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The discovery of chemosynthetic ecosystems at deep-sea hydrothermal vents in 1977 changed our view of biology. Chemosynthetic bacteria and archaea form the foundation of vent ecosystems by exploiting the chemical disequilibrium between reducing hydrothermal fluids and oxidizing seawater, harnessing this energy to fix inorganic carbon into biomass. Recent research has uncovered fundamental aspects of these microbial communities, including their relationships with underlying geology and hydrothermal geochemistry, interactions with animals via symbiosis and distribution both locally in various habitats within vent fields and globally across hydrothermal systems in diverse settings. Although ‘black smokers’ and symbioses between microorganisms and macrofauna attract much attention owing to their novelty and the insights they provide into life under extreme conditions, habitats such as regions of diffuse flow, subseafloor aquifers and hydrothermal plumes have important roles in the global cycling of elements through hydrothermal systems. Owing to sharp contrasts in physical and chemical conditions between these various habitats and their dynamic, extreme and geographically isolated nature, hydrothermal vents provide a valuable window into the environmental and ecological forces that shape microbial communities and insights into the limits, origins and evolution of microbial life.Hydrothermal vents are unique habitats for chemosynthetic bacteria and archaea and the animals that live in symbiosis with them. In this Review, Dick explores the challenges and opportunities that vent ecosystems provide for microbial life and their relationship to biogeography.

The Trans‐Atlantic Geotraverse (TAG) field on the Mid‐Atlantic Ridge is one of the largest currently active seafloor hydrothermal fields known. An underlying detachment is inferred to maintain TAG's long‐lived hydrothermal discharge, but the detachment lacks a widespread corrugated surface. We used dense wide‐angle seismic data to define TAG's detachment structure at a finer scale than has previously been possible. We generated two P‐wave velocity profiles of the shallow section of the detachment using first‐arrival travel‐time tomography, preconditioned by downward continuation. Our results reveal a low‐angle detachment, dipping at ∼15° (±5°) at 5 km east of the ridge axis, and evidence for uplifted lower‐crustal gabbro in the footwall. Increasing footwall velocities southward suggest a more intense exhumation of deep‐seated rocks, showing the detachment's geometry changes along the ridge axis. We conclude the detachment is a complex 3‐D structure, and a young system without a dome‐shaped footwall can exhumes deep‐seated crustal rocks. Plain Language Summary Hydrothermal vents, where seawater is superheated by magma and discharges mineral‐rich fluids through the seafloor, help regulate global ocean chemistry and are a potential resource for base metals. The Trans‐Atlantic Geotraverse (TAG) field on the Mid‐Atlantic Ridge is one of the largest known deep‐sea hydrothermal systems. A long‐lived extensional fault, called an oceanic detachment, is believed to localize hydrothermal circulation and venting off the ridge axis. However, current knowledge is still limited on the 3‐D geometry of the underlying detachment and how it influences high‐temperature hydrothermal activity. We present active‐source seismic data to characterize the detachment's subseafloor structure and properties at TAG, where no widespread seafloor outcrop of the fault surface is observed. Our results reveal lower crustal rocks are uplifted by the detachment, with possibly more intense fault deformation to the south of the TAG field. We suggest that the TAG detachment is a young system and expresses variable geometry along strike, with a series of concurrent faults to the north merging into one main fault dominating the south. This observation indicates detachments are complex 3‐D structures and even a young detachment lacking a clear exposed fault surface, can accommodate significant tectonic displacement and uplift of deep‐seated lithologies. Key Points P‐wave velocity model from dense seismic refraction data reveal the detailed structure of the detachment at the TAG hydrothermal field The TAG hydrothermal field is underlain by a detachment fault with a complex 3‐D geometry Young detachments, such as under TAG, could exhume lower‐crustal gabbro despite limited corrugations and a lack of a dome‐shaped footwall

Volcanic tremor is a crucial indicator for assessing the state and hazard potential of volcanic systems. At Whakaari (White Island volcano, Aotearoa New Zealand), a pulsed tremor signal emerged after a hydrothermal explosion in August 2012. The tremor accompanied the extrusion of a lava dome, before gradually disappearing prior to the onset of renewed hydrothermal activity in January 2013. We interpret this seismic signal to represent discrete gas transfers from a magmatic intrusion toward a permeable cap—possibly a hydrothermal seal—in the upper layers of Whakaari's hydrothermal system. Such tremor may thus be associated with heightened potential for hazardous explosive activity but is difficult to detect using conventional seismic monitoring parameters. To highlight the emergence of subtle periodic signals, we experiment with Lomb‐Scargle periodograms (LS). LS detect the tremor 5 days before it becomes visible in seismograms, thus facilitating the recognition of such elusive seismic patterns. Plain Language Summary A periodic seismic signal was observed at Whakaari (White Island volcano, Aotearoa New Zealand) in 2012, a few weeks after an explosion took place at the volcano. This signal persisted over more than 3 months and consists of slowly emerging, then slowly disappearing and regularly spaced “pulses.” Similar signals have been observed at other volcanic systems, where they are usually linked to rising magma, which then releases gases. Subsequently, gas slugs forming from the magma rise toward the surface and interact with and excite more solid layers of the system, which is visible in the seismic records. Therefore, such seismic signals could indicate increased potential for dangerous volcanic activity. Common techniques applied to track volcano activity struggled to highlight the emergence of this very subtle pattern. Instead, a new visualization approach allowed us to track the emergence and decline of the signal over time. This shows that such subtle patterns can be discovered days before they become recognizable in seismograms. We therefore suggest ongoing testing and validating this approach before adding it to current monitoring techniques. This work helps to identify and better understand the physical processes behind the patterns hidden in the seismic signals of volcanoes. Key Points An unusually long‐lasting episode of pulsed tremor was recorded at Whakaari volcano during its 2012/13 eruptive unrest episode The tremor may reflect discrete gas transfers from a magmatic intrusion toward a permeable cap or sulfuric seal in a hydrothermal system Subtle, periodic seismic patterns can efficiently be visualized via Lomb‐Scargle periodograms

The Baishuizhai, Shituling and Zhushanxia deposits from the Xiazhuang district represent to date the only known occurrences of early Yanshanian (Middle to Upper Jurassic) granite-related high-temperature hydrothermal uranium deposits (175–145 Ma) in the Nanling Metallogenic Belt, South China. Whole-rock geochemistry of ore samples combined with chemical and mineralogical signatures of the hydrothermal phases associated with the U mineralisation characterised a coeval potassic and propylitic alteration fingerprint: (i) the potassic alteration is defined by Na and Ca depletion of the granitic host rock and precipitation of adularia, dioctahedral Fe-muscovite, biotite and secondary quartz; and (ii) the propylitic alteration is marked by whole-rock enrichment in Ca, Fe, Mg, Mn and Ti mainly associated with the precipitation of (Mn)-epidote, Fe-chlorite, fluorapatite, titanite, calcite, APS and Fe-Cu-Pb-Cd-Bi-Mo-sulfide minerals. The high-temperature conditions of the hydrothermal system was demonstrated by the typologies of alteration such as greisen, chlorite geothermometry giving temperature estimates of the ore fluid ranging from 316 to 455°C, minor W mineralisation and the high Zr contents in titanite. Besides, high Rb, Ba, Be, Y, Nb, W, Ta and Mo contents in ore samples, mineral assemblages and chemical signatures of the hydrothermal phases showed evidence for the alteration of fractionated felsic granitic host rocks and the contribution of enriched magmatic-derived fluids. Therefore, these characteristics define a magmatic-hydrothermal genetic model directly related to the intrusion of early Yanshanian granites in the Nanling belt. In this new metallogenic model, highly fractionated high-K calc-alkaline A2-type granitic plutons have provided magmatic fluids, heat and metal sources to the early Yanshanian high-temperature hydrothermal U system. Uranium (±W-Sn-Nb-Ta-Li)-rich fluids were derived from fractionated peraluminous residual silicate melts. Uranium was enriched in a high-temperature, highly saline, F-rich, acid and reducing fluid, and dominantly carried as fluoride complexes. This mineralising fluid percolated in the Indosinian U-rich host granites within the cupolas of early Yanshanian granites and produced characteristic propylitic and potassic (including greisen) hydrothermal alteration. During the hydrothermal alteration, the pH and T variations of the mineralising fluid and the subsequent precipitation of F- and P-bearing hydrothermal phases induced the destabilisation of U complexes, winch eventually triggered the deposition of the U mineralisation.

Hydrothermal systems can generate phreatic and/or phreatomagmatic explosions with little warning. Understanding the temporal and spatial evolution of geophysical and geochemical signals at hydrothermal systems is crucial for detecting precursory signs to unrest and to inform on hazard. Thermal signatures of such systems are poorly defined because data records are often too short or discrete compared to activity timescales, which can be decadal. La Fossa system of Vulcano has been monitored since the 1980s and entered a period of unrest in 2021. We assessed the thermal signature of La Fossa using ground- and satellite-based data with various temporal and spatial scales. While continuously-recording stations provided continuous but point-based measurements, fumarole field vent surveys and infrared images obtained from satellite-flown sensors (ASTER and VIIRS) allowed lower temporal resolution but synoptic records to be built. By integrating this multi-resolution data set, precursory signs of unrest could retrospectively be detected from February to June 2021. Intensity of all unrest metrics increased during summer 2021, with an onset over a few days in September 2021. By September, seismic, CO2, SO2 and other geochemical metrics also indicated unrest, leading Civil Protection to raise the alert level to yellow on October 1. Heat flux, having been 4 MW in May 2019, increasing to 90 MW by September, and peaking at 120 MW in March 2022. We convolved our thermal data sets with all other monitoring data to validate a Vulcano Fossa Unrest Index (VFUI), framework of which can be potentially applied to any hydrothermal system. The VFUI highlighted four stages of unrest, none of which were clear in any single data set: background, precursory, onset and unrest. Onset was characterized by sudden release of fluids, likely caused by failure of sealed zones that had become pressurized during the precursory phase that began possibly as early as February 2021. Unrest has been ongoing for more than 18 months, and may continue for several more years. Our understanding of this system behavior has been due to hindsight, but demonstrates how multiparametric surveys can track and forecast unrest.

Inflations at active volcanoes are indicators of overpressure in the subsurface, which is known to be a phenomenon that precedes eruptions. Volcanic overpressure is induced by the injection of magmatic fluids, accumulated magma, or heat supply from greater depths. Azuma volcano (Japan) has experienced several episodes of volcanic unrest with increases in seismicity at the depth of the hydrothermal system, implying a potential increase in phreatic eruptions. The time series of interferometric synthetic aperture radar data, associated with the unrest episodes occurring in 2014–2015 and 2018–2019, revealed spatiotemporal variations of inflation episodes, centered around Oana crater, the most active fumarole of Azuma volcano. The modeled best-fit geometry of the elongated pressure source for the local deformation has the same dip as the overlying topographic slope direction and angle around Oana crater, suggesting the existence of topography-correlated layered structures within the hydrothermal system. In contrast, the broader deformation associated with the 2014–2015 unrest was explained by the overpressure of a horizontal flat source at 360–1500 m below sea level, showing the similar depth of the top as the conductive low-resistivity or low-viscosity body suggested by previous studies. The unrest episodes were thus interpreted as resulting mainly from the supply of magmatic fluids, or the transfer of heat from greater depths. Our study helps in understanding the shallow structure of this volcanic system and contributes to evaluating the potential for forthcoming eruptions in Azuma volcano. Graphical Abstract

We present coupled textural, elemental, and boron isotopic data of tourmaline from the large Zhunuo–Beimulang collision-related porphyry copper deposits (PCDs) located within the western Gangdese, Tibet. Based on morphology and high-resolution mapping, the tourmaline is classified into three paragenetic generations. The first generation of schorlitic Tur-1 occurs in the monzogranite porphyry as disseminations intergrown with porphyritic K-feldspar and plagioclase. It shows decreasing Fe and Ca and increasing Mg and Al contents from core to rim and has relatively homogeneous δ11B values (− 9.9 to − 8.6‰); low Fe3+/(Fe2+  + Fe3+), Cu, F, H2O, and Sr/Y ratios; and high rare earth elements. These features indicate Tur-1 formed in a low fO2 and metal-poor granitic magma during the pre-mineralization stage. The second generation of porphyritic euhedral Tur-2 is hosted in diorite porphyry enclaves and dikes, where it is intergrown with plagioclase and biotite. It forms part of the schorl-dravite solid solution, with high Fe3+/(Fe2+  + Fe3+), Cu, F, H2O, Sr/Y, and δ11B (− 9.7 to − 5.1‰) values. These features indicate it crystallized from a hydrous, oxidized, metal-, and volatile-rich diorite magma. The third generation of Tur-3 is the most volumetrically important and occurs as veinlets and disseminations in the porphyry, or around Tur-1 and Tur-2. It shows radial and oscillatory zoning and is locally intergrown with chalcopyrite and pyrite within the main mineralization assemblage. It has δ11B values (− 10.5 to − 6.0‰) that overlap with Tur-1 and Tur-2 values. Tur-3 also has variable Fe3+/(Fe2+  + Fe3+), Cu, and volatiles (F and H2O), indicating it crystallized from oxidized to relatively reducing metal- and volatile-rich hydrothermal fluids. Overall, the three generations of tourmaline show a narrow range of δ11B values between − 10.5 and − 5.1‰ that are indicative of a single magmatic source. The high Cu, ferric iron, volatiles, and δ11B values in Tur-2 are interpreted to reflect injection of diorite magma into an open crustal magma storage system that led to the formation of an oxidizing and metal-volatile-rich porphyry system. The three stages of tourmaline formation reflect evolution of the magmatic–hydrothermal system from low fO2 conditions towards more oxidizing, volatile-rich conditions and then a return to more reducing conditions that accompanied Cu precipitation. Overall, the injection of oxidized metal-rich magma into a long-lived magma reservoir is a critical driving force for the development of collision-related PCDs.

The deep-sea hydrothermal vent habitat hosts a diverse community of archaea and bacteria that withstand extreme fluctuations in environmental conditions. Abundant viruses in these systems, a high proportion of which are lysogenic, must also withstand these environmental extremes. Here, we explore the evolutionary strategies of both microorganisms and viruses in hydrothermal systems through comparative analysis of a cellular and viral metagenome, collected by size fractionation of high temperature fluids from a diffuse flow hydrothermal vent. We detected a high enrichment of mobile elements and proviruses in the cellular fraction relative to microorganisms in other environments. We observed a relatively high abundance of genes related to energy metabolism as well as cofactors and vitamins in the viral fraction compared to the cellular fraction, which suggest encoding of auxiliary metabolic genes on viral genomes. Moreover, the observation of stronger purifying selection in the viral versus cellular gene pool suggests viral strategies that promote prolonged host integration. Our results demonstrate that there is great potential for hydrothermal vent viruses to integrate into hosts, facilitate horizontal gene transfer, and express or transfer genes that manipulate the hosts' functional capabilities.

Shallow-sea hydrothermal systems, like their deep-sea and terrestrial counterparts, can serve as relatively accessible portals into the microbial ecology of subsurface environments. In this study, we determined the chemical composition of 47 sediment porewater samples along a transect from a diffuse shallow-sea hydrothermal vent to a non-thermal background area in Paleochori Bay, Milos Island, Greece. These geochemical data were combined with thermodynamic calculations to quantify potential sources of energy that may support in situ chemolithotrophy. The Gibbs energies ([DELTA]G.sub.r) of 730 redox reactions involving 23 inorganic H-, O-, C-, N-, S-, Fe-, Mn-, and As-bearing compounds were calculated. Of these reactions, 379 were exergonic at one or more sampling locations. The greatest energy yields were from anaerobic CO oxidation with NO.sub.2 .sup.- (-136 to -162 kJ/mol e.sup.- ), followed by reactions in which the electron acceptor/donor pairs were O.sub.2 /CO, NO.sub.3 .sup.- /CO, and NO.sub.2 .sup.- /H.sub.2 S. When expressed as energy densities (where the concentration of the limiting reactant is taken into account), a different set of redox reactions are the most exergonic: in sediments affected by hydrothermal input, sulfide oxidation with a range of electron acceptors or nitrite reduction with different electron donors provide 85~245 J per kg of sediment, whereas in sediments less affected or unaffected by hydrothermal input, various S.sup.0 oxidation reactions and aerobic respiration reactions with several different electron donors are most energy-yielding (80~95 J per kg of sediment). A model that considers seawater mixing with hydrothermal fluids revealed that there is up to ~50 times more energy available for microorganisms that can use S.sup.0 or H.sub.2 S as electron donors and NO.sub.2 .sup.- or O.sub.2 as electron acceptors compared to other reactions. In addition to revealing likely metabolic pathways in the near-surface and subsurface mixing zones, thermodynamic calculations like these can help guide novel microbial cultivation efforts to isolate new species.

Metal stable isotopes (e.g., Zn, Cd, and Cu) have been used to track metal sources in different types of hydrothermal systems. However, metal isotopic variations in sulphides could be triggered by various factors such as mineral precipitation and fluid mixing. Thus, tracking the metal sources of hydrothermal systems is still a big challenge for metal isotopes. In this study, we investigated the Cd isotopic systematics of sphalerite from the Nayongzhi Zn–Pb deposit, which is a Mississippi Valley‐type (MVT) deposit in the Sichuan–Yunnan–Guizhou mineralization province (SYGMP). We reinterpreted the published S isotope data for the SYGMP and found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. As such, a model that involves mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction (TSR) can explain the ore formation in the Nayongzhi deposit. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing, and thus the Cd isotopic variations of sphalerite were inherited from the source rocks. The large range of Zn/Cd ratios and uniform Cd isotopic compositions of the sulphides are similar to those of igneous rocks but different from those of sedimentary rocks, indicating that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Our results reaffirm that metal stable isotopes, particularly Cd isotope compositions of sphalerite, are powerful geochemical tracers for investigating the formation mechanisms of ore deposits. Plain Language Summary Metal stable isotopes, particularly Cd isotopes, have been widely used in investigating the metal sources, fluid evolution, and formation mechanisms of ore deposits. Here, we studied the Cd isotopic compositions of sphalerite from the Nayongzhi Zn–Pb deposit in the Sichuan–Yunnan–Guizhou mineralization province. The range of δ114/110CdNIST‐3108 value is smaller in the Nayongzhi deposit (−0.16–0.21‰), but the published S isotopic composition has significant variation (11.8–33.0‰). We found that the large S isotopic variations were controlled by Rayleigh fractionation between sulphide and reduced S. Thus, a mineralization model of the Nayongzhi deposit has been proposed, which involves the mixing of a metal‐rich fluid with a reduced S pool formed by thermochemical sulfate reduction. Based on this model, no Cd isotopic fractionation was observed due to its low solubility in fluids during mixing. Therefore, the Cd isotopic variations of sphalerite were inherited from the source rocks. Combining the Zn/Cd ratios and Cd isotopic composition characteristics of the sulphides, igneous rocks, and sedimentary rocks, it is indicated that Zn and Cd were derived mainly from basement rocks (e.g., migmatite, gneiss, and granulite). Key Points S isotopic variations caused by Rayleigh fractionation between sulphide and reduced S; Cd isotopic variations inherited from source rocks Zn/Cd ratios and Cd isotopic compositions reveal that Zn and Cd were dominantly derived from basement rocks The Nayongzhi deposit was formed by mixing between metal‐rich and reduced sulfur ore‐forming fluids