Diamond-hosted majoritic garnet inclusions provide unique insights into the Earth's deep, and otherwise inaccessible, mantle. Compared with other types of mineral inclusions found in sub-lithospheric diamonds, majoritic garnets can provide the most accurate estimates of diamond formation pressures because laboratory experiments have shown that garnet chemistry varies strongly as a function of pressure. However, evaluation using a compilation of experimental data demonstrates that none of the available empirical barometers are reliable for predicting the formation pressure of many experimental majoritic garnets and cannot be applied with confidence to diamond-hosted garnet inclusions. On the basis of the full experimental data set, we develop a novel type of majorite barometer using machine learning algorithms. Cross validation demonstrates that Random Forest Regression allows accurate prediction of the formation pressure across the full range of experimental majoritic garnet compositions found in the literature. Applying this new barometer to the global database of diamond-hosted inclusions reveals that their formation occurs in specific pressure modes. However, exsolved clinopyroxene components that are often observed within garnet inclusions are not included in this analysis. Reconstruction of inclusions, in the 8 cases where this is currently possible, reveals that ignoring small exsolved components can lead to underestimating inclusion pressures by up to 7 GPa (similar to 210 km). The predicted formation pressures of majoritic garnet inclusions are consistent with crystallization of carbon-rich slab-derived melts in Earth's deep upper mantle and transition zone.

Magma intrusion rate is a key parameter in eruption triggering but is poorly quantified in existing geodetic studies. Here we examine two episodes of rapid inflation in this context. Two noneruptive microseismic swarms were recorded at Semisopochnoi Volcano, Alaska in 2014-2015. We use differential SAR techniques and TerraSAR-X images to document surface deformation from 2011 to 2015, which comprises island-wide radial inflation totaling similar to 25 cm (+/-1 cm) line of sight displacement in 2014-2015. Multiple source geometries are tested in an inversion of the deformation data, and InSAR data are best fit by a spheroid trending to the northeast and plunging to the southeast, with a major axis of similar to 4 km and minor axes of similar to 1 km, directly under the central caldera of Semisopochnoi. In 2014, a modeled influx of 0.043 km(3) of magma caused line of sight displacement of similar to 17 cm. This magma was stored at a depth of similar to 8 km, until 2015 when 0.029 km(3) was added. Along with the definition of inflation source parameters, the recorded seismic events are relocated using differential travel times. These relocated events outline a linear aseismic area within a larger zone of shallow (<10 km) seismicity. This aseismic region aligns with the centroid of the deformation model. Based on these geodetic and seismic models, the plumbing system at Semisopochnoi is interpreted as a spheroidal magma storage zone at a depth of similar to 8 km below a linear feature of partial melt. The observed deformation and seismicity appear to result from rapid injection into this main storage region.

Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto's haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan's haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels similar to 0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan's detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.

Several hypotheses posit a link between the origin of Homo and climatic and environmental shifts between 3 and 2.5Ma. Here we report on new results that shed light on the interplay between tectonics, basin migration and faunal change on the one hand and the fate of Australopithecus afarensis and the evolution of Homo on the other. Fieldwork at the new Mille-Logya site in the Afar, Ethiopia, dated to between 2.914 and 2.443Ma, provides geological evidence for the northeast migration of the Hadar Basin, extending the record of this lacustrine basin to Mille-Logya. We have identified three new fossiliferous units, suggesting in situ faunal change within this interval. While the fauna in the older unit is comparable to that at Hadar and Dikika, the younger units contain species that indicate more open conditions along with remains of Homo. This suggests that Homo either emerged from Australopithecus during this interval or dispersed into the region as part of a fauna adapted to more open habitats.

Geophysical and geochemical evidence suggests that Earth's core is predominantly made of iron (or iron-nickel alloy) with several percent of light elements. However, Earth's solid inner core transmits shear waves at a much lower velocity than expected from mineralogical models that are consistent with geochemical constraints. Here we investigate the effect of hydrogen on the elastic properties of iron and iron-silicon alloys using ab initio molecular dynamic simulations. We find that these H-bearing alloys maintain a superionic state under inner-core conditions and that their shear moduli exhibit a strong shear softening due to the superionic effect, with a corresponding reduction in V-S. Several hcp-iron-silicon-hydrogen compositions can explain the observed density, V-P, V-S, and Poisson's ratio of the inner core simultaneously. Our results indicate that hydrogen is a significant component of the Earth's core, and that it may contain at least four ocean masses of water. This indicates that the Earth may have accreted wet and obtained its water from chondritic and/or nebular materials before or during core formation. (C) 2021 Elsevier B.V. All rights reserved.

The atmospheres of ultra-hot Jupiters have been characterized in detail through recent phase curve and low- and high-resolution emission and transmission spectroscopic observations. Previous numerical studies have analyzed the effect of the localized recombination of hydrogen on the atmospheric dynamics and heat transport of ultra-hot Jupiters, finding that hydrogen dissociation and recombination lead to a reduction in the day-to-night contrasts of ultra-hot Jupiters relative to previous expectations. In this work, we add to previous efforts by also considering the localized condensation of clouds in the atmospheres of ultra-hot Jupiters, their resulting transport by the atmospheric circulation, and the radiative feedback of clouds on the atmospheric dynamics. To do so, we include radiatively active cloud tracers into the existing MITgcm framework for simulating the atmospheric dynamics of ultra-hot Jupiters. We take cloud condensate properties appropriate for the high-temperature condensate corundum from CARMA cloud microphysics models. We conduct a suite of general circulation model (GCM) simulations with varying cloud microphysical and radiative properties, and we find that partial cloud coverage is a ubiquitous outcome of our simulations. This patchy cloud distribution is inherently set by atmospheric dynamics in addition to equilibrium cloud condensation, and causes a cloud greenhouse effect that warms the atmosphere below the cloud deck. Nightside clouds are further sequestered at depth due to a dynamically induced high-altitude thermal inversion. We post-process our GCMs with the Monte Carlo radiative transfer code gCMCRT and find that the patchy clouds on ultra-hot Jupiters do not significantly impact transmission spectra but can affect their phase-dependent emission spectra.

Mount Cleveland is one of Alaska's most active volcanoes, yet little is known about the magmatic system driving persistent and dynamic volcanic activity. Volcanic gas and melt inclusion (MI) data from 2016 were combined to investigate shallow magmatic processes. SO2 emission rates were between 166 and 324 t/day and the H2O/SO(2)was 600 +/- 53, whereas CO2 and H2S were below detection. Olivine-, clinopyroxene-, and plagioclase-hosted MIs have up to 3.8 wt.% H2O, 514 ppm CO2, and 2,320 ppm S. Equilibration depths, based on MI H2O contents, suggest that a magmatic column extended from 0.5 to 3.0 km (similar to 10-60 MPa). We used MI data to empirically model open-system H-C-S degassing from 0 to 12 km and found that a column of magma between 0.5 and 3 km could produce the measured gas H2O/SO2 ratio. However, additional magma deeper than 3 km is required to sustain emissions over periods greater than days to weeks, if the observed vent dimension is a valid proxy for the conduit. Assuming an initial S content of 2,320 ppm, the total magma supply needed to sustain the annual SO2 flux was 5 to 9.8 Mm(3)/yr, suggesting a maximum intrusive-to-extrusive ratio of 13:1. The model predicts degassing of <50 t/day CO(2)for July 2016, which corresponds to a maximum predicted CO2/SO2 of 0.2. Ultimately, frequent recharge from deeper, less degassed magma is required to drive the continuous activity observed over multiple years. During periods of recharge we would expect lower H2O/SO2 and measurable volcanic CO2.

Empirical constraints of fundamental properties of protoplanetary disks are essential for understanding planet formation and planetary properties(1,2). Carbon monoxide (CO) gas is often used to constrain disk properties(3). However, estimates show that the CO gas abundance in disks is depleted relative to expected values(4-7), and models of various disk processes impacting the CO abundance could not explain this depletion on observed -1Myr timescales(8-14). Here we demonstrate that surface energy effects on particles in disks, such as the Kelvin effect, that arise when ice heterogeneously nucleates onto an existing particle can efficiently trap CO in its ice phase. In previous ice formation models, CO gas was released when small ice-coated particles were lofted to warmed disk layers. Our model can reproduce the observed abundance, distribution and time evolution of gaseous CO in the four most studied protoplanetary disks(7). We constrain the solid and gaseous CO inventory at the midplane and disk diffusivities and resolve inconsistencies in estimates of the disk mass-three crucial parameters that control planetary formation.

A seismic low velocity layer (LVL) above the mantle transition zone (MTZ), often thought to be caused by volatile-induced melting, can significantly modulate planetary volatile cycles. In this work, we show that an LVL observed beneath northeast Asia is characterized by small, 0.8 +/- 0.5 vol%, average degrees of partial melting. Seismically derived P-T conditions of the LVL indicate that slab-derived CO2, possibly combined with small amounts of H2O, is necessary to induce melting. Modeling the reactive infiltration instability of the melt in a stationary mantle above a stalled slab, we demonstrate that the volatile-rich melt slowly rises above the stalled slab in the MTZ, with percolation velocities of 200-500 mu m/yr. The melt remains stable within the LVL for this geologically significant period of time, potentially transferring up to 52 Mt/yr of CO2 from the subducting slab to the mantle for an LVL similar in areal extent (3.4x106km2) to the northeast Asian LVL. Reaction between the melt channels and the LVL mantle precipitates up to 200 ppmw solid C in localized zones. Using the inferred small melt volume fraction to model trace element abundances and isotopic signatures, we show that interaction between this melt and the surrounding mantle can over the long-term produce rocks bearing a HIMU like geochemical signature.

The timing and processes that govern the end of volcanic eruptions are not yet fully understood, and there currently exists no systematic definition for the end of a volcanic eruption. Currently, end of eruption is established either by generic criteria (typically 90days after the end of visual signals of eruption) or criteria specific to a given volcano. We explore the application of supervised machine learning classification methods: Support Vector Machine, Logistic Regression, Random Forest and Gaussian Process Classifiers and define a decisiveness index D to evaluate the consistency of the classifications obtained by these models. We apply these methods to seismic time series from two volcanoes chosen because they display contrasting styles of eruption: Telica (Nicaragua) and Nevado del Ruiz (Colombia). We find that, for both volcanic systems, the end-date we obtain by classification of seismic data is 2-4 months later than end-dates defined by the last occurrence of visual eruption (such as ash emission). This finding is in agreement with previous, general definitions of eruption end and is consistent across models. Our classifications have a higher correspondence of eruptive activity with visual activity than with database records of eruption start and end. We analyze the relative importance of the different features of seismic activity used in our models (e.g. peak event amplitude, daily event counts) and find little consistency between the two volcanic systems in terms of the most important features which determine whether activity is eruptive or non-eruptive. These initial results look promising and our approach may offer a robust tool to help determine when an eruption has ended in the absence of visual confirmation. (C) 2020 Elsevier B.V. All rights reserved.