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1.
火山"熔岩流气泡古高度计"及其在云南腾冲火山区的应用   总被引:6,自引:5,他引:1  
通过对火山熔岩流及其气泡特征的研究能够确定熔岩流喷发时的古高度,本文将这一方法称为火山“熔岩流气泡古高度计”.“熔岩流气泡古高度计”是在实地测量熔岩流厚度和实验室对熔岩流顶底气泡体积精确测定的基础上,利用流体力学原理和气体状态方程,通过计算古大气压强,最终获得火山喷发时的古高度.由于火山岩是开展同位素测年的理想材料,并且利用熔岩流计算古高度所需的参数(熔岩流厚度和气泡体积)不受古气候等因素(温度、降雨量等)影响,因此,这一方法以其可靠的年龄和独立的计算参数明显区别于其它古高度计.“熔岩流气泡古高度计”核心技术包括:(1)熔岩流的挑选与厚度测量;(2)熔岩流底部和顶部气泡体积的计算.中等规模、具简单冷凝历史,并且厚度稳定的偏基性熔岩流,是开展古高度计算的理想对象.熔岩流气泡体积的测试手段包括注胶、岩石抛光-扫描、体视学转换和三维CT扫描4种方法.“熔岩流气泡古高度计”最终计算结果误差为400m左右.本文利用“熔岩流气泡古高度计”计算了腾冲火山区熔岩流的古高度,研究结果显示:“熔岩流气泡古高度计”计算的黑空山熔岩流高程与目前的实际高程相吻合.开展“熔岩流气泡古高度计”研究的前提是研究区必须出露保存完好的熔岩流.我国青藏高原的隆升历史一直是国际学术界争论的热点课题,那里出露大面积熔岩流.可以预见,“熔岩流气泡古高度计”将会逐渐成为研究青藏高原隆升历史的有效手段之一.  相似文献   

2.
Just like in sedimentary stratigraphy, the volcanostratigraphic boundary is an important factor for constructing volcanostratigraphic framework. The fundamental factor of volcanostratigraphic boundaries is to classify the types and define their characteristics. Based on field investigation and cross-wells section analysis of Mesozoic volcanostratigraphy in NE China, 5 types of volcanostratigraphic boundaries have been recognized, namely eruptive conformity boundary(ECB), eruptive unconformity boundary(EUB), eruptive interval unconformity boundary(EIUB), tectonic unconformity boundary(TUB) and intrusive contacts boundary(ICB). Except ICB, the unconformity boundaries can be divided into angular unconformity and paraconformity. The time spans and signs of these boundaries are analyzed by using age data of some volcanic fields that have been published. The time spans of ECB and EUB are from several minutes to years. In lava flows, cooling crust is distributed above and below ECB and EUB; in pyroclastic flows, airfalls and lahars, a fine layer below these boundaries has no discernable erosion at every part of the boundary. EUB may be curved or cross curved and jagged. The scale of ECB/EUB is dependent on the scale of lava flow or pyroclastic flows. The time span of EIUB is from decades to thousands of years. There is also weathered crust under EIUB and sedimentary rock beds overlie EIUB. In most instances, weathered crust and thin sedimentary beds are associated with each other laterally. The boundary is a smooth curved plane. The scale of EIUB is dependent on the scale of the volcano or volcano groups. The characteristics of TUB are similar to EIUB’s. The time interval of TUB is from tens of thousands to millions of years. The scale of TUB depends on the scale of the basin or volcanic field. Both the lab data and logging data of wells in the Songliao Basin reveal that the porosity is greatly related to the boundaries in the lava flows. There is a high-porosity belt below ECB, EUB or EIUB, and the porosity decreases when it is apart from the boundary. The high-porosity belt below ECB and EUB is mainly contributed by primary porosity, such as vesicles. The high-porosity belt below EIUB is mainly contributed by primary and secondary porosity, such as association of vesicles and spongy pores, so the area near the boundary in lava flows is a very important target for reservoirs.  相似文献   

3.
We present a new model for the evolution of volcanic table mountains, based on volcanological and petrological studies of Herdubreid/Herdubreidartögl, an upper Pleistocene volcanic complex within the active Icelandic rift zone. The evolution of these table mountains is highly complex and influenced substantially by different eruptive environments as well as changing magma sources and volcanic and magmatic processes. Whereas current models imply entirely subglacial conditions and continuous compositional (“monogenetic”) evolution for these volcanoes, we subdivide their evolution into four eruptive periods characterized by different environments: (a) Subaerial lava flows erupted during an interglacial period. (b) Lavas and voluminous hydroclastic deposits formed in a lake during a waning period of the last glaciation. (c) Subglacial eruptions during thickening of the ice sheet as a result of a climatic deterioration built pillow lava piles overlain by steep-sided complexes of hydroclastic deposits. These deposits differ from those of the second eruptive period in structure, texture, and degree of alteration. Subaerial lava flows and agglutinates covered these deposits after buildup above the ice sheet. (d) Subaerial lava flows and fallout deposits during a postglacial period. The detailed analysis of volcanic table mountains appears to be a very sensitive indicator of climatic fluctuations. Although most deposits of the studied volcanoes were formed during the waning period of the last glaciation, the subglacial deposits in the upper part of the volcanic complex reflect a temporary, but major, thickening of the ice sheet.  相似文献   

4.
During emplacement, lavas modify the pre‐existing topography and release a large amount of heat. In spite of the relevance of both heat and mass release, combined morphological and thermal analyses have been seldom carried out at a flow‐field scale. Here, we consider a channelised lava flow unit formed at Mt Etna during the 2001 flank eruption, and we show that, by combining a morphological analysis of the pre‐ and post‐emplacement topography with the analysis of the syn‐eruptive thermal signature, critical insights about the processes driving mass and heat dissipation can be derived. Our results suggest that, in the considered lava flow, the pre‐emplacement slope controls heat dissipation and can influence the thickness of the final lava deposit, with possible implications for hazard assessment. The width of the lava channel, instead, appears less sensitive to the pre‐emplacement slope, and tends to regularly increase with increasing distance from the vent.  相似文献   

5.
塔里木溢流玄武岩的喷发特征   总被引:5,自引:3,他引:2  
上官时迈  田伟  徐义刚  关平  潘路 《岩石学报》2012,28(4):1261-1272
通过对柯坪地区二叠系野外火山岩露头剖面和英买力、哈拉哈塘井区二叠系火山岩钻井剖面的对比,将塔里木早二叠世溢流玄武岩划分为三个旋回,从老到新依次是:库普库兹满溢流玄武岩旋回(KP),长英质火山碎屑岩旋回(FP)和开派兹雷克溢流玄武岩旋回(KZ)。KP旋回以巨厚溢流玄武岩夹凝灰岩为特征,在柯坪露头区和英买力井区均可划分出三层巨厚玄武质熔岩流,至哈拉哈塘井区减少为一层玄武岩流,但长英质火山碎屑岩和熔岩厚度增加。FP旋回在柯坪露头区自下而上包括空落相凝灰岩,熔结凝灰岩,再沉积火山碎屑岩和正常碎屑岩夹火山灰层,该层可与英买力及哈拉哈塘井区的凝灰岩层对比,表明在塔北存在一期面积广泛的长英质火山喷发。KZ旋回以溢流玄武岩为主,在开派兹雷克剖面识别出四期喷发共8层溢流玄武岩和一期安山质玄武岩,每期喷发之间夹少量碎屑岩,但未见长英质火山碎屑岩夹层,该特征与英买力和哈拉哈塘井区的火山层序组合不同,而与塔中溢流玄武岩类似。三个火山旋回的划分表明塔里木大火成岩省经历了"基性溢流玄武岩-酸性火山碎屑岩-基性溢流玄武岩"的演变过程,与Afro-Arabian溢流玄武岩省相似,可进行对比研究。  相似文献   

6.
The amphitheater of Catania is one of the main architectural structures built during Roman domination of the town. It was constructed in two successive phases between the 1st and 2nd centuries A.D. and fell into disuse from the second half of the 4th century. Detailed geological and petrographic investigations allow better geomorphological reconstruction of the area where the monument was built. In particular, the western and eastern portions of the amphitheater are built on prehistoric lava flows, named Barriera del Bosco and Larmisi, respectively. We infer that the choice of site to build the monument was highly influenced by the morphological setting of the area. In fact, the location at the contact between two lava flow fields facilitated excavation and removal of rocks due to the incoherence of the scoriaceous lateral border of the lava flows. Integrating both archaeological and geological data has revealed that a large number of Neolithic, Greek, and Roman sites are located in the lava fields of Barriera del Bosco and Larmisi within the present urban district of Catania, indicating that during its long history the city was directly impacted by only one lava flow, namely in A.D. 1669.  相似文献   

7.
Gran Canaria, like most of the Canary Islands, shows evidence for young basaltic volcanism in the form of cinder cones and valley‐hugging lava flows. These landforms were of no particular use to the aboriginal population, nor to the subsequent Spanish settlers, and young lava flows and lava fields are still referred to as ‘malpaís’ (badlands) in the Canary Islands. In north‐west Gran Canaria, one such lava flow fills the bottom of a steep‐sided valley, which reaches the sea at the present day village of Agaete. The lava flow erupted c. 3030 ± 90 yr bp and displays a total length of ~ 11 km. At its distal end, just outside Agaete, it hosts one of Europe’s largest and most important pre‐historic burial sites constructed of volcanic rock: the Maipés necropolis. Over 700 pre‐historic tombs (or tumuli) constructed from the aa‐type clinker materials have been identified on top of the valley‐filling lava flow. The up to soccer‐ball sized vesicular clinker fragments are sufficiently low in density to provide abundant, workable basalt blocks for the construction of the tumuli, allowing the pre‐hispanic aboriginal population to create a large and magnificent ‘sacred ground’ in an otherwise barren landscape.  相似文献   

8.
戴紧根  丁文君  王成善 《地质通报》2010,29(203):268-277
古高程可以重建高山地区(尤其是高原)的隆升历史,可以更好地约束造山带的地球动力学过程。气孔玄武岩古高程计是通过熔岩流顶部和底部标准气孔体积比计算出古大气压,进而计算古高程的方法。该方法的研究对象是厚度为1~5m的且具有简单侵位历史的玄武质熔岩。高原隆升之前、期间和后期喷发的熔岩均可应用该方法。尽管该方法已经趋于成熟,但是国内还没有任何报道。对其基本原理、研究方法与应用做了详细的综述,并探讨了该方法在青藏高原和中国东部高原应用的潜力。  相似文献   

9.
The extensive volcanic activity of Rajmahal occurred during early Cretaceous (~117 Ma). Potentially perspective Gondawana sediments containing coal seam is partially covered by these basalts. Basalts as well as coal are already known to be of immense economic importance over Rajmahal traps. The present study mainly deals with delineation of basaltic lava flows and associated coal layers using the Audio-magneto-telluric (AMT) study in the south central region of Rajmahal traps near Suri, West Bengal, India. Initially, the field situations have been simulated using forward model with top alluvium cover followed by basaltic lava flows, a wedge shaped inter-trappean sedimentary formation with second basaltic lava flows and basement at the bottom. The model was constrained using available litholog. The model study reveals the presence of moderately resistive basalts, relatively conductive inter-trappeans and the basement, except the top alluvium layer and thin inter-trappeans. Subsequently, threeAMT sounding have been carried out over Cholaguria, Hatgacha and Pachami, Suri, West Bengal. The field AMT study reveals three basaltic lava flows with varying thickness from ~40m to ~350m and composite thickness of ~620m to ~640m, which match well with the published borehole litholog. The inter-trappeans have been identified at 500m to 620m, 310m to 400m and 500m to 640m depths over Cholaguria, Hatgacha and Pachami, respectively. It is interesting to mention that the identified inter-trappeans are inferred to be coal/shaly-coal which are matching very well with the published borehole lithologs.  相似文献   

10.
长白山天池火山气象站期晚期碱流质熔岩的岩石学研究   总被引:3,自引:0,他引:3  
通过野外火山堆积物的相分析、岩石显微鉴定和造岩矿物化学分析,可以确认气象站期晚期碱流质熔岩是典型的溢流熔浆冷却固结形成的,不是碎成熔岩。熔岩流的顶部和底部是黑曜质碱流岩的表壳相,中部是致密厚层与薄层相间产出的、具有塑性变形的碱流岩的内部相。组成熔岩流的岩石具有斑状和聚斑结构,从表壳相向内部相基质依次发育玻璃质结构、(微)球粒结构和霏细结构。斑晶矿物钠透长石、钙铁辉石、铁橄榄石和少量石英出现在熔岩流的所有岩相中,而钠铁闪石、铁钠透闪石和钛铁矿则作为内部相基质中的显微斑晶出现。气象站期晚期碱流质熔岩是过铝质、过碱性的钠闪碱流质熔岩,属于碱性系列,与意大利潘泰莱里亚岛碱流岩相比,富Si、Al、K、Mg、Ca和P而贫Fe、Na、Mn和Ti。  相似文献   

11.
Falling stage systems tract(FSST)is an offlap strata with strong relationship with hydrocarbon exploration,which is driven by relative lake-level fall and developed above the highstand systems tract and below the lowstand systems tract of a new sequence. It has no relationship with sediment supply. Based on the theory of sequence stratigraphy and sedimentology,3D seismic data,drilling core data,and well-logging data were comprehensively analyzed. The study showed that the FSST strata was formed in the Member 3 of Shahejie Formation in the Laizhouwan sag. The FSST can be divided into three units,namely as units P1,P2,and P3 from bottom to top. The P1 is the first unit of progradation downlap the bottom of the FSST. The top of the unit P3 is a sequence boundary exhibits subaerial unconformity. The seismic profile along the source direction is characterized by the low-angle oblique progradation reflection that downstream the center of lake basin from west to east. Incised valleys developed on the top of the FSST perpendicular to the source direction. Gamma-ray logging response is manifested by a series of funnel-shaped complex,indicating that the sedimentary response of the FSST was a cycle of coarsening-upward parasequence sets. Comprehensive studies on core interpretation and well-logging analysis showed that the FSST was a fluvial-delta sedimentary system with slumped fan deposits associated with the delta front. Consequently,the FSST is a common result of relative dry climate and falling of lake level,considering regional tectonic evolution,sediment supply,and paleo-climate change. The discovery of the FSST in the Laizhouwan sag has an important geological significance for the sedimentological interpretation,and it offers a guidance for further oil exploration in the study area. In addition,it also serves as a significant reference for future research on the FSST development and exploration in the continental lacustrine rift basin.  相似文献   

12.
徐家围子断陷火山岩充填的层序地层   总被引:15,自引:6,他引:9  
松辽盆地徐家围子断陷晚侏罗世-早白垩世期间火山岩十分发育,火山喷发岩的盆地充填样式与其在盆地中喷发的构造位置和构造断阶样式有关。根据火山岩的喷发构造位置和赋存情况,徐家围子断陷火山岩的盆地充填样式可以分为三种类型:沿断裂喷发-赋存样式、在上升盘喷发-赋存样式和在下降盘喷发-赋存样式。这些火山岩的充填样式具有不同的几何学特征。在层序发育过程中火山的喷发与火山岩的充填分别出现在低水位早期、低水位晚期和水进期。在层序地层格架中不同火山岩的充填样式影响或控制了盆地的地形、沉积作用类型、沉积体几何学和层序结构。这种构造[CD*2]火山活动背景下的层序地层模式可以作为油气勘探的地质模型,进行储集层预测。  相似文献   

13.
强制湖退体系域(FSST)是由相对湖平面下降驱动、发育于相同层序高位体系域之上及新层序低位体系域之下、在相对湖平面下降时期形成的、与油气勘探关系密切的一种退覆地层,与沉积物供给的变化无关。基于三维地震、钻井岩心和测录井资料,在层序地层学和沉积学理论指导下,发现莱州湾凹陷古近系沙河街组三段发育一套强制湖退体系域地层,垂向上可划分为3期,自下而上命名为P1、P2和P3,P1向湖盆中央终止于FSST底界面,P3顶部为显著不整合的层序界面。顺物源方向地震响应特征为缺失顶积层的低角度斜交前积反射,该反射自西向东推进到湖盆中央;在垂直物源方向的地震剖面上,可见下切谷地震响应。测井响应GR曲线呈漏斗状的复合体,表明沉积响应为上粗下细的反旋回。岩心及测井相分析结果表明,该FSST为一套河流—三角洲沉积体系,三角洲前缘伴生滑塌湖底扇沉积体。综合盆地区域构造演化、沉积物供给和气候变化等因素,认为该套沉积体系是气候相对干旱和绝对湖平面下降的共同产物。莱州湾凹陷沙三段FSST的发现对其沉积解释具有重要地质意义,对研究区进一步的油气勘探开发具有指导意义,也对研究陆相断陷湖盆FSST的形成与发现具有借鉴意义。  相似文献   

14.
热释光的用途很广,但在判断火山活动旋回(期次)以及火山岩类型鉴定方面,尚未涉及。本文通过对大庆徐家围子升深7和杨参1井岩石样品以及其他井部分火山岩样品的热释光特征的研究,发现:①升深7井中,顶部峰型和总积分强度近似,可指示为同期喷发产物;中下部热释光特征表现为“顶底韵律效应”,可能是较晚阶段的火山喷发物对前一阶段顶部有热改造而消耗了部分辐射积累。②杨参1井中根据热释光特征可划分2个旋回和4个期次。下部旋回发育双峰,主峰积分强度差别较大,可能指示底部为多源喷出产物(如多机构产物)混堆,小旋回产物之间叠加;主峰积分强度从下到上依次减小,反映了火山岩喷发强度的降低。上部旋回发育单峰,热释光积分强度相差不大,可能为一套同源产物。③升深7井中未发生明显蚀变作用的安山岩热释光特征相似而杨参1井中岩相均一、未蚀变的凝灰质岩热释光特征也很相似,这表明热释光特征技术应用于火山空落相岩石和火山熔岩岩性判别是有可能的。最后总结了火山岩热释光研究应注意的问题。  相似文献   

15.
Changes of the susceptibility to lava flow invasion at Mount Etna are quantified by using lava flow simulations on four Digital Elevation Models documenting the morphostructural modifications of the volcano in the time interval 1986–2007. The probabilistic code DOWNFLOW is used to derive the areas invaded by several thousands of lava flows obtaining, for each DEM, maps of the susceptibility to lava flow invasion and of the lava flow hazard. These maps show, for the first time, the evolution of these surficial properties with time, and render a quantitative image of the effects of topographic changes on the preferential lava flow drainage paths. The results illustrate how the emplacement of new lava flows and the growth of scoria cones affect the probability of inundation by lava flows. We conclude that the persistent activity of this volcano requires a frequent updating of the topography for a reliable lava flow hazard assessment.  相似文献   

16.
Felpeto  A.  Araña  V.  Ortiz  R.  Astiz  M.  García  A. 《Natural Hazards》2001,23(2-3):247-257
This paper presents an evaluation of the lava flowhazard on Lanzarote (Canary Islands) by means of aprobabilistic maximum slope model. This model assumesthat the topography plays the major role indetermining the path that a lava flow will follow. Thearea selected for containing future emission centreshas been chosen taking into account thecharacteristics of the recent eruptive activity andthe present activity of the island. The results of thesimulations constitute hazard maps whose values ateach point represent the probability of being coveredby lava. These results are qualitatively analysed toprovide some indication of the risk to the lifelines(electricity, drinking water etc.) of the island.  相似文献   

17.
Weathering rates based on temporal changes in a variety of rock properties were examined for four dated lava domes made of porous rhyolite. The lava domes were erupted at 1.1, 2.6, 20 and 40 ka BP. The time from each eruptive event to the present provide elapsed weathering times. The lava domes have many cooling joints formed immediately after eruption. Joint-bounded blocks have a high porosity, resulting in deep weathering. The blocks have almost uniform characteristics from top to bottom in one outcrop. The mineralogical, chemical, physical and mechanical properties of the four rhyolites were analysed. These results show that the chemical properties and physical properties, including specific surface area, change slowly in the early stage of weathering (0–20,000 years) and quickly in the later stage (20,000–40,000 years), while mechanical strength and bulk density or porosity of the rhyolites change rapidly in the early stage and slowly in the later stage. Mechanical strength reduces by 70–90% relative to fresh rock in 40,000 years, although chemical and physical properties change by only 1023̄0 %. It is concluded that different weathering properties exhibit different rates and patterns of change over 40,000 years, and that mechanical strength is the property most susceptible to weathering.  相似文献   

18.
Ambrym is one of the most voluminous active volcanoes in the Melanesian arc. It consists of a 35 by 50 km island elongated east–west, parallel with an active fissure zone. The central part of Ambrym, about 800 m above sea level, contains a 12 kilometre-wide caldera, with two active intra-caldera cone-complexes, Marum and Benbow. These frequently erupting complexes provide large volumes of tephra (lapilli and ash) to fill the surrounding caldera and create an exceptionally large devegetated plateau “ash plain”, as well as sediment-choked fluvial systems leading outward from the summit caldera. Deposits from fall, subordinate base surge and small-volume pyroclastic (scoria) flows dominate the volcaniclastic sequences in near vent regions. Frequent and high-intensity rainfall results in rapid erosion of freshly deposited tephra, forming small-scale debris flow- and modified grain flow-dominated deposits. Box-shaped channel systems are initially deep and narrow on the upper flanks of the composite cones and are filled bank-to-bank with lapilli-dominated debris flow deposits. These units spill out into larger channel systems forming debris aprons of thousands of overlapping and anastomosing long, narrow lobes of poorly sorted lapilli-dominated deposits. These deposits are typically remobilised by hyperconcentrated flows, debris-rich stream flows and rare debris flows that pass down increasingly shallower and broader box-shaped valleys. Lenses and lags of fines and primary fall deposits occur interbedded between the dominantly tabular hyperconcentrated flow deposits of these reaches. Aeolian sedimentation forms elongated sand dunes flanking the western rim of the ash-plain. Outside the caldera, initially steep-sided immature box-canyons are formed again, conveying dominantly hyperconcentrated flow deposits. These gradually pass into broad channels on lesser gradients in coastal areas and terminate at the coast in the form of prograding fans of ash-dominated deposits. The extra-caldera deposits are typically better sorted and contain other bedding features characteristic of more dilute fluvial flows and transitional hyperconcentrated flows. These outer flank volcaniclastics fill valleys to modify restricted portions of the dominantly constructional landscape (lava flows, and satellite cones) of Ambrym. Apparent maturity of the volcanic system has resulted in the subsidence of the present summit caldera at a similar rate to its infill by volcaniclastic deposits.  相似文献   

19.
Mount Etna is an open conduit volcano, characterised by persistent activity, consisting of degassing and explosive phenomena at summit craters, frequent flank eruptions, and more rarely, eccentric eruptions. All eruption typologies can give rise to lava flows, which represent the greatest hazard by the volcano to the inhabited areas. Historical documents and scientific papers related to the 20th century effusive activity have been examined in detail, and volcanological parameters have been compiled in a database. The cumulative curve of emitted lava volume highlights the presence of two main eruptive periods: (a) the 1900–1971 interval, characterised by a moderate slope of the curve, amounting to 436 × 106 m3 of lava with average effusion rate of 0.2 m3/s and (b) the 1971–1999 period, in which a significant increase in eruption frequency is associated with a large issued lava volume (767 × 106 m3) and a higher effusion rate (0.8 m3/s). The collected data have been plotted to highlight different eruptive behaviour as a function of eruptive periods and summit vs. flank eruptions. The latter have been further subdivided into two categories: eruptions characterised by high effusion rates and short duration, and eruptions dominated by low effusion rate, long duration and larger volume of erupted lava. Circular zones around the summit area have been drawn for summit eruptions based on the maximum lava flow length; flank eruptions have been considered by taking into account the eruptive fracture elevation and combining them with lava flow lengths of 4 and 6 km. This work highlights that the greatest lava flow hazard at Etna is on the south and east sectors of the volcano. This should be properly considered in future land-use planning by local authorities.  相似文献   

20.
古高程可以重建高山地区(尤其是高原)的隆升历史,可以更好地约束造山带的地球动力学过程.气孔玄武岩古高程计是通过熔岩流顶部和底部标准气孔体积比计算出古大气压,进而计算古高程的方法.该方法的研究对象是厚度为1~5m的且具有简单侵住历史的玄武质熔岩.高原隆升之前、期间和后期喷发的熔岩均可应用该方法.尽管该方法已经趋于成熟,但是国内还没有任何报道.对其基本原理、研究方法与应用做了详细的综述,并探讨了该方法在青藏高原和中国东部高原应用的潜力.  相似文献   

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