Contributions to Mineralogy and Petrology最新文献

Volcanic mineral texture and compositional zoning offer crucial insights into magmatic processes and their timing preceding an eruption. Each mineral may capture different aspects of the pre-eruptive magmatic processes. Here we use a multimineral (plagioclase, orthopyroxene, and magnetite) approach to decipher the magma dynamics prior the 2010 magmatic eruption of Kizimen volcano (Kamchatka). The eruption comprised explosive episodes generating pyroclastic density currents followed by the extrusion of a thick lava flow. We combined crystal system analysis with diffusion chronometry on plagioclase and magnetite, together with the orthopyroxene data of Ostorero et al. (3:290, 2022). Plagioclase crystals record up to four different magmatic environments which include two distinct magma mixing events. The first one involved the injection of mafic magma into an initially dacitic reservoir. The magma intrusion led to significant environmental changes within the reservoir which became thermally and compositionally zoned, with remnant dacitic magma at the top and newly created andesitic magma at its base. Both plagioclase and orthopyroxene record the interaction between the dacitic and andesitic magmas during a second mixing event at their interface. This event can be linked to a seismic crisis approximately 1.5 years before the eruption, and is also recorded by Fe–Mg diffusion chronometry in orthopyroxene. Magnetite zoning recorded a final heating event of a few days, potentially marking magma ascent and storage in the lava dome. The compositional zoning plagioclase and magnetite crystals is consistent with the spatio-temporal interpretations made from orthopyroxene crystals zoning and timescales. Plagioclase serves as a reliable yet more complex archive compared to orthopyroxene. Correlating different mineral records enables a more precise reconstruction of magmatic history. Combining petrological and monitoring data provides a more robust understanding of pre-eruptive reactivation.

Chilled margin compositions are commonly used to estimate the parental magmas of mafic–ultramafic layered intrusions. Chilling along intrusion margins is associated with supercooling, which typically results in the development of a marginal reversal—a zone characterised by chemical trends that become more primitive from the margin towards the centre, accompanied by a reversed crystallisation sequence. However, marginal reversals may also form through alternative geological processes, complicating the interpretation of chilled margins as true proxies for parental magma compositions. In this study, we use Fe–Mg equilibria and thermobarometric calibrations between the chilled margin and adjacent cumulus phases of the Koillismaa Deep Intrusion to demonstrate that both the chilled margin and the associated marginal reversal formed through magma supercooling. Our age determination confirms that the intrusion belongs to the 2.44 Ga Tornio–Näränkävaara Belt, which is of considerable economic interest, with a continuous history of PGE–Cu–Ni, V–Ti–Fe, and Cr exploration and mining from the 20th century to the present. Our results indicate that the magma which formed the Koillismaa Deep Intrusion resembles the siliceous high-Mg basalt composition proposed for the 2.44 Ga diabase dykes of Fennoscandian Shield. Validating chilled margin compositions is crucial for the Tornio–Näränkävaara Belt and other 2.51–2.43 Ga Fennoscandian mafic–ultramafic layered intrusions due to their significant economic potential. However, the literature-sourced data used for comparison have not been adequately validated, and multiple sources of error may affect their reliability.

Mineral stratification has long been inferred to develop in basaltic magma bodies within the summit of Kīlauea Volcano, HI, primarily as a result of gravitational settling or redistribution of early crystallizing olivine, as indicated, particularly, in studies of Hawaiian lava lakes. Direct evidence from Kīlauea’s voluminous lava flows of such mineral stratification has been lacking or subject to challenge, however, because of magma mixing, post-eruptive reequilibration, and evidence that flows initially thought to derive from a single magma body had multiple sources. Tephra from Kīlauea’s Kulanaokuaiki-3 eruption (≥ 1.0 ka) offers an unusual manifestation of vertical stratification among phenocryst phases. The tephra deposits appear to constitute inverted products of a magma body comprising a lower zone enriched in olivine phenocrysts and an olivine-depleted upper zone enriched in plagioclase and clinopyroxene phenocrysts. Small proportions of microphenocrysts of all three phases occur throughout both zones. A relatively narrow compositional range among most olivine—Fo_80–82 in the lower zone and Fo_78–80 in the upper zone—suggests reequilibration within that magma body during cooling. Combined with a range in plagioclase compositions—generally, An_69–73 in the lower zone and An_63–68 in the upper—and other data, the analyses also suggest a slight change in conditions, such as a narrow thermal gradient, between the lower and upper zones of that magma body. A comparison with studies of Kīlauea’s lava lakes suggests broad similarities in stratification among olivine, plagioclase, and clinopyroxene phenocrysts. One feature commonly found in lava lakes—segregation veins—also is suggested by pumice and differentiated lithic blocks, whereas other features, such as pipelike olivine-rich bodies, have not been documented in the Kulanaokuaiki-3 deposits. The stratified body inferred from these deposits offers a model for zonation applicable to similar shallow, basaltic magma bodies.

In situ U-Pb geochronology has been performed via laser ablation inductively coupled mass spectrometry on relict zircon and apatite from the ~ 8 km-diameter Pilot Lake impact structure, Canada. Zircon results, filtered to mitigate the effects of post-impact Pb loss, yield an upper intercept date of 1900 ± 22 Ma (MSWD = 0.9). This corresponds to the age of the Slave granites of the Taltson Magmatic Zone. A lower intercept date of 420.4 ± 19.2 Ma (MSWD = 0.9) is interpreted to record the impact event. Apatite results yield a triangular isotopic array with an older regression intercepting concordia at 1830.7 ± 8 Ma (MSWD = 0.59) and a younger regression with an intercept date of 420 ± 13 Ma (MSWD = 0.14). The older date is coincident with the age of the regional Sparrow Dyke Swarm and/or Hudsonian metamorphism. The younger date is synchronous with the zircon lower intercept. With a slightly improved error, apatite provides the best-estimate age for the Pilot Lake impact event. While shock has caused important structural effects in zircon and apatite, it has primarily been the subsequent thermal overprinting and its duration that have controlled the U-Pb systematics. Laser analyses of zircon and apatite juxtaposed with hotter (melt-bearing) areas have been reset to the impact age, while cooler settings have preserved target rock ages.

Determining exhumation and cooling rates of regional metamorphic rocks is essential for deciphering orogenic dynamics and heat transport in the Earth's crust. Although radiometric dating is commonly used, its temporal resolution becomes coarser for older rocks, limiting its ability to resolve Precambrian metamorphic timescales. Diffusion chronometry, based on mineral zoning, offers age-independent temporal resolution but is affected by uncertainties in pressure–temperature conditions and diffusion coefficients, which have not been fully evaluated in Paleoproterozoic or older orogens. This study integrated Monte Carlo-based garnet Fe–Mg-Ca-Mn diffusion simulations with phase equilibria modeling to quantify exhumation and cooling rates of pelitic granulites from the Paleoproterozoic Jiao–Liao–Ji orogen, explicitly addressing uncertainty propagation. The granulites record peak pressures of 13–14 kbar at 850–870 °C, followed by heating during decompression to ultra-high-temperature conditions (~ 940 °C, ~ 6.5 kbar) within 2–9 Myr at ca. 1.86 Ga. Subsequent cooling to ~ 5 kbar and ~ 600 °C is nonlinear, with rapid cooling (up to 148 °C/Myr) above 800 °C, and slower cooling (~ 5 °C/Myr) below 700–600 °C. These diffusion-based timescales and rates, with uncertainties of 0.3–0.5 orders of magnitude (1σ), outperform current in situ radioisotope geochronology methods, providing refined constraints on Orosirian geodynamics. The heating during decompression and subsequent nonlinear cooling suggest potential parallels with modern mantle upwellings and extensional tectonics; slower cooling and exhumation rates obtained in this study (when compared to modern systems) potentially reflects a weaker Paleoproterozoic lithosphere. This research highlights the power of diffusion chronometry for understanding of early Earth history.

Recent investigations into the factors controlling the formation of Cu (± Mo) porphyry deposits—through the integration of bulk-rock geochemical and isotopic data with the composition of accessory minerals such as zircon and apatite—are yielding valuable new insights into the magmatic processes that govern ore fertility. This research focuses on an Eocene post-collisional porphyry system and its Late Cretaceous host rocks within the Central Tethyan belt in the Eastern Sakarya Zone (Türkiye) to understand magmatic evolution and to identify geochemical markers in bulk rocks, zircon, and apatite that can effectively distinguish ore-forming magmatism from barren (Late Cretaceous) magmatism in the same zone. Combined bulk-rock major/trace elements and Sr–Nd-Pb-Hf isotopic data, along with in-situ Hf- and Nd-isotope analyses of zircon and apatite, suggest that the Eocene dacite porphyries were derived from an enriched sub-continental lithospheric mantle (SCLM). The compositions of zircon and apatite support the reliability of established fertility indicators for distinguishing between fertile and barren porphyry systems. Our results demonstrate that mineralization-related porphyries contain zircons with higher Eu/Eu* and Ce/√(U × Ti) ratios and show trends of decreasing Dy_(n)/Yb_(n) and Eu/Eu* (with Yb), which point to deep crustal amphibole fractionation. Apatite from the mineralized dacite porphyries is characterized by higher Eu/Eu*, Sr/Y, and V/Y ratios, along with elevated εNd(t) values, compared to apatite from the Late Cretaceous magmatic rocks. These geochemical and isotopic signatures suggest that the mineralized dacite porphyries were derived from an oxidized and hydrous magma source generated within an enriched lithospheric mantle domain, reflecting a more fertile arc-related magmatic environment than the evolved and less fertile sources of the Late Cretaceous magmatism.

Partition coefficients (Ds) are an integral tool for understanding geochemical processes within the deep parts of the mantle. However, their availability is limited due to their challenging experimental determination. Leveraging the power of machine learning (ML) approaches, we developed a model to predict partition coefficients between clinopyroxene and liquid (ranging from anhydrous and hydrous melts to aqueous fluids) for 31 trace elements. The model was trained on experimental data covering pressures from 0.5 to 6 GPa, temperatures of 700 to 1635 °C, and compositions ranging from eclogite to peridotite. The predictive model achieved high accuracy, with an R² = 0.94 and RMSE = 3.77. The five most influential features were temperature, ionic charge, radii, and the clinopyroxene Al₂O₃ and SiO₂ wt%. Our model’s predictive capabilities enabled a detailed investigation of how pressure–temperature-composition conditions impact crystal lattice strain and electrostatic parameters. The model demonstrated that water content in the liquid phase substantially impacts trace element partitioning. As H₂O increases in the liquid phase, the optimum valence in the M2 site increases, while the D₀^Δe=0 in both M2 and M1 sites significantly decreases. To demonstrate our model’s utility, we applied it to calculate trace element patterns of fluids equilibrated with low-temperature metasomatic xenoliths from the Kaapvaal craton. The calculated fluids exhibited ribbed and planar patterns, remarkably similar to those of natural High-Density Fluids (HDFs) found within diamonds from the same geological region. This development advances our understanding of geochemical processes and establishes a powerful ML approach that could develop predictive modeling in complex geological systems.

Garnet is a common minor phase in S-type granites and pegmatites, but its petrogenesis remains poorly constrained. Garnet in these systems may have crystallized from the melt or it may represent inherited grains derived from the source or xenocrysts from the wall rocks. Although garnet has the potential to provide unique insights into the magmatic evolution and crystallization intervals of S-type granites and pegmatites, its geochemical and chronological record is underexplored. In this study, we investigate the Lu–Hf age and trace-element record of garnet in the Neoarchean Decelles Batholith (c. 2670–2620 Ma), southeastern Superior Craton, Canada. The batholith comprises one of the most voluminous granites in the region and was likely sourced from anatexis of the metasedimentary Pontiac Group at depth. Garnet Lu–Hf geochronology yielded ages between 2667.5 ± 3.9 and 2656.0 ± 7.1 Ma, overlapping with U–Pb monazite ages from the batholith and Lu–Hf ages from the host rocks. LA-ICP-MS trace-element mapping revealed well-preserved sharp oscillatory—locally sector—zoning in Li, P, Sc, Ti, Y, Zr, REE, Hf, Th, and U, contrasting with weak major element zoning. Garnet grains exhibit a core with concentric zoning and an overgrowth domain truncating core patterns, reflecting both trace-element uptake controlled by varying crystal growth rates, element supply and diffusion at the garnet-matrix interface in the presence of melt, and cation supply limitations due to co-crystallization of muscovite, monazite, apatite, and zircon. The data support a magmatic origin for garnet in the peraluminous granite and demonstrate that the oscillatory zoning can be diagnostic. Moreover, the new Lu–Hf garnet dates place new constraints on the timing of crystallization of the Decelles Batholith. This study provides new insights into the conditions of garnet crystallization in granitic systems and illustrates the versatility of garnet in constraining the onset and later evolution of peraluminous granitoid magmatism. Ultimately, our study underscores the necessity of case-by-case assessment of garnet origins in S-type granites, emphasizing trace-element mapping as a key tool for petrogenetic interpretation.

This study tests the efficacy of commonly used chemical fertility indicators in apatite and zircon for distinguishing Cu–Au porphyry intrusions of the Ordovician–Silurian Macquarie Arc from unmineralised I-type intrusions of the adjacent Silurian-Devonian Lachlan Orogen (south-eastern Australia). Chemical data were collected from apatite, zircon, and apatite inclusions in zircon, allowing the integration of petrological information from these two common accessory minerals. Melt Cl and F estimates, determined with available mineral-melt partitioning models for apatite, indicate that the precursor melts to fertile intrusions of the Macquarie Arc were generally not elevated in Cl relative to unmineralised intrusions, or to arc-related melts more generally. Melt oxidation sensitive trace elements in zircon (Ce) and apatite (S, Mn and Fe) suggest that porphyry Cu–Au fertile melts of the Macquarie Arc were not invariably more oxidised than unmineralised I-type granitic intrusions. Apatite Sr and Y concentrations and Eu/Eu* and Dy/Yb in zircon offer evidence of hornblende stability and delayed plagioclase crystallisation in most Cu–Au fertile melts of the Macquarie Arc, supporting a critical role for elevated water content in determining the metallogenic potential of arc-related magmas. Evidence of dynamic melt hydration and oxidation conditions are preserved in zircon and apatite populations of the fertile intrusions. We find that devolatilisation may affect ore fertility indicators in apatite and zircon to the extent that these signatures become indistinguishable from unmineralised intrusions of a similar composition. Zircon fertility indictors are found to be less effective at discriminating alkalic (shoshonitic) porphyries associated with Au mineralisation from infertile arc igneous suites, but these intrusions can instead be distinguished by high Sr/Y in apatite.