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The grade and morphological character of kimberlite-hosted diamonds were compared to crystallization temperature (T) and oxygen fugacity (fO2) estimated from groundmass spinels in six kimberlite pipes in the North China Craton (NCC). Crystallization temperatures calculated at an assumed pressure of 1 GPa are in the range of 1037–1395 °C, with a mean of 1182 °C. At these temperatures, the estimated fO2 varies from 1.2 to 3.1 log units below the nickel-nickel oxide (NNO) buffer. Generally, individual kimberlite pipe shows a small variation of the T (50–100 °C) and fO2 (0.4–0.6 log units), whereas different kimberlite pipes present great changes of T and fO2 which can be up to 300 °C and 2 units respectively. The fO2 of kimberlite magma shows a strong negative correlation with the diamond grade of kimberlite, suggesting that the fO2 plays an important role in diamond resorption, whereas the T shows no relationship with the diamond grade, indicating the T plays no role in diamond resorption. The conditions of kimberlite crystallization (fO2) can be a useful parameter in evaluating diamond survival in diamond exploration. [ABSTRACT FROM AUTHOR]

Proterozoic igneous rocks in the southern margin of the North China Craton can place constraints on its crustal evolution. This paper reports geochemistry, zircon U-Pb ages, Sr-Nd isotopes and Lu-Hf isotopes for the Proterozoic Angou granite from the southwestern margin of the North China Craton (NCC). The Angou granite has zircon LA-ICP-MS U-Pb age of 1819 ± 14Ma (MSWD = 1.3, n = 37), which is synchronous with the Proterozoic Xiong'er Group in the southeastern margin of the NCC. The granite has A-type granite affinity: (1) high SiO2 (67.12% to 73.16%) and alkali (Na2O+K2O = 7.18% to 8.75%) contents, with K2O/Na2O ratios of 1.04 to 4.78; (2) high FeOT/MgO values (4 to 36); (3) significantly negative Eu anomalies (Eu*/Eu = 0.33 to 0.53) and negative Sr anomalies (38.1 to 102ppm); (4) high 104× Ga/Al (2.55 to 4.75, with an average of 3.43) values and Zr+Ce+Nb+Y (634 to 1022ppm) contents; (5) high zircon saturation temperatures (871 to 957°C). In combination with its slightly peraluminous (A/CNK = 1.02 to 1.26) nature, the Angou granite can be classified as slightly peraluminous A-type granite. It displays negative ɛNd(t) values of −2.0 to −3.9, variable εHf(t) values (−8.81 to +1.98) with Hf model ages of 2194 to 2721Ma, combined with its high Rb/Sr (1.05 to 3.26) and low Rb/Ba (0.08 to 0.18) ratios, suggesting that the Angou granite was derived from high temperature melting of tonalite in middle-lower crust. The formation of Angou A-type granite is consistent with the mafic dyke swarms and Xiong'er bimodal volcanic rocks in NCC, indicating a Paleoprotozoic extensional setting in the southwestern margin of the NCC. [ABSTRACT FROM AUTHOR]

Geochemical variations in granitic rocks may be controlled by their source rocks, melting reactions and subsequent magmatic processes, which resulted from various geodynamic processes related to subduction, collision, or slab break-off. Here we report new LA–ICP-MS zircon U–Pb ages and Hf isotopes, whole-rock chemistry and Sr–Nd isotopes for the late Early Cretaceous quartz diorite, granodiorite and monzogranite in the Gaoligong belt, southeastern Tibet Plateau. The zircon U–Pb dating yield ages of 113.9 ± 1.6, 111.7 ± 0.8, and 112.8 ± 1.7 Ma for the quartz diorite, granodiorite, and monzogranite, respectively, which are coeval with bimodal magmatism in the central and northern Lhasa sub-terrane. There are the distinct sources regions for the quartz diorite and granodiorite–monzogranite association. The quartz diorites are sodic, calc-alkaline and have high Mg# (52–54) values. They also have elevated initial 87 Sr/ 86 Sr (0.707019 to 0.709176) and low εNd(t) (− 5.16 to − 7.63), with variable zircon εHf(t) values (+ 5.65 to − 9.02). Zircon chemical data indicate a typical crustal-derived character with high Th (142–1260 ppm) and U (106–1082 ppm) and moderate U/Yb ratios (0.30 to 2.32) and Y content (705–1888 ppm). Those data suggest that the quartz diorites were derived from partial melting of ancient basaltic lower crust by a mantle-derived magma in source region. The granodiorite–monzogranite association has high-K calc-alkaline, weakly peraluminous characters. They show lower Nb/Ta (5.57 to 13.8), CaO/Na 2 O (0.62 to 1.21), higher Al 2 O 3 /TiO 2 (24.4 to 44.4) ratios, more evolved whole-rock Sr–Nd and zircon Hf isotopic signatures, all of which suggest derivation from mixed basaltic and metasedimentary source rocks in a deep crustal zone. We propose that the granitic magmatisms at ca. 113–110 Ma in the Gaologong belt was triggered by the slab break-off of Bangong–Nujiang Tethyan oceanic lithosphere. [ABSTRACT FROM AUTHOR]

Voluminous Neoproterozoic mafic–ultramafic, felsic, and alkaline intrusions are found in the northern Yangtze Block, South China. Here, we present whole-rock major and trace element, and Sr–Nd isotopic compositions, together with zircon U–Pb ages, for syenite and gabbro samples from the Shuimo–Zhongziyuan alkaline intrusive complex in the Micang Mountains region at the northwestern margin of the Yangtze Block. Zircon U–Pb dating yields crystallization ages for the Na- and K-rich Shuimo syenites of 869 ± 4 (MSWD = 0.85, 2σ) and 860 ± 5 Ma (MSWD = 0.47, 2σ), respectively, and for the Zhongziyuan gabbros of 753 ± 4 Ma (MSWD = 0.23, 2σ), indicating that the syenites and gabbros represent different stages of magmatism. The syenites include both Na- and K-rich types and have high values of the Rittman index (σ), and high SiO2and Na2O + K2O contents. These syenites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE), but depleted in high-field-strength elements (HFSE), with high (La/Yb)Nvalues and small negative and positive Eu anomalies (Eu/Eu* = 0.74–1.17). In contrast, the gabbros have lower SiO2and Na2O + K2O contents, are only slightly enriched in LREEs, are enriched in LILE but depleted in HFSEs, and have small negative and positive Eu anomalies (Eu/Eu* = 0.86–1.37). The syenites have low initial87Sr/86Sr (0.703340) andɛNd(t) values (+1.9 to +7.7). The gabbros have relatively high initial87Sr/86Sr (0.703562–0.704933) and positiveɛNd(t) values (+1.6 to +4.5). These data suggest that the syenites and gabbros are isotopically similar and were largely derived from melts of depleted mantle. The syenites underwent significant fractional crystallization and small amounts of crustal contamination during magma evolution. In contrast, the gabbros were formed by partial melting (>15%) of a garnet lherzolite source and might also have experienced crustal assimilation. Taking into account the geochemical signatures and magmatic events, we propose that the Shuimo syenites formed in an intra-arc rifting setting, however, the Zhongziyuan gabbros were most likely produced in a subduction-related, continental margin arc setting during the Neoproterozoic, thus suggesting that the alkaline intrusive complex were formed by the arc-related magmatism in the Micang Mountains. [ABSTRACT FROM PUBLISHER]

The geological record of the Neoproterozoic to early Palaeozoic Proto-Tethyan Ocean in Southeast Asia is not clear. To better constrain the evolution of the Proto-Tethys, we present new geochronology, geochemistry, and petrology of the late Cambrian to Ordovician Pinghe pluton monzogranite from the Baoshan block, western Yunnan, southwest China. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of four zircon samples yield ages of 482–494 and 439–445 Ma for the pluton, interpreted as two episodes within one magmatic event accompanying the whole process of subduction–collision–orogeny between buoyant blocks and oceanic crust of the Proto-Tethys. The monzogranite belongs to the strong peraluminous, high-K, calc-alkaline series and shows characteristics of both I-type and S-type granitic rocks. It is characterized by extremely high Rb/Sr and Rb/Ba but low TiO2, MgO, FeOt, and CaO/Na2O ratios. The monzogranite is also moderately enriched in light rare earth elements (LREEs), depleted in heavy rare earth elements (HREEs), lacks HREE fractionation, and has strongly negative Eu (Eu/Eu* = 0.06–0.49), Ba, Nb, Ta, Sr, and Ti anomalies. Whole-rockεNd(t) andεHf(t) values range from −8.7 to −11.6 and −5.55 to −9.58, respectively. Nd and Hf two-stage model ages range from 1.66 to 2.06 Ga and 2.14 to 3.00 Ga, respectively, with variable radiogenic206Pb/204Pb(t)(16.547–18.705),207Pb/204Pb(t)(15.645–15.765), and208Pb/204Pb(t)(38.273–38.830). These signatures suggest that the monzogranite magma was derived from partial melting of heterogeneous metapelite, which was generated from Neoarchean to Palaeoproterozoic materials mixed with basaltic magma. The monzogranite magma underwent crystallization differentiation of plagioclase, K-feldspar, and ilmenite. Magmatism to form the Pinghe pluton occurred in a post-collisional setting. Based on the comparison of coeval granites throughout adjacent regions (e.g. Himalayan orogen, Lhasa Terrane, and parts of Gondwana supercontinent), we propose that the Baoshan block was derived from the northern Australian Proto-Tethyan Andean-type active continental margin of Gondwana and experienced subduction of the Proto-Tethyan oceanic crust and accretion of an outboard micro-continent. The Pinghe pluton could have formed when a subducting oceanic slab broke off during collision. [ABSTRACT FROM AUTHOR]

There are two genetic types of spinel (magmatic spinel crystallizing directly from kimberlite magma and xenocrystic spinel derived from mantle xenoliths) in the No.30 kimberlite pipe (Liaoning Province, North China Craton). Their geochemistry is investigated to reveal processes of diamond capture and resorption during kimberlite magmatism to constrain the diamond potential. Magmatic spinels are mostly euhedral to subhedral, 20 to 60 µm in size, and have compositional zones: the cores are classified as chromite with high Cr and Mg contents, and the rims are classified as magnetite with low Cr and high ferric Fe. The compositional trends suggest that magmatic spinel and olivine phenocrysts are crystallized contemporaneously during the early stages of kimberlite crystallization. During this period, temperature (T) and oxygen fugacity (fO2) values calculated at an assumed pressure of 1 GPa are in the range of 994–1274 °C and 1.6–2.4 log fO2 units below the nickel-nickel oxide (NNO) buffer, respectively. The high values of fO2 suggest heavy diamond resorption during kimberlite magmatism. Estimated temperatures of xenocrystic spinel range from 828 to 1394 °C, and their distributions indicate that only a small proportion of xenocrystic spinels are derived from the diamond stabilization field, which suggests a low potential of diamond capture. The low diamond capture and heavy diamond resorption during kimberlite magmatism contributed to the low diamond grade of the No.30 kimberlite. [ABSTRACT FROM AUTHOR]

• The Miaoya carbonatite-syenite complex derived from enriched mantle source. • The Miaoya carbonatite-syenite complex was formed by liquid immiscibility. • The enriched mantle source and the liquid immiscibility provide a prerequisite for REE mineralization of the Miaoya carbonatite-syenite complex. As one of the largest carbonatite-syenite complexes enriched in rare earth elements (REE) in China, the magma-hydrothermal processes of the Miaoya carbonatite-syenite complex (MCSC) are of great significance with respect to the enrichment of REE, and have therefore attracted much attention. Although the hydrothermal mineralization process of the Miaoya carbonatite-associated REE deposits has been well addressed, studies concerning its detailed magmatic process remain relatively limited. Here, we present new zircon U-Pb age, whole-rock major and trace element, and Sr-Nd-Pb isotope composition data of the MCSC, to help provide a comprehensive understanding of its source characteristics and related liquid immiscibility process. The Miaoya syenites studied here formed at 410.8 ± 1.9 Ma, consistent with the formation ages of alkaline rocks (377–455 Ma) in the South Qinling Belt. Both samples in the MCSC share homogeneous Sr-Nd-Pb isotopes (i.e., carbonatites: 87Sr/86Sr (i) = 0.70361–0.70366, ε Nd (t) = +2.6–+2.8, 206Pb/204Pb = 17.81–18.13, 207Pb/204Pb = 15.51–15.53, and 208Pb/204Pb = 37.67–38.27; syenites: 87Sr/86Sr (i) = 0.70286–0.70524, ε Nd (t) = +2.0–+2.6, 206Pb/204Pb = 18.33–18.83, 207Pb/204Pb = 15.55–15.57, and 208Pb/204Pb = 37.88–38.38), suggesting a common enriched mantle source. The plagioclase identified in the carbonatites and the calcite observed in the syenites fully support the interaction between carbonate and silicate melts during the liquid immiscibility process. Similar to the liquid immiscibility experimental results, the Miaoya carbonatites are more enriched in Ca, Mn, Sr, and REE than the syenites, but are more depleted in Na, K, Al, Si, and high field strength elements, such as Nb, Ta, Zr, and Hf, further demonstrating that liquid immiscibility provided a crucial contribution to the formation of the MCSC. In combination with typical REE-rich carbonatite-alkaline complexes (e.g., the Mianning-Dechang carbonatite-associated REE deposit belt of the western Yangtze Block, South China, and the Mountain Pass carbonatite-associated REE deposits of California, USA), we propose that the enriched mantle and the liquid immiscibility are significant for the REE enrichment of carbonatite-alkaline complexes. [ABSTRACT FROM AUTHOR]

• The newly identified Yunnongfeng intrusion in the southwestern margins of the Yangtze Block is formed at ca. 782.5–763 Ma. • They originated from metasomatized mantle source enriched by subducted slab fluids, and sediment melts and underwent remarkable fractional crystallization. • Neoproterozoic magmatism in western margins of Yangtze Block formed in persistent oceanic-crust subduction and back-arc basin setting. • Sediment-melt react with lithospheric mantle would form K-enriched mafic-intermediate intrusive rocks. The study of K-enriched intrusive rocks is essential for deciphering mantle metasomatism beneath active continental arcs. In this contribution, high-precision zircon U–Pb–Hf isotope, whole-rock geochemistry, Sr–Nd isotope, and mineral chemistry analyses were performed to evaluate the petrogenesis and geodynamic system of the Yunnongfeng intrusion on the southwestern margin of the Yangtze Block. The Yunnongfeng intrusion consists of a high-K to shoshonitic rock assemblage with variable lithology from gabbro-diorite to granite. Zircon U–Pb dating gives concordant crystallization ages of ca. 782.5 ± 3.8 Ma for gabbro-diorite, ca. 774 ± 4.1 and 776 ± 4.1 Ma for diorite, ca. 770 ± 4.7 Ma for quartz monzonite, ca. 763 ± 3.4 Ma for quartz syenite, and ca. 764 ± 16 Ma for granite. These samples also show similar Sr–Nd, and Lu–Hf isotopic compositions, implying a common magma source. The similar crystallization age and regular variation of major and trace element contents suggest that these rocks were formed through fractional crystallization of cogenetic primitive mantle magmas. The enriched εNd(t) (−5.7 to − 5.1) and εHf(t) (−6.7 to − 1.2) values, high Rb/Y and Th/La ratios, slight Nd–Hf decoupling, and high-K and Th contents demonstrate that their lithospheric mantle source was enriched by slab-related fluid and sediment-related melt. The samples also exhibit remarkable enrichment in large-ion lithophile elements and depletion in high-field-strength elements, indicative of subduction-related arc magmatism. Taking into account previous studies, we suggest that the western margin of the Yangtze Block experienced a long-term subduction process during the Neoproterozoic, and the Yunnongfeng intrusion formed in an extensional back-arc basin. Based on the K-enriched mafic–intermediate rocks from the western margin of the Yangtze Block commonly show high K 2 O/Na 2 O, Rb/Sr, low Ba/Rb ratios, and enriched εNd(t) values, our study, coupled with numerous previous reports, proposes that the K-enrichment resulted from the breakdown of phlogopite, owing to subduction-related sediment melt reacting with peridotite in the mantle source area. [ABSTRACT FROM AUTHOR]

Rare disperse elements (RDEs) have received substantial attention due to their intense application in industry. Sphalerite from some Pb–Zn deposits of MVT, skarn, VMS, SEDEX and epithermal type, containing considerable RDEs contents that could be used as by-product. Here, the concentrations of RDEs in sphalerite from the Dalingkou deposit is examined by in situ laser-ablation inductively coupled mass spectroscopy (LA–ICP–MS), to discuss their substitution mechanism in sphalerite, controlling factors, and genesis model in epithermal system. The Dalingkou deposit is the largest epithermal Ag–Zn–Pb deposit in Zhejiang, South China, with proven reserves of 702 t Ag, 0.10 Mt Pb, 0.15 Mt Zn, and potential resources for RDEs. Orebodies are predominately hosted by intermediate–acid Yanshanian volcanics and subvolcanics and controlled by N–S and NW–SE trending faults. The ores are dominated by abundant base metal sulfides with gangue minerals mainly composed of quartz and rhodochrosite. The hydrothermal activities occurred in four stages: pre-ore stage (stage 1), Pb–Zn mineralization stage (stage 2), Ag–Pb–Zn mineralization stage (stage 3) and post-ore stage (stage 4). Two types of sphalerite were observed (i.e. Sp2 from the stage 2, and Sp3 from the stage 3), according to crosscutting and overprinting relationships of ores. LA–ICP–MS analysis shows that, relative to the Sp3, the Sp2 has higher contents of Fe, Mn, Cd, and In, but slightly lower contents of Ga and Ge. Correlation analyses reveal the incorporation of RDE into sphalerite via both simple substitution, such as Zn2+ ↔ (Cd2+), and coupled substitution, such as 3Zn2+ ↔ In3+ + Sn3+ + □ (vacancy), 3Zn2+ ↔ Ge4+ + 2Cu+, and 2Zn2+↔ (Ag, Cu)+ + Ga3+. Geothermometry of impurity elements (Ga, Ge, In, Mn, and Fe) in sphalerite suggests that the sulfides precipitated from an intermediate- to low-temperature hydrothermal system. It further reveals temperature decrease from stage 2 to stage 3, suggesting fluid mixing between magmatic fluids and meteoric water was involved. Deep parental magma may have contributed In and Cd during the mineralization stage, whereas Ga and Ge were released from surrounding rocks due to hydrothermal alteration, despite that they are not enriched in orebodies. The LA–ICP–MS analysis also reveals that the In, Ga and Ge contents in both Sp2 and Sp3 are too low to be economic. However, compared with sphalerite Cd concentrations from different deposit types worldwide, the Sp2 and Sp3 in Dalingkou have enough high Cd grade as an economic by-product, suggesting that the Dalingkou deposit is also a Cd deposit. • Substitution mechanisms of Zn by RDEs in sphalerite were identified. • Enrichment laws of RDEs in sphalerite were investigated. • Indium and Cd are derived from magma but Ga and Ge from host rocks. • Mineralization was induced by mixing of cooler meteoric water and magmatic fluids. • Dalingkou Ag–Zn–Pb deposit is also a Cd deposit. [ABSTRACT FROM AUTHOR]

The Maluntou Au deposit is located in Southeast Coastal Volcanic Belt in South China. Its orebodies are hosted by the Cretaceous intermediate to silicic volcanic rocks and controlled by tensional NW-trending faults. The types of ore-related wall rock alterations consist of silicification, argillization, pyritization, and weak chloritization. Based on detailed field and microscopic petrography observation, three mineral paragenetic stages can be divided, i.e. Pb Zn stage, Au Ag stage and post-ore stage. Electron microprobe analysis reveals slightly different composition of metal sulfides between Pb Zn stage and Au Ag stage. The Fe content of Maluntou sphalerite is generally <2 %, indicating a typical Fe-poor sphalerite. Fluid inclusions microthermometric analysis of the early Pb Zn mineralization stage and late Au Ag stage yielded homogenization temperatures (T h , 205–260 °C, 138–234 °C) and salinities (1.0–4.0 wt% NaCl equiv., 0.3–3.4 wt% NaCl equiv.), respectively. The low-moderate T h and low salinity ranges indicate an epithermal mineralization environment. From early stage to late stage, δD V-SMOW values show similar ranges from −69.4 ‰ ~ −64.3 ‰ to −68.2 ‰ ~ −64.9 ‰, with δ18O H2O ‰ values ranges from −4.6 ‰ ~ −2.6 ‰ to −5.6 ‰ ~ −4.3 ‰, indicating ore-forming fluids derived from a magmatic and meteoric mixed source. The microthermometric data and H − O isotopic compositions of ore fluids suggest fluid mixing contributed to metal precipitation. The δ34S V–CDT values of sulfide minerals (i.e. pyrite, sphalerite, galena, chalcopyrite; −3.1 to 3.4 ‰) indicate a magmatic sulfur source. The relatively homogeneous lead isotopic compositions of the ore minerals (206Pb/204Pb = 18.4203–18.4814, 207Pb/204Pb = 15.6712–15.6853, and 208Pb/204Pb = 38.7730–38.8636) suggest a crustal origin. All the above results imply that the Maluntou Au deposit is a transitional type epithermal deposit between low- and intermediate-sulfidation styles which occurred distal to the magmatic hydrothermal system. Considering the close time and space relationship of this type deposit with other epithermal type and porphyry type mineralization, our results also suggest a possible exploration potential for the epithermal-porphyry type mineralization in the surrounding altered volcanic rocks in Zhenghe–Jian'ou area. [Display omitted] • Detailed observations reveal distinctive stages of hydrothermal activity. • Fluid inclusion data reveal prevalence of meteoric water input in epithermal environments. • Mineralization is mainly induced by mixing of meteoric and magmatic fluids. • An transition epithermal type is proposed to the Maluntou deposit. [ABSTRACT FROM AUTHOR]

The giant Dexing porphyry copper deposit is one of the largest porphyry copper deposits in South China. This paper presents new LA-ICP-MS zircon U–Pb dating, element and Sr–Nd–Hf isotopic data for the ore-related porphyries in the Dexing porphyry deposit. The Dexing ore-related porphyries were emplaced during the Middle Jurassic (ca. 170 Ma), and were characterized by high-Mg adakitic geochemical features, including high MgO and Sr contents and high Mg#, Sr/Y and La N /Yb N ratios, low Y and Yb contents, and lacking a negative Eu anomaly, which suggest that they were probably derived from the delaminated thickened lithosphere. A non-arc setting in the Middle Jurassic is indicated by the absence of arc rocks and the presence of rifting-related igneous rock associations in the interior of South China. The non-arc setting suggests that the copper-rich lithosphere in the Dexing area was enriched by an ancient subduction event prior to the Late Mesozoic. The regional geological history and the Neoproterozoic two-stage Nd–Hf isotope model ages imply that the ancient subduction event occurred in the Neoproterozoic in response to the Jiangnan Orogen between the Yangtze and Cathaysia blocks. Thus, we infer that the giant Dexing porphyry copper deposit was formed in the Middle Jurassic by remelting of the copper-rich Neoproterozoic subduction-modified lithosphere. Previous studies of the low-Mg ore-related porphyries in the adjacent Yinshan copper polymetallic deposit proposed a copper-rich juvenile crust as their magma source. In this study, the high Mg contents of the Dexing ore-related porphyries stress the significant contribution of the subduction-modified lithospheric mantle or a higher melting temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • Both granodiorites and monzogranites of the Mopanshan pluton are coeval and formed at ca. 820 Ma. • They were generated by mixing of metasomatized mantle-derived magmas and ancient crust-derived melts. • The adakitic signatures of the Mopanshan pluton were caused by hornblende-dominated fractional crystallization. • The Neoproterozoic magmatic event was due to the intensive crust-mantle interaction in a back-arc extension setting. Crust- and/or mantle-derived igneous rocks in the Neoproterozoic continental magmatic arc along the western Yangtze Block (South China) have been extensively studied, but the crust-mantle interaction that might have been involved in the formation of these rocks was poorly understood. In this paper, we present an integrated study on petrology, whole-rock compositions, in-situ plagioclase Sr and zircon U-Pb-Hf isotopes for granodiorites and monzogranites from the Neoproterozoic Mopanshan pluton in the western Yangtze Block. Our objective is to provide vital constraint on the magma mixing process in the formation of these rocks. The new LA-ICP-MS zircon U-Pb dating results reveal that both granodiorites and monzogranites of the Mopanshan pluton were coeval and formed at ca. 820 Ma. They are calc-alkaline to high-K calc-alkaline (SiO 2 = 66.06–70.30 wt%, K 2 O = 2.24–3.34 wt%) and metaluminous to slightly peraluminous (A/CNK = 0.99–1.10) rocks, and characterized by middle-upper crustal trace element patterns (e.g., enrichment in Rb, K, Th, U, and Pb, and depletion in Nb, Ta, Sr, and Ti). The magma mixing process is supported by following ample evidence, including (1) the disequilibrium mineral textures and an abruptly increased An values (up to 60) as well as significant decrease of (87Sr/86Sr) i ratios from core to rim in plagioclase crystals, (2) higher Mg# values (45–50 > 40) than those of experimental melts from basalts at the same silica contents, (3) positive and negative whole-rock εNd(t) (–0.72 to + 1.01) values as well as variable whole-rock (87Sr/86Sr) i (0.702778–0.705404) and zircon εHf(t) (+1.76 to + 7.72) values. The special geochemical characteristics and element modeling support that the Mopanshan pluton was generated by magma mixing of ancient crust-derived melts and relatively mafic melts from metasomatized mantle source. The adakitic signatures observed in the Mopanshan pluton were attributed to subsequent hornblende-dominant intra-crustal fractional crystallization, rather than derived from a thickened lower crust source. In combination with regional geology and our compilation for Nd-Hf isotopes of Neoproterozoic igneous rocks, the Mopanshan pluton is magmatic response of intensive crust-mantle interaction induced by underplating of voluminous mantle-derived magma in a back-arc extension setting. This research highlights that the crust-mantle interaction is significant for the petrological and geochemical diversity of Neoproterozoic granitoids from the western Yangtze Block. [ABSTRACT FROM AUTHOR]

Early Paleozoic volcanic–intrusive rocks in the South Qinling Belt, central China, consist of bimodal alkaline suites ranging in composition from basalt to trachyte, with an apparent scarcity of intermediate silicic components (the so-called "Daly gap"). A series of trachytic rocks have been identified in the Quanxi area of the South Qinling Belt. In this work, we combine mineralogical evidence with whole-rock major- and trace-element data, Sr–Nd–Pb isotope data, and the results of thermodynamic modeling to gain a better understanding of the petrogenesis and evolutionary process of the Quanxi trachytic rocks, as well as their compositional discontinuity with coeval mafic rocks. Our samples can be clearly classified into two lithological groups based on their phenocryst content: Group 1, phenocryst-poor trachytes (<5 vol% phenocrysts; SiO 2 = 63.91–66.13 wt%) and Group 2, trachytic tufflavas (30–45 vol% pyroclasts; SiO 2 = 53.34–59.03 wt%). All of the samples exhibit typical oceanic island basalt-like enrichment in light rare earth elements and high field strength elements, as well as marked depletion of Ba, Sr, and Ti. A cogenetic metasomatized lithosphere source for the Quanxi trachytic rocks and contemporaneous mafic rocks is indicated by their homogeneous isotopic features (ε Nd (t) = +2.3 to +3.4; initial 206Pb/204Pb = 17.92–18.69; initial 207Pb/204Pb = 15.53–15.57; initial 208Pb/204Pb = 37.96–38.99) and linear geochemical variations, with protracted fractional crystallization regarded as the key mechanism for the compositional variations among these cogenetic rocks. The results of Rhyolite-MELTS modeling predict 72%–80% crystallization involving plagioclase, pyroxene, biotite, apatite, and Fe Ti oxide, to yield the magmatic compositions from an evolved mafic progenitor to the Quanxi trachytes under conditions of low pressure (1.5–2 kbar), high H 2 O content (2–3 wt%), and high f O 2 (FMQ–0.5). Some incompatible elements in trachytic tufflavas deviate markedly from the liquid lines of descent from coeval mafic rocks to the Quanxi trachytes: this deviation is attributed to a combination of the involvement of large proportions of alkali-feldspar pyroclasts and post-magmatic hydrothermal alteration. The presence of the "Daly gap" in early Paleozoic alkaline suites can be explained by an accelerated differentiation rate (i.e., dSiO 2 /d t) in the SiO 2 -intermediate field, which is driven by the simultaneous separation of a considerable scale of SiO 2 -poor phases. • South Qinling Belt, central China, contains trachytes and trachytic tufflavas. • Trachytic rocks and contemporaneous mafic rocks had a cogenetic mantle source. • Trachytes underwent fractional crystallization from an evolved mafic progenitor. • Fractionation of SiO 2 -poor minerals resulted in the presence of "Daly gap". [ABSTRACT FROM AUTHOR]

Under the condition of paucity of mantle-derived ferromagnesian components, peritectic assemblage entrainment (PAE) model can properly explain a large variation of Fe, Mg, Ti, and Ca contents as well as positive linear trends for Ti and Ca plotted against maficity (molar Fe + Mg) exhibited by more mafic I-type granitic melts. Herein we present a comprehensive study of zircon U–Pb–Hf isotopes, whole-rock major and trace elements, and Sr–Nd isotopes for newly identified Neoproterozoic high-maficity I-type granitoids collected from the Yonglang area in the western Yangtze Block, South China, in order to evaluate PAE process acting on the petrogenesis of these more mafic granitoids. Zircon U-Pb geochronological results show that the Yonglang granitoids, including the granodiorites, monzogranites, and biotite granites, yield the weighted mean 206Pb/238U ages of ca. 850–825 Ma. They are geochemically characterized by high SiO 2 (64.63–72.62 wt.%) and K 2 O (3.49–6.59 wt.%) contents as well as variable A/CNK (0.94–1.09) and molar Fe + Mg values (0.0452–0.1210), and display a negative correlation of A/CNK and Fe + Mg, indicating an I-type affinity. Isotopically, they display negative whole-rock εNd(t) (−4.06 to−6.38) and highly evolved zircon εHf(t) values (−9.36 to +1.92) as well as old two-stage Nd model ages (1.69–1.85 Ga) and crustal Hf model ages (1608–2139 Ma), implying a crustal source. In comparison with the geochemical composition of fluid-absent experimental melts, the Yonglang I-type granitoids have Fe, Mg, Ti, and Ca contents that are too high to equilibrium with those of pure crustal melts, indicating the additional incorporation of a ferromagnesian, Ti-, and Ca-rich component into primary melts. Like the Cotoncello–Monte Capanne granitic complex in Elba Island and Verdenburg I-type granite in South Africa, the Yonglang I-type granitoids exhibit highly positive linear correlations for Ti vs. maficity and Ca vs. maficity as well as negative correlation for A/CNK vs. maficity, suggesting that these high-maficity I-type granitoids predominantly underwent the peritectic assemblage entrainment of Ca-Fe-Mg-Ti bearing minerals (e.g., clinopyroxene, plagioclase, ilmenite, etc.) during coupled melting of biotite and hornblende phases in crustal source. The process of peritectic assemblage entrainment thus play a vital role in moulding geochemical compositions of more mafic I-type granites. [Display omitted] • Newly identified Neoproterozoic high-maficity I-type granitoids were formed at ca. 850-835 Ma. • They originated from coupled melting of biotite and hornblende phases in ancient crustal source. • They predominantly underwent the peritectic assemblage entrainment (PAE) process. [ABSTRACT FROM AUTHOR]

• ~860 Ma mafic rocks originated from an amphibole-bearing spinel peridotite source. • There existed Neoproterozoic metasomatic mantle beneath the western Yangtze Block. • The Neoproterozoic metasomatic agents include the slab fluids, sediment melts, and oceanic slab melts. Mafic rocks contain important information about the nature of the mantle source and tectonic settings. Here we present results of whole-rock geochemistry and zircon U-Pb-Hf isotopes for the Early Neoproterozoic mafic rocks (Ganyuhe hornblende gabbros and Guandaoshan gabbro-diorites) in the western Yangtze Block, South China, in order to constrain the petrogenesis and the mantle metasomatism processes under subduction setting. LA-ICP-MS zircon U-Pb dating results display concordant crystallization ages of 857.4 ± 2.0 Ma for the hornblende gabbros and 856.4 ± 2.8 Ma for the gabbro-diorites, respectively. These mafic rocks possess low SiO 2 contents (45.5–53.3 wt%) as well as high MgO contents (3.27–9.20 wt%) and Mg# (48.6–62.6) values, and show characteristics of arc-like trace element patterns with enriched Rb, Ba, Sr, K, and Pb but depleted Nb, Ta, Zr, Hf, and Ti. The prominently positive whole-rock εNd(t) (+4.9 to + 5.8) and zircon εHf(t) (+8.48 to + 20.6) values suggest a depleted lithospheric mantle source. We therefore infer that the mafic rocks investigated here were derived from an amphibole-bearing spinel peridotite source that was affected by metasomatism between the overlying mantle wedge and subduction-related fluids. In conjunction with the compiled data of Neoproterozoic mafic rocks from the western Yangtze Block, we propose that there exist Neoproterozoic metasomatized mantle sources beneath the western Yangtze Block during the subduction process in response to the evolution of the supercontinent Rodinia. The Neoproterozoic metasomatic agents in mantle sources include the slab fluids, sediment melts, and oceanic slab melts. [ABSTRACT FROM AUTHOR]

Early Paleozoic mafic dykes are widespread in the South Qinling Belt, central China. In this study, we present new major and trace element, zircon U–Pb age and Sr–Nd–Hf isotopic results of Early Paleozoic diabases dykes in the South Qinling Belt to explore the nature of their mantle source. The zircon U–Pb dating yielded ages of 455.9 ± 1.5 Ma and 446.2 ± 1.1 Ma. The South Qinling Belt diabases had low SiO 2 (42.1–49.5 wt%), high TiO 2 (2.89–5.17 wt%) and variable MgO (4.0–9.4 wt%) contents. In primitive mantle normalized multi-element diagrams, all samples were strongly enriched in the majority of incompatible trace elements but showed systematic depletion in Rb, K, Pb, Zr and Hf. The negative K and Rb anomalies, together with high TiO 2 and high Na 2 O/K 2 O, suggests magma was derived from a source rich in amphibole. Partial melting modeling indicated that 20%–36% partial melting of amphibole-clinopyroxene-phlogopite veins with subsequent dissolution of ~30% orthopyroxene from the wall-rock peridotite within the spinel stability field can produce the observed diabase compositions. Additionally, the South Qinling Belt diabases were characterized by moderately depleted Nd (ε Nd(t) = +2.2 to +3.3) and Hf (ε Hf(t) = +6.2 to +7.2) isotopic compositions without pronounced isotope decoupling, indicating mantle metasomatism occurred prior to Early Paleozoic magmatism. We propose that low-degree silicate melts released from the asthenosphere infiltrated and solidified within the lithospheric mantle, forming non-peridotitic lithologies rich in amphibole, clinopyroxene and phlogopite. Subsequent lithospheric extension caused the melting of the most easily fusible material in the lithosphere, which gave rise to the Early Paleozoic alkaline magmatism in South Qinling. • Alkali diabases in South Qinling Belt. • Vein-plus-wall rock melting model. • Lithospheric mantle was metasomatized by silicate melts. • The formation of amphibole-rich veins. [ABSTRACT FROM AUTHOR]

The Shangshan'gang Au deposit is located in the Cretaceous Dongkeng volcanic basin of northern Fujian Province in southeast China. The deposit is hosted by altered intermediate to silicic volcanic rocks along NE–SW- and ENE–WSW-trending faults. The main types of wall-rock alteration are silicification, sericitization, argillization, and chloritization. Ore mineralization occurred in three stages, which were the base metal, Au Ag, and post-ore stages. Electrum and kustelite are the main Au Ag minerals. Laser ablation–inductively coupled plasma–mass spectrometry analyses revealed different compositions for the two stages of pyrite, galena, and sphalerite, which reflect changing mineralization conditions. Fluid inclusions revealed an epithermal mineralization environment with low–moderate temperature and salinity. Mixing of ore fluids is the main ore-forming mechanisms which occurred from the early to late stages, as evidenced by the H and O isotopic compositions of the ore-forming fluids. The proportion of meteoric fluid in the ore-forming hydrothermal fluid gradually increased with time. Fluid boiling may have locally occurred in the early stage and promoted ore precipitation. Our results show that the Shangshan'gang Au deposit is an intermediate-sulfidation-type epithermal deposit that gradually changed to a low-sulfidation-type during late mineralization. Given the close temporal and spatial relationship between intermediate-sulfidation-type and porphyry deposits, there is potential for porphyry deposits to exist in the Zhenghe–Jian'ou area. • An intermediate-sulfidation genesis was proposed to the Shangshan'gang deposit. • In-situ major and trace element of sulfides reveals divers mineralization conditions. • Ore-forming fluid were characterized by low-medium temperature and salinity fluids. • Mineralization was induced by mixing of dominant meteoric and minor magmatic fluids. [ABSTRACT FROM AUTHOR]

• The Xiaban gold deposit is a low-sulfidation epithermal gold deposit. • Dominated by a quartz + sericite + illite + chalcedony alteration assemblage. • Mineralization was formed from low-temperature and low-salinity fluids. • Isotope data indicate that ore-forming fluids were predominantly of meteoric origin. • Gold deposition was caused by mixing of dominant meteoric and minor magmatic fluids. The Xiaban gold deposit is located in the Dehua goldfield of central-eastern Fujian Province, southeast China. Detailed field observations combined with mineral exploration in the study area indicate that the majority of mineralization within the Xiaban gold deposit is hosted by porphyritic rhyolite units in areas proximal to E–W trending faults with lesser amounts located within alteration zones along lithological contacts. The deposit contains silicified banded, disseminated, brecciated, fine-grained stockwork, and quartz–sulfide vein-hosted mineralization, all of which is associated with a quartz–sericite–illite–chalcedony alteration assemblage. The main ore minerals are electrum and pyrite with lesser amounts of galena, Fe-rich sphalerite, and marcasite, all of which are associated with sericitic and argillic alteration as well as silicification. Fluid inclusion microthermometric analysis of quartz-hosted fluid inclusions associated with the main stage of mineralization yielded homogenization temperatures (T h) of 157–207 °C (mean of 180 °C) and salinities of 0.7–2.9 wt% NaCl equivalent, which are indicative of an epithermal-type system. The precipitation of gold was most likely caused by fluid mixing between dominant meteoric and minor magmatic fluid components. Fluids within quartz-hosted fluid inclusions have H and O isotopic compositions (δD H2O = −106.3‰ to −81.8‰; δ18O H2O = −5.8‰ to −3.0‰) that are indicative of ore-forming fluids derived from a meteoric-water-dominated source. Pyrite in the study area has S isotopic compositions that vary between −2.8‰ and −1.6‰, indicative of S derived from a homogeneous magmatic source. Lead isotopic compositions of the pyrite within the deposit (206Pb/204Pb = 18.2953–18.3203, 207Pb/204Pb = 15.6458–15.6502, and 208Pb/204Pb = 38.6974–38.7271) plot between the orogenic-belt and upper-crustal evolution lines on tectonic discrimination diagrams as well as in the upper-crustal zone of a Δγ–Δβ genetic classification diagram, indicating that Pb within the Xiaban deposit was derived from a homogeneous upper-crustal source. Taken together, these mineralization and alteration, gangue and ore mineral assemblage, fluid inclusion, and H–O–S–Pb isotopic characteristics suggests that the Xiaban gold deposit is a low-sulfidation epithermal deposit. This result, together with the inferred minor amount of denudation that has affected the study area, means that the surrounding region should be considered prospective for this style of mineralization, with further exploration for epithermal mineralization within the Dehua goldfield ideally focusing on areas that show similar alteration characteristics to those found in the Xiaban deposit. [ABSTRACT FROM AUTHOR]

Deciphering the geochemical diversity of S-type granites is crucial for obtaining more profound insight into their petrogenesis. We therefore undertook an integrated study of whole-rock geochemistry, Sr-Nd isotopes, and zircon U-Pb-Hf isotopes for newly recognized Late Mesoproterozoic S-type granites, including two-mica-, biotite-, garnet-bearing two-mica granites, from the western Yangtze Block, South China. The crystallization ages of these granites are ca. 1040 Ma (weighted mean 206Pb/238U age = 1036.4 ± 4.5 Ma to 1042.2 ± 1.1 Ma). They are peraluminous to strongly peraluminous (A/CNK = molar ratio of Al 2 O 3 /(CaO + Na 2 O + K 2 O) = 1.02–1.67), high-K calc-alkaline rocks, and display high concentrations of normative-corundum (0.54–7.04 wt%) as well as positive correlations of A/CNK and FeOT + MgO values, which are characteristics of S-type granites. These S-type granites are characterized by enriched in Rb, Th, K, and Pb, depleted in Ba, Sr, Ti, and Eu, with negative whole-rock εNd(t) (−0.3 to −6.8) and predominantly negative zircon εHf(t) values (−8.09 to +5.70), indicating the affinity of middle-upper crustal trends and a heterogeneous metasedimentary source. Compared with the geochemical diversity of S-type granites around the world, the variably negative εNd(t) values as well as positive and negative εHf(t) values of our S-type granites may be caused by source heterogeneity and disequilibrium melting processes. More importantly, similar to typical more mafic S-type granites from the Cape Granite Suite (South Africa) and north Queensland (Australia), the high and variable FeOT + MgO contents (2.21–6.64 wt%) are significantly attributed to coupled co-entrainment of peritectic and accessory minerals (e.g., garnet, ilmenite, zircon, and monazite), evidenced by positive relationships between FeOT + MgO and TiO 2 , CaO, Zr, Th, Hf, Y, Yb, light rare earth elements (LREEs). In conjunction with the existence of coeval rift-related A-type igneous rocks, depleted asthenosphere-derived mafic rocks, marine sedimentary sequences, and subsequent extensive Neoproterozoic arc magmatism along the western Yangtze Block, we infer that the ca. 1040 Ma S-type granites studied here were produced in a continental rifting basin that was transformed into a compression setting during the Neoproterozoic. • Late Mesoproterozoic (ca. 1040 Ma) S-type granites in the western Yangtze Block. • They originated from heterogeneous metasedimentary sources. • Source heterogeneity & disequilibrium melting cause heterogeneous Nd-Hf isotopes. • Co-entrainment of peritectic and accessory minerals cause high FeOT + MgO contents. [ABSTRACT FROM AUTHOR]

• Neoproterozoic gabbro-diorites, adakitic granites, A-type granites in South China. • Ca. 810 Ma gabbro-diorites were derived from metasomatized lithospheric mantle. • Ca. 800 Ma adakitic granites were derived from the juvenile thickened lower crust. • Ca. 750 Ma A-type granites were derived from a felsic crustal source. • These rocks imply a persistent subduction process during the Neoproterozoic. The occurrence of A-type granites following adakitic granites can provide unique insights into the tectonic evolution of subduction zone. This paper presents a comprehensive study of zircon U-Pb-Hf isotopes and whole-rock geochemistry on the Neoproterozoic gabbro-diorites, biotite granites, and K-feldspar granites in the southwestern margin of the Yangtze Block, South China. Zircon U-Pb dating of three distinctive intrusions yield concordant ages of 810.4 ± 2.0 Ma for gabbro-diorites, 800.3 ± 2.1 Ma for biotite granites, and 749.1 ± 2.0 Ma for K-feldspar granites. The gabbro-diorites are sodic and calc-alkaline rocks with low SiO 2 (52.62–53.87 wt%), medium MgO (2.67–3.41 wt%), high Fe 2 O 3 T (7.18–7.49 wt%) and CaO (5.68–7.50 wt%) contents. They display high Th/Zr and Rb/Y ratios but low Nb/Zr and Nb/Y ratios. Together with their positive whole-rock εNd(t) (+1.0 to +1.5) and zircon εHf(t) values (+3.66 to +8.18), we suggest that these gabbro-diorites were derived from the partial melting of depleted lithospheric mantle modified by subduction-related fluids. The biotite granites display relatively high Sr contents (335–395 ppm), Sr/Y ratios (38.9–54.3), low Y (7.04–9.71 ppm) and Yb contents (0.78–1.08 ppm), resembling the adakitic granites. Their low Mg# (36–41) values, Cr (2.94–3.59 ppm) and Ni (1.32–1.55 ppm) contents as well as positive εNd(t) (+0.5 to +0.6) and εHf(t) values (+1.62 to +8.07) indicate that they were formed by partial melting of thickened juvenile mafic lower crust, probably within the existence of garnet. The K-feldspar granites have high SiO 2 (76.61–77.14 wt%) and alkalis (Na 2 O + K 2 O = 8.55–9.69 wt%) contents, high 10,000 * Ga/Al (2.56–2.80) ratios and differentiation index (95.3–96.9), indicating the affinity to highly fractionated A-type granites. We suggest that these A-type granites were mainly generated by the partial melting of felsic crustal rocks under low pressure condition and subsequently extensive fractional crystallization is significant. Taking into account previous studies from the western Yangtze Block, South China, we propose that the gabbro-diorites, adakitic granites and A-type granites in this study were formed in persistent subduction process during the Neoproterozoic. [ABSTRACT FROM AUTHOR]