Simulation of the 2011 South Sakhalin mud volcano eruption based on the GPS data

Sakhalin Island is the only region in the Russian Far East where mud volcanism is manifested on land. The South Sakhalin mud volcano is located in the south of the island in the zone of the Central Sakhalin Fault (upthrow-thrust). The horizontal and vertical displacements of the earth’s surface after this mud volcano erupted in 2011 are revealed for the first time based on the GPS observation data. On the basis of the inversion of the measured displacements for the homogeneous elastic half-space, a model of the finite spherical eruption source is constructed. The coordinates, depth, and possible size of the source are defined and the volumes of the erupted clay rock, water, and gas are estimated.     

Isotopic-geochemical peculiarities of gases in mud volcanoes of eastern Georgia

Isotopic-geochemical study revealed the presence of mantle He (³He/⁴He up to 223 × 10^?8) in gases from mud volcanoes of eastern Georgia. This fact confirms that the Middle Kura basin fill encloses an intrusive body previously distinguished from geophysical data. Wide variations in the carbon isotopic composition δ¹³C of CH₄ and CO₂ and the chemical composition of gas and water at a temporally constant ³He/⁴He ratio indicate their relation with crustal processes. Unusual direct correlations of the ³He/⁴He ratio with the contents of He and CH₄ and the ⁴⁰Ar/³⁶Ar ratio can be explained by the generation of gas in the Cenozoic sequence of the Middle Kura basin.     

Dynamics of the gryphon activity of gas-water lithoclastic (Mud) volcanoes and their relation to the natural seismicity as exemplified by Yuzhno-Sakhalinsk volcano (Sakhalin Island)

This paper reports detailed evidence on the dynamics of the gryphon activity of the Yuzhno-Sakhalinsk gas-water lithoclastic (mud) volcano. It was obtained by visual observations during periods between the short-term eruptions of 1959, 1979, and 2001 and, especially, during continuous monitoring between June 18 and September 3, 2005. In addition to the direct observations, the monitoring included measurements (three times per day) of the air temperature and pressure, the temperature of the liquid lithoclastic mass filling the crater hollows of several gryphons of various types, and the amounts of gases released by the two largest and most active gryphons. Liquid lithoclastic mass was collected daily in the crater of the largest (main or central) gryphon for the subsequent ICP AES analysis for five elements (Al, Fe, Ca, Mn, and Ba). The results of the monitoring were compared with the measurements of natural seismicity using the system of Dat and Datamark digital seismic stations. The acquired information was used to unequivocally demonstrate the existence of a direct causal relation between the activity of the Yuzhno-Sakhalinsk mud volcano, the dynamics of the chemical composition of the liquid lithoclastic mass ejected from its main gryphon, and the regional and local natural seismicity, which was previously conjectured. The dynamics of one of the measured elements (Al) is potentially useful for the prediction of eruptions.     

Structure of the sedimentary cover of the Pugachevo mud volcano area in Sakhalin: Evidence from geophysical modeling

The geological-geophysical data on the Pugachevo mud volcano group located in the zone of the submeridional Central Sakhalin Fault (CSF) are analyzed. The results of the density and geothermal modeling along two orthogonal profiles passing through the central part of the Pugachevo area are examined. It is found that the Late Cretaceous sequence of this fault-related area contains a subvertical narrow anomalous deconsolidation cone-shaped zone widening from 1 km on the surface to 4 km at its base (at the depths more than 6 km). The density of the deconsolidation blocks is 2.20–2.22 g/cm³, whereas that of the adjacent blocks reaches around 2.4–2.5 g/cm³. The largest deconsolidation block is located in the Lower Cretaceous Ai Formation, where a vast reservoir zone with mainly hydrocarbon gas (HC) is inferred at depths of more than 4400 m with temperatures of more than 140°C. The modeling results showed that the main reservoir of gases periodically ejected from the Pugachevo mud volcano is localized in the Ai Formation sequence in the tectonically weakened zone of the CSF at depths of 4.5–5.6 km. The overlying sequences contain smaller intermediate reservoirs. The Pugachevo area is promising for economic hydrocarbon reservoirs.     

Geochemical characteristics of the mud volcano fluids in southwestern Taiwan and their possible linkage to elevated arsenic concentration in Chianan plain groundwater

Fluid and mud samples were collected from Wushanting (WST), Hsiaokunshui (HKS), Yenshuikeng (YSK), Kuantzeling (KZL), and Kunshuiping (KSP) mud volcanoes of southwestern Taiwan. Concentrations of major ions and trace elements in mud volcanic fluids were analyzed to find the possible linkage to elevated arsenic (As) concentrations in the Chianan plain groundwater. The elevated Na⁺, K⁺, and Cl⁻ concentrations indicated possible marine origin of the fluids. The trace element concentrations in the mud volcanic fluids were generally low, but the As concentrations were up to 0.12 mg/L. High contents of As, Fe, and Mn were observed in the mud samples. Saturation index calculations indicated that both carbonate and oxide minerals acted as potential sinks for As in the mud volcanic fluids. Arsenic in the dewatering fluids and muds may be transported by the subsurface flow and surface streams as suspended solids and eventually deposited in the Chianan plain aquifers. Under reducing conditions, As may be released from the host minerals (such as Fe- and Mn-oxides/hydroxides), thereby causing widespread groundwater As pollution.     

Geochemical characteristics of mud volcano fluids in the southern margin of the Junggar basin,NW China: implications for fluid origin and mud volcano formation mechanisms

Mud volcanoes can provide important information about the underlying strata, hydrocarbon accumulation, and recent neotectonic movements in an area. The fluids erupting from mud volcanoes provide important information about their formation and evolution. The ion concentration and the hydrogen and oxygen isotopes of the fluids that were erupted from the three mud volcano groups, Baiyanggou, Aiqigou, and Dushanzi, and nearby rivers in the southern margin of the Junggar basin, northwestern China, are studied. The concentrations of Na and Cl in mud volcano fluids are clearly elevated, displayed as the Na-Cl type. The δD and δ18O values of the fluids are similar between the Baiyanggou and Dushanzi mud volcanoes, which are mainly from ancient sedimentary pore water. However, the Aiqigou mud volcano is depleted in dissolved Cl and shows lower δ18O values with mixed sources, including deep pore and local meteoric water. Two types of mud volcanoes are proposed in this study. One type is low-energy mud volcanoes with a low volume of fluid of deep origin on the hillcrest, which display as mud pool/pie/hole. The other type is high-energy mud volcanoes having mixed fluid origin in the valley and formed in the shape of a mud cone (dome).     

Joint patterns and their relationship to regional trends

An analysis of joint patterns in the Grampians Group rocks o£ Western Victoria has established that the dominant directions are north‐north‐west, east‐north‐east, west‐north‐west, north‐north‐east and north. The master joints are steeply‐dipping structures which formed after the sediments were lithified and folded. The joint‐formation is not genetically related to the folding and post‐dates the emplacement of the igneous intrusions. Joint orientation is independent of lithology and the sediments have reacted as a uniform mass to an applied stress.

The joint pattern conforms with the regional tectonic pattern of faults and lineaments which includes directions of the regmatic shear pattern of Sonder (1947). The jointing and major faulting took place during the Kanimblan Orogeny. The faulting and joint‐formation may have been contemporaneous, the faults being directions along which displacement occurred; conversely the actual movements along faults may have induced the jointing into the sediments.     

Isotopic-geochemical characteristics of the lost city hydrothermal field

The isotopic (δD, δ¹⁸O, δ¹³C, and ⁸⁷Sr/⁸⁶Sr) and geochemical characteristics of hydrothermal solutions from the Mid-Atlantic Ridge and the material of brucite-carbonate chimneys at the Lost City hydrothermal field at 30°N, MAR, were examined to assay the role of the major factors controlling the genesis of the fluid and hydrothermal chimneys of the Lost City field. The values of δD and δ¹⁸O in fluid samples indicates that solutions at the Lost City field were produced during the serpentinization of basement ultramafic rocks at temperatures higher than 200°C and at relatively low fluid/rock ratios (<1). The active role of serpentinization processes in the genesis of the Lost City fluid also follows from the results of the electron-microscopic studying of the material of hydrothermal chimneys at this field. The isotopic (δ¹⁸O, δ¹³C, and ⁸⁷Sr/⁸⁶Sr) and geochemical (Sr/Ca and REE) signatures indicate that, before its submarine discharging at the Lost City field, the fluid filtered through already cold altered outer zones of the Atlantis Massif and cooled via conductive heat loss. During this stage, the fluid could partly dissolve previously deposited carbonates in veins cutting serpentinite at the upper levels of the Atlantis Massif and the carbonate cement of sedimentary breccias underlying the hydrothermal chimneys. Because of this, the age of modern hydrothermal activity at the Lost City field can be much younger than 25 ka.     

新疆乌苏泥火山地球化学特征及其泥浆源

泥火山是地质流体活动的结果,喷发需具备泥浆源、泥浆运移通道和水补给3个条件。对乌苏泥火山8个喷口泥浆进行岩石地球化学分析,轻稀土元素富集,重稀土元素亏损,轻、重稀土元素平均比值为6.81,泥浆中富集大离子亲石元素Ba、Rb等,高场强元素Nb、Ta强烈亏损,Th弱亏损,(La/Yb)_N值为5.47,Ce/La值为2.22,球粒陨石标准异常值δEu显示中等负异常(0.760~0.805);Sr/Ba值为0.33~1.01(平均值0.60),表明源岩为陆相沉积且古盐度较低,Ce/La(2.22)、Ce_(anom)(-0.007)、V/(V+Ni)(0.78)值均指示源岩形成于还原环境。稀土、微量元素分析及地层对比分析表明,乌苏泥火山源岩来自于下侏罗统八道湾组、三工河组,为河流沼泽相-半深湖相含煤地层代表的弱还原-还原沉积环境,源岩的最大埋藏深度为7~8km。泥火山源岩的研究为指示油页岩、烃类物质的位置提供了证据。     

Modeling of the temperature regime of mud volcano gryphons

This paper is devoted to modeling of the dynamics of the temperature regime of mud volcano gryphons. The model is elaborated on the basis of a nonstationary equation of thermal conductivity with a convective component and describes well the observed regularities of thermal regime of South Sakhalin mud volcano gryphons. It is shown that anomalous changes in the temperature of the water-mud mixture after the Gornozavodsk and Nevelsk earthquakes in 2006–2007 are caused by variations in motion velocity of the mixture in the supply pipes of gryphons. It also has been shown that influx of deep geofluids cannot be considered as the main reason for thermal anomalies.     

Neotectonic and modern stresses of South Sakhalin

Tectonophysical studies are conducted in South Sakhalin for identification of temporal–spatial changes in the geodynamic settings of the formation of the local structures. Analysis of the field data reveals 11 local stress state (LSS) in the large newest megastructures, which were formed on geological basement of different ages. The parameters of the tectonic stresses are significantly distinct in each LSS, especially the orientations (up to reindexation) of the compression and extension axes in different fault wings. Tectonic stresses of two ages and constant latitudinal and horizontal compression axis are reconstructed. The earlier cofold shear stress field with a horizontal and longitudinal extension axis is post-Miocene and the later stress field of the reversed fault with a vertical extension axis is orogenic. The LSSs reconstructed for the first time by the displacement vectors on slickensides, along with the data on the earthquake mechanisms, substantiate the reindexation of the horizontal extension axis with the vertical intermediate axis of major normal stresses at the postfold orogenic stage of evolution of the territory. These results are in agreement with previous data on the transformation of the dextral to reverse thrust displacements along the longitudinal fault systems. The young stress field is more confidently interpreted in the activation fault zones, which limit the orogenic blocks, whereas the traces of cofold deformations without younger orogenic stress fields better remain inside the blocks which are composed of older and strongly dislocated Mesozoic rocks.     

东沙群岛海域沉积物游离烃和孔隙水特征及其地球化学意义

对东沙群岛海域HD170和HD196A两个站位，通过系统的顶空气和孔隙水离子取样测试，对柱状样沉积物和底层水中游离甲烷的含量和沉积物孔隙水的离子组成特征以及孔隙水的来源进行了分析。游离气的分析表明，多数沉积物样品中游离甲烷的含量小于20μL／kg，但在HD196A站位，随着沉积物在海底以下埋深的增加，其中的游离甲烷含量迅速增加，在754～774cm，沉积物中游离甲烷的含量达到了7468．66μL／kg，推测其下存在巨大的烃类供应源。孔隙水的^86St／^87Sr同位素测试显示，本文所研究的两个站位沉积物孔隙水来源于正常的海洋沉积过程，而δ^11B的特征表明，沉积物中存在着与海水交换的吸附水，并且HD170站位的交换更多。柱状样沉积物孔隙水中，Ca^2＋、Mg^2＋与SO4^2-浓度表现出随着深度增加而明显降低的趋势，其中HD196A站位的硫酸盐甲烷界面小于10mbsf，暗示了该站位深部很可能赋存天然气水合物。     

Geochemistry of mud volcano fluids in the Taiwan accretionary prism

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.     

火山、泥火山/泥底辟及含气陷阱与油气运聚关系

火山、泥火山/泥底辟及含气陷阱这些特殊的地质体,不仅是揭示地球深部构造运动的窗口和地球深部流体活动特点的表征,而且其与油气运聚关系密切,具有非常重要的油气地质意义。火山与泥火山/泥底辟的主要差异及区别是所形成的物质基础及源动力不同,前者主要反映地壳深部地球动力学过程,其物资基础来源于火山幔源活动上侵和喷发的岩浆物资;后者则是在结晶基底以上的沉积盆地中,由快速沉积充填的欠压实泥页岩发生塑性流动而产生底辟上拱所形成的产物,其物质基础为巨厚欠压实泥页岩。含气陷阱则为气侵或富含气地层所形成的地震反射畸变之痕迹。火山、泥火山/泥底辟发育演化及展布与油气运聚成藏存在明显的成因联系和耦合关系,且控制和制约了沉积盆地中油气分布与聚集。     

South African seismicity, April 1997 to April 1999, and regional variations in the crust and uppermost mantle of the Kaapvaal craton

Events induced by deep gold-mining activity on the edge of the Witwatersrand basin dominate the seismicity of South Africa. The deployment of 54 broad-band seismic stations at 84 separate locations across southern Africa between April 1997 and April 1999 (Kaapvaal network) enabled the seismicity of South Africa to be better defined over a 2-year period. Seismic events located by the South African national network, and by localized seismic networks deployed in mines or across gold-mining areas, were used to evaluate earthquake location procedures and to show that the Kaapvaal network locates mining-induced tremors with an average error of 1.56±0.10 km compared with 9.50±0.36 km for the South African network. Travel times of seismic events from the mines recorded at the Kaapvaal network indicate regional variations in the thickness of the crust but no clearly resolved variations in seismic wavespeeds in the uppermost mantle. Greater average crustal thicknesses (48–50 km compared with 41–43 km) are observed in the northern parts of the Kaapvaal craton that were affected by the Bushveld magmatism at 2.05 Ga. Estimates of average crustal thickness for the southern part of the Kaapvaal craton from receiver functions (38 km) agree well with those from refracted arrivals from mining-induced earthquakes if the crustal thicknesses below the sources are assumed to be 40–43 km. In contrast, the average crustal thickness inferred from refracted arrivals for the northern part of the Kaapvaal craton is larger by about 7 km (51 km) than that inferred from receiver functions (44 km), suggesting a thick mafic lower crust of variable seismic properties due to variations in composition and metamorphic grade. Pn wavespeeds are high (8.3–8.4 km/s), indicating the presence of highly depleted magnesium-rich peridotite throughout the uppermost mantle of the craton. Seismic Pg and Sg phases indicate that the upper crust around the Witwatersrand basin is comparatively uniform in composition when averaged over several kilometres.