Hydrothermal Activity Research Articles

Deeply Derived Magma Controlling the Polymetallic Mineralization at Shuikoushan, South China: Constraints from Mineral U–Pb Dating and Whole-Rock Geochemistry

Various magmatic–hydrothermal activities have resulted in different styles of polymetallic mineralization in South China. Shuikoushan is a large Fe-Cu-Pb-Zn-Au-Ag orefield situated in fold-and-thrust belts within the South China Block. Two types of granodiorite have been identified in recent drilling work. The early-stage, coarse-grained granodiorite has developed magnetite-bearing skarns in the deep level. The late-stage, fine-grained granodiorite is associated with garnet-hematite–magnetite–pyrite–sphalerite–chalcopyrite-bearing skarns in its contact zone. Away from the garnet-bearing skarn are calcite–quartz–pyrite–sphalerite–galena veinlets in faulted breccia. Fieldwork has identified iron mineralization in both skarns, whereas copper mineralization was only discovered in the garnet-bearing skarns. Lead, zinc, gold, and silver mineralization were observed in the garnet-bearing skarns and faulted breccia. Zircon U–Pb analyses suggested the emplacement of two granodiorite at 167.8 ± 0.8 Ma (MSWD = 1.1, N = 31) and 163.6 ± 0.7 Ma (MSWD = 1.3, N = 32). Apatite and garnet U–Pb dating further indicated the magnetite-bearing skarns of 166.2 ± 1.9 Ma (MSWD = 4.5, N = 27), the hematite–magnetite–sulfide-bearing skarns of 158.6 ± 2.8 Ma (MSWD = 1.3, N = 34), and the calcite–quartz–sulfide veinlets of 159.5 ± 5.2 Ma (MSWD = 1.7, N = 24). The time–space relationship between the two intrusions and hydrothermal activities suggests that the fine-grained granodiorite is responsible for polymetallic mineralization. Whole-rock geochemistry analyses demonstrated the enrichment of LILEs and the depletion of Nb and Ta in two granodiorites, with a slight enrichment in LREEs and flat HREE patterns. These granodiorite bodies therefore belong to high-K calc-alkaline magma generated via the crust’s partial melting. The fine-grained granodiorite generally has a lower HREE and higher Dy/Yb, Sr/Y ratios than coarse-grained granodiorite, corresponding to the source of magma in garnet stable lower crust. The residual garnet keeps ferric iron in melts, leaving the fine-granodiorite more oxidized for copper and gold concentration. Through these analyses and our drilling work, a continuous skarn–hydrothermal–epithermal system has been identified for Cu-Pb-Zn-Au-Ag targeting in Shuikoushan.

Enrichment of rare earth elements in epigenetic dolomite occurring in contact metamorphosed Witbank coals (South Africa)

The emplacement of igneous intrusions into coal alters both the organic and inorganic components, and may result in the addition of specific components, including rare earth elements (REEs), into the country rock. Previous studies on the intruded coals of the Main Karoo Basin (South Africa) have mainly focused on understanding changes to their organic fraction despite the likelihood that the inorganic composition is also affected, as demonstrated by others studying intruded coals elsewhere in the world. This study reports on the effects of a 0.4 m thick dolerite dyke on the mineralogy and geochemistry of Witbank coals, South Africa. Coal samples were collected at 0.25 m intervals on both sides of the dyke (west and east); in addition to the intruded coals, an unaltered coal from the same seam and a sample of the dolerite were included. The samples were assessed using petrography, X-Ray Diffraction, X-Ray Fluorescence, Scanning Electron Microscopy, and Inductively Coupled Plasma Mass Spectrometry following sequential leaching, focusing on REEs for the latter analysis. Inertinite is the main maceral group in the coal samples; as a result, the impact of the intrusion on the organic fraction is compared using mean random total reflectance (%RoTmr). Total reflectance increases from 1.65 %RoTmr (for the unaltered coal) to 4.17 %RoTmr closer to the dyke on the western side. In contrast, the eastern side reports lower values (max. 1.94 %RoTmr). Similar to reflectance, dolomite is higher in samples from the western side of the dyke. Dolomite is also found in the unaltered coal (4 wt%) and the dolerite sample (15 wt%). Syngenetic dolomite and a weak positive Gd anomaly for the unaltered coal (ΣREE = 83.7 μg/g) suggest the presence of acidic groundwaters during peatification. Subsequently, the coals were also affected by hydrothermal activity, related to the intrusion of the dolerite dyke. For the intruded coals, dolomite (fracture-infilling) and ΣREEs are higher on the western side, at a maximum of 24 wt% and 153.0 μg/g, respectively. Carbonate associated REEs are higher for the intruded coals than the total for the dolerite (ΣREE = 23.3 μg/g). This reflects the incompatibility of REEs with early-formed minerals in the dolerite, concentrating them in the residual melt. Increased reflectance and dolomite (and associated REEs) in coals from the western side suggest pronounced hydrothermal activity, related to the availability of accommodation space (i.e., fractures).

Phylogenetic relationships and adaptation in deep-sea carideans revealed by mitogenomes

The deep-sea environment is characterized by extreme and inhospitable conditions, including oxygen depletion, low temperatures, high pressure, absence of light, and limited food availability. Mitochondria and mitogenomes play a crudial role in aerobic respiration to generate energy for eukaryotes. Here, using the Illumina Hiseq 4000 platform, we performed mitogenome sequencing for five deep-sea caridean species: Lebbeus shinkaiae, Lebbeus Formosus, Glyphocrangon regalis, Heterocarpus dorsalis, and Heterocarpus laevigatus, and five deep-sea caridean mitogenomes were assembled and identified. Each of the five mitogenomes contained 13 protein-coding genes, 2 rRNAs and 22 tRNAs. Specific elements, such as tandem repeats and AT-rich sequences, were observed in the control regions of Lebbeus formosus and Lebbeus shinkaiae, potentially take a role in regulating mitochondrial genome replication and transcription. The gene order of all obtained mitogenomes follows caridean ancestral type organization. Phylogenetic analysis shows a robustly supported phylogenetic tree for the infraorder Caridea. The monophyly of the families included in this study was strongly supported. This study supports the monophyly of Oplophoroidea, but rejects the monophyletic status of Nematocarcinoidea, Crangonoidea, and Alpheoidea. At the genus level, Plesionika is polyphyletic and Rimicaris is paraphyletic in our analysis. Furthermore, Paralebbeus may be considered invalid and synonymous with Lebbeus. Positive selection analysis reveals evidence for adaptive changes in the mitogenome of different deep-sea caridean lineages. Nine residues located in cox1, cox3, atp6, nad1, nad2, nad4, nad5, nad6 and cytb were determined to have undergone positive selection. Mitogenome of different deep-sea lineages experienced different positive selection, and the lineage represented by Alvinocarididae living in deep-sea hydrothermal vents experienced the strongest positive selection. This study provides valuable insights into the adaptive evolution of deep-sea shrimps at the mitochondrial, highlighting the mitogenomic strategy that contribute to their unique adaptations in the deep-sea environment.

Kueishanamides A and B from the Hydrothermal Vent Sediment Derived Streptomyces sp. WU20.

Marine actinomycetes are known for their production of remarkable organic molecules, particularly those featuring polyoxygenated long-chain backbones. Determining the absolute configurations of these compounds remains a challenging task even today. In this study, we successfully established the planar structures and absolute configurations of two highly flexible amide alkaloids from Streptomyces sp. WU20: kueishanamides A (1) and B (2). These compounds possess a C13 linear backbone and each contains five stereogenic carbon centers. Our approach involved a combination of spectroscopic and computational methods, including J-based configurational analysis and VCD calculations, ensuring the unambiguous determination of their configurations. Kueishanamide A (1) and kueishanamide B (2) showed moderate antifungal activity against pathogenic fungus Crytococcus neoformans, with MIC values of 25 μg/mL each.

Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin

AbstractIron (Fe) is an essential micronutrient for diazotrophs, which are abundant in the Western Tropical South Pacific Ocean (WTSP). Their success depends on the numerous trace metals, particularly Fe, released from shallow hydrothermal vents along the Tonga Arc. This study aimed to explore the spatio‐temporal impact of hydrothermal fluids on particulate trace metal concentrations and biological activity. To identify the composition of sinking particles across a wide area of the WTSP, we deployed sediment traps at various depths, both close and further west of the Tonga Arc. Seafloor sediments were cored at these deployment sites, including at a remote location in the South Pacific Gyre. The sinking particles were composed of a large amount of biological material (up to 88 mg d−1), indicative of the high productivity of the region. A significant portion of this material (∼21 ± 12 wt.%) was lithogenic of hydrothermal origin, as revealed through Al‐Fe‐Mn tracing. The sinking material showed similar patterns between lithogenic and biogenic fractions, indicating that hydrothermal input within the photic layer triggered surface production. A hydrothermal fingerprint was suggested in the sediments due to the high sedimentation rates (>47 cm kyr−1) and the presence of large, heterogeneous, metal‐rich particles. The presence of nearby active deep hydrothermal sources was suspected near the Lau Ridge due to the large particle size (1–976 μm) and the significant excess of Fe and Mn (2–20 wt.%). Overall, this study revealed that hydrothermal sources have a significant influence on the biogeochemical signature of particles in the region.

Sulfur isotopic systematics of hydrothermal precipitates in the Okinawa Trough: Implication for the effect of sediments and magmatic volatiles

The Okinawa Trough is a sediment-covered intra-continental back-arc basin with active hydrothermal activities. The sulfur isotopic systematics of the hydrothermal systems in the Okinawa Trough remain unclear owing to the complex sulfur reservoirs. To address these uncertainties, we conducted in situ S isotopic combined with whole-rock geochemical, Pb isotopic, and barite Sr isotopic analyses of typical hydrothermal precipitates from three hydrothermal fields with varying sediments thickness (Iheya North Knoll (INK) < Yonaguni Knoll IV (YK) < Noho) in the Okinawa Trough. The δ34S values of barite from INK (+16.4‰ to +19.6‰, median + 18.5‰) and YK (+16.2‰ to +22.2‰, median + 19.5‰) mostly indicate lower values than those obtained for seawater (~ +21‰), combined with the observation of high S and O fugacity (fO2–fS2) mineral assemblages (e.g., low-Fe sphalerite ± enargite ± tennantite ± chalcopyrite), and high Cu and Au contents of hydrothermal precipitates, consistent with the addition of magmatic volatile to these two fields. In contrast, the in situ δ34S values of sulfide minerals from INK (+5.6‰ to +10.4‰, median + 9.0‰) and YK (+3.5‰ to +5.5‰, median + 4.7‰) fields were all positive, inconsistent with the S isotopic characteristics of H2S formed from SO2 disproportionation. We conclude that a large proportion of thermochemical SO42− reduction-derived heavy sulfur likely obscure the characteristics of H2S sourced from disproportionation. This was likely resulting from (1) sediment controlled long-scale lateral hydrothermal circulation, (2) the existence of early precipitated anhydrite, and (3) high concentrations of H2 in the high-temperature reaction zone. The Noho field have low δ34S values (−0.2‰ to +5.3‰, median + 0.9‰) of sulfide minerals, combined with high sediment contributions reflected by high Pb isotopic ratios and low-fS2–fO2 mineral assemblages (e.g., high-Fe sphalerite ± pyrrhotite ± isocubanite), which indicates that the low δ34S value sulfur was derived from leaching of biogenic pyrite in thick sedimentary strata by hydrothermal fluid. Near surface, the high-temperature discharging hydrothermal fluids interacted with different thicknesses of sedimentary strata and leached different proportions of biogenetic pyrite, resulting in a negative correlation of sedimentary strata thickness and sulfide δ34S values of the Okinawa Trough hydrothermal fields.

The mechanism of organic matter accumulation in the archipelago marine sediments: Insights from the Middle Devonian Givetian mudstone with low TOC in the Youjiang Basin, South China

Despite the fact that the mean values of total organic carbon (TOC) content in the Luofu Formation are relatively low, at or below 1.0 wt%, it still has the potential to be a veritable source rock. To elucidate the influences of various paleogeographic factors on sedimentary environments, 25 samples from Well A on the slope and 32 samples from Well B in the basin centre were selected for study. The samples were analyzed by thin section microscopy and field emission-scanning electron microscopy, along with X-ray diffraction and geochemical analyses (TOC content, sulfur content, organic petrography, inorganic carbon isotope and major and trace elements) in order to understand variations in and controls on the mineralogy, lithofacies, depositional environments, as well as the organic matter accumulation mechanism. The results of our study indicate that mudstone of the Luofu Formation was deposited into 4 lithofacies groups, namely as the siliceous lithofacies, mixed lithofacies, argillaceous lithofacies and calcareous lithofacies. The siliceous lithofacies mudstone was developed in the deep-water columns, while the mixed lithofacies mudstone was deposited on shallow-water columns. The organic matter accumulation model of the Luofu Formation can be further divided into the following four stages, each with its own unique characteristics: (1) The organic matter accumulation was caused by the relatively high productivity and dysoxic basin bottom water columns; (2) The organo-mineral complexes may promote the organic matter accumulation to some extent; (3) The organic matter enrichment was facilitated by the dysoxic/anoxic conditions and relatively high productivity from the basin to the slope; (4) The organic matter was preserved at shortened exposure duration of oxic conditions on the slope. The correlations between various geochemical indicators (redox, paleoproductivity and terrestrial debris flux) and TOC content suggest that oxic water columns and low productivity are the main reasons for the widespread mudstone with low TOC. The organic-rich mudstone, as the target stratigraphic section for exploration, may be deposited in the basin bottom water columns away from upwelling and close to hydrothermal activity in stage 3.

Hydrothermal vent fauna of the western Pacific Ocean: Distribution patterns and biogeographic networks

AbstractAimDeep‐sea hydrothermal vent habitats support a low‐diversity fauna in which most species are unique to the ecosystem. To inform conservation planning around this vulnerable marine ecosystem, we examine species distributions over a wide area to assess the underlying beta‐diversity components and to examine biogeographic patterns. We assess the concept of a highly connected fauna that would repopulate areas of local extinction from distal locations.LocationWestern Pacific Ocean from Japan to New Zealand.MethodsWe assemble a database of 295 confirmed species records for 11 western Pacific vent systems. The SET beta‐diversity framework supports query of the distribution of pairwise pattern components in comparisons among vent systems. We build a network based in graph theory to examine connectivity among vent systems based on shared species similarity. A bipartite network revealed the relative role of each species in linkages among vent system nodes. We assess the importance of sampling bias and distance between systems.ResultsOverall, two‐thirds of the taxa are restricted to a single basin or arc. The Mariana Trough system has the highest corrected weighted endemism for vent‐specific species, followed by that of the Okinawa Trough. Species replacement is the dominant feature of beta‐diversity. Eleven vent systems form seven network modules with stronger connectivity in the Southwest than Northwest Pacific. The Manus Basin vent system emerges as a network ‘hub’ reflecting its central geographic near the equator.Main ConclusionTwo western Pacific biogeographic provinces arise, north and south of the equator that few species transcend. Local and regional conservation plans should consider the low network connectivity and high system endemism in management of hydrothermal vent ecosystems in the event of seabed mining. Species recruitment is unlikely to transcend vent system boundaries. We identify Okinawa Trough, Mariana Trough, Manus Basin, Feni‐Tabar Arc and Kermadec Arc for development of conservation plans that initiate or expand protection.

A Study on the Geological Characteristics and Metallogenic Laws of the Xilahe Copper Deposit in Yuanjiang County

The Xilahe copper deposit in Yuanjiang County, Yunnan Province, China, is a highly concerned copper mining area. The geological characteristics, structural characteristics, distribution of magmatic rocks, ore body characteristics, metamorphism and wall rock alteration, as well as the ore-forming horizon and mineralization characteristics of the deposit are described and analyzed in this article, revealing its mineralization laws. The strata of the ore deposit is mainly composed of the upper section of the Fei weihe Formation, and the structural characteristics show the development of multiple faults in the mining area, including magmatic rocks such as diabase. The characteristics of the ore body indicate the presence of five copper ore bodies, mainly sulfide ore, and the main metal mineral is Fool's Gold. Metamorphism and wall rock alteration are manifested as silicification, carbonization, and pyritization. The mineralization pattern is influenced by various geological factors, including geological structure, magnetic action, hydrothermal activity, and time factors. The deposit belongs to a sedimentary metamorphic copper deposit. Comprehensive analysis shows that the copper deposits in the study area have great potential for ore exploration, which has important theoretical and practical significance for subsequent exploration and application of ore exploration methods.

Magnetic multi-fabrics as tools for understanding ignimbrite emplacement processes: An example from late-Variscan Tharandter Wald Caldera, Bohemian Massif

Felsic collapse calderas pose a hazard to our society, thus detailed knowledge of collapse mechanisms and behavior of eruptive products could help us to better understand the active calderas. We present a model of the eruption and collapse of Late Carboniferous Tharandter Wald Caldera (Variscan Bohemian Massif) based on field mapping and a magnetic multi-fabric approach. We investigate intra-caldera rhyolitic ignimbrites using a combination of conventional in-phase and relatively new out-of-phase anisotropy of magnetic susceptibility, along with the anisotropy of anhysteretic remanent magnetization. A two-stage caldera evolution model is proposed. (1) The high-energetic and high-temperature ignimbrites filled the paleo-valleys to form a thick ignimbrite sheet with welded to rheomorphosed central portion. Concurrently, eruptions emptied the source magma chamber triggering the piston caldera collapse. (2) The subsidence caused a monoclinal ductile bending of the still-hot and ignimbrite sheet around the caldera rim towards its center. Caldera activity was terminated by the emplacement of subvolcanic ring and radial dikes associated with hydrothermal activity. The latter likely induced abundant magneto-mineralogical alteration and formed composite fabrics. Hence, the application of the multi-fabric approach may serve as a useful tool to extrapolate reliable geodynamic proxies from the magnetic fabric of old, eroded, or altered caldera ignimbrites.

Comparative genomics of a vertically transmitted thiotrophic bacterial ectosymbiont and its close free-living relative.

Thiotrophic symbioses between sulphur-oxidizing bacteria and various unicellular and metazoan eukaryotes are widespread in reducing marine environments. The giant colonial ciliate Zoothamnium niveum, however, is the only host of thioautotrophic symbionts that has been cultivated along with its symbiont, the vertically transmitted ectosymbiont Candidatus Thiobius zoothamnicola (short Thiobius). Because theoretical predictions posit a smaller genome in vertically transmitted endosymbionts compared to free-living relatives, we investigated whether this is true also for an ectosymbiont. We used metagenomics to recover the high-quality draft genome of this bacterial symbiont. For comparison we have also sequenced a closely related free-living cultured but not formally described strain Milos ODIII6 (short ODIII6). We then performed comparative genomics to assess the functional capabilities at gene, metabolic pathway and trait level. 16S rRNA gene trees and average amino acid identity confirmed the close phylogenetic relationship of both bacteria. Indeed, Thiobius has about a third smaller genome than its free-living relative ODIII6, with reduced metabolic capabilities and fewer functional traits. The functional capabilities of Thiobius were a subset of those of the more versatile ODIII6, which possessed additional genes for oxygen, sulphur and hydrogen utilization and for the acquisition of phosphorus illustrating features that may be adaptive for the unstable environmental conditions at hydrothermal vents. In contrast, Thiobius possesses genes potentially enabling it to utilize lactate and acetate heterotrophically, compounds that may be provided as byproducts by the host. The present study illustrates the effect of strict host-dependence of a bacterial ectosymbiont on genome evolution and host adaptation.

The Ahadawa deposit—A newly discovered porphyry Cu–Mo system in the North Qaidam, Northern Qinghai-Tibet Plateau, NW China

Ongoing exploration in the North Qaidam, Northern Qinghai-Tibet Plateau, NW China, has led to the identification of a porphyry Cu-Mo system centered on Ahadawa. In this study, we conducted a detailed geochronological and geochemical study on porphyritic monzogranite from the Ahadawa deposit, which hosts the Cu-Mo mineralization. The weighted mean zircon U-Pb ages for three mineralized porphyritic monzogranite samples from different sites range from 218.8 ± 1.2 Ma (MSWD = 1.5) to 224.7 ± 1.6 Ma (MSWD = 1.8), and finally to 233.1 ± 0.9 Ma (MSWD = 1.4, n = 23). These results, combined with antecrystic grains as old as ∼ 245.7 Ma, collectively indicate more than 25 Ma multi-stage magmatic emplacement activity in the Ahadawa deposit. Corresponding to complex magma episodes, six studied molybdenite samples yielded variable Re-Os model ages ranging from 436.7 ± 6.6 to 232.6 ± 1.2 Ma, with the three youngest dates constraining a weighted mean Re-Os age of 234.0 ± 6.8 Ma. The 234 Ma mineralization age is consistent with the observed Late Triassic magmatism, whereas the Re-Os model ages of 436.7 to 245.7 Ma, if they remain robust through future investigation, may highlight a long-lived hydrothermal activity in the Ahadawa deposit. Whole-rock and zircon compositions indicate that the Late Triassic porphyries occurring at the surface display distinct geochemical features, with the early porphyritic monzogranite of 233.1 Ma characterized by much higher whole-rock Sr/Y, and zircon Eu/Eu* and Ce/Ce* than the younger (218.8 Ma and 224.7 Ma, respectively) porphyritic monzogranite. This suggests that the Late Triassic magmas were initially characterized by high water content and high oxidation state and the differences between the old and two younger groups might be related to plagioclase-dominated fractionation. The finding of the Ahadawa porphyry system highlights the need for ongoing exploration (especially in poorly studied remote areas) and systematically geochronological and geochemical studies to constrain the temporal and spatial evolution of mineralized episodes within a complex, protracted magmatic history.

Nanophase magnetite in matrix of anomalous EL3 chondrite Northwest Africa (NWA) 8785

AbstractNWA 8785 is a remarkable EL3 chondrite with a high abundance (~34 vol%) of an Fe‐rich matrix. This is the highest matrix abundance known among enstatite chondrites (ECs) and more similar to the matrix abundances in some carbonaceous and Rumuruti chondrites. X‐ray diffraction and TEM data indicate that the fine‐grained portion of the NWA 8785 matrix consists of nanoscale magnetite mixed with a noncrystalline silicate material and submicron‐sized enstatite and plagioclase grains. This is the first report of magnetite nanoparticles in an EL3. The Si content of the metal (0.7 wt%), presence of ferroan alabandite, and its O isotopic composition indicate NWA 8785 is EL3‐related. Having more abundant matrix than in other ECs, and that the matrix is rich in magnetite nanoparticles, which are not present in any other EC, suggest classification as an EL3 anomalous. Although we cannot completely exclude any of the mechanisms or environments for formation of the magnetite, we find a secondary origin to be the most compelling. We suggest that the magnetite formed due to hydrothermal activity in the meteorite parent body. Although ECs are relatively dry and likely formed within the nebular snow line, ices may have drifted inward from just beyond the snow line to the region where the EL chondrites were accreting, or more likely the snow line migrated inward during the early evolution of the solar system. This may have resulted in the condensation of ices and provided an ice‐rich region for accretion of the EL3 parent body. Thus, the EL3 parent body may have had hydrothermal activity and if Earth formed near the EC accretion zone, similar bodies may have contributed to the Earth's water supply. NWA 8785 greatly extends the range of known characteristics of ECs and EC parent body processes.

A new species of Orchomenella (Amphipoda, Tryphosidae) described from hydrothermal vent in the Okinawa Trough, Northwest Pacific.

A new species of the family Tryphosidae, Orchomenellacompressasp. nov., is described from hydrothermal vents in the Okinawa Trough. This is the first known Orchomenella species found in vent fields. Important morphological characters that differentiate O.compressasp. nov. from its congeners are the absence of eyes, the compressed distal three articles of gnathopod 2, the shape of the posterior margin of epimerons 2 and 3, and the number of dorsal spines on the telson. The genetic divergence of the analyzed COI gene clearly supports this new taxon.

The Holocene silicon biogeochemistry of Yellowstone Lake, USA

Silicon (Si) is an essential macronutrient for diatoms, an important component of lacustrine primary productivity that represents a link between the carbon and silicon cycles. Reconstructions of lake silicon cycling thus provide an underexploited window onto lake and catchment biogeochemistry. Silicon isotope geochemistry has potential to provide these reconstructions, given the competing source and process controls can be deconvolved. The silica-rich volcanic and hydrothermal systems in Yellowstone National Park are a great source of dissolved silicon into Yellowstone Lake, a system with high silicon, and thus carbon, export rates and the formation of diatom–rich sediment. Yellowstone Lake sediments should be an archive of past silicon biogeochemistry, although the effect of sublacustrine hydrothermal activity or hydrothermal explosion events is unclear.Here, we analysed lake water, tributaries, and hydrothermal vent fluids from Yellowstone Lake for their dissolved Si concentrations, isotope composition (δ30Si) and Ge/Si ratios to evaluate the sources of variability in the lake's Si cycle. Bulk elemental composition and biogenic SiO2 (bSiO2) content, together with δ30Si and Ge/Si ratios from a single diatom species, Stephanodiscus yellowstonensis, were analysed in two sediment cores spanning the last 9880 cal. yr BP. We investigate these datasets to identify long term Holocene changes in hydrothermal activity and effects of large and short-term events i.e., hydrothermal and a volcanic eruption.Combinations of bSiO2, δ30Si and Ge/Si with XRF and lithology data revealed that Yellowstone Lake has a resilient biogeochemical system: hydrothermal explosions are visible in the lithology but have no identifiable impact on bSiO2 accumulation or on the δ30Si signature. Both cores show similarities that suggest a stable and homogeneous dSi source across the entire lake. A narrow range of δ30Si and Ge/Si values suggests that the productive layer of the lake was well mixed and biogeochemically stable, with consistently high hydrothermal inputs of Si throughout the Holocene to buffer against the disturbance events. Variation in bSiO2 concentration through time is weakly correlated with an increase towards younger sediment in the δ30Si fossil diatom record in both cores. This increase mirrors that seen in ocean records, and follows changes known in summer insolation, summer temperatures and lake water-column mixing since the deglaciation. This suggests that climate forcing, and soil formation ultimately govern the silicon isotope record, which we suggest is via a combination of changes in weathering stoichiometry, diatom production, and relative proportion of dSi sources.

Tectonic and hydrothermal activity at the Yellow Lake fissure in response to the 2004 Dallol dyke intrusion event in Afar

The Danakil depression in Ethiopia, at the southern end of the Red Sea, has been the place of volcanic crises in 2004–10, with emplacement of at least 15 dykes. One of them, non-emergent, occurred in dry lake Asale next to Black Mountain and south of Mount Dallol during fall 2004. We report on the opening of a 4.5 km-long fissure in the ground at the same time the Black Mountain dyke was intruding the crust 2 km westward and parallel to it. The fissure, located north and south of Yellow Lake (Gaet’ale) and trending NNW-SSE, is still hydrothermally active. First, we describe the remarkable diversity of morphologic expressions of the fissure, made possible by development in an evaporite sequence. Satellite image monitoring reveals that its formation is coeval with the latest intrusion stage of the Black Mountain dyke. Hydrothermal activity in the fissure area is, however older than ∼60 years. It is suggested that hydrothermal activity is primarily a side effect of the igneous processes, probably sill intrusion, that resulted in the uplift of Mount Dallol area, in a ∼400 m thick, fluid-saturated evaporite pile. We suggest that, in 2004, emplacement of the Black Mountain dyke caused dilation within the evaporite pile overlying it, where extension was also facilitated by pressured pore fluids. This study documents the delicate intermingling of magmatic, tectonic, hydrothermal, and geomorphologic processes in evaporitic environments at the transition between continental rifting and oceanic spreading.

Isolation and Characterization of a Serratia rubidaea from a Shallow Water Hydrothermal Vent.

Microbial life present in the marine environment has to be able to adapt to rapidly changing and often extreme conditions. This makes these organisms a putative source of commercially interesting compounds since adaptation provides different biochemical routes from those found in their terrestrial counterparts. In this work, the goal was the identification of a marine bacterium isolated from a sample taken at a shallow water hydrothermal vent and of its red product. Genomic, lipidomic, and biochemical approaches were used simultaneously, and the bacterium was identified as Serratia rubidaea. A high-throughput screening strategy was used to assess the best physico-chemical conditions permitting both cell growth and production of the red product. The fatty acid composition of the microbial cells was studied to assess adaptation at the lipid level under stressful conditions, whilst several state-of-the-art techniques, such as DSC, FTIR, NMR, and Ultra-High Resolution Qq-Time-of-Flight mass spectrometry, were used to characterize the structure of the pigment. We hypothesize that the pigment, which could be produced by the cells up to 62 °C, is prodigiosin linked to an aliphatic compound that acts as an anchor to keep it close to the cells in the marine environment.

Hydrothermal amorphous silica, barite and orpiment from the crater area of seamount (SM-13) off Nicobar island, Andaman sea: Indications for the development of a new hydrothermal field

The Andaman sea characterized by trench-arc-backarc elements (Andaman-Nicobar island-arc, the Andaman back-arc spreading center, the seamount complex, and the back-arc basin) is a complex active basin and is known for hydrothermal activity in some of the seamounts (subaerial and submarine) of the volcanic arc. In the present study, 13 submarine seamounts (SM1- SM13) in the southern Andaman volcanic arc, extending from 6°47′N: 94°43′E to 7° 56′ N: 94° 2.47′E, were surveyed onboard RV Sindhu Sadhana (November 2021) to find the evidences for the hydrothermal activity. Out of the 13 seamounts, at one crater seamount (SM-13) we have observed evidence for hydrothermal activity characterized by plumes rich in dissolved gases (mainly CO2) in the water column, live chemosymbiotic organisms (Bathymodiolus species), and neoforming minerals such as amorphous silica, barite and orpiment. We observed two plumes rich in dissolved gases (mainly CO2), called GP1 and GP2, in the water column at two different water depths i.e. 400 and 380 mbsl respectively. Geochemical analysis of the water samples shows enhanced TCO2 concentrations within the plumes rich in dissolved gases (mainly CO2) observed in sub-bottom profiler data, however, the dissolved methane concentrations do not show any enrichment when compared with ambient seawater concentrations. Apart from the enhancement in the TCO2 concentrations, pH and total alkalinity data also show fluctuations within the same depth zone which may be attributed to the hydrothermal plume exhausting from the crater seamount. The occurrence of live chemosymbiotic organism Bathymodiolus species indicate an active and continuous supply of H2S. The precipitation of neoforming hydrothermal minerals such as amorphous silica, tabular barite, and orpiment on the surface of the rock samples further supports the hydrothermal activity. Previous studies carried out in 2007 have reported hydrothermal ferromanganese oxides precipitated from low-temperature hydrothermal fluids (Surya prakash et al., 2012) and inferred SM-13 as a dormant submarine volcano (Kamesh Raju et al., 2012). However, after 14 years, we observe volatile emissions to the water column, hydrothermal mineral precipitation and live chemosymbiotic organisms from the same seamount. These observations of the present study infer development of a new hydrothermal field in the least explored Andaman Sea. This study adds up a new active site to the global hydrothermal inventory which may allow better estimation of global hydrothermal flux and its role in oceanic elemental cycle.

Potential signs of life on Europa

This paper discusses the possibility of life on Europa, the moon of Jupiter by analyzing the biological components, energy source, and ocean environment on Europa. The biological components, especially amino acids, have great possibilities of forming or have already existed on Europa since its compositive elements are present and the environment on Europa is very similar to the primitive Earth. Energy sources are expected to come from the hydrothermal vents at the ocean bottom, which are formed by tidal forces and tidal heating. The hydrothermal vents are rich in chemicals and elements and have the possibility of forming lives in the future. The ocean environment is thought to be rich in oxygen, which comes from the planet Jupiter, it is first reflected on the surface of Europa, but later on, transported to the ocean through the ice layer and a lake in between. Furthermore, the freezing point of the ocean might be affected by the fact that it contains salt, but not by the fact that it has very low air pressure. To conclude, there is a great possibility that lives exist on Europa, but it cannot be 100% positive since no specific experiments have been done throughout the research, and there are so many uncertainties in space that have not been discovered yet.

Hydrothermal origin of heavy potassium isotope compositions in altered oceanic crust: Implications for tracing the elemental cycle

Stable potassium isotopes are easily fractionated by fluid-rock interactions and provide a tool to probe the role of hydrothermal alteration of the oceanic crust in modifying the chemical composition of seawater and, through subduction, the deep Earth. An in-depth understanding of K isotope fractionation during high-temperature hydrothermal oceanic crust alteration is necessary to refine the use of K isotopes to track geochemical processes. This study investigated a suite of samples of altered upper oceanic crust, that formed at the East Pacific Rise and is exposed at the Hess Deep, to constrain K isotope fractionation by combining mineralogical, elemental, isotopic, and synchrotron-based spectroscopic approaches. Relative to the protolith, isotopically heavy K is enriched in the sheeted dike complex (δ41K of -0.48 ± 0.15 to 0.14 ± 0.13‰, ave. -0.22‰) where the rocks are generally depleted in K through high-temperature (hundreds of °C) fluid-rock reaction. In contrast, samples from the lava/dike boundary (-0.59 ± 0.14 to -0.48 ± 0.12‰, ave. -0.54‰) and lavas (-0.54 ± 0.10 to -0.42 ± 0.09‰, ave. -0.46‰), commonly exhibit net enrichment of K relative to the protolith due to low-temperature (tens of °C) fluid-rock reaction and have δ41K similar to fresh basalts. We interpret the observed isotopic variation in the sheeted dikes as being primarily due to one or both of the following: (i) diffusive K loss, with 39K diffusing faster than 41K, and (ii) neoformation of albitic plagioclase, which is identified as an important 41K host in altered sheeted dikes. Using isotope mass balance calculation, we show that isotopic fractionation occurring during high-temperature alteration may be difficult to identify in hydrothermal vent fluids because the δ41K of the K leached from the rocks is similar to that of the protolith. Hydrothermal K outputs to the ocean may not contribute significantly to elevating the δ41K of modern seawater relative to the silicate Earth. In contrast to upper oceanic crust altered at low-temperature and seafloor sediments, subducting ocean crust altered at high-temperature adds rocks with δ41K higher than the protolith to the mantle. Because the high δ41K value of the sheeted dikes is generated during the loss of K from these rocks, hence expressed most strongly in K-depleted samples, tracking this signature in arc magma and the mantle will be challenging.