Experimental Petrology Research Articles

Experimental petrology constraints on kamafugitic magmas

Abstract. Kamafugites are rare volcanic igneous rocks, characterized by the presence of kalsilite and variable amounts of leucite, nepheline, melilite, clinopyroxene, olivine and phlogopite, which may not necessarily be present all together. Kamafugites are silica-poor (moderately ultrabasic to basic), CaO- and alkali-rich (mostly ultrapotassic) lithologies, generated from strongly metasomatized and heterogeneous mantle sources, with abundant phlogopite and little or no orthopyroxene. Melting of phlogopite- and carbonate-bearing veins is often invoked as being responsible for the ultrapotassic and ultracalcic signatures observed in many kamafugites. Nevertheless, many questions still persist about their mantle sources, such as the paragenesis of the metasomatic veins within the lithospheric mantle and the degree of interaction between the initial melts and the peridotite matrix. We experimentally investigated four natural kamafugite samples to determine the mantle assemblages that were in equilibrium with these melts at the onset of partial melting and their genesis. The kamafugites were collected from the three known areas where they occur: Uganda, Italy and Brazil. Near-liquidus experiments were carried out at 1 to 2 GPa and temperatures from 1250 to 1380 °C. These experiments provide information on the mineralogy of the potential mantle sources in each of the volcanic provinces, also allowing a comparison among them. The experiments confirm the common presence of clinopyroxene and phlogopite as the main near-liquidus phases, with olivine joining the near-liquidus phase assemblage in one Italian sample (San Venanzo) and in the Brazilian kamafugite. Other minor phases (apatite and Fe–Ti oxides) also crystallized in near-liquidus conditions, highlighting their importance for at least the Ugandan and Brazilian kamafugites. Our results demonstrate that various amounts of clinopyroxene (∼40 % in Italy and 50 %–60 % in Uganda and Brazil), phlogopite (∼20 %–30 % in Brazil, ∼40 % in Uganda and ∼60 % in Italy) and accessory phases (up to 4 % titanite in Uganda, up to 3 % apatite in Uganda and up to 5 % oxides in Uganda and Brazil) are required for the formation of kamafugite melts. The contribution of olivine differs among the four samples, being negligible for the Ugandan kamafugites and in one of the Italian kamafugites but up to 5 % in the second Italian kamafugite and 10 % in Brazil.

Symplectite formation in ultramafic achondrites by impact percolation of a sulfide melt

The ungrouped dunitic achondrite Northwest Africa (NWA) 12217 contains symplectic spinel-pyroxene veins that are mineralogically identical to symplectites in other ultramafic planetary materials. The morphology and amount of chromite present in these features relative to the Cr in their olivine hosts suggest an exogenous origin. Petrological experiments show that a Cr laden sulfide liquid reacts with olivine to produce pyroxene by scavenging Mg and Fe from olivine to crystallize chromite. The liquid infiltrates cracks and grain boundaries within the olivine and produces a vein-like symplectic chromite-pyroxene mineralogy similar to that observed in NWA 12217. This process is likely responsible for forming the symplectites in the related ultramafic achondrites NWA 12319, 12562, and 13954, along with many other achondrites. The nucleosynthetic Cr isotopic composition of chromites appears to be in disequilibrium with that of silicates in NWA 12217, suggesting that the liquids responsible for the symplectite forming reaction are at least partially sourced from a different parent body and result from an impact.

Petrographic and Geochemical Evidence for a Complex Magmatic Plumbing System beneath Bagana Volcano, Papua New Guinea

Abstract Bagana is a persistently active stratovolcano located on Bougainville Island, Papua New Guinea. Characteristic activity consists of prolonged lava effusion over months to years, with occasional shifts to explosive vulcanian or sub Plinian eruptions that threaten surrounding communities. Satellite observations have shown that Bagana is a major SO2 emitter, particularly during eruptive intervals. Despite persistent and potentially hazardous activity, no previous geophysical, petrological, or geochemical studies have constrained the magma storage conditions and reservoir processes at Bagana. To address this knowledge gap, we present new bulk rock major, trace element, and radiogenic isotope data, plus mineral phase major element compositions, for Bagana lavas erupted in 2005 and 2012 and ash erupted in 2016. We use our new data to understand the magmatic processes controlling the typical effusive activity and provide the first estimates of magma storage conditions beneath Bagana. The basaltic andesite bulk rock compositions (56–58 wt% SiO2) of our Bagana lavas reflect accumulation of a plagioclase + clinopyroxene + amphibole + magnetite + orthopyroxene crystal cargo by andesitic-dacitic (57–66 wt% SiO2) carrier melts. Constraints from clinopyroxene and amphibole thermobarometry, amphibole hygrometry, and experimental petrology suggest that the high-An plagioclase + clinopyroxene + amphibole + magnetite assemblage crystallizes from basaltic-basaltic andesite parental magmas with >4 wt% H2O, over a temperature interval of ~1100–900°C, at pressures of ~130–570 MPa, corresponding to ~5–21 km depth. Continued crystallization in the magma storage region at ~5–21 km depth produces andesitic to dacitic residual melts, which segregate and ascend towards the surface. These ascending melts entrain a diverse crystal cargo through interaction with melt-rich and mushy magma bodies. Degassing of carrier melts during ascent results in crystallization of low-An plagioclase and the formation of amphibole breakdown rims. The radiogenic isotope and trace element compositions of Bagana lavas suggest that parental magmas feeding the system derive from an enriched mantle source modified by both slab fluids and subducted sediments. Our findings suggest that the prolonged lava effusion and persistently high gas emissions that characterise Bagana’s activity in recent decades are sustained by a steady state regime of near-continuous ascent and degassing of magmas from the crustal plumbing system. Our characterisation of the Bagana magmatic plumbing system during effusive activity provides a valuable framework for interpreting ongoing monitoring data, and for identifying any differences in magmatic processes during any future shift to explosive activity.

Plagioclase‐Saturated Melt Hygrothermobarometry and Plagioclase‐Melt Equilibria Using Machine Learning

AbstractCompositions of plagioclase‐melt pairs are commonly used to constrain temperatures (T), dissolved water contents (H2O) and pressures (P) of pre‐eruptive magma storage and transport. However, previous plagioclase‐based thermometers, hygrometers, and barometers can have significant errors, leading to imprecise reconstructions of conditions during plagioclase growth. Here, we explore whether we can refine existing plagioclase‐based hygrothermobarometers with either plagioclase‐melt or melt‐only chemistry (±T/H2O), calibrated using random forest machine learning on experimental petrology data (n = 1,152). We find that both the plagioclase‐melt and melt‐only models return similar cross‐validation root‐mean‐square errors (RMSEs), as the melt holds most of the P‐T‐H2O information rather than the plagioclase. T/H2O‐dependent melt models have test set RMSEs of 25°C, 0.70 wt.% and 76 MPa for temperature, H2O content and pressure, respectively, while T/H2O‐independent models have RMSEs of 38°C, 0.97 wt.% and 91 MPa. The melt thermometer and hygrometer are applicable to a wide range of plagioclase‐bearing melts at temperatures between 664 and 1355°C, and with H2O concentrations up to 11.2 wt.%, while the melt barometer is suitable for pressures of ≤500 MPa. An updated plagioclase‐melt equilibrium model has also been calibrated, allowing the equilibrium anorthite content to be predicted with an error of 5.8 mol%. The new P‐T‐H2O‐An models were applied to matrix glasses and melt inclusions from the 1980 Mount St Helens (USA) and 2014–2015 Holuhraun (Iceland) eruptions, corroborating previous independent estimates and observations. Models are available at https://github.com/kyra‐cutler/Plag‐saturated‐melt‐P‐T‐H2O‐An, enabling assessment of plagioclase‐melt equilibrium and characterization of last‐equilibrated P‐T‐H2O conditions of plagioclase‐saturated magmas.

Partial melting of multiple mantle domains underneath the Paleo-Tethyan cold subduction zone triggered by slab rollback

It is widely believed that the melting of mantle wedge in a subduction zone is triggered by the influx of fluids. However, experimental petrology studies have yielded conflicting results regarding temperatures for the wet solidus of mantle metasomatite, either below or above that of mantle wedge. In the latter case, the influx of fluids cannot trigger mantle melting, particularly in a cold subduction zone. Late Paleozoic magmatic rocks in the Western Yunnan Tethyan belt have been interpreted as being products of the first-stage subduction-related magmatism in the cold subduction zone and are thought to carry crucial information about mantle–wedge melting. Here, we report zircon ages and whole-rock geochemical data for these magmatic rocks to identify both the origin of the magmatism and the mechanism of mantle melting. Rock samples collected from the Nanlianshan complex and the Daxinshan Formation yielded zircon ages ranging from 303 Ma to 297 Ma. The samples can be classified into two groups based on geochemical features. Group I magmatic rocks have higher Ba/Th and lower Th/Nb ratios and depletion in NdHf isotopes [εNd(t) 2.9–5.0; εHf(t) 5.7–14.6], whereas Group II rocks show relatively lower Ba/Th and higher Th/Nb ratios and relative enrichment in NdHf isotopes [εNd(t) 0.7–4.0; εHf(t) 4.1–10.7]. The two groups of rocks may have originated from different mantle domains that were metasomatized by slab-derived aqueous fluids and by sediment-derived melts, respectively. We hypothesize that slab rollback during closure of the Paleo-Tethyan Ocean prompted mixing of different mantle domains; subsequently, the multiple mantle was heated by the laterally flowing asthenosphere, and partial melting occurred.

Experimental study of the interaction between garnets of eclogitic and lherzolitic parageneses and H2O-CO2 fluid under the P-T parameters of the lithospheric mantle

Experimental modeling of the interaction between garnets of mantle parageneses with H2O–CO2 fluid was performed in order to determine the characteristic features and trends in garnet compositions due to metasomatic alterations, and to study the patterns of formation of carbon and carbon-bearing phases in these processes. Experiments were carried out in the lherzolitic garnet–CO2–H2O–C and eclogitic garnet–CO2–H2O–C systems at 6.3 GPa in the temperature range of 950–1550 °C using double graphite+platinum ampoule on a multi-anvil high-pressure apparatus of a split-sphere type (BARS). The interaction of mantle garnets with H2O–CO2 fluid was found to cause garnet recrystallization and formation of new phases, namely magnesian carbonate, coesite, kyanite, corundum–eskolaite solid solution and silicate–carbonate melt, as well as metastable graphite (950–1550 °C) and diamond growth on seeds (1250–1550 °C). It was established that the garnet-fluid interaction was accompanied by the bivalent cations' redistribution between recrystallized garnet, carbonate and carbonate–silicate melt. In these processes calcium was preferentially partitioned in the melt, while magnesium was partitioned in garnet and carbonate. Recrystallization of garnets of lherzolitic and eclogitic parageneses under effect of H2O–CO2 fluid resulted not only in compositional changes, but in the formation of carbonate, kyanite, coesite, graphite, corundum–eskolaite solid solution and carbonate-silicate melt inclusions in these garnets. The revealed patterns of variations in garnet compositions, as well as the typical inclusions in them, can be regarded as indicators of metasomatic alteration of garnets of mantle parageneses involving H2O–CO2 fluid. The obtained results allow one to infer that H2O–CO2 fluids play a crucial role in redistribution of divalent cations under the P-T parameters of the lithospheric mantle and control over the composition of carbonate–silicate melts coexisting with the eclogitic and lherzolitic assemblages. Another important result of this study is the experimental demonstration that graphite capsules on their own fail to ensure reliable hermeticity with respect to the fluid and melt phases in the high-pressure, high-temperature experiments. It was substantiated that the procedure involving a hermetically sealed platinum ampoule with inner graphite capsule prevents uncontrollable loss of matter in long-term petrological experiments and is optimal for modeling systems containing melts and fluids.

Geophysical and Geochemical Constraints on Magma Storage Depths Along the Cascade Arc: Knowns and Unknowns

AbstractThe iconic volcanoes of the Cascade arc stretch from Lassen Volcanic Center in northern California, through Oregon and Washington, to the Garibaldi Volcanic Belt in British Columbia. Recent studies have reviewed differences in the distribution and eruptive volumes of vents, as well as variations in geochemical compositions and heat flux along strike (amongst other characteristics). We investigate whether these along‐arc trends manifest as variations in magma storage conditions. We compile available constraints on magma storage depths from InSAR, geodetics, seismic inversions, and magnetotellurics for each major edifice and compare these to melt inclusion saturation pressures, pressures calculated using mineral‐only barometers, and constraints from experimental petrology. The availability of magma storage depth estimates varies greatly along the arc, with abundant geochemical and geophysical data available for some systems (e.g., Lassen Volcanic Center, Mount St. Helens) and very limited data available for other volcanoes, including many which are classified as “very high threat” by the USGS (e.g., Glacier Peak, Mount Baker, Mount Hood, Three Sisters). Acknowledging the limitations of data availability and the large uncertainties associated with certain methods, available data are indicative of magma storage within the upper 15 km of the crust (∼2 ± 2 kbar) beneath the main edifices. These findings are consistent with previous work recognizing barometric estimates cluster within the upper crust in many arcs worldwide. There are no clear offsets in magma storage between arc segments that are in extension, transtension or compression, although substantially more petrological work is needed for fine scale evaluation of storage pressures.

Experimental Study of Sulfur Solubility in Ca–Mg Carbonate Melt under P–T Parameters of Lithospheric Mantle

Abstract —Modeling the compositions, properties, and conditions of generation of natural agents of mantle metasomatism is one of the most topical subjects in experimental petrology. Particular attention is paid to the study of C- and S-bearing metasomatic agents and their role in the global carbon and sulfur cycles and in the processes of natural diamond formation. Experimental studies aimed at the estimation of sulfur solubility in carbonate melts under lithospheric mantle conditions were carried out on a multianvil high-pressure apparatus of the “split-sphere” type (BARS) in the carbonate–sulfur ((Mg,Ca)CO3–S) and carbonate–pyrite ((Mg,Ca)CO3–FeS2) systems at 6.3 GPa and 1050–1550 °C for 20–60 h. It has been experimentally established that the main processes occurring in the carbonate–sulfur system are the recrystallization of carbonate in a sulfur melt (1050–1350 °C) and the generation of a high-calcium carbonate melt with dissolved sulfur (5.0–6.5 wt.%) (1450–1550 °C) as well as graphite recrystallization and the initial stage of diamond growth (1550 °C) in this melt. The work demonstrates that the carbonate–pyrite interaction is accompanied by the recrystallization of carbonates and pyrite (1050–1250 °C) and the generation of two immiscible melts (sulfide one with dissolved oxygen and carbonate one with dissolved sulfur (1.7–2.5 wt.%) (1350–1550 °C)) along with the formation of graphite and the growth of diamond on seed crystals (1550 °C). It has been found that the solubility of sulfur in carbonate melts increases with temperature, which goes together with a decrease in CaO (±FeO) concentrations and an increase in MgO concentrations. The present study has shown for the first time that melts of alkaline-earth carbonates are capable of dissolving up to 6.5 wt.% sulfur and they are probable sulfur concentrators under the conditions of the lithospheric mantle.

Relationship between the Texture and Composition of Titanomagnetite in Hannuoba Alkaline Basalt: A New Geospeedometer

The nucleation and growth of crystals in igneous rocks is usually thought to occur under thermodynamic equilibrium conditions. However, recent studies on igneous textures and mineral compositions have shown that these processes probably occur under thermodynamic disequilibrium conditions. Titanomagnetite with variable crystal sizes can be observed in Hannuoba alkaline basalt, indicating disequilibrium crystallization processes (different cooling rates). The ratio of the maximum particle size to the area abundance of titanomagnetite, as determined by an analysis of previous studies on the texture of minerals, was negatively correlated with the apparent cooling rate. We analyzed the chemical composition and crystal size distribution of titanomagnetite in ten Hannuoba alkaline basalt samples to determine the connection between the apparent cooling rate and titanomagnetite composition. In Hannuoba samples, the cooling rate was found to affect cationic substitution in the titanomagnetite solid solution, and an increase in cooling rate led to a decrease in Ti4+ and an increase in Fe3+. The partition coefficient of Ti between titanomagnetite and the melt (DTi) is negatively correlated with the apparent cooling rate. These findings are consistent with those in experimental petrology and help us propose a better, more general geospeedometer. The cooling rate also impacted Mg2+ and Al3+, but they were more impacted by the melt composition and crystallinity of the coexisting melt. Therefore, a new geospeedometer was calibrated by considering the titanomagnetite composition, melt composition and the content of the clinopyroxene.The cooling rates of the Hannuoba basalt samples measured using the new geospeedometer calibrated in this study range from 0.7 to 7.0 (±0.5) °C/min. It cannot accurately predict the cooling rate from titanomagnetite in intermediate rock, felsic rock or Fe-rich basaltic melts. The new titanomagnetite geospeedometer can better measure the cooling rate of alkaline basalt and may help identify the effects of kinetically controlled crystallization on isotope fractionation, evaluate mineral thermobarometers and better recognize thermal remanence magnetization and ancient magnetic fields.

The use of boron nitride to impose reduced redox conditions in experimental petrology

Abstract Boron nitride (BN) is a commonly used pressure-transmitting material in experimental petrology. It is often considered to be as inert as MgO or Al2O3, and its redox potential is seldomly discussed. It is generally implied that, when used as a capsule sleeve, BN may impose relatively reduced conditions, similar to the effect of the fayalite-magnetite-quartz (FMQ) buffer. However, sediment melting experiments performed at 1050 °C and 3 GPa with BN as the capsule sleeve, produced a hydrous rhyolitic melt with dissolved H2S and CH4 (Li et al. 2021). The resulting fO2 estimate is significantly more reduced than that for the magnetite-wüstite (MW)-buffered experiment where H2S and CH4 were undetected (Li et al. 2021), possibly to the extent of the quartz-iron-fayalite (QIF) buffered conditions produced when BN is used as a capsule or crucible (Wendlandt et al. 1982). To establish an explanation for such a discrepancy, we have conducted further investigation to better constrain the fO2 imposed by BN, when used as a capsule sleeve. Here we report results on analyses of Fe content in Au capsules, a comparative experiment using a QIF buffer and an experiment with an Fe-(Mg,Fe) O sensor for direct analysis of fO2. The calibration of the equilibrium between FeO in melt and Fe in the Au capsule, from Ratajeski and Sisson (1999) appears to be inadequate in constraining fO2 for our experiments. However, we were able to obtain Fe diffusion coefficients in Au from the Fe diffusion profiles observed in the capsule of the Fe-(Mg,Fe)O sensor experiment, and both the inner and outer capsules of the MW-buffered experiment, with resulting values of 1 × 10–13 m2/s, 3 × 10–14 m2/s, and 5 × 10–14 m2/s, respectively. The QIF-buffered and Fe-(Mg,Fe)O sensor experiments provide several lines of evidence supporting the observation that BN imposes QIF-like redox conditions. First, the Fe-(Mg,Fe)O sensor returned an fO2 value of QIF. Second, the “apparent” partition coefficients between FeO content in melt and Fe in the Au capsules are similar between the BN experiment and the QIF-buffered experiment. Third, we observe CH4 and H2O peaks with similar intensities in the Raman spectra of melts from these two experiments, suggesting similar H2 and thus O2 fugacity. As our experiments were performed on a cubic press with the experimental assembly encased in a pyrophyllite cube, we interpret that the significantly reduced conditions imposed by BN are likely due to high H2O activity maintained by dehydration of pyrophyllite, which can be explained using the reaction 2BN + 3H2O = B2O3 + N2 + 3H2. Lower H2O activity will reduce or inhibit the oxidation of BN and its fO2 buffering ability. If heat-treated, BN acts as a highly efficient H2 barrier, as shown by Truckenbrodt et al. (1997). Through our efforts to determine the fO2 imposed by using BN as a capsule sleeve in our experimental assembly, we are able to demonstrate the reducing ability of BN as an assembly component and, furthermore, shed light on the process by which BN imposes such reduced fO2. We hereby present what we have learned during the course of this investigation in the hope that the effect of BN on fO2 control is both recognized and further exploited in future experimental studies.

Magma–Shale Interaction in Large Igneous Provinces: Implications for Climate Warming and Sulfide Genesis

Abstract Large igneous provinces (LIPs) whose magma plumbing systems intersect sedimentary basins are linked to upheavals of Earth’s carbon and sulfur cycles and thus climate and life history. However, the underlying mechanistic links between these phenomena are elusive. We address this knowledge gap through short time-scale petrological experiments (1200°C and 150 MPa) that explore interaction between basaltic melt and carbonaceous shale (mudstone) using starting materials from the Canadian High Arctic LIP and the Sverdrup Basin in which it intrudes. Here we show that entrainment of shale xenoliths in basaltic melt causes shale to shatter due to incipient thermal stress and devolatilization, which accelerates assimilation by increasing reactive surface area. Shale assimilation therefore facilitates transfer of sediment-derived volatile elements to LIP magma plumbing systems, whereupon carbon dominates the vapor phase while sulfur is partitioned into sulfide melt droplets. This study reveals that although carbon and sulfur are efficiently mobilized as a consequence of shale assimilation, sulfides can sequester sulfur—an important climate cooling agent—thus enhancing net emissions of climate warming greenhouse gases by shale-intersecting LIPs.

Reflectance of silicate glasses in the mid-infrared region (MIR): Implications for planetary research

Volcanic phenomaena shaped the surface of all terrestrial planets in the solar system, and silicate glasses represent a major component in pyroclastic deposits and lavas. Spectral features of silicate glasses therefore influence spectral characteristics of large portions of planetary surfaces.In this study, experimental petrology techniques have been used to produce 19 silicate glass samples having natural chemical composition corresponding to four of the most common magmatic series on planet Earth. Reflectance of such products was investigated in the mid-infrared region (MIR) to observe the evolution of their spectral characteristics with changing degree of evolution (expressed as silica content) and alkaline content. We have observed how chemical features have a clear influence in shifting the spectral features (to lower wavelengths with increasing silica, such as for previously studied volcanic rocks) and on the spectral shape, which is substantially different between mafic and highly silicic products. This allowed us to propose a model to retrieve chemical information (SiO2 and SiO2 + Al2O3 + TiO2 content) from the wavelength at which spectral features (CF and RBpeak) occur. Moreover, by comparing our results with previous MIR studies we have observed that our model can be applied, to a certain extent, to interpret chemical fingerpint volcanic rocks in general. Here, it is also shown how granulometry influences spectral shape, but does not affect spectral shift.This study will be useful to interpret planetary information and assess how amorphous silicate phases influence spectral characteristics of volcanic areas on planetary surfaces.

Compositional variability of San Carlos olivine

Forsterite (Fo)-rich olivine compositions from San Carlos (Arizona, SW USA) are commonly used as starting material in experimental petrology. In comparison to the San Carlos reference material USNM 111312/444, it has been shown that the major element variability of non-USNM San Carlos olivine is significant. We complement the characterization of the compositional variability of the non-USNM San Carlos olivine with new data, including minor and trace element analyses. High precision analyses reveal that selected minor elements (e.g., ~6% NiO, ~10% MnO, ~16% CaO, relative) and trace elements (e.g., ~75% Cr, ~120% Cu, ~160% P and Ti, relative) present significant concentration variations between grains. At the scale of the individual grain, however, San Carlos Fo-rich olivines appear homogeneous with no systematic core-rim variations. We also discuss the origin of olivine pyroxenites associated with the peridotite xenoliths and argue that they are derived by melt-rock reaction resulting in olivine dissolution and pyroxene precipitation from the peridotite host. Further segregation and in situ crystallization of the hybrid residual melt can produce Fe-rich olivine-poor pyroxenites. Finally, we discuss the origin of the P variability in San Carlos mantle olivine and suggest that P enrichment by metasomatism implies a highly reactive process with fast dissolution-reprecipitation of solid phases.

Sediment and ocean crust both melt at subduction zones

Hydrous arc magmas are produced when water-bearing materials from subducted oceanic plates are transported to the mantle beneath volcanic arcs, though the mechanism of mass transport remains debated. The geochemical characteristics of the slab component have important implications for the thermal structures of down-going plates and the fluxes of elements into the deep mantle. If slab temperatures are low, then elemental fluxes from the slab will be carried in a dilute fluid. If temperatures are high, the slab may melt instead. While a long-standing paradigm for arc volcanism has been that sediments melt and ocean crust dehydrates, a growing body of evidence from arc geochemistry and experimental petrology suggests both sediment and ocean crust melt. The low solubility of many elements in aqueous fluids prevents them from making a substantial contribution to arc mass-balance. Constraints from Sr concentrations and 87Sr/86Sr ratios require a large flux of Sr from the ocean crust, which is only possible if the crust melts. H2O/Sr ratios of arc volcanics are also inconsistent with slab fluids. These conclusions are supported by thermo-mechanical models indicating that slab temperatures exceed the hydrous solidus for both ocean crust and sediments. Examination of experimental data shows a likely strong effect of oxygen fugacity on residual phases during slab melting. Arc data are best explained if the ocean crust melts beneath all arcs under oxidizing conditions somewhere between FMQ and NNO+2. Experimental constraints on sediments also require melting and that sediment melt compositions depend on bulk composition as well as temperature. If these experiments serve as analogs to sediment melting beneath arcs, then sediment bulk compositions are a necessary input for any rare earth element-based slab thermometer. We present compositions for ocean crust partial melts and partition coefficients for sediment melting based on existing experiments, physical models, and arc data, that can be used in geochemical models of arc volcanism.

Paradigm shift for controls on basalt magmatism: Discussion with Lustrino et al on the paper I recently published in Earth-Science Reviews

I recently published “Lithosphere thickness controls the extent of mantle melting, depth of melt extraction and basalt compositions in all tectonic settings on Earth – A review and new perspectives” in this journal to demonstratively summarize a major component of my 30-year dedicated research on the basalt problem with the emphasis that the paradigm “mantle potential temperature controls the extent and pressure of mantle melting and basalt compositions” that is inconsistent with observations and experimental petrology must be abandoned. As the change from “temperature control” to “lithosphere thickness control” is fundamental and unfamiliar to many, I encourage members of the community for debate. The community interest in the theme of the paper is reflected by more than 1000 reads and 50 recommendations in RG within 10 days of its publication. In addition to a few email exchanges, the commentary by Lustrino et al. (2022) is the first written discussion with interesting comments of both breadth and depth. Overall, their commentary is more highly affirmative rather than criticism. Most of the comments are not about Niu (2021) but more general and may be shared by the scientific community. Therefore, my response is intended to be thorough, in particular on issues and concepts that I consider the community needs to be correctly informed of. My reply follows four basic principles: [1] I maintain “Objectiveness and open-mindedness (vs. ‘confirmation bias’) are requisite twins for insights and discoveries.”; [2] I express my views based on observations, experimental petrology, well-understood concepts, logical reasoning and objective analysis, rather than personal opinions to “believe” or “disbelieve”; [3] I emphasize that some misattributions may be innocent, but should be avoided because they serve no favor to our science and scientific discussion; and [4] I try to use plain language to ensure my writing readily understood by the reader. For clarity, my reply follows the same numbered questions as in the commentary and I do not discuss issues on which the commenters agree with me. Figures referenced in quotations are those in Niu (2021). For consistency, mantle potential temperature is denoted with TMP (vs. TP)

Research advances in experimental petrology and geochemistry of rare earth elements in magmatic and hydrothermal systems

Research advances in experimental petrology and geochemistry of rare earth elements in magmatic and hydrothermal systems

Magma evolution and mineralization of Longmenshan lithium-beryllium pegmatite in Dahongliutan area, West Kunlun

西昆仑大红柳滩地区相继发现了众多伟晶岩型锂铍矿床，已成为我国新的锂资源基地。目前关于这些锂铍花岗伟晶岩的成因多强调其源于地壳深熔形成的二云母二长花岗岩的结晶分异，但研究区出露的同时代的黑云母花岗岩与成矿的关系没有被讨论和关注。为了探讨黑云母花岗岩与成矿的关系，作者对龙门山矿区黑云母花岗岩、二云母二长花岗岩、花岗伟晶岩以及与成矿相关的细晶花岗岩开展了详细的地球化学及年代学研究。结果显示：1）黑云母花岗岩与二云母二长花岗岩具相似的地球化学特征，富集Rb、La和Nd，亏损Ba、Nb、Sr、P和Ti元素，均表现出S型花岗岩的特征；2）从黑云母花岗岩→二云母二长花岗岩→细晶花岗岩，表现出连续分异演化的特征；3）黑云母花岗岩的锆石LA-ICP-MS U-Pb年龄为216.8±0.85Ma，二云母二长花岗岩的锆石SIMS U-Pb年龄为216.0±1.5Ma，细晶花岗岩的锆石LA-ICP-MS U-Pb年龄为209.5±1.2Ma，花岗伟晶岩的锡石LA-MC-ICP-MS U-Pb年龄为211.3±5.0Ma，这意味着从黑云母花岗岩到二云母二长花岗岩与细晶花岗岩的形成时间是连续的并且是接近的。基于此，作者认为大红柳滩地区的二云母二长花岗岩与锂铍伟晶岩源于黑云母花岗岩的结晶分异。实验岩石学显示，变杂砂岩或黑云母片麻岩的黑云母脱水熔融可形成黑云母花岗岩，据此推测大红柳滩地区的大规模黑云母花岗岩源于地壳深部麻粒岩相变质过程黑云母和少量角闪石的脱水熔融。;Several lithium-beryllium deposits of pegmatite type have been found in Dahongliutan area, West Kunlun, which is a new lithium resource base in China. The origin of these deposits was emphasized as crystallization differentiation of the two-mica monzonitic granite formed by anatexis of the crust, but the relationship between the biotite granite in the study area and mineralization has never been discussed and concerned. In order to explore this problem, we conducted geochemistry and chronology studies of biotite granite, two-mica monzonitic granite, granitic pegmatite, and aplitic granite related to mineralization in Longmenshan. The results show:1) The biotite granite and two-mica monzonitic granite have similar geochemical features of S-type granite and are enriched in Rb, La and Nd, depleted in Ba, Nb, Sr, P and Ti; 2) From biotite granite, two-mica monzonitic granite to aplitic granite, the process exhibits a continuous differential evolution of the magma; 3) The zircon LA-ICP-MS U-Pb age of biotite granite is 216.8±0.85Ma, the zircon SIMS U-Pb age of two-mica monzonitic granite is 216.0±1.5Ma, the zircon LA-ICP-MS U-Pb age of aplitic granite is 209.5±1.2Ma, and the cassiterite LA-MC-ICP-MS U-Pb age of granitic pegmatite is 211.3±5.0Ma. This means that the formation time of granite from biotite granite, two-mica monzonitic granite to aplitic granite is continuous and contiguous. Based on this, we believe that the two-mica monzonitic granite and the lithium-beryllium pegmatite in Dahongliutan area are formed by the crystallization differentiation of biotite granite. Experimental petrology showed that biotite dehydration-melting of meta-greywacke or biotite gneiss forms biotite granite, and it is speculated that the extensive biotite granite in Dahongliutan area originated from the dehydration-melting of biotite and some amphibole during granulite facies metamorphism in the lower crust.

Advances in experimental petrology study on the evolution of the lunar magma ocean

Advances in experimental petrology study on the evolution of the lunar magma ocean

Visible and near-InfraRed (VNIR) reflectance of silicate glasses: Characterization of a featureless spectrum and implications for planetary geology

Silicate glasses represent a major component in volcanic products, both in pyroclastic deposits and lavas. To date, their spectral characteristics are not thoroughly investigated in the context of their characterization as possible analogues of planetary surfaces, mainly due to their lack of spectral features. Nevertheless, featureless VIS-NIR spectra for which it is only possible to retrieve relative parameters (slope, albedo) are commonly observed on the surface of planetary bodies, and volcanic structures are supposed to be widely present in all terrestrial planets within the Solar System. Therefore, the correct interpretation of their geochemical signature is important in the attempt to shed new light on the evolution of these planets, and detailed knowledge about the spectral response of silicate glasses is fundamental for such a purpose.In this study, experimental petrology techniques have been used to produce 15 silicate glasses having complex chemical composition corresponding to three of the most common magmatic series on planet Earth. These glasses have been investigated in the Visible and Near/Infrared range to observe and interpret the variation of slope, albedo, and spectral ratio R1.55/R0.8 as a function of chemical composition. We found that, despite the complexity of factors influencing the spectral response, a good correlation can be derived linking spectral parameters with both iron content and composite Silicium-Calcium-Iron-Magnesium content (SCFM parameter). Results presented in this work might represent the baseline for new research lines focused on deciphering the significance of silicate glasses in the context of planetary exploration, opening new windows to access information on planetary differentiation that cannot be obtained using only existing materials and methods.

Hidden Water in Magma Ocean Exoplanets

Abstract We demonstrate that the deep volatile storage capacity of magma oceans has significant implications for the bulk composition, interior, and climate state inferred from exoplanet mass and radius data. Experimental petrology provides the fundamental properties of the ability of water and melt to mix. So far, these data have been largely neglected for exoplanet mass–radius modeling. Here we present an advanced interior model for water-rich rocky exoplanets. The new model allows us to test the effects of rock melting and the redistribution of water between magma ocean and atmosphere on calculated planet radii. Models with and without rock melting and water partitioning lead to deviations in planet radius of up to 16% for a fixed bulk composition and planet mass. This is within the current accuracy limits for individual systems and statistically testable on a population level. Unrecognized mantle melting and volatile redistribution in retrievals may thus underestimate the inferred planetary bulk water content by up to 1 order of magnitude.