Concentration of earthquake energy in and around the Aegean volcanic belt

The seismic energy concentration within the volcanic chain of the Aegean Sea is calculated. The definition of the concentration of earthquake energy is briefly treated mathematically. According to the results, in the lower half of the part of the lithosphere under the respective volcanoes there exist cylinder-like volumes, with a radius of at least 25 km, in which the rigidity of the material is presumably too low for the slow accumulation of mechanical strains. These cylindric aseismic domains are to be found beneath all of the volcanoes considered, and can be regarded as the place of deep volcanic vents (“translithospheric chimneys”), corresponding to the theory of Ninkovich and Hays (1971) as well as that of Gorshkov (1969). As regards the upper half of the lithosphere, the continuation of these translithospheric volcanic vents is there much narrower.     

火山岩储层质量预测方法探讨——以松辽盆地徐家围子断陷为例

松辽盆地徐家围子断陷深层火山岩储层具有埋藏深、 温度高、 压力大、 物性差、 非均质性强的特征。为了预测火山岩储层类型和质量在平面上的变化规律,本文讨论了影响火山岩储层物性的主要地质因素。结果表明,火山岩的物性主要受火山岩相（组）和所处对应碎屑岩成岩阶段的影响。距火山口越远的火山岩相组的火山岩储层,其孔隙度和渗透率越低。火山岩工业气层主要分布在晚成岩阶段A期以前的火山岩储层中。在晚成岩阶段B期,只有少量低产气层。本文充分考虑徐家围子断陷火山岩相和成岩作用对火山岩储层物性的影响与控制,应用成岩模拟软件,预测了成岩阶段的横向展布,通过叠合营三段火山岩相图和成岩阶段预测图,预测了火山岩储层的类型和质量,目前已发现工业气流的井主要分布在断陷中部的Ⅱ、 Ⅲ类火山岩储层中。     

Tracing the Seepage of Subsurface Sinkhole Vent Waters into Lake Huron Using Radium and Stable Isotopes of Oxygen and Hydrogen

Exchange of water between groundwater and surface water could alter water quality of the surface waters and thereby impact its ecosystem. Discharges of anoxic groundwater, with high concentrations of sulfate and chloride and low concentrations of nitrate and oxygen, from three sinkhole vents (El Cajon, Middle Island and Isolated) in Lake Huron have been recently documented. In this investigation, we collected and analyzed a suite of water samples from these three sinkhole vents and lake water samples from Lake Huron for Ra, radon-222, stable isotopes of oxygen and hydrogen, and other ancillary parameters. These measurements are among the first of their kind in this unique environment. The activities of Ra are found to be one to two orders of magnitude higher than that of the lake water. Isotopic signatures of some of the bottom lake water samples indicate evidences for micro-seeps at distances farther from these three vents. A plot of δD versus δ¹⁸O indicates that there are deviations from the Global Meteoric Line that can be attributed to mixing of different water masses and/or due to some subsurface chemical reactions. Using the Ra isotopic ratios, we estimated the transit times of the vent waters from the bottom to the top of the vent (i.e., sediment–water interface) to be 4–37 days. More systematic studies on the distribution of the radioactive and stable isotope studies are needed to evaluate the prevalence of micro-seeps in Lake Huron and other Great Lakes system.     

川东北天然气单体烃氢同位素组成特征

采用气-水平衡法及同位素分馏平衡方程技术标定工作标准气,测定样品的氢同位素比值,使误差控制在5‰以内。采取川东北、鄂西和川西三个地区的天然气样品,分别测定它们的单体烃氢同位素比值。分析表明,川东北普光气田海相成因天然气甲烷氢同位素δD平均值为-126‰(SWOM),比新疆塔河油田海相环境生成的天然气甲烷氢同位素δD平均值-164‰重约40‰。对比研究认为,这与其共存地层水的δD值密切相关,也与这些天然气的成熟度有直接关系。     

松辽盆地深层火山岩储层中的CH4包裹体:产状特征及其地质意义

营城组火山岩是松辽盆地深层油气藏的主要储层之一,本次研究我们在该组火山岩中首次发现了较多的纯CH4包裹体,这类包裹体主要以原生及次生形式产于流纹岩石英斑晶及玄武岩气孔充填矿物石英之中。综合分析认为,伴随营城组火山岩喷发活动,产生了较多的无机成因的CH4等气体,它们连同可能存在的其它有机成因的烃类气体一起,沿流纹岩中的微裂隙及玄武岩中的气孔等构造运移、聚集,从而形成深层火山岩储层中的富CH4天然气藏。因此,营城组火山岩不仅仅作为被动的油气储层存在,而且该期火山活动可能也为深层油气成藏提供了至少部分CH4等气体的来源。     

Distribution and accumulation rate of Hg in the upper quaternary sediments of the Deryugin Basin,Sea of Okhotsk

The Hg distribution and some mineralogical-geochemical features of bottom sediments up to a depth of 10 m in the Deryugin Basin showed that the high and anomalous Hg contents in the Holocene deposits are confined to a spreading riftogenic structure and separate fluid vents within it. The accumulations of Hg in the the sediments were caused by its fluxes from gas and low-temperature hydrothermal vents under favorable oceanological conditions in the Holocene. The two mainly responsible for the high and anomalous Hg contents are infiltration (fluxes of hydrothermal or gas fluids from the sedimentary cover) and plume (Hg precipitation from water plumes with certain hydrochemical conditions forming above endogenous sources). The infiltration anomalies of Hg were revealed in the following environments: (1) near gas vents on the northeastern Sakhalin slope, where high Hg contents are associated only with Se and were caused by the accumulation of gases ascending from beneath the gas hydrate layer; (2) in the area of inferred occasionally operating low-temperature hydrothermal seeps in the central part of the Deryugin Basin, in which massive barite chimneys, hydrothermal Fe-Mn crusts, and anomalous contents of Mn, Ba, Zn, and Ni in sediments develop.     

周口店洞穴堆积物及大同火山烘烤层的热发光年龄

本文是对采自北京周口店洞穴及山西大同火山地区的一批样品进行热发光年龄测定的结果。 1.在周口店第一地点,自上而下采集了4-4、4-5、10-6三个灰烬样。测定结果表明,天然热发光强度随取样的层位变低而增强。4-4、10-6测样热发光相对强度4.5和9.5,为一底部较宽的不完全对称的200℃左右的中温峰。     

Origin of sulfur species in acid sulfate-chloride thermal waters,northeastern Japan

Acid sulfate-chloride thermal water samples collected together with fumarolic gases from various volcanic areas in northeastern Japan were studied chemically and isotogdically. δ³⁴S (COT) values of sulfate and hydrogen sulfide from these volcanic hot springs range from +4.0 to +31 and from ?15.0 to ?2.0% respectively, with δ³⁴S_ys value of +2.5 to +31. The δ³⁴S of the sulfate in the more saline waters tends to become smaller with increasing ratio of SO₄ to Cl, although the chemical and isotopic composition of acid thermal water within some areas may be altered by secondary processes during the discharge of the thermal waters. This trend can be explained by the reaction of the volcanic gases, having S/Cl of 4 ~ 7 and total sulfur of ~0% in δ³⁴S, with ground water at 200°C, and/or the removal of sulfide phase depleted in ³⁴S from the acid thermal water formed by the disproportionation of volcanic sulfur. The sulfur species in acid sulfate-chloride thermal water are shown to be volcanic exhalations.     

松辽盆地北部火山岩CO2脱气参数及其对CO2资源量估算的意义

为了定量评价火山岩脱CO2气量的潜力，选择松辽盆地北部火山岩进行了低温脱气实验。将火山岩加热到250℃时，脱出挥发份总量为0.0299～0.0790ml/g；其中CO2脱出量为0.0218～0.0706 ml/g（0.429～1.387wt％）。脱挥发份总量与其中CO2量具有良好的正线性相关；挥发份以CO2气为主，其次是Ｎ2气，还伴有H2、CO、CH4等还原性气体，以及更少量的低碳烷烃；基性火山岩比中、酸性火山岩脱出CO2数量较多。火山岩吸附大量CO2气，成为充足气源，火山岩脱出的吸附气主要是辗转而来的深源气，火山岩成为探索幔源气成藏的主要源岩，尤其是基性火山岩。估算CO2资源量，可将250℃时火山岩挥发份含量作为岩石挥发份及残余CO2量的下限值，而全岩分析的总碳含量可作为CO2脱出量的上限值。     

辽宁北部秀水盆地下白垩统义县组火山岩LA-ICP-MS锆石U-Pb年龄及其地质意义

为查明秀水盆地烃源岩层位形成时代,对侵位到秀D1井义县组三段沉积地层中的次火山岩样品和地表发育的义县组火山岩样品,分别进行LA-ICP-MS锆石U-Pb测年,获得火山岩同位素年龄值为121.5±1.2~121.3±3.5 Ma,时代为早白垩世。通过与区域相同时代火山岩同位素年代学对比研究表明,秀水盆地火山岩形成时期为义县组末期火山活动。秀水盆地义县组末期火山岩年龄的确定,不仅确定了义县组末期火山岩形成的上限年龄(121.3 Ma),同时也确定了秀水盆地主力烃源岩层位(义县组三段)的上限年龄(约121 Ma)。明确了义县组三段沉积层作为辽宁西北地区重要的油气勘探目的层系,为松辽盆地外围断陷盆地群油气勘探提供了新的目的层系。     

Paleostress analysis of the volcanic margins of Yemen

The western part of Yemen is largely covered by Tertiary volcanics and is bounded by volcanic margins to the west (Red Sea) and the south (Gulf of Aden). The Oligo–Miocene evolution of Yemen results from the interaction between the emplacement of the Afar plume, the opening of the Red Sea, and the westward propagation of the Gulf of Aden. Structural and microtectonic analyses of fault slip data collected in the field reveal that the volcanic margins of Yemen are affected by three main extensional tectonic events. The chronological order of these events is as follows: first E–W extension was associated with the emplacement of volcanic traps of Yemen, then NE–SW extension was related to the Red Sea rifting, and finally, the volcanic margin was submitted to N160°E extension, perpendicular to the overall trend of the Gulf of Aden, which we interpret as induced by the westward propagation of the oceanic ridge of the Gulf of Aden.     

Dissolved helium isotope ratios in ground-waters: a new technique based on gas–water re-equilibration and its application to Stromboli volcanic system

Here, a new technique for the determination of dissolved He isotope ratios in ground-waters is presented. This method is based on the extraction and subsequent equilibrium of dissolved gases in an added “host” gas phase. Ultra pure N₂ is placed in glass flasks (250 cc), containing water samples, that were hermetically sealed after their collection. After shaking in an ultrasonic bath for 10 min, an aliquot of the separated gas phase was removed from the flask for MS analysis. ³He/⁴He ratios are measured by using a modified double collector mass spectrometer (VG 5400-TFT). Helium and Ne concentrations are calculated by comparing the partial pressures of masses 4 and 20 of the samples with those of the air-standard measured by a quadrupole mass spectrometer (QMS;VG Quartz). Using He and Ne equilibrium partitioning coefficients, it is possible to calculate the amount of gas originally dissolved in the water. The technique was tested on both air-saturated waters (ASW) and thermal waters from Stromboli (Aeolian Islands, South Italy), the results of which confirmed good reproducibility (≌5%) and accuracy (≌3%) of the data. The method was then applied to three thermal water samples collected from the same volcanic area and the results compared with those of a fumarolic and a soil gas. The isotope ratios for dissolved He gave values of 4.06–4.23 Ra, which are significantly higher than those previously reported in the literature (3.0, 3.5 and 2.9 Ra) and that measured at the fumarole (3.09 Ra), suggesting a newer and higher isotopic signature for the volcanic system. The proposed method appears to be a useful tool in the determination of ³He/⁴He ratios in ground-water systems, especially when free gases are not available or are dangerous to collect.     

Martian volcanism: Current state of knowledge and known unknowns

Much has been discovered about volcanism on Mars over the past fifty years of space exploration. Previous reviews of these discoveries have generally focused on the volcanic constructs (e.g., Olympus Mons and the other volcanoes within the Tharsis and Elysium regions), the analysis of individual lava flows, and how volcanic activity on Mars has evolved over time. Here we focus on attributes of volcanology that have received less attention and build upon characteristics of terrestrial volcanoes to pose new questions to guide future analyses of their Martian equivalents either with existing data sets or with new types of measurements that need to be made. The remarkable lack of exposed dikes at eroded ancient volcanoes attests to an internal structure that is different from terrestrial equivalents. Enigmatic aspects of the origin of the ridged plains (commonly accepted to be volcanic but with few identifiable flow fronts and only rare vents), the style(s) of volcanism during the earliest period of Martian history (the Noachian), and the possible mode(s) of formation of the Medusae Fossae Formation are considered here. Martian meteorites have been dated and are volcanic, but they cannot be correlated with specific geographic areas, or the chronology of Mars derived from the number of superimposed impact craters. Some of these questions about Martian volcanism can be addressed with existing instrumentation, but further progress will most likely rely on the acquisition of new data sets such as high-resolution gravity data, the return of samples from known localities, the flight of a synthetic aperture imaging radar, penetrators sent to the Medusae Fossae Formation, and detailed in situ field observations of selected volcanic sites.     

火山岩体地震特征识别技术与应用研究

利用地震反射特征和反演所得的特征参数等相结合的地震特征识别技术在无井或少井的火山岩地区可以直接识别火山岩体的位置及范围.将此识别技术对某油田的营城组火山岩体进行识别与评价中,圈出4个最佳有利火山岩体,并利用密度技术对新圈出的最佳有利火山岩体进行油气检测,密度小于或等于2.53 g/cm3的火山岩体部位为天然气富集部位或富集空间,钻井后证实有很好的地质效果和较高的勘探开发成功率,为复杂的火山岩体的识别与预测提供了新的技术支持.在营城组火山岩体的识别与评价中发现火山岩储层在空间中存在复杂多变性,表现出较强的非均质性和特征差异性,其储层存在分割现象,但是,在好的岩性和构造背景下仍可形成局部天然气的富集.     

Helium isotopes in geothermal systems: Iceland,The Geysers,Raft River and Steamboat Springs

Helium isotope ratios have been measured in geothermal fluids from Iceland, The Geysers, Raft River, Steamboat Springs and Hawaii. These ratios have been interpreted in terms of the processes which supply He in distinct isotopic ratios (i.e. magmatic He, ~10 R_a; atmospheric He, R_a; and crustal He, ~0.1 R_a) and in terms of the processes which can alter the isotopic ratio (hydrologic mixing, U-Th series alpha production and weathering release of crustal He, magma aging and tritiugenic addition of ³He). Using this interpretational scheme, Iceland is found to be an area of hot-spot magmatic He implying an active volcanic source although the data are suggestive of high-temperature weathering release of crustal He incorporated in the geothermal fluids. By comparison to fumarolic gases from Hawaii and Juan De Fuca and Cayman Trench basaltic glass samples, The Geysers contains MOR type magmatic He again implying an active volcanic source possibly a “leaky” transform related to the San Andreas Fault System. Raft River contains only crustal He indicating no active volcanic sources. Steamboat Springs He isotope ratios are distinctly less than typical plate margin volcanics but must still have a magmatic source. A preliminary assessment of the cause for this low ratio is made assuming an “aging” magma source.     

The behavior of 232Th and the 238U decay chain nuclides during magma formation and volcanism

Concentrations of the members of the ²³⁸U decay chain and ²³²Th were determined in volcanic rocks from convergent plate margins, intraplate volcanoes and oceanic spreading centers. Contemporary and historical volcanic rocks from Mt. St. Helens, Arenal, El Chichon, Hawaii and Iceland and submarine basaltic glass from the Galapagos spreading center all show no fractionation of U and Th in the mantle source or during magma formation at least for the past 300,000 years. Mauna Kea (Hawaii) rocks of alkaline composition greater than 4000 years old and an old submarine basalt show disequilibrium for several of the nuclides in the ²³⁸U decay chain. We interpret these as resulting from post-emplacement processes.     

Geochemical study of products associated with spontaneous oxidation of coal in the Cerro Pelado Formation,Venezuela

The aim of this research work is a geochemical, mineralogical, and textural characterization of spontaneously smouldered coal-derived products in northwestern Venezuela (Cerro Pelado Formation, some 10 km from Pedregal city). Several solid samples were collected from this formation, six of unweathering coal, an other six of resulting unmelted rocks forming on a surface coal bed, and the last four of mineralizations found accumulating around gas vents. The fresh coal and the unmelted material were analysed by scanning electron microscopy, X-ray diffraction, and proximate techniques. Products such as magnetite and chabazite-K were identified in the alteration rocks. Likewise, both materials were also studied in order to determine the mobilization of 17 elements into the environment; such elements were analysed through inductively coupled plasma atomic emission spectroscopy on extracts obtained by a sequential extraction method: each sample was firstly extracted with MilliQ water and then the resultant residue was washed. This and the subsequently resulting residues are extracted according to the mentioned procedure by using, respectively, ammonium acetate, chlorhydric acid, peroxide and chlorhydric acid, nitric acid and fluorhydric acid, and nitric acid. The studied elements are classified as highly mobile (Na, Ni, ...), nearly immobile (Ti, P) and partially mobile (Mg, Fe, K, ...). In regards to mineralizations around fumaroles associated with smoldering coal seams, Fourier-transform infrared spectroscopy and X-ray diffraction analyses have revealed the presence of salammoniac, mascagnite and other solid combustion compounds formed by reaction of gas emitted from coal oxidation, in addition to previously non-reported sulfur-rich by-products associated with gas fissures, particularly ammonium thiosulfate, a phase first obtained only synthetically in the laboratory. Another objective of the research was to collect and analyse gases escaping from surficial vents. Relatively high concentrations of several aromatic compounds were detected in the gas collected at the studied coal outcrop, as well as aliphatic hydrocarbons including ethane, propane, butanes, among others. High contents of carbon monoxide, methane and carbon dioxide were also measured for gas samples.     

CFD油田火山岩展布特征及其对油藏的控制作用

火山岩复合油气藏特征独特,为揭示该类油气藏的特征和拓展勘探思路,论述了火山岩的特征及其对油藏的控制作用.综合薄片、钻井、测井和地震资料研究火山岩的岩相特征和发育模式,采用岩电分析和测井响应特征研究手段定量识别玄武岩和凝灰岩.在此基础上,依据地球物理手段确定火山岩和砂泥岩的波阻抗界限值,并基于测井约束下的波阻抗反演和东营组局部井区杂乱反射的地震特征,实现复杂岩性背景下火山岩的刻画和分布预测.论证结果:馆陶组为火山大规模活动期,发育大套火山岩,火山岩主要分布于油田南部和西南部.东营组和沙河街组火山小规模活动,发育少量火山岩,零星分布于油田的局部井区;主断裂区火山岩较厚,远离断裂区火山岩相对较薄,主断裂控制火山岩的发育程度和分布;火山岩岩性致密,可作为油藏的盖层和侧向遮挡层,并占据外来碎屑岩的沉积空间;火山岩是研究区油气成藏的必要条件,但其分割圈闭,控制和限制碎屑岩储层的分布,也限定了油藏的类型和规模,并对原油物性具有一定的影响.研究成果揭示了渤海湾盆地中新生界新的勘探领域,也可为该类油田的油藏评价和开发部署提供范例.      

Cones and craters on Mount Pavagadh,Deccan Traps: Rootless cones?

Rootless cones, also (erroneously) called pseudocraters, form due to explosions that ensue when a lava flow enters a surface water body, ice, or wet ground. They do not represent primary vents connected by vertical conduits to a subsurface magma source. Rootless cones in Iceland are well studied. Cones on Mars, morphologically very similar to Icelandic rootless cones, have also been suggested to be rootless cones formed by explosive interaction between surface lava flows and ground ice. We report here a group of gentle cones containing nearly circular craters from Mount Pavagadh, Deccan volcanic province, and suggest that they are rootless cones. They are very similar morphologically to the rootless cones of the type locality of Myvatn in northeastern Iceland. A group of three phreatomagmatic craters was reported in 1998 from near Jabalpur in the northeastern Deccan, and these were suggested to be eroded cinder cones. A recent geophysical study of the Jabalpur craters does not support the possibility that they are located over volcanic vents. They could also be rootless cones. Many more probably exist in the Deccan, and volcanological studies of the Deccan are clearly of value in understanding planetary basaltic volcanism.     

松辽盆地庆深气田储层火山岩锆石地质年代学研究

庆深气田储层火山岩由多期火山喷发叠置形成,分布于白垩系下统营城组,以酸性喷发岩为主。火山岩离子探针(SHRIMP)U-Pb锆石年龄测定结果表明,储层火山岩年龄集中在111~115Ma,介于早白垩世晚期阿普第阶(Aptian)和阿尔布阶(Albian)分界线附近。兴城与升平两个天然气产区储层火山岩测年结果对比表明,它们是同一时代火山作用产物,并非以前所认为的兴城地区火山岩属营城组一段,升平地区火山岩属营城组三段。该成果对于松辽盆地火山岩气藏的勘探开发具有重要的实际意义。