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1.
Mud volcanoes have provided much meaningful information about the deep Earth and the recent crustal and neotectonic movements in an area for over 200 years. However, the triggering mechanisms have puzzled geologists for a long time. This study investigated the factors controlling mud volcano activity and the triggering mechanisms of mud volcano eruptions on the southern margin of the Junggar Basin, NW China. The Baiyanggou, Aiqigou and Dushanzi mud volcanoes are all located along the Dushanzi Anticline, which belongs to the third anticline belt on the southern margin of the basin. The extensive, thick mudstone at depth provides a wealth of material for the formation of mud volcanoes. Simultaneously, the overpressure serves as the driving force for the eruption of the mud volcanoes. The torsional–compressional stress field created by the collision between the Indian and Eurasian plates not only enhanced the abnormal formational pressure in the region but also lead to the development of extensional faults in the core of the Dushanzi Anticline, which served as the conduits for the mud volcanoes. The continuous collision between the Indian and Eurasian plates and the regional torsional–compressional stress field may largely control the cyclical activity of the mud volcanoes and serve as their primary trigger mechanism. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
《Applied Geochemistry》2004,19(5):695-707
Taiwan is located at the collision boundary between the Philippine Sea Plate and the Asian Continental Plate and is one of the most active orogenic belts in the world. Fluids sampled from 9 sub-aerial mud volcanoes distributed along two major geological structures in southwestern Taiwan, the Chishan fault and the Gutingkeng anticline, were analyzed to evaluate possible sources of water and the degree of fluid-sediment interaction at depth in an accretionary prism. Overall, the Taiwanese mud volcano fluids are characterized by high Cl contents, up to 347 mM, suggesting a marine origin from actively de-watering sedimentary pore waters along major structures on land. The fluids obtained from the Gutingkeng anticline, as well as from the Coastal Plain area, show high Cl, Na, K, Ca, Mg and NH4, but low SO4 and B concentrations. In contrast, the Chishan fault fluids are much less saline (1/4 seawater value), but show much heavier O isotope compositions (δ18O=5.1–6.5 ‰). A simplified scenario of mixing between sedimentary pore fluids and waters affected by clay dehydration released at depth can explain several crucial observations including heavy O isotopes, radiogenic Sr contents (87Sr/86Sr=0.71136–0.71283), and relatively low salinities in the Chishan fluids. Gases isolated from the mud volcanoes are predominantly CH4 and CO2, where the CH4–C isotopic compositions show a thermogenic component of δ13C=−38 ‰. These results demonstrate that active mud volcano de-watering in Taiwan is a direct product of intense sediment accretion and plate collision in the region.  相似文献   

3.
ABSTRACT In the foothills of the Northern Apennines mud volcanoes are locally aligned along active normal faults, which allow surface leakage of fluids derived from deep sources (>3–6 km). The chemical and isotopic analysis of the fluids of a mud volcano, coupled with the reconstruction of its geological setting, allowed an investigation of the processes of migration and fluid flow. The fault system associated with the Regnano mud volcano drains a deep Miocene reservoir (foredeep marine deposits), which supplies formation water and thermogenic methane that has migrated from underlying Mesozoic carbonates. The muds from the volcano contain late Eocene microfossils and are extruded only during paroxysmal events. They have a shallower origin (about 1 km) from the base of Tertiary marine deposits deposited upon the upper tectonic nappe of the chain (Ligurian unit). This case study suggests that normal faults are very effective in controlling surface emissions.  相似文献   

4.
ABSTRACT This paper presents new geochemical data on gas-hydrate-bearing mud volcanoes discovered for the first time in the Gulf of Cadiz during cruises TTR9 and TTR10 of the R/V Professor Logachev in 1999–2000. The estimated gas hydrate content is 3–16% of sediment volume and 5–31% of pore space volume. Estimated values of the water isotopic composition for the Ginsburg mud volcano are very heavy for δ18O (up to +53‰) and light for δD (up to − 210‰). Gas released from the hydrates contains 81% of C1 and 19% of C2+. The inferred source of the gas in the hydrates is enriched in C2–C6 (≤ 5%), indicating that the gas has a thermogenic origin. Gas hydrate of cubic structure II should be formed from a gas of such composition. It is interpreted that the composition of the mud volcano fluid corresponds to deep oil basins below the Gulf of Cadiz.  相似文献   

5.
Direct observation of active emission of fluids and mud from a submarine mud volcano were made for the first time in an extensive field of mud diapirs and mud volcanoes on the Mediterranean Ridge using a video camera towed 2 m above the seafloor in 1800 m of water. This recent research using both long range and deep-towed sidescan sonar systems indicates also that diapirism and eruption of mud along the crest of the ridge is more common than previously thought. The southwards increase in age of rock fragments carried within the erupted mud supports the hypothesis that the fluid mud becomes overpressured within a southward-dipping backthrust from the Inner Deformation Front of this accretionary prism.  相似文献   

6.
A comprehensive study was performed to characterize, for the first time, the mud, water, and gases released from onshore mud volcanoes located in the southern margin of the Junggar Basin, northwestern China. Chemical compositions of mud, along with the geology of the basin, suggest that a source of the mud is Mesozoic or Cenozoic shale. Oxygen and H isotope compositions of the released water suggest a local meteoric origin. Combined with the positive Eu anomalies of the water, a large 18O shift of the water suggests extensive interaction with rocks. Gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons, and the high δ13C values (>+20‰ VPDB) for CO2 gases and dissolved carbonate in muddy water suggest secondary methanogenesis with CO2 reduction after oil biodegradation.The enrichments of Eu and 18O in water and the low thermal gradient of the area suggest that the water-rock interactions possibly occur deeper than 3670 ± 200 m. On the other hand, considering the relationship to the petroleum reservoir around the mud volcanoes, the depth of the gases can be derived from about 3600 m, a depth that is greater than that generally estimated for reservoirs whose gas is characterized by 13C-enriched CO2. Oil biodegradation with CO2 reduction likely occurs at a shallower depth along the seepage system of the mud volcano. The results contribute to the worldwide data set of gas genesis in mud volcanoes. Moreover, they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation, an important problem in the petroleum industry.  相似文献   

7.
台湾西南部乌山顶泥火山的成因机制初探   总被引：2，自引：0，他引：2  
乌山顶泥火山位于台湾西南部旗山断层沿线.由于台湾西南部具有独特的地质构造背景,沿着古亭坑背斜和旗山断层沿线分布了许多泥火山.本文以乌山顶泥火山为例,研究泥火山的成因.在了解泥火山地质背景、活动现状的基础上,分析了喷出物的矿物组成、古生物组合、流体地球化学特征.喷出的主要矿物有石英、伊利石、高岭石-蒙脱石混层矿物、伊利石-蒙脱石混层矿物,古生物有Reticulofenestra minuta、 Sphenolithus abies等,流体中的离子主要是Cl-、Na+等.由此探讨了泥浆来源和成因机制,认为泥火山的活动与深部古亭坑组地层存在异常高压有关,构造活动是泥火山活动的主要诱发因素.  相似文献   

8.
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9.
Mud volcanism in the Gulf of Cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the European-African plate boundary, affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness. The investigation of six active sites shows that mud volcano (MV) fluids, on average, are highly enriched in CH4, Li, B, and Sr and depleted in Mg, K, and Br. The purity of the fluids is largely controlled by the intensity of upward directed flow. Flow rates could be constrained by numerical modelling and vary between <0.05 and 15 cm yr−1. Application of δD-δ18O systematics identifies clay mineral dehydration, most likely within Mesozoic and Tertiary shales and marls, as the major source of fluids. Hence, Cl and Na in the pore fluids are mostly depleted below seawater values, following a general trend of dilution. However, deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits. Other secondary processes overprinting the original fluid composition may occur along the flow path, such as dissolution of anhydrite or gypsum and/or the formation of calcite and dolomite. Different sources of fluids are also indicated by variations in 87Sr/86Sr, which range from 0.7086 to 0.7099 at the different sites. Dehydration may be induced primarily by overburden and tectonic compression; however, very high concentrations of Li and B, specifically at Captain Arutyunov MV (CAMV) indicate additional leaching at temperatures above 150 °C, which could be explained by the injection of hot fluids along deep penetrating, major E-W strike-slip fault systems. This hypothesis is supported by the occurrence of generally thermogenic, but significantly CH4-enriched, light volatile hydrocarbon gases at CAMV which cannot be explained by shallow microbial methanogenesis. Li and Li/B ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies.  相似文献   

10.
A large collection of fluids (54 interstitial fluids and four expelled fluids) were sampled at the Manon site, at the outer edge of the Barbados accretionary complex. These warm fluids (up to 20°C) are expelled by sub-marine (5000 mbsl) mud volcanoes consisting of diapirs (unchanneled flow) and diatremes (channeled).Chlorine stable isotope ratios of these fluids were measured by IRMS with a reproducibility of ± 0.05‰ (1σ) versus SMOC (Standard Mean Ocean Chloride).A large range of δ37Cl between −5.3‰ and +0.1‰ is observed. Data from each volcanic structure describe a mixing between seawater and a low-δ37Cl fluid. The whole set of data is interpreted as the result of a mixing between two deep components and seawater. The two deep fluids are chemically distinct (e.g., in Ca, Mg, K, Li, Sr and Br contents and Br/Cl ratio). They display low and significantly different 87Sr/86Sr ratios (0.707790 and 0.707892, respectively) and δ37Cl values (−4.51 and −5.24‰, respectively).Physicochemical processes such as mineralogical transformation, diffusion, compaction or ion filtration are known to fractionate chlorine stable isotopes and can produce fluids with negative δ37Cl values. Ion filtration due to sediment compaction appears to be the more likely process to explain the negative δ37Cl values observed at the Manon site. A model for the generation of these signatures is proposed where a residual negative δ37Cl fluid reservoir is created at the bottom of the prism or the sediment pile. Further compaction/fracturing and/or dewatering of the slab may flush out these fluids and focus them towards the décollement zone. Mixing between the fluids and ultimately with seawater and water released during gas hydrate destabilizations may explain the data set within the individual cores and between the different structures.  相似文献   

11.
Hypersaline (Na–Ca–Cl) fluids are associated with late‐stage quartz veining and retrogression of garnet, kyanite and other high P–T phases in the vicinity of thrusts and major lithological boundaries in the Scandian nappes of the Troms‐Ofoten region, northern Norway. They record early Devonian fluid infiltration during rapid exhumation in the final stages of Caledonian orogenesis. The δ18O and δD characteristics of these late fluids provide compelling evidence for deep circulation of meteoric fluids. The sub‐greenschist to low greenschist facies retrogression (P=2±1 kbar; T =300–350 °C) suggests infiltration to depths of 7–9 km in a regime of supra‐hydrostatic fluid pressure. Peak metamorphic quartz veins and associated fluids have δD and δ18O characteristics consistent with a metamorphic origin (δD ?47 to ?75; δ18O+8.6 to +17.4). However, late quartz veins and associated fluids show a broad spread of δD from ?42 to ?148, interpreted in terms of meteoric fluid infiltration. Such negative δD values are only recorded in present‐day high‐latitude or high‐altitude settings, and since north Norway was in an equatorial setting (10° S) in the early Devonian, a high‐altitude origin is deduced. By calculation, and by comparison with modern examples, the early Devonian mountains of the north Norwegian Caledonides are interpreted to have had a topography in excess of 5 km. The deep circulation of surface waters is interpreted in terms of topographically driven flow, linked with a hydrothermal system induced by elevated geothermal gradients due to rapid uplift. Whilst the case for deep penetration of surface‐derived fluids has been promoted for Mesozoic and younger mountain belts, this study represents one of the first documented examples for a Palaeozoic orogenic belt. It suggests that many of the fundamental processes operating during the exhumation of mountain belts are similar irrespective of age.  相似文献   

12.
The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and 87Sr/86Sr ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light δ7Li values, partly close to those of hydrothermal vent fluids (δ7Li: +11.9‰), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic 87Sr/86Sr ratios (∼0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic 87Sr/86Sr ratios (∼0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 °C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments.  相似文献   

13.
The gases emitted from mud volcanoes in the Copper River Basin of Alaska fall into two distinct types which are not mixed during vertical migration. The gases in the eastern volcanoes are nearly pure carbon dioxide, whereas the western ones contain methane and nitrogen and almost no carbon dioxide. Chemical and carbon isotopic compositions suggest the carbon dioxide rich gases originated by solution of limestones and that methane rich gases probably formed by thermal decomposition of coals.Permafrost may be a strong factor in separating the Copper River Basin gases. Extending downward for several hundred feet, the permafrost would prevent shallow lateral migration and focus the energy of the gas into occasional mud volcano vents. Soil gas analyses show rapidly decreasing amounts of the methane to about 150 m and of carbon dioxide to about 20–40 m away from the mud volcano pools. Isotopic variations of these natural methane and carbon dioxide gases, which are not intermixed, indicate that calculations of formation temperatures based on δ13C ratios cannot be used generally.  相似文献   

14.
在羌塘盆地唢呐湖地区发现现代泥火山,通过采集泥浆样、水样等样品,开展水化学离子、水溶烃类气体、碳氢氧稳定同位素等测试分析,对现代泥火山的油气地质意义进行了探讨。水化学类型和氢氧同位素表明,该地区地下可能存在油气藏;水溶烃类气体测试结果表明,气体成分为C1~C5,以甲烷为主,与常规气藏的气体成分一致;碳同位素判别结果表明,其为热解成因的油成气。结合泥火山的地质背景,表明泥火山为油气藏破坏渗漏的产物,在保存良好的未泄露地区,油气勘探具有良好前景。  相似文献   

15.
The chemical and isotopic composition of pore fluids is presented for five deep-rooted mud volcanoes aligned on a transect across the Gulf of Cadiz continental margin at water depths between 350 and 3860 m. Generally decreasing interstitial Li concentrations and 87Sr/86Sr ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin. Although highest Li concentrations at the near-shore mud volcanoes coincide with high salinities derived from dissolution of halite and late-stage evaporites, clayey, terrigenous sediments are identified as the ultimate Li source to all pore fluids investigated. Light δ7Li values, partly close to those of hydrothermal vent fluids (δ7Li: +11.9‰), indicate that Li has been mobilized during high-temperature fluid/sediment or fluid/rock interactions in the deep sub-surface. Intense leaching of terrigenous clay has led to radiogenic 87Sr/86Sr ratios (0.7106) in pore fluids of the near-shore mud volcanoes. In contrast, non-radiogenic 87Sr/86Sr ratios (0.7075) at the distal locations are attributed to admixing of a basement-derived fluid component, carrying an isotopic signature from interaction with the basaltic crust. This inference is substantiated by temperature constraints from Li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures (>200 °C) for the least radiogenic pore fluids of the most distal location.Advective pore fluids in the off-shore reaches of the Gulf of Cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous, fine-grained sediments, resulting in a chemical and isotopic signature similar to that of fluids in near-shore ridge flank hydrothermal systems. This suggests that deep-rooted mud volcanoes in the Gulf of Cadiz represent a fluid pathway intermediate between mid-ocean ridge hydrothermal vent and shallow, marginal cold seep. Due to the thicker sediment coverage and slower fluid advection rates, the overall geochemical signature is shifted towards the sediment-diagenetic signal compared to ridge flank hydrothermal environments.  相似文献   

16.
The Dvurechenskii mud volcano (DMV) is located in permanently anoxic waters at 2060 m depth (Sorokin Trough, Black Sea). The DMV was studied during the RV Meteor expedition M72/2 as an example of an active mud volcano system, to investigate the significance of submarine mud volcanism for the methane and sulfide budget of the anoxic Black Sea hydrosphere. Our studies included benthic fluxes of methane and sulfide, as well as the factors controlling transport, consumption and production of both compounds within the sediment. The pie-shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at its summit north of the geographical center. The anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was repressed in this zone due to the upward flow of sulfate-depleted fluids through recently deposited subsurface muds, apparently limiting microbial methanotrophic activity. Consequently, the emission of dissolved methane into the water column was high, with an estimated rate of 0.46 mol m−2 d−1. On the wide plateau and edge of the mud volcano surrounding the summit, fluid flow and total methane flux were lower, allowing higher SR and AOM rates correlated with an increase in sulfate penetration into the sediment. Here, between 50% and 70% of the methane flux (0.07-0.1 mol m−2 d−1) was consumed within the upper 10 cm of the sediment. The overall amount of dissolved methane released from the entire mud volcano structure into the water column was significant with a discharge of 1.3 × 107 mol yr−1. The DMV maintains also high areal rates of methane-fueled sulfide production and emission of on average 0.05 mol m−2 d−1. This is a difference to mud volcanoes in oxic waters, which emit similar amounts of methane, but not sulfide. However, based on a comparison of this and other mud volcanoes of the Black Sea, we conclude that sulfide and methane emission into the hydrosphere from deep-water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the Black Sea.  相似文献   

17.
文中对准噶尔盆地南缘乌苏四棵树和独山子泥火山的构造背景进行了分析,指出其形成主要是由于天山北缘中新生 代沉积层中地势高低造成的水压差和地层层间压力差,导致丰富的地下水沿着背斜顶端发育的断裂带上升,与通道周围的 泥质岩石相遇,泥浆形成并喷出地表而成为泥火山。论文还对四棵树和独山子泥火山的伴生油苗进行了全油色谱和生物标 记化合物研究,对比相关烃源岩地球化学特征及前人有关研究成果,指出油样有机质均处于成熟阶段,油源可能是侏罗系 与古近系烃源岩的混合产物。研究结果对探索该区泥火山的成因和油气成藏条件具有重要意义。  相似文献   

18.
In order to establish the origin of fluids expelled from mud volcanoes in Trinidad, we analyzed their major-element, trace-element, and isotopic (H, O, Sr) compositions. The mineralogical, chemical, and Sr isotope compositions of associated expelled muds were also determined.On the basis of their chemical and Sr isotope compositions, the fluids were divided into two groups—those southwest and northeast of a major right lateral wrench fault (the Los Bajos fault) that both controls the chemical quality of the fluids and acts as a drain. Strontium isotopes were derived via mixing between a radiogenic source (0.71135) and a nonradiogenic source (≤0.70671) for both southwest and northeast groups. However, the nonradiogenic source possibly feeding the northeast group showed a lower Sr concentration than that of the southwest group. H and O isotope data show that the fluids became enriched in δ18O through interaction with wall rocks. The fluids were originally oceanic, but their properties were subsequently modified by diagenesis as evidenced by chemical data, and mixing between fluids issued from two deep-seated reservoirs and surface aquifer end-members.The gas phase expelled with the mud and the fluid through the mud volcanoes is composed mainly of methane with minor carbon dioxide. The amount of expelled gas seems the same in samples from both sides of the Los Bajos fault. The almost unique methane content of the gas phase and the large positive δ18O shifts of the reservoir end-member, as well as B, Li, and Ba contents, reveal that the fluids from the deep-seated reservoirs inherited their chemical compositions at high-temperature fluid–rock interactions. Estimates of equilibrium temperatures of the two deep-seated reservoirs suggest that, to acquire the estimated higher temperature (150°C), the mud volcanoes must have been fed partly by a reservoir located at a depth of more than 3 km. This depth corresponds to previous geologic information, which located the deep-seated reservoir in Miocene sediments at such a comparable depth. The mixing of the original fluids with a less deep-seated reservoir and meteoric waters on the ascending path suggests the presence of a recharge mechanism and contributes to the dynamics of the expulsion itself.  相似文献   

19.
Microbial methane turnover at mud volcanoes of the Gulf of Cadiz   总被引：2，自引：0，他引：2  
The Gulf of Cadiz is a tectonically active area of the European continental margin and characterised by a high abundance of mud volcanoes, diapirs, pockmarks and carbonate chimneys. During the R/V SONNE expedition “GAP-Gibraltar Arc Processes (SO-175)” in December 2003, several mud volcanoes were surveyed for gas seepage and associated microbial methane turnover. Pore water analyses and methane oxidation measurements on sediment cores recovered from the centres of the mud volcanoes Captain Arutyunov, Bonjardim, Ginsburg, Gemini and a newly discovered, mud volcano-like structure called “No Name” show that thermogenic methane and associated higher hydrocarbons rising from deeper sediment strata are completely consumed within the seabed. The presence of a distinct sulphate-methane transition zone (SMT) overlapping with high sulphide concentrations suggests that methane oxidation is mediated under anaerobic conditions with sulphate as the electron acceptor. Anaerobic oxidation of methane (AOM) and sulphate reduction (SR) rates show maxima at the SMT, which was found between 20 and 200 cm below seafloor at the different mud volcanoes. In comparison to other methane seeps, AOM activity (<383 mmol m−2 year−1) and diffusive methane fluxes (<321 mmol m−2 year−1) in mud volcano sediments of the Gulf of Cadiz are low to mid range. Corresponding lipid biomarker and 16S rDNA clone library analysis give evidence that AOM is mediated by a mixed community of anaerobic methanotrophic archaea and associated sulphate reducing bacteria (SRB) in the studied mud volcanoes. Little is known about the variability of methane fluxes in this environment. Carbonate crusts littering the seafloor of mud volcanoes in the northern part of the Gulf of Cadiz had strongly 13C-depleted lipid signatures indicative of higher seepage activities in the past. However, actual seafloor video observations showed only scarce traces of methane seepage and associated biological processes at the seafloor. No active fluid or free gas escape to the hydrosphere was observed visually at any of the surveyed mud volcanoes, and biogeochemical measurements indicate a complete methane consumption in the seafloor. Our observations suggest that the emission of methane to the hydrosphere from the mud volcano structures studied here may be insignificant at present.  相似文献   

20.
Submarine mud volcanism is an important pathway for transfer of deep-sourced fluids enriched in hydrocarbons and other elements into the ocean. Numerous mud volcanoes (MVs) have been discovered along oceanic plate margins, and integrated elemental fluxes are potentially significant for oceanic chemical budgets. Here, we present the first detailed study of the spatial variation in fluid and chemical fluxes at the Carlos Ribeiro MV in the Gulf of Cadiz. To this end, we combine analyses of the chemical composition of pore fluids with a 1-D transport-reaction model to quantify fluid fluxes, and fluxes of boron, lithium and methane, across the sediment-seawater interface. The pore fluids are significantly depleted in chloride, but enriched in lithium, boron and hydrocarbons, relative to seawater. Pore water profiles of sulphate, hydrogen sulphide and total alkalinity indicate that anaerobic oxidation of methane occurs at 34-180 cm depth below seafloor. Clay mineral dehydration, and in particular the transformation of smectite to illite, produces pore fluids that are depleted in chloride and potassium. Profiles of boron, lithium and potassium are closely related, which suggests that lithium and boron are released from the sediments during this transformation. Pore fluids are expelled into the water column by advection; fluid flow velocities are 4 cm yr−1 at the apex of the MV but they rapidly decrease to 0.4 cm yr−1 at the periphery. The associated fluxes of boron, lithium and methane vary between 7-301, 0.5-6 and 0-806 mmol m−2 yr−1, respectively. We demonstrate that fluxes of Li and B due to mud volcanism may be important on a global scale, however, release of methane into the overlying water column is suppressed by microbial methanotrophy.  相似文献   

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