Search Results (110)

The southern Great Xing’an Range is located in the overlap zone of the Paleo-Asian Ocean metallogenic domain and the Circum-Pacific metallogenic domain. It hosts numerous Sn-polymetallic deposits, such as Weilasituo, Bianjiadayuan, Huanggang, and Dajing, and witnessed multiple episodes of magmatism during the Late Mesozoic. The study area is situated within the Huanggangliang-Ganzhuermiao metallogenic belt in the southern Great Xing’an Range. The region has witnessed extensive magmatism, with Mesozoic magmatic activities being particularly closely linked to regional mineralization. We present petrographic, zircon U-Pb chronological, lithogeochemical, and Lu-Hf isotopic analyses of the Yexilinhundi granites. The results indicate that the granite porphyry and granodiorite were emplaced during the Late Jurassic. Both rocks exhibit high SiO₂, K₂O + Na₂O, differentiation index (DI), and 10,000 Ga/Al ratios, coupled with low MgO contents. They show distinct fractionation between light and heavy rare earth elements (LREEs and HREEs), exhibit Eu anomalies, and have low whole-rock zircon saturation temperatures (T_zr), collectively demonstrating characteristics of highly fractionated I-type granites. The εHf(t) values of the granites range from 0.600 to 9.14, with young two-stage model ages (T_DM2 = 616.0~1158 Ma), indicating that the magmatic source originated from partial melting of Mesoproterozoic-Neoproterozoic juvenile crust. This study proposes that the granites formed in a post-collisional/post-orogenic extensional setting associated with the subduction of the Mongol-Okhotsk Ocean, providing a scientific basis for understanding the relationship between the formation of Sn-polymetallic deposits and granitic magmatic evolution in the study area. Full article

The Qieliekeqi siderite deposit, located in the Tashkurgan block of western Kunlun, is a carbonate-hosted iron deposit with hydrothermal sedimentary features. This study integrates whole-rock geochemistry, stable isotopes, and zircon U–Pb–Hf data to investigate its metallogenic evolution. Coarse-grained siderite samples, formed in deeper water, exhibit average Al₂O₃/TiO₂ ratios of 29.14, δEu of 2.69, and δCe of 0.83, indicating hydrothermal fluid dominance with limited seawater mixing. Banded samples from shallower settings show an average Al₂O₃/TiO₂ of 17.07, δEu of 3.18, and δCe of 0.94, suggesting stronger seawater interaction under oxidizing conditions. Both types are enriched in Mn, Co, and Ba, with low Ti and Al contents. Stable isotope results (δ¹³C_PDB = −6.0‰ to −4.6‰; δ¹⁸O_SMOW = 16.0‰ to 16.9‰) point to seawater-dominated fluids with minor magmatic and meteoric contributions, formed under open-system conditions at avg. temperatures of 53 to 58 °C. Zircon U–Pb dating yields an age of 211.01 ± 0.82 Ma, with an average εHf(t) of −3.94, indicating derivation from the partially melted ancient crust. These results support a two-stage model involving Late Cambrian hydrothermal sedimentation and Late Triassic magmatic overprinting. Full article

Late Paleozoic to Early Mesozoic granitoids in the East Kunlun Orogenic Belt (EKOB) provide critical insights into the complex and debated relationship between Paleo–Tethyan magmatism and tectonics. This study presents integrated bulk-rock geochemical and zircon isotopic data for the Xingshugou monzogranite (MG) to address these controversies. LA-ICP-MS zircon U-Pb dating constrains the emplacement age of the MG to 247.1 ± 1.5 Ma. The MG exhibits a peraluminous and low Na₂O A₂-type granite affinity, characterized by high K₂O (4.69–6.80 wt.%) and Zr + Nb + Ce + Y (>350 ppm) concentrations, coupled with high Y/Nb (>1.2) and A/CNK ratios (1.54–2.46). It also displays low FeO^T, MnO, TiO₂, P₂O₅, and Mg^# values (26–49), alongside pronounced negative Eu anomalies (Eu/Eu* = 0.37–0.49) and moderately fractionated rare earth element (REE) patterns ((La/Yb)_N = 3.30–5.11). The MG exhibits enrichment in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; such as Sr and Ba), and depletion in high field strength elements (HFSEs; such as Nb, Ta, and Ti), collectively indicating an arc magmatic affinity. Zircon saturation temperatures (T_Zr = 868–934 °C) and geochemical discriminators suggest that the MG was generated under high-temperature, low-pressure, relatively dry conditions. Combined with positive zircon ε_Hf(t) (1.8 to 4.7) values, it is suggested that the MG was derived from partial melting of juvenile crust. Synthesizing regional data, this study suggests that the Xingshugou MG was formed in an extensional tectonic setting triggered by slab rollback of the Paleo-Tethys Oceanic slab. Full article

The South Tianshan records the latest accretionary and collisional events in the southwestern Altaids, but the internal subduction-related processes are controversial. This study provides an integrative analysis of a newly identified Late Carboniferous adakitic granodiorite from the South Tianshan, incorporating geochronological, zircon U-Pb and Lu-Hf isotopic, whole-rock geochemical, and Sr-Nd isotopic data. Zircon U-Pb analysis indicates that the granite was emplaced at 310 ± 2.5 Ma. Based on major element compositions, the granodiorite belongs to medium-K calc-alkaline weakly peraluminous series (A/CNK = 0.95–1.09). The samples exhibit typical high-silica adakitic affinity, as evidenced by the elevated contents of SiO₂ (67.75–69.27 wt.%), Al₂O₃ (15.29–15.90 wt.%), Sr (479–530 ppm), and Ba (860–910 ppm); low concentrations of Yb (0.43–0.47 ppm) and Y (7.12–7.44 ppm); high Sr/Y ratios (67–72); and slight Eu anomalies (δEu = 0.89–1.03). The sodium-rich composition (K₂O/Na₂O = 0.48–0.71) is comparable to adakitic rocks from slab-derived melts. Elevated concentrations of Ni (22.12–24.25 ppm), Cr (33.20–37.86 ppm), Co (6.32–6.75 ppm), and V (30.33–32.48 ppm), along with high Mg# values (55–57), suggest melt–mantle interaction during magma ascent. The slightly enriched isotopic signatures, characterized by higher initial ⁸⁷Sr/⁸⁶Sr ratios (0.706086–0.706205) and lower ε_Nd(t) (−3.09 to –2.47) and ε_Hf(t) (−3.11 to +7.66) values, point to notable sedimentary contributions, potentially through source contamination and/or shallow-level crustal contamination. By integrating the new results with previously published data, we consider that the adakitic granodiorite was generated by partial melting of the subducted oceanic crust, triggered by asthenospheric upwelling associated with the southward rollback of the north-dipping South Tianshan oceanic lithosphere. Our data provide new insights into Late Carboniferous retreating subduction along the southern active margin of the Yili-Central Tianshan and the accretionary architecture of the southern Altaids. Full article

The Late Paleozoic granitoids widely distributed in the central section of the East Kunlun Orogenic Belt (EKOB) are responsible for the constraints on its post-collisional extensional processes. We report the whole-rock geochemical compositions, zircon U-Pb ages, and zircon Hf isotope data of granites in the western Kendewula area. The granites, dated between 413.7 Ma and 417.7 Ma, indicate emplacement during the Early Devonian period. The granite is characterized by high silicon content (72.45–78.96 wt%), high and alkali content (7.59–9.35 wt%), high 10,000 × Ga/Al values, and low Al2O3 (11.29–13.32 wt%), CaO (0.07–0.31 wt%), and MgO contents (0.16–0.94 wt%). The rocks exhibit enrichment in large-ion lithophile element (LILE) content and high-field-strength element (HFSE) content, in addition to strong losses, showing significant depletion in Ba, Sr, P and Eu. These geochemical characteristics correspond to A2-type granites. The values of Rb/N and Ba/La and the higher zircon saturation temperature (800~900 °C) indicate that the magma source is mainly crustal, with the participation of mantle materials, although limited. In addition, the zircon εHf(t) values (−4.3–3.69) also support this view. In summary, the A2-type granite exposed in the western Kendewula region formed against a post-collisional extensional setting background, suggesting that the Southern Kunlun Terrane (SKT) entered a post-orogenic extensional phase in the evolution stage since the Early Devonian. The upwelling of the asthenospheric mantle of the crust, triggered by crustal detachment and partial melting, likely contributed to the flare-up of A2-type granite during this period. By studying the nature of granite produced during orogeny, the evolution process of the formation of orogenic belts is discussed, and our understanding of orogenic is enhanced. Full article

The Southern Beishan Orogenic Belt (SBOB), an integral part of the Southern Central Asian Orogenic Belt (CAOB), is characterized by extensive Late Paleozoic magmatism. These igneous rocks are the key to studying the tectonic evolution process and the ocean–continent tectonic transformation in the southern margin of the CAOB and Paleo-Asian Ocean. We present zircon U-Pb chronology, in situ Lu-Hf isotopes, and whole-rock geochemistry data for Early–Middle Devonian volcanic rocks in the Sangejing Formation and granites from the Shuangyingshan-Huaniushan (SH) unit in the SBOB. The Wudaomingshiu volcanic rocks (Ca. 411.5 Ma) are calc-alkaline basalt-basaltic andesites with low SiO₂ (47.35~55.59 wt.%) and high TiO₂ (1.46~4.16 wt.%) contents, and are enriched in LREEs and LILEs (e.g., Rb, Ba, and Th), depleted in HREEs and HFSEs (Nb, Ta, and Ti), and weakly enriched in Zr-Hf. These mafic rocks are derived from the partial melting of the depleted lithosphere metasomatized by subduction fluid and contaminated by the lower crust. Wudaomingshui’s high-K calc-alkaline I-type granite has a crystallization age of 383.6 ± 2.2 Ma (MSWD = 0.11, n = 13), high Na₂O (3.46~3.96 wt.%) and MgO (1.25~1.68 wt.%) contents, and a high DI differentiation index (70.69~80.45); it is enriched in LREEs and LILEs (e.g., Rb, Ba, and Th) and depleted in HREEs and HFSEs (e.g., Nb, Ta, and Ti). Granites have variable zircon ε_Hf(t) values (−2.5~3.3) with Mesoproterozoic T_DM2 ages (1310~1013 Ma) and originated from lower crustal melting with mantle inputs and minor upper crustal assimilation. An integrated analysis of magmatic suites in the SBOB, including rock assemblages, geochemical signatures, and zircon ε_Hf(t) values (−2.5 to +3.3), revealed a tectonic transition from advancing to retreating subduction during the Early–Middle Devonian. Full article

The attributes of Late Paleozoic magmatic events are of paramount significance in elucidating the tectonic evolution of the Ulanhot region, which is located in the middle of the Hegenshan–Heihe tectonic belt (HHTB). This study undertook a comprehensive investigation of the petrography, LA–ICP–MS zircon U–Pb dating, whole rock geochemistry, and zircon Hf isotopes of the Early Carboniferous volcanic rocks. The volcanic rocks are predominantly composed of andesite, schist (which protolith is rhyolitic tuff), and rhyolitic tuff. The results of zircon U–Pb dating reveal that the formation ages of volcanic rocks are Early Carboniferous (343–347.4 Ma). Geochemical characteristics indicate that the andesites possess a comparatively elevated concentration of Al₂O₃, alongside diminished levels of MgO and TiO₂, belonging to the high-K calc-alkaline series. The zircon εHf(t) of the andesites range from −13 to 9.4, while the two-stage Hf model ages span from 697 to 1937 Ma. The felsic volcanic rocks have high contents of SiO₂ and Na₂O + K₂O, low contents of MgO and TiO₂, and belong to high-K to normal calc-alkaline series. The zircon εHf(t) values of the felsic volcanic rocks range from −12.8 to 10, while the two-stage Hf model ages span from 693 to 2158 Ma. The Early Carboniferous volcanic rocks exhibit a notable enrichment in large ion lithophile elements (LILEs, such as Rb, K, Ba) and light rare earth elements (LREEs), depletion in high-field-strength elements (HFSEs, including Nb, Ta, Ti, Hf), as well as heavy rare earth elements (HREEs). The distribution patterns of the rare earth elements (REEs) demonstrate a conspicuous right-leaning tendency, accompanied by weak negative Eu anomalies. These characteristics indicate that the andesites represent products of multistage mixing and interaction between crustal and mantle materials in a subduction zone setting. The felsic volcanic rocks originated from the partial melting of crustal materials. Early Carboniferous igneous rocks formed in a volcanic arc setting are characteristic of an active continental margin. The identification of Early Carboniferous arc volcanic rocks in the Central Great Xing’an Range suggests that this region was under the subduction background of the oceanic plate subduction before the collision and amalgamation of the Erguna–Xing’an Block and the Songnen Block in the Early Carboniferous. Full article

A diverse range of granitoids in the North Qilian Orogenic Belt (NQOB) offers valuable insights into the region’s tectonomagmatic evolution. In this study, we undertook a geochronological, mineralogical, geochemical, and zircon Hf isotopic analysis of granodiorites from the Yaogou area of the NQOB. Zircon U-Pb dating reveals that the Yaogou granodiorites formed during the Early–Middle Ordovician (473–460 Ma). The Yaogou granodiorites have high SiO₂ (63.3–71.1 wt.%), high Al₂O₃ (13.9–15.8 wt.%) contents, and low Zr (96–244 ppm), Nb (2.9–18 ppm), as well as low Ga/Al ratios (10,000 × Ga/Al ratios of 1.7–2.9) and FeO^T/MgO ratios (1.9–3.2), and are characterized by elevated concentrations of light rare earth elements and large-ion lithophile elements such as Rb, Th, and U, coupled with significant depletion in heavy rare earth elements and high-field-strength elements including Nb, Ta, and Ti. Additionally, the presence of negative europium anomalies further reflects geochemical signatures typical of I-type granitic rocks. The zircon grains from these rocks display negative ε_Hf(t) values (−14.6 to −10.7), with two-stage Hf model ages (T_DM2) from 2129 to 1907 Ma. These characteristics suggest that the magmatic source of the Yaogou granodiorites likely originated from the partial melting of Paleoproterozoic basement-derived crustal materials within a tectonic environment associated with subduction in the North Qilian Ocean. Integrating regional geological data, we suggest that during the Early Paleozoic, the North Qilian Oceanic slab underwent double subduction: initially southward, followed by a northward shift. Due to the deep northward subduction of the Qaidam continental crust and oceanic crust along the southern margin of the Qilian Orogenic Belt, the southward subduction of the North Qilian ocean was obstructed, triggering a reversal in subduction polarity. This reversal likely decelerated the southward subduction and initiated northward subduction, ultimately leading to the formation of the Yaogou granodiorites. These findings enhance our understanding of the complex tectonic processes that shaped the North Qilian Orogenic Belt during the Early Paleozoic, emphasizing the role of subduction dynamics and continental interactions in the region’s geological evolution. Full article

Ion-adsorption rare earth deposits are mainly formed by the weathering and leaching of granite ore-forming parent rocks, and heavy rare earth elements (HREEs) are predominantly hosted in this type of deposit. In this study, we focused on the Late Jurassic REE mineralization parent rock, specifically the Shuitou pluton. We employed chronology, petrogeochemistry, and isotope geochemistry to elucidate the REE enrichment process in the granite. The results show that the zircon U–Pb age of the Shuitou pluton is ~150 Ma, and the monazite U–Pb age is ~145 Ma, suggesting that the pluton was formed in the Yanshan Stage. The rocks have high SiO₂ (72.85–75.55 wt%), Al₂O₃ (12.85–14.63 wt%), and K₂O (4.46–5.27 wt%) content, with A/CNK values of 1.05–1.19, differentiation index (DI) values of 87.48–95.59, zircon saturation temperature values of 689–746 °C, Nb/Ta ratios of 2.72–9.54, and Zr/Hf ratios of 7.12–26.11. In addition, the rocks also contain peraluminous minerals such as muscovite and garnet. These characteristics indicate that these rocks belong to highly fractionated S-type granite. The ε_Hf(t) values of zircon and monazite range from −10.04 to −6.78 and from −9.3 to −8.2, respectively, indicating that the magma was primarily derived from Proterozoic metamorphosed sedimentary rocks of crustal origin. In the extensional tectonic setting of South China, a high temperature promotes the melting of REE-enriched accessory minerals, and a higher content of F increases the solubility of REEs in the molten mass. The presence of heavy rare earth minerals, such as garnet, in these rocks contributes to a high content of heavy rare earth elements (HREEs). Additionally, REE-enriched minerals like titanite, bastnaesite, and allanite create the necessary material conditions for the formation of ion-adsorption REE deposits. Full article

Magma mixing or mingling is not just a geological phenomenon that widely occurs in granitoid magmatism, but a complex dynamic process that influences the formation of mafic microgranular enclaves (MMEs) and the diversity of granitic rocks. Herein, we carried out a comprehensive study that encompassed the petrology, mineral chemistry, zircon U-Pb ages, Lu-Hf isotopes, whole-rock elements, and Sr-Nd isotope compositions of the Menyuan Granodioritic Pluton in the northern margin of the Qilian Block, to elucidate the petrogenesis and physical and chemical processes occurring during magma mixing. The Menyuan Granodioritic Pluton is mainly composed of granodiorites accompanied by numerous mafic microgranular enclaves (MMEs) and is intruded by minor gabbro dikes. LA-ICP-MS zircon U-Pb dating reveals that these rocks possess a similar crystallization age of ca. 456 Ma. The Menyuan host granodiorites, characterized as metaluminous to weakly peraluminous, belong to subduction-related I-type calc-alkaline granites. The MMEs and gabbroic dikes have relatively low SiO₂ contents and high Mg^# values, probably reflecting a mantle-derived origin. They are enriched in large ion lithophile elements (LILEs) and light, rare earth elements (LREEs) but are depleted in high field strength elements (HFSEs), indicating continental arc-like geochemical affinities. The host granodiorites yield relatively enriched whole-rock Sr-Nd and zircon Hf isotopic compositions (⁸⁷Sr/⁸⁶Sr_i = 0.7072–0.7158; ε_Nd(t) = −9.21 to −4.23; ε_Hf(t) = −8.8 to −1.2), implying a derivation from the anatexis of the ancient mafic lower continental crust beneath the Qilian Block. The MMEs have similar initial Sr isotopes but distinct whole-rock Nd and zircon Hf isotopic compositions compared with the host granodiorites (⁸⁷Sr/⁸⁶Sr_i = 0.7078–0.7089; ε_Nd(t) = −3.88 to −1.68; ε_Hf(t) = −0.1 to +4.1). Field observation, microtextural and mineral chemical evidence, geochemical characteristics, and whole-rock Nd and zircon Hf isotopic differences between the host granodiorites and MMEs suggest insufficient magma mixing of lithospheric mantle mafic magma and lower continental crust felsic melt. In combination with evidence from regional geology, we propose that the anatexis of the ancient mafic lower continental crust and subsequent magma mixing formed in an active continental arc setting, which was triggered by the subducted slab rollback and mantle upwelling during the southward subduction of the Qilian Proto-Tethys Ocean during the Middle-Late Ordovician. Full article

Permian magmatic rocks are extensively distributed in the East Kunlun Orogenic Belt (EKOB), yet controversies persist regarding the petrogenesis of granitoid rocks and the tectonic evolution of the Buqingshan-A’nyemaqing Ocean (BAO), which is a part of the Paleo-Tethys. This study addresses these debates through petrological analyses, whole-rock geochemistry and zircon U-Pb-Lu-Hf isotopic investigations of newly identified granitoids in the EKOB. Monzogranite (MG) and quartz porphyry (QP) yield weighted mean ages of 254.7 ± 1.1 Ma and 254.3 ± 1.1 Ma, respectively. Geochemically, the MG shows metaluminous to weakly peraluminous low-K calc-alkaline I-type affinity, characterized by high SiO₂ and low K₂O, MgO and FeO^T contents, as well as marked enrichment in light rare earth elements (LREEs), but depletion in Eu, Ba, Sr, P and Ti anomalies. In contrast, the QP exhibits a peraluminous high-K calc-alkaline I-type affinity, displaying high SiO₂ but low Na₂O and P₂O₅ contents. It is enriched in LREEs and Rb but displays negative Nb, Sr, P and Ti anomalies. Zircon ε_Hf(t) values range from −1.6 to 2.6 for MG and −4.4 to 1.5 for QP. We suggest that both MG and QP were derived from the partial melting of juvenile mafic lower crust, and that MG underwent a high degree of fractional crystallization. A synthesis of multiscale geological evidence allows us to propose a five-stage tectonic evolution for the BAO in the EKOB: (1) oceanic basin initiation before ca. 345 Ma; (2) incipient northward subduction commencing at ca. 278 Ma; (3) slab rollback stage (263–240 Ma); (4) syn-collisional compression (240–230 Ma); (5) post-collisional extension (230–195 Ma). Full article

The North Qilian Orogen experienced a series of late Neoproterozoic to early Paleozoic tectonic events, including the opening and closure of the Proto-Tethyan Qilian Ocean, as well as post-subduction processes. This study investigated the Shandan adakites in the Longshoushan area of the North Qilian Orogen, focusing on zircon U–Pb geochronology, whole-rock geochemistry, and Sr–Nd–Hf–O isotopic compositions. The Shandan adakites yield ages of ca. 446–440 Ma, suggesting they crystallized during the collision between the Alxa and Qilian blocks following the closure of the Proto-Tethyan North Qilian Ocean. High Sr/Y (40.9–117) ratios and enrichments in light rare earth elements indicate that the Shandan adakites were formed by partial melting of thickened magnesian lower crust. They have relatively rich ε_Nd (t) (−7.66 to −6.32), ε_Hf(t) (3.30 to −12.4), and δ¹⁸O (5.34‰–7.52‰). Zircon Hf–O and whole-rock Sr–Nd isotopes confirm significant contributions from the ancient crust and mantle-derived melts, suggesting complex crust–mantle interactions in their magma sources. We propose that the Shandan adakites formed during the (early) post-collisional stage of orogenesis. Based on regional geological evidence and previous studies, we suggest the Alxa and Central Qilian blocks collided during ca. 446–440 Ma, leading to the thickening of the lower crust. After ca. 440 Ma, the tectonic setting of the Northern Qilian Orogen transitioned from a collisional to a post-collisional stage. Full article

This study examines the origin, tectonic setting, and Cu–Pb–Zn polymetallic mineralization of the Yangjiayu Complex, situated on the southwestern margin of the Jiaolai Basin. We present detailed geochemical, zircon U–Pb geochronological, and Hf isotopic data for rhyolite porphyry and monzodiorite samples. Zircon U–Pb dating reveals that the emplacement of both intrusions occurred in the Early Cretaceous. While the monzodiorite (122.5 ± 0.7 Ma) is numerically slightly older than the rhyolite porphyry (121.2 ± 0.6 Ma), considering the error ranges, their ages are essentially similar. The rhyolite porphyry displays higher SiO₂ and Na₂O + K₂O contents and a lower Al₂O₃ content relative to the monzodiorite. Geochemically, both intrusions are classified as high-K calc-alkaline and peraluminous, characterized by enrichment in large-ion lithophile elements (LILEs; e.g., Ba, Rb, Pb) and light rare earth elements (LREEs), along with depletion in high-field-strength elements (HFSEs; e.g., Nb, P, Ta) and heavy rare earth elements (HREEs). The rhyolite porphyry further exhibits middle rare earth elements (MREEs; e.g., Eu, Gd, Tb, Dy) depletion. Similar zircon εHf(t) values (monzodiorite: −23.0 to −26.1; rhyolite porphyry: −23.2 to −25.0) suggest a shared source derived from partial melting of the thickened lower crustal rocks. In comparison to the monzodiorite, the rhyolite porphyry shows lower total REE contents, a more pronounced negative Eu anomaly and stronger MREE depletion, higher Rb, Th, and U concentrations, and more significant P depletion, features indicative of more extensive assimilation-fractional crystallization (AFC). These geochemical and geochronological data indicate that the Yangjiayu Complex originated within an extensional tectonic setting associated with the Early Cretaceous subduction of the Paleo-Pacific Plate underneath the Eurasian Plate. Cu–Pb–Zn mineralization, primarily localized within the monzodiorite, is interpreted to be generated by magmatic-hydrothermal fluids. Therefore, ~120 Ma dioritic intrusions within the Jiaolai Basin constitute prospective targets for (Cu)–Pb–Zn polymetallic exploration. Full article

The tectonic evolution of Hainan Island during the Late Permian–Early Triassic period is still unclear. This study identified two types of basalts on the island and presented detailed geochronology, whole-rock geochemistry, and Hf isotope data of the Late Permian–Early Triassic basalts. U-Pb dating results indicated that baddeleyites and zircons of one sample from Group 1 basalts had formation ages of 256 ± 3 Ma and 255 ± 3 Ma, respectively, and two samples from Group 2 gave formation ages of 241 ± 2 Ma and 240 ± 3 Ma, respectively. Both groups are characterized by negative anomalies of Nb, Ta, and Ti, and enrichment in Ba, Th, U, and K. Group 1 belongs to sub-alkaline basalt and exhibited SiO₂ contents ranging from 50.50% to 51.05%, with ΣREE concentration of 136–148 ppm. Hf isotope analysis showed that the ε_Hf(t) values of baddeleyites and zircons were −10.56 to −4.70 and −14.94 to −6.95, respectively. Group 2 belongs to alkaline basalt and had a higher SiO₂ content of 52.48%–55.49% and ΣREE concentration of 168–298 ppm. They showed more depleted Hf isotopic composition with ε_Hf(t) values ranging from −2.82 to +4.74. These data indicate that the source area of Group 1 was an enriched mantle, likely derived from partial melting of spinel lherzolite mantle, and was modified by subduction-derived fluids. Group 2 was derived from depleted mantle, most likely originating from partial melting of garnet + spinel lherzolite mantle. They were contaminated by crustal materials and metasomatized by subduction-derived fluids with a certain degree of fractional crystallization. Comprehensive analysis suggests that Group 1 samples likely formed in an island arc tectonic setting, while Group 2 formed in a continental intraplate extensional (or initial rift) tectonic setting. Their formation was mainly controlled by the Paleo-Tethys tectonic domain. Group 1 basalts implied that subduction of the Paleo-Tethys oceanic crust lasted at least in the late Permian (ca. 255 Ma). Group 2 basalts revealed that the intra-plate extensional (or initial rift) stage occurred in the middle Triassic (ca. 240 Ma). Full article

The Kongco area of Nima in the northern part of the Lhasa terrane has a suite of alkaline granitic porphyry dykes associated with Early Cretaceous granites and accompanied by Cu/Mo mineralization. LA-ICP-MS ²⁰⁶Pb/²³⁸U zircon geochronology performed on the dykes produced an age of 104.15 ± 0.94 Ma (MSWD = 0.98), indicating the Early Cretaceous emplacement of the dykes. The dykes exhibit high silica (SiO₂ = 76.22~77.90 wt.%), high potassium (K₂O = 4.97~6.21 wt.%), high alkalinity (K₂O + Na₂O = 8.07~8.98 wt.%), low calcium (CaO = 0.24~0.83 wt.%), low magnesium (MgO = 0.06~0.20 wt.%), and moderate aluminum content (Al₂O₃ = 11.93~12.45 wt.%). The Rieterman index (σ) ranges from 1.93 to 2.34. A/NK (molar ratio Al₂O₃/(Na₂O + K₂O)) and A/CNK (molar ratio Al₂O₃/(CaO + Na₂O + K₂O)) values of the dykes range from 1.06 to 1.18 and 0.98 to 1.09, respectively. The dykes are relatively enriched in Rb, Th, U, K, Ta, Ce, Nd, Zr, Hf, Sm, Y, Yb, and Lu, and they show a noticeable relative depletion in Ba, Nb, Sr, P, Eu, and Ti, as well as an average differentiation index (DI) of 96.42. The dykes also exhibit high FeO_T/MgO ratios (3.60~10.41), Ga/Al ratios (2.22 × 10⁻⁴~3.01 × 10⁻⁴), Y/Nb ratios (1.75~2.40), and Rb/Nb ratios (8.36~20.76). Additionally, they have high whole-rock Zr saturation temperatures (884~914 °C), a pronounced Eu negative anomaly (δEu = 0.04~0.23), and a rightward-sloping “V-shaped” rare earth element pattern. These characteristics suggest that the granitic porphyry dykes can be classified as A2-type granites formed in a post-collisional tectonic environment and that they are weakly peraluminous, high-potassium, and Calc-alkaline basaltic rocks. Positive ε_Hf(t) values = 0.43~3.63 and a relatively young Hf crustal model age (T_DM2 = 826~1005 Ma, ⁸⁷Sr/⁸⁶Sr ratios = 0.7043~0.7064, and ε_Nd(t) = −8.60~−2.95 all indicate lower crust and mantle mixing. The lower crust and mantle mixing model is also supported by (²⁰⁶Pb/²⁰⁴Pb)t = 18.627~18.788, (²⁰⁷Pb/²⁰⁴Pb)t = 15.707~15.719, (²⁰⁸Pb/²⁰⁴Pb)t = 39.038~39.110). Together, the Hf, Sr and Pb isotopic ratios indicate that the Kongco granitic porphyry dykes where derived from juvenile crust formed by the addition of mantle material to the lower crust. From this, we infer that the Kongco granitic porphyry dykes are related to a partial melting of the lower crust induced by subduction slab break-off and asthenospheric upwelling during the collision between the Qiangtang and Lhasa terranes and that they experienced significant fractional crystallization dominated by potassium feldspar and amphibole. These dykes are also accompanied by significant copper mineralization (five samples, copper content 0.2%), suggesting a close relationship between the magmatism associated with these dykes and regional metallogenesis, indicating a high potential for mineral exploration. Full article