Search Results (424)

Crystal size distributions (CSDs) of metamorphic minerals provide quantitative constraints on nucleation-growth kinetics and metamorphic thermal regimes. Early interpretations linked CSD shape to type of metamorphism, associating near-linear CSDs with rapid-contact metamorphism and bell-shaped CSDs with prolonged regional metamorphism. Subsequent works showed that diffusion-controlled nucleation and growth can also produce bell-shaped CSDs without annealing, leaving unresolved how contrasting thermal regimes are expressed in interface-controlled systems. The Fangshan tectonic dome at the northern margin of the North China Craton comprises multiple metamorphic zones, recording Mesozoic contact metamorphism of Fangshan plutons and a concealed pluton in the Nanjiao area. We employed high-resolution X-ray micro-computed tomography (micro-CT) to quantify the 3D crystal size distributions of garnets of contact metamorphic samples from the Nanjiao area and the Fangshan contact aureole. Integrated 3D CSDs with spatial statistics, reconstructed nucleation curves, garnet compositional zoning, and thermodynamic phase equilibrium modeling were used to decipher crystallization kinetics in interface-controlled systems. Nucleation and growth of garnets from the Nanjiao area, and one sample from the Fangshan contact aureole, which is separated from the main heat source by an earlier intruded magma body, are interface-controlled, and display bell-shaped CSDs together with sigmoidal nucleation curves that record a progressive increase followed by a gradual decline in nucleation rate. Phase equilibrium modeling and garnet compositional profiles of a sample from Nanjiao demonstrate that the late-stage deceleration of nucleation in interface-controlled systems is fundamentally driven by whole-rock constituents’ exhaustion rather than the geometric impingement of diffusion halos. In contrast, another contact sample, which is collected near the main heat source, is diffusion-controlled, and displays a steep J-shaped nucleation curve with a delayed, broad peak nucleation rate followed by rapid late-stage suppression. The 3D textures of these metamorphic rocks suggest that contact and regional thermal regime alone do not determine garnet population characteristics; bell-shaped CSDs can be produced in contact metamorphic environments. We propose that heating rate is the primary control on the resulting crystal size distributions. 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 magmatic Ni-Co-Cu mineralization in the Iken deposit in the central part of the Kun-Manie complex, Amur Oblast, Russia, hosted by an olivine-bearing websterite, is of a low-sulfide type. The fine-grained disseminations of base metal sulfides (BMS), dominantly pyrrhotite, pentlandite (a major source of Ni of industrial importance), and chalcopyrite, are followed by a scarce Pd-Pt-Ag mineralization. Elevated contents of Al in orthopyroxene (mean 2.78 wt.% Al₂O₃) along with Al–Na enrichment in clinopyroxene (diopside; mean 5.10 wt.% Al₂O₃) are associated with highly aluminous compositions of low-chromium members of the spinel–hercynite series. High levels of TiO₂ in kaersutite and titanian phlogopite also reflect a pronounced degree of fractionation of the ore-forming melt. Minor portions of sulfide melt are distributed evenly as a result of immiscibility at advanced stages of orthopyroxene crystallization, after the formation of olivine. Differentiated grains of droplet-like BMS largely settled in situ close to grain boundaries of orthopyroxene or occupied interstitial spaces of pyroxenes and olivine in association with spinel–hercynite and fluorapatite. A combination of late saturation in S with relatively quick cooling rates of the hypabyssal body prevented the effective settlement and accumulation of sulfide droplets in the ore zone. The well-developed lamellae of troilite (Fe₅₀S₅₀) exsolved from the host pyrrhotite Fe₄₈S₅₂ during subsolidus cooling, as a consequence of a low-temperature reaction triggered by a sudden drop in fO₂. An influx of mantle-derived fluid bearing CO₂, CO, and CH₄ with the rising magma could be the primary cause of the fO₂ reduction. Also, graphite-bearing metasedimentary rocks could have been assimilated. Tiny grains of minerals of noble metals (moncheite and merenskyite with essential amounts of melonite component, sperrylite, hessite, alloy Au_63.2Ag_36.8, and argentopentlandite) deposited late in a fluid-enriched medium under submagmatic conditions. Full article

Volcanic rocks of the Qi’eshan Group, which are widely distributed in the Dananhu arc of the Eastern Tianshan, NW China, have long been debated in terms of their formation age and tectonic setting. In this study, we conducted an integrated study of U-Pb apatite geochronology, whole-rock major and trace element geochemistry, in situ major element analyses of clinopyroxene, and “Rhyolite-MELTS” thermodynamic modeling on the basalts from the Qi’eshan Group. Geochronological data show that the weighted mean of ²⁰⁶Pb/²³⁸U ages of apatite is 329 ± 10 Ma. The basalts belong to the tholeiitic series and are characterized by enrichment in large ion lithophile elements (LILEs), depletion in high field strength elements (HFSEs), and enrichment of light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs) with weak negative Eu anomalies. They were derived by partial melting of garnet-spinel lherzolite in a depleted mantle source metasomatized by subduction-related fluids, followed by fractional crystallization of spinel, olivine, and clinopyroxene. Clinopyroxene is dominated by augite, characterized by high Mg and Ca contents and low Al and Na contents. Machine-learning-based thermobarometry indicates that clinopyroxene crystallized at temperatures of 1027–1033 °C and pressures of 1.1–1.6 kbar. “Rhyolite-MELTS” isobaric crystallization simulations suggest that mantle-derived magma, with an initial water content of 4 wt.% and oxygen fugacity of FMQ, can generate melts compositionally similar to the volcanic rocks of the Qi’eshan Group through fractional crystallization at a pressure of 1.5 kbar. Combined with previous studies, we propose that the Qi’eshan Group basalts formed in an extensional arc setting related to southward rollback of the northward-subducting Kanguer oceanic slab, which caused asthenosphere upwelling and lithospheric extension, thereby promoting partial melting of the subduction-metasomatized mantle. Our data provide new insights into the Carboniferous rollback of the Kanguer oceanic slab in the northern part of the Eastern Tianshan. Full article

The Dadonggou Mo deposit in Western Hebei, within the Yanshan–Liaoning Mo metallogenic belt, is a newly recognized medium-sized porphyry Mo system. Exploration has delineated 126 orebodies, most of which are blind, with identified resources of ~22,000 t Mo at an average grade of 0.071% Mo. Integrated lithogeochemistry, zircon U-Pb chronology, molybdenite Re-Os geochronology, quartz fluid-inclusion microthermometry, and H-O-S isotope analyses constrain the mineralization age, ore-fluid evolution, and sources of ore-forming materials. The zircon U-Pb dating of the ore-bearing granite porphyry and quartz porphyry from the Dadonggou molybdenum deposit yields ages ranging from 135.8 Ma to 141.5 Ma. The low Ti content in zircons indicates that they are super-wet magmatic rocks. The magmatic evolution experienced a change in oxygen fugacity from oxidizing to reducing conditions, which facilitated the initial enrichment of molybdenum. Molybdenite yields a Re-Os isochron age of 135.9 ± 4.0 Ma and a weighted mean model age of 134.2 ± 1.6 Ma, indicating Early Cretaceous mineralization. Ore fluids evolved from an early CO₂-H₂O-NaCl system with relatively high temperature and salinity to a later H₂O-NaCl system with lower temperature and salinity. Isotopic data indicate progressive meteoric-water incorporation into dominantly magmatic fluids. Sulfur isotopes and high Re contents in molybdenite indicate a mixture of mantle magma mixed with some seawater. Lower late-stage trapping pressures record post-ore depressurization and hydrothermal-system shallowing. Full article

The Santorini volcano attracts global interest. The 17th century BCE Minoan eruption was likely the largest ever occurring in the Holocene. The evaluation of an enriched collection of documentary sources combined with geological observations showed that in historical times, 15 eruption episodes were recorded from the 2nd century BCE up to 1950 CE. Little-known episodes occurring in 1667 CE and 1773 CE were uncovered, analyzed and included in the catalogue. Due to many uncertainties and inconsistencies involved in the historical sources, a reliability score ranging from 1 (lowest) to 4 (highest) has been assigned to each one of the 15 episodes. This procedure was based on a Reliability Assessment Matrix, which is a novelty in historical volcanology. The size of an eruption was evaluated in terms of the 8-grade Volcanic Explosivity Index (VEI) by introducing a bimodal assignment form of “V or V + 1”, an approach used for the first time, instead of the traditional unimodal assignment of “V”. The VEI of 4–5 was assigned to the eruptions of 725/726 CE in the Santorini caldera and of 1650 CE in the Kolumbo submarine volcano. The rest of the eruptions were assigned with smaller VEIs. Completeness analysis of the catalogue with statistical tests and Monte Carlo simulation with random and non-random models as baselines showed a 10-fold increase in the eruption record in 450 years after the breakpoint of 1572 CE eruption compared to the 1747 years before that point implying that there are about 30 missing eruption events that escaped record in the pre-1572 CE historical interval. This statistically significant difference is interpreted as a bias discovery effect of anthropogenic origin, but further research is needed to show that it does not represent a drastic change of magma plumbing rate. Full article

This paper presents systematic petrological, whole-rock geochemical, and Sr-Nd-Pb isotopic studies on the mafic–ultramafic rocks of the Daaobaogou Ni-Cu sulfide deposit in the Dunhuang Block, Gansu Province. This study aims to reveal the nature of its source region, parent magma composition, and magma evolution processes. The results indicate that the parent magma of the ore-bearing intrusion in Daaobaogou originated from an enriched lithospheric mantle metasomatized by Paleozoic subduction processes. It exhibits high-magnesium characteristics and represents the product of a certain degree of evolution from a primitive magma. The magma evolution underwent significant fractional crystallization, with olivine beginning to crystallize at 1328 °C, following the crystallization sequence: olivine, clinopyroxene, plagioclase, and orthopyroxene. Sr-Nd-Pb isotopes and trace elements indicate that the magma experienced intense crustal contamination (approximately 10–20% upper crust) during its ascent. Full article

The Abitagua batholith is a 120 km long plutonic body located in the northern sub-Andean zone of Ecuador. Despite its size, previous studies have focused on its northern and southern sectors, leaving the central sector uncharacterized. This study presents the first petrographic and geochemical evidence from a single outcrop exposed along the Jatunyacu River, in the central part of the Abitagua Batholith, in order to understand its magmatic evolution and tectonic affinity. Petrographically, the dominant lithology is an equigranular monzogranite. The fractured zones show localized hydrothermal alteration, including epidote, sericitization of plagioclase, and chloritization of biotite. Subordinate bodies include tonalitic enclaves, felsic dikes, and an andesitic dike. Geochemically, the studied sector shows a calc-alkaline affinity, peraluminous character, and a volcanic arc granite (VAG) signature broadly consistent with I-type granitoids formed in a continental arc related to subduction. Samples from fractured zones show small shifts toward the S-type field in the K₂O vs. Na₂O diagram, attributed to hydrothermal alkali mobility rather than primary magmatic variation, as supported by petrographic evidence. Multi-element normalized diagrams reveal distinct signatures among subordinate bodies: tonalitic enclaves show strong enrichment in mafic components and Nb, suggesting a primitive mafic source; felsic dikes display enrichment in incompatible elements (Nb, Rb) consistent with evolved residual melts; and the andesitic dike exhibits the most primitive composition with apparent minimal interaction with the felsic host. These are interpreted as evidence of a complex magmatic evolution involving mafic recharge, magma mixing, late injection of residual melts, and localized hydrothermal alteration. Comparison with previous studies suggest that the studied outcrop records an arc signature similar to that reported for the northern and southern sectors, although further work is needed to confirm the extent of this affinity across the central sector. 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 lamprophyre dikes and multi-generational pyrite and arsenopyrite developed in the Jinshan gold deposit in the West Qinling metallogenic belt provide critical evidence for understanding the role of mantle-derived magmatism in gold mineralization processes. In this study, we conducted zircon U-Pb dating of lamprophyre to constrain the timing of magmatic activity and the mineralization age, and performed EMPA and LA-ICP-MS analyses on sulfides from the main metallogenic stage (Py II–III, Apy II–III) and lamprophyre-hosted pyrite (Py L) to constrain the formation conditions and metal sources of the Jinshan deposit. The results show that the mantle-derived magmatism represented by lamprophyre yields an age of 206 ± 2 Ma, which provides a lower-limit constraint on the timing of gold mineralization, corresponding to the subduction-to-extension transition period in the region. Stage II mineralization occurred at 270–320 °C with logƒS₂ of −9 to −5, dominantly as Au-HS complexes, indicating medium-temperature hydrothermal conditions with low sulfur fugacity, consistent with microscopic mineral assemblages and thermodynamic simulations. Systematic δ³⁴S variations reveal: stage II values (9.24–5‰) indicate granitic/Devonian sedimentary sources; Py L values (2.19–3.6‰) reflect mantle contributions; stage III signatures (−2.3–1.93‰) record late meteoric water mixing. Complementary δ⁵⁶Fe data show that Py II (0.2–0.3‰) and Py L (0.58–0.68‰) preserve magmatic fingerprints, while negative values of Py III (−2.29 to −0.71‰) document increasing sedimentary Fe incorporation. Combined with geochronology, S-Fe isotopes, and physicochemical constraints, we propose that the Jinshan gold deposit formed in a tectonic setting transitioning from compression to extension during the Late Indosinian (ca. 237–201 Ma). Mineralization was initiated by the partial melting of the metasomatized mantle, where hydrous magmas efficiently extracted Au and volatiles. These components ascended through transcrustal faults, with Au partitioning into exsolved fluids that precipitated gold through immiscibility and boiling in secondary structures. Full article

Magma-heated geothermal systems have garnered significant attention in academia due to their unique formation mechanisms and vast potential. This paper focuses on the Rehai, Ruidian, and Banglazhang geothermal fields in the Tengchong area. We present the element geochemistry and isotope compositions of hot springs, cold springs, and surface water to explore magmatic fluid input into geothermal systems and investigate the release of deep mantle-derived components. Based on our findings, we propose a conceptual model and theoretical framework for geothermal system genesis constrained by magmatic heat source influences. Results indicate that magma-heated geothermal systems coexist with three types of geothermal water: neutral chloride-rich water, acidic sulfate-rich water, and alkaline bicarbonate-rich water. The infusion of magmatic fluids into geothermal systems. The enrichment of trace elements in hot springs is jointly controlled by magmatic fluid input and host rock leaching. The magma chamber is the primary factor influencing the reservoir temperature. The parent geothermal fluid can be identified within the geothermal system. During circulation, the parent geothermal fluid undergoes three cooling processes: adiabatic cooling, conductive cooling, and mixing with cold water. We propose that the release of mantle-derived materials is a key factor in element enrichment within magma-heated geothermal systems, and mantle-derived components are more enriched in areas with active magma chambers. The findings of this study provide insights into magmatic fluid input into geothermal systems and highlight the critical role of the release of mantle-derived components in the formation of high-temperature geothermal resources. Full article

The Neoproterozoic Wadi Mahasin metavolcanics (WMVs) in the Central Eastern Desert, Egypt, were remapped using Landsat-8 and Sentinel-2 imagery and verified by field observations, and their petrogenesis was evaluated using petrography, whole-rock geochemistry, and Pb isotopes. The image processing techniques of decorrelation stretch (DS), band ratios (BR), principal component analysis (PCA), and Minimum Noise Fraction (MNF) were applied to three remotely sensed datasets from Landsat-8, Sentinel-2B, and Planet to produce an updated geologic map of the study area. Moreover, two robust supervised classification techniques, maximum likelihood (MLC) and the support vector machine (SVM), enhanced geological contacts, structural elements, and produced classified images by 95.68% and 96%, respectively. The WMV suite comprises metadacite and metarhyolite with SiO₂ contents of 61.8–66.5 and 77.8–79.8 wt.%, respectively, and belongs to a subalkaline calc–alkaline series with a transitional medium- to high-K character at the felsic end. Primitive mantle-normalized patterns show enrichment in LILEs (Rb, U, K, and Pb) and depletion in Nb, Ta, Ti, and P, consistent with subduction-related felsic magmatism. Chondrite-normalized REE patterns are characterized by enriched LREEs, flat to weakly fractionated HREEs ((Gd/Yb)_N ≈ 1.5), and negative Eu anomalies (Eu/Eu* = 0.30–0.81). The flat HREE segment suggests melting of a garnet-free source, most plausibly a plagioclase–amphibole-bearing crustal assemblage. Eu/Eu* correlates positively with Sr for the suite as a whole, indicating plagioclase control during differentiation. Metarhyolite samples form a tightly clustered evolved group, whereas metadacites show broader scatter that mainly reflects differentiation. Pb isotopes and crust-like trace-element ratios (high Y/Nb, low Ce/Pb, and low Nb/U) indicate strong crustal involvement. Although assimilation–fractional crystallization from a mantle-derived parent magma cannot be excluded completely, the available isotopic data do not define a simple mantle-to-crust differentiation trend, and the uniformly evolved major- and trace-element signatures favor direct partial melting of felsic continental crust, followed by limited fractional crystallization. The WMV suite is, therefore, interpreted as a mature continental-arc felsic assemblage within the Arabian–Nubian Shield. 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 Guposh an orefield within the western segment of the Nanling Range hosts a globally significant tungsten and tin metallogenic province whose formation is tied to the intense Middle Jurassic granitic magmatism. Nonetheless, critical ambiguities remain regarding the metallogenetic ages and origin of ore-related hydrothermal fluids for W-Sn polymetallic deposits in this orefield. Here, we integrate in situ U-Pb geochronology of monazite and cassiterite and sulfur isotope analyses of pyrite from the Helukou W-Sn polymetallic deposit to resolve this outstanding question. In situ monazite U-Pb geochronology yielded lower intercept ages of 164.4 ± 1.1 Ma and 162.0 ± 2.0 Ma for the fine-grained and medium- to coarse-grained biotite monzogranite phases of the Guposhan pluton, respectively, bracketing its formation during the Middle Jurassic era. The initial ²⁰⁷Pb/²⁰⁶Pb ratio of 0.85 for the monazite grains is within the range of crustal and mantle materials, likely indicating a mantle–crust mixing source for the magma. Cassiterite from skarn-type ores yields a lower intercept U-Pb age of 165.9 ± 3.2 Ma, confirming a genetic relationship between the Guposhan magmatism and Helukou W-Sn mineralization. In situ pyrite δ³⁴S_V-CDT values show a uniform range from −0.66‰ to +0.79‰, indicating a uniform magmatic-derived sulfur source for the ore-forming fluids. We further demonstrate that fluid-rock interaction, rather than fluid mixing, acts as a crucial factor in the ore precipitation of W-Sn metals of the Helukou deposit. Full article

Mafic ultrapotassic volcanics (kamafugites, mafurites) are the youngest eruptives in the Bunyaruguru volcanic field, which is part of the Toro Ankole Province at the northernmost reach of the West Branch of the East African Rift Valley. We obtained new data using LA-ICP-MS on the trace element contents (rare earth, large ion lithophile, high field strength and compatible elements) in clinopyroxene phenocrysts from mafurite lava of the Bunyaruguru volcanic field. The clinopyroxenes are notable for their anomalously high zirconium contents (up to 800–1000 ppm), which is unusual in mafic silicate magmas but typical for clinopyroxenes from carbonatite lavas. This distinctive signature is not found in clinopyroxene in coeval mafic lavas from neighboring vents. Carbonate is also found in the Bunyaruguru volcanic rocks in the form of inclusions in high-Mg olivine phenocrysts, suggesting carbonated material exists in the source of kamafugite magmas. Carbonatites are widespread in the neighboring Fort Portal volcanic field, and we interpret the high-zirconium clinopyroxene as evidence for mixing of mafurite magmas with carbonatite melts. Full article