Tschauner et al. (Reports, 11 November 2021, p. 891) present evidence that diamond GRR-1507 formed in the lower mantle. Instead, the data support a much shallower origin in cold, subcratonic lithospheric mantle. X-ray diffraction data are well matched to phases common in microinclusion-bearing lithospheric diamonds. The calculated bulk inclusion composition is too imprecise to uniquely confirm CaSiO3 stoichiometry and is equally consistent with inclusions observed in other lithospheric diamonds.

Cleveland and Tana are remote volcanoes located in the central Aleutian volcanic arc on the eastern end of the Islands of Four Mountains (IFM). The persistently active Mount Cleveland volcano, on the western side of Chuginadak Island, is surrounded by several closely spaced Quaternary volcanic centers including Carlisle, Herbert, Kagamil, Tana, and Uliaga, and numerous small satellite vents on Chiginadak between Cleveland and Tana. The Alaska Volcano Observatory (AVO) installed two permanent broadband seismometers on Chuginadak Island in 2014, and we operated a temporary broadband network focused on the western side of the island in 2015-2016. Collectively, these stations provided the first seismic observations of this frequently active volcano and the surrounding Holocene-aged volcanic vents. During the study period (July 2014-January 2019), eruptive activity at Cleveland was characterized by small explosions separated by periods of lava effusion that formed small domes in the volcano's summit crater. We characterize seismicity beneath Chuginadak Island through automated analysis of event waveform frequency content, development of a one-dimensional P-wave velocity model, calculation of earthquake hypocenters, magnitudes, focal mechanisms, and identification of earthquake families. This analysis reveals the full range of seismic event types expected in a highly active volcanic environment and includes Volcano-Tectonic (vr) earthquakes, Long-Period (LP) events, and explosion signals. LP events appear to cluster at shallow depth beneath the active crater of Mount Cleveland and almost all of the explosions occur without identifiable short-term (hours to days) seismic precursors. VT earthquakes beneath Mount Cleveland occur at depths of 2 to 8 km below sea level (BSL) and range in magnitude from -0.2 to 1.8. VT focal mechanisms have horizontal P-axes that align with the regional axis of maximum stress. These observations, and a relatively slow one-dimensional seismic velocity model, are consistent with a shallow body of magma that is fed through a deeper conduit system. The time-history of VT earthquakes and shallow LP events suggest their occurrence may track the transfer of magma and fluids from the mid-crust to the shallow portions of the conduit system and may provide a means to anticipate future explosions and periods of dome growth. VT hypocenters also extend similar to 7 km northeast of Cleveland's summit at depths of 5 to 10 km BSL, under a group of Holocene-aged vents between Mount Cleveland and Tana. These earthquakes have vertically-oriented P-axes and a greater percentage occur in families. These observations, combined with observations of vent orientation and morphology and gas flux, suggest the area between Cleveland and Tana represents a zone of complicated volcano-tectonic interaction, similar to calderas elsewhere in the Aleutian arc. The presence of a larger volcanic system in the eastern IFM could influence magmatism and account for the multiple closely spaced volcanic centers in this region. Published by Elsevier B.V.

Gold mining is the largest source of mercury (Hg) pollution worldwide. The discharge of mercury in the environment bears direct human health risks and is likely to increase cascading effects throughout local food chains. In the Peruvian Amazon the mining process consists of slashing and burning trees, followed by extraction of goldbearing sediment, amalgamation with Hg and gold recovery, leading each year to the degradation of 6,00010,000 ha and the release of 180 metric tons of Hg per year to the enviroment. The purpose of this study was to determine soil Hg levels in soils of abandoned alluvial gold mine spoils and undisturbed forest in the Madre de Dios region, the epicenter of alluvial gold mining in Peru. We selected gold mine spoils of the two most important technologies locally applied for gold extraction, i.e., Minimally Mechanized Mining (MMM) and Highly Mechanized Mining (HMM), in the native communities of Laberinto and Kotzimba, respectively. We collected 127 and 35 soil samples (0-20cm depth) from potentially contaminated sites and undisturbed forest, respectively. Physicochemical analysis and determination of Hg levels were determined for all soil samples. None of the samples had Hg concentrations above Peruvian, Canadian and British Environmental Quality Standards for Agricultural Soil (6.6mg/kg). Hg levels in MMM and HMM were not significantly different between the two areas. The main variables explaining variation of soil Hg concentrations were the vegetation cover, soil organic matter, soil pH and clay particle content, which explained up to 80% of data set variation. Surprisingly, highest Hg concentrations were found in untouched old-growth forest bordering the mine spoils, but there was also a trend of increasing Hg concentrations with the regenerating vegetation. Our findings suggest that Hg concentrations in old mine spoils are low and shouldn?t stand in the way of efforts to restore soil conditions and develop sustainable land uses. However, it is urgent to end the use of Hg in mining operation to decrease human and environmental risks.

Harzburgites and dunites forming the base of the Late Cretaceous-Paleocene Papuan Ultramafic Belt (PUB) and Marum ophiolites of Papua New Guinea (PNG) are among the most refractory mantle peridotites on Earth. We present a new integrated dataset of major element, bulk plus mineral trace element and Re-Os isotopic analyses aimed at better understanding the genesis of these peridotites. The PUB harzburgites contain olivine (Fo(92-93)), low-Al enstatite (less than or equal to 0.5 wt. % Al2O3 and CaO), and Cr-rich spinel (Cr#= 0.90-0.95). The Marum harzburgites are less refractory with olivine (Fo(91.9)-(92.7)), enstatite (similar to 0.5-1.0 wt. % Al2O3 and CaO), minor clinopyroxene (diopside), and spine! (Cr# = 0.71-0.77). These major element characteristics reflect equivalent or greater levels of melt depletion than that experienced by Archean cratonic peridotites. Whereas bulk-rock heavy rare earth element (HREE) abundances mirror the refractory character indicated by the mineral chemistry and major elements, large-ion lithophile elements indicate a more complex melting and metasomatic history. In situ olivine and orthopyroxene REE measurements show that harzburgites and dunites have experienced distinct melt-rock interaction processes, with dunite channels/lenses, specifically, showing higher abundances of HREE in olivine. Distinctive severe inter-element fraction of platinum group elements and Re result in complex patterns that we refer to as 'M-shaped'. These fractionated highly siderophile element (HSE) patterns likely reflect the dissolution of HSE-rich phases in highly depleted peridotites by interaction with subduction-related melts/fluids, possibly high-temperature boninites. Osmium isotope compositions of the PNG peridotites are variable (Os-187/Os-188 = 0.1204 to 0.1611), but fall within the range of peridotites derived from Phanerozoic oceanic mantle, providing no support for ancient melt depletion, despite their refractory character. This provides further evidence that highly depleted peridotites can be produced in the modern Earth, in subduction zone environments. The complex geochemistry indicates a multi-stage process for the formation of the PNG mantle peridotites in a modern geodynamic environment. The first stage involves partial melting at low-pressure (<2 GPa) and high-temperature (similar to 1250 degrees C-1350 degrees C) to form low-K, low-Ti tholeiitic magmas that formed the overlying cumulate peridotite-gabbro and basalt (PUB only) sequences of the ophiolites. This is inferred to have occurred in a fore-arc setting at the initiation of subduction. Later stages involved fluxing of the residual harzburgites with hydrous fluids and melts to form replacive dunites and enstatite dykes and interaction of the residual peridotites in the overlying mantle wedge with high-temperature hydrous melts from the subducting slab to generate the extremely refractory harzburgites. This latter stage can be linked to the eruption of low-Ca boninites at Cape Vogel, and other arc-related volcanics, in a nascent oceanic island arc. Both ophiolites were emplaced shortly after when the embryonic oceanic island arc collided with the Australian continent.

Tschauner et al. (Reports, 11 November 2021, p. 891) present evidence that diamond GRR-1507 formed in the lower mantle. Instead, the data support a much shallower origin in cold, subcratonic lithospheric mantle. X-ray diffraction data are well matched to phases common in microinclusion-bearing lithospheric diamonds. The calculated bulk inclusion composition is too imprecise to uniquely confirm CaSiO3 stoichiometry and is equally consistent with inclusions observed in other lithospheric diamonds.

The Earth could have experienced sulfide segregation during its differentiation due to sulfur (S) saturation within a magma ocean. The relative timing of sulfide saturation during magma ocean crystallisation is strongly dependent on the solubility of S at sulfide saturation (SCSS). Here, we present SCSS data directly relevant for a deep terrestrial magma ocean obtained from laser heated diamond anvil cell experiments. Our new data, along with existing SCSS data obtained for similar compositions, was parameterised to derive a new predictive equation. Our parameterisation predicts that existing models strongly underestimate the SCSS over the P-T range of a deep magma ocean. Our SCSS models provide the S abundances required at any given stage of terrestrial accretion, and imply that sulfide saturation is much less efficient at stripping the Earth's mantle of S during accretion than previously predicted. Applying our results to the most recent mantle S evolution models shows that the SCSS would be far too high to achieve sulfide saturation, until only perhaps the final stages of magma ocean crystallisation. To satisfy highly siderophile element systematics, either the S content of the magma ocean was considerably higher than currently assumed, or highly siderophile element abundances were affected by other processes, such as iron disproportionation.

Magma viscosity strongly controls the style (for example, explosive versus effusive) of a volcanic eruption and thus its hazard potential, but can only be measured during or after an eruption. The identification of precursors indicative of magma viscosity would enable forecasting of the eruption style and the scale of associated hazards(1). The unanticipated May 2018 rift intrusion and eruption of Kilauea Volcano, Hawai'i(2) displayed exceptional chemical and thermal variability in erupted lavas, leading to unpredictable effusion rates and explosivity. Here, using an integrated analysis of seismicity and magma rheology, we show that the orientation of fault-plane solutions (which indicate a fault's orientation and sense of movement) for earthquakes preceding and accompanying the 2018 eruption indicate a 90-degree local stress-field rotation from background, a phenomenon previously observed only at high-viscosity eruptions(3), and never before at Kilauea(4-8). Experimentally obtained viscosities for 2018 products and earlier lavas from the Pu'u 'O'o vents tightly constrain the viscosity threshold required for local stress-field reorientation. We argue that rotated fault-plane solutions in earthquake swarms at Kilauea and other volcanoes worldwide provide an early indication that unrest involves magma of heightened viscosity, and thus real-time monitoring of the orientations of fault-plane solutions could provide critical information about the style of an impending eruption. Furthermore, our results provide insight into the fundamental nature of coupled failure and flow in complex multiphase systems.

How and when Earth's volatile content was established is controversial with several mechanisms postulated, including planetesimal evaporation, core formation and the late delivery of undifferentiated chondrite-like materials. The isotopes of volatile elements such as sulfur can be fractionated during planetary accretion and differentiation and thus are potential tracers of these processes. Using first-principles calculations, we examine sulfur isotope fractionation during core formation and planetesimal evaporation. We find no measurable sulfur isotope fractionation between silicate and metallic melts at core-forming conditions, indicating that the observed light sulfur isotope composition of the bulk silicate Earth relative to chondrites cannot be explained by metal-silicate fractionation. Our thermodynamic calculations show that sulfur evaporates mostly as H2S during planetesimal evaporation when nebular H-2 is present. The observed bulk Earth sulfur isotope signature and abundance can be reproduced by evaporative loss of about 90% sulfur mainly as H2S from molten planetesimals before nebular H-2 is dissipated. The heavy sulfur isotope composition of the Moon relative to the Earth is consistent with evaporative sulfur loss under 94-98% saturation condition during the Moon-forming giant impact. In summary, volatile evaporation from molten planetesimals before Earth's formation probably played a key role in establishing Earth's volatile element content.

Raikoke, a small, unmonitored volcano in the Kuril Islands, erupted in June 2019. We integrate data from satellites (including Sentinel-2, TROPOMI, MODIS, Himawari-8), the International Monitoring System (IMS) infrasound network, and global lightning detection network (GLD360) with information from local authorities and social media to retrospectively characterize the eruptive sequence and improve understanding of the pre-, syn- and post-eruptive behavior. We observe six infrasound pulses beginning on 21 June at 17:49:55 UTC as well as the main Plinian phase on 21 June at 22:29 UTC. Each pulse is tracked in space and time using lightning and satellite imagery as the plumes drift eastward. Post-eruption visible satellite imagery shows expansion of the island's surface area, an increase in crater size, and a possibly-linked algal bloom south of the island. We use thermal satellite imagery and plume modeling to estimate plume height at 10(-12) km asl and 1.5-2 x 10(6) kg/s mass eruption rate. Remote infrasound data provide insight into syn-eruptive changes in eruption intensity. Our analysis illustrates the value of interdisciplinary analyses of remote data to illuminate eruptive processes. However, our inability to identify deformation, pre-eruptive outgassing, and thermal signals, which may reflect the relatively short duration (similar to 12 h) of the eruption and minimal land area around the volcano and/or the character of closed-system eruptions, highlights current limitations in the application of remote sensing for eruption detection and characterization. (c) 2021 Elsevier B.V. All rights reserved.