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Olivine crystals in alkaline basalts preserve important information about the Oxygen fugacity and thermal condition of the mantle‐derived magma. This paper presents new olivine mineral chemistry and whole‐rock geochemistry for Early‐Cretaceous alkali basalts in the Ganjia area, northeastern margin of the Tibetan Plateau. The olivine phenocrysts of Ganjia basalts have low Ni (74–2261 ppm) and high Ca contents (1217–4443 ppm), similar to the olivines in MORB, suggesting that they were crystallized from peridotite‐derived basaltic magma. Al‐in‐olivine/spinel thermometer results indicate crystallization temperatures of olivine around 1202 ± 46°C, corresponding to a mantle potential temperature of 1279 ± 47°C, with low oxygen fugacity of FMQ −1 to FMQ 0, suggesting a reduced mantle source. Whole‐rock geochemical compositions of the Ganjia basalts were characterized by low SiO2 contents (45.39%–48.70 wt%), high alkali contents (3.88–5.11 wt%), positive Nb and Ta anomalies, and enrichment in LREEs, HFSEs and LILEs, similar to those of OIB rocks, with high ratios of (Dy/Yb)N (1.38–1.54) and (La/Yb)N (5.37–7.42) ratios, indicating garnet residue. The above results suggest that the Early Cretaceous intraplate alkaline basalts in West Qinling were formed by a low degree of partial melting of peridotite and that no high‐temperature mantle plume existed. The Qinling Orogenic Belt may have been affected by the subduction of the Palaeo‐Pacific. We propose that the Ganjia basalts originated from the interaction between the upwelling asthenosphere and a lithospheric source. [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]

Early Palaeozoic alkaline magmatism is widely preserved in the North Daba Mountains, South Qinling Belt (SQB), predominately composed of basalt–diabase and trachyte–syenite. The petrogenesis of the felsic rocks and their genetic connections with the mafic members remain controversial. Here, an integrated investigation, combining geochronology and whole-rock and Sr–Nd isotopic geochemistry, is conducted to further constrain the origin and tectono-magmatic evolution of the trachytes in Pingli–Zhuxi area, North Daba Mountains. Zircon U–Pb dating for the Pingli–Zhuxi trachytes yield ages of 406.0 to 427.9 Ma, which are close to those of the mafic rocks (420–455 Ma) in research area. The trachytes show relatively high SiO2 (60.88–63.87 wt.%) and total alkali (Na2O + K2O = 10.19–12.24 wt.%) contents, and are characterized by pronounced enrichment in LREEs and HFSEs, with insignificantly negative Eu anomalies and significantly negative Sr anomalies. All of the samples display low and variable initial 87Sr/86Sr ratios of 0.6959 to 0.7083 and narrow range initial 143Nd/144Nd ratios of 0.5123 to 0.5125 with positive εNd(t) values of +3.0 to +7.3, suggesting a depleted source. Together with the published data from coeval SQB diabases, our geochemistry evidences show regular and linear variations between mafic and felsic end-members, suggesting their closely genetic link. A plausible petrogenetic hypothesis for the genesis of the Pingli–Zhuxi trachytes implies a protracted process of fractional crystallization driven by separation of K-feldspar, plagioclase, biotite, apatite, and Ti-magnetite from a basaltic melt. Enrichment in REEs and HFSEs and similar geochemical characteristics point to that the Pingli–Zhuxi trachytes and the coeval mafic rocks originate from a cogenetic metasomatized lithosphere source in rift setting. Asthenospheric upwelling is a key factor for continental break up and lithosphere metasomatism. Collectively, melting of the metasomatized source, followed by protracted K-feldspar-dominated fractional crystallization, leading to the occurrence of the Pingli–Zhuxi trachytes in the North Daba Mountains. [ABSTRACT FROM AUTHOR]

Decoding the trans-crustal magmatic evolution processes from exposed paleo-depth that are otherwise inaccessible above continental arc zone is instructive to understand the geochemical fractionation of arc magmatism and geochemical stratification of continental crust. To unravel trans-crustal magmatic processes leading to the formation of Neoproterozoic continental arc, we combined a comprehensive dataset of petrography, zircon U Pb geochronology, whole-rock major and trace elements, and Sr Nd isotopes as well as zircon Lu Hf isotopes for the Neoproterozoic calc-alkaline Luding Intrusive Complex (LIC) in the western Yangtze Block, South China. The LIC is composed of monzodiorites, gabbro-diorites, diorites, and granodiorites that formed at ca. 783–779 Ma. The LIC lithologies are calc-alkaline with highly variable Mg# values (40.8–70.6) and subduction-related trace elemental patterns. In combination with predominantly depleted and comparable whole-rock Sr Nd (initial 87Sr/86Sr = 0.703244–0.704248 and εNd(t) = +2.35 ∼ +5.10) and zircon Hf isotopes (εHf(t) = +4.47 ∼ +9.99), the LIC originated from a common subduction fluids-metasomatized mantle source. The hornblende geothermobarometry and whole-rock normative mineral trajectories as well as previously experimental results collectively suggest that the crystallization of LIC occurred within the middle crustal level (11.4–20.9 km) at various temperatures (776–875 °C) and pressures (2.50–5.50 kbar), and underwent different degrees of fractional crystallization of predominant hornblende and plagioclase phases during the assemblage and solidification of cogenetic and multiple batches magmatic pluming. The diorites-granodiorites result from fractionation of early olivine + clinopyroxene phases followed by subsequent amphibole + plagioclase phases, and the monzodiorites mainly represent accumulation residues of dominant hornblende + plagioclase phases from more fractionated melts, while the gabbro-diorites underwent the fractionation from an isotopically homogeneous mantle source, but differ in their elemental compositions. The LIC from Neoproterozoic continental arc suggests that the cogenetic fractional crystallization of mantle-derived melts in intra-crustal magmatic system can account for the petrochemical diversities of arc magmatic rocks during the construction of the Neoproterozoic continental arc crust in the western Yangzte Block, South China. • Neoproterozoic Luding Intrusive Complex (LIC) formed at 783–779 Ma. • It sourced from slab fluids-modified mantle and underwent cogenetic fractionation. • It represents middle crustal magmatic system of Neoproterozoic continental arc. [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]

• Early Cretaceous high-Mg# granodiorites in the NE Lhasa terrane. • Intensive granitic magmatism occurred at ca. 133–113 Ma. • Mantle-derived materials play a necessary role in the generation. • Interaction between ancient lower crust and mantle-derived peridotites. • Evolved isotopic component was gradually decreased from 140 to 100 Ma. High-Mg# (molar Mg/[Mg + Fe]) intermediate to felsic rocks, such as high-Mg andesitic rocks (HMA) and Mg andesites (MA), are usually produced by melting of mantle-derived peridotites and/or interaction with mantle-derived peridotites. Both are crucial in tracking mantle-crust interaction processes in the deep crust. We present LA-ICP-MS in-situ zircon U-Pb isotopic data, whole-rock geochemistry and whole-rock Sr-Nd-Pb-Hf isotopic data for the Basu granodiorites which are exposed between the Jiali fault and the Bangong-Nujiang suture, SE Tibet. The LA-ICP-MS zircon U-Pb data show that the granodiorites were formed at ca. 122.1 ± 1.0 Ma, coeval with other granitoids in this region. The granodiorites belong to the high-K calc-alkaline and high-Mg# (49.7–53.7) series, similar to typical MA. The decreasing A/CNK from 0.97 to 0.87 and increasing FM (molar Fe + Mg) from 0.08 to 0.16 indicate a clinopyroxene entrainment and I-type trend. The rocks also display enriched Rb, Th, U and Pb, but depleted P, Ti and obvious negative Eu anomalies. Evolved whole-rock isotopic compositions of Basu granodiorites include high initial 87Sr/86Sr (0.7097–0.7114), negative ε Nd(t) (−12.0 to −7.2) and ε Hf(t) values (−9.6 to −7.9), and lower to upper crustal affinity of Pb isotopes which imply that they were derived from an ancient and evolved lower crust source. Therefore, we suggest that these granodiorites were products of interaction between partial melting of ancient basaltic lower crust and mantle-derived peridotites. Together with a geochronology dataset from the literature, we suggest that there was intensive granitic magmatism occurred in the Early Cretaceous range from 133 to 113 Ma in the northeastern Lhasa terrane, similar to those in the central and northern Lhasa terrane. Furthermore, we have compared with the dataset of in-situ zircon Lu-Hf isotopes, whole-rock Sr-Nd from the literatures and the relationship with zircon U-Pb ages in the northeastern Lhasa terrane, all of which indicate the importance of evolved and ancient continental crust source in the Early Cretaceous magmatism in the northeastern Lhasa terrane, but also that the mantle-derived materials play a necessary role in the generation. In addition, the amount of enriched and evolved isotopic component gradually decreased from ca.140 to 100 Ma. [ABSTRACT FROM AUTHOR]

Abstract In order to address the causes of compositional variations of crust-derived granitic rocks in continental margin arc, we focused on the petrogenesis of Eocene granitic host rocks with enclosed MMEs, associated metagabbro, fine-grained quartz-diorite in Xima-Tongbiguan area, the Tengchong Block, which is a continental margin arc related to the subduction of Neo-Tethys. Both the Eocene granitic and mafic rocks are characterized by gradual increment in enriched compositions, such as K, Rb, Th, LREE, initial 87Sr/86Sr, ε Nd (t), and ε Hf (t), but decreasing Pb isotopic ratios from the west to the east of the Tengchong Block. Zircon U Pb age data of granitic host rocks, MMEs, metagabbro and fine-grained quartz-diorite reveal a similar age range of 55–50 Ma. The lithologies, zircon Hf compositions, geochemical and isotopic signatures of host granitic rocks show that the origin of these host rocks are mainly controlled by magma mixing between felsic and mafic magma. The products of the mafic magma are dominated by metagabbro, fine-grained quartz-diorite and MMEs enclosed in granitic rocks, which are all resulted from the reaction and mixture between different mafic magmatic products and felsic magma. The metagabbros could be the products of felsic magma mixing with early crystallized mafic magma, and the fine-grained quartz-diorites could be the products of felsic magma mixing with crystal-rich mafic magma, and the MMEs could be the products of felsic magma mixing with crystal-poor mafic magma or melt. The metagabbro has positive ε Hf (t) values of 1.8 to 10.9, which could provide the relative primitive Lu Hf isotopic compositions of mafic magma, indicating that the mafic magma is derived from a depleted mantle. The host granitic rocks have negative ε Nd (t) values of −5.2 to −6.5, indicating that the felsic magma is derived from partial melting of an ancient mafic lower crust. Furthermore, there are excess reactions after magma mixing between the mafic and felsic magma, such as multi-stage reactions between solidified MMEs and felsic magma, and the disaggregation of MMEs, finally resulting in the basification of felsic magma. Magma mixing is therefore the main mechanism of the formation of granitic rocks in the Tengchong Block. The compositional variation of intermediate to acid igneous rock in a continental margin arc is likely dominated by the characteristics of mafic magma because the intermediate to acid igneous rock is derived from mixing of crust-derived granitic and different mantle sources-derived mafic magma. Highlights • Eocene granitic and mafic rocks in Tengchong block are coeval at 55-50 Ma • Granitic and mafic rocks have similar compositional change and genetic correlation • Compositional change of granitic rock in continental arc is caused by magma mixing [ABSTRACT FROM AUTHOR]

Neoproterozoic igneous rocks along the northern Yangtze Block are closely related to the evolution of the Rodinia supercontinent. This paper presents zircon U–Pb dating, whole‐rock geochemistry and Sr‐Nd isotopes of the gabbro–granite association from the Micangshan area, northern Yangtze Block. Zircon LA‐ICP MS U–Pb dating indicates that the tonalite and monzogranite from the Pinghe display identical ages of 869 ± 4 Ma (MSWD = 1.3, 2σ) and 859 ± 8 Ma (MSWD = 1.9, 2σ), respectively. According to the regional geology, the gabbro may be younger. The monzogranite and tonalite display almost identical geochemical features, both of them have high Na2O/K2O ratios, with insignificant negative Eu anomalies, relatively juvenile Sr‐Nd isotopic compositions. The monzogranite has initial (87Sr/86Sr)i ratios of 0.703403 to 0.705218, and positive ɛNd(t) values of +1.23 to +2.98. The tonalite have (87Sr/86Sr)i ratios of 0.700387 to 0.706222, positive ɛNd(t) values of +1.98 to +7.79, indicating that they were derived from juvenile source. The 860 Ma monzogranite–tonalite association suggests crustal growth event in an active continental margin. The gabbro has low (La/Yb)N ratios (1.80 to 7.61) and total rare earth element contents (∑REE = 44.95 to 83.92 ppm), they have initial (87Sr/86Sr)i ratios of 0.701913 to 0.704815, positive ɛNd(t) values of +0.65 to +5.73, indicating an island‐arc affinity. In combination with the other Neoproterozoic igneous rocks along the western and northern margin of the Yangtze Block, we propose that the gabbro and granitoid association from the Micangshan area represent two stage crustal growth events in the active continental margin setting, and these results imply that the Neoproterozoic crustal growth events in the Yangtze Block may be controlled by subduction. [ABSTRACT FROM AUTHOR]

Strongly peraluminous fractionated S-type granites are important indicators of compositional maturity of the continental crust. Here we report the finding of strongly peraluminous fractionated S-type granites from the western Baoshan Block in the southeastern Tibetan–Himalayan orogenic belt. We present LA ICP-MS zircon U–Pb ages from biotite- and two-mica- granites which reveal two distinct periods of magmatism at 121.8 ± 1.1 Ma and 81.9–79.7 Ma. These Cretaceous granites are strongly peraluminous (A/CNK = 1.18–1.31), high-K calc-alkaline, enriched in Rb, Th, K, and Pb, and depleted in Ba, Sr and Ti. They also show high normative- corundum contents of 2.84–4.42 wt%, moderately high P 2 O 5 content (0.22–0.28 wt%) and high differentiation index (DI) of 93.1–96.8, similar to the features of fractionated S-type granites. The low total Fe 2 O 3 T + MgO + TiO 2 contents (<3.0 wt%) are also consistent with the results from experimental studies on S-type granite melts. The S-type granites from Baoshan show high Al 2 O 3 /TiO 2 (93.8–182.9), Rb/Ba (6.19–23.5), and Rb/Sr (17.0–30.5) values, and low CaO/Na 2 O (0.09–1.19). They also display negative εNd( t ) values (−11.7 to −13.6) and εHf( t ) ranges (−5.47 to −0.77 for biotite granites and −7.67 to −0.81 for two-mica granites) suggesting evolved and heterogeneous continental crustal sources for the magma. The initial 206 Pb/ 204 Pb (17.527 to 19.277), 207 Pb/ 204 Pb (15.772 to 15.888), and 208 Pb/ 204 Pb (39.237 to 39.498) isotopic ratios are also consistent with lower to upper crustal affinity. Our data, in conjunction with those from experimental studies suggest that the strongly peraluminous S-type granites were derived from partial melting of metasedimentary, pelite-dominated source within continental crustal basement, similar to typical fractionated S-type granites from the Jiangnan Orogen (SE China), Erzgebirge (Central Europe), Eastern Australia and the low-temperature SP granites in the Himalayas. We correlate the Early- to Late- Cretaceous magmatism with two-stage melting of fertile continental materials following the final closure and termination of Bangong-Nujiang Tethys ocean. [ABSTRACT FROM AUTHOR]

The Zheduoshan Miocene granitic pluton is exposed at the eastern margin of Tibet and along the strike-slip Xianshuihe Fault, and is the product of syn-tectonic magmatism closely related to this fault. This paper is focused on the petrogenesis of different granitic lithological units in the Zheduoshan composite intrusion, and the results of geochronology and lithology show that the Zheduoshan Miocene granitic pluton is incremental assembly by three stages of granitic magma influx and growth, represented by fine-grain biotite granite at 18.0 Ma, corase-grain and porphyraceous biotite monzogranite at 16.0 Ma and medium-grain two-mica monzogranite at 14.0 Ma. Combining with the geochemical signatures, these granitic rocks have high intial 87 Sr/ 86 Sr ratios, enriched Nd and Hf isotopic compositions, revealing that the sources of these granitic rocks are metabasatic rocks for fine-grain biotite granite, greywackes for coarse-grain biotite monzogranite and medium-grain monzogranite. These granites have high Sr/Y ratios, revealing that these granitic magma form at high pressure condition. The Sr/Y ratios and calculated crystallization pressure gradually decreased, implying the pressure gradually decreasing with the formation of these three stages of granites, which is probably caused by the tectonic mechanism transition from compression to strike-slip extension during the generation of these granites at 18.0–14.4 Ma. This tectonic mechanism change implied the initial activity of Xianshuihe Fault at least before 14.4 Ma. [ABSTRACT FROM AUTHOR]

This paper presents precise zircon U–Pb, bulk-rock geochemical, and Sr–Nd–Pb isotopic data for metagabbro, quartz diorite, and granite units within the Tengchong Block of SW China, which forms the southeastern extension of the Himalayan orogeny and the southwestern section of the Sanjiang orogenic belt, a key region for furthering our understanding of the evolution of the eastern Paleo-Tethys. These data reveal four groups of zircon U–Pb ages that range from the late Paleozoic to the early Mesozoic, including a 263.6 ± 3.6 Ma quartz diorite, a 218.5 ± 5.4 Ma two-mica granite, a 205.7 ± 3.1 Ma metagabbroic unit, and a 195.5 ± 2.2 Ma biotite granite. The quartz diorite in this area contains low concentrations of SiO2 (60.71–64.32 wt%), is sodium-rich, and is metaluminous, indicating formation from magmas generated by a mixed source of metamafic rocks with a significant metapelitic sedimentary material within lower arc crust. The two-mica granites contain high concentrations of SiO2 (73.2–74.3 wt%), are strongly peraluminous, and have evolved Sr–Nd–Pb isotopic compositions, all of which are indicative of a crustal source, most probably from the partial melting of felsic pelite and metagreywacke/psammite material. The metagabbros contain low concentrations of SiO2 (50.17–50.96 wt%), are sodium-rich, contain high concentrations of Fe2O3T (9.79–10.06 wt%) and CaO (6.88–7.12 wt%), and are significantly enriched in the Sr (869–894 ppm) and LREE (198.14–464.60 ppm), indicative of derivation from magmas generated by a metasomatized mantle wedge modified by the sedimentary-derived component. The biotite granites are weakly peraluminous and formed from magmas generated by melting of metasedimentary sources dominated by metagreywacke/psammite material. Combining the petrology and geochemistry of these units with the regional geology of the Indosinian orogenic belt provides evidence for two stages of magmatism: an initial stage that generated magmas during partial melting of mantle-derived material associated with late Permian-to-Early Triassic subduction of the Paleo-Tethys, and a second stage that generated granitoid magmas by the partial melting of crustal-derived sources during the Late Triassic collision between the Lhasa and Tengchong blocks and the northern margin of the Australian continent. These rocks, therefore, provide evidence of a systematic late Permian-to-Late Triassic transition from a pre-collision/volcanic arc setting through a collisional setting to a final within-plate phase of magmatism. The previous research involving bulk-rock Sr–Nd analyses of units from the southern Sanjiang orogenic belt and zircon Hf isotopic analyses of units from the Tengchong Block suggests that these areas may record similar magmatic evolutionary trends from mantle- to crustal-derived sources during the evolution of the eastern Paleo-Tethys. [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]

The Na-rich intermediate-to-felsic granitic rocks provide insights into the generation of magmas in subduction zones. This paper presents zircon LA-ICP-MS U–Pb ages as well as whole-rock geochemical, mineral chemical, and in situ zircon Hf isotopic data on Na-rich granitic rocks from the Tengchong Block, SW China. The granodiorites and associated mafic magmatic enclaves (MMEs) from the Menglian batholith yield zircon U–Pb ages of 116.1 ± 0.8 to 117.8 ± 0.6 Ma and 117.7 ± 0.7 Ma, respectively. Both host granodiorites and enclaves show calc-alkaline and sodium-rich nature, enrichment in large-ion lithophile elements (LILEs), and variable depletion in zircon Hf isotopic compositions. Euhedral amphiboles in both granodiorites and associated enclaves are magnesian-hornblende with high Mg and Ca and contain euhedral plagioclase inclusions of labradorite to andesine (An 36–57 ) composition. The granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources. The quartz monzodiorite–granodiorites and associated MMEs from the Xiaotang-Mangdong batholith yield zircon U–Pb ages of 120.3 ± 1.3 to 122.6 ± 0.8 Ma and 120.7 ± 1.5 Ma. These rocks are also sodium-rich and show calc-alkaline trend with negative zircon Hf isotopic compositions (− 5.55 to + 0.58). The MMEs in the host intrusions are monzogabbro with variable and depleted zircon Hf isotopic compositions. The amphiboles in the both host intrusions and the enclaves show Al-rich ferro-tschermakite composition. We infer that the quartz monzodiorite–granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle-derived mafic magmas. The formation of the different types of Na-rich granitic rocks is correlated to the subduction of Bangong–Nujiang Tethyan ocean. A comparison with magmatism in the northern magmatic belt suggests that mantle-derived magmas played an important role in the genesis of Early Cretaceous intrusions from Tengchong to Lhasa Blocks, although crustal melting is the dominant contributor. [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 Tengchong Block of Southwestern China is key to tracing the eastward subduction of Neo-Tethys and collision between Indian and Asian continents. The block contains a magmatic belt that represents the southeastward continuation of the Gangdese belt, produced by the eastward subduction of eastern Neo-Tethyan oceanic lithosphere. In this paper we present geochemical and geochronological data of Late Cretaceous to Early Paleocene (~ 64 Ma) granitic rocks of the Guyong and Husa batholiths in the Tengchong Block. These can be subdivided into high-silica peraluminous granites and low-silica metaluminous granodiorites, and all belong to the high-K calc-alkaline series, are enriched in LILE, and depleted in HFSE. The Guyong granitoids have high initial Sr ratios of 0.706511–0.711753, negative ε Nd (t) values of − 9.2 to − 11.6, two-stage model ages of 1.39–1.55 Ga, and Pb isotopic compositions that indicate a crustal affinity. The Husa granodiorites also have high initial Sr ratios of 0.716496, negative ε Nd (t) value of − 16.5, two-stage model age of 1.89 Ga, variable ε Hf (t) values of 3.4 to − 18.1 and Pb isotopic compositions similar to lower crustal values. These geochemical and isotopic data indicate that the Guyong granitoids were likely derived from partial melting of ancient crustal metapelite or mixed pelite-greywacke sources, while the Husa granodiorites were derived from the partial melting of lower crustal mixed sources involving metasedimentary and metaigneous rocks. To understand the thermal state and architecture of the Late Cretaceous to Early Paleocene magmatic arc crust, the crust-derived intermediate to acidic igneous rocks of the southern-central Lhasa and Tengchong blocks and eastern Himalayan syntaxis are compared. We infer that partial melting of crust occurred at great depth in the southern Lhasa Block, intermediate depths in the eastern Himalayan syntaxis, and shallow depths in the central Lhasa and Tengchong Block. Sr/Y ratios indicate that the Tengchong Block was characterized by thin crust, while the eastern Himalayan syntaxis and northernmost part of southern Lhasa Block contained crust of normal thickness, and the southernmost part of the southern Lhasa Block contained thickened crust. [ABSTRACT FROM AUTHOR]

Zircon U–Pb ages and geochemical and isotopic data for Late Ordovician granites in the Baoshan Block reveal the early Palaeozoic tectonic evolution of the margin of East Gondwana. The granites are high-K, calc-alkaline, metaluminous to strongly peraluminous rocks with A/CNK values of 0.93–1.18, are enriched in SiO2, K2O, and Rb, and depleted in Nb, P, Ti, Eu, and heavy rare earth elements, which indicates the crystallization fractionation of the granitic magma. Zircon U–Pb dating indicates that they formed at ca. 445 Ma. High initial87Sr/86Sr ratios of 0.719761–0.726754, negative ɛNd(t) values of –6.6 to –8.3, and two-stage model ages of 1.52–1.64 Ga suggest a crustal origin, with the magmas derived from the partial melting of ancient metagreywacke at high temperature. A synthesis of data for the early Palaeozoic igneous rocks in the Baoshan Block and adjacent Tengchong Block indicates two stages of flare-up of granitic and mafic magmatism caused by different tectonic settings along the East Gondwana margin. Late Cambrian to Early Ordovician granitic rocks (ca. 490 Ma) were produced when underplated mafic magmas induced crustal melting along the margin of East Gondwana related to the break-off of subducted Proto-Tethyan oceanic slab. In addition, the cession of the mafic magmatism between late Cambrian-Early Ordovician and Late Ordovician could have been caused by the collision of the Baoshan Block and outward micro-continent along the margin of East Gondwana and crust and lithosphere thickening. The Late Ordovician granites in the Baoshan Block were produced in an extensional setting resulting from the delamination of an already thickened crust and lithospheric mantle followed by the injection of synchronous mafic magma. [ABSTRACT FROM AUTHOR]

Modern continental crust has evolved to a more potassic, granitic composition than early continental crust, which comprises largely sodic TTG-suite magmas. The present paradigm holds that the latter are largely "juvenile" (in the sense that the time from mantle extraction to felsic crust production is comparatively short, of the order 10–100 Ma) while the former represent recycled older crust of igneous or sedimentary composition. The data from high-Mg diorites, tonalites, granodiorites and potassic granites of the 125–115 Ma Menglian Batholith (SE Tibet) exemplify the modern situation and can therefore be used to constrain current crust formation processes. These rocks have higher concentrations of incompatible elements than magmatic rocks from typical continental arc settings, with a continuum of increasing K 2 O/Na 2 O ratios, SiO 2 , K 2 O, Rb, and Th concentrations juxtaposed with decreasing MgO, CaO, and Sr. They consistently record both higher zircon δ18O values than mantle values and decoupled Nd Hf isotope systems caused by the interaction of subducted sediments with the mantle wedge. Petrogenetic mechanisms that connect the suite include crystal fractionation within the diorites, melting of the lower crust induced by advection of heat and water by the diorites, and high-level fractionation of the tonalite-granodiorite suite to produce the high-silica granites. Therefore, this example of modern fertile continental crust had a five-stage evolution: (1) subduction-enrichment of the mantle source, (2) mantle melting to produce mafic magmas that pooled in or below the lower crust, (3) mafic magma differentiation to produce the tonalite-granodioritic magmas controlled by crystal-liquid equilibria, (4) crustal melting and admixture to the evolving felsic magmas and (5) final high-level fractionation and melt extraction to produce the silicic extreme, enriched in incompatible elements such as Rb, Th and K. This model could be a general mechanism for how modern mature continental crust evolves. Importantly, it indicates a significant role for mafic magmas and thence a more important role for juvenile additions than is generally accepted. [ABSTRACT FROM AUTHOR]

Eocene granitic and related igneous rocks in the western Tengchong Block are considered to be the result of eastward subduction of Neo-Tethyan oceanic lithosphere beneath the Tengchong Block. In this paper we show that the granitic and mafic rocks in the western Tengchong Block exhibit a systematic compositional variation from west to east, with Na-rich granodiorites in the Nabang area (west) that differ from coeval high-K calc-alkaline granodiorites in the Bangwan area (east), and with tholeiitic mafic rocks in the Nabang area that differ from shoshonitic mafic microgranular enclaves (MMEs) in granodiorites of the Bangwan area. In addition, high-silica biotite granites were intruded into the granodiorites in the Bangwan area. The host granodiorites, MMEs, and biotite granites in the Bangwan area yield zircon U–Pb ages of ca. 50 Ma. The MMEs have relatively low SiO 2 contents (53.1–64.95 wt%) and Mg# values (37–45), and high K 2 O (4.14–5.02 wt%) and ∑ REE contents (331–509 ppm); the MMEs contain acicular apatites that indicate quenching. The host granodiorites also have high K 2 O (4.48–5.95 wt%) and ∑ REE compositions (320–459 ppm), and together with the MMEs they are enriched in Th but depleted in Nb and Ti. The Sr–Nd–Pb isotopic compositions of the host granodiorites and the MMEs are similar, with ε Hf (t) values of − 1.0 to − 10.8 and 3.3 to − 11.1, respectively. The geochemical data and igneous textures suggest that the MMEs represent a mafic magma that was derived from the partial melting of mantle pyroxenite, with the melting induced by the influx of fluids/melts from the recycling of sediments in the subducted slab. The mafic melts then caused the partial melting of lower crustal tonalitic rocks to produce granodioritic magma that was subsequently mixed with mafic magma. The biotite granites have relatively high SiO 2 contents and low Mg# values that indicate a purely crustal origin and derivation from the partial melting of upper crustal metagraywacke. The similar isotopic compositions of the biotite granites and the granodiorites can be interpreted to reflect the influence of fluids released during crystallization of the granodiorites. A comparison of contemporaneous Eocene granitic and mafic rocks in Nabang, Tongbiguan, Longchuan, and Bangwan in the Tengchong Block reveals that the mafic rocks vary from tholeiitic through high-K calc-alkaline to shoshonitic in composition from west to east, while the granitic rocks vary from Na- to K-rich. These systematic compositional variations indicate that the arc magmatism in the western Tengchong Block was the result of the eastward subduction of the Neo-Tethyan oceanic lithosphere. Fluids or/and melts from the subducted slab (including sediments) are likely to have played an important role in producing these compositional variations. [ABSTRACT FROM AUTHOR]

Paleozoic igneous rocks in the junction zone between the western Qinling and Qilian orogenic belts preserve important message about the deep crustal structure and their tectonic relationship. By means of zircon U Pb dating, Lu Hf isotope, bulk-rock geochemistry for a suite of Paleozoic granites from the western Qinling and Qilian orogenic belt, three main granite pulses were identified: 1) First pulse (∼500 to 450 Ma) quartz diorite with typical island-arc affinity, i.e., intermediate SiO 2 (56.42 to 61.44 wt%) contents, variable Na 2 O/K 2 O ratios of 0.9 to 1.7, high MgO contents (3.14 to 4.40 wt%) with high Mg# values of 55.6 to 60, moderate Sr/Y (22 to 29) ratios and insignificant Eu*/Eu anomalies (0.77 to 0.84), zircons from the quartz diorite have positive ε Hf (t) values of +2.2 to +5.5; all these features indicate that the quartz diorite was formed by hydrous melting of depleted mantle wedge in subduction setting; 2) Second pulse (ca. 440 to 430 Ma), monzogranite (e.g., the Dangchuan and Caochuanpu monzogranite), they display higher SiO 2 (71.23 to 73.91 wt%) contents, K 2 O/Na 2 O (1.10 to 2.26) ratios, lower MgO (0.34 to 0.43 wt%) contents, significant negative Eu anomalies of 0.36 to 0.48, evolved Sr Nd isotopic compositions, and variable zircon Lu Hf (ε Hf (t) = −5.0 to +10.6) compositions, suggesting dehydration melting of heterogeneous crust; 3) Third pulse (ca. 420 to 410 Ma), biotite granite that display typical A-type affinity, i.e., high FeOT/MgO and Ga/Al (10,000 × Ga/Al = 2.7 to 3.0) ratios, high Zr (230 to 313 ppm), Nb (3.49 to 34.6 ppm) and Zr + Nb + Ce + Yb (351 to 512 ppm) contents, most zircons from these biotite granites have negative ε Hf (t) values of −2.7 to −26.6, in combination with their higher Zr saturation temperatures (822 to 842 °C), suggesting high temperature melting of matured continental crust in extensional setting. These results indicate that the western Qinling and Qilian orogenic belts experience a tectonic switch from subduction to extension in Early-Paleozoic (ca. 460 to 410 Ma). All these granites record the crustal evolution and switch of melting regime in convergent margin. [Display omitted] • Three Paleozoic magmatic pulses in the junction zone between North Qinling and Qilian. • Hydrous melting of depleted mantle wedge formed the first pulse. • Dehydration melting of juvenile mafic crust formed the second pulse. • High temperature melting of heterogeneous crust in extensional setting formed the third pulse. [ABSTRACT FROM AUTHOR]

Neoproterozoic magmatism along the western margin of the Yangtze Block can provide important information about the evolution of the Supercontinent Rodinia. For this reason, this study is focused on Neoproterozoic high-Mg# quartz monzodiorite and granodiorite from the Luding–Kangding area. Detailed zircon LA-ICP MS U–Pb dating indicates that the high-Mg# quartz monzodiorite and the granodiorite have identical ages of 754 ± 10 Ma (MSWD = 0.51, 2 σ ) and 748 ± 11 Ma (MSWD = 0.33, 2 σ ), respectively. The high-Mg# quartz monzodiorite are characterized by low SiO 2 contents (60.76–63.78%) and high TiO 2 contents (0.41–0.56%), and they are sodic and meta-aluminous. They are enriched in LREE, with (La/Yb) N values of 4.14–8.51, and without significant negative Eu anomalies (Eu * /Eu = 0.79–0.92). The high-Mg# quartz monzodiorite have relative low initial ( 87 Sr/ 86 Sr) i ratios of 0.703513–0.704519, and positive ɛ Nd ( t ) values of +2.4 to +4.8, and are depleted in HFSEs (Nb and Ta). Thus, it can be inferred that these high-Mg# quartz monzodiorite were formed by high degree (∼40%) partial melting of newly formed mafic lower crust, and that their high Mg# values were the result of assimilation of some residual mafic minerals in their source region. The granodiorite are characterized by higher SiO 2 contents (65.32–67.59%), and they are also sodic and meta-aluminous. They have more evolved Sr–Nd isotopic compositions and higher Sr (425–537 ppm) and Ba (705–1074 ppm) contents than the quartz monzodiorite, suggesting that they were derived from a plagioclase-rich source region. Based on their field occurrence and geochemical features, we propose that both the Neoproterozoic high-Mg# quartz monzodiorite and the granodiorite were formed in an active continental arc setting, but they derived from two distinct source regions. [ABSTRACT FROM AUTHOR]

Western Yunnan, an important constituent of the southeastern segment of the East Tethyan tectonic domain, lies along a transformed orientation from the NWW trending Himalayan–Tethyan segment to the northerly trending Southeast Asian segment. However, the geodynamical setting of the Early Cretaceous tectonothermal magmatism along the Bangong–Nujiang–Lushui–Luxi–Ruili belt as the Tethyan branch in western Yunnan (SW China) remains controversial. The Donghe granitoid, which is located between the Gaoligong and Tengliang belts in the northern Tengchong block, reveals its petrogenesis and its tectonics, both of which play a vital role in resolving previous disputes. Our zircon laser ablation inductively coupled plasma mass spectrometry U–Pb dating of granites from the Donghe batholith yields ages of 119.9 ± 0.9–130.6 ± 2.5 Ma. These granites display features typical of highly fractionated I-type granites: high SiO 2 contents (>71 wt.%), high K contents (K 2 O = 3.88–5.66 wt.%), calc-alkaline character, slight peraluminosity (A/CNK = 1.02–1.16), and a highly differentiated index ranging from 83.6 to 95.6. In addition, as SiO 2 contents increase, the rare earth element (REE) abundances, especially heavy REE abundances, and REE pattern slopes change gradually, but the negative Eu anomalies increase sharply, while the degree of enrichment in Rb, Th, U, and Pb and depletion in Ba, Nb, Sr, P, and Ti are enhanced. These features indicate that K-feldspar, ±plagioclase, ±biotite, ±amphibole, ±apatite, ±sphene/garnet, and ±Fe–Ti oxides such as ilmenite play the major role in the fractional crystallization process. The high initial 87 Sr/ 86 Sr (0.7067 and 0.7079) and negative ε Nd ( t ) values (−8.6 to −10.1), with T 2DM ranging from 1.39 to 1.49 Ga, indicate that the sources were mainly derived from the mature ancient middle to lower crust and minor mantle-derived materials. The initial 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of 18.462–18.646, 15.717–15.735, and 38.699–39.007, respectively, signify that some subduction-related material such as ocean island volcanic rocks and mature arc primitive rocks may be involved as sources. Based on an analysis of similar zircon saturated temperature and geochemical characteristics of typical highly fractionated I-type granites in SE and SW China, and consideration of the regional geological setting, we suggest that the parent magma may be derived from the ancient middle to lower continental crust and mantle-derived basaltic magma. These were generated in the setting of a westward subducted Lushui–Luxi–Ruili (LLR) Tethyan oceanic slab, where mantle-wedge-derived sources provided enough heat and material to melt the middle to lower ancient crust. Taking into account the temporal–spatial distributions of Early Cretaceous magmatic rocks in the region, we further suggest the existence of an Andean-type active continental margin from the Lhasa block to the Tengchong block along the Bangong–Nujiang–LLR Tethys Ocean during the Early Cretaceous. [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]

Arc magmatism is an important process in the formation and evolution of the continental crust. Various arcs developed in the southern margin of Eurasian continent that recorded the final formation and growth of these micro-continent before the final India-Eurasia amalgamation. We have examined the often neglected Tengchong arc segment in southeastern Tibet using compiled zircon U-Pb-Hf and whole-rock geochemistry with GPS location and lithology control. The aim is to better understand the driving mechanism of spatial migration and temporal evolution of multi-stage high-MAR (magma addition rate) events and its role in formation and growth of Tengchong arc segment. Results indicate three magmatic "flare-ups" during east-to-west arc migration, from ~131–111 Ma (eastern), ~76–64 Ma (central), to ~55–49 Ma (western), during amalgamation of Lhasa-Tengchong and Qiangtang-Baoshan blocks and final collision of India-Asia plate following subduction of Neo-Tethys. Zircon Hf isotopes and geochemical analyses shows the significant increasing juvenile and/or mantle-derived materials and the range of isotopes also broaden during flare-ups, indicating the melting of diverse lithospheric and upper plate domains. Through comparison with geophysical parameters, these pulses are closely coupled with the arc migration along with changes of crustal thickness, but not correlated with angle and rates of convergence. The spatial arc migration of the multi-stage high-MAR events in Tengchong arc segment was potentially driven by slab steepening and break-off following the initial collision, and abrupt changes of subduction slab dynamics. These processes are well coupled with multi-stage interactions of crust-mantle and transitional Moho-depths. • High-magma addition rate events in formation and growth of Tengchong arc, SE Tibet. • Three magmatic "flare-ups" during east-to-west arc migration. • High-MAR events has been driven by the initial collision and abrupt changes of subduction slab dynamic. • Coupling with multi-stage interactions of crust-mantle and transitional Moho-depth. [ABSTRACT FROM AUTHOR]

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]

Abstract: The origin of high-Mg adakitic granitoids in collisional orogens can provide important information about the nature of the lower crust and upper mantle during the orogenic process. Late-Triassic high-Mg adakitic granite and its mafic enclaves from the Dongjiangkou area, the Qinling orogenic belt, central China, were derived by partial melting of subducted continental crust and underwent interaction with the overlying mantle wedge peridotite. Adakitic affinity of the different facies of the Dongjiangkou granite body are: high Sr, Ba, high La/Yb and Sr/Y, low Y,Yb, Yb/Lu and Dy/Yb, and no significant Eu anomalies, suggesting amphibole+garnet and plagioclase-free restite in their source region. Evolved Sr-Nd-Pb isotopic compositions [(87Sr/86Sr) i =0.7050 to 0.7055,εNd(t)=–6.6 to –3.3; (206Pb/204Pb) i =17.599 to 17.799, (207Pb/204Pb) i =15.507 to 15.526, (208Pb/204Pb) i =37.775 to 37.795] and high K2O, Rb, together with a large variation in zircon Hf isotopic composition (εHf(t)=−9.8 to +5.0), suggest that the granite was derived from reworking of the ancient lower continental crust. CaO, P2O5, K2O/Na2O, Cr, Ni, Nb/Ta, Rb/Sr and Y increase, and SiO2, Sr/Y and Eu/Eu* decrease with increasing MgO, consistent with interaction of primitive adakitic melt and overlying mantle peridotite. Zircons separated from the host granites have U-Pb concordia ages of 214±2Ma to 222±2Ma, compatible with exhumation ages of Triassic UHP metamorphic rocks in the Dabie orogenic belt. Mafic microgranular enclaves and mafic dykes associated with the granite have identical zircon U-Pb ages of 220Ma, and are characterized by lower SiO2, high TiO2, Mg# and similar evolved Sr-Nd-Pb isotopic composition. Zircons from mafic microgranular enclaves (MMEs) and mafic dykes also show a large variation in Hf isotopic composition with εHf(t) between −11.3 and +11.3. It is inferred that they were formed by partial melting of enriched mantle lithosphere and contaminated by the host adakitic granite magma. In combination with the regional geology, high-Mg# adakitic granitoid rocks in the Dongjiangkou area are considered to have resulted from interaction between subducted Yangtze continental crust and the overlying mantle wedge. Triassic continental collision caused detachment of the Yangtze continental lithosphere subducted beneath the North China Craton, at ca. 220Ma causing asthenosphere upwelling and exhumation of the continental crust. Triassic clockwise rotation of the Yangtze Craton caused extension in the Dabie area which led to rapid exhumation of the subducted continental lithosphere, while compression in the Qinling area and high-P partial melting (amphibole±garnet stability field) of the subducted continental crust produced adakitic granitic magma that reacted with peridotite to form Mg-rich hybrid magma. [Copyright &y& Elsevier]

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]

Earth's evolution involves deep, hot rocks rising upward by convection to near-surface environments, as well as the unique scenarios such as the formation and breakup of Gondwana and Pangea. These processes have been well recorded by the widely distributed magmatism. To understand the tectonic evolution and Gondwana assembly, we compiled early Paleozoic zircon U–Pb ages (n = 67), in-situ zircon Hf isotopes (n = 1011), and bulk-rock elemental compositions (n = 293) and Sr–Nd isotopes of magmatic rocks in the Tibetan–Himalayan orogen. Three stages of Paleozoic magmatism were identified here, including early (>490 Ma) to middle (490–470 Ma) to late (<470 Ma) stages, in response to the final assembly of the Gondwana supercontinent. Early-stage magmatic rocks are characterized by highly variable SiO 2 (48.0–80.0 wt%) and MgO (0.02–9.65 wt%) contents with Mg# range from 5.4 to 78, K 2 O/Na 2 O ratios ranging from 0.14 to 2.81, and whole-rock Sr–Nd (87Sr/86Sr(i) (0.7035–0.7340), ε Nd (t) (-9.5–+1.0)) and zircon Hf (ε Hf (t) = –15 to + 8.0) isotopic compositions with significant mantle contributions; they could be generated in an Andean-type arc setting along the active northern continental Gondwana margin. Middle-stage magmas were dominated by fertile continental crustal signatures (SiO 2 > 70 wt%, A/CNK > 1.10, MgO < 2.69 wt%) in a crustal thickening setting. Late-stage magmas also have highly variable Si, Mg and isotopic components, with coeval mantle-derived magmas developing in an extensive setting. Importantly, the widespread presence of early Cambrian to late Ordovician peraluminous high-K calc-alkaline magmatism in the Tibetan–Himalayan orogen indicates that the reworking of ancient continental crustal materials played a key role in reconstructing and stabilizing the final Gondwana assembly. [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 granite is one of most widely distribution rocks in crust, and its petrogenesis is crucial to advance our knowledge of thermal condition in continental crust. The long-time tectonic evolution of crust in the active continental margin could be recorded by multi-stages of granitic assemblage. In order to reveal the subduction of Neo-Tethys and initial collision of Indian-Asian continents in eastern Tibetan Plateau, we selected the Early Paleocene to Early Eocene granitic rocks with associated enclaves in Tengchong Block, southeastern extension of Gangdese magmatic belt, to clarify their different derivation regimes using geochemical and isotopic compositions, mineral compositional variation. The zircon data show that Early Paleocene granites formed at 64 Ma, and Early Eocene granitic rocks formed at 54 Ma. Combing with the field contact relationship, the similar and enriched Sr-Nd-Pb and zircon Hf isotopic compositions indicate that the two stages of granitic rocks have a common and ancient lower crustal source. The enclaves in Early Paleocene granites could represent crystallization of coeval and cognate magmas at margin of magmatic conduit, but the enclaves in Early Eocene granitic rocks are products of magma mixing between mafic and felsic magma. According to rock assemblages and geochemical signatures of granitic rocks during Early Paleocene to Early Eocene in Tengchong Block, we propose that Early Paleocene granitic rocks are derived from partial melting of lower crustal rocks induced by long-lived heat accumulation with no or minimal basalt flux during the Neo-Tethyan subduction, whereas Early Eocene granitic rocks are derived from melting of crustal materials resulted from high mafic magma flux during Indian-Asian continental collision. The initial collision occurred at ca. 55 Ma. • Granitic pluton in Sudian area is assembly during Early Paleocene and Early Eocene. • Two stages of granites are derived from a common lower crustal mafic source. • Granite at 64 Ma is formed by long-lived heat accumulation during subduction. • Granite at 55-50 Ma is derived from high mafic magma flux during syn-collision. [ABSTRACT FROM AUTHOR]

Silicic magmas, primarily felsic I- and S-type granite (sensu lato), play a key role in understanding the compositional evolution and differentiation of the continental crust. However, the genetic models of felsic I-type granites remain controversial. Herein we investigate the Gaoligong granite (sensu lato) belt in southern Tibet and compare its features with an extensive dataset that we compiled on high‑potassium calc-alkaline peraluminous I-type granite from typical granitic belts around the word with a view to gain insights on the genesis of felsic I-type granites. The Early-Cretaceous granites from Gaoligong belt mostly belong to high-K calc-alkaline peraluminous I-type series. Zircon Lu Hf (εHf(t) = −16.3 – +0.9) and whole-rock Sr Nd isotopic data (εNd(t) = −14.6 – +3.0) on these rocks show highly variable and evolved nature, suggesting that the granites were generated by partial melting of lower crustal materials with possible involvement of upper crustal materials, followed by mixing, leading to marked variation in source compositions. Compilation of the dataset and comparison with felsic I- and S-type granites show the following salient features: (1) possibly distinct trends of Al 2 O 3 , P 2 O 5 , K 2 O, Rb, Sr, Pb, Th, U and Ga vs. MgO + FeOT between the felsic I-type granites and those S-types; and (2) there are notably higher and variable zircon Hf (εHf(t) > 10ε units) and whole-rock Sr Nd (εNd(t) > 5ε units) isotopic compositions of I-type granites than those of the S-types. Comparison with experimental liquids and other typical cases around the world, indicate that the felsic I-type granites from Gaoligong are similar to those secondary I-type granites, where mixing processes and extensive partial melting of the heterogeneous lower crust by a mantle-like magma control the variable components. The range of compositional diversity is significantly higher for the studied felsic I-type granites than those typical S-type granites from north Queensland. Our study provides further insights into the application of geochemical and isotopic proxies to differentiate felsic I- and S-type granites. • Melting of lower crustal materials followed by mixing in source compositions. • Higher variable isotopic compositions of I-type granites than those S-types. • Distinctly geochemical evolution between the felsic I- and S-type granites. • Genesis indicators for the high-K calc-alkaline peraluminous I-type granites [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]

The high Ba–Sr rocks can provide significant clues about the evolution of the continent lithosphere, but their petrogenesis remains controversial. Identifying the Late Cretaceous high Ba–Sr granodiorites in the SE Lhasa Block could potentially provide valuable insights into the continent evolution of the Qinghai-Tibet Plateau. Zircon U–Pb ages suggest that the granodiorites were emplaced at 87.32 ± 0.43 Ma. Geochemically, the high Ba–Sr granodiorites are characterized by elevated K2O + Na2O contents (8.18–8.73 wt%) and K2O/Na2O ratios (0.99–1.25, mostly > 1), and belong to high-K calc-alkaline to shoshonitic series. The Yonglaga granodiorites show notably high Sr (653–783 ppm) and Ba (1346–1531 ppm) contents, plus high Sr/Y (30.92–38.18) and (La/Yb)N (27.7–34.7) ratios, but low Y (20.0–22.8 ppm) and Yb (1.92–2.19 ppm) contents with absence of negative Eu anomalies (δEu = 0.83–0.88), all similar to typical high Ba–Sr granitoids. The variable zircon εHf(t) values of − 4.58 to + 12.97, elevated initial 87Sr/86Sr isotopic ratios of 0.707254 to 0.707322 and low εNd(t) values of − 2.8 to − 3.6 with decoupling from the Hf system suggest that a metasomatized mantle source included significant recycled ancient materials. The occurrence of such high Ba–Sr intrusions indicates previous contributions of metasomatized mantle-derived juvenile material to the continents, which imply the growth of continental crust during the Late Cretaceous in the SE Lhasa. Together with regional data, we infer that the underplated mafic magma provides a significant amount of heat, which leads to partial melting of the juvenile crust. The melting of the metasomatized mantle could produce a juvenile mafic lower crust, from which the high Ba–Sr granitoids were derived from reworking of previous mafic crust during the Late Cretaceous (ca. 100–80 Ma) in the SE Lhasa. [ABSTRACT FROM AUTHOR]

The relationship between the Shangdan and Erlangping suture zone (ESZ) and the initiation stretch time of the Early Paleozoic back‐arc system in the Qinling Orogen still remains unclear. This paper reports the chronological and geochemical data of the Miaogou mafic intrusion along the southern margin of the Shangdan suture. The pyroxenite in the mafic intrusion has a zircon U–Pb age of 485 ± 5 Ma (Mean Standard Weighted Deviation (MSWD) = 0.08, n = 18). It has low SiO2 (45.41–46.02 wt%), K2O (0.42–0.44 wt%), and TiO2 (0.73–0.83 wt%) contents, high MgO (13.9–15.13 wt%) contents with high Mg# (74–77). In combination with its high clinopyroxene portion, the pyroxenite represented the accumulates from the mafic magma. Some sieve rims of the clinopyroxene indicate that the primitive pyroxenite was metasomatized by subduction‐related fluids. However, their consistent trace element and rare earth element (REE) patterns suggest that the metasomatism process has insignificant effects on their geochemical features. Zircons from the pyroxenite have positive εHf(t) (+7.18 to +11.75) values, reveal a depleted source region. In combination with its high V (322–1,093 ppm) contents, low Ti/V (10–15) ratios and smooth REE patterns, we propose that the pyroxenite was derived from metasomatized depleted mantle wedge in a back‐arc basin. In considering the duration limit (<475 Ma) of the back‐arc basin along the ESZ, we argued that the ~485 Ma Miaogou pyroxenite represented the initiation back‐arc basin in the Shangdan suture, which might represent the initial rifting of the North Qinling microcontinent induced by the northward subduction of the Shangdan Ocean. [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]

The Lesser Xing'an–Zhangguangcai Range is located in the eastern part of the Central Asian Orogenic Belt (CAOB). Early Mesozoic igneous rocks in this area can place constraints on the crustal growth mechanism in the Northeastern China. This paper reports a suite of Late Triassic high‐Mg diorites and mafic dikes from the southern Lesser Xing'an–Zhangguangcai Range. The mafic dikes have younger zircon U–Pb ages of 195 ± 2 Ma. They display intermediate SiO2 (50.58% to 58.20%) and high Na2O/K2O ratios of 1.90 to 3.20, low A/CNK ratios of 0.75 to 0.84, low (87Sr/86Sr)i ratios of 0.7045 to 0.7046, and high εNd(t) values of +3.1 to +3.5. Most zircons in the mafic dikes exhibit positive εHf(t) values from +8.6 to +16.0, with single‐stage Hf model ages ranging from 0.2 to 0.5 Ga in combination with their enrichment in LREE and LILEs and depletion in HFSEs. They are considered to be formed by melting of metasomatized subarc lithosphere mantle. The diorite and quartz diorite have older zircon U–Pb ages of 200 ± 3 and 202 ± 2 Ma, respectively. They have SiO2 = 54.45% to 61.18%, Al2O3 = 17.16% to 19.10%, TiO2 = 0.74% to 1.13%, and Mg# = 46.6 to 49.5, and they also display moderately depleted Sr–Nd (εNd(t) = +2.3 to +4.3) and zircon Lu–Hf (εHf(t) = +8.6 to +16.0) isotopic compositions. These features suggest that they were formed by melting of juvenile arc crust in active continental margin. Considering the occurrence of the contemporaneous and latter igneous rocks in the Zhangguangcai Range, we argue that the diorite, quartz diorite, and mafic dikes from the Lengshan area were also related to the westward subduction of Palaeo‐Pacific Plate (Izanagi Plate) beneath the Eurasian Plate. The strike‐like fault along the eastern margin of the Songneng–Zhuangguangcai Block may play an important role in the genesis of diorite melt. [ABSTRACT FROM AUTHOR]

Establishing the nickel (Ni) isotopic composition of the upper continental crust (UCC) is crucial for using the Ni isotope system to trace biogeochemical processes and understand crust-mantle interactions. This study reports the Ni isotopic composition of eighty-four well-characterized upper crustal samples, including granites, granodiorites, tonalite-trondhjemite-granodiorite (TTG), loess, river sediments and glacial diamictites, to constrain the Ni isotopic composition of the UCC. Significant variations in δ60Ni are revealed for I-type (0.02–0.26‰), A-type (−0.05–0.08‰) and S-type (0.08–0.36‰) granites for the first time. These Ni isotopic variations are attributed to magmatic differentiation for I- and A- type granites and source heterogeneity for S-type granites. The δ60Ni values of fine-grained clastic sediments (including loess, river sediments and glacial diamictites) range from −0.01‰ to 0.23‰. Such δ60Ni variations cannot be explained by Ni isotopic fractionation during chemical weathering because there are no clear correlations between δ60Ni and Ni/Al 2 O 3 , or the chemical index of alteration (CIA). Instead, the δ60Ni variations in fine-grained clastic sediments are likely inherited from source rocks. The δ60Ni values of our samples for 3.2–3.5 Ga TTGs (0.00–0.13‰), 2.4–2.5 Ga TTGs (0.04–0.13‰) and < 0.4 Ga granites (excluding S-type granites) are statistically indistinguishable (P < 0.05, student's t -test), implying limited variation of δ60Ni in the felsic igneous UCC since 3.5 Ga. Similarly, the δ60Ni values of glacial diamictites suggest insignificant temporal variation in the weathered UCC since 2.4 Ga. The data gathered in this study combined with literature data yields an arithmetic mean δ60Ni value of 0.12 ± 0.15‰ (2SD) for the UCC (ranging from −0.07‰ to 0.36‰). And the weighted average δ60Ni is estimated to be 0.07 ± 0.10‰ (2SD) or 0.11 ± 0.09‰ (2SD) depending on the assumed δ60Ni of the metamorphic rocks. Thus, a lithology-weighted average δ60Ni needs to be further determined by future studies when the δ60Ni values of metamorphosed sedimentary rocks in the UCC are constrained. [ABSTRACT FROM AUTHOR]

The fractionation of hornblende is a common phenomenon in arc magmas, and gives rise to a number of notable geochemical characteristics. However, it is often cryptic, with limited direct petrographic evidence for the fractionation, or even presence of amphibole in volcanic suites. Newly identified hornblendites in the SE Tibet represent direct evidence for hornblende fractionation in the Gangdese arc. The hornblendites have age ranges from 95.3 ± 0.2 to 92.6 ± 0.2 Ma, recording magmatic activities over a ca. 2 Myr interval. Textural relationships indicate that hornblendites form by peritectic reactions between an evolving melt and earlier-formed clinopyroxenites. Relict clinopyroxenes and primitive pargasite record melt evolution from high Sr/Y basaltic andesite to dacite, during cooling from ∼1050 °C to ∼850 °C in the mid to lower crust. The clinopyroxene precursors interacted with water-rich high SiO 2 fluids/melts at ca. 800 °C. Zircons have high δ18O values (up to 7.62‰) and positive ε Hf (t) values (up to +13.0), but bulk rock data show high 87Sr/86Sr ratios (up to 0.7093) and negative ε Nd (t) values (ca. −3.2). This decoupled signature implies the primary magmatic source was metasomatized by 5–10% recycled subducted sediments. Magmas have a high oxygen fugacity (ΔNNO can up to +2.40) through a combination of metasomatism during subduction, and subsequent melt-mush interaction that is recorded by zoned hornblendes. Metasomatism, widespread and long-term fractionation of amphibole ± garnet ± clinopyroxene, and high oxygen fugacity, are all positive indicators for the fertility of arc magmas with respect to porphyry copper formation. This study demonstrates that late-stage melt-mush interaction can contribute to peritectic hornblendite formation and facilitate magma fertility. [ABSTRACT FROM AUTHOR]