Magmatic Differentiation Research Articles

Petrology of Granitoids of the Mayorka Massif (Gorny Altay): Contribution to the Problem of High-Silica Magma Formation

Abstract —The paper presents data from a comprehensive study of granitoids identified in the Mayorka intrusion that is located in the western part of the Altai Mountains. It is shown that the massif is composed of rocks of four intrusive phases, the age of these rocks ranges from 391 to 372 Ma, and the intrusion of the main volume of granitoids dates back to a relatively short interval of 386–384 Ma. The massif contains rocks of two geochemical types. The first type is differentiated calc-alkaline granite-leucogranites with near-clark contents of high-field-strength elements and rare earth elements: ɛNd(T) = + 4.3…+ 4.5 and σ18O V-SMOW = +10.7…+11.2 ‰. The second is alkaline and moderately alkaline A-type alaskites, strongly enriched in high-field-strength elements and rare earth elements, having ɛNd(T) + 5.3 and σ18O V-SMOW = +11.6 ‰. Granitoids of the first group are of crustal source, while the rocks of the second group contain a significant portion of mantle material. The near-simultaneous introduction of these melts to the level of formation of the intrusion caused their interaction and the formation of hybrid magmas. Low crystallization temperatures of granitoids (<700 °C) and the presence of syngenetic melt and fluid inclusions in most rock varieties indicate a high fluid saturation of the melts. The abundance of leucogranites, whose geochemical characteristics cannot be explained from the standpoint of shallow differentiation of primary magmas, indicates the leading role of fluid-magmatic interaction processes in the formation of high-silica magmas.

Tourmaline geochemical and B isotopic constraints on pegmatite Li mineralization and exploration

Pegmatite–related deposits represent one of the most significant types of mineral deposits housing rare–metal elements such as Li, Be, Nb, Ta, Rb, Cs, and Sn. Although extensively studied for almost two centuries, the mechanism controlling the rare–metal mineralization in pegmatites remains controversial. In addition to the enrichment of rare–metal elements in the source region, differentiation processes (e.g., fractional crystallization and liquid immiscibility) after emplacement may have also contributed to the concentration and mineralization of rare–metal elements. However, compared to fractional crystallization, the role of liquid immiscibility in pegmatite mineralization has received limited attention. In this study, the element and boron (B) isotopic compositions of tourmalines from different textural zones (Zones I–VI) of the rare–metal–mineralized Koktokay No. 3 pegmatite, Altai, NW China, as well as from the altered country rock and the border zone, were analyzed to evaluate the role of liquid immiscibility in the generation of Li–mineralized pegmatites. Tourmalines display a variety of compositions, ranging from schorl and elbaite in the outer zones to elbaite in the inner zones of the Koktokay No. 3 pegmatite. Tourmalines from Zones I–III exhibit no obvious internal textures, whereas some tourmalines from Zones IV–VI have replacement textures or abrupt zonations. The distinction is attributed to the absence and presence of exsolving fluids during their formation, respectively. Tourmalines in Zones I–III and VII–VIII display less variable δ11B values (–15.07 ‰ to –12.21 ‰ and –14.16 ‰ to –13.10 ‰, respectively), reflecting a negligible B isotope fractionation produced by fractional crystallization during the pegmatite evolution. By contrast, tourmalines in Zones IV–VII exhibit more significant variations in δ11B values (–14.83 ‰ to –8.09 ‰) compared to those in Zones I–III and VII–VIII. The high δ11B tourmalines in Zones IV–VII were most likely crystallized from the fluids exsolving from the highly evolved pegmatite–forming magma. Their occurrence indicates the fluid exsolution occurring between zones IV and V, where Li mineralization began in the Koktokay No. 3 pegmatite. The mineralization of rare–metal elements is closely linked to the evolution of magma into a coexisting magma–fluid system. In addition, Li–mineralized pegmatites are characterized by tourmalines with Fe3+Al-1 substitution and higher Zn, Li, Li/Sr, and V/Sc than barren pegmatites. These differences are believed to be due to the higher fO2 and greater extent of magmatic differentiation in Li–mineralized pegmatites compared to the barren ones. These findings provide new insights into using the geochemical compositions of tourmalines as a guide for exploring Li–mineralized pegmatites.

The Petrogenesis and Geological Implications of the Sanggeda Gabbros, Southern Tibet: Insights from the Amphibole Crystal Population

Amphibole is an important mineral during the differentiation of arc magmas but rarely as a phenocryst in arc lavas or eruptive pyroclastic rocks. The Sanggeda complex, intruded into the ophiolite of the Indus–Yarlung Zangbo Suture Zone (IYZSZ), Zedong, southern Tibet, mainly consists of amphibole-rich, fine-grained, and porphyritic gabbros. The complex provides an opportunity to study the differentiation of arc magmas through amphibole crystals. Four distinct amphibole crystal populations can be recognized according to petrographic observations, EMPA, and LA–ICP–MS analysis. The first ones (Type 1) are fined-grained and euhedral, are crystallized during ascent, and are the product of the shallow emplacement of host magma. The second ones (Type 2) are euhedral, with slight negative Eu and Sr anomalies, and crystallize from an evolved magma that previously experienced plagioclase fractionation. Type 3 amphiboles have similar morphological characteristics to Type 2 but are without Eu and Sr anomalies. Type 4 crystals are shown as pseudomorphs, formed by the reaction–replacement between the clinopyroxene and melt. Type 1 crystals are autocrysts. Other amphiboles within host magma, whether presented as phenocrysts or cumulate nodules, are antecrysts. Based on the amphibole crystal population developed in the complex, in this study, a trans-crustal magma plumbing system is proposed, containing at least three magma reservoirs located at different crust depths: the shallow emplaced crust (~4.8 km), the mid-crust (~12.9 km), and the lower crust (~21.8–24.9 km). Early amphibole crystallization is an effective process to generate silicic residual melts. Gravity could help in that sense. Precursor amphibole and clinopyroxene can efficiently delaminate back into the mantle and promote the generation of silicic continental crust.

Chemical classification of spherules recovered from the Pacific Ocean site of the CNEOS 2014-01-08 (IM1) bolide

We have conducted an extensive towed-magnetic-sled survey during the period of June 14–28, 2023, over the seafloor about 85 km north of Manus Island, Papua New Guinea, centered around the calculated path of the bolide CNEOS 2014-01-08 (IM1). We found about 850 spherules of diameter 0.1–1.3 mm in our samples. The samples were analyzed by micro-XRF, Electron Probe Microanalyzer and ICP Mass spectrometry. Here we report major and trace element compositions of the samples and classify spherules based on that analysis. We identified 78 % of the spherules as primitive, in that their compositions have not been affected by planetary differentiation. We divided these into four groups, three of which correspond to previously described cosmic spherule types. Spherules in the fourth group, comprising 22 % of the collection, appear to all reflect planetary igneous differentiation and are all different from previously described spherules. We call them D-type spherules. At least five of the D-type spherules are suggested to be terrestrial in origin, although many spherules exhibit elemental ratios that are distinct from known planetary bodies and their origins are undetermined. A subset of the D-spherules show an excess of Be, La and U, by up to three orders of magnitude relative to the solar system standard of CI chondrites. Detailed mass spectrometry of 12 of these “BeLaU”-type spherules, the population of which may constitute up to ∼10 % of our entire collected sample, suggests that they are derived from material formed by planetary igneous fractionation. Their chemical composition is unlike any known solar system material. We compare these compositions to known differentiated bodies in the solar system and find them similar to those of evolved planetary materials–with lunar KREEP the closest in terms of its trace element enrichment pattern, but unusual in terms of their elevated CI-normalized incompatible elements. The “BeLaU”-type spherules reflect a highly differentiated, extremely evolved composition of an unknown source.

Geochronology and Geochemical Characteristics of Granitoids in the Lesser Xing’an–Zhangguangcai Range: Petrogenesis and Implications for the Early Jurassic Tectonic Evolution of the Mudanjiang Ocean

This article focuses on zircon U-Pb isotope dating and a whole-rock elemental analysis of granodiorites, monzonitic granites, granodioritic porphyries, and alkali feldspar granites in the Yangmugang area of the Lesser Xing’an–Zhangguangcai Range. The zircon U-Pb isotope-dating results revealed that these granitic rocks formed during the late Early Jurassic period (182.9–177.2 Ma). Their geochemical characteristics and zircon saturation temperatures suggest that the granodiorites are moderately differentiated I-type granites and the monzonitic granite, granodioritic porphyries, and alkali feldspar granites are highly differentiated I-type granites. The degree of magma differentiation progressively increased from granodiorites to alkali feldspar granites. By combining the regional Nd and Hf isotope compositions, it was inferred that the magma source involved the melting of lower crustal material from the Mesoproterozoic to the Neoproterozoic eras. By integrating these findings with contemporaneous intrusive rock spatial variations, it was indicated that the late Early Jurassic granitoids in the Lesser Xing’an–Zhangguangcai Range formed within an extensional tectonic setting after the collision and closure of the Songnen–Zhangguangcai Range and Jiamusi blocks. Additionally, this study constrains the closure of the Mudanjiang Ocean to the late Early Jurassic period (177.2 Ma).

Petrogenesis of magmatic charnockite-biotite granite suite from parts of the Chotanagpur Granite Gneissic Complex (CGGC), eastern Indian shield: Implication for the break down of the Columbia Supercontinent

A rare porphyritic charnockite that is girdled by and mineralogically grades to biotite granite occurs as a part of the Chotanagpur Granite Gneissic Complex (CGGC) in and around Massanjore, Jharkhand, India. Preservation of certain textural features, including (a) euhedral to subhedral grains of orthopyroxene, (b) low dihedral angle subtended by orthopyroxene and plagioclase grains, and (c) relict intergranular and porphyritic textures, are consistent with the view that orthopyroxene in the studied rocks has a magmatic origin. Preserved magmatic features and other petrological attributes of these rocks do not support any significant mass change beyond a few tens of microns during the overprinting high-grade metamorphism. The geochemical variation of the felsic rock suite (porphyritic charnockite and biotite granite) indicates that they are cogenetic and are derived from a ferroan A-type granitoid magma by crystal fractionation. The observed geochemical trend of the studied felsic rock suites has been simulated by phase equilibria modelling in the open system using the system components Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O2. The observed mineralogical and geochemical attributes and the results of the modelling study are consistent with a petrogenetic process in which high magma temperature (> 900 °C), low pressure, and low water activity in the parental melt favoured the separation of an orthopyroxene bearing cumulate assemblage (orthopyroxene + plagioclase + quartz + K-feldspar + ilmenite + magnetite) in the initial part of the magmatic differentiation. Removal of this anhydrous cumulitic assemblage raised the bulk H2O content in the residual melt. Orthopyroxene became unstable with respect to biotite in the evolved melt that eventually crystallised minerals that formed the biotite granite. An increase in magma fO2 also restricts the orthopyroxene stability in felsic magma. Taken together all the petrological and geochemical attributes, we demonstrate that fractionation of an orthopyroxene-bearing crystal cumulate from the melt is essential to form the charnockites, and that the biotite granite forms from the evolved melt after the fractionation. The charnockite-biotite granite association of the studied area was formed in an extensional tectonic setting, presumably during the breakdown of the Columbia Supercontinent.

Magma storage conditions of Lascar andesites, central volcanic zone, Chile

Abstract. Lascar volcano, located in northern Chile, is among the most active volcanoes of the Andean Central Volcanic Zone (CVZ). Its activity culminated in the last major explosive eruption in April 1993. Lascar andesites which erupted in April 1993 have a phase assemblage composed of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxides, and rhyolitic glass. To better constrain storage conditions and mechanisms of magmatic differentiation for andesitic magmas in a thick continental crust, crystallization experiments were performed in internally heated pressure vessels at 300 and 500 MPa, in the temperature (T) range of 900–1050 °C, at various water activities (aH2O) and oxygen fugacities (logfO2 between QFM+1.5 and QFM+3.3 at aH2O =1; QFM is quartz–fayalite–magnetite oxygen buffer). The comparison of experimental products with natural phase assemblages, phase compositions, and whole-rock compositions was used to estimate magma storage conditions and to reconstruct the magma plumbing system. We estimate that Lascar two-pyroxene andesitic magmas were stored at 975±25 °C, 300±50 MPa, and logfO2 of QFM+1.5±0.5, under H2O-undersaturated conditions with 2.5 wt % to 4.5 wt % H2O in the melt. The geochemical characteristics of the entire suite of Lascar volcanics indicates that a fractionating magmatic system located at a depth of 10–13 km is periodically replenished with less evolved magma. Some eruptive stages were dominated by volcanic products resulting most probably from the mixing of a mafic andesitic magma with a felsic component, whereas compositional variations in other eruptive stages are better explained by crystal fractionation processes. The relative importance of these two mechanisms (mixing vs. crystal fractionation) may be related to the amount and frequency of magma recharge in the reservoir.

Control of magmatic halogen composition and redox state on the zonation of metal mineralization across active continental margins: Perspectives from the world-class South China metallogenic province

Active continental margins are the major sites of continental magmatism and associated hydrothermal ore deposits with a broad metal spectrum. Mineralization across active continental margins typically displays spatial zonation, with porphyry copper-(molybdenum‑gold) deposits in volcanic arcs and tin- and tungsten-dominated mineralization occurring further inland in a back-arc setting. Particularly, tin and tungsten commonly form separate deposits in back-arc regions, even though both metals exhibit similar lithophile behavior. The key factors governing this metallogenic zonation remain unclear. The world-class South China metallogenic province hosts over 50 % of the global tungsten resources, along with a significant amount of tin and copper resources distributed in different mineralization belts, making it an ideal location in which to study regional metal zonation. Here, we comprehensively integrate a very large dataset of the halogen volatile composition (F, Cl) and oxygen fugacity of granites related to tin, tungsten, and copper mineralization in the South China continental margin. Our compilation, derived from a substantial collection of zircon, apatite, mica, and whole-rock geochemistry data, suggests that lateral variations in granite magmatism (away from the trench), transitioning from chlorine-rich and oxic to fluorine-rich and reduced conditions, exert the primary control on copper versus tin‑tungsten mineralization in the arc and back-arc regions, respectively. Differences in oxygen fugacity have a minor impact on the decoupling of tin and tungsten mineralization despite tin granites being universally reduced (ΔFMQ = −1.8 to −0.1, where FMQ is the fayalite-magnetite-quartz redox buffer) and tungsten granites having a broader redox range (ΔFMQ = −1.5 to +1.2). Instead, the disparity in fluorine content plays a more crucial role in controlling the spatial separation of tin and tungsten mineralization observed in the back-arc setting. Nd-Hf and He-Ar isotopic modeling calculations suggest that magmas linked to tin mineralization have a more pronounced involvement of F-rich mantle components compared to those associated with tungsten. Elevated fluorine (ca. 650–8000 ppm) in tin-associated magmas allowed an extreme degree of magmatic differentiation and delayed fluid exsolution due to high H2O solubility in F-rich silicate melts, ensuring Sn enrichment in highly evolved melts. In contrast, early fluid exsolution under less F-rich conditions (ca. 100–700 ppm) led to early tin loss from the melts, ultimately resulting in tungsten-dominant mineralization. This work emphasizes the combined influence of halogen composition and redox state on the regional mineralization zonation in world-class metallogenic provinces, providing vectors for global metal exploration in both past and currently active continental margins.

Two-stage mineralization of the Jinkeng Sn-Cu deposit in Eastern Guangdong, Southeast China: Response to magmatic activities and tectonic transformation

The Jinkeng Sn-Cu polymetallic deposit in South China consists of two different types of orebodies: 1) NE-striking skarn- and vein-type Cu-Pb-Zn-Sn orebodies in volcanic rocks suffering subsequent ductile shear deformation, and 2) NW-striking quartz-cassiterite-sulfide veins filled in the faults at the porphyritic granodiorite outward from the fine-grained granite which does not exhibit deformation. The relationships among Sn-Cu polymetallic mineralization, regional magmatism, and deformation metamorphism are still controversial. To address it, the geochronological, whole-rock and mineral geochemical research along with the detailed field investigation were conducted in this study. Our zircon U-Pb dating results show that the volcanic rocks formed at 158–162 Ma, earlier than the porphyritic granodiorite which yields the emplacement age of 146–147 Ma. In-situ LA-ICP-MS U-Pb dating of cassiterite from the deformed skarn ores indicates the early-stage mineralization occurred at 146 ∼ 148 Ma, which is similar to the emplacement age of the porphyritic granodiorite, but earlier than the formation of quartz-cassiterite-sulfide veins and the fine-grained granite (141∼144 Ma). Further, the whole-rock and biotite geochemistry, and zircon Hf isotope compositions suggest that the porphyritic granodiorite exhibits a lower degree of magma differentiation, higher oxygen fugacity, higher Cl and lower F contents than the fine-grained granite. The porphyritic granodiorite might provide the most Cu-Pb-Zn budget accompanied by minor Sn for early-stage mineralization. Overall, our study suggests that the Jinkeng Sn-Cu polymetallic deposit formed in two scenarios where the early dominated Cu-Pb-Zn and minor Sn mineralization related to the emplacement of the porphyritic granodiorite is superimposed by the late vein-type Sn-dominated mineralization related to the emplacement of the fine-grained granite. The two isolated mineralizing events (∼147 Ma and ∼141 Ma, respectively) in Jinkeng were probably responded to the regional magmatic activities triggered by the tectonic transformation where two extensional tectonic events were separated by a short contractional event (147–144 Ma).

Petrophysical and petrographic data correlation and the discrimination of magmatic environments and processes in Santos Basin, offshore SE Brazil

The igneous rocks in the context of oil & gas exploratory sedimentary basins have been a paradigm and challenge for industry and academia due to the difficulty of reconnaissance and interpretation using indirect methods, e.g. geophysical data. We presented the combination of the petrographic and well log data of distinct magmatic sections from wells of Santos Basin, SE Brazil. Effusive and explosive felsic rocks, mafic volcanic subaerial and subaqueous and plutonic mafic rocks were recognized by petrography and petrophysics proprieties data, as radioactive (GR), electric resistivity (R), acoustic property (Δt), porosity (Φ) and density (ρ), showed different patterns along sections. This enables the division on magmatic subsections and allowed the recognition of rock types and igneous setting. The compositional influences are clearly distinguished by GR, as felsic and mafic rocks, presence of amygdales in mafic effusive rocks and inter-pillow intervals in subaqueous environments, can interfere with GR patterns. In plutonic environment, GR can show evidence of magmatic differentiation. Δt and Φ are directly proportional with similar pattern and both are inversely proportional to R and ρ. Felsic rocks, effusive or explosive, and inter-pillow intervals makes Φ and ρ curves closer. Less dense and more porous rocks, as explosive, tend to imprint the Φ and ρ pattern to the left of the log. Welding processes are distinguished by gradual decrease of Φ and increase of ρ. Otherwise, denser mafic rocks, volcanic or plutonic, tend to show separate Φ and ρ curves on the right of the log, while amygdaloidal portions are lighter and more porous than the massive one, showing the separate pattern on the left. The subaqueous mafic volcanic rocks imprint GR, ρ and Φ intermediate patterns between mafic massive and amygdaloidal. The recognition of the type of magmatic rock, the environment and the physical properties can aid to improve not only the decisions of exploration and production but also the elaboration of a geodynamic context for offshore sedimentary basins.

The gold content of mafic to felsic potassic magmas

Many epithermal gold and gold-rich porphyry-type ore deposits are associated with potassic magmas. Hence, potassic magmas are commonly assumed to have been unusually Au-rich or to have contained high Au/Cu ratios. However, these hypotheses remain poorly tested. Here, we report Au concentrations and Au/Cu ratios in silicate melt inclusions analyzed in potassic rocks worldwide. The results suggest that mafic potassic magmas generally contain only 2‒7 ng/g Au, despite common sulfide exhaustion during partial mantle melting. Both the absolute Au concentrations and Au/Cu ratios are comparable to those of mafic calc-alkaline magmas, and they vary little during subsequent magma differentiation because magmatic sulfide precipitation is strongly dominated by monosulfide solid solution that is relatively poor in Au and Cu. We thus suggest that the close association of Au-rich deposits with potassic magmas is not due to Au enrichment in the magma, but rather due to selective Au precipitation at the hydrothermal stage.

53Mn-53Cr chronometry of ureilites: Implications for the timing of parent body accretion, differentiation and secondary reduction

Establishing the temporal evolution of the ureilite parent body(ies) is crucial for understanding the quantitative timescale of planetesimal formation and evolution in the protoplanetary disk. In order to establish a timeline for these early processes, age constraints on the accretion, differentiation and secondary reduction were obtained with the short-lived 53Mn-53Cr chronometer to whole-rock and sequentially digested fractions of main group ureilites. A whole-rock isochron dates the reservoir-scale Mn-Cr fractionation in the ureilite parent body(ies), associated with magmatic differentiation, to 2.89-0.51+0.56 Ma after CAI formation. This age implies that the ureilite parent body(ies) accreted no later than ∼1.5 Ma after CAI formation, at a time when the NC-CC dichotomy was already established. The 53Mn-53Cr systematics of fractions from chromite-bearing ureilites yield an age of 4.29-0.45+0.49 Ma after CAI formation for a secondary reduction event on the parent body. This event is commonly associated with the catastrophic disruption of the ureilite parent body while still hot. The chromite model ages are consistent with the isochron ages obtained from chromite-bearing ureilites. Collectively these ages indicate that chemical differentiation processes were underway on the ureilite parent body(ies) during the time interval when undifferentiated meteorite parent bodies were forming, and may have paused at the peak of planetesimal formation when planetary collisions were common.

Vanadium isotope records of the transformation from carbonated melt to alkali basalt

Volcanic clasts from the International Ocean Discovery Program Site U1431 in the South China Sea (SCS) were analyzed for V isotopic compositions in this study. These volcanic clasts represent mantle-derived carbonated melts and record the transition from carbonated melts to alkali basalts. Based on the formation sequence, these clast samples were divided into early-stage (> 8.3 Ma) and late-stage (< 8.3 Ma) clasts. The early-stage volcanic clasts have δ51V values of −0.76‰ to −0.67‰, which provide an estimate for the V isotopic composition of primary carbonated melts. Their V isotopic compositions are slightly heavier than those of mid-ocean ridge basalts (−0.84‰ ± 0.10‰) and bulk silicate Earth (−0.86‰ to −0.91‰), reflecting the control of low-degree partial melting under conditions of high oxygen fugacity. The late-stage volcanic clasts have δ51V values ranging from −0.62‰ to 0.29‰, which are systematically heavier than those of early-stage volcanic clasts. The carbonated melts rose through and reacted with the lithospheric mantle and were transformed into alkali basalts by dissolving orthopyroxene and precipitating olivine and/or clinopyroxene. Because the reactants and reaction products do not lead to significant V isotope fractionation, the V isotopes show limited variations during transformation from carbonated melts to alkali basalts. The alkali basalts were emplaced into shallow crust by multiple pulses, in which the magma experienced variable degrees of magma differentiation, with δ51V values close to those of the initial alkali basalts or increasing due to fractional crystallization of FeTi oxides. The change in V isotopic compositions from early-stage volcanic clasts to late-stage volcanic clasts was driven by the varying magnitude of influence exerted by different magmatic processes en route from the deep mantle to the shallow crust.

Magnetite geochemistry of giant alkalic-type epithermal gold deposits: Insights into the magmatic evolution of mineralized alkaline systems

Magnetite, a common mineral in alkaline magmatic complexes hosting giant epithermal Au deposits, is examined to obtain insights into the magmatic evolution and ore fertility of alkaline systems. Textural and compositional analyses of magmatic magnetite from Cripple Creek, USA, and Lihir Island, Papua New Guinea, reveal distinct magma sources and evolution paths. High HFSE concentrations and high La/Yb ratios in magnetite from Cripple Creek suggest relatively low-degree partial melting of lithospheric and asthenospheric mantle sources, whereas magnetite from Lihir Island indicates higher degree partial melting from subduction-modified mantle. Chromium concentrations track magma evolution, while V systematics record decreasing oxygen fugacity with magma differentiation. Sulfide saturation is observed at Cripple Creek, potentially affecting ore fertility. Magnetite itself bears the capability to scavenge Au from melts as indicated by Au concentrations of up to 40 ng/g. This might point towards elevated Au concentrations in the parental magmas, although experimental data on Au partitioning is lacking. Magnetite compositions overlap across different mineralization styles, challenging its reliability as an exploration tool but analysis of noble metals in magnetite and its inclusion cargo could offer promising alternative approaches. Overall, magnetite serves as a valuable tool for investigating ore deposit petrogenesis and holds potential for exploration.

Osmium and oxygen isotope constraints on magma-crust interactions and the transport of copper at the roots of arcs

The formation of copper-rich cumulates at the base of arc crusts has been proposed as a key process modulating the geochemical evolution of the continental crust and the genesis of giant ore deposits of copper. Despite the importance of these phenomena, the degree to which the lower crustal evolution of magmatic systems is influenced by open-system interaction and the assimilation of pre-existing crustal materials remains unclear. To tackle this issue, we provide direct isotopic constraints on the evolution of deep magmatic systems in arcs by measuring the osmium and oxygen isotope composition of hydrous copper-rich (∼730 μg·g−1 Cu) ultramafic cumulates formed at the base of the Acadian orogen (∼40 km deep) in the New England Appalachians (northeastern USA). The radiogenic 187Os/188Os initial ratios (ranging from 0.31 to 0.67) and the elevated δ18O values (8.97 ± 0.42 ‰ for orthopyroxene; 9.25 ± 0.26 ‰ for phlogopite) suggest a significant role of open-system magmatic differentiation, involving crustal assimilation, in the formation of these cumulates. Modeling of the 187Os/188Os and δ18O composition of the cumulates suggests that the observed isotopic compositions result from the initial evolution of parental magmas under sulfide-undersaturated conditions, followed by saturation after approximately 15% to 20% of assimilation and fractional crystallization progression. These results suggest that the assimilation of crustal material led to a drop in the magmatic system's fO2 (∼ΔFMQ < −1), triggering sulfide segregation and the formation of copper-rich cumulates. Our findings align with the hypothesis that magma-crust interactions can lead to the formation of lower crustal domains enriched with Cu, which may constitute a pre-stage in the formation of some porphyry copper deposits, particularly in collisional orogens.

Tin isotope heterogeneity and baseline of the upper continental crust

Stable Sn isotope ratios are emerging as a novel tracer for a wide range of geological processes; however, the Sn isotopic baseline of the upper continental crust (UCC) is not yet well-constrained. Here, we report high-precision Sn isotope data of a wide range of UCC samples, including granites, pegmatites, and sediments, to document the Sn isotopic composition of UCC. Significant variations in δ122/118Sn3161a (per mil deviation in 122Sn/118Sn relative to NIST 3161a) values are revealed for I-type (δ122/118Sn3161a = 0.025 ± 0.026‰ to 0.495 ± 0.046‰, n = 20) and S-type (δ122/118Sn3161a = 0.156 ± 0.018‰ to 0.501 ± 0.075‰, n = 22) granites. More extreme Sn isotope variability is observed for pegmatites, which have δ122/118Sn3161a from 0.256 ± 0.047‰ to 0.930 ± 0.049‰ (n = 13). The δ122/118Sn3161a of I-type granites decrease with decreasing TFe2O3 (total Fe as Fe2O3) and MgO contents and are attributed to the segregation of Fe-bearing minerals. Conversely, the Sn isotope variation of S-type granites appears to reflect source heterogeneity, whereas the Sn isotope variability of pegmatites may reflect fluid activity. In contrast, the loess samples display homogeneous δ122/118Sn3161a values (0.132 ± 0.034‰ to 0.239 ± 0.020‰, n = 20) that show no correlation with the degree of chemical weathering, suggesting that loess is representative of the average Sn isotope composition of UCC. The δ122/118Sn3161a values of modern sediments and sedimentary rocks range from 0.080‰ to 0.490‰ (n = 25) and the Sn isotope variations may be related to chemical weathering or sediment provenance. Based on the lithology-weighted average δ122/118Sn3161a of UCC samples (41 granites and 45 sediments) in this study, the δ122/118Sn3161a value of UCC is estimated to be 0.233 ± 0.099‰, providing a reference point for further investigations. Tin is isotopically lighter in UCC compared to the mantle, owing to magmatic differentiation and crustal evolution processes.

Applications of zinc stable isotope analysis in environmental and biological systems: a review

Zinc (Zn) is an essential trace element that is involved in both biotic and abiotic processes in Earth's surface environments. Over the last 20 years, advances in mass spectrometry instrumentation have enabled unprecedented high-precision Zn isotope abundance ratio determinations in natural and anthropogenic samples. Supported by a solid theoretical background inherited from the traditional non-metal stable isotopes (C, N, H, O, S), the understanding of the controlling factors of Zn isotope fractionation has rapidly evolved. In this article, we review the main applications and findings of Zn isotopes in a variety of scientific domains, including metal contamination, magmatic differentiation, plant uptake, weathering, global climate change, dietary and trophic chains, and biomedicine. The analytical aspects of Zn isotope determination in solid and water samples and the principles and mechanisms of Zn isotope fractionation are also reviewed. This work aims to provide a general yet in-depth panorama of Zn isotope chemistry and to demonstrate the versatility and potential of this isotope system for studying the biological, geological and chemical cycling of Zn.

A record of magmatic differentiation in plutonic xenoliths from Santorini (Greece)

Plutonic xenoliths from volcanic arcs provide unique insights into transcrustal magmatic systems in subduction zone settings. At Santorini volcano in the Central Aegean Volcanic Arc (Greece), plutonic xenoliths occur throughout a sequence of lavas and pyroclastic rocks erupted within the last ~360 ka. They are mineralogically variable, ranging from troctolites to olivine gabbros, gabbros, gabbronorites, and diorites. Thermobarometric calculations based on mineral and melt inclusion compositions indicate equilibration over a range of temperatures (1100 to 750 °C) at shallow to mid-crustal depths (P &lt;400 MPa), but there is no evidence for crystallisation at lower crustal depths. Oxygen isotope data of mineral separates and calculated δ18O melt values are in line with extensive closed-system fractional crystallisation at magmatic temperatures, without a requirement for extensive assimilation of the subvolcanic continental basement. The xenolith minerals compositionally overlap with phenocrysts from the volcanic rocks, but they also contain evidence for the presence of highly evolved melt compositions in the form of melt inclusions with extremely silica-rich compositions (up to 82 wt.% SiO2) and high enrichments of incompatible trace elements coupled with increasing negative Eu anomalies in clinopyroxenes. Since these characteristics correlate systematically with differentiation indices and rock type, they are interpreted to reflect melt evolution via fractional crystallisation as the dominant differentiation process with no significant role of reactive porous flow. These observations highlight that trapped melt fractions can influence mineral compositional variations in the plutonic xenoliths, and in turn the mineral compositions demonstrate a melt compositional variability not preserved in the volcanic rock record.

Understanding the extreme differentiation of granitic magmas through elemental geochemistry and Fe isotope signatures

The petrogenesis of extremely fractionated igneous rocks is closely linked to the evolution of the continental crust and the formation of rare metal mineralization. Extremely fractionated magmas evolve via fractional crystallization, hydrothermal evolution, and volatile-rich fluid–melt interaction, but the specific effects of these magmatic and magmatic–hydrothermal processes remain unclear. To understand the mechanisms by which extremely fractionated granitic magmas evolve, we characterized the geochemical and Fe isotope signatures of a suite of granites and pegmatites from the Baishitouquan (BST) granitic pluton in northwest China. The BST granitic system evolved from a high SiO2 and volatile-poor system to a low SiO2 and volatile-rich system as it transitioned from an evolutionary stage dominated by magmatic processes to one dominated by magmatic–hydrothermal processes. This transition is supported by changes in the degree of melt polymerization (NBO/T) and other geochemical indicators of fluid activity (e.g., TE1,3 (REE tetrad effect), Zr/Hf, Nb/Ta, and F/Cl ratios), suggesting that extremely fractionated granites form as a result of a combination of fractional crystallization and volatile-rich fluid–melt interactions. The bulk-rock samples of the BST pluton exhibit significant Fe isotope variability, with δ56Fe values ranging from 0.40 ± 0.02‰ in the least evolved leucogranite (Zone-a) to 0.65 ± 0.02‰ in the most evolved topaz albite granite (Zone-e). Notably, the increase in bulk-rock δ56Fe values during magma evolution is accompanied by a decrease in SiO2 contents, which is opposite to the general trend during granitic magma evolution. Given the correlations between δ56Fe values and indicators of magmatic differentiation (e.g., Fe2O3T, Rb, (Na + K)/(Mg + Ca), and (La/Lu)N), the variability in bulk-rock Fe isotope composition of granites is likely due to changes in magma composition, with garnet removal being the most likely mechanism fractionating Fe isotopes. Rhyolite-MELTS modeling, coupled with geochemical and petrographic characterization, indicate that the high concentrations of F and H2O in felsic magmas likely play critical roles in structurally modifying granitic melts by dramatically reducing their viscosity and enhancing fluid flow. The distinct geochemical–isotopic features of granites can, therefore, be used as tracers for identifying magmatic–hydrothermal processes and, potentially, rare metal mineralization.

Famatinian magmatism in the SW Gondwana margin: A review focused on the Sierras Pampeanas (Argentina)

The Famatinian orogeny along the proto-Pacific margin of Gondwana, from Venezuela to northeastern Patagonia, was of the accretional type during the Paleozoic (Ordovician to Silurian). Information gathered from the Sierras Pampeanas (Argentina) reveals magmatism (plutonism and volcanism) between 490 and 465 Ma, with a peak at 473–467 Ma, similar to other regions along the margin. Metamorphic events in the middle crust occurred between 484 and 465 Ma, and at ca. 440 Ma. Recent reviews propose a lithospheric extension phase (>480 Ma) before contraction episodes (ca. 470 and 440 Ma). Magmatism transitioned from peraluminous to metaluminous intrusions, with prolonged mafic magmatism throughout. Mafic intrusions show a broad spectrum of isotope compositions (87Sr/86Srt = 0.705 to 0.711 and ƐNdt = +5 to −6) but with general trends toward isotopically enriched magmas. The main arc consists of tonalite-granodiorite magmas (ca. 480–470 Ma) with <25% crustal contamination but crustal-like isotopic signatures (87Sr/86Srt = 0.707 to 0.711 and ƐNdt = −4 to −6). The wide isotopic variations in granodiorite-monzogranite (and volcanic equivalents) (87Sr/86Srt = 0.705 to 0.711 and ƐNdt = +3 to −6) suggest two origins: differentiation and contamination of tonalite-granodiorite magmas (AFC model) for the most evolved, and differentiation from juvenile mafic additions for the isotopically juvenile ones. Regardless of depth (∼1–6 kbar) and position within the magmatic arc, analyzed areas display north-south striking and steep magmatic fabrics. These fabrics may have rotated by no more than 20–28° from its original position. The petrogenetic model involves isotopically diverse sub-arc mantle sources. Famatinian magmatism ceased abruptly around 465 Ma (magmatic lull), correlating with arcs along the SW Gondwana margin, indicating significant geodynamic changes in the subduction regime.