Search Results (90)

Caledonian hydrothermal vein-type Mo deposits are largely restricted to eastern Guangxi, South China, yet the magmatic controls on molybdenum (Mo) mineralization remain poorly constrained. The adjacent Guiling (Mo–mineralized) and Daning (Mo–barren) plutons in this region represent a natural pair for deciphering these issues. Zircon U–Pb dating, whole-rock geochemistry, and mineralogical characteristics indicate that the Daning pluton (~440 Ma) is an I-type granite, whereas the younger Guiling pluton (~425 Ma) is a more evolved I-type granite, with higher SiO₂ contents (avg. 71.17 wt.% vs. 65.88 wt.%), stronger negative Eu anomalies (avg. 0.53 vs. 0.63), lower Nb/Ta ratios (avg. 6.5 vs. 9.9), and Zr/Hf ratios (avg. 30.6 vs. 33.4), as well as higher Rb/Sr ratios (avg. 3.6 vs. 1.1). Sr–Nd–Hf isotopes are consistent with a Paleoproterozoic crustal source for both plutons, whereas coeval mafic microgranular enclaves in the Guiling pluton exhibit positive ε_Nd(t) values (+3.43 to +3.58), providing evidence for mantle input. Biotite geochemistry shows that the Guiling pluton is enriched in F and Cl, as reflected by lower log(ƒ_H2O/ƒ_HF)^fluid values and higher log(ƒ_H2O/ƒ_HCl)^fluid values. Our integrated study suggests that the Daning and Guiling plutons were emplaced in an intracontinental orogenic setting during the transition from compression to extension, but the more pronounced extension facilitated a greater input of mantle-derived heat and volatiles into the Guiling pluton, favoring Mo enrichment. However, the similar biotite crystallization temperatures and moderate oxygen fugacities of both plutons suggest that these factors were not the decisive factors. Collectively, we propose that the contrasting Mo fertility between the two plutons reflects the interplay of magmatic and structural factors. Magmatically, crust–mantle source mixing, high degrees of fractionation, and volatile enrichment promoted Mo concentration, whereas ductile shear zones likely served as fluid conduits that facilitated mineralization. Accordingly, the southwestern segment of the Yingyangguan (YYG) ductile shear zone between the Daning and Guiling plutons could be a prospective target for Mo prospecting in eastern Guangxi. Full article

The interaction between mantle plumes and the lithospheric mantle is critical for understanding the genesis of flood basalts. The Emeishan Large Igneous Province (ELIP), composed predominantly of basalts with minor picritic rocks and radiating mafic dyke swarms, offers an exceptional natural laboratory for studying this process. In this contribution, we present geochemical and Sr-Nd-Hf-Pb isotopic data for high-Ti basalts from Weng’an, at the easternmost margin of the ELIP. These basalts (TiO₂ > 2.8 wt.%, Ti/Y > 500) are enriched in large ion lithophile elements (LILEs: Ba, Th, U) and slightly depleted in high field strength elements (HFSEs: Nb, Ta, Zr, Hf, Y). They exhibit initial (⁸⁷Sr/⁸⁶Sr)_t ratios of 0.70594–0.70697, ε_Nd(t) of +1.2 to +1.8, ε_Hf(t) of +1.1 to +1.9, and (²⁰⁶Pb/²⁰⁴Pb)_t of 18.11–18.51. Their geochemical signatures resemble those of other high-Ti ELIP basalts and ocean island basalts (OIB) but are distinct from those of depleted mantle sources. Trace element patterns and Pb–Pb isotope systematics indicate derivation from a garnet + spinel lherzolite source linked to the Emeishan mantle plume, with ~8–10% input from sub-continental lithospheric mantle (SCLM) metasomatized by slab-derived fluids during ascent. These results provide direct evidence for heterogeneous SCLM contributions to plume-derived magmas and highlight the role of lithospheric heterogeneity in shaping the composition of LIP magmatism. Full article

The giant Dulong Sn-Zn polymetallic deposit, located in the eastern part of the southeastern Yunnan metallogenic belt, is a world-class ore system. Despite extensive research on the source of tin and its mineralization processes, the specific ore-related intrusion and the source of copper remain highly debated. Recent deep exploration has revealed a deep-seated granite porphyry, yet its geochronological and geochemical characteristics, along with its genetic link to mineralization, are poorly constrained. This study presents new zircon U-Pb age, whole-rock geochemistry, and Sr-Nd-Hf isotopic compositions of this granite porphyry, integrated with a regional comparison to multi-phase Laojunshan granites. LA-ICP-MS zircon U-Pb dating yields a Late Cretaceous age of 85.1 ± 1.2 Ma. The Dulong granite porphyry is strongly peraluminous and high-K calc-alkaline to shoshonitic, exhibiting typical S-type granite affinities with enrichment in Rb, U, and Ta, as well as depletions in Ba, Sr, Nb, and Eu. Isotopic signatures (ε_Nd(t) = −12.5 to −12.0, t_DM2(Nd) = 1.87 to 1.91 Ga; zircon ε_Hf(t) = −10.24 to −1.44, t_DM2(Hf) = 1.24 to 1.79 Ga) suggest that the parental magma was derived from the partial melting of ancient crust, with possible minor input of mantle-derived components in an extensional tectonic setting. The Dulong granite porphyry represents a moderate-to-high temperature, reduced, and highly evolved magmatic system. Notably, its high concentrations of Sn, W, Zn, and Cu indicate that the parental melt was metal-rich, possessing potential for Sn and Cu mineralization. Accordingly, future exploration should prioritize areas characterized by well-developed granite porphyry dykes, skarn–wallrock contact zones, and deep-seated structural intersections. Full article

The Cretaceous represents a key period in the geodynamic evolution of the Tibetan Plateau and the initial development of its paleotopography. While widespread orogenesis and magmatism associated with the Lhasa–Qiangtang collision are well documented in southern Tibet, coeval magmatic records in northern Tibet are extremely limited, hindering constraints on the deep processes responsible for surface uplift. Zircon U–Pb ages, whole-rock geochemistry, and Sr–Nd–Hf isotopes are presented for two mafic dyke swarms from the East Kunlun Orogen, northern Tibet. The two dyke swarms were emplaced at 91.8 ± 2.0 Ma and 84.8 ± 0.6 Ma, indicating a previously underrecognized episode of Late Cretaceous mafic magmatism in northern Tibet. They are subalkaline tholeiites enriched in LILEs and LREEs, depleted in HFSEs, and characterized by negative Nb–Ta anomalies. Their decoupled Nd-Hf isotopes (εNd(t) = −4.96 to +0.94; εHf(t) = +3.75 to +5.76) indicate derivation from an enriched lithospheric mantle metasomatized by slab-related fluids during Permian-Triassic Paleo-Tethyan subduction. Partial melting modeling indicates that the magmas were generated by low-degree (1–5%) decompression melting of lherzolite within the spinel–garnet transition zone. We propose that these mafic dyke swarms formed in an intraplate extensional setting triggered by far-field stresses associated with the Lhasa–Qiangtang collision, which reactivated lithosphere-scale faults and induced localized mantle melting. These results provide new petrological constraints on Late Cretaceous intracontinental extension in northern Tibet and highlight mafic dyke swarms as key probes for linking lithospheric reactivation to early surface uplift of the Tibetan Plateau. Full article

Early Cretaceous volcanic rocks are widely developed in the Longzi area, southern Tibet. Their petrogenesis and tectonic setting are important for understanding the initial breakup of eastern Gondwana and its deep geodynamic mechanisms. This study integrates field observations, petrography, zircon U-Pb geochronology and trace elements, whole-rock major and trace element geochemistry, and Sr-Nd-Pb isotopes to investigate the origin and tectonic significance of these rocks. The analyzed suite comprises diabase and rhyolite, with no intermediate compositions in the studied samples, thus defining a mafic–felsic volcanic association. Zircon U-Pb ages indicate Early Cretaceous magmatism at 132–138 Ma for the diabase and 132–134 Ma for the rhyolite. Geochemically, the mafic rocks are enriched in LREEs and HFSEs and display OIB-like trace-element characteristics, with ε_Nd(t) values ranging from −0.2 to +4.4, indicating derivation from low-degree partial melting of a spinel–garnet lherzolite source modified by limited interaction with the lithospheric mantle. The felsic rocks show pronounced negative Eu anomalies, A-type granite affinities, and ε_Nd(t) values ranging from −12.2 to −11.9, indicating derivation mainly from partial melting of upper-crustal materials. The marked geochemical and isotopic contrast between the mafic and felsic rocks argues against simple fractional crystallization from a common parental magma. Combined with regional geological data, these results indicate that the Longzi mafic–felsic volcanic association formed in an intraplate extensional setting related to Kerguelen-plume thermal input during the initial breakup of eastern Gondwana. Full article

The hornblende gabbro investigated in this study crops out in northwestern Elazığ, eastern Türkiye, within the Southeastern Anatolian Orogenic Belt (SAOB), where Late Cretaceous ophiolitic, volcanic, plutonic, and metamorphic units are widely exposed. This study examines the petrology, whole-rock geochemistry, Sr–Nd isotopic composition, mineral chemistry, and crystallisation conditions of these gabbroic bodies to constrain their petrogenesis and tectonomagmatic significance. Field observations show that the rock occurs as rounded to sub-rounded blocks with fresh inner cores and altered outer rims. Petrographic and XRD data indicate that the fresh gabbro mainly consists of plagioclase and amphibole, whereas the altered outer rims contain quartz and minor secondary phases. Whole-rock geochemical data classify the samples as low- to medium-K, tholeiitic, and predominantly metaluminous gabbro. Primitive mantle-normalised trace-element patterns display enrichment in large-ion lithophile elements and depletion in high-field-strength elements, whereas chondrite-normalised REE patterns show slight LREE enrichment, relatively flat HREE patterns, and weak Eu anomalies. Sr–Nd isotopic compositions are characterised by positive εNd_(T) values (+4.4 to +5.3) and moderately radiogenic initial ⁸⁷Sr/⁸⁶Sr ratios (0.704792–0.705344), indicating a predominantly mantle-derived magma source affected by subduction-related modification, with limited crustal contribution. Mineral chemistry data show that amphiboles belong to the calcic amphibole group and plot in the magnesio-hornblende field. Amphibole thermobarometric calculations yielded temperatures of 873–991 °C and pressures of 1.49–3.26 kbar, corresponding to crystallisation depths of 5.1–15.3 km. Overall, the results indicate that the hornblende gabbro was derived from a mafic magma generated from a spinel lherzolite mantle source and crystallised in a subduction-related tectonomagmatic setting. Full article

The Indosinian granitoids of Guangdong Province, South China, record a complex history of crust–mantle interactions during the Triassic assembly of the South China Block (SCB) and Indochina Block (ICB). Integrated zircon U–Pb geochronology, geochemistry, and Sr–Nd–Hf isotopes from these plutons reveal two magmatic episodes: an Early Indosinian phase (253–230 Ma) of large, west-to-east younging batholiths, and a later scattered phase (230–200 Ma). While most granitoids are peraluminous S-types formed by the melting of the Paleoproterozoic crust with limited mantle input (0–30%), the Taibao pluton and its enclaves are anomalous. They are more mafic and record a substantial mantle contribution (40–65%), pointing to focused, high-heat flux magmatism. This spatial and petrogenetic heterogeneity, coupled with the granitoids’ NE–SW trend orthogonal to the collisional zone, cannot be explained by simple crustal thickening. We propose that these features are the direct result of the slab tearing of the subducting Paleo-Tethys oceanic plate, triggered by an oblique collision between the SCB and ICB. This tearing induced asthenospheric upwelling, providing the thermal engine for widespread crustal anatexis and localized mantle melting. Our findings establish slab tearing as a key catalyst for syn-collisional, high-temperature magmatism, offering a unified framework for interpreting lithospheric processes during continental collisions. Full article

This study presents integrated zircon U-Pb geochronology, whole-rock geochemistry, and Sr-Nd-Hf isotopic investigations of quartz diorite and gneissic quartz diorite from the Datian Complex along the western Yangtze Block, elucidating their petrogenesis and tectonic implications. Key findings reveal: (1) The crystallization ages of the Datian Complex (~770–755 Ma) record episodic magmatic activity over a ~16 Ma period, indicating a multi-stage tectonic evolution; (2) Both rock types exhibit intermediate SiO₂ (57–64.58 wt.%), high Al₂O₃ (15.44–17.80 wt.%), and MgO (2.18–3.67 wt.%; Mg# = 47.41–52.65) with calc-alkaline signatures (Na₂O/K₂O = 1.14–2.65), coupled with adakitic traits including pronounced LREE/HREE fractionation (La_N/Yb_N = 3.83–26.4), negative Eu anomalies (δEu = 0.61–1.05), elevated Sr (372–701 ppm), and Sr/Y ratios (24.6–56.2), collectively classifying the complex as high-Si adakite; (3) The isotopic homogeneity (whole-rock Sr-Nd: ⁸⁷Sr/⁸⁶Sr(i) = 0.7038–0.7048, εNd(t) = −1.5 to–3.8; zircon Hf: εHf(t) = 1.24–6.88) supports a two-stage petrogenetic model involving partial melting of subducted oceanic slab, followed by mantle wedge metasomatism during magma ascent. These results position the Datian Complex as a Neoproterozoic arc-related adakitic magmatic system within the active continental margin of the Yangtze Block. Full article

The Jianggang sand ridges (JSR) in the southwestern Yellow Sea are a radiating tidal sand ridge system that plays crucial roles in ecological preservation, coastal protection, and terrestrial resource supply. Clay and silt fractions constitute important sediment components of the Jianggang sand ridges. In this study, the Sr-Nd isotopes of clay fractions and the Pb isotopes of K-feldspar in the silt fractions, along with their elemental geochemistry, are investigated to reveal the provenance and transport patterns of clay-size and silt-size sediments in the study areas. The results show that in both the clay-size sediments and the K-feldspar of the silt-size sediments, Ba exhibits the highest content, with the ranges of 432.24 μg/g to 531.05 μg/g and 398.02 μg/g to 2822.36 μg/g, respectively. In contrast, Lu shows the lowest abundance (<0.5 μg/g and <0.1 μg/g, respectively). The ⁸⁷Sr/⁸⁶Sr and ε_Nd(0) values of the clay fraction vary from 0.7158 to 0.7265 and from −14.65 to −10.92, respectively. The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb of K-feldspar in silt fraction are 17.959~18.429, 15.450~15.689, and 38.066~38.551, respectively. Through the MixSIAR model, it is suggested that the Yangtze River Mouth is the dominant contributor to clay-size sediments in both the onshore and offshore sand ridges (53.9 ± 8.8% and 51.9 ± 8.4%, respectively), followed by the Modern Yellow River Mouth and the Old Yellow River Delta (sum of contributions: <36%). For the silt fraction, the primary sediment sources of the onshore and offshore sand ridges are the Yangtze River Mouth (46.8 ± 5.5%) and the Old Yellow River Delta (42.4 ± 5.3%), while the Modern Yellow River contributes less than 16%. The Northern Chinese Deserts and the Korean rivers make only minor contributions to both fractions. Elemental and isotopic tracers indicate that the silt-size and clay-size sediments derived from the Modern Yellow River are transported southward along the Jiangsu coast by the Subei Coastal Current. Meanwhile, the silt fraction from the Yangtze River Mouth is carried northward along the coast under the influence of the Subei Coastal Current, whereas the clay fraction of it has another longer path, which moves through the central Yellow Sea and migrates southward along the Jiangsu coast to the Jianggang sand ridges under the influence of the Yellow Sea Warm Current. This study enriches the geochemical dataset of the southern Yellow Sea. Full article

The early crustal evolution of microcontinental fragments in the Central Asian Orogenic Belt remains poorly constrained. Among these fragments, the Erguna Block records extensive Neoproterozoic magmatism that provides key constraints on its tectono-magmatic development in relation to the Rodinia supercontinent cycle. To furthering constrain the Neoproterozoic magmatic evolution of the Erguna Block, an integrated investigation combining petrography, zircon U-Pb and Lu-Hf isotopic analyses, whole-rock geochemistry, and Sr-Nd isotope data was carried out on the newly recognized Fengshuishan intrusion in northern Alongshan. Zircon U-Pb ages of 810 ± 5 Ma and 807 ± 4 Ma were obtained from granitic samples, while the dioritic sample gave an age of 773 ± 2 Ma, representing a major Neoproterozoic magmatic episode. The 810–807 Ma granites show positive zircon εHf(t) (+0.09 to +12.1) and whole-rock εNd(t) (+0.50 to +1.77), suggesting derivation mainly from partial melting of Mesoproterozoic juvenile crust with minor contribution from mantle-derived materials. In contrast, ca. 773 Ma gabbroic diorite exhibits εHf(t) values of −1.23 to +4.3 and an εNd(t) value of +1.33, implying a contribution from an enriched mantle source. These Fengshuishan igneous rocks show A-type geochemical signatures, enriched in Rb, Th, and Pb but depleted in Ba, Sr, and Eu. Integrating these data with regional geological evidence, we infer that the Fengshuishan intrusion formed in an intraplate extensional regime, recording an important phase of crust–mantle interaction during the Neoproterozoic. These results expand the record of Neoproterozoic igneous rocks in the Erguna Block and offer new constraints on its role within the Rodinia supercontinent. Full article

The Zhilingtou Au-Mo-Pb-Zn polymetallic deposit is located in the southwestern Zhejiang Province, NE China, and is tectonically situated in the Shaoxing-Longquan uplift belt. Although previous studies have indicated that Au mineralization in this area occurred between 135 Ma and 145 Ma, evidence for coeval intrusive rocks has been lacking. Furthermore, it remains controversial whether the Au mineralization and (~113 Ma) Mo-Pb-Zn mineralization belong to the same magmatic-hydrothermal system. This study conducted comprehensive high-precision geochronological, petrochemical, and Sr-Nd isotopic analyses on the newly discovered granite porphyry intrusion in the mining area. The aim is to constrain the emplacement age of the intrusion, reveal the petrogenesis and source of ore-forming materials, and further discuss the mineralization mechanism. LA-ICP-MS zircon U-Pb dating results indicate that the granite porphyry was formed at 137.8 ± 0.95 Ma, which is broadly consistent with previously reported ages of Au mineralization. It is inferred that this intrusion may be related to a Au mineralization event at around 138 Ma. Geochemical characteristics show that the rock is peraluminous I-type granite, enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti, indicating an “island arc-type” geochemical signatures. Sr-Nd isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr = 0.712364–0.712711; ε_Nd(t) = −13.9 to −13.4; two-stage Nd model ages T_DM2 = 1877–1908 Ma) suggest that the magma was derived from ancient crustal materials with the addition of mantle-derived components. Integrating existing geochronological, isotopic, and fluid inclusion evidence, it is proposed that the Zhilingtou deposit may have experienced two mineralization events: an early event (~138 Ma) involving Au-Ag mineralization related to the granite porphyry and a later event (~113 Ma) comprising Mo-Pb-Zn mineralization associated with a porphyry–epithermal system. Together, these events form a composite mineralization system. This study has important implications for refining regional metallogenic theories and guiding future ore exploration. Full article

Research on the Mesozoic–Cenozoic magmatism and the tectonic framework within the Lhasa Terrane is voluminous. However, the sparse documentation of Early Cretaceous magmatism in this region fuels ongoing debate over the prevailing tectonic regime during this time period (i.e., normal subduction vs. flat subduction). The present study investigates the Luerma pyroxenite and Boyun granitoid in the Western Lhasa Terrane through zircon U-Pb dating, whole-rock geochemistry, mineral chemistry, and Sr-Nd-Hf isotopes. The findings date the formation of Luerma pyroxenite at 115 Ma and Boyun granites at 113 Ma to the Early Cretaceous period (115–113 Ma). SiO₂ content of pyroxenite is relatively low (34.27–44.16 wt.%), characterized by an enrichment in large ion lithophile elements (LILEs), light rare earth elements (LREEs), and a depletion in heavy field strength elements (HSFEs), indicative of a metasomatic origin. The εNd (t) and εHf (t) values of the Early Cretaceous ultrabasic rocks range from +2.1 to +2.7 and −0.8 to +10.1, respectively, suggesting their derivation from an enriched mantle source with asthenospheric material incorporation. The Early Cretaceous granodiorites and their mafic enclaves belong to the high-K calc-alkaline series, and show enrichment in LILEs (e.g., Rb, Ba, U, and Th) and depletion in HFSEs (e.g., Nb, Ta, Ti, and Zr). The acidic rocks and their developed mafic enclaves exhibit the geochemical characteristics of trace elements found in island arc magmas. Their εNd (t) values are (−6.0–−5.0), while their εHf (t) values are (−11.7–−1.8); the MMEs εHf (t) values are (−4.1–+0.9). In summary, the Early Cretaceous pyroxenite in the Gangdese Belt originated from a combination of asthenospheric and enriched lithospheric mantle melts, while the granitoids were generated by partial melting of the mantle wedge, a process driven by metasomatism resulting from the slab-derived fluids. At the same time, heat from upwelling mantle-derived melts induced the partial melting of lower crustal materials, leading to the formation of acidic magmas through varying degrees of mixing with basic magmas. This study suggests that Early Cretaceous magmatic activity occurred within a northward subduction setting, characterized by the rotation and fragmentation of the Neo-Tethys oceanic crust. Full article

Large-scale Mesozoic granites are widespread in the offshore area of eastern Shandong Province, China. This study aims to refine the granite classification and explore the degree of granite differentiation and ore-bearing potential in the study area. We conducted field investigations in Dazhushan, Xiaozhushan, and Laoshan plutons. The analytical methods included petrography, whole-rock geochemistry, Sr–Nd–Pb–Li isotopes, zircon U–Pb dating, in situ Hf isotopes, and microanalysis (LA-ICP-MS) of plagioclase. The results reveal high-silica (SiO₂ > 70%), highly differentiated (DI > 90) granites emplaced during the Early Cretaceous (113.12–121.78 Ma). Sr–Nd–Pb isotopes indicate magma derived from a crustal source (I_Sr = 0.7032–0.7242; εNd(t) = −12.45~−20.46). Critically, the spodumene-bearing Dazhushan granites exhibit high Li content with limited isotopic fractionation (δ⁷Li = 1.00–4.62‰; Li = 8.64–93 ppm), signaling high ore potential. In contrast, the Xiaozhushan granites are barren (δ⁷Li = 3.31–4.92‰; Li = 0.66–4.01 ppm). This study identified I-type (Laoshan) and I-S type (Dazhushan and Xiaozhushan) highly differentiated granites formed by plagioclase fractionation, with Dazhushan being the most promising for mineralization. Full article

The Altyn Tagh Fault plays a critical role in understanding the tectonic evolution of the northern margin of the Tibetan Plateau. However, considerable debate persists regarding its activity and deformation history. This study investigates volcanic rocks from the Beidayao-Jianquanzi-Hanxia-Hongliuxia area in the eastern segment of the fault. By employing zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotope analysis, we aim to elucidate their petrogenesis and tectonic setting, thereby providing new insights into the crustal evolution of the eastern Altyn Tagh Fault. Zircon U-Pb dating of the Hongliuxia rhyolite yields a weighted mean ²⁰⁶Pb/²³⁸U age of 106.6 ± 0.6 Ma, indicating an Early Cretaceous eruption. Geochemically, the western part of the study area (Beidayao and Jianquanzi) is dominated by basalts that exhibit significant enrichment in large ion lithophile elements and light rare earth elements, together with high Nb concentrations (>20 ppm), as well as high Nb/La (0.64–1.12) and Nb/U (29.8–35.42) ratios, consistent with the characteristics of high-Nb basalt. In contrast, the eastern area (Hanxia and Hongliuxia) is characterized by andesitic rocks that display typical continental arc affinities, marked by enrichment in Th, U, and Pb and depletion in Nb, Ta, and Ti. Isotopically, the basalts show initial ⁸⁷Sr/⁸⁶Sr ratios of 0.706–0.707 and ε_Nd (t) values ranging from −3.2 to 0.8, whereas the andesites possess more radiogenic Sr isotopic compositions, with (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.710–0.717, and more negative ε_Nd (t) values from −11.4 to −1.5, suggesting derivation from an enriched mantle source. Integrating geochemical data with regional geological records, we propose that the eastern part of the Altyn Fault experienced a significant intracontinental extensional setting during the Early Cretaceous, where asthenospheric mantle upwelling played a key role in the generation of the volcanic rocks. This study provides key petrological and geochemical constraints on Early Cretaceous deformation and activity along the Altyn Tagh Fault, and also offers a valuable reference for understanding the evolution of similar fault systems. Full article

Kimberlite has attracted considerable interest among geologists as the primary source of natural gem-quality diamonds. The term “transitional kimberlite” was previously introduced to categorize rocks that exhibit bulk geochemical and Sr–Nd isotopic characteristics intermediate between those of archetypal kimberlite (formerly Group-I) and orangeite (formerly Group-II). Nevertheless, the petrogenesis of transitional diamond-bearing kimberlites remains poorly understood due to limited research. The diamondiferous transitional Wafangdian kimberlite in the North China Craton (NCC) thus provides a valuable opportunity for a detailed case study. We investigated fresh hypabyssal transitional Wafangdian kimberlites using bulk-rock major and trace element geochemistry to constrain near-primary parental magma compositions and decipher their petrogenesis. Geochemical compositions identify samples affected by crustal contamination based on elevated SiO₂, Pb, heavy rare earth element (HREE) concentrations, and Sr isotopic ratios. Compositional variations among macrocrystic samples (MgO: 29.7–31.5 wt.%; SiO₂: 30.6–34.7 wt.%; CaO: 3.9–7.5 wt.%; Mg^# [atomic Mg/(Mg + Fe²⁺) × 100]: 85–88) result from substantial entrainment and partial assimilation of peridotite xenoliths (up to 35%). In contrast, variations within aphanitic samples (MgO: 24.0–29.7 wt.%; SiO₂: 27.7–30.9 wt.%; CaO: 6.0–11.8 wt.%; Mg^#: 81–85) are attributed to fractional crystallization of olivine and phlogopite (~1–32%). Based on these constraints, the near-primary parental magma composition for the Wafangdian kimberlite is estimated as ~29.7 wt.% SiO₂, ~29.7 wt.% MgO, and Mg^# 85. Trace element concentrations in the transitional Wafangdian kimberlites resemble those of archetypal kimberlites globally (e.g., Nb/U > 26, La/Nb < 1.4, Ba/Nb < 16, Th/Nb < 0.25), indicating a shared convective mantle source. However, the Wafangdian kimberlites exhibit distinct characteristics: ε_Nd(t) values ranging from −3.44 to −1.77, higher Al₂O₃ and K₂O contents, and lower Ce/Pb ratios (10–20) compared to archetypal kimberlites. These features suggest the mantle source region was profoundly influenced by deeply subducted oceanic material. Full article