77 research outputs found
Geochemistry of Sublacustrine Hydrothermal Deposits in Yellowstone LakeâHydrothermal Reactions, Stable-Isotope Systematics, Sinter Deposition, and Spire Formation
Geochemical and mineralogical studies of hydrothermal deposits and altered vent muds from the floor of Yellowstone Lake indicate that these features form due to hydrothermal fluid quenching in shallow flow conduits or upon egress into bottom waters. Siliceous precipitates occur as conduits within the uppermost sediments, as tabular deposits that form along sedimentary layers, and as spires as much as 8 m tall that grow upward from crater-like depressions on the lake bottom. These deposits are enriched in As, Cs, Hg, Mo, Sb, Tl, and W.
Variations in major-element geochemistry indicate that subaerial sinters from West Thumb and spire interiors are nearly pure SiO2, whereas sublacustrine conduits are less SiO2 rich and are similar in some cases to normal Yellowstone Lake sediments due to incorporation of sediments into conduit walls. Vent muds, which are hydrothermally altered lake sediments, and some outer conduit walls show pervasive leaching of silica (~63 weight percent silica removal). This hydrothermal leaching process may explain the occurrence of most sublacustrine vents in holes or vent craters, but sediment winnowing by vent fluids may also be an important process in some cases.
Stable-isotope studies indicate that most deposits formed at temperatures between 78°C and 160°C and that vent fluids had oxygen-isotope values of â3.2 to â11.6 per mil, significantly higher than lake waters (â*16.5 per mil). Sulfur-isotope studies indicate that vent waters and lake waters are dominated by sulfur derived from volcanic rocks with δ34S ~ 2.5 per mil.
Geochemical reaction modeling indicates that spires form from upwelling hydrothermal fluids that are saturated with amorphous silica at temperatures 80°â96°C. Reaction calculations suggest that silica precipitation on the lake bottom is initially caused by mixing with cold bottom waters. Once a siliceous carapace is established, more rapid silica precipitation occurs by conductive cooling. Silicification of thermophilic bacteria is a very important process in building spire structures
Integrated Fe- and S-isotope study of seafloor hydrothermal vents at East Pacific Rise 9â10°N
Author Posting. Š Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 252 (2008): 214-227, doi:10.1016/j.chemgeo.2008.03.009.In this study, we report on coupled Fe- and S-isotope systematics of hydrothermal fluids and
sulfide deposits from the East Pacific Rise at 9-10°N to better constrain processes affecting Fe-
isotope fractionation in hydrothermal environments. We aim to address three fundamental
questions: (1) is there significant Fe isotope fractionation during sulfide precipitation? (2) Is there
significant variability of Fe-isotope composition of the hydrothermal fluids reflecting sulfide
precipitation in subsurface environments? (3) Are there any systematics between Fe- and S-
isotopes in sulfide minerals? The results show that chalcopyrite, precipitating in the interior wall
of a hydrothermal chimney displays a limited range of δ56Fe values and δ34S values, between â0.11 to â0.33â° and 2.2 to 2.6â° respectively. The δ56Fe values are, on average, slightly higher by
0.14Ⱐrelative to coeval vent fluid composition while δ34S values suggest significant S-isotope
fractionation (-0.6Âą0.2â°) during chalcopyrite precipitation. In contrast, systematically lower
δ56Fe and δ34S values relative to hydrothermal fluids, by up to 0.91Ⱐand 2.0Ⱐrespectively, are
observed in pyrite and marcasite precipitating in the interior of active chimneys. These results
suggest isotope disequilibrium in both Fe- and S-isotopes due to S-isotopic exchange between
hydrothermal H2S and seawater SO42- followed by rapid formation of pyrite from FeS precursors,
thus preserving the effects of a strong kinetic Fe-isotope fractionation during FeS precipitation. In
contrast, δ56Fe and δ34S values of pyrite from inactive massive sulfides, which show evidence of
extensive late-stage reworking, are essentially similar to the hydrothermal fluids. Multiple stages
of remineralization of ancient chimney deposits at the seafloor appear to produce minimal Fe-isotope fractionation. Similar affects are indicated during subsurface sulfide precipitation as
demonstrated by the lack of systematic differences between δ56Fe values in both high-temperature, Fe-rich black smokers and lower temperature, Fe-depleted vents.Support for W. Bach and
K. Edwards was provided by NSF grant OCE-0241791 and support for O. Rouxel was provided
by funding from the WHOI Deep Ocean Exploration Institute and NSF grant OCE-0622982 and
OCE-0647948
Cycling of sulfur in subduction zones: The geochemistry of sulfur in the Mariana Island Arc and back-arc trough
The sulfur contents and sulfur isotopic compositions of 24 glassy submarine volcanics from the Mariana Island Arc and back-arc Mariana Trough were determined in order to investigate the hypothesis that subducted seawater sulfur ([delta]34S = 21[per mille sign]) is recycled through arc volcanism. Our results for sulfur are similar to those for subaerial arc volcanics: Mariana Arc glasses are enriched in 34S ([delta]34S = up to 10.3[per mille sign], mean = 3.8[per mille sign]) and depleted in S (20-290 ppm, MEAN = 100 ppm) relative to MORB (850 ppm S, [delta]34S = 0.1 +/- 0.5[per mille sign]). The back-arc trough basalts contain 200-930 ppm S and have [delta]34S values of 1.1 +/- 0.5[per mille sign], which overlap those for the arc and MORB. The low sulfur contents of the arc and some of the trough glasses are attributed to (1) early loss of small amounts of sulfur through separation of immiscible sulfide and (2) later vapor-melt equilibrium control of sulfur contents and loss of sulfur in a vapor phase from sulfide-undersaturated melts near the minimum in sulfur solubility at [function of (italic small f)]O2 [approximate] NNO (nickel-nickel oxide). Although these processes removed sulfur from the melts their effects on the sulfur isotopic compositions of the melts were minimal. Positive trends of [delta]34S with 87Sr/86Sr, LILE and LREE contents of the arc volcanics are consistent with a metasomatic seawater sulfur component in the depleted sub-arc mantle source. The lack of a 34S-rich slab signature in the trough lavas may be attributed to equilibration of metasomatic fluid with mantle material along the longer pathway from the slab to the source of the trough volcanics. Sulfur is likely to have been transported into the mantle wedge by metasomatic fluid derived from subducted sediments and pore fluids.Gases extracted from vesicles in arc and back-arc samples are predominantly H2O, with minor CO2 and traces of H2S and SO2. CO2 in the arc and back-arc rocks has [delta]13C values of -2.1 to -13.1[per mille sign], similar to MORB. These data suggest that degassing of CO2 could explain the slightly lower [delta]13C values for some Mariana Trough volcanic glasses, and that incorporation of subduction-derived organic carbon into the Mariana Trough mantle source may not be necessary. More analyses are required to resolve this question, however.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30563/1/0000196.pd
Geological and thermal control of the hydrothermal system in northern Yellowstone Lake: inferences from high-resolution magnetic surveys
Author Posting. Š American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(9), (2020): e2020JB019743, doi:10.1029/2020JB019743.A multiscale magnetic survey of the northern basin of Yellowstone Lake was undertaken in 2016 as part of the Hydrothermal Dynamics of Yellowstone Lake Project (HDâYLAKE)âa broad research effort to characterize the causeâandâeffect relationships between geologic and environmental processes and hydrothermal activity on the lake floor. The magnetic survey includes lake surface, regional aeromagnetic, and nearâbottom autonomous underwater vehicle (AUV) data. The study reveals a strong contrast between the northeastern lake basin, characterized by a regional magnetic low punctuated by stronger local magnetic lows, many of which host hydrothermal vent activity, and the northwestern lake basin with higherâamplitude magnetic anomalies and no obvious hydrothermal activity or punctuated magnetic lows. The boundary between these two regions is marked by a steep gradient in heat flow and magnetic values, likely reflecting a significant structure within the currently active ~20âkmâlong Eagle BayâLake Hotel fault zone that may be related to the ~2.08âMa Huckleberry Ridge caldera rim. Modeling suggests that the broad northeastern magnetic low reflects both a shallower Curie isotherm and widespread hydrothermal activity that has demagnetized the rock. Along the western lake shoreline are sinuousâshaped, highâamplitude magnetic anomaly highs, interpreted as lava flow fronts of upper units of the West Thumb rhyolite. The AUV magnetic survey shows decreased magnetization at the periphery of the active Deep Hole hydrothermal vent. We postulate that lower magnetization in the outer zone results from enhanced hydrothermal alteration of rhyolite by hydrothermal condensates while the vaporâdominated center of the vent is less altered.The lake surface and AUV magnetic data were acquired under National Park Service research permit YELLâ2016âSCIâ7018 and the 2016 aeromagnetic data under research permit YELLâ2016âSCIâ7056. We thank Sarah Haas, Stacey Gunther, Erik Oberg, Annie Carlson, and Patricia Bigelow at the Yellowstone Center for Resources for assistance with permitting and logistics, Ranger Jackie Sene for assistance with logistics and safety at Bridge Bay, Bob Gresswell for providing us with the U.S. Geological Survey (USGS) boat Alamar, the boat pilot Nick Heredia, and Robert Harris and Shaul Hurwitz for fruitful discussions. We are very thankful to Ocean Floor Geophysics (Brian Claus and Steve Bloomer) who provided the magnetometer for the AUV survey and preprocessed the data, and to the REMUS 600 team (Greg Packard and Greg Kurras) for operating and optimizing the AUV during lake operations. Data from the Newport and Boulder observatories were used to process the survey data. We thank the USGS Geomagnetism Program for supporting their operation and INTERMAGNET for promoting high standards of magnetic observatory practice (www.intermagnet.org). This research was funded by the National Science Foundation's Integrated Earth Systems program EARâ1516361 (HDâYLAKE project), USGS Mineral Resource and Volcano Hazard Programs, and benefited from major inâkind support from the USGS Yellowstone Volcano Observatory. Maurice Tivey was supported under National Science Foundation Grant OCEâ1557455. During the course of this study, Claire Bouligand was a visiting scientist at the USGS in Menlo Park, California, USA, benefited from a delegation to Centre National de la Recherche Scientifique (CNRS), and received funding from CNRSâINSU program SYSTER. ISTerre is part of Labex OSUG@2020 (ANR10 LABX56). Any use of trade, firm, or product names is for descriptive purposes and does not imply endorsement by the U.S. Government.2021-01-2
Geochemistry of hydrothermal fluids from the PACMANUS, Northeast Pual and Vienna Woods hydrothermal fields, Manus Basin, Papua New Guinea
Processes controlling the composition of seafloor hydrothermal fluids in silicic back-arc or near-arc crustal settings remain poorly constrained despite growing evidence for extensive magmaticâhydrothermal activity in such environments. We conducted a survey of vent fluid compositions from two contrasting sites in the Manus back-arc basin, Papua New Guinea, to examine the influence of variations in host rock composition and magmatic inputs (both a function of arc proximity) on hydrothermal fluid chemistry. Fluid samples were collected from felsic-hosted hydrothermal vent fields located on Pual Ridge (PACMANUS and Northeast (NE) Pual) near the active New Britain Arc and a basalt-hosted vent field (Vienna Woods) located farther from the arc on the Manus Spreading Center. Vienna Woods fluids were characterized by relatively uniform endmember temperatures (273â285 °C) and major element compositions, low dissolved CO2 concentrations (4.4 mmol/kg) and high measured pH (4.2â4.9 at 25 °C). Temperatures and compositions were highly variable at PACMANUS/NE Pual and a large, newly discovered vent area (Fenway) was observed to be vigorously venting boiling (358 °C) fluid. All PACMANUS fluids are characterized by negative δDH2O values, in contrast to positive values at Vienna Woods, suggesting substantial magmatic water input to circulating fluids at Pual Ridge. Low measured pH (25 °C) values (âź2.6â2.7), high endmember CO2 (up to 274 mmol/kg) and negative δ34SH2S values (down to â2.7â°) in some vent fluids are also consistent with degassing of acid-volatile species from evolved magma. Dissolved CO2 at PACMANUS is more enriched in 13C (â4.1â° to â2.3â°) than Vienna Woods (â5.2â° to â5.7â°), suggesting a contribution of slab-derived carbon. The mobile elements (e.g. Li, K, Rb, Cs and B) are also greatly enriched in PACMANUS fluids reflecting increased abundances in the crust there relative to the Manus Spreading Center. Variations in alkali and dissolved gas abundances with Cl at PACMANUS and NE Pual suggest that phase separation has affected fluid chemistry despite the low temperatures of many vents. In further contrast to Vienna Woods, substantial modification of PACMANUS/NE Pual fluids has taken place as a result of seawater ingress into the upflow zone. Consistently high measured Mg concentrations as well as trends of increasingly non-conservative SO4 behavior, decreasing endmember Ca/Cl and Sr/Cl ratios with increased Mg indicate extensive subsurface anhydrite deposition is occurring as a result of subsurface seawater entrainment. Decreased pH and endmember Fe/Mn ratios in higher Mg fluids indicate that the associated mixing/cooling gives rise to sulfide deposition and secondary acidity production. Several low temperature (⊽80 °C) fluids at PACMANUS/NE Pual also show evidence for anhydrite dissolution and waterârock interaction (fixation of B) subsequent to seawater entrainment. Hence, the evolution of fluid compositions at Pual Ridge reflects the cumulative effects of water/rock interaction, admixing and reaction of fluids exsolved from silicic magma, phase separation/segregation and seawater ingress into upflow zones
S-33 constraints on the seawater sulfate contribution in modern seafloor hydrothermal vent sulfides
Author Posting. Š Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 71 (2007): 1170-1182, doi:10.1016/j.gca.2006.11.017.Sulfide sulfur in mid-oceanic ridge hydrothermal vents is derived from leaching of basaltic-sulfide and seawater-derived sulfate that is reduced during high temperature water rock
interaction. Conventional sulfur isotope studies, however, are inconclusive about the mass-balance
between the two sources because 34S/32S ratios of vent fluid H2S and chimney sulfide
minerals may reflect not only the mixing ratio but also isotope exchange between sulfate and
sulfide. Here, we show that high-precision analysis of S-33 can provide a unique constraint
because isotope mixing and isotope exchange result in different Î33S (⥠δ33S â 0.515 δ34S) values
of up to 0.04 â° even if δ34S values are identical. Detection of such small Î33S differences is
technically feasible by using the SF6 dual-inlet mass-spectrometry protocol that has been
improved to achieve a precision as good as 0.006 â° (2Ď).
Sulfide minerals (marcasite, pyrite, chalcopyrite, and sphalerite) and vent H2S collected
from four active seafloor hydrothermal vent sites, East Pacific Rise (EPR) 9-10° N, 13° N, and
21° S and Mid-Atlantic Ridge (MAR) 37° N yield Î33S values ranging from â0.002 to 0.033 and
δ34S from â0.5 to 5.3 â°. The combined δ34S and Î33S systematics reveal that 73 to 89 % of vent
sulfides are derived from leaching from basaltic sulfide and only 11 to 27 % from seawater-derived
sulfate. Pyrite from EPR 13° N and marcasite from MAR 37° N are in isotope
disequilibrium not only in δ34S but also in Î33S with respect to associated sphalerite and
chalcopyrite, suggesting non-equilibrium sulfur isotope exchange between seawater sulfate and
sulfide during pyrite precipitation. Seafloor hydrothermal vent sulfides are characterized by low
Î33S values compared with biogenic sulfides, suggesting little or no contribution of sulfide from
microbial sulfate reduction into hydrothermal sulfides at sediment-free mid-oceanic ridge
systems. We conclude that 33S is an effective new tracer for interplay among seawater, oceanic
crust and microbes in subseafloor hydrothermal sulfur cycles.S. Ono thanks the Agouron Institute for financial support and funding from the NASA Astrobiology Institute and Carnegie Institution
of Washington for supporting the analytical costs. Funding for O. Rouxel is from the Deep Ocean Exploration Institute at WHOI
The Floor of Yellowstone Lake is Anything but QuietâNew Discoveries from High-Resolution Sonar Imaging, Seismic- Reflection Profiling, and Submersible Studies
Discoveries from multibeam sonar mapping and seis-mic-reflection surveys of Yellowstone Lake provide new insight into the recent geologic forces that have shaped a large lake at the active front of the Yellowstone hot spot, a region strongly affected by young (\u3c2 \u3em.y.), large-volume (\u3e100â1,000s km3) silicic volcanism, active tectonism, and accompanying uplift.
Specifically, our mapping has identified the extent of postcaldera-collapse volcanism and active hydrothermal processes occurring above a large magma chamber beneath the lake floor. Multiple advances and recessions of thick glacial ice have overlapped volcanic and hydrothermal activity leaving a lake basin that has been shaped predominantly by fire and ice. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic,and sedimentary processes. Detailed bathymetric, seismic-reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake morphology and localization of hydrothermal activity in the northern, West Thumb, and central basins. Many previously unknown features have been identified and include more than 660 hydrothermal vents, several very large (\u3e500-m diameter) hydrothermal-explosion craters, many small hydrothermal-vent craters (~1-to 200-m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting postglacial sediments, siliceous hydrothermal-spire structures, sublacustrine landslide deposits, submerged former shorelines, large glacial melting features, incipient faulting along the trace of the Eagle Bay fault zone, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal-explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem
The Floor of Yellowstone Lake is Anything but QuietâNew Discoveries from High-Resolution Sonar Imaging, Seismic- Reflection Profiling, and Submersible Studies
Discoveries from multibeam sonar mapping and seis-mic-reflection surveys of Yellowstone Lake provide new insight into the recent geologic forces that have shaped a large lake at the active front of the Yellowstone hot spot, a region strongly affected by young (\u3c2 \u3em.y.), large-volume (\u3e100â1,000s km3) silicic volcanism, active tectonism, and accompanying uplift.
Specifically, our mapping has identified the extent of postcaldera-collapse volcanism and active hydrothermal processes occurring above a large magma chamber beneath the lake floor. Multiple advances and recessions of thick glacial ice have overlapped volcanic and hydrothermal activity leaving a lake basin that has been shaped predominantly by fire and ice. Yellowstone Lake has an irregular bottom covered with dozens of features directly related to hydrothermal, tectonic, volcanic,and sedimentary processes. Detailed bathymetric, seismic-reflection, and magnetic evidence reveals that rhyolitic lava flows underlie much of Yellowstone Lake and exert fundamental control on lake morphology and localization of hydrothermal activity in the northern, West Thumb, and central basins. Many previously unknown features have been identified and include more than 660 hydrothermal vents, several very large (\u3e500-m diameter) hydrothermal-explosion craters, many small hydrothermal-vent craters (~1-to 200-m diameter), domed lacustrine sediments related to hydrothermal activity, elongate fissures cutting postglacial sediments, siliceous hydrothermal-spire structures, sublacustrine landslide deposits, submerged former shorelines, large glacial melting features, incipient faulting along the trace of the Eagle Bay fault zone, and a recently active graben. Sampling and observations with a submersible remotely operated vehicle confirm and extend our understanding of the identified features. Faults, fissures, hydrothermally inflated domal structures, hydrothermal-explosion craters, and sublacustrine landslides constitute potentially significant geologic hazards. Toxic elements derived from hydrothermal processes also may significantly affect the Yellowstone ecosystem
Oxygen and hydrogen isotope fractionation in serpentineâwater and talcâwater systems from 250 to 450°C, 50 MPa
Author Posting. Š The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 73 (2009): 6789-6804, doi:10.1016/j.gca.2009.07.036.Oxygen and hydrogen isotope fractionation factors in the talc-water and serpentine-water systems
have been determined by laboratory experiment from 250 to 450°C at 50 MPa using the partial
exchange technique. Talc was synthesized from brucite + quartz, resulting in nearly 100%
exchange during reaction at 350 and 450°C. For serpentine, D-H exchange was much more rapid
than 18O-16O exchange when natural chrysotile fibers were employed in the initial charge. In
experiments with lizardite as the starting charge, recrystallization to chrysotile enhanced the rate
of 18O-16O exchange with the coexisting aqueous phase.This work was supported by NSF Grants OCE-9313980 to the Woods Hole Oceanographic Institution and OCE-9820287 to Bridgewater State College (BSC)
Hydrothermal alteration and microbial sulfate reduction in peridotite and gabbro exposed by detachment faulting at the MidâAtlantic Ridge, 15°20â˛N (ODP Leg 209): A sulfur and oxygen isotope study
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95304/1/ggge1087.pd
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