Sulfide geochronlogy along the Southwest Indian Ridge

NASA Astrophysics Data System (ADS)

Yang, W.; Tao, C.; Li, H.; Liang, J.; Liao, S.

2017-12-01

Dragon Flag and Duanqiao hydrothermal field is located between the Indomed and Gallieni fracture zones in the ultraslow-spreading Southwest Indian Ridge (SWIR). Ten subsamples from active and inactive vents of Dragon Flag hydrothermal field and twenty-eight subsamples from Duanqiao hydrothermal field were dated using the 230Th/238U method. Four main episodes of hydrothermal activity of Duanqiao were determined according to the restricted results: 68.9-84.3, 43.9-48.4, 25.3-34.8, and 0.7-17.3 kyrs. Hydrothermal activity of Duanqiao probably started about 84.3 (±0.5) kyrs ago and ceased about 0.737 (±0.023) kyrs ago. And sulfide samples from the nearby Dragon Flag filed at the same time and the results show that the ages of most sulfides from Dragon Flag field range from 1.496(±0.176) to 5.416 (±0.116) kyrs with the oldest age estimated at 15.997 (±0.155) kyrs Münch et al. (2001) reconstructed the evolution history of Mt. Jourdanne hydrothermal field. The age dating results indicate activity in two episodes, at 70-40 and 27-13 kyrs. The hydrothermal activity in Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. The massive sulfides are younger than the sulfides from other hydrothermal fields such as Rainbow, Sonne and Ashadze-2. All these results suggest that hydrothermal activity of Dragon Flag field is much more recent than that of Duanqiao or Mt. Jourdanne fields. Mt. Jourdanne is situated on an axial volcanic ridge which has both volcanic and tectonic activity. This is necessary to develop the heat source and pathways for the fluid convection, which enables the hydrothermal circulation. Hydrothermal activity in Dragon Flag Field is located next to the detachment fault termination. The detachment fault system provides a pathway for hydrothermal convection. Such style of heat source can contribute to continuous hydrothermal activity for over 1000 years. Duanqiao field is located near the central volcano and there is a hot mantle and/or fertile melt beneath Duanqiao field. The crust thickness is 9.5 km, suggesting the existence of AMC (Axial Magma Chamber) which provides magma source to the field (Li et al. 2015; Mendel et al. 2003). The periodic hydrothermal activity at Duanqiao may be related to the heat source provided by the local interaction of magmatism and tectonism.

Distribution, structure and temporal variability of hydrothermal outflow at a slow-spreading hydrothermal field from seafloor image mosaics.

NASA Astrophysics Data System (ADS)

Barreyre, Thibaut; Escartin, Javier; Cannat, Mathilde; Garcia, Rafael; Science Party, Momar'08; Science Party, Bathyluck'09

2010-05-01

The Lucky Strike hydrothermal site, located South of the Azores along the Mid-Atlantic Ridge, is one of the largest and best-known active hydrothermal fields along the ridge system. This site within the MoMAR area is also the target for the installation in 2010 of a pilot deep-sea observatory with direct telemetry to land, to be part of the European Seafloor Observatory Network (ESONET). The Lucky Strike hydrothermal site has seen extensive high-resolution, near-bottom geophysical surveys in 1996 (Lustre'96), 2006 (Momareto06), 2008 (MOMAR08) and 2009 (Bathyluck09). Vertically acquired black-and-white electronic still camera images have been projected and georeferenced to obtain 3 image mosaics covering the zone of active venting, extending ~ 700x800 m2, and with full image resolution (~10 mm pixels). These data allow us to study how hydrothermal outflow is structured, including the relationships between the zones of active high-temperature venting, areas of diffuse outflow, and the geological structure (nature of the substrate, faults and fissures, sediments, etc.). Hydrothermal outflow is systematically associated with bacterial mats that are easily identified in the imagery, allowing us to study temporal variability at two different scales. Over the 13-year period we can potentially track changes in both the geometry and intensity of hydrothermal activity throughout the system; our preliminary study of the Eiffel Tower, White Castle and Mt Segur indicate that activity has been sustained in recent times, with small changes in the detailed geometry of the diffuse outflow and its intensity. At longer times scales (hundreds to 1000 years?) imagery also shows evidence of areas of venting that are no longer active, often associated with the active structures. In combination with the high-resolution bathymetry, the imagery data thus allow us to characterize the shallow structure of hydrothermal outflow at depth, the structural and volcanic control, and ultimately quantify the heat flux associates with this hydrothermal outflow. Image mosaics are also key for the installation of instrumentation required by temporal studies, and for the infrastructure of the ESONET pilot seafloor observatory. This type of survey techniques and studies can also be extended to other areas of interest, such as hydrothermal fields, cold seeps, etc.

Vein networks in hydrothermal systems provide constraints for the monitoring of active volcanoes.

PubMed

Cucci, Luigi; Di Luccio, Francesca; Esposito, Alessandra; Ventura, Guido

2017-03-10

Vein networks affect the hydrothermal systems of many volcanoes, and variations in their arrangement may precede hydrothermal and volcanic eruptions. However, the long-term evolution of vein networks is often unknown because data are lacking. We analyze two gypsum-filled vein networks affecting the hydrothermal field of the active Lipari volcanic Island (Italy) to reconstruct the dynamics of the hydrothermal processes. The older network (E1) consists of sub-vertical, N-S striking veins; the younger network (E2) consists of veins without a preferred strike and dip. E2 veins have larger aperture/length, fracture density, dilatancy, and finite extension than E1. The fluid overpressure of E2 is larger than that of E1 veins, whereas the hydraulic conductance is lower. The larger number of fracture intersections in E2 slows down the fluid movement, and favors fluid interference effects and pressurization. Depths of the E1 and E2 hydrothermal sources are 0.8 km and 4.6 km, respectively. The decrease in the fluid flux, depth of the hydrothermal source, and the pressurization increase in E2 are likely associated to a magma reservoir. The decrease of fluid discharge in hydrothermal fields may reflect pressurization at depth potentially preceding hydrothermal explosions. This has significant implications for the long-term monitoring strategy of volcanoes.

Fluid circulation and structural system of Cerritos Colorados geothermal field in La Primavera volcanic caldera (Mexico) inferred from geophysical surveys

NASA Astrophysics Data System (ADS)

Bolós, X.; Cifuentes-Nava, G.; Macias, J. L.; Sosa-Ceballos, G.; García-Tenorio, F.; Albor, M., III; Juarez, M.; Gamez, V.

2017-12-01

Hydrothermal activity in volcanic calderas is the consequence of energy transfer between deep magmatic chambers and subsurface layers saturated in water. This hydrothermal system is generated by convection of the groundwater supplied by meteoric water recharged and the ascent of hot volcanic gasses exsolved from deep magma reservoirs. Calderas are heterogeneous geological structures that due to their formation and evolution produced a complex stratigraphy. All of these heterogeneities can be affected by deformation and also by the presence of fractures and faults which constitute the main pathways whereby hydrothermal fluids can move easily through the surface as spring discharges and fumarolic activity. Geophysical methods have been used in the last decades to investigate the relationship between structural geology and hydrothermal systems in different volcanic areas around the world. In this work, we have focused on the role of subsurface structures to understand and localize the pathways of fluids related to the hydrothermal system of the Cerritos Colorados geothermal field. We focused in the central area of the caldera (P12 well and Cerritos Colorados graben), where active hydrothermal activity is evidenced by fumaroles, thermal anomalies, CO2 diffuse emission, and sulfur precipitation. We have applied a self-potential method (SP) that combined with temperature measurements that allowed to identify the main infiltration and ascending fluid zones in the area, and their specific surface temperature coinciding with fumarolic activity. From this data we an applied Electrical Resistivity Tomography (ERT) survey in two selected places. One ERT profile (1.2 km in length) was located in the P12 well area. A 3D resistivity model used with the equatorial method was carried out on the Cerritos Colorados graben area. Combining the results of the SP, TºC, and ERT data with a detailed structural map we identified the main degassing zones (i.e. fumaroles) that correspond to higher permeability zones located along normal and strike-slip faults. In conclusion, a strong structural control of the surface manifestation of these hydrothermal systems is deduced from our new data. Then, our results emphasize the importance of old structural boundaries that are controlled by intra-caldera tectonic structures.

Geologic and hydrologic controls on the economic potential of hydrothermal systems associated with upper crustal plutons

NASA Astrophysics Data System (ADS)

Weis, Philipp; Driesner, Thomas; Scott, Samuel; Lecumberri-Sanchez, Pilar

2016-04-01

Heat and mass transport in hydrothermal systems associated with upper crustal magmatic intrusions can result in resources with large economic potential (Kesler, 1994). Active hydrothermal systems can form high-enthalpy geothermal reservoirs with the possibility for renewable energy production. Fossil continental or submarine hydrothermal systems may have formed ore deposits at variable crustal depths, which can be mined near today's surface with an economic profit. In both cases, only the right combination of first-order geologic and hydrologic controls may lead to the formation of a significant resource. To foster exploration for these hydrothermal georesources, we need to improve our understanding of subsurface fluxes of mass and energy by combining numerical process modelling, observations at both active and fossil systems, as well as knowledge of fluid and rock properties and their interactions in natural systems. The presentation will highlight the role of non-linear fluid properties, phase separation, salt precipitation, fluid mixing, permeability structure, hydraulic fracturing and the transition from brittle to ductile rock behavior as major geologic and hydrologic controls on the formation of high-enthalpy and supercritical geothermal resources (Scott et al., 2015), and magmatic-hydrothermal mineral resources, such as porphyry copper, massive sulfide and epithermal gold deposits (Lecumberri-Sanchez et al., 2015; Weis, 2015). References: Kesler, S. E., 1994: Mineral Resources, economics and the environment, New York, McMillan, 391. Lecumberri-Sanchez, P., Steele-MacInnis, M., Weis, P., Driesner, T., Bodnar, R.J. (2015): Salt precipitation in magmatic-hydrothermal systems associated with upper crustal plutons. Geology, v. 43, p. 1063-1066, doi:10.1130/G37163.1 Scott, S., Driesner, T., Weis, P. (2015): Geologic controls on supercritical geothermal resources above magmatic intrusions. Nature Communications, 6:7837 doi: 10.1038/ncomms8837 Weis, P. (2015): The dynamic interplay between saline fluid flow and rock permeability in magmatic-hydrothermal systems. Geofluids, 15, 350-371.

The North Tanganyika hydrothermal fields, East African Rift system: Their tectonic control and relationship to volcanism and rift segmentation

NASA Astrophysics Data System (ADS)

Coussement, C.; Gente, P.; Rolet, J.; Tiercelin, J.-J.; Wafula, M.; Buku, S.

1994-10-01

The two branches of the East African Rift system include numerous hydrothermal fields, which are closely related to the present fault motion and to volcanic and seismic activity. In this study structural data from Pemba and Cape Banza hydrothermal fields (western branch, North Tanganyika, Zaire) are discussed in terms of neotectonic phenomena. Different types of records, such as fieldwork (onshore and underwater) and LANDSAT and SPOT imagery, are used to explain structural controls on active and fossil hydrothermal systems and their significance. The Pemba site is located at the intersection of 000-020°-trending normal faults belonging to the Uvira Border Fault System and a 120-130°-trending transtensional fault zone and is an area of high seismicity, with events of relatively large magnitude ( Ms < 6.5). The Cape Banza site occurs at the northern end of the Ubawari Peninsula horst. It is bounded by two fault systems trending 015° and is characterized seismically by events of small magnitude ( Ms < 4). The hydrothermal area itself is tectonically controlled by structures striking 170-180° and 080°. The analysis of both hydrothermal areas demonstrates the rejuvenation of older Proterozoic structures during Recent rift faulting and the location of the hydrothermal activity at the junctions of submeridian and transverse faults. The fault motion is compatible with a regional direction of extension of 090-110°. The Cape Banza and Pemba hydrothermal fields may testify to magma chambers existing below the junctions of the faults. They appear to form at structural nodes and may represent a future volcanic province. Together with the four surface volcanic provinces existing along the western branch, they possibly indicate an incipient rift segmentation related to 'valley-valley' or 'transverse fault-valley' junctions, contrasting with the spacing of the volcanoes measured in the eastern branch. These spacings appear to express the different elastic thicknesses between the eastern and western branches of the East African Rift system, perhaps related to a difference in stage of evolution of the two branches.

Ultramafics-Hydrothermalism-Hydrogenesis-HyperSLiME (UltraH3) Linkage is a key for Occurrence of Last Universal Common Ancestral (LUCA) Community: Where is it, Lost City or Kairei (Rainbow)?

NASA Astrophysics Data System (ADS)

Takai, K.; Inagaki, F.; Nakamura, K.; Suzuki, K.; Kumagai, H.

2005-12-01

Deep-sea hydrothermal system has been recognized one of the most plausible places for origin of life in this planet. This hypothesis has been supported by evidences from multidisciplinary scientific fields. In geology, it has been demonstrated that the potentially most ancient microbial fossils are retrieved from the paleoenvironment, that might be related with deep-sea hydrothermal systems in the Archean. Chemical reactions suggesting prebiotic chemical evolution (synthesis of amino acids, nucleic acids and hydrocarbon, and polymerization of these molecules) are observed under the simulated physical and chemical conditions of the deep-sea hydrothermal vents in the laboratory. In addition, phylogenetic analyses of all the lives in this planet have clearly revealed that hyperthermophiles inhabiting deep-sea hydrothermal systems represent the deepest lineage of the life. Supposed that the Archean deep-sea hydrothermal system hosted the origin of life, what was the first life? We are pursuing the energy metabolism of our last universal common ancestor (LUCA) and the environmental settings hosting the LUCA. It is definitely expected that the genesis of LUCA occurred at high temperatures of locally organics-rich microenvironment around deep-sea hydrothermal field and the first energy metabolism depended on fermentation of simple amino acids, organic acids and sugars. However, these organics were immediately consumed by the hyperthermophilic LUCA activity. Inheritance of the LUCA needed to evolve the energy and carbon acquisitions to more stable and efficient mode. Chemolithoautotrophy might be the best because a plenty of reductive gas components were always provided by the hydrothermal activity. Hyperthermophilic chemolithoautotrophs could serve as the primary producers and could foster the heterotrophic fellows. This was the genesis of the last universal common ancestral (LUCA) community of life. We hypothesize that the LUCA community was metabolically approximated to hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) currently discovered beneath the Central Indian Ridge hydrothermal field. The environmental settings for the occurrence of HyperSLiME are now being characterized and an important linkage among the occurrence of HyperSLiME, extraordinary amount of hydrogen in the hydrothermal fluids and ultramfics-hosted hydrothermal systems is proposed. This ultramafics-hydrothermalism-hydrogen-HyperSLiME (UltraH3) linkage is very likely a key for the genesis of the LUCA community. We would like to discuss the possible UltraH3 linkage in the Archean earth. In addition, we would like to discuss which of modern deep-sea hydrothermal systems is the most plausible proxy for the Archean LUCA habitats.

Anatomy of Old Faithful From Subsurface Seismic Imaging of the Yellowstone Upper Geyser Basin

NASA Astrophysics Data System (ADS)

Wu, Sin-Mei; Ward, Kevin M.; Farrell, Jamie; Lin, Fan-Chi; Karplus, Marianne; Smith, Robert B.

2017-10-01

The Upper Geyser Basin in Yellowstone National Park contains one of the highest concentrations of hydrothermal features on Earth including the iconic Old Faithful geyser. Although this system has been the focus of many geological, geochemical, and geophysical studies for decades, the shallow (<200 m) subsurface structure remains poorly characterized. To investigate the detailed subsurface geologic structure including the hydrothermal plumbing of the Upper Geyser Basin, we deployed an array of densely spaced three-component nodal seismographs in November of 2015. In this study, we extract Rayleigh wave seismic signals between 1 and 10 Hz utilizing nondiffusive seismic waves excited by nearby active hydrothermal features with the following results: (1) imaging the shallow subsurface structure by utilizing stationary hydrothermal activity as a seismic source, (2) characterizing how local geologic conditions control the formation and location of the Old Faithful hydrothermal system, and (3) resolving a relatively shallow (10-60 m) and large reservoir located 100 m southwest of Old Faithful geyser.

Tide-related variability of TAG hydrothermal activity observed by deep-sea monitoring system and OBSH

NASA Astrophysics Data System (ADS)

Fujioka, Kantaro; Kobayashi, Kazuo; Kato, Kazuhiro; Aoki, Misumi; Mitsuzawa, Kyohiko; Kinoshita, Masataka; Nishizawa, Azusa

1997-12-01

Hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone (OBSH) and a composite measuring system (Manatee) including CTD, current meter, transmission meter and cameras at a small depression on the TAG hydrothermal mound in the Mid-Atlantic Ridge. Low-frequency pressure pulses detected by the hydrophone with semi-diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short-lived smoker vent close to the observing site. The peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release. Microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting. Temporal variations in bottom water temperature also have semi-diurnal periodicity but are more complicated than the pressure events. Temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide.

Study of hydrothermal channels based on near-bottom magnetic prospecting: Application to Longqi hydrothermal area

NASA Astrophysics Data System (ADS)

Tao, W.; Tao, C.; Li, H.; Zhaocai, W.; Jinhui, Z.; Qinzhu, C.; Shili, L.

2014-12-01

Mid-ocean ridges, largely present far from the continental plates, are characterized by complex geological structures and numerous hydrothermal systems with complex controlling factors. Exploring seafloor sulfide resources for industrial and scientific applications is a challenge. With the advent of geophysical surveys for seabed investigation, near-bottom magnetic prospecting, which yields shallow geological structure, is an efficient method for investigating active and inactive hydrothermal fields and for researching the structure of hydrothermal systems (Tivey et al., 1993, 1996；German et al., 2008). We collected near-bottom magnetic data in the Longqi hydrothermal area, located in the southwest Indian ridge (49.6° E; Zhu et al., 2010; Tao et al., 2014), using the autonomous benthic explorer, an autonomous underwater vehicle, during the second leg of the Chinese cruise DY115-19 on board R/V DaYangYiHao. Based on the results of the intensity of the spatial differential vector method (Seaman et al., 1993), we outline the hydrothermal alternation zone. By building models, we subsequently infer a fault along the discovered hydrothermal vents; this fault line may be connected to a detachment fault (Zhao et al., 2013). In addition, we discuss the channels of the hydrothermal circulation system (Figure 1), and presume that heat was conducted to the sea subsurface by the detachment fault; the aqueous fluid that infiltrated the fault is heated and conveyed to the seafloor, promoting the circulation of the hydrothermal system.

Simulating Electrochemistry of Hydrothermal Vents on Enceladus and Other Ocean Worlds

NASA Astrophysics Data System (ADS)

Barge, L. M.; Krause, F. C.; Jones, J. P.; Billings, K.; Sobron, P.

2017-12-01

Gradients generated in hydrothermal systems provide a significant source of free energy for chemosynthetic life, and may play a role in present-day habitability on ocean worlds such as Enceladus that are thought to host hydrothermal activity. Hydrothermal vents are similar in some ways to typical fuel cell devices: redox/pH gradients between seawater and hydrothermal fluid are analogous to the oxidant and fuel reservoirs; conductive natural mineral deposits are analogous to electrodes; and, in hydrothermal chimneys, the porous chimney wall can function as a separator or ion-exchange membrane. Electrochemistry, founded on quantitative study of redox and other chemical disequilibria as well as the chemistry of interfaces, is uniquely suited to studying these systems. We have performed electrochemical studies to better understand the catalytic potential of seafloor minerals and vent chimneys, using samples from a black smoker vent chimney as an initial demonstration. Fuel cell experiments with electrodes made from black smoker chimney material accurately simulated the redox reactions that occur in a geological setting with this particular catalyst. Similar methods with other geo-catalysts (natural or synthetic) could be utilized to test which redox reactions or metabolisms could be driven in other hydrothermal systems, including putative vent systems on other worlds.

Hydrothermal Venting at Hinepuia Submarine Volcano, Kermadec Arc: Understanding Magmatic-Hydrothermal Fluid Chemistry

NASA Astrophysics Data System (ADS)

Stucker, Valerie K.; Walker, Sharon L.; de Ronde, Cornel E. J.; Caratori Tontini, Fabio; Tsuchida, Shinji

2017-10-01

The Hinepuia volcanic center is made up of two distinct edifices aligned northwest to southeast, with an active cone complex in the SE. Hinepuia is one of several active volcanoes in the northern segment of the Kermadec arc. Regional magnetic data show no evidence for large-scale hydrothermal alteration at Hinepuia, yet plume data confirm present-day hydrothermal discharge, suggesting that the hydrothermal system may be too young to have altered the host rocks with respect to measurable changes in magnetic signal. Gravity data are consistent with crustal thinning and shallow mantle under the volcanic center. Following the discovery of hydrothermal plumes over Hinepuia, the submersible Shinkai 6500 was used to explore the SE cone and sample hydrothermal fluids. The chemistry of hydrothermal fluids from submarine arc and backarc volcanoes is typically dominated by water-rock interactions and/or magmatic degassing. Chemical analyses of vent fluids show that Hinepuia does not quite fit either traditional model. Moreover, the Hinepuia samples fall between those typically ascribed to both end-member fluid types when plotted on a K-Mg-SO4 ternary diagram. Due to evidence of strong degassing, abundant native sulfur deposition, and H2S presence, the vent sampled at Hinepuia is ultimately classified as a magmatic-hydrothermal system with a water-rock influence. This vent is releasing water vapor and magmatic volatiles with a notable lack of salinity due to subcritical boiling and phase separation. Magmatic-hydrothermal fluid chemistry appears to be controlled by a combination of gas flux, phase separation processes, and volcano evolution and/or distance from the magma source.

Radon surveys and monitoring at active volcanoes: an open window on deep hydrothermal systems and their dynamics

NASA Astrophysics Data System (ADS)

Cigolini, Corrado; Laiolo, Marco; Coppola, Diego

2017-04-01

The behavior of fluids in hydrothermal systems is critical in volcano monitoring and geothermal prospecting. Analyzing the time series of radon emissions on active volcanoes is strategic for detecting and interpreting precursory signals of changes in volcanic activity, eventually leading to eruptions. Radon is a radioactive gas generated from the decay of U bearing rocks, soils and magmas. Although radon has been regarded as a potential precursor of earthquakes, radon anomalies appear to be better suited to forecast volcanic eruptions since we know where paroxysms may occur and we can follow the evolution of volcanic activity. Radon mapping at active volcanoes is also a reliable tool to assess diffuse and concentrated degassing as well as efficiently detecting earthquake-volcano interactions. Systematic radon monitoring has been shown to be a key factor for evaluating the rise of volcanic and hydrothermal fluids. In fact, the decay properties of radon, the duration of radon anomalies together with sampling rates may be cross-checked with the chemistry of hydrothermal fluids (and their transport properties) to constrain fluids ascent rates and to infer the permeability and porosity of rocks in sectors surrounding the active conduits. We hereby further discuss the data of radon surveys and monitoring at Somma-Vesuvius, Stromboli and La Soufrière (Guadeloupe, Lesser Antilles). The integrated analysis of seismic and geochemical data, including radon emissions, may be successfully used in testing temperature distributions and variations of porosity and permeability in volcanic hydrothermal systems and can be used as a proxy to analyze geothermal reservoirs.

On the Interaction of a Vigorous Hydrothermal System with an Active Magma Chamber: The Puna Magma Chamber, Kilauea East Rift, Hawaii

NASA Astrophysics Data System (ADS)

Gregory, R. T.; Marsh, B. D.; Teplow, W.; Fournelle, J.

2009-12-01

The extent of the interaction between hydrothermal systems and active magma chambers has long been of fundamental interest to the development of ore deposits, cooling of magma chambers, and dehydration of the subducting lithosphere. As volatiles build up in the residual magma in the trailing edge of magmatic solidification fronts, is it possible that volatiles are transferred from the active magma to the hydrothermal system and vice versa? Does the external fracture front associated with vigorous hydrothermal systems sometimes propagate into the solidification front, facilitating volatile exchange? Or is the magma always sealed at temperatures above some critical level related to rock strength and overpressure? The degree of hydrothermal interaction in igneous systems is generally gauged in post mortem studies of δ18O and δD, where it has been assumed that a fracture front develops about the magma collapsing inward with cooling. H.P. Taylor and D. Norton's (1979; J. Petrol.)seminal work inferred that rocks are sealed with approach to the solidus and there is little to no direct interaction with external volatiles in the active magma. In active lava lakes a fracture front develops in response to thermal contraction of the newly formed rock once the temperature drops to ~950°C (Peck and Kinoshita,1976;USGS PP935A); rainfall driven hydrothermal systems flash to steam near the 100 °C isotherm in the solidified lake and have little effect on the cooling history (Peck et al., 1977; AJS). Lava lakes are fully degassed magmas and until the recent discovery of the Puna Magma Chamber (Teplow et al., 2008; AGU) no active magma was known at sufficiently great pressure to contain original volatiles. During the course of routine drilling of an injection well at the Puna Geothermal Venture (PGV) well-field, Big Island, Hawaii, a 75-meter interval of diorite containing brown glass inclusions was penetrated at a depth of 2415 m, continued drilling to 2488 m encountered a melt of dacitic composition of ~67 wt.% SiO2. The melt flowed up the borehole, quenched, and was repeatedly re-drilled over a depth interval of ~8 m, producing several kilograms of clear, colorless vitric cuttings. The melt is of low crystallinity, vesicle-free, at a minimum temperature of ~865°C, and with an apparent viscosity of ~106.5 Pa-s. The magma is separated from the deepest hydrothermal regime at 356°C by 526 m of sealed rock. Heat flux from the magma into the overlying geothermal reservoir at ~2784 mW/m2 is an order of magnitude greater than that for mid-ocean ridges. Typical Hawaiian basalt contains ~0.25 wt.% water. The dacite melt contains ~2.44 wt.% water, and is of normal magmatic δ18O (5.4 ‰) and δD (-61.8‰), which is in contrast to the surrounding hydrothermal waters. A similar preliminary analysis of the water content in the altered basalt just outside the sealed zone shows it to heavily hydrated (~4.94 wt.%) and altered by the hydrothermal field. This suggests that volatile under-saturated magmas are sealed with respect to hydrothermal fields and deeper systems may be even more strongly sealed.

Asymmetrical hydrothermal system below Merapi volcano imaged by geophysical data.

NASA Astrophysics Data System (ADS)

Byrdina, Svetlana; Friedel, Sven; Budi-Santoso, Agus; Suryanto, Wiwit; Suhari, Aldjarishy; Vandemeulebrouck, Jean; Rizal, Mohhamed H.; Grandis, Hendra

2017-04-01

A high-resolution image of the hydrothermal system of Merapi volcano is obtained using electrical resistivity tomography (ERT), self-potential, and CO2 flux mappings. The ERT inversions identify two distinct low-resistivity bodies, at the base of the south flank and in the summit area, that represent likely two parts of an interconnected hydrothermal system. In the summit area, the extension of the hydrothermal system is clearly limited by the main geological structures which are actual and ancient craters. A sharp resistivity contrast at ancient crater rim Pasar-Bubar separates a conductive hydrothermal system (20 - 50 Ωm) from the resistive andesite lava flows and pyroclastic deposits (2000 - 50 000 Ωm). High diffuse CO2 degassing (with a median value of 400g m -2 d -1) is observed in a narrow vicinity of the active crater rim and close to the Pasar-Bubar. The existence of preferential fluid circulation along this ancient crater rim is also evidenced by self-potential data. The total CO2 degassing across the accessible summit area with a surface of 1.4 · 10 5 m 2 is around 20 td -1. Before the 2010 eruption, Toutain et al. (2009) estimated a higher value of the total diffuse degassing from the summit area (about 200 - 230 td -1). This drop in the diffuse degassing can be related to the decrease in the magmatic activity, to the change of the summit morphology or to a combination of these factors. On the south flank of Merapi, the resistivity model shows spectacular stratification. While surficial recent andesite lava flows are characterized by resistivity exceeding 100 000 Ωm, resistivity as low as 10 Ωm has been encountered at a depth of 200 m at the base of the south flank and was interpreted as a presence of the hydrothermal system. We suggest that a sandwich-like structure of stratified pyroclastic deposits on the flanks of Merapi screen and separate the flow of hydrothermal fluids with the degassing occurring mostly through the fractured crater rims, while the liquid water flows down to the base of the volcanic dome. Our ERT results suggest the existence of a peripheral hydrothermal system below the south and west flanks in agreement with previous electromagnetic studies. In contrast, no evidence of hydrothermal system is found below the north flank, where the resistivity values are too high to be assigned to a hydrothermal system, at least to the ERT investigation depth. A probable cause of this asymmetry could be a non-axial location of the magmatic heat source. Such non-axial location of the magmatic source relative to the edifice is suggested by the shift of the volcanic activity to the south as proposed in the geological model by Camus et al, (2000). In addition, the hypocenters of seismic events located by Budi-Santoso et al, (2013) seem to be distributed to the SW from the active crater suggesting that the magma conduits and likely, the magmatic source, are shifted to the SW with respect to the actual crater.

Origin of Abiotic Methane in Submarine Hydrothermal Systems

NASA Astrophysics Data System (ADS)

Seewald, J. S.; German, C. R.; Grozeva, N. G.; Klein, F.; McDermott, J. M.; Ono, S.; Reeves, E. P.; Wang, D. T.

2018-05-01

Results of recent investigations into the chemical and isotopic composition of actively venting submarine hydrothermal fluids and volatile species trapped in fluid inclusions will be discussed in the context of processes responsible for abiotic CH4 formation.

Explosive Deep Sea Volcanism Produces Composite Volcanoes (Stratocones) with Predominantly Diffuse Flow Hydrothermal Ecosystems

NASA Astrophysics Data System (ADS)

Rubin, K. H.; Chadwick, W. C.; Embley, R. W.; Butterfield, D. A.

2018-05-01

Newly-discovered extensive explosive deep sea volcanism produces distinct stratovolcano structures and physical rock characteristics, and host primarily diffuse flow hydrothermal activity, unlike focused flow systems at effusive submarine volcanoes.

Hydrothermal systems in small ocean planets.

PubMed

Vance, Steve; Harnmeijer, Jelte; Kimura, Jun; Hussmann, Hauke; Demartin, Brian; Brown, J Michael

2007-12-01

We examine means for driving hydrothermal activity in extraterrestrial oceans on planets and satellites of less than one Earth mass, with implications for sustaining a low level of biological activity over geological timescales. Assuming ocean planets have olivine-dominated lithospheres, a model for cooling-induced thermal cracking shows how variation in planet size and internal thermal energy may drive variation in the dominant type of hydrothermal system-for example, high or low temperature system or chemically driven system. As radiogenic heating diminishes over time, progressive exposure of new rock continues to the current epoch. Where fluid-rock interactions propagate slowly into a deep brittle layer, thermal energy from serpentinization may be the primary cause of hydrothermal activity in small ocean planets. We show that the time-varying hydrostatic head of a tidally forced ice shell may drive hydrothermal fluid flow through the seafloor, which can generate moderate but potentially important heat through viscous interaction with the matrix of porous seafloor rock. Considering all presently known potential ocean planets-Mars, a number of icy satellites, Pluto, and other trans-neptunian objects-and applying Earth-like material properties and cooling rates, we find depths of circulation are more than an order of magnitude greater than in Earth. In Europa and Enceladus, tidal flexing may drive hydrothermal circulation and, in Europa, may generate heat on the same order as present-day radiogenic heat flux at Earth's surface. In all objects, progressive serpentinization generates heat on a globally averaged basis at a fraction of a percent of present-day radiogenic heating and hydrogen is produced at rates between 10(9) and 10(10) molecules cm(2) s(1).

A large hydrothermal reservoir beneath Taal Volcano (Philippines) revealed by magnetotelluric resistivity survey: 2D resistivity modeling

NASA Astrophysics Data System (ADS)

Yamaya, Y.; Alanis, P. K. B.; Takeuchi, A.; Cordon, J. M.; Mogi, T.; Hashimoto, T.; Sasai, Y.; Nagao, T.

2013-07-01

Taal Volcano, located in the southwestern part of Luzon Island, Philippines, has frequently experienced catastrophic eruptions from both the Main Crater on Volcano Island and flank eruptions. These eruptions have been magmatic, phreatomagmatic, and hydrothermal, with the latter implying the existence of a large-scale hydrothermal system beneath the volcano. We conducted an electrical resistivity survey using the magnetotelluric method in order to identify the location and geometry of the hydrothermal reservoir and sealing cap rock. Two-dimensional inversion using the observed data indicates four similar resistivity sections. The structure at shallow depths corresponds to volcanic deposits and an aquifer. Below 1 km, the structure features a relatively resistive zone beneath the main crater surrounded by a conductive shell. We interpreted these to be a large hydrothermal reservoir with an impermeable cap rock sealing it. Recent ground deformation detected by GPS measurements suggests that the hydrothermal reservoir is active. The interpreted cap rock thins just beneath the main crater and could easily be destroyed by an imbalance in the hydrothermal system. We conclude that this hydrothermal reservoir plays a significant role in driving catastrophic eruptions that begin with a hydrothermal explosion at the main crater.

Understanding the eruption mechanisms of the explosive Bellecombe Eruptions on Piton de la Fournaise, La Réunion

NASA Astrophysics Data System (ADS)

Morgan, K.; Ort, M. H.; Di Muro, A.; Parnell, R. A.; Huff, W. D.

2017-12-01

Piton de la Fournaise (PdF) is an active basaltic volcano on La Réunion island. The Bellecombe Tephra was deposited from at least three unusually explosive eruptions between 3000-5000 ka. The Bellecombe eruptions were interpreted recently to have been due to rapid depressurization of the hydrothermal system when a deep fracture opened after lateral, seaward-directed sliding of the eastern flank, late in a large effusive eruption. This project tests this hypothesis by physically, mineralogically, and chemically characterizing the Bellecombe Tephra to look for evidence of the involvement of the PdF hydrothermal system in the eruptions and understand where the eruptions initiated. The Bellecombe tephra consists of three units separated by incipient soils. Both the Upper and Lower Bellecombe deposits are mostly medium to very fine ash. Lower Bellecombe deposits, from the first two eruptions, are mostly beds of glassy ash containing minor lithic grains and olivine crystals. Hydrothermal minerals, mostly smectite, are present in a few Lower Bellecombe beds. Since these minerals are only present in some beds, the smectite formed before deposition rather than as a product of surficial alteration. The Upper Bellecombe deposits record a third eruption and vary between clast-supported crystal- and lithic-rich lapilli beds and ash beds with abundant ash pellets. The crystals are mostly olivine, with lesser pyroxene and plagioclase and sparse hydrothermal quartz. Gabbro and oceanite clasts are abundant and trachytic pumice rare in these deposits. Hydrothermal minerals are common in most Upper Bellecombe beds. The presence of smectite in some of the Lower Bellecombe beds suggests these deposits came from a system below 200 ºC. Clays in the Upper Bellecombe beds - smectite and mixed layer R0 illite/smectite - imply a system at 40-140 ºC. The hydrothermal system was involved, but might not have been the primary impetus for these eruptions, since hydrothermal minerals are not present in all of the beds, but we find no evidence of high temperatures. The lower Bellecombe vent was near the active summit whereas the Upper Bellecombe vent was from a previously more active area, and this may be reflected in the temperatures of the hydrothermal system. The abundant olivine crystals confirm a relation to a large effusive oceanite eruption.

Structure and evolution of an active resurgent dome evidenced by geophysical investigations: The Yenkahe dome-Yasur volcano system (Siwi caldera, Vanuatu)

NASA Astrophysics Data System (ADS)

Brothelande, E.; Lénat, J.-F.; Chaput, M.; Gailler, L.; Finizola, A.; Dumont, S.; Peltier, A.; Bachèlery, P.; Barde-Cabusson, S.; Byrdina, S.; Menny, P.; Colonge, J.; Douillet, G. A.; Letort, J.; Letourneur, L.; Merle, O.; Di Gangi, F.; Nakedau, D.; Garaebiti, E.

2016-08-01

In this contribution, we focus on one of the most active resurgences on Earth, that of the Yenkahe dome in the Siwi caldera (Tanna Island, Vanuatu), which is associated with the persistently active Yasur volcano. Gravity and magnetic surveys have been carried out over the past few years in the area, as well as electrical methods including electrical resistivity tomography (ERT), time domain electro-magnetics (TDEM) and self-potential (SP). These investigations were completed by thermometry, CO2 soil gas measurements, field observations and sampling. This multi-method approach allows geological structures within the caldera to be identified, as well as associated hydrothermal features. The global structure of the caldera is deduced from gravity data, which shows the caldera rim as a high density structure. Large lava fields, emplaced before and after the onset of resurgence, are evidenced by combined gravity, magnetic and resistivity signals. In the middle of the caldera, the Yenkahe dome apparently results from a combination of volcanic and tectonic events, showing that lava extrusion and resurgence have been operating simultaneously or alternately during the Siwi caldera post-collapse history. There is a clear distinction between the western and eastern parts of the dome. The western part is older and records the growth of an initial volcanic cone and the formation of a small caldera. This small caldera (paleo-Yasur caldera), partially filled with lava flows, is the present-day focus of volcanic activity and associated fluid circulation and alteration. The eastern part of the dome is presumably younger, and is characterized by intense, extensive hydrothermal alteration and activity. Its northern part is covered by lava flow piles and exhibits a shallow hydrothermal zone in ERT. The southern part has hydrothermal alteration and activity extending at least down to the base of the resurgent dome. This part of the dome is built up of low cohesion rock and is thus potentially prone to gravitational landslides. Lastly, while self-potential and temperature data suggest that widespread hydrothermal circulation occurs throughout almost all of the caldera, and possibly beyond, the most active parts of this hydrothermal system are associated with the dome. The presence of this active hydrothermal system is the clearest indicator that these methods can provide of a potential shallow magmatic body underneath the dome.

Magma-Hydrothermal Transition: Basalt Alteration at Supercritical Conditions in Drill Core from Reykjanes, Iceland, Iceland Deep Drilling Project.

NASA Astrophysics Data System (ADS)

Zierenberg, R. A.; Fowler, A. P.; Schiffman, P.; Fridleifsson, G. Ó.; Elders, W. A.

2017-12-01

The Iceland Deep Drilling Project well IDDP-2, drilled to 4,659 m in the Reykjanes geothermal system, the on-land extension of the Mid Atlantic Ridge, SW Iceland. Drill core was recovered, for the first time, from a seawater-recharged, basalt-hosted hydrothermal system at supercritical conditions. The well has not yet been allowed to heat to in situ conditions, but temperature and pressure of 426º C and 340 bar was measured at 4500 m depth prior to the final coring runs. Spot drill cores were recovered between drilling depths of 3648.00 m and 4657.58 m. Analysis of the core is on-going, but we present the following initial observations. The cored material comes from a basaltic sheeted dike complex in the brittle-ductile transition zone. Felsic (plagiogranite) segregation veins are present in minor amounts in dikes recovered below 4300 m. Most core is pervasively altered to hornblende + plagioclase, but shows only minor changes in major and minor element composition. The deepest samples record the transition from the magmatic regime to the presently active hydrothermal system. Diabase near dike margins has been locally recrystallized to granoblastic-textured orthopyroxene-clinopyroxe-plagioclase hornfels. High temperature hydrothermal alteration includes calcic plagioclase (up to An100) and aluminous hornblende (up to 11 Wt. % Al2O3) locally intergrown with hydrothermal biotite, clinopyroxene, orthopyroxene and/or olivine. Hydrothermal olivine is iron-rich (Mg # 59-64) compared to expected values for igneous olivine. Biotite phenocrysts in felsic segregation veins have higher Cl and Fe compared to hydrothermal biotites. Orthopyroxene-clinopyroxene pairs in partially altered quench dike margins give temperature of 955° to 1067° C. Orthopyroxene-clinopyroxene pairs from hornfels and hydrothermal veins and replacements give temperature ranging from 774° to 888° C. Downhole fluid sampling is planned following thermal equilibration of the drill hole. Previous work has suggested that the Reykjanes geothermal system has been active since the last glaciation, 10ka. No shallow melt bodies have been detected on the Reykjanes Peninsula suggesting that hydrothermal circulation typical of black smoker systems can be sustained with out a magmatic heat source.

Mathematical Models of Seafloor Hydrothermal Systems Driven by Serpentinization of Peridotite

NASA Astrophysics Data System (ADS)

Lowell, R. P.; Rona, P. A.; Germanovich, L. N.

2001-12-01

Most seafloor hydrothermal systems are driven by heat transfer from subsurface magma bodies. At slow spreading ridges of the Atlantic and Indian oceans, however, magma supply is low; and tectonic activity brings mantle rocks to shallow depths in the crust. Then, the heat of formation released upon serpentinization of peridotite provides the energy source for hydrothermal circulation. This latter class of system has been relatively unstudied, but recent discoveries of peridotite-hosted hydrothermal systems along the Mid-Atlantic Ridge suggest that such systems may play an important role in geochemical cycling and biogeochemical processes. The likelihood that peridotite-hosted hydrothermal systems was more prevalent during the Archean further suggests that such systems may have played a role in the origin of life. We present the first mathematical models of seafloor hydrothermal systems driven by heat released upon serpentinization of peridotite. We assume seawater circulates through a major crack network in the host-peridotite and that cooling of the host-rock leads to the formation of microcracks through which the fluid infiltrates. Reaction of the fluid in microcracks with the host rock results in serpentinization and the heat released upon serpentinization is transported to the seafloor by the fluid circulating in the main crack network. The temperature and heat output of the resulting hydrothermal system is a function of the main network permeability and the rate at which the serpentinization reaction proceeds via diffusion and propagation of the microcracks. Although the temperature of such a system can be quite variable, vent temperatures between 10° C and 100° C are likely for typical crustal parameters.

Hydrothermal activity lowers trophic diversity in Antarctic hydrothermal sediments

NASA Astrophysics Data System (ADS)

Bell, James B.; Reid, William D. K.; Pearce, David A.; Glover, Adrian G.; Sweeting, Christopher J.; Newton, Jason; Woulds, Clare

2017-12-01

Hydrothermal sediments are those in which hydrothermal fluid is discharged through sediments and are one of the least studied deep-sea ecosystems. We present a combination of microbial and biochemical data to assess trophodynamics between and within hydrothermal and background areas of the Bransfield Strait (1050-1647 m of depth). Microbial composition, biomass, and fatty acid signatures varied widely between and within hydrothermally active and background sites, providing evidence of diverse metabolic activity. Several species had different feeding strategies and trophic positions between hydrothermally active and inactive areas, and the stable isotope values of consumers were not consistent with feeding morphology. Niche area and the diversity of microbial fatty acids was lowest at the most hydrothermally active site, reflecting trends in species diversity. Faunal uptake of chemosynthetically produced organics was relatively limited but was detected at both hydrothermal and non-hydrothermal sites, potentially suggesting that hydrothermal activity can affect trophodynamics over a much wider area than previously thought.

Hydrothermal deposition on the Juan de Fuca Ridge over multiple glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Costa, Kassandra M.; McManus, Jerry F.; Middleton, Jennifer L.; Langmuir, Charles H.; Huybers, Peter J.; Winckler, Gisela; Mukhopadhyay, Sujoy

2017-12-01

Hydrothermal systems play an important role in modern marine chemistry, but little is known about how they may have varied on 100,000 year timescales. Here we present high-resolution records of non-lithogenic metal fluxes within sediment cores covering the last 500,000 years of hydrothermal deposition on the flanks of the Juan de Fuca Ridge. Six adjacent, gridded cores were analyzed by x-ray fluorescence for Fe, Mn, and Cu concentrations, corrected for lithogenic inputs with Ti, and normalized to excess initial 230Th to generate non-lithogenic metal flux records that provide the longest orbitally resolved reconstructions of hydrothermal activity currently available. Fe fluxes vary with global sea level over the last two glacial cycles, suggesting higher hydrothermal deposition during interglacial periods. The observed negative relationship between Fe and Mn indicates variable sediment redox conditions and diagenetic remobilization of sedimentary Mn over time. Thus, Mn fluxes may not be a reliable indicator for hydrothermal activity in the Juan de Fuca Ridge sediment cores. Cu fluxes show substantial high-frequency variability that may be linked to changes in vent temperature related to increased magmatic production during glacial periods. Deglacial hydrothermal peaks on the Juan de Fuca Ridge are consistent with previously published records from the Mid-Atlantic Ridge and the East Pacific Rise. Moreover, on the Juan de Fuca Ridge, the deglacial peaks in hydrothermal activity are followed by relatively high hydrothermal fluxes throughout the ensuing interglacial periods relative to the previous glacial period.

State of the hydrothermal activity of Soufrière of Guadeloupe volcano inferred by VLF surveys

NASA Astrophysics Data System (ADS)

Zlotnicki, J.; Vargemezis, G.; Mille, A.; Bruère, F.; Hammouya, G.

2006-04-01

La Soufrière (1467 m) is the active island arc volcano of Guadeloupe Island in the Lesser Antilles arc. Its historical eruptions are more or less violent phreatic outbursts the last of which, in 1976-1977, led to the evacuation of nearly 70 000 persons. The subsurface structure of the volcano consists of calderas, craters, and avalanche amphitheatres nested within the composite pile of eruptive products. Since the last magmatic eruption, dated ca. 1440 AD, the four phreatic eruptions have developed radial fractures on Soufrière dome favouring the development of a huge active hydrothermal system emphasized by a tropical environment. After the eruptions, the thermal state and the stable ground water flow are completely disorganised during several years during which the slow mineralization of rocks is becoming again preponderant. Sealing of fractures and decay of rocks permeability act as a cap for upward thermal transfers. Therefore Soufrière dome operates as a valve, resealing the hydrothermal system underlying the volcano thus providing over pressurization that could lead to the next phreatic eruption. In 1992 new small seismic swarms have appeared. Several of them are recorded every year while the emission of acid gas slowly increases. In order to recognise the superficial electrical resistive and conductive zones (less than 100 m depth) as well as the cavities on Soufrière volcano, we have made Very Low Frequency (VLF) surveys in 2000. Electrical conductive zones are clearly associated with major radial faults starting from the summit in which the hydrothermal activity takes place. In the continuation of these active hydrothermal fractures hot springs are located down slope. Conversely some of the resistive zones are associated with inactive clayed and sealed or opened faults. The distribution of the conductive zones allows detailing the state of the superficial part of the hydrothermal system of La Soufrière. The distribution of vertical clayed zones associated with major faults supposes Soufrière dome constituted of more or less consolidated blocks joined side by side and lying on the hydrothermally floor of crater Amic.

Volcano-hydrothermal system and activity of Sirung volcano (Pantar Island, Indonesia)

NASA Astrophysics Data System (ADS)

Caudron, Corentin; Bernard, Alain; Murphy, Sam; Inguaggiato, Salvatore; Gunawan, Hendra

2018-05-01

Sirung is a frequently active volcano located in the remote parts of Western Timor (Indonesia). Sirung has a crater with several hydrothermal features including a crater lake. We present a timeseries of satellite images of the lake and chemical and isotope data from the hyperacid hydrothermal system. The fluids sampled in the crater present the typical features of hyperacidic systems with high TDS, low pH and δ34SHSO4-δ34SS0 among the highest for such lakes. The cations concentrations are predominantly controlled by the precipitation of alunite, jarosite, silica phases, native sulfur and pyrite which dominate the shallow portions of the hydrothermal system. These minerals may control shallow sealing processes thought to trigger phreatic eruptions elsewhere. Sparse Mg/Cl and SO4/Cl ratios and lake parameters derived from satellite images suggest gradual increase in heat and gas flux, most likely SO2-rich, prior to the 2012 phreatic eruption. An acidic river was sampled 8 km far from the crater and is genetically linked with the fluids rising toward the active crater. This river would therefore be a relevant target for future remote monitoring purposes. Finally, several wells and springs largely exceeded the World Health Organization toxicity limits in total arsenic and fluoride.

Modeling mid-ocean ridge hydrothermal response to earthquakes, tides, and ocean currents: a case study at the Grotto mound, Endeavour Segment, Juan de Fuca Ridge

NASA Astrophysics Data System (ADS)

Xu, G.; Bemis, K. G.

2014-12-01

Seafloor hydrothermal systems feature intricate interconnections among oceanic, geological, hydrothermal, and biological processes. The advent of the NEPTUNE observatory operated by Ocean Networks Canada at the Endeavour Segment, Juan de Fuca Ridge enables scientists to study these interconnections through multidisciplinary, continuous, real-time observations. The multidisciplinary observatory instruments deployed at the Grotto Mound, a major study site of the NEPTUNE observatory, makes it a perfect place to study the response of a seafloor hydrothermal system to geological and oceanic processes. In this study, we use the multidisciplinary datasets recorded by the NEPTUNE Observatory instruments as observational tools to demonstrate two different aspects of the response of hydrothermal activity at the Grotto Mound to geological and oceanic processes. First, we investigate a recent increase in venting temperature and heat flux at Grotto observed by the Benthic and Resistivity Sensors (BARS) and the Cabled Observatory Vent Imaging Sonar (COVIS) respectively. This event started in Mar 2014 and is still evolving by the time of writing this abstract. An initial interpretation in light of the seismic data recorded by a neighboring ocean bottom seismometer on the NEPTUNE observatory suggests the temperature and heat flux increase is probably triggered by local seismic activities. Comparison of the observations with the results of a 1-D mathematical model simulation of hydrothermal sub-seafloor circulation elucidates the potential mechanisms underlying hydrothermal response to local earthquakes. Second, we observe significant tidal oscillations in the venting temperature time series recorded by BARS and the acoustic imaging of hydrothermal plumes by COVIS, which is evidence for hydrothermal response to ocean tides and currents. We interpret the tidal oscillations of venting temperature as a result of tidal loading on a poroelastic medium. We then invoke poroelastic theories to estimate the crustal permeability, a fundamental property of subsurface hydrothermal circulation, from the phase shift of the tidal oscillations of venting temperature relative to ambient ocean tides. These results together shed light on the influences of seismic and oceanic processes on a seafloor hydrothermal system.

Evidence of a modern deep water magmatic hydrothermal system in the Canary Basin (eastern central Atlantic Ocean)

NASA Astrophysics Data System (ADS)

Medialdea, T.; Somoza, L.; González, F. J.; Vázquez, J. T.; de Ignacio, C.; Sumino, H.; Sánchez-Guillamón, O.; Orihashi, Y.; León, R.; Palomino, D.

2017-08-01

New seismic profiles, bathymetric data, and sediment-rock sampling document for the first time the discovery of hydrothermal vent complexes and volcanic cones at 4800-5200 m depth related to recent volcanic and intrusive activity in an unexplored area of the Canary Basin (Eastern Atlantic Ocean, 500 km west of the Canary Islands). A complex of sill intrusions is imaged on seismic profiles showing saucer-shaped, parallel, or inclined geometries. Three main types of structures are related to these intrusions. Type I consists of cone-shaped depressions developed above inclined sills interpreted as hydrothermal vents. Type II is the most abundant and is represented by isolated or clustered hydrothermal domes bounded by faults rooted at the tips of saucer-shaped sills. Domes are interpreted as seabed expressions of reservoirs of CH4 and CO2-rich fluids formed by degassing and contact metamorphism of organic-rich sediments around sill intrusions. Type III are hydrothermal-volcanic complexes originated above stratified or branched inclined sills connected by a chimney to the seabed volcanic edifice. Parallel sills sourced from the magmatic chimney formed also domes surrounding the volcanic cones. Core and dredges revealed that these volcanoes, which must be among the deepest in the world, are constituted by OIB-type, basanites with an outer ring of blue-green hydrothermal Al-rich smectite muds. Magmatic activity is dated, based on lava samples, at 0.78 ± 0.05 and 1.61 ± 0.09 Ma (K/Ar methods) and on tephra layers within cores at 25-237 ky. The Subvent hydrothermal-volcanic complex constitutes the first modern system reported in deep water oceanic basins related to intraplate hotspot activity.