Generation of seafloor hydrothermal vent fluids and associated mineral deposits

Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 1 (2007): 50-65.In the nearly 30 years since the discovery of hydrothermal venting along open-ocean spreading centers, much has been learned about the generation of vent fluids and associated deposits. The hot, reducing, metal-rich, magnesium- and sulfatepoor hydrothermal fluids that exit “black smoker” and “white smoker” chimneys are formed through interactions of seawater with oceanic crust. These interactions (1) modify the composition of oceanic crust, (2) affect ocean chemistry, (3) form metal-rich deposits (possible analogs to ore deposits present on land), and (4) provide energy sources for biological communities in the deep sea.Support for M.K.T. was provided by National Science Foundation grants OCE-0241796 and OCE- 0327448

The Trans-Atlantic Geotraverse hydrothermal field : a hydrothermal system on an active detachment fault

© The Author(s), 2015. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 121 (2015): 8-16, doi:10.1016/j.dsr2.2015.02.015.Over the last ten years, geophysical studies have revealed that the Trans-Atlantic Geotraverse (TAG) hydrothermal field (26°08’N on the Mid-Atlantic Ridge) is located on the hanging wall of an active detachment fault. This is particularly important in light of the recognition that detachment faulting accounts for crustal accretion/extension along a significant portion of the Mid-Atlantic Ridge, and that the majority of confirmed vent sites on this slow-spreading ridge are hosted on detachment faults. The TAG hydrothermal field is one of the largest sites of high-temperature hydrothermal activity and mineralization found to date on the seafloor, and is comprised of active and relict deposits in different stages of evolution. The episodic nature of hydrothermal activity over the last 140 ka provides strong evidence that the complex shape and geological structure of the active detachment fault system exerts first order, but poorly understood, influences on the hydrothermal circulation patterns, fluid chemistry, and mineral deposition. While hydrothermal circulation extracts heat from a deep source region, the location of the source region at TAG is unknown. Hydrothermal upflow is likely focused along the relatively permeable detachment fault interface at depth, and then the high temperature fluids leave the low-angle portion of the detachment fault and rise vertically through the highly fissured hanging wall to the seafloor. The presence of abundant anhydrite in the cone on the summit of the TAG active mound and in veins in the crust beneath provides evidence for a fluid circulation system that entrains significant amounts of seawater into the shallow parts of the mound and stockwork. Given the importance of detachment faulting for crustal extension at slow spreading ridges, the fundamental question that still needs to be addressed is: How do detachment fault systems, and the structure at depth associated with these systems (e.g., presence of plutons and/or high permeability zones) influence the pattern of hydrothermal circulation, mineral deposition, and fluid chemistry, both in space and time, within slowly accreted ocean crust?We acknowledge the National Science Foundation which has supported our research at the TAG hydrothermal field through many awards for cruises, technological advancement of equipment, analytical, and modeling work.2016-02-2

Building a window to the sea : Ocean Research Interactive Observatory Networks (ORION)

Author Posting. © Oceanography Society, 2004. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 17, 2 (2004): 113-120.For centuries, oceanographers have relied on data and observations about the ocean and the seafloor below gathered from ships during cruises of limited duration. This expeditionary research approach has resulted in major advances in understanding global ocean circulation, the energy associated with mesoscale circulation, plate tectonics, global ocean productivity, and climate-ocean coupling. These and many other successes have expanded our view of Earth and ocean processes, and have demonstrated a need for sampling strategies spanning temporal and spatial scales not effectively carried out using ships. To address this observational gap, community efforts in the United States consistently have recommended that funding agencies support development of the capability to maintain a continuous sampling and monitoring presence in the ocean.MKT is grateful for support from a WHOI Deep Ocean Exploration Institute fellowship

Manus 2006 : hydrothermal systems in the Eastern Manus Basin: fluid chemistry and magnetic structure as guides to subseafloor processes

Cruise Report R/V Melville MAGELLAN-06, Rabaul, Papua New Guinea to Suva, Fiji July 21st 2006 to September 1st 2006The hydrothermal systems in the Manus Basin of Papua New Guinea (PNG) were comprehensively investigated through a combination of sampling and mapping using the Remotely-Operated Vehicle (ROV) Jason, the autonomous underwater vehicle (AUV) ABE (Autonomous Benthic Explorer) and ship-based CTD work and multi-beam bathymetric mapping using the RV Melville. The objectives of the cruise (July 21st to Sept. 1st, 2006) were to identify the tectonic/geologic settings of the vent systems, examine the interactions of seawater with felsic rocks that constitute the high silica end-member range of seafloor basement compositions, determine the extent of volatile magmatic inputs into these systems and to examine the evolution of hydrothermal activity through time. The first 10-day portion of the cruise was funded by Nautilus Minerals in a collaborative research effort to examine the Manus Spreading Center and the Vienna Woods basalt-hosted hydrothermal vent systems. The second 32-day portion of the cruise, funded by the National Science Foundation (NSF), focused on the felsic-hosted hydrothermal systems of the PACMANUS (Papua New Guinea – Australia – Canada Manus) vents drilled by the Ocean Drilling Program (ODP) in 2000 and the nearby seafloor volcano vent systems of Desmos and SuSu Knolls. Nautilus Minerals generously funded the add-on use of ABE throughout the NSF program allowing for high resolution mapping to be completed on all the major vent sites within the eastern Manus Basin. A total of 30 ROV dives (497 operational hours) were completed collecting 198 vent sulfides, 83 altered substrate and 43 fresh lava samples along with 104 black, gray and clear fluid samples using gastight and major samplers. ABE successfully completed 14 high resolution bathymetric, CTD and magnetic field mapping dives covering a total of 364 line km of seafloor. We located and mapped in detail the Vienna Woods and nearby Tufar-2 and -3 vent areas on Manus Spreading Center documenting the strong tectonic control on the distribution of the vent systems and the presence of reduced magnetization i.e. “magnetic burnholes”, that help define the lateral extent of the vent fields. The Vienna Woods vent systems (273°-285°C) form treetrunk- like chimneys 5-15 m tall, that emit black to gray fluids with pH and compositions similar to other documented midocean ridge (MOR) systems like the East Pacific Rise. At PACMANUS, high-resolution mapping by ABE reveals a distinctive seafloor morphology associated with dacitic lava flows along with discrete magnetic burnholes associated with the active venting systems of Roman Ruins, Satanic Mills, Snowcap, Tsukushi and a new vigorous vent system discovered southeast of the Satanic Mills area named Fenway. Another vent field in its waning stages was also discovered ~8 km northeast of PACMANUS on the Northeast Pual Ridge. At PACMANUS, the 40 m diameter Fenway mound hosts outcrops of massive anhydrite on the seafloor beneath the sulfide chimneys, a rare occurrence as anhydrite is unstable at ambient seafloor conditions. Fenway is also boiling (356°C, 172 bar) with two-phase fluid producing a ”flashing” phenomenon when the Jason lights illuminated the vent orifices. The five PACMANUS vents (271° – 356°C) have ubiquitous low pH (2.3 to 2.8) relative to Vienna Woods and typical MOR fluids, presumably reflecting water-rock reaction with the felsic hosted lava, input of magmatic volatiles and the subsurface deposition of metal sulfides. We investigated two strongly magmatically influenced vent systems associated with seafloor volcanoes. Desmos is a breached caldera with white smokers (70°-115°C) that are highly acidic (pH 1 – 1.5) and sulfur lava flows. SuSu Knolls and the adjacent Suzette mound (Solwara-1 of Nautilus Minerals) were mapped in detail and sampled intensively. Hydrothermal activity at SuSu Knolls showed a remarkable range from boiling black smokers to white sulfur-rich fluids, native sulfur flows and massive anhydrite outcrops. Vent fluids from North Su (48° – 325°C) are 2 characterized by a measured pH of 0.87, more than an order of magnitude more acidic than any deep-sea vent fluid sampled to date. Many of the low pH fluids sampled at North Su and Desmos were actively precipitating native sulfur creating thick plumes of dense white smoke. In general, sampled fluids show a considerable range in pH and gas contents, sometimes within individual hydrothermal fields. The pronounced variability of fluid chemistry within 10’s to 100’s of m at North Su is probably unparalleled in systems studied to date. The most plausible explanation for the observed variability is that different fluid-rock reaction pathways are expressed in regimes of variable magmatic volatile input and extent of subsurface cooling. This hypothesis is supported by the distribution of alteration types at the seafloor, where the occurrence of advanced argillic alteration - that relates to interactions with acid-sulfate waters such as sampled at Desmos and North Su – is patchy and spatially confined to patches of active (Desmos, North Su) and past (Snowcap) venting of such fluids. In relationship to the ODP drilling results at PACMANUS we identified and sampled examples of advanced argillic rock alteration similar to that seen in the drill core. Good examples came from Snowcap and from the North Su pillar. We sampled highly clay-altered basement from just underneath extinct chimney complexes at two locations in the Satanic Mills hydrothermal field. Both samples have dense networks of sulfide veins and may represent the stockwork or feeder zone through which hydrothermal fluids rise up to the seafloor. These samples, in addition to the other altered rock types recovered, will provide useful stepping stones in bridging the knowledge gap between the extensive surface sampling now accomplished and the basement rocks recovered by ODP, where coring was almost nil shallower than 40 m subseafloor depth. Overall, the quality and quantity of solid and fluid samples that can be put in a direct geochemical context is remarkably high. This unique dataset encompasses a broad range of geological environments that includes hydrothermal activity in basalt-hosted oceanic style spreading centers to hydrothermal systems associated with arc-style volcanism. For the first time, alteration assemblages that are commonly observed in drillcore and outcrop on land have been observed in the aqueous environment responsible for their formation.NSF Grant – OCE0327448; NSF Grant – OCE042559

A dual sensor device to estimate fluid flow velocity at diffuse hydrothermal vents

Author Posting. © 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 Deep Sea Research Part I: Oceanographic Research Papers 56 (2009): 2065-2074, doi:10.1016/j.dsr.2009.06.008.Numerous attempts have been made over the last thirty years to estimate fluid flow rates at hydrothermal vents, either at the exit of black smoker chimneys or within diffuse flow areas. In this study, we combine two methods to accurately estimate fluid flow velocities at diffuse flow areas. While the first method uses a hot film anemometer that performs high frequency measurements, the second allows a relatively rapid assessment of fluid flow velocity through video imagery and provides in situ data to calibrate the sensor. Measurements of flow velocities on hydrothermal diffuse flow areas were obtained on the Mid-Atlantic Ridge (MAR). They range from 1.1 to 4.9 mm/sec., at the substratum level, in low temperature (4.5 to 16.4°C) diffuse flow areas from the Tour Eiffel sulfide edifice. A strong correlation was observed between fluid flow velocities and temperature, supporting the possible use of temperature as a proxy to estimate flow rates in diffuse flow areas where such a simple linear flow/temperature relation is shown to dominate.The first part of this research was sponsored by a NOAA/NURP grant award #NA96RU0221 and NSF grant OCE-9901563 to MKT and JS. JS was also supported by a FCAR (Quebec) post-doctoral fellowship. The last part of the project was supported through the ANR DEEP OASES (ANR06 BDV005)

Anisotropy in seafloor flange, slab, and crust samples from measurements of permeability and porosity : implications for fluid flow and deposit evolution

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q03018, doi:10.1029/2011GC003840.Seafloor hydrothermal vents accommodate the convective transfer of fluids from subsurface environments to the oceans. In addition to black smoker chimneys, a variety of other deposit-types form. Flanges protrude from the sides of edifices as horizontal ledges, below which vent fluids pool. Slabs are hydrothermally silicified layered volcaniclastic deposits. Crusts are deposits composed of previously deposited material underlain by hot fluids. Permeability and porosity measurements were conducted on flanges from Guaymas Basin and the Main Endeavour Vent Field, slabs from the Lucky Strike Vent Field, and a crust sample from the Trans-Atlantic Geotraverse (TAG) active mound. Cores taken parallel to textural layers have high permeabilities (≈10−12 m2) and porosities (30–40%) that follow a power law relationship with exponent α ≈ 1 to 2. Cores taken perpendicular to layering have permeabilities from 10−16 to 10−12 m2 and porosities from 20 to 45%, with α ≈ 5 to 8. The two distinct trends result from the heterogeneity of textural layers within these deposits. Microstructural observations show large variations in grain packing and pore distributions between layers, consistent with flow perpendicular to layering being more susceptible to changes in permeability that result from mineral precipitation than flow parallel to layering. These results imply that the primary flow direction in these deposits is parallel to layering, whereas flow perpendicular to layering is more restricted. Quantification of anisotropic permeability provides important constraints for determination of fluid flux from these layered deposits, and temperatures, chemistry, and availability of nutrients to organisms living in and at exteriors of deposits.This work was supported by the National Science Foundation under grants EAR-0741339 and OCE-0648337. Partial support for JG and WZ from DOE # DEFG0207ER15916 is also acknowledged.2012-09-2

Permeability-porosity relationships in seafloor vent deposits : dependence on pore evolution processes

Author Posting. © American Geophysical Union, 2007. 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 112 (2007): B05208, doi:10.1029/2006JB004716.Systematic laboratory measurements of permeability and porosity were conducted on three large vent structures from the Mothra Hydrothermal vent field on the Endeavor segment of the Juan de Fuca Ridge. Geometric means of permeability values obtained from a probe permeameter are 5.9 × 10−15 m2 for Phang, a tall sulfide-dominated spire that was not actively venting when sampled; 1.4 × 10−14 m2 for Roane, a lower-temperature spire with dense macrofaunal communities growing on its sides that was venting diffuse fluid of <300°C; and 1.6 × 10−14 m2 for Finn, an active black smoker with a well-defined inner conduit that was venting 302°C fluids prior to recovery. Twenty-three cylindrical cores were then taken from these vent structures. Permeability and porosity of the drill cores were determined on the basis of Darcy's law and Boyle's law, respectively. Permeability values range from ∼10−15 to 10−13 m2 for core samples from Phang, from ∼10−15 to 10−12 m2 for cores from Roane, and from ∼10−15 to 3 × 10−13 m2 for cores from Finn, in good agreement with the probe permeability measurements. Permeability and porosity relationships are best described by two different power law relationships with exponents of ∼9 (group I) and ∼3 (group II). Microstructural analyses reveal that the difference in the two permeability-porosity relationships reflects different mineral precipitation processes as pore space evolves within different parts of the vent structures, either with angular sulfide grains depositing as aggregates that block fluid paths very efficiently (group I), or by late stage amorphous silica that coats existing grains and reduces fluid paths more gradually (group II). The results suggest that quantification of permeability and porosity relationships leads to a better understanding of pore evolution processes. Correctly identifying permeability and porosity relationships is an important first step toward accurately estimating fluid distribution, flow rate, and environmental conditions within seafloor vent deposits, which has important consequences for chimney growth and biological communities that reside within and on vent structures.Support from the National Science Foundation under grants NSF OCE-9986456 (W.Z. and M.K.T.) and NSF OCE-0327488 (P.R.C.) is gratefully acknowledged. We also thank the WHOI summer student fellowship for providing support to H.G

Links from mantle to microbe at the Lau Integrated Study Site : insights from a back-arc spreading center

Author Posting. © The Oceanography Society, 2012. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 25, no. 1 (2012): 62–77, doi:10.5670/oceanog.2012.04.The Lau Integrated Study Site (ISS) has provided unique opportunities for study of ridge processes because of its back-arc setting in the southwestern Pacific. Its location allows study of a biogeographical province distinct from those of eastern Pacific and mid-Atlantic ridges, and crustal compositions along the ridge lie outside the range of mid-ocean ridge crustal compositions. The Lau ISS is located above a subduction zone, at an oblique angle. The underlying mantle receives water and other elements derived from the downgoing lithospheric slab, with an increase in slab influence from north to south. Water lowers the mantle melting temperature and leads to greater melt production where the water flux is greater, and to distinctive regional-scale gradients along the ridge. There are deeper faulted axial valleys with basaltic volcanism in the north and inflated axial highs with andesites in the south. Differences in igneous rock composition and release of magmatic volatiles affect compositions of vent fluids and deposits. Differences in vent fluid compositions and small-scale diffuse-flow regimes correlate with regional-scale patterns in microbial and megafaunal distributions. The interdisciplinary research effort at the Lau ISS has successfully identified linkages between subsurface processes and deep-sea biological communities, from mantle to microbe to megafauna.Support was provided by National Science Foundation grants OCE-1038135 to MKT, OCE-0732369 and OCE-0240985 to CRF, OCE-0732369 and OCE-0838107 to PRG, OCE-0242618 to CHL, OCE-0242902 and OCE-0752256 to PJM, OCE-0728391 and OCE-0937404 to A-LR, and a GRFP to RB

Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge

Forty-nine hydrothermal sulfide-sulfate rock samples from the Endeavour Segment of the Juan de Fuca Ridge, northeastern Pacific Ocean, were dated by measuring the decay of 226Ra (half-life of 1600 years) in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years. This dating method is effective for samples ranging in age from ∼200 to 20,000 years old and effectively bridges an age gap between shorter- and longer-lived U-series dating techniques for hydrothermal deposits. Results show that hydrothermal venting at the active High Rise, Sasquatch, and Main Endeavour fields began at least 850, 1450, and 2300 years ago, respectively. Barite ages of other inactive deposits on the axial valley floor are between ∼1200 and ∼2200 years old, indicating past widespread hydrothermal venting outside of the currently active vent fields. Samples from the half-graben on the eastern slope of the axial valley range in age from ∼1700 to ∼2925 years, and a single sample from outside the axial valley, near the westernmost valley fault scarp is ∼5850 ± 205 years old. The spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship, with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift. These relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years