Fractional Crystallization Research Articles

Large-volume and swift magmatic response to Late Cenozoic segmentation of the subducted Neotethyan oceanic slab: evidence from the Galatian Volcanic Province, northwestern Turkey

ABSTRACT The Miocene Galatian Volcanic Province (GVP) is one of the largest volcanic provinces in central-western Anatolia, with an extent of ~ 8,900 km2. The volcanic activity is extended from 22.5 to 7.5 Ma. The volcanic compositions straddle the alkaline-subalkaline fields, from basic to acid compositions and mostly transitional to sodic affinity. Major oxides show good correlation with SiO2 indicating prolonged effects of fractional crystallization. Primitive mantle-normalized multi-element patterns indicate overall similarities among the different samples of the three geographic sectors, sharing strong negative anomalies in Nb–Ta–Ti, strong positive peaks at Cs and K, coupled with a common, albeit not always present, positive anomaly at Pb. Mineral-melt geothermobarometric estimates indicates ~1070–1235°C and ~7–19 kbar for melting conditions of basaltic compositions and ~1000–1150°C and ~3–12 kbar for andesitic-dacitic rocks. The absence of correlation between radiogenic isotopes and SiO2 and MgO is here interpreted as consequence of assimilation-fractional-crystalization processes involving lower continental crust as contaminant. The GVP parental magmas are generated from ~2% to 10% partial melting of a lherzolitic mantle with high spinel/garnet ratio based on intra-REE fractionation constraints. The subduction-related metasomatism inferred for the GVP mantle sources based on their chemistry is interpreted to be linked to the northward subduction of the northern branch of the Neo-Tethys slab. Successive slab retreat resulted in extension for the critical stress distribution through the Cyprus slab, favouring magma propagation for the GVP volcanic region. The eventual break-off of the slab after the continent-continent collision of Arabian and Eurasian plates could have caused a toroidal mantle flow, favouring the widely distributed 15–16 Ma alkaline magmatism in the eastern GVP, associated with passive hot asthenospheric upwelling imaged by teleseismic P-wave tomography.

Harnessing dimethyl ether with ultra-low-grade heat for scaling-resistant brine concentration and fractional crystallization

Solvent-driven separations may enable scalable concentration of hypersaline brines, supporting a circular resource economy from the extraction of lithium and rare earth elements from spent battery and magnet leachates. This work analyses a novel solvent-driven water extraction (SDWE) system employing dimethyl ether (DME) and ultra-low-grade heat for brine concentration and fractional crystallization. SDWE exploits DME’s unique properties: (1) a low dielectric constant that promotes water solubility over charged solutes by a factor of 103, and (2) a high volatility that facilitate efficient DME reconcentration with ultra-low-grade heat. The techno-economic viability of SDWE is assessed with a computational framework that encompasses a liquid–liquid separator and a solvent concentrator. We integrate the extended universal quasichemical model with the virial equation of state to predict the compositions of the complex three-phase DME-water mixture at vapor–liquid and liquid–liquid equilibrium. Subsequently, we optimize the thermodynamic and economic performance of SDWE, by controlling the interstage flash pressure, heat source temperature, and the number of concentrating stages. DME-based SDWE concentrates an input saline feed to 5.5 M and regenerates over 99 % of the DME using ultra-low-grade heat below 50 °C, with a DME/water selectivity ratio of 125. Our calculations reveal that optimal performance is achieved at interstage flash pressures of 0.4 – 0.5 bar for heat source temperatures between 323–373 K, with improved exergetic efficiencies at lower temperatures. At a heat source temperature of 323 K and an interstage pressure of 0.489 bar, DME-driven SDWE achieves an optimal thermodynamic efficiency of 20.5 % and a projected specific cost of US$ 1.93 m−3. These specific costs suggest that SDWE is competitive with commercialized thermal distillation technologies, while mitigating the traditional risks associated with scaling in heat and mass exchangers with hypersaline brines.

Experimental re-melting of a continental crust: probing the deep storage zone of Campi Flegrei and Vesuvius magmas

Mantle magmas interact with surrounding rocks during their ascent and storage in the continental crust, leading to open system processes as wall rock partial melting. In this study, we have experimentally investigated the reactions between a leucosome depleted migmatite and a primitive K-basaltic of Campi Flegrei (Italy). Experiments were carried out at pressure of 0.8 GPa temperatures from 1250 °C to 1050 °C and constant temperature and thermal gradient conditions. The experimental products consist of biotite-free migmatite, glass and crystals of clinopyroxene, olivine, plagioclase and Cr-spinel with proportions that vary as a function of temperature. Open system isothermal experiments indicate that the chemistry of melts and phase relationships are controlled by the high Al2O3 content of leucosome depleted migmatite with the glass composition shifting from K-trachybasalt towards shoshonite as the temperature decreases from 1200 °C to 1125 °C. At temperatures \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document}1150°C, migmatite assimilation is not exclusively due to the assimilation fractional crystallization process because evidence of mingling and mixing is observed. T-gradient experiment shows melt composition ranging from shoshonite to phono-tephrite moving from the slightly crystalline zone (T = 1250 –1210 °C) at the bottom of the capsule towards the highly crystalline zone (T = 1160 –1140 °C). This SiO2-constant trend indicates that at temperature below the basalt solidus, the assimilation of leucosome depleted crust is represented almost exclusively by the biotite breakdown, leading to the increase in Al, Mg, Fe, Ti, and K activities in the system. The shoshonitic composition obtained in our experiments could represent the parental magma for both Campi Flegrei volcanic district and Vesuvius magmatic systems, indicating modification in a deep storage zone through mixing with the partial melts derived from restitic continental crust.

Low Viscosity of Peridotite Liquid: Implications for Magma Ocean Dynamics

AbstractTransport properties of silicate melts control magma ocean dynamics on the early terrestrial planets and rocky exoplanets. Here we calculate the viscosity (transport of momentum) of peridotite liquid at potential magma ocean conditions (0–159 GPa, 2,200–6,000 K) using ab initio molecular dynamics simulations. We find that, unlike MgSiO3 or basaltic melts, the viscosity of the highly depolymerized peridotite liquid (a) increases monotonically with pressure without an anomalous drop and (b) is lower than those of other melts over the entire mantle pressure range. Low viscosity would promote fractional crystallization in a less polymerized magma ocean and thus contribute to mantle heterogeneity from its earliest stage. Given the compositional dependence of magma ocean properties, emphasis on multicomponent bulk silicate Earth‐like composition, instead of simple end‐members, are rendered necessary, in order to better understand high‐energy planetary accretion processes and their aftermaths.

Magnesium isotope behavior during titanomagnetite fractionation in basaltic lavas

Knowledge of the behavior of magnesium (Mg) isotopes during magmatic differentiation is a prerequisite for applying Mg isotopes as a tracer of crustal recycling and mantle heterogeneity. Crystal fractionation of mafic silicate minerals leads to limited Mg isotope fractionation; hence, Mg isotopic variations in basalts largely result from contributions of subducted crustal materials into their mantle sources. However, recent studies have revealed that the segregation of iron oxides, such as chromite during early-stage basaltic differentiation and titanomagnetite and ilmenite during late-stage differentiation, can potentially modify Mg isotopic compositions of mantle-derived lavas. Titanomagnetite is much more commonly observed in terrestrial basaltic lavas than chromite and ilmenite, and can also form during early-stage basaltic differentiation. To constrain the effects of titanomagnetite crystallization on Mg isotopic systematics of basaltic magma, we report Mg isotopic data for a suite of well-characterized alkaline basaltic lavas (MgO wt% = 4.99 to 6.52) from Gerba Guracha, western Ethiopian Plateau, which have undergone extensive titanomagnetite fractionation. Their δ26Mg values range from −0.29‰ to −0.17‰ and do not correlate with indicators of titanomagnetite fractionation such as TiO2 and V. These observations suggest that the segregation of titanomagnetite produced limited Mg isotope fractionation, possibly because of its composition-dependent, highly variable Δ26MgTi-Mgt−melt (Δ26MgTi-Mgt−melt = δ26MgTi-Mgt − δ26Mgmelt) values. Considering that most iron oxides occur as complex solid solutions that are controlled by the oxygen fugacity of magmas, the effects of oxide segregation on Mg isotopic systematics of basalts require further evaluation.

Chemical and boron isotopic compositions of tourmaline from the pegmatite in Ke'eryin rare metal orefield, Eastern Tibet: Implications for pegmatitic evolution

Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or syn-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(Xvac, Al)−1, (Mg, OH)(Al, O)−1, and (Ca, Mg2)(Xvac, Al2)−1 exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.

Petrogenesis and REE mineralogical characteristics of Shitouping granites in southern Jiangxi Province: Implication for HREE mineralization in South China

The enrichment of heavy rare earth elements (HREE) in the granitic host-rocks is crucial for generating ion-adsorption HREE deposits in South China. The Shitouping pluton, located in the southern part of Jiangxi Province, South China, develops large-scale HREE deposits in its weathering profile identified by recent geological surveys. These granites can be divided into medium to coarse-grained biotite monzogranite (MGBG), medium to coarse-grained syenogranite (MGSG) and fine-grained alkali feldspar granite (FGAG) based on field observations and mineral assemblages. New geochronologic results show that this composite pluton intruded during the Early Cretaceous (ca. 140 Ma). Three granitic units displaying comparable whole-rock Nd [εNd(t) = −4.5 to −3.4] and zircon Hf compositions [εHf(t) = −4.4 to +1.2], combined with mineral association, hydrothermally altered zircon and whole-rock geochemistry, indicate they were derived from partial melting of hybridized crustal source, followed by intense fractional crystallization and fluid metasomatism in the highly evolved granitic system. The MGSG and FGAG have higher Rb, Nb, HREE contents and Rb/Sr ratios, as well as lower Nb/Ta, K/Rb ratios in comparison with the MGBG, implying they are more evolved units. The overlapping magmatic zircon trace element compositions between MGBG and MGSG, coupled with the subvertical contact boundary between the FGAG and the MGBG, suggest that the generation of Shitouping pluton should be attributed to the periodic magma replenishment, remobilization, and differentiation process in the long-lived magmatic system rather than simple fractional crystallization from a single parental magma. Hydrothermally altered zircon with elevated concentration of HREE and the paragenetic relationship between LREE-phosphate and HREE minerals in the MGSG suggest that the fluid metasomatism promotes the migration and accumulation of HREE. This is consistent with the high HREE concentration recorded in the MGSG, which contains abundant HREE minerals associated with fluorites. Thus, this study highlights that magma differentiation and fluid metasomatism during the late magmatic stage could achieve the relatively high HREE contents in granites to favor the formation of ion-adsorption HREE deposits.

The first finding of a highly evolved Mg-rich carbonatite intrusion in NW Anatolia (Arıklı-Çanakkale)

The carbonatite-alkaline rock suites are quite unique for hosting high grade critical metals including rare earth elements (REE), niobium (Nb), tantalum (Ta), thorium (Th) and uranium (U). Most of these rock suites are generally associated with continental rifting in overthickened Precambrian cratonic environments. In Turkey, despite majority of magmatism is quite young, a few number of carbonatite intrusions were identified in Central Anatolian Crystalline block. However, the scientific literature which focused on the magmatic activities of NW Anatolia with its numerous articles involving magmatic intrusions and their extrusive counterparts lacked genuine magmatic carbonatite data until the present day. The Arıklı carbonatite intrusion is the first magmatic carbonatite identified in NW Anatolia, and also interesting for its unusual mineralogical and geochemical features. The carbonatite body is generally composed of multiple phases of calcite and apatite mineralizations. Carbonatitic rocks of Arıklı show a highly evolved nature with considerable Mg and Ca contents accompanied by Th (up to 0.36 wt%), U (up to 373.6 ppm) and heavy rare earth elements (HREE) (up to 194.7 ppm). The δ13C (PDB) and δ18O (SMOW) values show that fractional crystalization and hydrothermal activities effected the composition of initial carbonatitic melt. The metasomatic halo of Arıklı carbonatites are enriched in terms of K (up to 12 wt%), P (up to 9 wt%), Th (248 ppm), and U (up to 0.27 wt%). However, the LREE values of both carbonatites and metasomatic rocks are pretty low compared to other carbonatite-fenite complexes. The effects of magmatic and post-magmatic events (partial melting, fractional crystalization, liquid immiscibility, and fenitization) played an important role in the formation of Arıklı carbonatite intrusion.

Enhanced electrical properties of polypropylene insulation based on β‐nucleated crystallization regulation for high‐voltage direct current cable

AbstractThis study investigates the effect of crystallisation regulation on the electrical properties of β‐modified polypropylene (PP) insulation. Various β‐modified polypropylene insulation samples are prepared by controlling the melting temperature within the range of 180°C–200°C, and the ensuing crystallization characteristics of polypropylene insulation are evaluated. It is observed that the crystallinity decreased with increase in melting temperature, while the β crystal fraction and the lamellae long period increased. Notably, PP insulation subjected to a melting temperature of 200 °C demonstrates a substantial 47.1% decrease in DC conductivity, accompanied by a notable 22.6% reduction in space charge accumulation, concomitant with a significant 14.6% enhancement in DC breakdown strength. Additionally, a higher β crystal fraction in PP insulation is found to correspond to an increased density of deep traps, notably at an energy level of 0.95 eV. The elevated melting temperature effectively eradicates the melting memory effect, thereby facilitating the induction of β crystals by the β‐nucleating agents. The parallel lamellae structure inherent in β crystals serves to diminish interface defects between spherulites, consequently mitigating carrier mobility, curtailing space charge accumulation and enhancing breakdown strength.

Tracing Deep Carbon Cycling by Zinc Isotopes in a Peralkaline‐Carbonatite Suite

AbstractSedimentary carbonates are known to be carried into the deep mantle by subducted slabs, and studies on mantle‐derived magmas have attempted to trace the recycled carbonate in their mantle source. However, the final depth of storage of recycled carbonate and the role of recycled carbonate in the partial melting of mantle remain controversial. Peralkaline‐carbonatite suites are considered to have been derived from a carbonated mantle source and are windows to evaluate carbon in the mantle. In this study, we report the Zn isotopic compositions of a peralkaline‐carbonatite suite from the Tarim Large Igneous Province (Tarim LIP). The peralkaline‐carbonatite suite has heavier δ66Zn than normal mantle with δ66Zn of 0.34–0.40 ‰ for nephelinite, 0.35–0.47 ‰ for aillikite, 0.51–0.55 ‰ for nepheline syenite, 0.58–0.67 ‰ for calciocarbonatite and 0.38–0.56 ‰ for magnesiocarbonatite. The heavy Zn isotopic compositions of the peralkaline‐carbonatite suite in the Wajilitag complex suggest the incorporation of recycled carbonate‐bearing materials into the deep mantle. We infer that the calciocarbonatite was produced by the initial partial melting of subducted MgSiO3/MgO + C‐bearing carbonated eclogite, whereas the magnesiocarbonatite, aillikite, and nephelinite are considered as reacted melts between carbonated eclogite‐derived melts and peridotite. The heavy Zn isotopic compositions of the nepheline syenite are attributed to fractional crystallization from nephelinite magma in the magma reservoir. Our study highlights the incorporation of carbonated eclogite as an important agent of recycled carbon in the deep mantle and interactions between carbonated eclogite‐derived melts and peridotite lead to the complex lithological heterogeneities in the peralkaline‐carbonatite suite in Tarim LIP.

Source and parental melts of poikilitic shergottites: Implications for martian magmatism

Martian poikilitic shergottites are cumulate rocks that can help advance the understanding of magmatic evolution from near the base of the crust (∼10 kbar) to near-surface conditions. Through a comprehensive petrographic and geochemical study, we aim to better understand poikilitic shergottite formation and the evolution in the martian interior. A suite of poikilitic shergottites, including Northwest Africa (NWA) 7755, NWA 11043, NWA 11065, NWA 10618 and Alan Hills (ALHA) 77005, were investigated for their major, minor, and trace element compositions of olivine-hosted melt inclusions (MI). The MI occur within both the early-evolutional stage textural and late-evolution stage textural domains in olivine. Major element compositions of MI indicate fractional crystallization between the early and late-crystallizing domains. Calculated parental melt compositions from these MI data yielded results that also petrogenetically link the poikilitic shergottites with the olivine-phyric shergottite subgroup. Trace element compositions of MI show that the later-crystallizing MI could have undergone open-system processes, such as fluid exsolution. Lutetium-Hf and Sm-Nd isotopic analyses were performed on NWA 7755 and NWA 11043 to constrain their age and source isotopic compositions. Northwest Africa 7755 shows a 176Lu/177Hf crystallization age of 223 ± 46 Ma, which fits into the expected range for enriched shergottites of ∼165 Ma to 225 Ma. A similar crystallization age and 176Lu/177Hf and 147Sm/144Nd source composition of NWA 7755 to the other enriched shergottites suggest that this specimen likely shares a long-lived geochemical source with these samples that has lasted for at least 60 Ma. Northwest Africa 11043 shows scatter throughout the Lu-Hf and Sm-Nd isotopic data, suggesting that this sample is not in isotopic equilibrium. This sample was possibly inherited from high-temperature processes, such as incomplete magmas mixing from a similar, but distinct, source. We conducted in situ U-Th-Pb isotope analyses of Ca-phosphate minerals for NWA 11043 and found an unreliable crystallization age of 59.2 ± 138.4 Ma: phosphates are likely recording the period of shock metamorphism related to the ejection event. Consistent crystallization ages and magmatic histories support previous work that suggest there is a common magmatic system on Mars that is responsible for the formation of enriched shergottites.

Stratigraphy, geochronology, geochemistry and Nd isotopes of the Ouarzazate Group, Anti-Atlas, Morocco: Evidence of a Late Neoproterozoic LIP in the northwestern part of the West African Craton

In the eastern and central Anti-Atlas of Morocco, the Late Neoproterozoic Ouarzazate Group (OG) forms a ∼ 2 km-thick section of volcano-sedimentary rocks deposited during intermittent magmatic activity, spanning a time period between 590 and 540 Ma. In the eastern Anti-Atlas, the stratigraphy of the OG, termed IMS (Imiter Mine succession), includes four units that reflect a gradual change from fluvial to lacustrine depositional sedimentary environments. In the central Anti-Atlas, the deposition of the OG occurs within a caldera environment, consisting of five units referred to as BMS (Bou Azzer Mine succession). UPb dating on zircon from the rhyolite lava flow at the top of the IMS constrains the latest lava flow of the IMS to 570.7 ± 2.1 Ma. In the Bou Azzer inlier, the stratigraphically correlated basal andesite and top dacite lava flows were emplaced at 590.6 ± 4.2 Ma and 555.9 ± 20.4 Ma, respectively, suggesting that the OG was constructed through successive pulses within a long-lived magmatic episode. The magmatic rocks display geochemical signatures typical of continental arc magmas, including high-K calc-alkaline to shoshonite composition, enrichment in LILE, and negative Nb, Sr, Ti and P anomalies. Nd isotopes indicate that magmas supplying the plumbing systems of the IMS and BMS constitute transitional products resulting from a combination of orogenic and intraplate volcanism, involving deep crustal recycling. The compositions of these magmas evolved through processes of crustal contamination, bulk assimilation, and minor fractional crystallization of the parent melt. High εNd values of the BMS rocks argue for a juvenile origin, whereas lower εNdt recorded in the IMS likely reflect old crustal protoliths and an overall less contribution of juvenile material in their source. The magmatic rocks of the OG are interpreted as products of a large igneous province (LIP) developed by a post-collisional delamination model that initiated tens of millions of years after the subduction-collision process stage of the Pan-African orogeny in the northwestern part of the West African Craton (WAC).

The Zircon U-Pb Age, Hf Isotopes, and Lithogeochemistry of Ore-Bearing Rocks from the Archean Hongtoushan Volcanogenic Massive Sulfide Deposit in the North China Craton: Implications for Tectonic Setting

Volcanogenic massive sulfide (VMS) deposits are globally significant sources of metals. The Hongtoushan VMS deposit is the only large Archean Cu-Zn VMS deposit in the North China Craton, carrying substantial economic value. Significant deformation and metamorphism have made the tectonic setting of the Hongtoushan VMS deposit the subject of extensive debate. This study investigates the petrogenesis and chronology of the ore-bearing host rocks from the Hongtoushan Cu-Zn VMS deposit in the North China Craton. By utilizing whole-rock geochemical analyses and zircon dating, this research sheds light on the origin and evolution of the ore-bearing rocks within the deposit. The whole-rock geochemical analysis data indicate that the Hongtoushan ore-bearing rock series is mainly composed of amphibole plagioclase gneiss (basalt protolith) and biotite plagioclase gneiss (andesite and rhyolite protolith), suggesting a complete volcanic cycle from basic to medium-acidic volcanic rocks. The amphibole plagioclase gneiss has slight LREE enrichment patterns with unremarkable depletions of Nb, Ta, and Ti and belongs to contaminated ocean plateau basalt (OPB) in terms of composition, which is generally interpreted as being generated from the mantle plume head. Meanwhile, the biotite plagioclase gneiss has relatively steep LREE enrichment distribution patterns with remarkable negative Ta, Nb, and Ti anomalies and a wide range of Zr/Y ratios, indicating their classification as FI- and FII-type felsic rocks; they were likely formed through the fractional crystallization of basic magma combined with crustal assimilation. When combined with the zircon dating results, the ore-bearing host rocks of the Hongtoushan VMS deposit were generated via a continuous magmatic evolution process. The zircon dating of the host rocks indicates a formation age of between 2609 and 2503 Ma, with metamorphic events between 2540 and 2466 Ma, which is consistent with the 2.5 Ga-related global mantle plume event. Further research shows that the ore-bearing host rocks are more likely to have been formed in a mantle plume-related stretching environment, possibly a margin rift.

Young KREEP-like mare volcanism from Oceanus Procellarum

The Moon’s mare volcanism predominantly occurs within the Procellarum KREEP Terrane (PKT), which is widely thought to be associated with KREEP components within the lunar interior. The Chang’e-5 (CE-5) mission sampled a young (2 Ga) mare basalt Em4/P58 unit of northern Oceanus Procellarum. The geochemistry of the CE-5 mare basalt enables assessment of mantle source compositions which are essential to understand the thermo-chemical mechanism for prolonged volcanism during secular cooling of the Moon. Geochemical compositions of the CE-5 bulk soil, breccias, and basalt clasts from various depths within the drill core consistently display high concentrations of incompatible trace elements (ITE: ∼ 0.3 × high-K KREEP; ∼ 5 μg/g Th) with KREEP-like inter-element ratios, for example for La/Sm, Nb/Ta, and Zr/Y. Exotic impact ejecta, extensive magma differentiation (<70 % fractional crystallization) and significant assimilation of KREEP materials during magma transit and eruption cannot account for the ITE contents and ratios or radiogenic isotope compositions (e.g., εNdinitial of + 8 to + 9 and εHfinitial of + 40 to + 46) of the CE-5 basalts; instead, partial melting of their mantle source played a dominant role. The Chang’e-5 basalt is a chemically evolved low-Ti mare basalt (Mg# of ∼ 34) with enriched KREEP-like ITE compositions but high long-term time-integrated Sm/Nd and Lu/Hf ratios, which represent a hitherto unsampled type of mare basalt. It formed by melting of an augite-rich mantle source (late-stage magma ocean cumulates containing > 30–60 % augite, and little or no ilmenite), with a small amount of late-stage interstitial melt that resembles KREEP (∼1–1.5 modal %, equivalent to 0.2–0.3 μg/g Th in the mantle source). The voluminous mare basalts making up the Em4/P58 unit (>1500 km3) provide compelling evidence for large-scale, ITE enriched young mare magmatism within Oceanus Procellarum. In combination with remote sensing data and with the unique Th-rich Apollo 12 basalt fragment 12032,366–18 (impact ejecta likely from Oceanus Procellarum), this implies that significant portions of the FeO- and Th-rich mare regions of the western PKT may also have formed in a similar way.

Timescales of mafic magmatic fractionation documented by paleosecular variation in basaltic drill core, Snake River Plain volcanic province, Idaho, USA

The timescales over which fractional crystallization and recharge work in mafic volcano-plutonic provinces is subject to great uncertainty. Currently modeled processes are subject to the scale of measurement: monogenetic basaltic fields accumulate over hundreds of thousands of years, consistent with U-Th-Ra isotopic variations that imply 50% crystallization of basic magmas on timescales of 100,000 years or more, whereas crystal diffusion modeling implies phenocryst residence times of ∼1−1000 years. Monogenetic basalts of the Snake River Plain in southern Idaho, USA, are up to 2 km thick and postdate passage over the Yellowstone−Snake River Plain hotspot. Detailed lithologic and geophysical logging of core from deep drill holes, along with chemical stratigraphy and high-resolution paleomagnetic inclination measurements, document individual eruptive units, compound lava flows, and basaltic flow groups that accumulated over 1−6 m.y. Hiatuses are commonly marked by loess or fluvial interbeds that vary from ∼0.1 m thick to 20 m thick. Radiometric (40Ar-39Ar, detrital zircon U-Pb) and paleomagnetic timescale ages show that the deepest hole (Kimama drill hole, 1912 m total depth) accumulated over ∼6 m.y. Cycles of fractional crystallization and recharge are recognized in the chemical stratigraphy as up-section shifts in major and trace elements; these fractionation cycles commonly represent 40%−50% fractionation. Individual fractionation cycles may comprise 20−40 eruptive units (8−17 lava flows) with little to no change in paleomagnetic inclination (0°−1°), whereas adjacent cycles may differ by several degrees from one another or reflect changes in polarity. Rates of paleosecular variation in Holocene lavas and sediments dated using 14C document significant shifts in magnetic inclination over short timescales, ranging from ∼0.05° to 2°/decade, with an average of ∼0.5°/decade and a minimum rate of 0.05°/decade. This implies that fractionation cycles with ≤1° variation in magnetic inclination formed on timescales of a few decades up to a few centuries (20−200 years). Thus, the lavas collectively represent only a few thousand years of eruptive activity, with major flow groups separated in time by tens to hundreds of thousands of years. We suggest that the rates defined by paleosecular variation capture the timescales of magmatic chamber evolution (fractionation/recharge) in the seismically imaged mid-crustal sill complex; in contrast, we suggest that crystal diffusion modeling captures the residence times in shallow subvolcanic magmatic chambers that underlie individual monogenetic volcanoes.

Evolution of A-type granites during the Late Paleoproterozoic orogenic cycle of North China craton: Implications for post-collisional magmatism

“A-type” granites were originally considered anorogenic, however current consensus closely associates them with orogenic settings. The correlation between the prolific emergence of A-type granites and the assembly of the Columbia (Nuna) supercontinent during the Late Paleoproterozoic remains ambiguous possibly being indicative of a geodynamic shift from the amalgamation to the fragmentation of the supercontinent. This study identifies a Late Paleoproterozoic pluton exhibiting A2-type granite characteristics in the Shaerqin area of the Khondalite belt, North China craton. The plutonic rocks exhibit evolved whole-rock Nd isotopic (εNd(t) = −6.6 to −8.0) and zircon Hf isotopic (εHf (t) = −6.3 to −2.9) compositions, along with notably high zircon δ18O values (averaging 8.35 ± 0.29 ‰, 1SD). The Hf–Nd–O isotope systematics imply that the Shaerqin A-type granites originated from the partial melting of preexisting crustal materials under conditions of low pressure and high temperature. Incorporating the outcomes of this research with a compiled dataset of 1.9–1.5 Ga A-type granites across the entire craton, we deduce that: 1) Key geochemical ratios and indices, such as 10,000 Ga/Al, Y/Nb, and Zr/Nb, in A-type granites exhibit temporal variations, signifying a transition from A2-type to A1-type granite; 2) There is an increasingly apparent involvement of mantle-derived magmas in their genesis, coupled with a more pronounced role of fractional crystallization in the development of A1-type granites compared to their A2-type counterparts. We contend that these compositional and isotopic transitions reflect the tectonic evolution from post-orogenic extension to anorogenic rifting occurring around 1.7 Ga. The refined geochemical variations revealed in this study may offer a paradigm for post-orogenic evolutionary processes in general.

Mechanism of beryllium mineralization in a granite-pegmatite system: Constraints from ore geology and beryl mineralogy of the large Arskartor Be-Nb-Mo deposit, southern Chinese Altai

The Arskartor Be-Nb-Mo deposit is the second largest Be deposit in the Chinese Altai, NW China, which hosts over 11,000 tons of BeO resource. The muscovite-albite granite and rare-metal pegmatite in the ore district are spatially and temporally coexisted and both are beryllium mineralized. The muscovite-albite granitic stock can be divided into a barren zone and a Be-mineralized zone. The pegmatite shows an well-developed internal zone including the layered muscovite-quartz-albite zone, (lower) beryl-muscovite-quartz zone, quartz core, (hanging) beryl-muscovite-quartz zone, and muscovite-quartz-microcline zone. Beryl is the dominant Be-bearing mineral and mainly occurs in the Be-mineralized granite, the layered muscovite-quartz-albite and the beryl-muscovite-quartz zones of the pegmatite. Subhedral to euhedral beryl in the Be-mineralized granite is interstitial to or intergrown with rock-forming minerals. In contrast, beryl crystals in the pegmatite are coarser in grain size and more euhedral in shape, and mainly coexist with coarse “booked” muscovite and blocky quartz. Concentrations of Li, Cs and Na/Li ratios of beryl are 184–760 ppm, 218–1996 ppm, and 2.13–21.3, respectively. The progressive variations of incompatible elements compositions and Na/Li ratios are consistent with the fractional crystallization mechanism of the granite-pegmatite system. Paragenesis and internal structure of beryl suggest nonequilibrium crystallization of a relatively incompatible elements and fluxes-enriched late granitic melt, generated the coarse-grained Be-mineralized granite. With the progressive enrichment of incompatible and fluxing elements and decreasing temperature, liquidus overcooling was achieved and generated the aplite and immediate zoned pegmatite that hosts abundant beryl. Moreover, the differentiating pegmatitic melt with varying amounts of aqueous fluids at different melt fractions, likely resulted in heterogeneous distribution of beryllium and subsequent variable amounts of beryl crystallization in different internal zones. The exsolution of aqueous fluids from the residual pegmatitic melt resulted in Mo-mineralization and related hydrothermal alteration. Consequently, both protracted fractional crystallization and subsolidus processes contributed the formation of the Arskartor granite-pegmatite system with Be-polymetallic mineralization.

The relationship between iron redox states and H2O contents in back-arc basin basaltic glasses from the North Fiji Basin

Island-arc basalts (IAB) from convergent plate margins tend to have both higher iron oxidation states (higher Fe3+/Fe2+) and higher H2O contents than the mid-ocean ridge basalts (MORB) produced by seafloor spreading, which raises the question of whether these two characteristics are causally related. Back-arc basin basalts (BABB) may help with this question, in that they are products of seafloor spreading, like MORB, but sourced from supra-subduction mantle, like IAB. Here we examine the relationship between Fe3+/Fe2+ (determined by XANES spectroscopy) and H2O contents in BABB glasses from the North Fiji Basin (NFB). The glasses cover a range of compositions from 6.1 to 8.5 wt% MgO, and from 0.16 to 1.6 wt% H2O, and have also been analysed for trace elements and Sr-Nd-Pb-isotopes. Measured Fe3+/Fe2+ range from MORB-like to slightly higher values and are positively correlated with H2O and heavy-halogen contents (Cl, Br and I). The correlation is due to lower Fe2+ rather than higher Fe3+ compared to the MORB array. This suite of BABBs is not significantly enriched in trace elements other than H2O and the heavy halogens, with MORB-like Ba/Th and other incompatible-element ratios, suggesting that the H2O and halogens may have come from dehydration of subducted lithospheric serpentinites under subsolidus conditions. Na2O is unusually variable for a suite of samples from such a limited area, and is not correlated with H2O, precluding a relationship between H2O and degree of melting. The link between H2O and low Fe2+ may be explained by H2O-rich fluids entering the transcrustal magma plumbing system, where they increase the proportion of olivine and augite to plagioclase crystallizing during the crustal evolution of the magmas. In this situation, relatively small additions of H2O can have an enhanced effect on major-element chemistry if the crustal evolution proceeds by cycles of replenish-mix-tap-crystallize (RMTX) rather than by simple fractional crystallization without repeated replenishment and tapping. The absence of any increase in Fe3+ with H2O, together with the lack of any correlation between H2O and Fe3+/Fe2+ in MORB glasses generally, suggest that various mechanisms, including more extensive olivine fractionation, were responsible for elevating Fe3+/Fe2+ in H2O-rich basalts from convergent margin settings. Proxy methods based on concentrations of elements with redox-variable partition coefficients (V, Eu) are not sensitive enough to record the subtle variations in Fe3+/Fe2+ observable by XANES spectroscopy.

Petrogenesis of the Early Paleogene North Island Syenite Complex, Seychelles

The Early Paleogene (63.65 ± 0.52 Ma, 63.11 ± 0.45 Ma) North Island syenitic complex of the Seychelles microcontinent is composed principally of diorite (SiO2 ≈ 57 wt%), syenite (SiO2 = 61–65 wt%), and microsyenite (SiO2 = ∼70 wt%). The rocks are metaluminous, ferroan, and alkalic, and are compositionally similar to the A1-type granitoids. The trace element compositions of the syenitic rocks show minor spatial variability between the eastern (Congoment, Bernica) and western portions (Grand’Anse, Mt. Des Cèdres) of the island. The whole rock Sr-Nd (87Sr/86Sri = 0.704095–0.707533; εNd(t) = +1.2–+1.9) and zircon Hf ( εHf(t) = +2.1–+8.4) isotopes are indicative of a juvenile magma source. The low Th/NbPM (0.3–1.5) and high Nb/U (30.9–109) ratios do not indicate a crustal origin of the rocks nor do they suggest crustal contamination was significant. Hydrous fractional crystallization modeling shows that a mafic alkaline parental magma can yield residual liquid compositions similar to the diorites and syenites under reducing conditions ( ΔFMQ = −1) at a pressure of 0.3 GPa. However, feldspar accumulation likely occurred as some rocks have elevated Eu/Eu* (&gt;1.1) values. The emplacement of the North Island complex is contemporaneous with the eruption of the Deccan Traps and rifting of the Seychelles microcontinent from India. Rifting and magmatism was likely related to the passage of the Indian plate over the Réunion hotspot. The modeling results of the study demonstrate that crystallization pressure has an influence on whether basalt-derived A-type granitoids will evolve to metaluminous or peralkaline compositions.

Partitioning of tin between mafic minerals, Fe-Ti oxides and silicate melts: Implications for tin enrichment in magmatic processes

The partition coefficients of Sn (tin) between minerals and silicate melts (DSnmin/melt) are vital for understanding the Sn enrichment during magmatic processes related to tin-granites. However, experimentally determined DSnmin/melt values remain scarce due to the difficulty in avoiding severe Sn loss to noble metal capsules. In this study, we performed mineral/melt Sn partitioning experiments at 0.5–1.0 GPa, 850–1000 °C, and fO2 of FMQ + 8 to ∼ FMQ − 1. The fO2s were imposed by solid buffers of Ru–RuO2, Re–ReO2, Ni–NiO, Co–CoO and graphite using three improved capsule designs: 1) a single sample capsule (Pt) for the Ru–RuO2 buffered runs, 2) double capsules with Pt95Rh05 as outer capsule and Re as inner sample capsule for the graphite and Re–ReO2 buffered runs, and 3) triple capsules for the Co–CoO and Ni–NiO buffered runs, with Pt95Rh05 (or Au) as outer capsule, Re lined Pt as inner sample capsule. These new capsule designs avoided significant Sn loss and enabled us to obtain accurate DSnmin/melt at a controlled fO2. The experimental results show that DSnmin/melt values are 0.08–12.66 for amphibole, 0.01–5.55 for biotite, 0.09–10.39 for clinopyroxene, 0.004–0.97 for orthopyroxene, < 0.01 for olivine, 1.34–108.43 for Ti-magnetite, 0.04–4.17 for spinel and 0.10–0.64 for ilmenite. The large variation of DSn for each mineral was mainly ascribed to the effect of fO2, which results in an arresting decrease of DSn with decreasing fO2. Under the reducing conditions (fO2 < FMQ), Sn is highly incompatible (DSn < 0.1) in almost all the minerals. Modeling results indicate that partial melting at low fO2 conditions results in Sn enrichment in the derived magma, while subsequent high degree of fractional crystallization is also important for the Sn enrichment in the residual melt. The experimental and modeling results thus explain why major primary tin deposits are always related to reducing and highly fractionated granites.