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At Lake Tecopa, in California, white play-of-color opals are found in vesicles of a volcanic ash layer from the Huckleberry Ridge Tuff super-eruption (2.1 Ma). They show characteristic traits of opal-AG by X-ray diffraction and scanning electron microscopy (silica spheres of ∼330 nm). These properties are not typical for volcanic opals, and are usually associated with opals formed in a sedimentary environment, such as opal-AG from Australia. The conditions under which opal was formed at Lake Tecopa were determined by oxygen and hydrogen isotopic analyses and give a better understanding of the formation of opal in general. Tecopa opal's δ18O is ∼30 ppm, which leads to a formation temperature between 5 and 10 °C from water composition similar to the present spring water composition (δ18O = -12 ppm), or between 15 and 30 °C (the present day spring water temperatures) in water having a δ18O between -9.5 and -5.5 ppm. As a result, opal experienced 25-50% evaporation at the Tecopa basin. Contrary to long-held views, the formation of opal-AG vs. opal-CT (or opal-C) is not determined by the type of deposits, i.e., respectively sedimentary vs. volcanic, but mostly by the temperature of formation, low (≤45 °C for opal-AG) vs. high (≥160 °C for opal-CT) as suggested in most recent papers. The isotopic composition of water contained in Tecopa opals is assessed and results show that water in opal records different stages of opal formation from groundwater. Opal seems to precipitate from groundwater that is undertaking isotopic distillation during its circulation, most likely due to 15% up to 80-95% evaporation. Hydrogen isotopes are poorly documented in opal and require more systematic work, but this study reveals that, in Tecopa opals, molecular water (H2Om) is isotopically heavier than structural water (OH), a phenomena already well known in amorphous volcanic glass. Overall, opal isotopic composition reflects the composition of the water from which it precipitated and for that reason could be (as established for amorphous silicic glass) a useful tool for paleoenvironments, and paleoclimatic reconstitutions on Earth and on other terrestrial planets.

The development of a refined conceptual model for the generation of volcanic-related uranium deposits includes studies in the character of magmatic, hydrothermal-metasomatic, and filtration-transport processes, as well as of the physicochemical conditions favoring the transport and deposition of uranium. We consider these issues using the examples of the Streltsovka caldera and the eponymous ore field in eastern Transbaikalia, the Xiangshan volcanic structure in South China, and the McDermitt caldera in the western United States (Oregon and Nevada). According to the IAEA classification ( Geological Classification …, 2018), these ore fields and deposits are of the volcanic-related type, while the Streltsovka and the Xiangshan ore field show a combination of the volcanic-related type in the volcanic-sedimentary cover and the granite-related type at the basement. Most industrially viable uranium deposits of the volcanic-related type were formed in the regions listed above during Mesozoic and Cenozoic times (although we know of older, Paleozoic objects of the type). Although the time spans in which ore-bearing volcanic-related edifices were formed are different, many features in the occurrence of magmatic, hydrothermal, and filtration transport processes in these edifices are rather similar. It is commonly supposed that these features are due to a common effect of intraplate tectonic regimes or to the evolution of outer parts in the ocean-continent zones where magmatic activity produced volcanism of the bimodal series in the dominant basites–acid volcanics–basites sequence, while the migration of uranium-transporting fluids was controlled by a joint action of seismogeodynamic and thermal convective processes.

The Late Ordovician (~459–444 million years ago) was characterized by global cooling, glaciation and severe mass extinction. These events may have been driven by increased delivery of the nutrient phosphorus (P) to the ocean and associated increases in marine productivity, but it is not clear why this occurred in the two pulses identified in the geological record. We link both cooling phases—and the extinction—to volcanic eruptions through marine deposition of nutrient-rich ash and the weathering of terrestrially emplaced ash and lava. We then reconstruct the influence of Late Ordovician volcanic P delivery on the marine system by coupling an estimate of bioavailable phosphate supply (derived from a depletion and weathering model) to a global biogeochemical model. Our model compares volcanic ash P content in marine sediments before and after alteration to determine depletion factors, and we find good agreement with observed carbon isotope and reconstructed temperature shifts. Hence, massive volcanism can drive substantial global cooling on million-year timescales due to P delivery associated with long-term weathering of volcanic deposits, offsetting the transient warming of greenhouse gas emission associated with volcanic eruptions. Such longer-term cooling and potential for marine eutrophication may be important for other volcanism-driven global events. Increased volcanism-related phosphorus delivery to the Late Ordovician ocean helps explain widespread cooling and eutrophication-driven extinctions, as shown by a biogeochemical model incorporating volcanic ash phosphorus and carbon isotope records.

The structure and composition of granites provide clues to the nature of silicic volcanism, the formation of continents, and the rheological and thermal properties of the Earth's upper crust as far back as the Hadean eon during the nascent stages of the planet’s formation 1 – 4 . The temperature of granite crystallization underpins our thinking about many of these phenomena, but evidence is emerging that this temperature may not be well constrained. The prevailing paradigm holds that granitic mineral assemblages crystallize entirely at or above about 650–700 degrees Celsius 5 – 7 . The granitoids of the Tuolumne Intrusive Suite in California tell a different story. Here we show that quartz crystals in Tuolumne samples record crystallization temperatures of 474–561 degrees Celsius. Titanium-in-quartz thermobarometry and diffusion modelling of titanium concentrations in quartz indicate that a sizeable proportion of the mineral assemblage of granitic rocks (for example, more than 80 per cent of the quartz) crystallizes about 100–200 degrees Celsius below the accepted solidus. This has widespread implications. Traditional models of magma formation require high-temperature magma bodies, but new data 8 , 9 suggest that volcanic rocks spend most of their existence at low temperatures; because granites are the intrusive complements of volcanic rocks, our downward revision of granite crystallization temperatures supports the observations of cold magma storage. It also affects the link between volcanoes, ore deposits and granites: ore bodies are fed by the release of fluids from granites below them in the crustal column; thus, if granitic fluids are hundreds of degrees cooler than previously thought, this has implications for research on porphyry ore deposits. Geophysical interpretations of the thermal structure of the crust and the temperature of active magmatic systems will also be affected. Thermobarometry and diffusion modelling in quartz crystals show that some granites may crystallize at much lower temperatures than we had thought, possibly explaining observations of cold magma storage.

Subsurface reflectors in radar sounder data from the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express spacecraft indicate significant dielectric contrasts between layers in the Martian Medusae Fossae Formation (MFF). Large density changes that create dielectric contrasts are less likely in deposits of volcanic ash, eolian sediments, and dust, and compaction models show that homogeneous fine‐grained material cannot readily account for the inferred density and dielectric constant where the deposits are more than a kilometer thick. The presence of subsurface reflectors is consistent with a multi‐layer structure of an ice‐poor cap above an ice‐rich unit analogous to the Martian Polar Layered Deposits. The volume of an ice‐rich component across the entire MFF below a 300–600 m dry cover corresponds to a global equivalent layer of water of ∼1.5 to ∼2.7 m or ∼30%–50% of the total estimated in the North Polar cap. Plain Language Summary The Medusae Fossae Formation (MFF), located near the equator of Mars along the dichotomy boundary between the lowlands of the northern hemisphere and the cratered highlands of the southern hemisphere, is one of the largest and least understood deposits on Mars. The Mars Advanced Radar for Subsurface and Ionospheric Sounding radar sounder detects echoes in MFF deposits that occur between the surface and the base which are interpreted as layers within the deposit like those found in Polar Layered Deposits of the North and South Poles. The subsurface reflectors suggest transitions between mixtures of ice‐rich and ice‐poor dust analogous to the multi‐layered, ice‐rich polar deposits. An ice‐rich part of the MFF deposit corresponds to the largest volume of water outside the polar caps, or a global equivalent layer of water of ∼1.5 to ∼2.7 m. Key Points Mars Advanced Radar for Subsurface and Ionospheric Sounding radar sounder data reveals layering in the Medusae Fossae Formation (MFF) deposits Layers are likely due to transitions between mixtures of ice‐rich and ice‐poor dust, analogous to those in Polar Layered Deposits An ice‐rich portion of the MFF deposit may contain the largest volume of water in the equatorial region of Mars

Spectral gamma ray borehole logging data can yield insights into the physical properties of lake sediments, serving as a valuable proxy for assessing climate and environmental changes. The presence of tephra layers resulting from volcanic ash deposition is not related to climate and environmental conditions. As a result, these layers pose challenges when attempting to analyze paleoclimate and environmental time series. Gamma rays are composed of photons, which are elementary particles of electromagnetic radiation. Tephra layers emit photons at specific energy levels that create a distinct pattern in their gamma-ray energy spectrum. The gamma-ray signature of tephra layers varies depending on the stage of the volcanic eruption. Additionally, there is a significant difference between the gamma-ray signature emitted by tephra layers and that of the background lake sediments. A composite signature can be used to predict tephra layers from background sediments by combining several gamma-ray signatures of tephra layers at different depths. We propose five-step protocol for detecting tephra layers within sediments through the utilization of gamma-ray spectroscopy. This protocol is based on a combination of physical aspects of gamma-ray spectroscopy and geological information specific to the lake system being studied. A subset of the training dataset is used, consisting of known tephra and non-tephra layers. The protocol involves identifying similarities between known tephra layers, analyzing differences in gamma-ray signals between tephra and non-tephra layers, and studying the composition of energy channels at various depths within the training dataset. Multiple linear regression models are used to predict the relationship between the composition of tephra layers as a dependent variable and the constituent energy channels of the gamma-ray signal as independent variables. The proposed protocol has the potential to accurately detect and identify thick tephra layers (> 10 cm in thickness) based on the rate of spectral gamma ray measurement in sedimentary sequences. This approach could enhance stratigraphic resolution by enabling finer subdivision of layers in an interior basin.

Volcanoes that deposit eruptive products into the ocean can trigger phytoplankton blooms near the deposition area. Phytoplankton blooms impact the global carbon cycle, but the specific conditions and mechanisms that facilitate volcanically triggered blooms are not well understood, especially in low nutrient ocean regions. We use satellite remote sensing to analyze the chlorophyll response to an 8‐month period of explosive and effusive activity from Nishinoshima volcano, Japan. Nishinoshima is an ocean island volcano in a low nutrient low chlorophyll region of the Northern Pacific Ocean. From June to August 2020, during explosive activity, satellite‐derived chlorophyll‐a was detectable with amplitudes significantly above the long‐term climatological value. After the explosive activity ceased in mid‐August 2020, these areas of heightened chlorophyll concentration decreased as well. In addition, we used aerial observations and satellite imagery to demonstrate a spatial correlation between blooms and ash plume direction. Using a sun‐induced chlorophyll‐a fluorescence satellite product, we confirmed that the observed chlorophyll blooms are phytoplankton blooms. Based on an understanding of the nutrients needed to supply blooms, we hypothesize that blooms of nitrogen‐fixing phytoplankton led to a 1010–1012 g drawdown of carbon. Thus, the bloom could have significantly mediated the output of carbon from the explosive phase of the eruption but is a small fraction of anthropogenic CO2 stored in the ocean or the global biological pump. Overall, we provide a case study of fertilization of a nutrient‐poor ocean with volcanic ash and demonstrate a scenario where multi‐month scale deposition triggers continuous phytoplankton blooms across 1,000s of km2. Plain Language Summary Volcanic eruptions can cause organisms known as phytoplankton to multiply and form what is known as a phytoplankton bloom in the ocean. Phytoplankton blooms can impact the life cycle of carbon in the earth system, but it is not always obvious why phytoplankton blooms happen. Using different satellite data, we observe phytoplankton blooms by viewing chlorophyll concentration in the ocean. Nishinoshima is a remote volcano in an area of the Pacific that lacks nutrients necessary for phytoplankton blooms. Nishinoshima erupted in 2019–2020 and deposited lava and ash into the ocean at different times. By looking at the chlorophyll concentration during the time periods lava and ash were deposited into the ocean, we found that chlorophyll concentration increased when ash was deposited into the ocean. These increases in chlorophyll concentration were determined to be phytoplankton blooms. These phytoplankton blooms may utilize nutrients from volcanic ash and the atmosphere, leading to a drawdown of atmospheric carbon. Key Points Ash deposition triggers phytoplankton blooms at Nishinoshima during the explosive phase of the 2019–2020 eruption Phytoplankton blooms were not present during the effusive phase of the 2019–2020 eruption Phytoplankton blooms triggered by ash deposition can lead to carbon drawdown that can mediate the carbon output from the eruption

Alpha Particle X‐ray spectrometer (APXS) analyses of the distinct Amapari Marker Band (AMB), Gale crater, Mars reveal the highest, in situ, FeO and Zn abundances (47.51, 2.23 wt%), and elevated MnO associated with a lower rippled unit. APXS analyses also reveal a marked shift in provenance, to a generally basaltic composition, compared to the underlying Mg‐sulfate‐bearing strata, which persists into the overlying stratigraphy. The AMB also records perturbation in the MgSO4‐forming conditions present above and below. AMB chemistry could be consistent with a volcanic ash source; high metal concentrations resulting from volatile reactions within an ash cloud. Alternatively, syn‐ and/or post‐depositional precipitation processes within a primary lake setting and/or a later diagenetic event or events may have played a role. Ongoing and future work will aim to further constrain processes responsible for deposition of the AMB, the high metal concentrations and its regional and global implications. Plain Language Summary The Amapari Marker Band (AMB) at Gale crater forms a distinct, dark‐toned, resistant horizon identified from orbit within rock layers of the Mg‐sulfate‐bearing, central mound. Curiosity recently investigated the AMB and found a lower rippled layer, consistent with a shallow lake, contrasting with windblown sediment deposition above and below it. Analysis of the AMB by the Alpha Particle X‐ray spectrometer also revealed a marked change in the chemistry of the rocks, with the highest in situ FeO and Zn abundances measured on Mars, elevated MnO, and a composition consistent with input of different sediment compared to underlying rocks. The change in bulk chemistry persists into the overlying rocks indicating that the AMB marks a significant event in the evolution of Gale crater, and possibly beyond. The AMB may record deposition of basaltic volcanic ash into a lake; the high metal concentrations resulting from gas reactions within an ash cloud. Alternatively, the high metals may be the result of water/sediment interactions: either in the lake, and/or after deposition and possibly after becoming a solid rock. Ongoing and future work will aim to further constrain processes responsible for deposition of the AMB, the high metal concentrations and its regional and global implications. Key Points APXS analysis reveals a marked change in chemistry and provenance associated with the Amapari Marker Band, Gale crater Highest in situ iron and zinc, and elevated manganese detected by APXS within the Amapari Marker Band The Amapari Marker Bands marks a significant event in the evolution of Gale crater, and possibly beyond

The Middle Triassic volcano-sedimentary successions deposited on the passive continental margin during a period of intense extensional tectonics related to the opening of the Neotethys Ocean were investigated in NW Croatia. A new palaeogeographic term, the Northwestern Croatian Triassic Rift Basin (NCTRB), is introduced for these successions. Pelagic sediments were deposited on top of older shallow-marine carbonates from the early Illyrian to possibly late Ladinian. Pelagic limestones containing Illyrian ammonites and redeposited benthic foraminifers of the same age indicate the existence of a contemporaneous shallow-marine carbonate environment that supplied material to the deeper parts of the basin. Stratigraphically stacked volcanic and volcanogenic rocks are intercalated with pelagic sedimentary rocks. Submarine basaltic rocks, geochemically characterized as trachy-basalts, are related to deep-rooted faults. Trachy-basaltic hyaloclastites, found intercalated within pelagic limestones, were formed by the quenching of magma that came into contact with cold sea water and subsequent resedimentation of the newly formed basaltic fragments. The majority of volcanogenic deposits belong to the Pietra Verde deposits found higher in the sections. The material for these deposits was produced by explosive volcanic eruptions and deposited by gravitational mechanisms, including pyroclastic density currents. Radiolarians from intercalated radiolarian cherts indicate late Illyrian to early Fassanian age for volcanic activity, as well as episodic eruptions and deposition of pyroclastic material. The uppermost part of the NTCRB successions is characterized by secondary volcaniclastic deposits generated by the rapid reworking of unconsolidated pyroclastic detritus and is deposited as medium- to fine-grained turbidites, marking the gradual filling of the basin. Based on regional correlations, late Ladinian is the most likely age for these deposits, indicating a significant stratigraphic gap in the NTCRB successions.

Background Volcanic activity alters earth surfaces creating environments where new ecosystems can be established. Just some plants are able to colonize this kind of environment. Low availability of nitrogen and phosphorus have been widely considered to restrict plant colonization on volcanic deposits worldwide. Root adaptations such as associations with mycorrhizal fungi, associations with nitrogen-fixing microorganisms, and root structures specialized to exude carboxylates, comprise mechanisms plants use to grow on low nutrient availability conditions, such as volcanic ash or tephra. Scope Most of the studies carried out on volcanic deposit colonizing plants have been focused on aboveground features such as plant survival, growth, and plant-plant interactions. Belowground processes, involving root activity and the rhizosphere, have been less studied. Plants that colonize different volcanically affected areas in the world, the effect on microorganisms associated mainly with the rhizosphere of these plants, microbe-microbe and microbe-plant interactions are reviewed here. Conclusions Plant-to-plant interactions, involving the different kind of roots adaptations, may be complementary to facilitate each other and positively influence the ecosystem recovery of volcanic deposits. At rhizosphere level, particular microbial communities can be recruited with specific beneficial functions (nitrogen-fixing, plant promoting growth, etc.) that improve soil development and plant colonization of volcanic deposits. New aspects such as the ability of mycorrhizal fungi to recruit bacteria able to solubilize phosphorus, and the presence of endophytes and their role in promoting the growth of early plant colonizers of volcanic are also discussed.