Structure of hydrothermal plumes at the Logatchev vent field, 14°45′N, Mid-Atlantic Ridge: evidence from geochemical and geophysical data

In the Seventh cruise of R/V “Professor Logatchev” anomalies of natural electric field (EF), Eh and pS were discovered using a towed instrument package (RIFT) at 14°45′N on the MAR (Logatchev hydrothermal field). The anomalous zone (AZ) is situated close (10–35 m) to two low-temperature venting areas of degrading sulphides and a black smoker (Irina-Microsmoke) forming a distinct buoyant plume. Over or close to the main area of high-temperature venting situated to the south-east from the AZ, no EF or Eh anomalies were observed. According to the results of Mir dives the highly mineralised solutions from smoking craters at the main mound mostly form non-buoyant plumes (reverse-plumes). The buoyant plume structure shows the differentiation of the electrical and Eh fields within the plume. Maxima of the EF, Eh and E_H2S anomalies were revealed in the lower part (15 m) of the plume. The negative redox potential plume coupled with a sulphide anomaly is more localized in comparison with the EF. This observation indicates a distinct change in the composition of buoyant plume water, which may be due to the formation and fallout of early formed Fe sulphide particles soon after venting.     

Magmatismes basiques dits “orogeniques” et “anorogeniques” et teneurs entro2: Les associations “Isotitanees” et “anisotitanfes”

The patterns of variation of TiO₂ conent during magmatic evolution are different in the so called “orogenic” and “anorogenie” basic associations; these last terms, which are the cause of much misunderstanding, can be replaced by the terms “isotitaniferous” and “anisotitaniferous”.     

Authigenic carbonates in sediments from the Gulf of Mexico

The carbon isotopic composition of diagenetic dolomite and calcite in some sediments of the Gulf of Mexico varies between “normal-marine” (δ¹³C ca. 0‰) and −14.6‰ which suggests that biogenic CO₂ contributed to the carbonate formation. The δ¹³O values of dolomite and coexisting calcite are very similar but variable down-core.Dolomite and calcite precipitated early from pore water where SO₄²⁻ was not reduced. However, during (and after?) SO₄²⁻ reduction dolomite and calcite still formed and there are at least two generations of carbonate minerals present.     

Self-diffusion studies of pore fluids in unconsolidated sediments by PFG NMR

The self-diffusion of water and hexadecane in medium and coarse sands from glacial sand deposits in central Germany were investigated by pulsed field gradient nuclear magnetic resonance (PFG NMR). Due to the restriction of the diffusion path at the pore/grain interface, the measured apparent self-diffusion coefficients (D(Δ)) in the pore space depend on the observation time (Δ) in the PFG NMR experiment. Although the bulk self-diffusion coefficients of water and hexadecane differ by about one order of magnitude, the apparent self-diffusion coefficients in the pore space obey the same characteristic time-behaviour, which depends only on geometrical properties of the pore system. Using the “short-time diffusion” model, surface-to-volume (S/V) ratios and inherent self-diffusion coefficients (D₀) of the pore fluids were extracted from these diffusion measurements. The S/V ratios obtained are independent of the pore fluid used and agree with known geometrical properties of the sand grains. Moreover, the D₀ values are consistent with the corresponding bulk self-diffusion coefficients measured separately. In contrast to these results of PFG NMR, simultaneous investigations of longitudinal (T₁) nuclear magnetic relaxation reveal that the relaxation time of the pore fluid is a less suitable parameter for a quantitative estimation of geometrical properties of the pore/grain interface in these unconsolidated sediments since it depends on chemical properties of the fluid/grain interface.     

The “wave turbopause”

The “wave turbopause” is defined as the mesospheric altitude level where the temperature fluctuation field indicates a substantial increase in wave amplitudes in the vertical direction.The turbopause altitude is analyzed on the basis of four years of SABER data (2002–2005, Version 1.06). Substantial seasonal and latitudinal variations are found, with some interannual variability also present. Seasonal changes are annual at high latitudes, semi-annual at low latitudes, and a mixture of both at middle latitudes. Southern hemisphere data are similar as in the North if shifted by half a year. Latitudinal variations show a minimum in the tropics and two relative maxima at middle latitudes.The “wave turbopause” is found near to zero-wind lines or low-wind zones (zonal wind). It is compared to rocket and other measurements, and interesting similarities are obtained. The wave turbopause can also be found in the HAMMONIA GCM. A preliminary analysis shows results similar to those of the SABER measurements.     

The Japan Trench and its juncture with the Kuril Trench: cruise results of the Kaiko project, Leg 3

This paper presents the results of a detailed survey combining Seabeam mapping, gravity and geomagnetic measurements as well as single-channel seismic reflection observations in the Japan Trench and the juncture with the Kuril Trench during the French-Japanese Kaiko project (northern sector of the Leg 3) on the R/V “Jean Charcot”. The main data acquired during the cruise, such as the Seabeam maps, magnetic anomalies pattern, and preliminary interpretations are discussed. These new data cover an area of 18,000 km² and provide for the first time a detailed three-dimensional image of the Japan Trench. Combined with the previous results, the data indicate new structural interpretations. A comparative study of Seabeam morphology, single-channel and reprocessed multichannel records lead to the conclusion that along the northern Japan Trench there is little evidence of accretion but, instead, a tectonic erosion of the overriding plate. The tectonic pattern on the oceanic side of the trench is controlled by the creation of new normal faults parallel to the Japan Trench axis, which is a direct consequence of the downward flexure of the Pacific plate. In addition to these new faults, ancient normal faults trending parallel to the N65° oceanic magnetic anomalies and oblique to the Japan trench axis are reactivated, so that two directions of normal faulting are observed seaward of the Japan Trench. Only one direction of faulting is observed seaward of the Kuril Trench because of the parallelism between the trench axis and the magnetic anomalies. The convergent front of the Kuril Trench is offset left-laterally by 20 km relative to those of the Japan Trench. This transform fault and the lower slope of the southernmost Kuril Trench are represented by very steep scarps more than 2 km high. Slightly south of the juncture, the Erimo Seamount riding on the Pacific plate, is now entering the subduction zone. It has been preceded by at least another seamount as revealed by magnetic anomalies across the landward slope of the trench. Deeper future studies will be necessary to discriminate between the two following hypothesis about the origin of the curvature between both trenches: Is it due to the collision of an already subducted chain of seamounts? or does it correspond to one of the failure lines of the America/Eurasia plate boundary?     

Diapirism in the earth's mantle: Experiments on the motion of a hot sphere in a fluid with temperature-dependent viscosity

The ascent of magma diapirs through the earth's mantle is modelled experimentally by the motion of a hot metal sphere through a fluid whose viscosity varies strongly with temperature. The dimensionless drag on the sphere (drag number D) and the heat transfer from it (Nusselt number Nu) are found as functions of the dimensionless velocity of the sphere (Peclet number Pe) and the viscosity contrast μ_∞/μ₀ = 10^γ, where μ_∞ and μ₀ are the viscosities of the fluid far from the sphere and at its surface. The drag D = D(Pe, γ) has two limits. For large Pe and small γ (“Stokes” limit), the drag approaches the Stokes' Law result. For small Pe and large γ (“lubrication” limit), the drag is orders of magnitude less than that predicted by Stokes' Law. Nu is a function of Pe alone. For reasonable values of the diapir radius and the viscosity contrast, the dimensionless scale height Pe/3 Nu may exceed a critical value, resulting in progressive melting during ascent. This suggests that diapirs may ascend great distances through the mantle while remaining largely molten. Lamont-Doherty Geological Observatory Contribution No. 3414.     

Noble gas elemental and isotopic abundances in deep-sea trenches in the western Pacific

Noble gas elemental and isotopic abundances were measured in seven deep-sea water samples from five different sampling sites in the Nankai Trough, the Japan Trench and the Kuril Trench. The samples were obtained by the manned submersible “Nautile”. Most of the sampling sites are associated with clam colonies and/or fluid venting. Excesses both in³He/⁴He ratio and He concentration are observed in a seawater sample collected a few kilometers off the clam colonies which were found at a depth of 3830 m at the mouth of the Tenryu Canyon. Concentrations of noble gases (Ne, Ar, Kr and Xe) in this sample show progressive depletion from Ne to Xe relative to those in 1°C air-saturated seawater, which can be attributed to mixing of hot water ( 15°C) with cold ambient water ( 1°C). Isotopic compositions of Ne, Ar, Kr and Xe in this sample are atmospheric. These observations may reflect venting of hot pore water around the Tenryu Canyon. All the other samples show a significant excess in concentration of all noble gases relative to 1°C air-saturated seawater and the isotopic compositions are atmospheric. This excess of noble gas concentrations may appear to be air contamination in the samples. However, results of hydrocarbon analyses of the Kaiko samples imply that such large amount of air contamination is improbable. Decomposition of gas hydrate in deep-sea sediments is a more likely explanation for the observed excess of noble gas concentration.     

V p /V s anomalies in dilatant rock samples

Summary In a series of triaxial experiments we have measuredV _p ,V _s and volumetric strain simultaneously in dilating dry and saturated rocks. For the first time these data permit quantitative comparison of seismic velocities or their ratio and dilatant volumetric strain. In air-dry samplesV _p /V _s decreases by a few per cent at strains of 10^–3; in saturated materials with high pore pressure,V _p /V _s increases by a comparable amount. Decreases in seismic velocity ratio are difficult to generate in initially saturated rocks even with low pore pressures and at strain rates of 10^–4/sec. A liquid-vapor transition will not produce a significant drop inV _p /V _s . If dilatancy and fluid flow are responsible for seismic travel time anomalies prior to earthquakes, our results suggest that such anomalies will occur only in regions where pore fluid source to sink dimensions are of the order of 10 km or more, or in regions where the rocks are not saturated to begin with.     

Geochemistry and isotopes of fluids from sulphur springs, Valles Caldera, New Mexico

Detailed geochemistry supported by geologic mapping has been used to investigate Sulphur Springs, an acid-sulfate hot spring system that issues from the western flank of the resurgent dome inside Valles Caldera. The most intense activity occurs at the intersection of faults offsetting caldera-fill deposits and post-caldera rhyolites. Three geothermal wells in the area have encountered pressures <1 MPa and temperatures of 200°C at depths of 600 to 1000 m. Hot spring and fumarole fluids may discharge at boiling temperatures with pH 1.0 and SO₄ 8000 mg/l. These conditions cause argillic alterations throughout a large area.Non-condensible gases consist of roughly 99% CO₂ with minor amounts of H₂S, H₂, and CH₄. Empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280°C. Comparison of ¹³C and ¹⁸O between CaCO₃ from well cuttings and CO₂ from fumarole steam indicates a fractionation temperature between 200 and 300°C by decarbonation of hydrothermally altered Paleozoic limestone and vein calcite in the reservoir rocks. Tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids (Baca #13, 278°C) are 2.1 and 1.0 T.U. respectively, suggesting the steam originates from a reservoir whose water is mostly >50 yrs old. Deuterium contents of fumarole steam, deep reservoir fluid, and local meteoric water are practically identical even though ¹⁸O contents range through 4‰, thus, precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation. From analysis of D and ¹⁸O values between fumarol steam and deep reservoir fluid, steam reaches the surface either (1) by vaporizing relatively shallow groundwater at 200°C or (2) by means of a two-stage boiling process through an intermediate level reservoir at roughly 200°C.Although many characteristics of known vapor-dominated geothermal systems are found at Sulphur Springs, fundamental differences exist in temperature and pressure of our postulated vapor-zone. We propose that the reservoir beneath Sulphur Springs is too small or too poorly confined to sustain a “true” vapor-dominated system and that the Sulphur Springs system may be a “dying” vapor-dominated system that has practically boiled itself dry.     

Composite titanomagnetite-ferrian ilmenite grains and correlative magnetic components in a dacite with self-reversed TRM

Electron microprobe and reflected light microscopic examinations confirm the presence of composite grains of ferrian ilmenite with X_ilm = 0.53 and titanomagnetite with X_usp = 0.13 in a dacite with self-reversed TRM. A parallel TRM component associated with titanomagnetite and a reversed component associated with self-reversing ferrian ilmenite are the principal NRM components. A subordinate, parallel component is associated with ferrian ilmenite which is not magnetically coupled to an “χ-phase”. The natural self-reversing properties are mainly a consequence of the dacite's high quenching temperature, calculated at 862–864°C using the Fe—Ti oxide geothermometer, and are most consistent with the self-reversal mechanism proposed by Lawson et al. [9].The conduction of thermal demagnetization and TRM induction tests in air had a much greater effect on the Fe—Ti oxides than did natural cooling, and resulted in significant oxidation with the consequent modification of some magnetic properties and the formation of another reversed TRM component. The subdivision of titanomagnetite grains by oxidation along fractures decreased its effective grain size and caused an apparent increase in its magnetic intensity, in addition to a slight increase in its resistance to alternating field demagnetization. The χ-phase associated with the reversed NRM component, with 0.42 > X_ilm 0.31, became Fe-enriched during the earlier stages of heat treatment. It is suggested that after heating at 600°C for two hours or more, this χ-phase exsolves as titanohematite with X_ilm < 0.33. The ferrian ilmenite host is consequently enriched in Ti, and another χ-phase much closer in composition to the host generates a reversed TRM component with T_b < 200°C.     

Hydrothermal silica chimney fields in the Galapagos Spreading Center at 86°W

Silica chimneys were discovered in 1985 at 86°W in the rift valley of the Galapagos Spreading Center at 2600 m depth (“Cauliflower Garden”). The inactive chimneys lack any sulfides and consist almost entirely of amorphous silica (up to 96 wt.% SiO₂, opal-A); Fe and Mn oxides are minor constituents. Oxygen isotope data show that formation of the silica chimneys took place at temperatures between 32°C (+29.9‰ δ¹⁸O) and 42°C (+27.8‰ δ¹⁸O).Th/Udating reveals a maximum age of 1440 ± 300y. Amorphous silica solubility relations indicate that the silica chimneys were formed by conductive cooling of pure hydrothermal fluids or by conductive cooling of a fluid/seawater mixture. Assuming equilibrium with quartz at 500 bars, initial fluid temperatures of more than 175°C (i.e., a concentration of > 182 ppm SiO₂) were required to achieve sufficient supersaturation for the deposition of amorphous silica at 40°C and 260 bars. If the silica chimneys originate from the same or a similar fluid as higher-temperature ( < 300°C) sulfide-silica precipitates found nearby (i.e., 2.5 km away), then subsurface deposition of sulfides may have occurred.     

Vent fluid chemistry in Bahía Concepción coastal submarine hydrothermal system, Baja California Sur, Mexico

Shallow submarine hydrothermal activity has been observed in the Bahía Concepción bay, located at the Gulf coast of the Baja California Peninsula, along faults probably related to the extensional tectonics of the Gulf of California region. Diffuse and focused venting of hydrothermal water and gas occurs in the intertidal and shallow subtidal areas down to 15 m along a NW–SE-trending onshore–offshore fault. Temperatures in the fluid discharge area vary from 50 °C at the sea bottom up to 87 °C at a depth of 10 cm in the sediments.Chemical analyses revealed that thermal water is enriched in Ca, As, Hg, Mn, Ba, HCO₃, Li, Sr, B, I, Cs, Fe and Si, and it has lower concentrations of Cl, Na, SO₄ and Br than seawater. The chemical characteristics of the water samples indicate the occurrence of mixing between seawater and a thermal end-member. Stable isotopic oxygen and hydrogen composition of thermal samples plot close to the Local Meteoric Water Line on a mixing trend between a thermal end-member and seawater. The composition of the thermal end-member was calculated from the chemistry of the submarine samples data by assuming a negligible amount of Mg for the thermal end-member. The results of the mixing model based on the chemical and isotopic composition indicate a maximum of 40% of the thermal end-member in the submarine vent fluid.Chemical geothermometers (Na/Li, Na–K–Ca and Si) were applied to the thermal end-member concentration and indicate a reservoir temperature of approximately 200 °C. The application of K–Mg and Na/Li geothermometers for vent fluids points to a shallow equilibrium temperature of about 120 °C.Results were integrated in a hydrogeological conceptual model that describes formation of thermal fluids by infiltration and subsequent heating of meteoric water. Vent fluid is generated by further mixing with seawater.     

Links between global CO<Subscript>2</Subscript> variability and climate anomalies of biomes

The global rate of fossil fuel combustion continues to rise, but the amount of CO₂ accumulating in the atmosphere has not increased accordingly. The causes for this discrepancy are widely debated. Particularly, the location and drivers for the interannual variability of atmospheric CO₂ are highly uncertain. Here we examine links between global atmospheric CO₂ growth rate (CGR) and the climate anomalies of biomes based on (1986–1995) global climate data of ten years and accompanying satellite data sets. Our results show that four biomes, the tropical rainforest, tropical savanna, C₄ grassland and boreal forest, and their responses to climate anomalies, are the major climate-sensitive CO₂ sinks/sources that control the CGR. The nature and magnitude by which these biomes respond to climate anomalies are generally not the same. However, one common influence did emerge from our analysis; the extremely high CGR observed for the one extreme El Niño year was caused by the response of the tropical biomes (rainforest, savanna and C₄ grassland) to temperature.     

Pore-fluid pressures and frictional heating on a fault surface

This study considers the effects of heat transfer and fluid flow on the thernal, hydrologic, and mechanical response of a fault surface during seismic failure. Numerical modeling techniques are used to account for the coupling of the thermal, fluid-pressure, and stress fields. Results indicate that during an earthquake the failure surface is heated to a tempeature required for the thermal expansion of pore fluids to balance the rate of fluid loss due to flow and the fluid-volume changes due to pore dilatation. Once this condition is established, the pore fluids pressurize and the shear strength decreases rapidly to a value sufficient to maintain the thermal pressurization of pore fluids at near-lithostatic values. If the initial fluid pressure is hydrostatic, the final temperature attained on the failure surface will increase with depth, because a greater pressure increase can occur before a near-lithostatic pressure is reached. The rate at which thermal pressurization proceeds depends primarily on the hydraulic characteristics of the surrounding porous medium, the coefficient of friction on the fault surface, and the slip velocity. If either the permeability exceeds 10^–15 m² or the porous medium compressibility exceeds 10^–8 Pa^–1, then frictional melting may occur on the fault surface before thermal pressurization becomes significant. If the coefficient of friction is less than 10^–1 and if the slip velocity is less than 10^–2 msec^–1, then it is doubtful that either thermal pressurization or frictional melting on the fault surface could cause a reduction in the dynamic shear strength of a fault during an earthquake event.     

Thermal surface characteristics of coal fires 1 results of in-situ measurements

Natural underground coal fires are fires in coal seams occurring subsurface. The fires are ignited through a process named spontaneous combustion, which occurs based on a natural reaction but is usually triggered through human interaction. Coal mining activities expose coal to the air. This leads to the exothermal oxidation of the carbon in the coal with the air's oxygen to CO₂ and – under certain circumstances – to spontaneous combustion. Coal fires occur in many countries world wide – however, currently the Chinese coal mining industry faces the biggest problems with coal fires. Coal fires destroy the valuable resource coal and furthermore lead to many environmental degradation phenomena such as the deterioration of surrounding vegetation, land subsidence and the emission of toxic gasses (CO, N₂O). They additionally contribute to the emission of green house relevant gasses such as CO₂ and CH₄ to the atmosphere.In this paper we present thermal characteristics of coal fires as measured in-situ during a field campaign to the Wuda coal fire area in south-central Inner Mongolia, China. Thermal characteristics include temperature anomaly measurements at the surface, spatial surface temperature profiles of fire areas and unaffected background areas, diurnal temperature profiles, and temperature measurements inside of coal fire induced cracks in the overlying bedrock. For all the measurements the effects of uneven solar heating through influences of slope and aspect are considered.Our findings show that coal fires result in strong or subtle thermal surface anomalies. Especially the latter can easily be influenced by heating of the surrounding background material through solar influences. Temperature variation of background rocks with different albedo, slope, aspect or vegetation cover can substantially influence the detectability of thermal anomalies. In the worst case coal fire related thermal anomalies can be completely masked by solar patterns during the daytime. Thus, night-time analysis is the most suitable for thermal anomaly mapping of underground coal fires, although this is not always feasible. The heat of underground coal fires only progresses very slowly through conduction in the rock material. Anomalies of coal fires completely covered by solid unfractured bedrock are very weak and were only measured during the night. The thermal pattern of underground coal fires manifested on the surface during the daytime is thus the pattern of cracks and vents, which occur due to the volume loss underground and which support radiation and convective energy transport of hot gasses. Inside coal fire temperatures can hardly be measured and can only be recorded if the glowing coal is exposed through a wider crack in the overlaying bedrock. Direct coal fire temperatures measured ranged between 233 °C and 854 °C. The results presented can substantially support the planning of thermal mapping campaigns, analyses of coal fire thermal anomalies in remotely sensed data, and can provide initial and boundary conditions for coal fire related numerical modeling.In a second paper named “Thermal Characteristics of Coal Fires 2: results of measurements on simulated coal fires” [Zhang J., Kuenzer C., Tetzlaff A., Oettl D., Zhukov B., Wagner W., 2007. Thermal Characteristics of Coal Fires 2: Result of measurements on simulated coal fires. Accepted for publication at Journal of Applied Geophysics. doi:10.1016/j.jappgeo.2007.08.003] we report about thermal characteristics of simulated coal fires simulated under simplified conditions. The simulated set up allowed us to measure even more parameters under undisturbed conditions — especially inside fire temperatures. Furthermore we could demonstrate the differences between open surface coal fires and covered underground coal fires. Thermal signals of coal fires in near range thermal remotely sensed imagery from an observing tower and from an airplane are presented and discussed.     

Stationary magnetospheric convection on November 24, 1981. 1. A case study of “pressure gradient/minimum-B” auroral arc generation

We present two case studies in the night and evening sides of the auroral oval, based on plasma and field measurements made at low altitudes by the AUREOL-3 satellite, during a long period of stationary magnetospheric convection (SMC) on November 24, 1981. The basic feature of both oval crossings was an evident double oval pattern, including (1) a weak arc-type structure at the equatorial edge of the oval/polar edge of the diffuse auroral band, collocated with an upward field-aligned current (FAC) sheet of ≈1.0 μA m⁻², (2) an intermediate region of weaker precipitation within the oval, (3) a more intense auroral band at the polar oval boundary, and (4) polar diffuse auroral zone near the polar cap boundary. These measurements are compared with the published magnetospheric data during this SMC period, accumulated by Yahnin et al. and Sergeev et al., including a semi-empirical radial magnetic field profile B_Z in the near-Earth neutral sheet, with a minimum at about 10–14 R_E. Such a radial B_Z profile appears to be very similar to that assumed in the “minimum B/cross-tail line current” model by Galperin et al. (GVZ92) as the “root of the arc”, or the arc generic region. This model considers a FAC generator mechanism by Grad-Vasyliunas-Boström-Tverskoy operating in the region of a narrow magnetic field minimum in the near-Earth neutral sheet, together with the concept of ion non-adiabatic scattering in the “wall region”. The generated upward FAC branch of the double sheet current structure feeds the steady auroral arc/inverted-V at the equatorial border of the oval. When the semi-empirical B_Z profile is introduced in the GVZ92 model, a good agreement is found between the modelled current and the measured characteristics of the FACs associated with the equatorial arc. Thus the main predictions of the GVZ92 model concerning the “minimum-B” region are consistent with these data, while some small-scale features are not reproduced. Implications of the GVZ92 model are discussed, particularly concerning the necessary conditions for a substorm onset that were not fulfilled during the SMC period.     

Geochemistry of the magmatic–hydrothermal system of Kawah Ijen volcano, East Java, Indonesia

Samples from Kawah Ijen crater lake, spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis. An extremely low pH (<0.3) lake contains SO₄–Cl waters produced during absorption of magmatic volatiles into shallow ground water. The acidic waters dissolve the rock isochemically to produce “immature” solutions. The strong D and ¹⁸O enrichment of the lake is mainly due to enhanced evaporation at elevated temperature, but involvement of a magmatic component with heavy isotopic ratios also modifies the lake D and ¹⁸O content. The large Δ_SO4–S⁰ (23.8–26.4‰) measured in the lake suggest that dissolved SO₄ forms during disproportionation of magmatic SO₂ in the hydrothermal conduit at temperatures of 250280°C. The lake δ¹⁸O_SO4 and δ¹⁸O_H2O values may reflect equilibration during subsurface circulation of the water at temperatures near 150°C. Significant variations in the lake's bulk composition from 1990 to 1996 were not detected. However, we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased SO₂-rich gas input to the lake system.Thermal springs at Kawah Ijen consist of acidic SO₄–Cl waters on the lakeshore and neutral pH HCO₃–SO₄–Cl–Na waters in Blawan village, 17 km from the crater. The cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock. The SO₄/Cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic SO₄–Cl water and ground water.The lakeshore fumarole discharges (T=170245°C) have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur. The apparent equilibrium temperature of the gas is 260°C. The proportions of the oxidized, SO₂-dominated magmatic vapor and of the reduced, H₂S-dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996. This may be the result of interaction of SO₂-bearing magmatic vapors with the summit acidic hydrothermal reservoir. This idea is supported by the lower H₂S/SO₂ ratio deduced for the gas producing the SO₄–Cl reservoir feeding the lake compared with that observed in the subaerial gas discharges. The condensing gas may have equilibrated in a liquid–vapor zone at about 350°C.Elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor. The sediments were precipitated in the past during inorganic oxidation of H₂S in the lake water. This process was not continuous, but was interrupted by periods of massive silica (poorly crystallized) precipitation, similar to the present-day lake conditions. We suggest that the factor controlling the type of deposition is related to whether H₂S- or silica-rich volcanic discharges enter the lake. This could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater. Quenched liquid sulfur products show δ³⁴S values similar to those found in the banded deposits, suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom.     

新疆天山地震带的地震流体地质效应

天山地区的高压自流水、高压油气藏及地热异常区的出露与天山地震带分布的一致性表明,孔隙水压异常高的动力条件可能成为触发浅源地震的重要机制。本文以丰富的震例为依据,认为天山地震带中强地震前地下流体出现两类异常:一类是应力应变能积累阶段的趋势性异常;一类是应力应变能预释放阶段的临震突发性异常。两类异常在形态上和时空分布上有完全不同的特征,它们显示出地震孕育过程中的两个完全不同的物理、化学过程。     

Flux and dispersion of gases from the “Drachenschlund” hydrothermal vent at 8°18' S, 13°30' W on the Mid-Atlantic Ridge

Hydrothermal emission of mantle helium appears to be directly related to magma production rate, but other processes can generate methane and hydrogen on mid-ocean ridges. In an on-going effort to characterize these processes in the South Atlantic, the flux and distribution of these gases were investigated in the vicinity of a powerful black smoker recently discovered at 8°17.9' S, 13°30.4' W. The vent lies on the shoulder of an oblique offset in the Mid-Atlantic Ridge and discharges high concentrations of methane and hydrogen. Measurements during expeditions in 2004 and 2006 show that the ratio of CH₄ to ³He in the neutrally buoyant plume is quite high, 4 × 10⁸. The CTD stations were accompanied by velocity measurements with lowered acoustic Doppler current profilers (LADCP), and from these data we estimate the methane transport to have been 0.5 mol s^− 1 in a WSW-trending plume that seems to develop during the ebb tidal phase. This transport is an order of magnitude greater than the source of CH₄ calculated from its concentration in the vent fluid and the rise height of the plume. From this range of methane fluxes, the source of ³He is estimated to be between 0.14 and 1.2 nmol s^− 1. In either case, the ³He source is significantly lower than expected from the spreading rate of the Mid-Atlantic Ridge. From the inventory of methane in the rift valley adjacent to the vent, it appears that the average specific rate of oxidation is 2.6 to 23 yr^− 1, corresponding to a turnover time between 140 and 16 days. Vertical profiles of methane in the surrounding region often exhibited Gaussian-like distributions, and the variances appear to increase with distance from the vent. Using a Gaussian plume model, we obtained a range of vertical eddy diffusivities between 0.009 and 0.08 m²m² s^− 1. These high values may be due to tidally driven internal waves across the promontory on which the vent is located.