钻井液性能对火山碎屑岩崩解性的影响——以青海阿克楚克塞矿区火山碎屑岩为例

为解决火山碎屑岩在钻进中易剥落、易崩塌的问题,探讨钻井液性能对火山碎屑岩崩解性的影响,以青海阿克楚克塞矿区火山碎屑岩为例,分析了其岩石样品的矿物成分,进行了岩石样品烘干和浸水循环实验,采用多元线性回归分析法分析了原1^#、2^#钻井液的主要参数和耐崩解性指数之间的关系。结果表明,钻井液的动塑比、静切力、失水量和漏斗黏度4项性能指标与火山碎屑岩崩解性的相关性可达83.37%,其中动塑比对火山碎屑岩崩解性的影响尤为显著。通过调整水解聚丙烯酰胺和褐煤树脂质量分数提高了钻井液的动塑比和稳定性,从而获得优选钻井液配方：水+4%膨润土+3% Na₂CO₃+0.1% NaOH+0.15% MV-CMC（中黏钠羧甲基纤维素）+0.5% LV-CMC（低黏钠羧甲基纤维素）+2% SPNH（褐煤树脂）+0.08% PHP（水解聚丙烯酰胺）。现场应用表明,钻进至429.00 m深度时使用优选钻井液孔底沉渣厚度较1^#钻井液降低了89.7%,较2^#钻井液降低了80.3%。     

松辽盆地白垩系营城组再搬运火山碎屑与相模式

以松辽盆地东南缘营城组二段两类火山碎屑岩(沉凝灰岩、凝灰质砂岩)为研究对象, 进行了火山碎屑粒度特征、碎屑组成和火山碎屑岩相研究.结果显示, 火山碎屑搬运除受火山作用激发控制外, 还受牵引流、重力流以及牵引流和重力流的双重机制影响.火山碎屑微观特征、成因分析和岩相分析认为, 本区火山碎屑堆积主体为热基浪堆积和热碎屑流堆积, 部分为空落堆积.火山碎屑组成特征为晶屑含量多, 玻屑和岩屑含量少, 且岩屑仅在较粗粒级颗粒组成中存在.研究认为, 本区发育的火山碎屑为沉积环境中的再搬运火山碎屑, 共识别出4种火山碎屑岩相, 河流故道上的热基浪, 河流故道上的热碎屑流, 冲积平原上的热基浪和空落相.建立了松辽盆地东南缘露头区营城组二段河流-冲积平原沉积环境的再搬运火山碎屑岩相模式.      

Study of Distal Pyroclastic-flow Stratum from Tianchi Volcano in 1215 (±15) Eruption: Pyroclastic-flow Over Water

In this paper,we describe three strata at the distal part of the pyroclastic-flow from the Tianchi volcano in 1215(±15) eruption.One of the strata with crosslayers that are different from typical pyroclastic-flow strata may come from a ground-surge.The grain-size and scanning electron microscopy(SEM) analysis was performed to study the origin of the pyroclastic-flow.Characteristics of grain-size distribution show that it is similar with the ash cloud.Through the SEM analyses,we found some quench structures with less damage on the surfaces of the vitric pumices.These phenomena indicate that there has been hydration in the transportation processes at the distal of pyroclastic-flow.It has partly changed the transportation mechanism of pyroclastic-flow,which transitions form dense flow to diluted flow.This paper develops a new distal pyroclastic-flow model in the Tianchi volcano that can be divided into three stages,i.e.the quench stage,expanding stage and depositing stage.     

Transport and deposition of pyroclastic density currents over an inhabited area: the deposits of the AD 79 eruption of Vesuvius at Herculaneum, Italy

Geological and volcanological studies were performed in the Herculaneum excavations, 7 km west of Vesuvius, Italy, to reconstruct the main features of the pyroclastic density currents and the temporal sequence of the ad 79 eruptive events that destroyed and buried the town. The identification of two distinctive marker beds allows correlation of these deposits with the better‐known sequences to the south of Vesuvius, along the dispersal axis of the Plinian fall deposit. Detailed observations from stratigraphic sections show that the pyroclastic density current deposits are characterized by several sedimentary facies, each recording different depositional and emplacement mechanisms. Facies analysis reveals both lateral and vertical variations from massive to stratified deposits, which can be related to the combined effects of flow dynamics and local irregularities of the substratum at centimetre or metre scales. These topographic irregularities enhanced turbulence and allowed rapid transition from non‐turbulent to turbulent transport within the flow. Fabric data from these deposits, both from roof tile orientations and anisotropy magnetic susceptibility (AMS) analyses carried out on some of the pyroclastic deposits, suggest that the pyroclastic density currents were strongly affected by the presence of buildings. These obstacles probably caused deflection and separation of flows into multiple lobes that moved in different directions.     

Identification of dacitic tephra by activation analysis of their primary mineral phenocrysts

Primary mineral phenocrysts from eight different late Quaternary pyroclastic deposits were fractionated for neutron-activation analysis with the purpose of characterizing each of the deposits on the basis of trace and minor element compositions. In hornblende separates, contents of several rare earch and transition elements were found to be distictive for the Mazama, Glacier Peak, and several St. Helens deposits. In magnetites, abundances of transition elements are characteristic and serve as good discriminants for the pyroclastic deposits examined in this investigation. Contents of transition and rare earth elements in hyperthenes also appear useful in distinguishing volcanic ash deposits. Trace and minor element abundances in plagioclase phenocrysts did not appear adequate for identification of pyroclastics due to elemental depletion and similarity of contents for feldspar separates. It was found that contents of Sm and Yb in hornblende phenocrysts would serve to distinguish between several pyroclastic deposits from the Pacific Northwest.     

安徽巢湖地区早三叠世火山碎屑流的岩石学特征及其形成机理

安徽巢湖早三叠世青龙组南陵湖段中的火山碎屑流沉积物,由火山碎屑岩组成,可分为英安 质角砾岩、英安质晶屑－玻屑凝灰角砾岩、英安质玻屑－晶屑凝灰岩和凝灰质灰岩四种岩石类型。沉积 层序分为两个旋回,包括Ｂｏｕｍａ序列的Ａ—Ｃ、Ａ—Ｅ段。层序分析表明,是介于近源和远源之间的过渡 相,属于斜坡沉积环境,物质来源于巢湖以南的浅海区火山喷发物质。     

Noble gases dissolved in groundwater in a volcanic aquifer: Helium isotopes in the Kumamoto Plain

This study Investigates a tracing method using dissolved noble gases to survey the groundwater flow in a large groundwater basin. The tracing method is based on measuring the concentrations of noble gases and the ratio of helium isotopes in groundwater samples. Since it is very difficult to detect trace amounts of noble gases and helium with high accuracy in a 15-ml groundwater sample, dissolved gases were extracted and purified, then a high-resolution mass spectrometer was used for measurement and comparison with standard samples. We used this method with samples from a confined aquifer formed by the deposition of pyroclastic flow in the Kumamoto Plain on the west side of Mt. Aso in central Kyushu, Japan. The groundwater basin under the plain is divided into four small basins, based on the helium concentrations and isotope ratios, with two major groundwater flows. One flow is buried by the Aso pyroclastic flow along the old Kase River; the other is along the Tsuboi River Valley. These two groundwater flows were identified from the different helium isotope-ratios. The helium component from the deep mantle is mixed into the groundwater under the Kumamoto Plain. Finally, data on the concentrations and ratios of³He to⁴He in groundwater samples were used to determine the location of faults in the volcanic aquifer.     

Effect of salt crystallization on weathering of pyroclastic rocks from Cappadocia,Turkey

Salt crystallization is the most significant factor in the degradation of the natural stones used in cultural and historical structures. Stones decay partially or fully as a result of this exposure. This study is the investigation of the degradation of historical monuments (underground cities and semi-underground settlements) carved in pyroclastic rocks in Cappadocian Region which takes part in World Cultural Heritage List. Samples of pyroclastic rocks were collected from six different quarries in Cappadocia, Turkey. To understand the contribution of salt crystallization to this weathering, dry weight loss (DWL) tests were performed on these samples. To investigate the correlations between salt crystallization and other rock properties, porosity, water absorption, ultrasonic velocity, uniaxial compressive strength, Brazilian tensile strength, and point load index were also measured. During the SC process of weathering, the results showed that porosity and water absorption increased for all the samples whereas ultrasonic velocity, uniaxial compressive strength, tensile strength, and point load index values decreased. Evaluation of the data obtained from these tests showed very high logarithmic correlations between the dry weight loss values and the mechanical properties.     

Impact area determination of pyroclastic deposits in Lascar volcano, eruptive process in the year 1993

By means of multi-temporal analysis of satellite images and statistical algorithms, the amount of pyroclastic material deposited on Lascar volcano walls after the gravitational collapse of the eruptive column caused by the eruption that occurred on April the 19th and the 20th in 1993 was determined and quantified. For this analysis, scenes corresponding to Landsat 4 TM in 1989 and Landsat 7 ETM+ in 2001 were used. By careful selection methods such as combination of bands, unsupervised classification, and the Karhunen–Loève transform, detailed analysis of zones of change that correspond to pyroclastic deposits were made. This analysis was complemented with in situ data in order to correct and calibrate the satellite images to identify zones of 1993s eruption pyroclastic deposits. Using Kittler’s and other thresholding algorithms, a search was performed for a proper threshold to binarize the images to determine the surface area covered by the eruptive process. Matlab™ software was used both for general programming and for digital image processing.     

松辽盆地营城组火山岩冷却单元及地层结构分析

火山岩冷却单元的识别是火山岩地层和岩相研究的重要环节。松辽盆地东南缘露头区和徐家围子断陷营城组火山岩剖面的剖析显示,冷却单元主要存在4种主要的单元类型:碎屑岩型、熔岩型、碎屑岩+熔岩型和熔岩+碎屑岩型。碎屑岩型和熔岩型是端元类型,分别反映蒸汽喷发和岩浆喷发的作用过程;碎屑岩+熔岩型是基本组合单元类型,反映蒸汽-岩浆喷发的连续作用过程;熔岩+碎屑岩型属于改造的或特殊机制的类型。冷却单元本身及其堆叠具有相的意义,是火山岩地层的基本成因地层单元,因此成为解释火山岩地层结构、了解形成与保存过程的重要基础。通过火山岩冷却单元识别与叠置分析,构建了松辽盆地徐家围子断陷营城组一段的地层结构。     

冀东晚古生代煤系中火山碎屑岩研究

通过对冀东蓟玉、车轴山,开平三煤田地层剖面观测、岩矿鉴定、粒度分析、岩石化学、氧同位素组成及K-Ar绝对年龄测定,发现在晚古生代煤系中含3-7层火山碎屑岩,主要为含角砾熔结凝灰岩、含角砾岩屑凝灰岩、晶屑岩屑凝灰岩、晶屑凝灰岩、沉凝灰岩、凝灰质砂岩及凝灰质石灰岩;经纵横向对比,可划分为三期七次喷发,物质搬运方向自西北而东南。这一研究成果,对该区地层和煤层对比及地质灾变事件的研究拓开新的局面。     

Pleistocene explosions and pyroclastic currents in west-central Anatolia

The discovery of unexpectedly young tephra, with K-Ar dates of 1.50 ± 0.18 and 1.38 ± 0.13 Ma BP, in the Lake Eirdir area sheds new light on the time-span and magnitude of explosive volcanism in west-central Anatolia and on the physical behaviour of pyroclastic currents. The Gölcük maar near Isparta, widely thought to have ceased its activity in Pliocene time, was apparently still erupting with strong explosions in the Early Pleistocene. The Eirdir tephra, 34 km NE from the volcano, indicate deposition from powerful pyroclastic surges directed by the topography. The depositing currents were fully turbulent and carried unusually large lithic clasts, up to 2–3 cm in diameter, in suspension, which is incompatible with the existing physical model for pyroclastic currents. Based on the tephra characteristics, a conceptual model of the pyroclastic current's segmentation, or lateral dynamic partition, is suggested and used further to explain the current's specific response to an encountered topographic barrier. The widely held concept of a pyroclastic current's vertical separation, or sharp rheological decoupling, is thought to describe a common secondary phenomenon.     

Archaeometric Study of Mortars from the Garum Shop at Pompeii,Campania, Italy

This paper presents the results of the compositional study of 29 samples of mortar from the so‐called “Garum Shop” (I, 12, 8) at Pompeii in Southern Italy. The characterization of the samples yielded information on the raw materials used in the mixtures, the production technology of mortars, and the building phases. It was carried out through polarized optical microscopy, X‐ray powder diffraction, X‐ray fluorescence, microanalysis energy‐dispersive X‐ray spectroscopic microanalysis, and image analysis through the JMicroVision software. The resultant data show great compositional homogeneity among the samples, suggesting the presence of a principal construction phase, probably associated with the first phase of the house. Apart from this main construction phase, there are some samples that show differences related either to their different function or to the fact that they come from different construction phases or restoration works. The raw materials used are related to the geology of the area and are fully compatible with the pyroclastic deposits of Vesuvius.     

Deterministic estimation of hydrological thresholds for shallow landslide initiation and slope stability models: case study from the Somma-Vesuvius area of southern Italy

Rainfall-induced debris flows involving ash-fall pyroclastic deposits that cover steep mountain slopes surrounding the Somma-Vesuvius volcano are natural events and a source of risk for urban settlements located at footslopes in the area. This paper describes experimental methods and modelling results of shallow landslides that occurred on 5–6 May 1998 in selected areas of the Sarno Mountain Range. Stratigraphical surveys carried out in initiation areas show that ash-fall pyroclastic deposits are discontinuously distributed along slopes, with total thicknesses that vary from a maximum value on slopes inclined less than 30° to near zero thickness on slopes inclined greater than 50°. This distribution of cover thickness influences the stratigraphical setting and leads to downward thinning and the pinching out of pyroclastic horizons. Three engineering geological settings were identified, in which most of the initial landslides that triggered debris flows occurred in May 1998 can be classified as (1) knickpoints, characterised by a downward progressive thinning of the pyroclastic mantle; (2) rocky scarps that abruptly interrupt the pyroclastic mantle; and (3) road cuts in the pyroclastic mantle that occur in a critical range of slope angle. Detailed topographic and stratigraphical surveys coupled with field and laboratory tests were conducted to define geometric, hydraulic and mechanical features of pyroclastic soil horizons in the source areas and to carry out hydrological numerical modelling of hillslopes under different rainfall conditions. The slope stability for three representative cases was calculated considering the real sliding surface of the initial landslides and the pore pressures during the infiltration process. The hydrological modelling of hillslopes demonstrated localised increase of pore pressure, up to saturation, where pyroclastic horizons with higher hydraulic conductivity pinch out and the thickness of pyroclastic mantle reduces or is interrupted. These results lead to the identification of a comprehensive hydrogeomorphological model of susceptibility to initial landslides that links morphological, stratigraphical and hydrological conditions. The calculation of intensities and durations of rainfall necessary for slope instability allowed the identification of deterministic hydrological thresholds that account for uncertainty in properties and observed rainfall intensities.     

Long-runout pyroclastic surge on a Cretaceous alluvial plain, Republic of Korea

Pyroclastic surge is a dilute and turbulent flow of volcanic gas and tephra that is commonly generated during explosive volcanic eruptions and can threaten lives along its flow paths. Assessing its travel distance and delineating future volcanic hazards have therefore been major concerns of volcanologists. Historical eruptions show that most pyroclastic surges travel a few tens of kilometres or less from their sources. Aeolian or aquagene processes have therefore been evoked for the emplacement of supposed surge deposits much beyond this distance. Here we show that a Cretaceous tuff bed in Korea was emplaced by an exceptionally powerful pyroclastic surge that flowed as far as the most powerful pyroclastic flows that formed the low-aspect-ratio ignimbrites (LARI). This has significant implications for interpreting ancient volcanic eruptions and delineating volcanic hazards by pyroclastic surges, and casts intriguing questions on the eruption dynamics and physics of long-runout pyroclastic surges and their distinction from LARI-forming pyroclastic flows.     

北京沿河城地区东岭台组酸性火山碎屑流的碎屑分形特征及其成因

火山碎屑岩中的碎屑颗粒形态、分布和显微结构保存着岩浆房内岩浆的结晶状态、火山爆炸过程中的岩浆气泡化和碎裂作用以及火山碎屑堆积和变形过程的大量物理信息。为揭示北京西山沿河城地区东岭台组酸性火山碎屑流形成的物理过程,本文以东岭台组第三岩性段的酸性熔结火山碎屑岩的火山地质、岩相学研究为基础,应用分形理论和方法对酸性熔结火山碎屑岩中的碎屑形态的分形特征开展了定量研究。不同类型碎屑的表面和边界盒维数的数值范围大小具有一致性。玻屑变幅较大,石英晶屑和岩屑变幅较小,这说明碎屑的塑性和流变性对碎屑形态多样性的影响较大。在几类碎屑中,熔蚀石英的边界盒维数和周长-面积法获得的分形维数最大,说明熔蚀作用对石英斑晶边界形态复杂性的影响超过了其它机制对火山碎屑形态复杂性的影响。东岭台组酸性火山碎屑岩中的熔蚀石英、石英碎屑、长石碎屑、玻屑和岩屑的分形特征有明显差异,反映了火山喷发过程中围岩和岩浆性质、物理化学条件以及火山作用机制的差异。火山碎屑形态的分形特征和幂率规律,证明火山爆炸过程是一种自组织临界条件下发生的。     

Volcanic glass textures, shape characteristics and compositions of phreatomagmatic rock units from the Western Hungarian monogenetic volcanic fields and their implications for magma fragmentation

The majority of the Mio-Pleistocene monogenetic volcanoes in Western Hungary had, at least in their initial eruptive phase, phreatomagmatic eruptions that produced pyroclastic deposits rich in volcanic glass shards. Electron microprobe studies on fresh samples of volcanic glass from the pyroclastic deposits revealed a primarily tephritic composition. A shape analysis of the volcanic glass shards indicated that the fine-ash fractions of the phreatomagmatic material fragmented in a brittle fashion. In general, the glass shards are blocky in shape, low in vesicularity, and have a low-to-moderate microlite content. The glass-shape analysis was supplemented by fractal dimension calculations of the glassy pyroclasts. The fractal dimensions of the glass shards range from 1.06802 to 1.50088, with an average value of 1.237072876, based on fractal dimension tests of 157 individual glass shards. The average and mean fractal-dimension values are similar to the theoretical Koch-flake (snowflake) value of 1.262, suggesting that the majority of the glass shards are bulky with complex boundaries. Light-microscopy and backscattered-electron-microscopy images confirm that the glass shards are typically bulky with fractured and complex particle outlines and low vesicularity; features that are observed in glass shards generated in either a laboratory setting or naturally through the interaction of hot melt and external water. Textural features identified in fine- and coarse-ash particles suggest that they were formed by brittle fragmentation both at the hot melt-water interface (forming active particles) as well as in the vicinity of the interaction interface. Brittle fragmentation may have occurred when hot melt rapidly penetrated abundant water-rich zones causing the melt to cool rapidly and rupture explosively.     

北京及邻区长城纪火山事件的沉积记录

北京及邻区的中元古代大红峪组中发育着与火山事件有关的沉积相,主要包括两种基本类型:火山源硅质-陆源砂-碳酸盐岩混积相和火山碎屑重力流沉积,后者又可分为火山碎屑基浪沉积相和火山-沉积角砾碳酸盐岩混积相。初步分析表明,大红峪期大量的硅质沉积主要来自同期的水下火山活动;火山碎屑基浪沉积与火山口内残余热气冲破熔岩封堵而爆发泄出,造成一定范围的海水涌浪作用有关。     

长白山火山历史上最大火山爆发火山碎屑物层序与分布

长白山火山历史时期规模最大的火山喷发发生在1199~1200年。这次大爆发分为两次普林尼（Plinian）式喷发:第一次（早期）喷发称赤峰期,第二次（晚期）喷发称园池期。赤峰期喷发模式为：普林尼式喷发柱（赤峰空落浮岩层）—火山碎屑流（长白火山碎屑流层）—火山泥流（二道白河火山泥流层）,主要由火山碎屑流诱发火山泥流;园池期火山喷发模式为：普林尼式喷发柱（园池空落浮岩火山灰层）—火山碎屑流（冰场火山碎屑流层）。两次普林尼式喷发空落火山碎屑物总量约120 km³,长白火山碎屑流层总量约8 km³,冰场火山碎屑流层总量约0.5 km³,火山泥流堆积总量约为2 km³。主要论述了这次大爆发的火山喷发碎屑堆积物的层序和分布。     

汝城拉张盆地基性火山碎屑岩建造

汝城拉张盆地中发育的侏罗系基性火山碎屑岩,与大致顺层侵入的辉绿岩及呈层状产出的玄武岩共同组成了一套基性火山岩系。该区基性火山碎屑岩建造属正常火山碎屑岩与正常沉积岩之间的过渡性岩类,包含沉积火山碎屑岩和火山碎屑沉积岩两个亚类。从北东向南西由厚(543 m)变薄(0.6 m)。具有快速堆积的逆向粒序构造特征。玄武岩角砾的化学成份在全碱-SiO_2相关图上投影点属拉斑玄武岩,其氧化系数(0.63)表明为近地表氧化环境形成。稀土元素模式与辉绿岩近于重合,表明两者同源。钾-氩法同位素年龄为145.6Ma。