共查询到20条相似文献，搜索用时 218 毫秒
1.
Raymond A. Duraiswami Purva Gadpallu Babaji Maskare Aishwarya Purwant Pooja Meena P. Krishnamurthy B. Mahabaleshwar 《Journal of the Geological Society of India》2017,90(6):742-747
Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme. 相似文献
2.
Agust Gudmundsson 《地学学报》1992,4(4):464-471
The divergent plate boundary in Iceland is characterized by 40–80 km long and 5–10 km wide swarms of tension fractures (∼102 m long) and normal faults (∼103 m long). The upper part of the crust is mainly composed of lava flows, with abundant columnar joints that are mostly perpendicular to the lava contacts. The lava flows are horizontal at the surface of the rift zone but become tilted at the rate of 1° for every 150 m depth in the crust. At the surface of the rift zone the joints are vertical and parallel to the vertical principal stress. Because of tilting of the lava pile, the columnar joints become oblique to this stress, hence becoming potential shear fractures, and form echelon sets at greater depths in the crust. Theoretical considerations suggest that normal faults start to nucleate on sets of en echelon columnar joints and/or large-scale tension fractures at crustal depths of 0.5–1.5 km. The width (depth) must be the smallest (controlling) dimension of many faults. Nevertheless, there is a positive linear relation (r = 0.91) between maximum throw and length of the Holocene faults. If the faults grow as self-similar structures, the throw-length relationship can be explained by a similar relation between fault length and width. 相似文献
3.
This study focuses on the compound pahoehoe lava flow fields of the 2000 eruption on Mount Cameroon volcano, West Africa and it comprehensively documents their morphology. The 2000 eruption of Mount Cameroon took place at three different sites (sites 1, 2 and 3), on the southwest flank and near the summit that built three different lava flow fields. These lava flow fields were formed during a long‐duration (28th May–mid September) summit and flank eruption involving predominantly pahoehoe flows (sites 2 and 3) and aa flows (site 1). Field observations of flows from a total of four cross‐sections made at the proximal end, midway and at the flow front, have been supplemented with data from satellite imagery (SRTM DEM, Landsat TM and ETM+) and are used to offer some clues into their emplacement. Detailed mapping of these lava flows revealed that site 1 flows were typically channel‐fed simple aa flows that evolved as a single flow unit, while sites 2 and 3 lava flow fields were fed by master tubes within fissures producing principally tube‐fed compound pahoehoe flows. Sites 2 and 3 flows issued from ∼ 33 ephemeral vents along four NE–SW‐trending faults/fissures. Pahoehoe morphologies at sites 2 and 3 include smooth, folded and channelled lobes emplaced via a continuum of different mechanisms with the principal mechanism being inflation. The dominant structural features observed on these flow fields included: fissures/faults, vents, levees, channels, tubes and pressure ridges. Other structural features present were pahoehoe toes/lobes, breakouts and squeeze‐ups. Slabby pahoehoe resulting from slab‐crusted lava was the transitionary lava type from pahoehoe to aa observed at all the sites. Transition zones correspond to slopes of > 10°. Variations in flow morphology and textures across profiles and downstream were repetitive, suggesting a cyclical nature for the responsible processes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
S. J. Sangode Rajiv Sharma Rasika Mahajan N. Basavaiah Priyeshu Srivastava Swapnil S. Gudadhe D. C. Meshram M. Venkateshwarulu 《Journal of the Geological Society of India》2017,89(6):631-642
Anisotropy of Magnetic Susceptibility (AMS) as a tool has been explored here to investigate the nature of petrofabrics in Deccan Volcanic Province (DVP) of west-central Indian region by representative sampling in typical pahoehoe and rubbly pahoehoe lava flows, dykes within flows, shear zone and the impact crater units. The rock magnetic analysis indicate varying degree of concentration of titanomagnetite compositions dominated by multi domain (MD) to pseudo single domain (PSD) grains favoring shape anisotropy of minerals that form primary fabrics. The pahoehoe type lava flows shows planar oblate fabrics without any preferred orientation of principle susceptibility axis (K1) depicting crystal settling (of magnetic grains) as chief mechanism of fabric development. The rubbly pahoehoe type lava flow exhibit prolate fabrics with well clustered maximum susceptibility axis within horizontal to sub-horizontal planes depicting their response to viscosity shear. The dykes show well clustered K1 parallel to it’s plane locked during rapid contractional cooling. The sampling at Lonar impact crater was unable to trace any clear fabric due to impact/shock induced deformation and rather preserve the primary fabrics. Further, the shear zone depict random fabrics demanding more detailed and systematic sampling in both the cases. The present investigation infer that the magnetic mineralogy and magnetic fabric variations in the DVP are controlled by the flow mechanism and style of cooling that is characteristic of the given flow unit or dyke and any secondary or superimposed fabric needs to be examined by critical sampling strategy. While more detailed attempts are required to establish the AMS as a tool to record various aspects including the flow dynamics and rate of effusion in the vast terrain of DVP; the present approach is useful to characterize and correlate the lava flow units and dyke occurrences. 相似文献
5.
文章通过大量岩芯、铸体薄片观察和测井资料分析,对准噶尔腹部石西石炭系火山岩风化壳储层进行了详细地研究。研究结果表明,该火山岩风化壳储层的储集空间主要有基质溶孔、气孔或杏仁体溶孔、角砾间溶孔、微裂缝和裂缝等,其中与裂缝连通的各类溶孔占主导地位;在岩石分布上以集块岩、条带状熔岩、角砾熔岩和致密凝灰岩为主,玄武岩、安山岩和流纹岩则相对较少;储层物性主要表现为高孔低渗,只有裂缝具有较高的渗透率,且裂缝以高角度缝和直立缝为主。研究还发现,岩性岩相、裂缝和风化淋滤作用是影响该风化壳储层的主要因素。区内油层主要聚中在构造高部位、靠近断裂带和有利岩相区域;油层分布在离石炭系风化壳顶面25~150 m的范围内。 相似文献
6.
The West Philippine basin (WPB) is a currently inactive marginal basin belonging to Philippine Sea plate, which has a complex formation history and various crust structures. Based on gravity, magnetic and seismic data, the tectonics in West Philippine basin is characterized by amagnma spreading stage and strike slip fractures. NNE trending Okinawa-Luzon fracture zone is a large fracture zone with apparent geomorphology and shows a right-handed movement. The results of joint gravity-magnetic-seismic inversion suggest that the Okinawa-Luzon fracture zone has intensive deformation and is a transform fault. Western existence of the NW trending fractures under Ryukyu Islands Arc is the main cause of the differences between south and north Okinawa Trough. The Urdaneta plateau is not a remained arc, but remnant of mantle plume although its lava chemistry is similar to oceanic island basalt (OIB). 相似文献
7.
柴达木盆地阿尔金山前斜坡带发现了规模分布的东坪基岩气田,其基岩风化壳的作用成为关注的问题。依据元素分析、X-射线衍射分析、岩心薄片观察,常规测井响应和成像测井响应特征,识别出东坪地区基岩风化壳发育不同结构层,且不同结构层的储集特征有很大差异。研究表明,基岩风化壳结构可划分为土壤层、完全风化层和半风化层,而半风化层又可进一步分为溶蚀带和崩解带;其中土壤层厚度0~2 m,完全风化层厚度4~15 m,溶蚀带厚度365~164 m,崩解带厚度300~1 000 m。基岩半风化层是储层发育带,其中溶蚀带储集物性好于崩解带,溶蚀带发育较多的溶蚀孔洞和溶蚀加宽的网状裂缝,孔隙度范围2%~16%;而崩解带发育弱溶蚀构造缝和节理缝,孔隙度范围2%~8%。东坪地区大规模发育基岩风化壳为柴达木盆地远离烃源岩灶的斜坡地区寻找油气提供了借鉴依据。 相似文献
8.
Unlike pahoehoe, documentation of true a′a lavas from a modern volcanological perspective is a relatively recent phenomenon in the Deccan Trap (e.g. Brown et al., 2011, Bull. Volcanol. 73(6): 737–752) as most lava flows previously considered to be a′a (e.g. GSI, 1998) have been shown to be transitional (e.g. Rajarao et al., 1978, Geol. Soc. India Mem. 43: 401–414; Duraiswami et al., 2008 J. Volcanol. Geothermal. Res. 177: 822–836). In this paper we demonstrate the co-existence of autobrecciation products such as slabby pahoehoe, rubbly pahoehoe and a′a in scattered outcrops within the dominantly pahoehoe flow fields. Although volumetrically low in number, the pattern of occurrence of the brecciating lobes alongside intact ones suggests that these might have formed in individual lobes along marginal branches and terminal parts of compound flow fields. Complete transitions from typical pahoehoe to ‘a′a lava flow morphologies are seen on length scales of 100–1000 m within road and sea-cliff sections near Uruli and Rajpuri. We consider the complex interplay between local increase in the lava supply rates due to storage or temporary stoppage, local increase in paleo-slope, rapid cooling and localized increase in the strain rates especially in the middle and terminal parts of the compound flow field responsible for the transitional morphologies. Such transitions are seen in the Thakurwadi-, Bushe- and Poladpur Formation in the western Deccan Traps. These are similar to pahoehoe–a′a transitions seen in Cenozoic long lava flows (Undara ∼160 km, Toomba ∼120 km, Kinrara ∼55 km) from north Queensland, Australia and Recent (1859) eruption of Mauna Loa, Hawaii (a′a lava flow ∼51 km) suggesting that flow fields with transitional tendencies cannot travel great lengths despite strong channelisation. If these observations are true, then it arguably limits long distance flow of Deccan Traps lavas to Rajahmundry suggesting polycentric eruptions at ∼65 Ma in Peninsular India. 相似文献
9.
准噶尔盆地克-百断裂带火山岩储层特征研究 总被引：2，自引：0，他引：2
为深入剖析准噶尔盆地克-百断裂带石炭系火山岩风化壳储层特殊性,寻找优质储层,对该区火山岩岩芯样品、普通薄片、铸体薄片、荧光薄片、成像测井等资料进行分析,探索火山岩风化壳孔缝基本特征和成因。研究结果认为:该火山岩储层孔缝类型和特征多样化,以次生溶孔、裂缝为主,为低孔特低渗储层;熔岩脆性大,构造裂缝较发育,熔岩层旋回顶部原生气孔发育;近断裂和风化壳顶面更易形成次生孔缝带。储集空间组合方式复杂,主要划分为裂缝-气孔、裂缝-颗粒间孔、裂缝-斑晶溶孔、裂缝-基质溶孔4种类型。后期的风化淋滤作用、构造破裂作用和溶蚀作用使风化壳的储集性能得到改善,而热液蚀变充填作用和胶结充填作用则对储层产生了破坏。油气聚集受断裂和不整合面的控制,可形成断裂控制的断阶式断块油气藏和不整合面控制的大型地层油气藏。 相似文献
10.
传统上研究含气页岩宏观缝网特征的方法多是基于小样品开展,通过观察小样品的裂缝展布特征来了解页岩的裂缝发育的宏观特性。但是这类方法因尺度过小,缺乏代表性,不能获取连续面上的裂缝特征,难以分析裂缝发育和地应力方向之间的关系。为获取更详细的大尺度含气页岩的宏观裂缝特征,本文从重庆市涪陵地区石柱县采样获取2m×3m×0.7m完整大尺度岩块,并采用有序标号切割来获取30cm3规格岩样,在此基础上提取小岩样的表面裂缝并按照大尺度岩样切割的相对顺序构建三维裂缝网络。分析观测大尺度的三维裂缝网络可以发现,含气页岩的裂缝分布具有明显的规律性:水平主应力方向上的裂缝发育度普遍高于最小水平主应力方向;垂直方向上的裂缝与最小水平主应力的夹角为-62°。分维研究表明所有不同面上的裂缝均符合分维特性,说明小尺度裂缝特征和大尺度裂缝特征具有相似的规律性。此外,研究还表明最大水平主应力上的裂缝密度和分形维数最大,缝网结构最为复杂,最小水平主应力方向缝网结构次之,垂直主应力方向的裂缝结构最为简单;水平应力方向上主要以层理裂缝为主,垂直方向上以剪切缝为主,且与最小水平主应力的夹角为-62°。在掌握宏观裂缝分布特征基础上,研究可为页岩显微观测实验提供相应的理论依据。 相似文献
11.
Abstract: Several native sulfur specimens, collected from Shiretoko-Iwozan volcano, eastern Hokkaido, Japan, exhibit spinifex texture, which appears to resemble that often observed in komatiite. The spinifex texture is exhibited by yellow-colored elongated skeletal native sulfur crystals up to 5 cm long settled in medium gray-colored fine–grained clayey matrix. One surface of a specimen is coated by layers of micro pillow lava of native sulfur. Such specimens were rarely found as clasts or fragments around the 1936 No. 1 crater that erupted native sulfur flows, together with the most common monomineralic native sulfur fragments of native sulfur flows having pahoehoe surface and of native sulfur dikes. The elongated spinifex native sulfur crystals presently consist of aggregated polygrains of orthorhombic sulfur crystals formed through crystallo-graphic transition from the single crystal of monoclinic sulfur initially crystallized. The spinifex texture exhibited by elongated skeletal native sulfur crystals is a product of rapid cooling of sulfur melt. Many lithic fragments of altered country rocks are present in the specimens exhibiting native sulfur spinifex texture. This suggests that segregation of the sulfur melt from the mixture of lithic fragments and sulfur melt was incomplete because the mixture was chilled before the melt segregation. Elongated skeletal native sulfur crystals may have nucleated and crystallized directly from the molten sulfur liquid. Lithic fragments mixed in the melt are supposed to have acted as nuclei for the nucleation of the native sulfur crystals. On the other hand, the most of native sulfur flows consist of monomineralic massive native sulfur with very scarce lithic fragments. Such massive monomineralic native sulfur crystallized from the supercooled, solidified amorphous sulfur. Such supercooled amorphous state may have been attained due to the lack of nuclei because of the scarcity of lithic fragments. The unique structures exhibited by native sulfur lava flow, including pahoehoe surface and spinifex texture, are due to the characteristic physical property of molten sulfur liquid, that is, low viscosity. 相似文献
12.
《Precambrian Research》1986,34(2):139-155
Spinifex veins, and veins filled with swirling, tabular olivine grains, intrude the upper part of a 120 m thick lava lake in Munro Township, Ontario, Canada. These veins are 20–200 cm wide, tens of metres long and are oriented roughly parallel to the upper surface of the lava lake. The spinifex texture differs from that found in simple layered komatiite flows: rather than increasing downwards, the size of skeletal olivine grains is greatest in the centres of the veins, or varies irregularly. Upper contacts meander and veinlets penetrate overlying rock; lower contacts are transitional. The other type of vein contains 50–70% of ∼5 mm long hopper olivine grains whose orientation varies widely to produce a swirling, contorted fabric. Both types of vein are believed to have formed when lava from the centre of the lake flowed into fractures in the solidified crust.The lava lake has a dunitic lower portion and an olivine porphyry upper portion. The composition of chill samples, the compositions of olivine phenocrysts, and variations in major element abundances throughout the unit are used to show that the lava originally was komatiite with about 22% MgO. The lava lake is overlain by mafic scorias and breccias with moderate vesicularity and welding structures suggesting eruption in shallow water. 相似文献
13.
M. Carracedo Sánchez F. Sarrionandia T. Juteau J. I. Gil Ibarguchi 《International Journal of Earth Sciences》2012,101(8):2201-2214
Distal pillows occur associated with a sheet flow and megapillows in the me?akoz outcrops of the Basque–Cantabrian Basin (N Spain). Basaltic volcanic rocks are interbedded with Turonian sediments and depict typical features of shallow submarine emissions. An exceptional basaltic flow displays four types of morphology: (1) sheet lava with columnar jointing, (2) welded columnar breccia, (3) megapillows, and (4) pillow lavas with sparse megapillows. The field data from me?akoz combined with experimental and field data from the literature for similar volcanic facies can be integrated into a new propagation model for the transition from sheet flows to pillow lavas in underwater environments. At near vent high emission rates, lava flows develop a thin crust immediately after its emplacement and break at the front under the magma pressure allowing for the massive propagation of lava as a sheet flow. Increased cooling promotes thickening of the lava outer crust far from the vent while continuous supply of fresh magma increases the pressure onto the thick crust until its rupture. The lava emitted in small volumes from the flow front promotes the formation of megapillows and pillow lavas that are later on covered by the advancing sheet flow. The lava flow freezes progressively toward more distal parts, gradually increasing its viscosity until it stops. The crust temporarily holds the residual melt pressure increasing the volume of the flow distal section by inflation. Finally, the internal magma pressure breaks the crust and liberates lava at moderate-to-low flow rates producing pillows, while lava drainage inside the inflated sheet flow produces lava tunnels and gravitational collapse of the roofs by hydrostatic pressure to form breccias nurtured by columnar lava fragments. 相似文献
14.
Numerical studies of subduction zone dynamics on a regional scale usually use a limited spatial extent for their models and therefore need to define boundary conditions on all model edges. These boundary conditions imply a choice for the mechanical and thermal state of the surrounding regions which may influence the evolution of the model system. We investigate the role of the surface and lateral boundary conditions for simple mechanical subduction models using a standard finite element method. We find that subduction is only possible if the slab can decouple from the surface. This decoupling can be achieved by a true free surface, a free-slip surface with a weak crust for the subducting plate, or a free-slip surface with a layer of low viscosity, low density material (‘sticky air’) between the model surface and the crust. Models of slab dynamics that employ a free-slip surface reproduce trench migration, slab sinking velocities and slab geometry of models with a free surface, as long as they use either a weak crust, which can be viscous, viscoelastic and/or brittle, or a ‘sticky air’ layer. The vertical topography will however not be reproduced for free-slip models without a ‘sticky air’ layer. For ocean–ocean convergent models we find that the application of inflow boundary conditions at the edges of the subducting or overriding lithosphere controls trench motion and the geometry of the subducting slab. Inflow on the overriding side causes trench retreat and a slab resting on the lower mantle, whereas inflow restricted to the subducting side can cause trench advance and a slab which folds on the lower mantle. 相似文献
15.
碧口群不同岩片火山岩微量元素组成差异与古构造意义 总被引：6，自引：2，他引：4
对碧口群内部大茅坪和筏子坝2个岩片变火山岩微量元素的研究表明,二者在岩石组合、源区组成及产出的构造环境等方面均存在系统差异。大茅坪岩片主要由偏碱性与非碱性的玄武质岩石组成,二者分别具有类似OIB和MORB的微量元素组成,起源于相对富集和相对亏损的地幔,并受到陆源物质不同程度的混染。偏碱性与非碱性的玄武质岩石分别显示板内火山岩（WPB）与洋脊玄武岩（MORB）的属性,表明大茅坪岩片火山岩主要形成于裂谷－有限洋盆环境。筏子坝岩片由玄武质与中酸性火山岩组成,岩石化学显示明显的“双峰式”组成特征,二者分别具有类似MORB和壳源岩石的微量元素组成,为亏损地幔与壳源岩石部分熔融的产物,形成于大陆裂谷环境。根据不同火山岩构造属性及组合特征,推断碧口群主要形成于陆内裂谷－有限洋盆构造环境。 相似文献
16.
秦岭造山带勉略缝合带构造变形与造山过程 总被引：23，自引：4，他引：23
秦岭晚古生代以来造山过程中的构造变形研究对建立华北板块与华南板块之间的最终拼合过程尤为重要。为此，选择勉略带进行了详细的野外调查，对其物质组成，几何学结构，变形序列，运动学和动力学作了系统解剖，认为：勉略带是有一定宽度，由一定实体组成的蛇构造混杂岩带，它包括不同时代，不同构造背景，不同起源的一系列构造岩片，如：基底岩片组，洋壳岩片组，岛弧岩片组，碰撞构造沉积楔形体，大陆边缘岩片组，它们被一系列的北倾南冲的断裂分割。勉略带到－高川段的北倾南冲逆冲断裂和勉略带北部南倾北冲的逆冲断裂组合成为现今不对称的正花状几何学结构，但勉略带的北界状元碑断裂和南界 到－略阳断裂走滑特征明显。结合勉略带邻区的构造特征，分别对带内重要断裂及岩片的构造解析表明，除主造山的大地构造演化阶段外，可将勉略带构造变形序列及演化历程总体归纳为三大阶段：俯冲变形阶段，主造山碰撞变形阶段的陆内造山调整变形阶段，并对不同变表阶段的时限，变形特征，运动学和动力学分别作了描述；最后针对该区复杂的楔入，挤出（逃逸）走滑，逆冲过程，提出了一个统一的动力学演化模式。 相似文献
17.
On the north coast of Iceland, the rift zone in North Iceland is shifted about 120 km to the west where it meets with, and joins, the mid-ocean Kolbeinsey ridge. This shift occurs along the Tjörnes fracture zone, an 80-km-wide zone of high seismicity, which is an oblique (non-perpendicular) transform fault. There are two main seismic lineaments within the Tjörnes fracture zone, one of which continues on land as a 25-km-long WNW-trending strike-slip fault. This fault, referred to as the Husavik fault, meets with, and joins, north-trending normal faults of the Theistareykir fissure swarm in the axial rift zone. The most clear-cut of these junctions occurs in a basaltic pahoehoe lava flow, of Holocene age, where the Husavik fault joins a large normal fault called Gudfinnugja. At this junction, the Husavik fault strikes N55°W, whereas Gudfinnugja strikes N5°E, so that they meet at an angle of 60°. The direction of the spreading vector in North Iceland is about N73°W, which is neither parallel with the strike of the Husavik fault nor perpendicular to the strike of the Gudfinnugja fault. During rifting episodes there is thus a slight opening on the Husavik fault as well as a considerable dextral strike-slip movement along the Gudfinnugja fault. Consequently, in the Holocene lava flow, there are tension fractures, collapse structures and pressure ridges along the Husavik fault, and pressure ridges and dextral pull-apart structures subparallel with the Gudfinnugja fault. The 60° angle between the Husavik strike-slip fault and the Gudfinnugja normal fault is the same as the angle between the Tjörnes fracture zone transform fault and the adjacent axial rift zones of North Iceland and the Kolbeinsey ridge. The junction between the faults of Husavik and Gudfinnugja may thus be viewed as a smaller-scale analogy to the junction between this transform fault and the nearby ridge segments. Using the results of photoelastic and finite-element studies, a model is provided for the tectonic development of these junctions. The model is based on an analogy between two offset cuts (mode I fractures) loaded in tension and segments of the axial rift zones (or parts thereof in the case of the Husavik fault). The results indicate that the Tjörnes fracture zone in general and the Husavik fault in particular, developed along zones of maximum shear stress. Furthermore, the model suggests that, as the ridge-segments propagate towards a zero-underlapping configuration, the angle between them and the associated major strike-slip faults gradually increases. This conclusion is supported by the trends of the main seismic lineaments of the Tjörnes fracture zone. 相似文献
18.
We examine the formation of the Michigan Basin in terms of elastic flexure of the lithosphere. The shape of the flexure accurately determines the flexural rigidity of the lithosphere and the lateral extent of the load responsible for the flexure. The amplitude of differential subsidence then gives the magnitude of the load. Gravity anomalies in the southern peninsula of Michigan further restrain the dimensions of the load. We propose a model for the formation of the Michigan Basin involving mantle diapirs. We suggest that the first stage in its evolution was diapiric penetration of the lithosphere by hot asthenospheric mantle rock to the vicinity of the Moho. The heating of the lower crust by these hot rocks caused the transformation of lower crust, meta-stable gabbroic rocks to eclogite. Initially the lighter mantle rocks nearly balanced the heavier eclogite. As the mantle rocks cooled by conduction, the basin subsided under the load of the eclogite. The thermal contraction mechanism is supported by evidence that the flexural rigidity of the lithosphere increases with time. This is the effect of thickening of the elastic lithosphere as cooling progresses. 相似文献
19.
锦屏二级水电站深埋隧洞大量岩爆案例表明板裂化围岩的失稳破坏与岩爆之间具有很强的相关性。采用高强石膏配制满足板裂化围岩结构特征的硬脆性模型试样,通过一侧约束条件下的单轴压缩试验研究板裂化模型试样的失稳破坏过程、强度与变形特性及其裂纹扩展特征。研究表明,（1）板裂化模型试样失稳破坏过程表现出应变型岩爆的特征,其典型的破坏过程为预制裂隙尖端张拉裂纹的萌生与扩展-试样劈裂成板-岩板屈曲变形-岩板压折、岩片弹射;（2）与完整试样相比,含1条、2条、3条预制裂隙模型试样的峰值强度、弹性模量均呈现稳定下降的趋势,而峰值轴向应变则是先减小后增大;（3）试样预制裂隙尖端张拉裂纹的产生会造成：相邻预制裂隙尖端横向应变值的突变、试样侧向变形量的突增以及侧向变形速率的显著增大;（4）临空面附近的预制裂隙,其尖端产生的张拉裂纹在很短的时间内便会失稳扩展,并造成试样的失稳破坏。最后,分析试样变形破坏过程中的声发射特性。研究结果对于揭示深埋硬岩隧洞板裂化围岩的失稳破坏规律、岩爆的发生机制具有重要意义。 相似文献
20.
Pierre Bérest Benoit Brouard Hippolyte Djakeun-Djizanne Grégoire Hévin 《Acta Geotechnica》2014,9(1):181-186
Rapid gas depressurization leads to gas cooling followed by slow gas warming when the cavern is kept idle. Gas temperature drop depends upon withdrawal rate and cavern size. Thermal tensile stresses, resulting from gas cooling, may generate fractures at the wall and roof of a salt cavern. However, in most cases, the depth of penetration of these fractures is small. These fractures are perpendicular to the cavern wall. The distance between two parallel fractures becomes larger when fractures penetrate deeper in the rock mass, as some fractures do not keep growing. These conclusions can be supported by numerical computations based on fracture mechanics. Salt slabs are created. However, these slabs remain strongly bounded to the rock mass and it is believed that in many cases their weight is not large enough to allow them to break off the cavern wall. Depth of penetration of the fractures must be computed to prove that they cannot be a concern from the point of view of cavern tightness. 相似文献