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Lunar silicic rocks were first identified by granitic fragments found in samples brought to Earth by the Apollo missions, followed by the discovery of silicic domes on the lunar surface through remote sensing. Although these silicic lithologies are thought to make up a small portion of the lunar crust, their presence indicates that lunar crustal evolution is more complex than originally thought. Models currently used to describe the formation of silicic lithologies on the Moon include in situ differentiation of a magma, magma differentiation with silicate liquid immiscibility, and partial melting of the crust. This study focuses on testing a crustal melting model through partial melting experiments on compositions representing lithologies spatially associated with the silicic domes. The experiments were guided by the results of modeling melting temperatures and residual melt compositions of possible protoliths for lunar silicic rocks using the thermodynamic modeling software, rhyolite-MELTS. Rhyolite-MELTS simulations predict liquidus temperatures of 950-1040 °C for lunar granites under anhydrous conditions, which guided the temperature range for the experiments. Monzogabbro, alkali gabbronorite, and KREEP basalt were identified as potential protoliths due to their ages, locations on the Moon (i.e., located near observed silicic domes), chemically evolved compositions, and the results from rhyolite-MELTS modeling. Partial melting experiments, using mixtures of reagent grade oxide powders representing bulk rock compositions of these rock types, were carried out at atmospheric pressure over the temperature range of 900-1100 °C. Because all lunar granite samples and remotely sensed domes have an elevated abundance of Th, some of the mixtures were doped with Th to observe its partitioning behavior. Run products show that at temperatures of 1050 and 1100 °C, melts of the three protoliths are not silicic in nature (i.e., they have <63 wt% SiO2). By 1000 °C, melts of both monzogabbro and alkali gabbronorite approach the composition of granite, but are also characterized by immiscible Si-rich and Fe-rich liquids. Furthermore, Th strongly partitions into the Fe-rich, and not the Si-rich glass in all experimental runs. Our work provides important constraints on the mechanism of silicic melt formation on the Moon. The observed high-Th content of lunar granite is difficult to explain by silicate liquid immiscibility, because through this process, Th is not fractionated into the Si-rich phase. Results of our experiments and modeling suggests that silicic lunar rocks could be produced from monzogabbro and alkali gabbronorite protoliths by partial melting at T < 1000 °C. Additionally, we speculate that at higher pressures (P ≥ 0.005 GPa), the observed immiscibility in the partial melting experiments would be suppressed.

Peridotites dredged from mid-ocean ridges and glassy mid-ocean ridge basalts (MORB) transmit information about the oxygen fugacity (fO2) of Earth's convecting upper mantle to the surface. Equilibrium assemblages of olivine+orthopyroxene+spinel in abyssal peridotites and Fe3+/ΣFe ratios in MORB glasses measured by X-ray absorption near-edge structure (XANES) provide independent estimates of MORB source region fO2, with the former recording fO2 approximately 0.8 log units lower than the latter relative to the quartz-fayalite-magnetite (QFM) buffer. To test cross-compatibility of these oxybarometers and examine the compositional effects of changing fO2 on a peridotite plus melt system over a range of Earth-relevant fO2, we performed a series of experiments at 0.1 MPa and fO2 controlled by CO-CO2 gas mixes between QFM-1.87 and QFM+2.23 in a system containing basaltic andesite melt saturated in olivine, orthopyroxene, and spinel Oxygen fugacities recorded by each method are in agreement with each other and with the fO2 measured in the furnace. Measurements of fO2 from the two oxybarometers agree to within 1σ in all experiments. These results demonstrate that the two methods are directly comparable and differences between fO2 measured in abyssal peridotites and MORB result from geographic sampling bias, petrological processes that change fO2 in these samples after separation of melts and residues, or abyssal peridotites may not be residues of MORB melting. As fO2 increases, spinel Fe3+ concentrations increase only at the expense of Cr from QFM-1.87 to QFM-0.11. Above QFM, Al is also diluted in spinel as the cation proportion of Fe3+ increases. None of the three spinel models tested, MELTS (Ghiorso and Sack 1995), SPINMELT (Ariskin and Nikolaev 1996), and MELT_CHROMITE (Poustovetov and Roeder 2001), describe these compositional effects, and we demonstrate that MELTS predicts residues that are too oxidized by >1 log unit to have equilibrated with the coexisting liquid phase. Spinels generated in this study can be used to improve future thermodynamic models needed to predict compositional changes in spinels caused by partial melting of peridotites in the mantle or by metamorphic reactions as peridotites cool in the lithosphere. In our experimental series, where the ratio of Fe2O3/FeO in the melt varies while other melt compositional parameters remain nearly constant, experimental melt fraction remains constant, and Fe3+ becomes increasingly compatible in spinel as fO2 increases. Instead of promoting melting, increasing the bulk Fe3+/ΣFe ratio in peridotite drives reactions analogous to the fayalite-ferrosilite-magnetite reaction. This may partly explain the absence of correlation between Na2O and Fe2O3 in fractionation-corrected MORB.

The Trans-Mexican Volcanic Belt (TMVB) is known for the chemical diversity in its erupted products. We have analyzed the olivine, pyroxene, and plagioclase mineral chemistry of 30 geochemically well-characterized mafic eruptives from Isla Maria at the western end of the arc to Palma Sola in the east. The mineral major oxide data indicate the dominance of open system processes such as antecryst uptake, and the scarcity of mineral-mineral and mineral-melt equilibria suggests that apart from forming microlites, erupted melts do not significantly crystallize during ascent. A combination of plagioclase antecryst chemistry and MELTS thermodynamic modeling of H2O-saturated isobaric fractional crystallization was employed to develop a pressure sensor aimed at determining the ponding depths of the co-genetic magmas from which the erupted plagioclase crystal assemblage originates. We show that the depth of magma-mush reservoirs increase eastward along the TMVB. We suggest that magma ponding is triggered by degassing-induced crystallization during magma ascent, and that the pressure sensor can also be regarded as a degassing sensor, with more hydrous melts beginning to degas at greater depths. Modeled initial magma H2O contents at the Moho range from ∼4 to ∼9 wt%. Magma-mush ponding depth variations fully explain the observed westward increase of average surface heat flux along the TMVB, supporting a new model of mafic arc magma ascent, where rapidly rising, initially aphyric melts pick up their antecrystic crystal cargo from a restricted crustal depth range, in which small unerupted batches of previously risen co-genetic magmas typically stall and solidify. This implies that, globally, mafic arc magmas may be used to constrain the depths of degassing and mush zone formation, as well as the amount of H2O in the primary melts.

Magmatic conditions prior to explosive eruption are often investigated using geo-chemical signatures in glassy components of pyroclastic deposits and related to magmatic processes at depth. One important process is fractional crystallization, which causes systematic changes to the SiO2/Al2O3 ratio of the residual melt that can be determined by observation of the mineralogy of fully crystallized lavas, by experimental petrology, and by magmatic modeling. However, for many alkaline-mafic pyroclastic deposits, the record of residual melt compositions is obscured by alteration, commonly affecting more than 50% of pyroclastic rock components including reactive glass and some susceptible minerals. In this study, melt signatures of SiO2/Al2O3 represented heterogeneously by the scarce fresh glass and abundant, zeolitized proxy-glass in the alkaline deposits of a major, caldera-forming eruption were used in conjunction with a model system (Rhyolite-MELTS) to reconstruct residual melt compositions and characteristics that existed immediately prior to explosive eruption. Through the model, full major oxide compositions of residual melts and fractionally crystallizing minerals become accessible, with associated constraints on volatiles and physical characteristics (melt temperature, density, viscosity). The use of zeolitized proxy-glass signatures relies on established and deposit-specific evidence for 'hydrologically closed' systems that suggests the SiO2/Al2O3 ratio is closely retained through initial alteration reactions and therefore closely representative of SiO2/Al2O3 in the precursor glass (erupted melt). The relationship is supported by a review of available, paired data (R2=0.94). Therefore, magmatic system data for the abundant and pervasive fine ash fraction of pyroclastic deposits can be investigated using this method and can progress more deeply beyond the widely used simple affiliation to igneous rock classification. Model-predicted magmatic mineral compositions (clinopyroxene, spinel, and nepheline as demonstrated here) serve to validate a case study reconstruction by comparison with compositions reported from natural and experimental samples. This predictive capability of the novel procedure is demonstrated in the case of a major caldera-forming eruption, the 355 ka Villa Senni event of the quiescent Colli Albani volcano, Rome, Italy, and its pervasively zeolitized Tufo Lionato deposit (>50 km3). The key finding is that a more-evolved residual melt fraction has been revealed, based on a reconstructed SiO2/Al2O3 ratio of 2.05 relative to that of the parent magma at 2.68, with implications for a reappraisal of pre-eruptive conditions and eruption mechanisms, and potentially for similar patterns across the volcanic stratigraphy and for other alkaline volcanoes.

The Wooley Creek batholith is a Late Jurassic, arc-related, calc-alkaline plutonic complex in the Klamath Mountain province of California. Post-emplacement tilting and erosion have exposed ∼12 km of structural relief. The complex consists of an older (∼159.1 Ma) lower zone (pyroxenite to tonalite) assembled by piecemeal emplacement of many magma batches, a younger (∼158.2 Ma) upper zone (quartz diorite to granite), and a transitional central zone. In the lower zone, pyroxenes are too Fe rich to be in equilibrium with a melt whose composition was that of the host rock. Mass-balance calculations and simulations using rhyolite-MELTS indicate that these rocks are cumulates of pyroxenes and plagioclase ± olivine and accessory apatite and oxides. Percentages of interstitial melt varied from ∼7.5-83%. The plagioclase/pyroxene ratios of cumulates vary considerably among the most mafic rocks, but are relatively uniform among quartz diorite to tonalite. This near-constant ratio results in compositional trends that mimic a liquid line of descent. In the upper zone, bulk-rock compositional trends are consistent with differentiation of andesitic parental magmas. Upward gradation from quartz dioritic to granitic compositions, modeled via mass-balance calculations and rhyolite-MELTS simulations, indicate that structurally lower parts of the upper zone are cumulates of hornblende and plagioclase ± biotite and accessory minerals, with 37-80% trapped melt. In contrast, the structurally higher part of the upper zone represents differentiated magma that escaped the subjacent cumulates, representing differentiated melt fractions remaining from 92-54%. The ratio of cumulate plagioclase/(plagioclase + mafic minerals) ∼0.48 among upper-zone cumulates, mimicking a liquid line of descent. The results suggest that compositional variation in many calc-alkaline plutons may be at least as representative of crystal accumulation as of fractional crystallization. If so, then the assumption that arc plutons geochemically resemble frozen liquids is dubious and should be tested on a case-by-case basis. Moreover, comparisons of plutonic rock compositions with those of potentially comagmatic volcanic rocks will commonly yield spurious results unless accumulation in the plutons is accounted for.

In many large, layered, mafic-ultramafic intrusions worldwide cumulus apatite commonly occurs in the highly fractionated Fe-Ti oxide-rich lithological units at the top of the intrusions and the associated plagioclase and olivine, if present, have An content <50 mol% and Fo content <40 mol%. These are not true for several Fe-Ti oxide ore-bearing mafic-mafic intrusions in the Emeishan large igneous province, SW China. A good example is the Taihe intrusion, which is described in this paper. In this intrusion the associated olivine and plagioclase are significantly more primitive, containing 69 mol% Fo and 59 mol% An, respectively. MELTS simulation reveals that such unusual association is the result of previous cotectic crystallization of Fe-Ti oxides with silicate minerals during magma evolution under oxidizing condition close to that of nickel-nickel oxide buffer. Supports for this new model include the observed upward decrease in plagioclase An contents coupled by lack of significant change in original olivine Fo contents in the Fe-Ti oxide ore-bearing sequence below the apatite-rich horizon, which is in turn supported by the facts that Fe-Ti oxide crystallization has a counter effect on MgO/FeO, but no effect on CaO/Na2O in the residual magma and that the addition of Fe-Ti oxides in the cumulus assemblage expedites the arrival of apatite on the liquidus. Our new findings support the interpretation that the oxide ores in the Taihe intrusion formed by gravitational accumulation of Fe-Ti oxides crystallizing from a basaltic magma, not a Fe-Ti-P-rich immiscible liquid segregated from such magma.

Silicic segregation veins in the Basement Sill, Dry Valleys, Antarctica, represent fracture-filling liquids differentiated from mid-Jurassic Ferrar tholeiitic basalt magmas. Geochemical and mineralogical characterizations for several of these veins and for their host gabbros within centimeters of sharp contacts with the veins provide information about silicic liquid produced from basalt in closed systems. The Basement Sill silicic veins are coarse- to pegmatite-textured diorites (∼60 wt% SiO2; 1.6%-2.6% MgO) composed of Fe-rich clinopyroxene (cpx; Fs20-60) and orthopyroxene (and pigeonite), ∼An50-60 plagioclase, and ∼20-30 vol% mesostases of micrographic quartz + alkali feldspar (∼Or80-90). The host gabbros (52-54 wt% SiO2; 5.5%-9.2% MgO) within ∼2 cm of veins contain pyroxene and feldspar with compositions that range from overlapping those in the diorite veins to those closer to characteristic of gabbro (e.g., cpx ∼Fs20; ∼An60-80) but unlike the more primitive mineral compositions representing the Basement Sill as a whole (e.g., ∼Fs15). The gabbros also contain interstitial micrographic quartz + alkali feldspar. Evolved minerals and quartz + alkali feldspar in gabbro at vein contacts are signatures consistent with evolved interstitial liquids having migrated through the sill's solidification zones to fill fractures formed by sag/collapse of roof-side solidification zones. MELTS software crystallization (at fO2 FMQ) of the sill magma (marginal chill zone as proxy), mass balance by linear regression, and Rayleigh fractionation all show that diorite forms after ∼72% at ∼1070°C but that it only generally resembles the diorite veins. Compositions that more fully resemble the actual segregations appear to require more than fractional crystallization, such as dioritic liquids admixed with up to ∼10% of the minerals in assemblages they crystallize. That is, evolved interstitial liquids produced from ∼70%-75% crystallization (e.g., SiO2 ∼60-65 wt%) over a volume of solidification zone framework and purged into fractures to crystallize \"dioritic\" pyroxene and plagioclase can produce varying diorite compositions and modes from place to place by admixing, a liquid-crystal process reasonable to expect for liquids purged into fractures.

This paper introduces Petrolog3, software for modeling (1) fractional and equilibrium crystallization, (2) reverse fractional crystallization at variable pressure, melt oxidation state and melt H2O contents, and (3) postentrapment reequilibration of melt inclusions in olivine. Petrolog3 offers an algorithm that allows calculations with a potentially unlimited number of (1) mineral‐melt equilibrium models for major and trace elements and (2) models describing melt physical parameters such as density and viscosity, melt oxidation state, and solubility of fluid components in silicate melts. The current version of the software incorporates 46 mineral‐melt equilibrium models for 8 minerals; 3 models describing distribution of trace elements between minerals and melt; 4 models of melt oxidation state; 1 model for H2O solubility in silicate melts; and 4 models describing melt density and viscosity. The idea behind the program is to provide the community of igneous petrologists and geochemists with a user‐friendly interface for using any combinations of available mineral‐melt equilibrium models for computer simulation of the crystallization process. Key Points New algorithm for crystallization modeling User friendly software interface Ability to compare available models

Magnesium aluminate spinel, (Mg,Fe)Al2O4, is uncommon in lunar rocks but petrologically significant. Recent near-infrared spectra of the Moon have delineated regions where spinel is the only ferromagnesian mineral; the rock is inferred to be spinel anorthosite. One hypothesis is that significant pressure is required for spinel formation; another is that spinel-bearing rocks form by low-pressure assimilation of highlands anorthosite into olivine-rich basaltic (i.e., picritic) magmas. Here, we evaluate the heat (i.e., enthalpy) required for this assimilation process. Magma compositions are the picritic Apollo 14 B green glass and an estimation of the magma parental to Mg-suite cumulate rocks. From calculated enthalpy-composition phase diagrams, assimilation of anorthite into either magma cannot produce spinel anorthosite unless the anorthite is already hotter than ∼1300 °C. For cooler anortho-site, assimilation will produce olivine- and/or pyroxene-bearing rocks. Such hot anorthite could be produced by the nearby passage of large volumes of magma, but this is not obviously consistent with occurrences of spinel far from outcrops of basaltic rocks. Hot anorthosite could also be produced by global tidal flexure; that mechanism could have only been efficient early in lunar history when a solid anorthosite crust floated above an evolved magma ocean, and it is not clear how picritic magma could pass through the magma ocean to interact with anorthite in the crust. On the other hand, spinel-bearing anorthosite can form directly upon cooling of superliquidus melts of anorthite-rich composition. Such superliquidus melts can be generated by impact events; this mechanism seems likely, given the Moon's ubiquity of impact craters, abundance of impact-metamorphosed lunar rocks, and common presence in lunar regolith of impact glasses (quenched superliquidus impact melts) of appropriate compositions. High pressure does stabilize spinel in basaltic and peridotitic systems, but available models do not permit quantitative evaluation of the effects of pressure on the enthalpy required for assimilation. Near the lunar surface, the most likely process of spinel formation is rapid crystallization of impact melts of anorthosite + picrite or peridotite compositions. The presence of spinel anorthosite on the walls and central peaks of impact craters results from rapid cooling and partial crystallization of superliquidus melts produced in the impacts, and not from uplift of deep material to the Moon's surface.

Prime editing (PE) applications are limited by low editing efficiency. Here we show that designing prime binding sites with a melting temperature of 30 °C leads to optimal performance in rice and that using two prime editing guide (peg) RNAs in trans encoding the same edits substantially enhances PE efficiency. Together, these approaches boost PE efficiency from 2.9-fold to 17.4-fold. Optimal pegRNAs or pegRNA pairs can be designed with our web application, PlantPegDesigner. Improved guide RNAs enhance the efficiency of prime editing.