sr-Nd-Hf isotope analyses, on the Late Permian and Early Triassic A-type granites on the margin of the Emeishan LIP in SW China. These granites show typical A-type geochemical characters, such as high total alkali (7.93-9.68 wt%) and field strength element (HFSE, e.g., Zr and Nb) contents, and high FeOT/(FeOT+MgO) (0.87-0.98) and Ga/Al (3.67-5.06) values. The Late Permian (ca. 259 Ma) and Early Triassic (ca. 248 Ma) granites show high Nb/Th (>3.0) and low Y/Nb (<1.2) and Yb/Ta (<2.0) ratios similar to the oceanic island basalts and have near-zero εNd(t) (-0.83 to -0.13 and -0.15 to +0.16, respectively) and depleted εHf(t) (+2.71 to +3.39 and +2.62 to +3.55, respectively). In situ zircon O-Hf analyses yielded anomalously low δ18O (0.2-2.0‰ and 3.2-4.8‰, respectively) and positive εHf(t) (1.6-7.0 and 3.9-8.8, respectively), suggesting varying proportions of hydrothermally altered oceanic crust in their source region. Our results imply that significant amounts of altered Paleotethyan oceanic crust have been subducted in the upper mantle beneath the western South China Block. The nearby rising Emeishan mantle plume may have rapidly entrained and incorporated these oceanic crustal materials to the shallow mantle so that their low-δ18O isotope feature was preserved. Subsequent decompression-related partial melting of this hybrid source formed parental rocks of the low-δ18O A-type granites. Our findings also suggest that LIPs could obtain their compositional (especially oxygen isotope) diversity through the interaction between the subducting slab and rising mantle plume. [ABSTRACT FROM AUTHOR]

The magmatic processes beneath the active continental margins are very complicated and affect structures and compositions of the arc roots. Neoproterozoic igneous rocks are widely distributed around the margins of the Tarim Block in NW China. The Xingdier mafic-ultramafic intrusion is a composite body, located at the northern margin of the Tarim Block, and consists of gabbro, pyroxenite, and peridotite units. The gabbro unit has a secondary ion mass spectrometry zircon U-Pb age of 727 ± 5 Ma. Rocks from the Xingdier intrusion have a large range of MgO (12.9--32.8 wt%) and SiO2 (43.0-57.9 wt%), and low K2O + Na2O (0.11-2.25 wt%) contents. They have right inclined chondrite-normalized rare earth element patterns with (La/Yb)N ratios of 2.2-8.6. Their primitive mantle normalized trace element patterns show arc-affinity geochemical features characterized by enrichment in Rb, Ba, Th, U, and Pb and depletion in Nb, Ta, and Ti. They have variable initial 87Sr/86Sr ratios (0.7063-0.7093), εNd(t) values (-2.9 to -7.8), 206Pb/204Pb (17.08-17.80), 207Pb/204Pb (15.42-15.49), and 208Pb/204Pb ratios (37.48-38.05), forming an evolution trend from the peridotite unit to the gabbro and pyroxenite units. Clinopyroxene in the three units is chemically similar to those formed in hydrous magmas. The spinel inclusions in olivine from the peridotite unit show unmixing texture and have high Al contents and oxygen fugacity of ~FMQ+1. Therefore, the parental magma was probably derived from a lithospheric mantle enriched by slab-derived fluids. Rocks from the gabbro and peridotite units are proposed to have been derived from olivine-normative melts, whereas rocks from the pyroxenite unit are cumulates from the quartz-normative melts. Such contrasting parental magmas resulted from variable degrees of crustal contamination and fractional crystallization in the arc root. [ABSTRACT FROM AUTHOR]

The nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn-Mg-Sr-Nd isotopes of a rare tephritic rock suite. The Sr--Nd isotopes [(87Sr/86Sr)i = 0.70368-0.70629; εNd(t) = -0.25-4.64] and δ26Mg values (-0.23‰ to -0.34‰) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28‰ to +0.46‰ and +0.30‰ to +0.39‰, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06‰) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05‰). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs. [ABSTRACT FROM AUTHOR]

Revealing the origin of explosive eruptions of silica-rich magma is of paramount importance for understanding the evolution of continental crust and volcanic hazards. However, it remains controversial as to how the erupted magmas form and how they connect with plutonic realms, partly owing to the rarity and the obscurity of the 'cumulate' complementary to such eruptions of silica-rich magmas. Here the issues are explored by comparing the volcanic rocks (rhyodacite + rhyolite) and their associated subvolcanic intrusions (monzodiorite + monzonite + quartz monzonite) within Tonglu volcanic basin (SE, China). The Tonglu plutonic and volcanic units are consistent with each other in age (~130 Ma), space and source materials (e.g. Sr-Nd-Hf isotopes), strongly suggesting that they are cogenetic. Mineral mapping demonstrates that abundant plagioclase clusters (and chains in monzodiorite) occur in plutonic units, implying the processes of crystal gathering and/or accumulation. Rhyolite-MELTS modeling, and geochemical studies coupled with textural observations suggest that the Tonglu volcanic and plutonic rocks represent the residual melts and the complementary cumulate residues, respectively. The compositional and mineral variations in the plutonic rocks can be explained by two-stage, low-pressure crystal-melt separation of a dacitic magma. The monzodiorite represents the first-stage cumulate that was unsaturated in zircon and biotite/K-feldspar on the basis of low Zr and Ba concentrations and the occurrence of these two phases in the interstices between plagioclase and amphibole. The monzonite and quartz monzonite are the second-stage cumulates after saturation of zircon and biotite/K-feldspar as indicated by abrupt increases in Zr and Ba concentrations and zircon inclusions within euhedral biotite. Mass balance calculation and textural estimation indicate that the cumulates actually are a mixture of crystals and melt, containing ~40 vol% interstitial melt. Interstitial zircons from monzodiorite, largely crystallized from trapped melt, show contrasting trace-element trends (e.g. Ti, Zr/Hf, Eu/Eu*, Gd/Yb) to those of the other rock types (i.e. monzonite, quartz monzonite, rhyodacite and rhyolite), consistent with fractional crystallization (FC). We interpret these divergences to heating-induced partial dissolution of a basal crystal framework of monzodiorite due to recharges of hot mafic magmas, but the limited dissolution fails to rejuvenate the crystal mush. The Tonglu volcanic–plutonic system demonstrates that compositional distillation via crystal–liquid separation within the upper crust is an effective mechanism by which a potentially eruptible rhyolitic cap can be generated. Recharges of hot mafic magmas at shallow crustal levels may prolong the lifespan of granitic magma reservoirs. A combined study including texture, geochemistry, thermodynamic modeling and mass-balance calculations can help us identify the fingerprints of cumulates in felsic magma systems and thus track the processes responsible for producing large eruptions of silica-rich magmas. [ABSTRACT FROM AUTHOR]

Late Mesozoic magmatism in southeastern China has been widely considered to be related to the subduction of the Paleo-Pacific Plate. However, it remains controversial whether mafic rocks are derived from the lithosphere or the asthenosphere. Here we present a comprehensive study on mafic dikes from Fujian Province in southeastern China, aiming to understand their source. Two types of mafic rocks have been recognized based on their trace-element features. Type-I rocks show arc-like trace-elemental characteristics, while type-II rocks are distinguished by their relatively flat patterns in primitive-mantle-normalized trace-element diagram. Despite such differences between two types of rocks, these mafic dikes show two trends in the plots of 87Sr/86Sr(i) versus La/Nb, which can be explained by the influences of crustal contamination and melt-lithospheric mantle interaction, respectively. 87Sr/86Sr(i), La/Nb, Sr/Y and Zr/Y ratios of type-I rocks are significantly correlated to the thickness of the underlying lithosphere, and the signals of lithosphere are clearer with increasing lithospheric thickness. This highlights the important influences of melt-lithosphere interaction during their formation. Such observations also indicate that these mafic rocks are more likely to have been originated from the asthenosphere rather than the lithospheric mantle. [ABSTRACT FROM AUTHOR]

The widespread W-(Mo)-Sn-Nb-Ta polymetallic mineralization in Southeast (SE) China is genetically associated with Mesozoic highly fractionated granitic rocks. Such rocks have enigmatic mineralogical and geochemical features, making its petrogenesis an intensely debated topic. To better understand the underlying magma evolution processes, petrography, garnet chemistry and whole-rock major and trace element data are reported for Jurassic highly fractionated granitic rocks and associated microgranite and aplitepegmatite dikes from Macao and compared with coeval similar granitic rocks from nearby areas in SE China. Despite the fact that the most evolved rocks in Macao are garnet-bearing aplite-pegmatite dikes, the existence of coeval two-mica and garnet-bearing biotite and muscovite granites displaying more evolved compositions (e.g, lower Zr/Hf ratios) indicates that the differentiation sequence reached higher degrees of fractionation at a regional scale. Although crystal fractionation played an important role, late-stage fluid/melt interactions, involving F-rich fluids, imparted specific geochemical characteristics to Macao and SE China highly fractionated granitic rocks such as the non-CHARAC (CHArge-and-RAdius-Controlled) behavior of trace elements, leading, for example, to non-chondritic Zr/Hf ratios, Rare Earth Elements (REE) tetrad effects and Nb-Ta enrichment and fractionation. Such process contributed to the late-stage crystallization of accessory phases only found in these highly evolved facies. Among the latter, two populations of garnet were identified in MGI (Macao Group I) highly fractionated granitic rocks: small grossular-poor euhedral grains and large grossular-rich skeletal garnet grains with quartz inclusions. The first group was mainly formed through precipitation from highly evolved Mn-rich slightly peraluminous melts under low-pressure and relatively low temperature (∼700 °C) conditions. Assimilation of upper crust metasedimentary materials may have contributed as a source of Mn and Al to the formation of garnet. The second group has a metasomatic origin related to the interaction of magmatic fluids with previously crystallized mineral phases and, possibly, with assimilated metasedimentary enclaves or surrounding metasedimentary strata. The highly fractionated granitic rocks in Macao represent the first stage in the development of granite-related W-(Mo)-Sn-Nb-Ta mineralization associated with coeval more evolved lithotypes in SE China. [ABSTRACT FROM AUTHOR]

The Dong'an Au deposit is a large-sized epithermal Au deposit discovered in the Lesser Xing'an Range, Northeastern China. Intermediate-acid volcanic rocks (e.g., trachyandesite, andesite, dacite, rhyolite, and rhyolitic tuff) of the Lower Cretaceous Fuminghe Formation are the important surrounding rocks for Au mineralization in the Dong'an Au deposit. However, the relationship between the intermediate volcanic rocks and the acidic volcanic rocks is unclear. The authors present new geochemical, zircon U-Pb and Hf isotope data for the trachyandesites in the Dong'an Au deposit. The whole-rock geochemical data indicate that the trachyandesite samples are high-K calc-alkaline. They are enriched in LILEs (e.g., K, Rb, and Ba), LREEs, and incompatible elements (e.g., Th and U), but are depleted in HFSEs (e.g., Nb, Ta, P, and Ti), showing characteristics of volcanic arc magmas. They have low Mg# values (32.77–48.12), Cr, Ni, and Co contents. Zircons U-Pb dating of the trachyandesites from sample DA-N1 and DA-N2 yield weighted average ages of 108.0 ± 1.1 Ma (MSWD = 0.91) and 104.7 ± 4.3 Ma (MSWD = 17). In situ zircon Hf isotope analyses of the trachyandesites from sample DA-N1 and DA-N2 yield εHf(t) values of −3.2 – 1.2 and −2.3 – 2.6, and two-stage model age (TDM2) of 1372-1090 Ma and 1321-1009 Ma, respectively. These suggest the trachyandesite were derived from partial melting of the juvenile lower crust with involvement of the ancient crustal materials. Combined with previous geological and petrogeochemical characteristics of the Lower Cretaceous Fuminghe Formation volcanic rocks in the Dong'an Au deposit, the Fuminghe Formation volcanic rocks are believed to be comagmatic, and fractional crystallization played an important role in the differentiation of these volcanic rocks. They were likely formed during the retreat of the subducted Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Songling and Majiayu peridotite blocks occur in the Eastern Block, North China Craton (NCC). Geothermobarometry data show that the Songling peridotites began exhumation from a depth of c. 70 km (c. 23 kbar). During exhumation, the Songling peridotites were intruded by an upper-crust-derived, high-δ18O (up to +7.28‰ in zircon) trondhjemitic dyke at 2.47 Ga and experienced granulite-facies metamorphism. The Songling peridotites have hybrid mantle wedge (HMW) -like high SiO2 (> 45 wt%), high FeOt (c. 10 wt%) content, high modal orthopyroxene abundance (> 35%) and high ϵNd(t) (+18.4 to +21.4), which were generated by the reaction between peridotite and eclogite-derived melts. The clinopyroxenes from the Songling peridotites were in equilibrium with a Nb-, Zr- and Ti-depleted arc-like magma. The Majiayu peridotites are characterized by depletion of Nb, Zr and Hf and are highly enriched in FeOt, Th and light rare earth elements (LREEs), which can be interpreted as an open system reaction between hydrous melts and fore-arc mantle peridotites. These two peridotite blocks are considered to be arc-related mantle peridotites that experienced melt extraction and metasomatism in different styles. They were exhumed to the north margin of the North China Craton during the c. 2.47 Ga arc–continent collision along the Zunhua structural belt. [ABSTRACT FROM AUTHOR]

Permian mafic‐ultramafic intrusions have great significance for understanding the geodynamic evolution of the Late Palaeozoic eastern Tianshan Orogen due to containing important information on the nature of mantle sources, crust–mantle interaction, and magmatic differentiation. Increasingly, more Permian mafic‐ultramafic intrusions are discovered in the Jueluotage belt, especially in the Kangguer ductile shear zone, whereas the mafic‐ultramafic intrusions in the Aqishan–Yamansu belt are ill‐informed. In this study, we provide zircon U–Pb geochronological, geochemical, and Sr–Nd–Pb–Hf isotopic data of a newly identified hornblende gabbro suite at the Shaquanzi Fe–Cu deposit in the Aqishan–Yamansu Belt. Zircon U–Pb dating results indicate that the Shaquanzi hornblende gabbro was emplaced at Early Permian (ca. 274–265 Ma). The rocks are calc‐alkaline and have arc‐like geochemical features, including enrichments in large‐ion lithophile elements (LILEs: Rb, Ba, K, Pb and Sr) and light rare‐earth elements (LREEs: Nb, Ta, Zr, Hf, and Ti), and depletions in high‐field‐strength elements (HFSEs) with markedly negative Nb and Ta anomalies. The rocks also exhibit depleted‐mantle isotopic signatures, with positive bulk‐rock εNd(t) values of +3.34 to +4.44 and positive zircon εHf(t) values of +2.8 − +8.7, which are relatively more enriched than those of coeval mafic‐ultramafic intrusions from the Kangguer ductile shear zone, but similar to those in the Central Tianshan Massif. We suggest that the Shaquanzi mafic intrusion suite was generated by 10–30% partial melting of a depleted‐mantle source at over 85 km depth, corresponding to the garnet to garnet‐spinel stability field. And the mantle source had likely been metasomatized by slab‐derived fluids of previous subduction. Integrating with geochemical data of the coeval mafic‐ultramafic and felsic intrusive rocks in the adjacent tectonic belts of eastern Tianshan Orogen, we speculate that the Shaquanzi mafic intrusion was formed in a post‐collision extensional setting, probably triggered by slab breakoff. Metasomatism of the depleted lithospheric mantle had likely occurred during the pre‐Permian subduction of the Kangguer oceanic slab. [ABSTRACT FROM AUTHOR]

The late Palaeozoic Yong'an–Meizhou depression belt is an important iron (Fe) and polymetallic metallogenic belt in southern China. It has undergone a transformation from Tethys to the circum-Pacific tectonic domain. The Luoyang deposit is one of the typical Fe skarn deposits in the Yong'an–Meizhou depression belt of eastern China. Garnet is a characteristic mineral in the deposit. Two generations of garnets are detected in the deposit based on their textural characteristics and trace-element contents, and are represented by Fe-enriched andradite. The first generation of garnets (Grt1) have two types of garnets (Grt1-A and Grt1-B). Type A garnets of the first generation (Grt1-A) (Adr80-88) replaced by massive diopside-magnetite assemblage exhibit distinct oscillatory zonings and display patterns of enriched light rare earth elements (LREE) to weak heavy rare earth elements (HREE), with weak negative to positive Eu anomalies, and highest U, ΣREE and Sn contents. Type B garnets of the first generation (Grt1-B) are irregular zones (Adr94-96) coexisting with magnetite, in which Grt1-A is generally dissolved, and have obviously LREE-enriched and HREE-depleted patterns, with weak negative to positive Eu anomalies, and moderate U, ΣREE and Zn contents. Garnets of the second generation (Grt2) (Adr96-99) that replaced massive magnetite together with sphalerite show unzoned patterns, with a flat REE pattern and pronounced negative Eu anomalies as well as contents of lowest U and ΣREE, and highest W. The substitution of REEs in garnets occurs as [X2+]VIII –1[REE3+]VIII +1[Si4+]IV –1[Z3+]IV +1in an Al-enriched environment. Luoyang hydrothermal fluids shifted from reducing conditions with relatively high-U and -ΣREE characteristics to oxidizing conditions with relatively low-U and -ΣREE characteristics. The reduced siderophile elements and increased fO2 in fluid during Grt1-B formation caused magnetite mineralization and reduced Zn contents during Grt2 formation, causing the deposition of sphalerite. All garnets formed from magmatic fluid and were controlled by infiltrative metasomatism in an opened system. [ABSTRACT FROM AUTHOR]

The North Qilian Belt in northwestern China contains a large number of ophiolites. Most ultramafic rocks from the ophiolites have been entirely transformed into serpentinites because of extensive serpentinization, making it difficult to determine their origin and tectonic significance and further hindering advancements in the understanding of the evolutionary history of the Palaeozoic North Qilian Ocean. In this study, we present new mineral chemistry and whole‐rock geochemistry analyses (including rare earth elements, [REE]) for the serpentinites from the Bianmagou ophiolite to discuss their protoliths, geodynamic environment, melt extractions, and melt/fluid interactions. The mineral chemistry of the relic minerals (e.g., olivine, orthopyroxene, and spinel) and the whole‐rock geochemical compositions (e.g., Mg#, Ni, etc.) strongly demonstrate that the protoliths of the serpentinites were refractory mantle residues after melt extractions and probably emplaced into a tectonic regime of mid‐ocean ridge akin to abyssal peridotites. They experienced high degrees of partial melting (15–20%) recorded by spinel Cr# values and bulk incompatible elements (e.g., Ti, heavy rare‐earth element), resulting from multiple episodes of melt depletion in the lithospheric mantle. Moreover, the serpentinites commonly have U‐shaped chondrite‐normalized REE patterns. The significantly elevated LREEs probably reflect the early partial‐melting processes overprinted by later melt‐dominated metasomatism. The medium to strong enrichment of certain fluid‐mobile elements (e.g., U, Pb, Ba, Sr, As, etc.) in the studied serpentinites was a consequence of the fluid/rock interactions during serpentinization. Overall, despite the variable serpentinization they experienced, this study indicates that the mineral chemical and geochemical proxies of serpentinites provide reliable constraints on the petrogenesis and mantle metasomatism of ancient ophiolites. [ABSTRACT FROM AUTHOR]

Mixing of cogenetic magmas represents an important process in granite petrogenesis but is difficult to identify and is consequently often overlooked due to the absence of obvious isotopic distinctions between the mixed melts. We have conducted in situ elemental and O isotope analyses on apatite from Cretaceous Zhangzhou calc-alkaline granite in southeast China. We integrated these data with microanalyses on other minerals (plagioclase, zircon, and titanite) as well as whole-rock geochemistry to decipher the mixing history of this granitic complex. The apatite occurs as an early crystallizing phase forming inclusions in biotite, plagioclase, and titanite, and is characterized by core-rim zonation textures with a dark core and bright rims in backscattered images. The core domains have remarkably higher SO3 and Li concentrations but much lower SiO2, REE, and Y concentrations than the rim domains. However, both the cores and rims show geochemical compositions similar to that from typical I-type granite and also have mantle-like O isotope compositions (the core has δ18O = 5.3-6.8‰ and the rim has δ18O = 5.2-6.4‰, respectively), indicating crystallization from granitic melts derived from newly accreted crust. The combined major and trace element and O isotope compositions of apatite and whole-rock geochemistry suggest that compositional evolution of the Zhangzhou granite involved mixing between two cogenetic magma batches, with variable degrees of subsequent differentiation. Batch I magma was a low-SiO2 and high-SO3 melt, whereas Batch II magma was a high-SiO2 and low-SO3 melt that experienced devolatilization. The high-S content in apatite cores further suggests the parental magma of the Zhangzhou granite likely originated from a sulfur-rich source comprising mainly newly accreted arc crust in response to subduction of the paleo-Pacific Ocean. The geochemical records of these magmatic processes are rarely observed in coeval zircon, titanite, and plagioclase. Our study, therefore, demonstrates that apatite geochemistry is potentially a more suitable monitor of complex magmatic evolution, including devolatilization and mixing of isotopically indistinguishable magmas. [ABSTRACT FROM AUTHOR]

Recently, a new kind of volcanic rock, felsite porphyry, has been revealed by drilling in Xiangshan area, Jiangxi Province, China. To better understand petrogenesis and magmatic evolution sequence of the Xiangshan volcanic-intrusive complex, we studied systematic petrology, geochemistry, LA-ICP-MS zircon U–Pb dating, and Hf isotope results of the felsite porphyry. Results show that the felsite porphyry has similar geochemical characteristics to the porphyroclastic rhyolite, which is the predominant lithology of Xiangshan uranium orefield. Felsite porphyry and porphyroclastic rhyolite have high SiO2, Al2O3, and K2O contents, low Na2O, and MgO contents, and slightly negative Eu anomalies. Moreover, these rocks are relatively depleted in large ion lithophile elements (K, Ba, and Sr) and are enriched in high field strength elements (Th, Zr, and Hf). LA-ICP-MS zircon U–Pb dating of the felsite porphyry yielded a crystallization age of 132.2 ± 0.9 Ma, which is coeval to that of the porphyroclastic rhyolite. These ages signified that Xiangshan volcanic-intrusive complex formed in the Early Cretaceous, during which the entire South China was in the back-arc extension tectonic setting related to the subduction of the Pacific Plate under the Euroasian Plate. In-situ zircon Hf isotope data on a felsite porphyry sample show εHf(t) values from − 8.82 to − 5.11, while the Hf isotope two-stage model age (TDM2-Hf) ranges from 1513 to 1747 Ma. Combined with petrological, mineralogical, geochemistry, and geochronology results of the felsite porphyry, it is concluded that the felsite porphyry in Xiangshan might be originated from the partial melting of the Mesoproterozoic ancient metamorphic rocks, with possible input of small amounts of mantle materials. [ABSTRACT FROM AUTHOR]

New zircon U–Pb ages and whole-rock chemical data from four adakitic and two non-adakitic igneous rocks as tectonic blocks in the southern West Junggar accretionary complexes, northwestern China and one gabbro enclave in adakitic block provide further constraints on the initial subduction and following rollback process of the Junggar Ocean as part of southern Palaeo-Asian Ocean. The oldest adakitic monzonite in Tangbale is intruded by the non-adakitic quartz monzonite at 549 Ma, and the youngest adakitic diorite in Tierekehuola formed at 520 Ma. The Ediacaran–Cambrian magmatism show a N-wards younger trend. The high-SiO2 adakitic rocks have high Sr (300–663 ppm) and low Y (6.68–12.2 ppm), with Sr/Y = 40–84 and Mg no. = 46–60, whereas the non-adakitic rocks have high Y (13.2–22.7 ppm) and Yb (2.32–2.92 ppm), with Mg no. = 36–40. The gabbro has high MgO (14.81–15.11 wt%), Co (45–48 ppm), Cr (1120–1360 ppm) and Ni (231–288 ppm), with Mg no. = 72–73. All the samples show similar large-ion lithophile element (LILE) and light rare earth element (LREE) enrichment and Nb, Ta, Ti and varying Zr and Hf depletion, suggesting that they were formed in a subduction-related setting. The adakitic rocks were produced by partial melting of subducted oceanic slab, but the melts were modified by mantle wedge and slab-derived fluids; the non-adakitic rocks were likely derived from partial melts of the middle-lower arc crust; and the gabbro originated from the mantle wedge modified by slab-derived fluids. The magmatism could have been generated during the Ediacaran initial subduction and Cambrian slab rollback of the Junggar Ocean. [ABSTRACT FROM AUTHOR]

The mechanics of crustal growth in the Altaids during the Phanerozoic is still not well understood. This paper reports new geochronological, geochemical, and isotopic data from Paleozoic adakitic intrusions in the Dananhu arc in the Chinese Eastern Tianshan with the aim of better understanding the specific mechanisms of crustal growth. Our new LA-ICPMS U–Pb zircon age data show that four phases of adakitic intrusions formed at 410–413 Ma, 385–387 Ma, 335 Ma, and 313–311 Ma. Combined with previous data of ours and from the literature, there were seven phases of adakitic intrusions from the Silurian to early Permian. All these adakitic intrusions have distinctive geochemical-isotopic signatures with high Na and Al, high Sr, low Yb and Y, high Sr/Y and (La/Yb)N values, relatively high MgO contents and Mg numbers (Mg# = 41–70), high abundances of compatible elements (Cr = 1.66–46.30 ppm, Ni = 2.40–26.96 ppm), and positive high εHf (t) (+ 7.1 to + 15.6) and a TDM (Ma) range from 325 to 670 Ma. These adakitic intrusions were associated with essential Cu polymetallic mineralization in the Dananhu arc. The above chemical data and relations indicate that the processes of oceanic slab melting generated these adakitic rocks. Our new geochronological, geochemical and isotopic data, integrated with the geology of the Dananhu intra-oceanic arc, lead us to conclude that multiphase of hot/young oceanic crust subduction and melting generated the massive crustal growth in the Silurian–early Permian. Our results indicate that the magmas were derived by slab melting of hot/young oceanic crust, which was one of the most critical mechanisms of continental crustal growth in the Paleozoic accretionary orogen of the Altaids. [ABSTRACT FROM AUTHOR]

Gejiu area in Yunnan is located at a faulted depression basin in the southwestern of Youjiang continental margin rift basin, which is the transitional zone between Yangtze platform and South China Caledonian geosyncline, and the tectonic location is in the southwestern South China. The geology, geochemistry of Late Ladinian-Norian meta-basalt in Tabai area of Gejiu, Yunnan indicate that these basalts have undergone strong metamorphism because of regional dynamic tectonics. The meta-basalts are characterized by low contents of silica, calcium, magnesium, and enrichment of incompatible elements(Ti, P, K, etc.). They can be classified as high-Ti alkaline basalts. The trace elements are characterized by extremely low contents of Rb and Ba, severely depletion in Sr and enrichment in Ta, Ti, Zr, Hf, Th, which is similar to the weak crustal contamination of the Emeishan high-Ti basalt. The chondrite-normalized REE pattern shows LREE enrichment and weak positive Eu anomaly. The Sr-Nd isotopes suggest that meta-basalts in Tabai area of Gejiu are mainly from the primitive mantle and fall in the oceanic island basalts(OIB), which are of the same origin as Emeishan high-Ti basalts. Emeishan mantle plume activity has ended in Late Permian. Therefore, the stretching of Yangtze massif in Triassic and the subduction of Simao massif to Yangtze massif induce Emeishan mantle plume stigma to a low degree of partial melting. Because the influence of mantle plume activity lasts for a long time, the energy of mantle plume activity is low in some areas, the basaltic magma does not erupt to the surface and forms magma chamber. Meta-basalts in Tabai area of Gejiu are formed in the relatively weak stage of the center of mantle plume magma activity, especially in the edge zone of mantle plume activity center, the relatively thick lithosphere, and low melting degree. The magma chamber activity in Late Triassic re-erupts and forms basalt. [ABSTRACT FROM AUTHOR]

• Hadean mantle was involved into formation-reworking process of NCC from 3.8Ga until 2.45Ga. • Early basalts can derive from a common 4.4Ga mantle formed shortly after lunar impact. • Eoarchean 142Nd heterogeneity seems analytical, rather than truly heterogeneous. • Hadean depleted domains can remain convectively isolated for 1.7 billion years. The 146Sm-142Nd systematics of Archean rocks have been extensively studied to decipher chronological and compositional constraints on Hadean differentiation processes. However, the paucity of 142Nd data on Meso- and Neoarchean mantle-derived rocks relative to earlier periods contributes to uncertainty about the ultimate fate of primordial silicate reservoirs in the convective system of the early Earth. Here we present 146,147Sm-142,143Nd and 176Lu-176Hf zircon data for Mesoarchean (3.0–3.1 Ga) to Paleoproterozoic (2.45 Ga) granitoids, amphibolites and sedimentary rocks representing the main lithological units of the eastern North China Craton (NCC). The analyzed samples have well-resolved positive 142Nd anomalies, suggesting that the Hadean materials have been involved into the generation and evolution of the Eoarchean-Neoarchean continental crust of the eastern NCC. The model age of differentiation (4. 44 − 0.07 + 0.05 Ga) and the 147Sm/144Nd source ratio (0.211 ± 0.002) estimated from the 3.1 Ga Caozhuang amphibolites are identical to those of the 3.8–3.6 Ga rocks from the North Atlantic Craton and the 2.7 Ga pyroxenites from the Abitibi Greenstone Belt, suggesting that these mantle-derived rocks originated from a common, moderately depleted reservoir that differentiated in the wake of the Moon-forming impact and evolved in closed-system until at least 2.7 Ga. These observations contradict the commonly accepted notion of progressive homogenization of 142Nd anomalies in the Archean due to crustal recycling and convective mixing, and instead suggest that primordial differentiation produced a long-lived, depleted reservoir that remained largely isolated from convective mixing on a timescale of several billion years. [ABSTRACT FROM AUTHOR]

[Display omitted] • The serpentinites were derived from the subducted lithospheric mantle. • They recorded a multi-episodic evolution of melt/fluid metasomatism in subduction zone. • The fossil mantle of North Qilian Ocean is compositionally heterogeneous. In nature, serpentinites act as reservoirs of water and fluid-mobile elements and play an essential role in arc magmatism, fluid metasomatism, and elemental circulation in subduction zones. This paper presents new mineral and whole-rock geochemical analyses of the Qingshuigou serpentinite massif and discusses its petrogenesis, tectonic setting, and mantle metasomatism. The chemical composition (e.g., REE, Y, Mg, and Al) and petrological observations (e.g., pseudomorph and hourglass textures) of serpentines demonstrate that the serpentinites' protoliths belong to the peridotites. Their degrees of partial melting were estimated to be 15–20 % using Yb, Cr, Ti, and HREEs, indicating that these peridotite protoliths were residual in origin after high degrees of mantle melting. They were relics of the subducted lithospheric mantle in the subduction zone, based on their geochemical similarities with subducted serpentinites. Notably, the Qingshuigou serpentinites show several geochemical fingerprints of melt-rock interactions, such as the U-shaped REE patterns, elevated Zr/Ti, Zr/Hf, and Nb/Ta ratios; this led us to propose that the peridotite protoliths of the serpentinites were not merely melting remnants but were significantly modified by melt metasomatism. Also, they experienced two stages of fluid/rock interactions in the subduction zone: early-stage serpentinization at shallow depths and lizardite/chrysotile to antigorite transition at an elevated depth. Combined with the published data of ophiolitic peridotites from the North Qilian Belt, the compositional heterogeneity of these peridotites and associated serpentinites might be associated with the nature of melt/fluid metasomatism under different geodynamic backgrounds. [ABSTRACT FROM AUTHOR]

Gabbro–granite complexes provide vital constraints on magmatism mechanisms, crust–mantle interaction processes, and regional tectonics. The petrogenesis and tectonic setting of Early Permian igneous rocks in the southeastern Central Asian Orogenic Belt have long been controversial. In this study, the Early Permian Wulajitu gabbro–granite complex in Xilinhot, Inner Mongolia was selected as a research object and an integrated study was conducted using field occurrence, petrology, zircon U–Pb ages, whole‐rock geochemistry, and in situ zircon Hf isotopes. The Wulajitu gabbro–granite complex consists of gabbro and syenogranite with crystallization ages of 277 ± 1 Ma and 274 ± 2 Ma, respectively, belonging to the Early Permian. Their SiO2 contents vary in the range from 43.07–51.60 wt% and 70.30–75.52 wt%, respectively, and exhibit a gap of 51.60–70.30 wt%, displaying a typical bimodal geochemical distribution. The gabbros are low‐K tholeiitic–calc‐alkaline series rocks that are enriched in large‐ion lithophile elements (e.g., Ba, K, and Sr), depleted in high‐field‐strength elements (e.g., Nb and Ta), and have positive εHf (t) values from +9.3 to +13.2, indicating that they likely originated from partial melting of depleted mantle modified by subduction slab fluids. The syenogranites are aluminous A‐type granites characterized by high SiO2 and K2O + Na2O; low Al2O3, CaO, and MgO; depletion in Ba, Nb, Ta, Sr, P, and Ti; enrichment in Rb, Th, U, K, Zr, and Hf; as well as a seagull‐type rare‐earth element distribution pattern with strongly negative Eu anomalies (Eu/Eu* = 0.30–0.52). They show homogeneous zircon Hf isotopic compositions (positive εHf (t) values from +11.4 to +13.7). All these geochemical signatures suggest that the syenogranites were generated from partial melting of juvenile crust under high temperature and low pressure. The Wulajitu gabbro–granite complex most likely formed in a back‐arc spreading basin. Such an extensional regime was closely related to asthenospheric mantle upwelling caused by the rollback of the subducted Palaeo‐Asian Ocean slab in the Early Permian. [ABSTRACT FROM AUTHOR]

Seamount accretion is one of the most significant accretionary orogenic processes in the Central Asian Orogenic Belt, but there are few paleo‐seamounts reported from and debate on the tectonic evolution of the Junggar Ocean still exists. In this study, we present geochronological, mineralogical, geochemical and isotopic data for basalts from the Chagantaolegai ophiolitic mélanges in Junggar. Zircon U‐Pb dating on one basalt yielded a weighted mean 206Pb/238U age of 469 ± 7 Ma, which suggests that it formed in the Middle Ordovician. All rock samples belong to alkaline basalt and show similar geochemical characteristics, displaying high TiO2 (∼3 wt%), (La/Yb)N (17.6–19.0), ΣREE (232–289 ppm) and enrichment in Nb and Ta, which implies an ocean island basalt (OIB) affinity. Based upon positive εNd(t) (+4.16 to +4.23), ΔNb (0.20–0.22) and low initial 87Sr/86Sr (0.70425 to 0.70452) and Zr/Nb (3.35–3.57), we suggest that the Chagantaolegai OIB samples were likely derived from a fertile mantle source related to plume. The OIB rock assemblage, chert and marble in the southern part of the Chagantaolegai ophiolitic mélange indicates that a Middle Ordovician seamount was accreted to the Boshchekul‐Chingiz arc due to the northward subduction of the Junggar‐Balkhash Ocean. [ABSTRACT FROM AUTHOR]

The Huangshui'an deposit located in East Qinling (China) is an unusual case of a Si-rich carbonatite hosting economic Mo and minor Pb and REE mineralization. The role of mantle-sourced carbonatite melts and fluids in the formation of the Mo mineralization remains poorly understood. Our integrated study based on field geology, petrography, microthermometry, and LA-ICP-MS analysis of single fluid inclusions, and noble gas isotopes of pyrite permits to reconstruct the source characteristics, the magmatic-hydrothermal evolution of the carbonatitic fluids, and their controls on Mo mineralization. Fluid inclusions hosted in calcite in the carbonatite dikes have the highest concentrations of Mo (9.9–62 ppm), Ce (820–9700 ppm), Pb (1800–19500 ppm), and Zn (570–5800 ppm) and represent the least modified hydrothermal fluid derived from the carbonatite melt. Fluid inclusions hosted in calcite (Cal) and quartz (Qz2 and Qz3) of the stage I carbonatite dikes have different metal concentrations, suggesting that they formed from two distinct end member fluids. The FIA in calcite represent fluid A evolved from carbonatite melt with relatively high-ore metal concentrations, and those in quartz characterize fluid B having a crustal signature due to metasomatic reactions with the wall rocks. The FIA in quartz (Qz1) within the altered wall rock have overlapping elemental concentrations with those of massive quartz (Qz2) and vuggy quartz (Qz3) in carbonatite. This suggests that the volumetrically significant quartz in the Huangshui'an carbonatite has been formed by the introduction of Si by fluid B. The positive correlations between Rb, B, Al, Cl, and Sr in stage II fluid inclusions in late fluorite + quartz + calcite veins indicate that this late mineralization formed from the mixing of primary hydrothermal fluid B with meteoric water. The He–Ar isotope data, in combination with available C–O–Sr–Nd–Pb isotope data, constrain the carbonatite source as an enriched mantle source modified by contributions from crustal material which was probably the fertile lower crust in the region. This distinct source facilitated the enrichment in Mo, REE, and Pb in the primary carbonatite magma. The carbonatite magmatism and Mo mineralization at 209.5–207 Ma occurred in the regional-scale extensional setting at the postcollision stage of the Qinling Orogenic Belt. [ABSTRACT FROM AUTHOR]

Highly Siderophile Elements (HSEs; Os, Ru, Ir, Rh, Pt, Pd, Au and Re) combined with their isotopic systematics (Re-Os and Pt-Os) are powerful tools for tracking evolution and genesis of mantle derived magmas. Given sulfides (accessory sulfide minerals and/or molten sulfides) are the primary hosts of HSEs in the mantle and low-degree carbonated melts are extracted from large portions of mantle volume, partitioning of HSEs between sulfide and carbonated melt might play a critical role in distributing HSEs between the mantle and crustal reservoirs. Although, partitioning of HSEs and chalcophile elements between sulfide melt and silicate melt has been previously studied, partitioning of these elements between sulfide melt and carbonated melts has not received much attention. Here we use high P-T experiments to determine the partitioning of HSEs and chalcophile elements (Ni, Co, Mo, Os, Ru, Pd, Pt and Re) between (i) sulfide melt and carbonated silicate melt (CO 2 ~ 17 wt.%) and (ii) sulfide melt and carbonatitic melt (CO 2 ~ >30 wt.%) at a pressure (P) of 3 GPa and temperatures (T) of 1300–1600 °C in graphite capsules. All experiments produced quenched Fe-sulfide melt blobs + carbonated silicate melt matrix. Concentrations of major elements were measured using electron microprobe, and HSEs and chalcophile elements were measured using LA-ICP-MS. We find that all the elements measured are compatible in the sulfide melt to varying degrees and their D sulfide/carb. melt sequence is Mo < Co < Ni < Re < Pt ≤ Pd < Ru ≤ Os varying from around 10 for Mo to 105 for Os. Comparing the D sulfide-carb. melt with D sulfide-silicate from previous studies, we show that the partition coefficients of HSEs between sulfide and carbonated melts are lower than the partition coefficients of these elements between sulfide and silicate melts, indicating greater mobilization of these elements in carbonatites and carbonated silicate melts. Calculating bulk D (D ¯) for carbonated peridotite using our experimentally measured D values, we model the HSE contents of mantle derived low-degree partial melts using an aggregate fractional melting equation and compare the primitive mantle normalized HSE patterns of our model with natural kimberlites, carbonatites, ocean island basalts, and alkaline basalts. We also calculate proportions of sub-lithospheric continental mantle (SCLM) xenolith detritus in the natural kimberlite and carbonatite samples from Karelian, Kaapvaal, Canadian shield and North China craton by using mass balance calculations based on Ru concentration in the primary carbonated melt and the SCLM xenoliths. Our calculations show that detritus proportion in natural kimberlites are 2–28% for Karelian, 7–28% for Kaapvaal, and 6–16% for Canadian shield, which are in agreement with previous studies using various other proxies. We also show that the extent of Re/Os fractionation is less for events of carbonate melt metasomatism as compared to similar events of basaltic melt metasomatism. [ABSTRACT FROM AUTHOR]

As a major tectonic unit along the southwestern rim of the Central Qilian Belt, the Lajishan region plays an important role in the amalgamation of continental plates in the Qilian Orogenic Belt. In this study, zircon laser ablation inductively coupled plasma mass spectrometry for U–Pb dating and Hf isotope analysis, as well as geochemical analysis of intermediate‐acid intrusive rocks from the Lajishan area were conducted. Results show that formation ages of the intermediate‐acid intrusive rocks are 438–452 Ma. Whole‐rock geochemistry results show that the diorite and monzodiorite are metaluminous, low‐ to medium‐K series, and characterized by obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments. The εHf(t) values of zircons from monodiorite range from +2.71 to +10.59 and the two‐stage model ages range from 751 to 1,253 Ma. A large transversal span of εHf(t) values suggests that the source of depleted mantle was mixed with a small amount of older crustal material. The diorite and monzodiorite show a covariant relationship between εHf(t) values and Th/U ratios, which imply the existence of source heterogeneity. The diorites and monzodiorites were most likely produced in an arc setting. The granites are low K in composition and metaluminous to weakly peraluminous. In view of obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments, parent magmas of the granites are suggested to have formed with the participation of crustal source materials. The εHf(t) values of zircons from granite range from +5.82 to +8.90, and the two‐stage model ages range from 861 to 1,057 Ma, indicating that magmas of the granites were mainly derived from partial melting of depleted mantle or juvenile thickened lower crust. The granites were most likely produced in an arc setting and share a similar source with the diorite and monzodiorite. Correlation between major oxides and SiO2 show that during the formation of the three kinds of rocks, crystallization and differentiation both played important roles. Combined with published data from the Central Qilian Belt and its vicinity, our results conclude that the northward subduction of oceanic crust contributed to the formation of an Early Palaeozoic subduction–accretion system in the Lajishan region. This model reveals a tectonic–magmatic thermal event and provides important insights into the tectonic evolution process in the Qilian region, as well as the Central Orogenic Belt during the Early Palaeozoic. [ABSTRACT FROM AUTHOR]

The Tulaergen magmatic Ni–Cu deposit is related to mafic‐ultramafic rocks of the Central Asian Orogenic Belt. The ore‐host rocks are lherzolite and websterite and the major ore types are net‐textured and sparsely disseminated ores. The disseminated ores host high‐Fo (82–85) olivine and hornblende with low‐Al contents, high‐rare earth element (REE) abundances and negative Eu anomalies. The net‐textured mineralized lherzolite contains low‐Fo (74–82) olivine and high‐Al hornblende, the latter characterized by low REE concentrations and no Eu anomaly. The contrasting composition of olivine and hornblende suggests two stages of magmatism. In situ analysis of pentlandite, chalcopyrite and pyrrhotite shows that platinum‐group elements contents in sulphides are low. Contrasting Ni, Co, Se, Ag, Cd, and Pb contents in sulphides from net‐textured and in disseminated ores also supports two pulses of magmas, each with a distinct chemical composition. High‐Mg basaltic magma characterized the first stage, followed by a second‐stage less basic magma with a high H2O content. Whole‐rock Sr and Nd isotopic signatures suggest that about 4–6% crustal materials were added to the depleted mantle source. The fractional crystallization of olivine and crustal contamination play important roles in sulphur segregation at Tulaergen based on sulphur content at sulphide saturation modelling. Injection of magma enriched in H2O further enhanced sulphide aggregation and deposit forming. It is proposed that two pulses of magma injections occurred at the Tulaergen deposit, with the products of the first pulse settling at the base, and of the second one with dense mineralization laying at the top of the deposit. [ABSTRACT FROM AUTHOR]

Oceanic arc subduction systems are the loci of substantial recycling of oceanic crust and production of juvenile arc crust that differentiates to more evolved felsic crust. Inevitably, some juvenile sediments are subducted with the oceanic crust. However, distinguishing the incorporation of juvenile sediments in oceanic arcs is not always straightforward, because they may not measurably shift many geochemical signatures, such as Sr and Nd isotopes, of oceanic arcs. Nevertheless, combined zircon U-Pb, Hf, and O isotope data can provide a powerful tool to decipher sedimentary flux into oceanic arc magmas, and here we report a case study for the late Paleozoic A-type granites from the West Junggar oceanic arc in the southern Central Asian Orogenic Belt. These plutons contain hastingsite and iron biotite diagnostic minerals and have high alkali, FeOT/MgO, Zr, and Ga/Al, but possess low CaO contents, and strongly negative Eu, Sr, and Ba anomalies, demonstrating their close affinity with A-type granites. Zircon U-Pb analyses indicate that these A-type granites emplaced in the Late Carboniferous to Early Permian (ca. 307-298 Ma). Their high zircon εHf(t) values (+12.4 to +15.5), suggest that the magmas were derived from a mantle or juvenile crustal source. However, their δ18Ozrn (+7.2‰ to +11.9‰) values are significantly higher than that of the mantle, and modeling using Hf-O isotope and rare earth element data indicate the assimilation of sedimentary materials at a proportion of ~50%. Our data suggest that juvenile sediments (e.g., greywacke) played an important role in the formation of the studied A-type granites. The re-melting of sedimentary material induced by the late Carboniferous ridge subduction can promote the transition from an intra-oceanic arc to continental crust. Our results show that the subduction and re-melting of juvenile sediments in oceanic arc systems could be an important mechanism for the maturation of oceanic arc crust. [ABSTRACT FROM AUTHOR]

Harzburgite–dunite associations in the Yushigou ophiolitic complex (North Qilian suture, NW China) offer insights into melt migration and melt–rock interaction above a subduction zone. Based on detailed petrographic and in situ analyses, we propose a three-stage model to describe the history of melt channel formation in oceanic arc mantle. In the first stage, high-degree melt extraction was followed by widespread infiltration of small-volume melts, which formed the harzburgite that makes up most of the Yushigou complex. The Yushigou harzburgites thus have highly refractory major-element compositions (olivine Fo = 91·1–93·2, spinel Cr# [atomic 100 × Cr/(Cr + Al)] = 55·2–62·9, whole-rock Mg# = 90·5–92·0, Al2O3 = 0·29–0·74 wt%, CaO = 0·35–0·54 wt%, and low Na2O = 0·02–0·05 wt%) but slight enrichment in the light rare earth elements (LREE). In the second stage, high-volume focused melts infiltrated into the mantle wedge and produced two types of dunite, with high-Cr# (mainly 63·1–73·6) versus low-Cr# (23·6–33·7) spinel. In the low-Cr# dunites, spinels have significantly fewer inclusions and lower Fo values (88·7–90·1) in olivine than in the high-Cr# dunite (Fo = 89·9–90·5), together with higher modal abundances of interstitial sulfides. The two groups of dunite show similar extremely low TiO2 (<0·01 wt%) but different igneous clinopyroxene trace-element patterns (ΣLREE/ΣHREE ≈ 1 in low-Cr# dunite versus ΣLREE/ΣHREE >10 in high-Cr# dunite), indicating distinct differences in the infiltrating melts. The low-Cr# dunite is a cumulate from an anhydrous Al- and S-enriched basaltic melt, whereas the high-Cr# dunite was produced by reaction of harzburgite with a carbon-bearing, alkaline hydrous silicate magma. The confluence of these melt migrations finally formed a channelized dunite network, and later magmatic activity was restricted to these channels. Pulsated melt supply after chromite crystallization formed pervasive sieve-textured rims around spinel in both kinds of dunite, but these are rare in the harzburgite. The third stage was marked by fluid-dominated metasomatism recorded by millimeter-scale veined conduits, which contain carbonate (dolomite and magnesite), amphibole, phlogopite and compound crystal assemblages in both kinds of dunite. CH4–N2–graphite-dominated fluid inclusions are widespread in all lithologies, recording the volatiles transported during the last metasomatic event. The Yushigou complex thus provides a detailed example of interaction between multiple batches of melt or fluid and a lithospheric mantle wedge dunitic channel system. The results of this study further suggest that the formation of podiform chromite requires melt participation, and the nature and origins of the melts can be diverse. [ABSTRACT FROM AUTHOR]

The Western Tianshan orogenic belt is essential for understanding the evolution of the Central Asian orogenic belt. However, no agreement exists among geologists about its tectonic environment during the Late Palaeozoic. The volcanic rocks of the Yishijilike and Wulang Formation in the Yili Block, Western Tianshan, formed in the Late Carboniferous to Early Permian, mainly consist of a bimodal suite of basalts – basaltic andesites and rhyolites, with only some intermediate rocks. Mafic rocks are slightly enriched in light rare earth elements (LREE) and depleted in Nb, Ta, Zr and Hf, suggesting a subduction-modified depleted mantle source. Some mafic samples in the Early Permian bimodal volcanic rocks have high Ti contents with relatively high concentrations of Nb and high field strength elements (HFSE) and low contents of heavy rare earth elements (HREE). These rocks are similar to the continental flood basalts, which suggests that they formed from an asthenospheric mantle. This paper indicates that mafic members were created by the partial melting of the asthenospheric mantle material and subduction-modified lithospheric mantle mixture. Some rhyolites and dacites in the Wulang formation were enriched in Ga, Nb, Zr, Ce and Y and depleted in Sr and Eu. Additionally, they showed fractionation of rare earth elements (REE) with negative Eu anomalies, which is indicative of an A-type affinity of felsic rocks. The genesis of mafic members and an A-type affinity of felsic members indicate that the Late Carboniferous – Early Permian magmatism in the Western Tianshan area formed as a result of an extensional setting. This study also reveals bimodal magmatism produced by delamination in an extensional tectonic setting. [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]

Volcanism represented by the Permian–Triassic boundary (PTB) volcanic ash beds in South China plays a vital role in the PTB mass extinction. However, the probable provenance of the PTB volcanic ashes has not been exactly identified until now. In this study, the geochemical analysis was conducted on newly found five volcanic ash beds from the Mao'ershan and Tielukou sections in the northern part of the Yangtze platform. Volcanic ashes geochemistry indicates a felsic nature and negative Eu anomalies. Zircons selected from the five ash beds yield LA‐ICP‐MS U–Pb ages varying from ca. 255 to 248 Ma, and εHf(t) values of −8.6 to 1.1, which indicates the earlier stage volcanic ash beds in Mao'ershan are likely derived from mantle material and partial melting of crustal rocks, and the later stage volcanic ash beds in Tielukou are derived largely from ancient crustal rocks. Combined with previous U–Pb ages, εHf(t) values, trace elements of zircons, and geological setting, the PTB volcanic ash beds probably drift from the Jomda–Weixi volcanic belt in Sanjiang region of SE Asia, and that are represented by the volcanic rocks in Misha regions, eastern margin of the Lanping Basin. New data and discussion on the provenance of the PTB volcanic ashes provide important implications for the trigger of PTB mass extinction. [ABSTRACT FROM AUTHOR]

• Fluid-mediated S mobilization and redistribution are studied by HP vein systems. • Medium f S 2 fluids stabilize Py + Po, promote δ34S mixing but with no [S] change. • High f S 2 fluids cause Po instability, cause significant S addition and δ34S change. • Sulfide Co–Ni maps and in-situ δ34S variations reveal multiple fluid events. • Seawater δ34S signature can be transported to great depths in subduction zones. Subduction zones mediate the sulfur exchange between Earth's interior and surface, and play a critical role in the long-term global sulfur cycle. Dehydration of the subducted slab releases aqueous fluids, which in turn interact with the surrounding wall-rocks during reactive flow through the slab. Fluids are regarded as the key agent for sulfur transfer within the slab and subsequently into the mantle wedge. However, the mechanisms underlying sulfur mobilization and redistribution during fluid–rock interaction are not fully understood. Here, we investigate three high-pressure blueschist/eclogite–selvage–vein systems from the Southwestern Tianshan metamorphic belt in northwestern China to explore sulfur behavior during fluid–rock interaction along channelized fluid pathways and within their alteration halos. Petrologic observations on mineral parageneses and δ34S compositions of sulfides reveal two different scenarios of sulfur mobilization and redistribution during fluid–rock interaction at HP conditions. Fe-rich and medium- f S 2 (near the pyrite–pyrrhotite buffer) fluids favor pyrrhotite stability over pyrite and can trigger the pyrite–to–pyrrhotite transition in the reaction halo. In this case the bulk-rock sulfur budget may not vary but the sulfur isotope exchange is still effective, producing a δ34S mixing trend in the metasomatic zones. In contrast, Fe-poor and high- f S 2 fluids cause conversion of pyrrhotite to pyrite, significant sulfur addition, and sulfur isotope exchange in alteration selvages. Medium- f S 2 fluids can transport sulfur and thus are effective in transferring sulfur out of the slab, whereas high- f S 2 fluids cause sulfur sequestration along fluid pathways and considerably reduce long-distance sulfur transfer. Multiple fluid infiltration events with different fluid sources result in several pyrite overgrowth sequences, recorded by contrasting Co–Ni element distributions and in-situ δ34S zoning of pyrite. The heaviest δ34S value (+25‰) thus far reported in HP rocks has been found in vein pyrite, suggesting that a seawater sulfate-derived δ34S signature can be transported to great depths in a subduction zone, even though the timing and mechanism of sulfate–to–sulfide reduction in the subduction zone remain unconstrained. Our study provides natural evidence for fluid-mediated sulfide transformation, sulfur transport/storage, and sulfur isotope exchange during fluid–rock interaction, and illuminates the role these processes play in sulfur release from the subducting slab and sulfur subduction into the deep mantle. [ABSTRACT FROM AUTHOR]

Abstract—The analysis of Nb–Zr–Y systematics and thermal regimes of lithospheric mantle of the Siberian, Kaapvaal, North American, North China, and South China cratons indicates their belonging to two types, one comprising the first three cratons (Siberian, Kaapvaal, and North American) (SKNA) and the other including the last two cratons (NCSC). Peridotites in the mantle of SKNA cratons have a Paleoarchaean age and are characterized by Nb content up to 5–6 ppm which is higher than in the primitive mantle (PM). The Zr and Y content in these peridotites is lower than in PM and, in a significant part of the samples, lower than in CI chondrite; these peridotites have superchondrite Nb/Y ratios (>1.0) and chondrite to superchondrite Zr/Y ratios. Thermal regimes in the mantle of SKNA cratons correspond to the model geotherm with surface heat flux density of 45 mW/m2 and fall in the diamond stability region; they are characterized by low (24.4 to 25.1°C/kb) quasi-thermal gradients (TG) reflecting the change in temperature with pressure increasing by 1 kb. The mantle peridotites of the North China Craton have a predominantly lower Nb content than in PM whereas the Nb content in the South China craton peridotites is somewhat higher than in PM. The Nb/Y ratios (ranging from subchondritic to superchondritic but remaining below 1.0) and the Zr/Y ratios (mainly subchondritic) correspond to those in peridotites of the ophiolite complexes of the South Urals and Northern Tibet. The thermal regimes in the mantle of the North China and South China cratons are characterized by the geotherms close to the model ones with heat flux densities of 55 and 60 mW/m2, respectively, and high average TG ​​(36.7 ± 0.5 and 41.3 ± 1.3°C/kb); these regimes correspond to the graphite stability region. The depth of the petrological boundary between the lithosphere and asthenosphere (lithosphere–asthenoasphere boundary, LAB) in the mantle of the SKNA cratons was ~200 km in the Paleoarchaean and, with the allowance for the geophysical data, has remained at the same level up to present. In the mantle of the North China and South China cratons as well as in the Baikal rift (Central Asian folded belt) and epi-Grenville Svalbard platform, since the end of the Paleoarchaean this boundary has been regularly rising to at least 70–80 km in Late Proterozoic. The difference of the mantle underlying the SKNA and NCSC cratons in terms of Nb–Zr–Y systematics and thermal regimes indicates the existence of different domains in the lithosphere since the end of the Paleoarchaean. The mantle of the first type of cratons is probably the relics of chondrite material that has not been completely reworked by melting and fractionation of the Fe-group elements and Nb with close properties. The mantle of the second type of cratons has geochemical features peculiar to PM. [ABSTRACT FROM AUTHOR]

Widespread Cenozoic intraplate basalts from eastern China offer the opportunity to investigate the consequences of interaction between the stagnant Pacific slab and overlying asthenosphere and chemical heterogeneity within this "big mantle wedge". We present and compile a comprehensive study of highly siderophile elements and Mg-Zn isotopes of this magmatic suite (60 samples including nephelinites, basanites, alkali basalts and tholeiites). The large-scale Mg-Zn isotopic anomalies documented in these basalts have been ascribed to mantle hybridization by recycled Mg-carbonates from the stagnant western Pacific plate. Our results reveal that the nephelinites and basanites are characterized by unfractionated platinum-group element (PGE) patterns normalized to primitive upper mantle (PUM) (e.g., Pd N /Ir N normalized to PUM = 1.1 ± 0.8, 1σ), relatively high total PGE contents (e.g., Ir = 0.25 ± 0.14 ppb) and modern mantle-like 187Os/188Os (0.142 ± 0.020). These characteristics are coupled with lighter Mg isotope (δ26Mg = −0.48 ± 0.07‰) and heavier Zn isotope (δ66Zn = +0.46 ± 0.06‰) compositions compared to the mantle values (δ26Mg: −0.25 ± 0.07‰; δ66Zn: +0.18 ± 0.05‰). Together, these data are interpreted to reflect the oxidative breakdown of low proportions of mantle sulfides in the sources of these small-degree melts, likely caused by recycled carbonates, which then release chalcophile-siderophile elements into carbonatitic melts. By contrast, the contemporaneous alkali basalts and tholeiites are characterized by highly fractionated PGE patterns (e.g., Pd N /Ir N = 4.4 ± 3.3; Ir = 0.037 ± 0.027 ppb) and radiogenic 187Os/188Os (0.279 ± 0.115) coupled with less fractionated Mg-Zn isotope compositions (δ26Mg: −0.39 ± 0.05‰; δ66Zn: +0.35 ± 0.03‰). In combination with other isotopic (e.g., Sr-Nd) and chemical (SiO 2 , Ce/Pb, Ba/Th, Fe/Mn) constraints, the alkali basalts and tholeiites were derived from higher degree melting of ancient pyroxenite-bearing mantle in addition to mixing with the aforementioned nephelinitic and basanitic melts. Collectively, we suggest that deep recycled carbonates promoted melting within the "big mantle wedge" leading to the generation of Cenozoic intraplate basalts across eastern China and the "redox freezing of carbonates" may cause the oxidation of Fe0 and S2-. This process may provide an important mechanism to oxidize mantle sulfides and transfer precious metals from deep mantle to crust. [ABSTRACT FROM AUTHOR]

The volcano‐sedimentary sequences from the Weixi belt provide significance for the Sanjiang Paleo‐Tethys evolution. This manuscript constrains the ages of volcano‐sedimentary sequences by LA‐ICPMS U–Pb, including bimodal volcanics (245.0–244.0 Ma) from Pantiange Formation, trachyandesite–basaltic andesite (234 ± 2.0 Ma) from Cuiyibi Formation, high silica subalkaline rhyolite (221 ± 1.4 Ma) from Waigucun Formation and Early Jurassic high silica subalkaline rhyolite (184 ± 2.2 Ma). The volcanics show various Hf isotopic composition, which includes Middle Triassic dacite (εHf[t] = −15.7 to −8.5, TDM2 = 2,006–1,613 Ma), Late Triassic rhyolite (εHf(t) = −9.8 to +1.9, TDM2 = 1,667–1,021 Ma), Late Triassic trachyandesite (εHf(t) = +2.6 to +5.7, TDM2 = 990–816 Ma) and Early Jurassic rhyolite (εHf(t) = −2.7 to +1.1, TDM2 = 1,250–1,145 Ma). The Middle–Late Triassic volcanics exhibit similar characteristics, the content of SiO2 exerts positive correlation with K2O and negative correlation with oxide of Ti, Fe, Al, Mg, Ca, Mn and P. The Hf isotopic and geochemical features indicate that the Middle Triassic basalt and rhyolite derived from mantle and crust by crystal fractionation, respectively. The absence of Lower Jurassic strata and existence of Triassic bimodal volcanic sequences suggest that the middle Sanjiang Tethys Orogen experienced collision during the Middle Triassic with local extension resulting from oblique convergence. Late Triassic–Early Jurassic rhyolite exhibit high SiO2 (77.12–77.81 wt%), K2O (4.35–6.10 wt%), Na2O (1.91–3.15 wt%) content, and a negative Eu anomaly. Together with the sedimentary sequence, the middle Sanjiang Tethys Orogen evolved into post‐collision phase during Late Triassic – Early Jurassic. [ABSTRACT FROM AUTHOR]