Contributions to Mineralogy and Petrology最新文献

The Ca-in-olivine geohygrometer, first calibrated in 2016 (Gavrilenko et al. J Petrol, 57(9):1811–1832, 2016a), has since been widely applied to diverse datasets, providing significant insights into magmatic H₂O contents. Building on extensive experience with this method, this study reviews the application of this petrological tool, summarizing its key features, strengths, and limitations. Using a large dataset of olivine-hosted melt inclusions (MIs) from Klyuchevskoy volcano, we highlight the method's advantages and challenges, propose strategies for optimizing its use, and suggest potential improvements for Ca-in-olivine hygrometry. Applying the Ca-in-olivine geohygrometer to extensive MI datasets for a given arc volcano can reveal the H₂O content variation during this magma evolution, showing magmatic H₂O accumulation at greater depth due to incompatible H₂O behavior, and then a degassing trend at shallow depth when H₂O saturation is reached. While effective for evolved compositions (Fo <  ~ 85), the method underestimates magmatic H₂O content in primitive compositions (Fo >  ~ 85). Based on the 1-atm and high-pressure experiments with Klyuchevskoy compositions, combined with secondary fluorescence modeling around olivine-hosted MIs, we suggest that refining current Ca partitioning models (olivine/melt) and routinely measuring CaO in host olivine for reported MIs can improve the method's accuracy and broaden its applicability in magmatic studies. These findings aim to enhance the accuracy and applicability of this technique in studying magmatic processes.

Understanding the extent by which layered intrusions have been modified by post-cumulus processes is important for unravelling primary magmatic histories. This study focusses on how upward migrating late-stage fluids or melts may have affected the bases of Bushveld magnetitite layers and their underlying anorthosites. Key observations include dramatic enrichments in the An-contents of plagioclase grains at the magnetitite-anorthosite contact, from An₅₉ to An₉₀, depletion of the lowermost few mm of the magnetitite layer in Cr, and an increase in the extent of ilmenite exsolution in the magnetitite, locally enriching the surrounding magnetite in Cr in some areas. Sr-isotopes from plagioclase are consistent with those recorded for the Upper Zone of the Bushveld Complex, suggesting that the fluids or melts were internally derived. Late-stage melts are unlikely to be responsible for the formation of Cr-rich domal structures at the bases of magnetitite layers because (a) cumulus magnetite underneath magnetitite layers are very poor in Cr, suggesting that late-stage melts were not Cr-rich, (b) where a large xenolith obstructs liquid migration from below, Cr contents within the magnetitite on top and adjacent to the xenolith are indistinguishable, and (c) a small scale protrusion of magnetitite into the underlying anorthosite that would have been submerged in late stage melt are depleted in Cr. While metasomatism at the base of magnetitite layers may have caused some minor redistribution and depletion of Cr, the macroscale Cr-distribution features are inferred as being of primary magmatic origin.

The Okinawa Trough, a continental-margin back-arc basin in the northwestern Pacific Ocean, is characterized by numerous hydrothermal fields and spatially consistent submarine volcanoes, indicating the presence of active, shallow magma chambers. The potential for volcanic eruptions, coupled with its proximity to populated areas, underscores the need for comprehensive studies of the underlying magmatic processes. In this study, we perform a detailed investigation of cathodoluminescence imaging, trace elements (Ti), and oxygen isotopes in quartz from two rhyolite samples collected from the middle and southwestern Okinawa Trough (MOT and SWOT). We observe varying proportions and CL patterns of rapid growth features in quartz from SWOT (40%) and MOT (4%), which imply different magmatic processes. Step zoning, involving Ti-poor and Ti-rich overgrowths, is prevalent in both regions and may reflect temperature variations rather than changes in TiO₂ activity or pressure. Oscillatory and step zoning represent the products of near-equilibrium crystallization, and their Ti contents can, therefore, be used to reconstruct the P-T conditions of the magma. Based on the estimated crystallization temperatures of 750 °C and 770 °C for SWOT and MOT quartz, respectively, the depths of the shallow silicic reservoirs for SWOT and MOT are inferred to be ~ 9 km. Jagged, bright cores (with high Ti content and variable δ¹⁸O values) in MOT quartz are interpreted as xenocrysts, providing mineralogical evidence for the assimilation of country rocks. The δ¹⁸O values, corrected for fractional crystallization and representing primary magmatic signatures, suggest that the SWOT magma has undergone greater contamination by upper crustal material (15–25%) than the MOT magma (< 18%). Moreover, our study reveals a slight negative correlation between δ¹⁸O values and grayscale values (or Ti content). This relationship can be readily explained by a near-wall crystallization mechanism, which also accounts for the common occurrence of Ti-poor overgrowths. Additionally, we attempted to constrain the crystal residence time using the diffusion of Ti in quartz, but the uncertainties of available calibrations largely hampered the interpretation. Nonetheless, if long-term near-wall crystallization is accepted, the mush model would imply that the magma chamber is primarily melt-dominated. Collectively, the distinctive textures and chemistry support the robustness of quartz as a reliable tracer for magmatic processes in shallow silicic reservoirs beneath the seafloor.

Naturally derived, fine-grained olivine ceramics were synthesized by an evacuated hot-pressing method that yielded samples with porosities of < 0.1%, a marked reduction compared to samples fabricated by conventional hot pressing with porosities of ≳1%. Evacuated hot pressing yields bright-green olivine samples that are transparent at the mm-scale, resembling the appearance of the single crystals from which they were synthesized, while conventional hot pressing produces milky-green aggregates that are opaque. This contrast in macro-scale transparency reflects the difference in micro-scale porosity. Annealing experiments on samples synthesized by the two different methods, some at 1 atm and others at 300 MPa confining pressure, reveal contrasting styles of grain and pore growth. During high-temperature annealing at both low and high pressures, evacuated hot-pressed samples underwent rapid, abnormal grain growth, while conventionally hot-pressed samples remained fine grained over long annealing times with very limited abnormal grain growth. During annealing at 1 atm, evacuated hot-pressed samples exhibited very little pore growth compared to conventionally hot-pressed samples that disaggregated due to pervasive pore growth. These experiments demonstrate the primary influence that porosity plays in grain growth in olivine aggregates. Further, the methods presented in this study provide a means to produce low-porosity olivine aggregates from naturally derived powders that can be used for high-temperature experiments at low pressures, as well as a method to make dense, coarse-grained olivine aggregates for laboratory studies.

Aso volcano in southwest Japan has produced four repeated caldera-forming eruptions over the last 270,000 years, each generating compositionally zoned ignimbrites that transition from silicic to more mafic magmas. To understand the magmatic processes behind these chemical and thermal zonations, we analyzed major and trace element compositions of melt inclusions and groundmass glasses. Our results reveal three distinct melt types: high-K silicic (HK-S), high-K mafic (HK-M), and medium-K (MK) melts. The HK-S and HK-M melts dominate the silicic and mafic units, respectively, while the MK melt is a minor component in the mafic units. Combining experimental petrology and mass balance modeling (mostly focusing on rare earth element compositions), we propose the following magmatic evolution: (1) The HK-M magma formed in a mid-lower crustal MASH zone through crystallization of basaltic magma and/or partial melting of basaltic rock; (2) this magma ascended and differentiated in a shallow upper crustal reservoir, generating the HK-S melt; (3) subsequent melt extraction from crystal mush, coupled with HK-M magma recharge, created a compositionally zoned shallow reservoir. The heat from the recharge also triggered partial melting and remobilization of the cumulate mush, producing the MK melt. These processes collectively explain the systematic zonation observed in Aso’s ignimbrites.

Garnet crystals in metapelites from the Goshen Formation, western Massachusetts, have experienced replacement by muscovite + biotite + quartz + plagioclase following decompression from ca. 1.0 to 0.35 GPa. The whole-rock reaction was garnet + muscovite = biotite + plagioclase + quartz; however, the phases replacing garnet (herein called the replacement mantles) always include muscovite as well as biotite, plagioclase, and quartz even though muscovite is a reactant. Numerical models are presented in which reactions only occur on a very local scale with adjacent phases and material in the grain boundaries and the progress of each local reaction is determined by the amount of available chemical affinity. Local reactions change the grain boundary composition, which sets up chemical potential gradients across the grid driving diffusive flux through the grain boundaries. This diffusion changes the grain boundary compositions elsewhere in the rock which changes the local chemical affinity and drives additional reactions in these localities. Thus, the local grain boundary composition drives muscovite dissolution in the rock matrix and precipitation in the replacement mantle surrounding garnet. Models are presented in which the amount of diffusion is varied from very little at one extreme to the other extreme with very long diffusion times such that the grain boundary composition remains homogeneous. The model results reveal that for very short diffusion times, the replacement mantle surrounding garnet is comprised largely of muscovite whereas with very long diffusion times the mantle is mostly biotite. Therefore, the ratio of muscovite to biotite in the replacement mantles may be interpreted to reflect the relative efficacy of grain boundary diffusion. This texture in which muscovite locally grows even though the whole rock reaction consumes muscovite is thus not the result of K-metasomatism but rather the consequence of grain boundary diffusion-limited metamorphic recrystallization.

Phase equilibrium experiments were used to determine conditions of melt evolution and phenocryst growth in high-Mg andesite magmas that were erupted at Whakaari (White Island) in New Zealand between 1976 and 2000. The high-Mg andesites are both mafic (7.21–10.3 wt% MgO) and silica-rich (55.3–58.6 wt% SiO₂) with phenocrysts of plagioclase, orthopyroxene, clinopyroxene, olivine, Cr-spinel and Fe–Ti oxides contained in a glassy to fine-grained matrix of mostly dacitic composition. Experiments were conducted on one of the most primitive samples available (the high-Mg andesite TRW34) at conditions ranged from 1 atm to 500 MPa at temperatures of 950 to 1200 °C with total water concentrations of 0 to 10 wt%. Except for the 500 MPa experiments, ƒO₂ was buffered at 1 or 2 log units above Ni–NiO. Consistent with earlier thermodynamic modelling, our results demonstrate that residual Whakaari melts (now represented by matrix glasses) evolved along a plagioclase + two-pyroxene cotectic (± magnetite ± ilmenite) under comparatively low-pressure, shallow conditions (< 200 MPa or < 6 km) and were relatively hot (> 950 °C) and dry (≤ 3 wt% melt-H₂O), with oxygen fugacities either at, or slightly above Ni–NiO + 1 log unit. Although the bulk-rock trends of Whakaari volcanic rocks are clearly calc-alkaline, those of the residual matrix glasses are only weakly so. A likely explanation for this contrast is that the primary magmas were relatively hydrous, but became dehydrated when intruded at shallow depths. The effectiveness of water in this role, combined with the demonstrable presence of primitive calc-alkaline magmas in the upper-crust, highlights the importance of magmatic water, in place of deep crustal fractionation, for shaping the calc-alkaline evolutionary trend.

The Fui Norte and Fui Sur small eruptive centres, together with the nearby Mocho-Choshuenco Volcanic Complex, are all located within what is potentially the most hazardous segment of the Southern Volcanic Zone of Chile. Developing comprehensive knowledge on the origin of evolution of these systems is not only important to better understanding of small eruptive centres, but also contributes to improved volcanic hazard prediction and mitigation. Using Sr–Nd isotopes, we determined that Fui Norte cluster has an independent plumbing system, while Fui Sur would be genetically related to the Mocho-Choshuenco stratovolcano. Through mixing models, we determined that the isotopic signatures of Fui Norte are closer to a MORB mantle isotopic composition, whereas the products from the Fui Sur cluster and Mocho-Choshuenco volcano exhibit a greater influence from slab components. This result shows that even in spatially constrained areas, magmas can record significant source differences. Using petrographic information and diffusion chronometry, we determined crustal timescales for the Fui Norte and Fui Sur SECs, from 1 month up to 4.5 years. This unexpectedly large time-scale range is interpreted as the lifespan of the crustal reservoir for these small eruptive centres. The significant differences in their source origin and the petrologic approaches reveal that both Fui Norte and Fui Sur have independent magmatic histories at the mid to upper crustal environment under similar timescales. Understanding that these systems operate independently from mantle to crust is relevant for future hazard assessment in the Southern Andes.

Carbonatites, originating from mantle-derived magmas, provide unique insight into both mantle composition and deep carbon cycling. As primary host rocks for REE deposits, their petrogenesis carries significant economic implications. However, key controversies persist regarding to (1) their ultimate mantle sources (primitive vs. metasomatized mantle), and (2) whether subducted carbonates participate in the mantle source and consequently contribute to REE enrichment. Here we present comprehensive study of bulk-rock and in-situ mineral (olivine, apatite, calcite, and dolomite) major, trace elements, and Ca-O-Sr-Nd isotopes for the Qieganbulake carbonatite, which formed during Neoproterozoic breakup of the Rodinia supercontinent and hosts considerable REE contents but no economic mineralization. The Qieganbulake carbonatite shows enriched Sr-Nd isotopes [(⁸⁷Sr/⁸⁶Sr)_i = 0.7059–0.7067; εNd(t) = -9.1 to -4.3], consistent with derivation from a metasomatized subcontinental lithospheric mantle (SCLM). Mantle-derived olivine xenocrysts in the carbonatite yield δ¹⁸O values (4.75 ± 0.92‰ to + 5.76 ± 0.26‰) overlapping with that of the metasomatized SCLM without significant involvement of ¹⁸O-rich recycled carbonate. The bulk-rock δ^44/42Ca values (0.33 ± 0.01‰ to 0.38 ± 0.02‰) are comparable to those of primary carbonatites and basalts, further excluding significant recycled carbonate contributions. Coupled Ca and olivine O isotopes thus implicate that slab-released fluids, rather than sedimentary carbonates, served as the predominant metasomatic agent in the mantle source. This finding also highlights that source fertilization by subducted carbonates is not a prerequisite for REE enrichment in carbonatites. Furthermore, we identify that the limited REE mineralization potential primarily results from extensive early apatite crystallization, which effectively sequestered REEs and inhibited the formation of REE minerals.

Diffusion chronometry has emerged as a valuable tool to track the timescales of magmatic processes and is now routinely applied on erupted volcanic products to infer crystal residence times and mixing-to-eruption timescales. Despite some attempts to apply such a technique to plutonic rocks, slow cooling in these systems complicates the interpretation of the retrieved timescales. Here we investigate the cooling rates and crystal–melt segregation timescales in the Western Adamello and Re di Castello units of the Adamello batholith (Italy). The Western Adamello is mainly composed of tonalite and volumetrically minor cumulative gabbro and leucotonalite, and segregated granite. The studied area from the Re di Castello exhibits a concentric structure mainly composed of tonalite, granodiorite, and aplitic and pegmatitic granite. Strongly zoned plagioclase crystals occur in both leucotonalite and granodiorite samples, while quartz crystals displaying normal Ti zoning are only observed in some granodiorites. After determining the crystallisation temperatures of plagioclase mantle and rim and quartz, as well as the initial conditions prior to diffusion, cooling rates were estimated based on plagioclase mantle-to-rim and quartz profiles. The retrieved cooling paths correspond, within uncertainty, to cooling rates calculated using thermal modelling and obtained by previous studies using ³⁹Ar/⁴⁰Ar dating. Crystal–melt segregation timescales were then calculated based on the diffusion modelling of plagioclase core-to-mantle profiles and the retrieved cooling rates. The calculated timescales (~ 10⁴–10⁵ yr) likely correspond to the plagioclase core-to-mantle residence time before crystallisation of the rim. Interestingly, these crystal residence times are similar to the zircon crystallisation timespan recorded in the Western Adamello and Re di Castello units, and to the crystal residence times obtained on historical volcanic eruptions (~ 10⁴–10⁶ yr). Overall, these findings highlight that plutonic systems can be used to reconstruct magmatic timescales and support the hypothesis of a close connection between plutonism and volcanism.