水对三峡库区碎石土的弱化作用   总被引：10，自引：1，他引：9  

刘文平  时卫民  孔位学  郑颖人 《岩土力学》2005,26(11):1857-1861

通过筛分试验对三峡库区现场取得的碎石土确定平均级配,然后用代替法设计其试验级配。结合碎石土的特点,采用细粒土含量控制试样的含水量,在同一竖向压力下制样。通过对库区不同含水量和不同含石量碎石土的剪切强度及参数的研究,结果表明,含水量不同,碎石引起强度变化的临界含石量也不同;碎石含量不变时,c值随含水量变化幅度不大,但 值随含水量变化会有较大变化;碎石土从天然状态到饱和状态,内摩擦角依据碎石含量不同,可降3°～10°左右。为估计三峡库区蓄水后旱桥桥基与路基承载力的降低提供了依据。  相似文献   

企鹅珍珠贝游离珠培育的初步观察     

符韶  邓陈茂  梁飞龙 《海洋湖沼通报》2008,(2):117-122

分别用锥形笼吊养法和塑料笼吊养法进行企鹅珍珠贝植核母贝的术前处理、在核位的左袋和右袋进行植核培育游离珍珠。经过13~15d的术前处理,锥形笼吊养法和塑料笼吊养法养殖的母贝成活率分别为93.67%和85.67%。经2个月休养,左袋插核的育珠贝死亡率和留核率分别为41.85~42.76%和10.34~12.96%;右袋插核的育珠贝死亡率及留核率分别为39.0%~40.0%和19.67%~20.00%。结果表明,合适的企鹅珍珠贝术前处理方法为锥形笼吊养法,合适的植核部位为右袋。  相似文献   

热带气旋“尤特”（2006）南海突然减弱的机理分析   总被引：1，自引：1，他引：0       下载免费PDF全文

刘彬贤  于玉斌  吕江津 《气象与环境学报》2010,26(4):28-34

应用NCEP/NCAR再分析资料,对热带气旋“尤特”（2006）在我国南海突然减弱的机理进行了分析。结果表明：水汽通道的切断是热带气旋“尤特”突然减弱的必要条件,“尤特”突然减弱对水汽来源切断的响应时间大约为12 h;对流层中低层水汽辐散区的出现,抑制了低层水汽向高层输送,导致“尤特”突然减弱;在其减弱过程中,贯穿对流层的位涡柱高值区不断向对流层中层收缩并加强,同时与平流层高位涡区迅速分离;在热带气旋“尤特”突然减弱前6 h,环境风垂直切变突然增大,同时在“尤特”不断减弱的过程中,环境风垂直切变呈现总体逐步增大的趋势。  相似文献   

Coupled trace element mobilisation and strain softening in quartz during retrograde fluid infiltration in dry granulite protoliths   总被引：1，自引：0，他引：1  

Bjørn Eske Sørensen  Rune B. Larsen 《Contributions to Mineralogy and Petrology》2009,157(2):147-161

This study focuses on the retrograde rheological and chemical evolution of quartz and the behaviour of quartzites during retrograde metamorphism following dry high grade metamorphism at 750°C, 7 kbar. SEM-CL and LA-HR-ICP-MS are applied to document quartz texture and chemistry, respectively. Four generations of quartz were distinguished by SEM-CL; Qz1, Qz2, Qz3 and Qz4. Qz1, brecciated and partly dissolved old grains, is enriched in B, Al and Ti when compared with the other types. Qz2, formed during brecciation and partial dissolution of Qz1, has low Al contents (<50 ppm) but, due to rutile inclusions, variable Ti contents when occurring in amphibolite (210–10 ppm) but more consistent values when occurring in quartzites (peak value 32 ppm). Qz3, dark grey luminescent quartz forming fluid migration channels (fluid pathways), has Ti < 5 ppm and Al contents below 10 ppm and B < 1 ppm. Qz4, comprises are group of quartz later than Qz3 filling micron thick cracks and pods with very low luminescent quartz, i.e. darker than Qz3. The textural and chemical evolution of quartz in our study is explained by two major influxes of aqueous fluids during regional uplift and retrogression. They facilitated rehydration and recrystallisation in the otherwise dry high grade quartzites. The first introduction of aqueous fluids was associated with brecciation of the high grade quartz (Qz1) and dissolution/precipitation of quartz (Qz2). Ti in quartz geothermometry (Wark and Watson, Contrib Mineral Petrol 152(6):637–652) gives 626°C in agreement with the retrograde PT-path deduced from phase diagrams. Later fluid influx associated with scapolitisation of amphibolite caused localised recrystallisation (Qz3) and alteration of biotite to muscovite along mm-wide fluid migration channels. During subsequent deformation, Qz3 deformed plastically and recovered by subgrain rotation recrystallisation (SGR), resulting in a reduction of grain size, whereas Qz1 quartz formed micro faults. Qz2 was plastic but did not experience SGR to the same degree as Qz3 quartz. Increased plasticity and recovery rates most likely relate to an increased H₂O fugacity and the depletion in trace elements of the quartz lattice by promoting strain softening processes dislocation climb and recovery. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

Initiation and development of the Twelve Mile Bay shear zone: the low viscosity sole of a granulite nappe     

C. C. GERBI  N. G. CULSHAW  J. POTTER  F. J. LONGSTAFFE  S. E. JOHNSON 《Journal of Metamorphic Geology》2011,29(2):167-191

Structural, microstructural and petrological data have enabled determination of the mechanical and geochemical processes involved in dynamic weakening and fabric transposition along the margins of a granulite nappe [the Parry Sound domain (PSD)] during transport to mid‐crustal levels of the Grenville Orogen. The data establish a genetic link between outcrop‐scale structures in the southern PSD and the development of the underlying Twelve Mile Bay shear zone (TMBSZ). Following granulite facies metamorphism (～11 kbar/～850 °C) in the southern PSD, the emplacement of pegmatite dykes resulted in hydration reactions within adjacent wall rocks and the development of thin (<1 m) amphibolite facies (～6.5 kbar/～700 °C) shear zones. The shear zones exhibit bulk H₂O and K₂O enrichment and oxygen isotope values similar to the adjacent pegmatites, suggesting metasomatic alteration by pegmatite‐derived fluids. Phase‐equilibrium models indicate that the destabilization of the pre‐existing pyroxene and garnet‐bearing assemblages, as observed within discrete shear zones in the southern PSD and the TMBSZ, requires H₂O‐saturated conditions at these (amphibolite facies) P–T conditions. The spacing between discrete shear zones and the depth of hydration into the adjacent wall rock are of comparable length‐scales (～metres), suggesting that this type of reworking process can be an effective means of hydrating kilometre‐scale areas of crust relatively rapidly. Furthermore, considering the well‐established effects of hydrous fluids on the creep strength of anhydrous minerals, a fracture‐initiated, localized hydration‐and‐shearing process may be an efficient mechanism for weakening strong, dry rocks (e.g. granulites) in the middle to lower orogenic crust.  相似文献   

断层带中假玄武玻璃成因机制及非稳态流变意义     

李文元  曹淑云 《地质论评》2022,68(1):2022010004-2022010004

假玄武玻璃呈玻璃质或隐晶质特性,常常与断层带相伴出现,其形成能有效地降低断层摩擦强度,被认为是古地震快速滑动的化石纪录。因此,对假玄武玻璃的研究对深入了解深部就位的断层变形和地震成因机制等具有重要意义。尽管国内外学者对假玄武玻璃开展了长期的研究,也积累了丰富的资料,然而,由于天然假玄武玻璃非常少见或零星地被报道,再加上其形成环境和过程的复杂性,对假玄武玻璃的构造特征、形成环境和成因机制仍然存在诸多争议及亟待解决的关键科学问题。研究表明,假玄武玻璃可以发育在大陆岩石圈不同深度范围内,即中下地壳乃至上地幔以糜棱岩为主的韧性变形领域（>60 km）,或中上地壳层次以碎裂岩为主的脆性变形域（<12 km）。越来越多证据也显示出在断层带的脆—韧性转换域中形成的假玄武玻璃跟浅源地震活动直接关联,也意味着中上地壳脆性变形和中下地壳塑性变形之间存在着更为复杂的耦合关联,同时对不同深部岩石强度和力学行为提出了挑战。对假玄武玻璃形成机制存在由断层面上的摩擦热导致的摩擦熔融体或仅仅是断层面岩石超碎裂粉碎作用认识的争议。而有研究认为干的环境有利于假玄武玻璃形成,因为流体的存在会降低断层面的有效正应力,不利于热量的积累以及摩擦熔融的进行;然而,另外一种观点认为流体的存在可以降低矿物熔融温度有利于断层摩擦熔融及形成假玄武玻璃。本文从假玄武玻璃的形成机制、形成深度、流体影响、形成后对断层强度的影响、以及保存与破坏机制几方面进行了最新总结,并对假玄武玻璃中非晶态物质的成因、脆—韧性转换带之下岩石的变形机制以及对陆壳强度的影响和非稳态流变意义进行探讨。  相似文献   

喜马拉雅造山带东段错那裂谷的地壳结构     

吴佳杰  徐啸  郭晓玉  卢占武  吴优  向波  于洋  李春森  余嘉豪  仝霄飞  罗旭聪 《地学前缘》2022,29(4):221-230

喜马拉雅造山带由印度与欧亚大陆板块的陆陆碰撞而形成。为何在挤压造山的碰撞前缘形成代表垮塌的藏南裂谷系存在巨大的争议。回答这个问题需要对裂谷的地壳结构有一个全面的认识。各裂谷带的起始活动年代自西向东逐渐年轻。本研究选取喜马拉雅东部较为年轻的错那裂谷,利用密集台阵接收的远震数据,通过P波接收函数方法,揭示错那裂谷的精细地壳结构,进而通过地壳结构分析裂谷的形成。结果显示错那裂谷为全地壳尺度结构,裂谷下方莫霍面发生明显错断,且壳内结构侧向不连续发育显著。本研究表明裂谷的形成可能关联更大尺度的区域构造运动,单一的重力垮塌是否能形成地壳尺度的裂谷需要进一步研究。综合前人对藏南裂谷系区域的超钾岩和埃达克岩研究以及深部地球物理观测结果,推断因俯冲的印度板片撕裂导致软流圈物质上涌弱化了错那裂谷区域下地壳,并且结合研究区内喜马拉雅淡色花岗岩研究显示中上地壳也存在弱化现象。因此,结合本研究结果推测全地壳尺度裂谷的形成需要不同深度的地壳弱化。  相似文献   

Shear localization,velocity weakening behavior,and development of cataclastic foliation in experimental granite gouge     

《Journal of Structural Geology》2015

Microstructural aspects of room-temperature deformation in experimental Westerly granite gouge were studied by a set of velocity stepping rotary-shear experiments at 25 MPa normal stress. The experiments were terminated at: (a) 44 mm, (b) 79 mm, and (c) 387 mm of sliding, all involving variable-amplitude fluctuations in friction. Microstructural attributes of the gouge were studied using scanning (SEM) and scanning transmission electron microscopy (STEM), image processing, and energy dispersive X-ray (EDX) analyses. The gouge was velocity weakening at sliding distances >10 mm as a core of cataclasites along a through-going shear zone developed within a mantle of less deformed gouge in all experiments. Unlike in experiment (a), the cataclasites in experiments (b) and (c) progressively developed a foliation defined by stacks of shear bands. The individual bands showed an asymmetric particle-size grading normal to shearing direction. These microstructures were subsequently disrupted and reworked by high-angle Riedel shears. While the microstructural evolution affected the effective thickness and frictional strength of the gouge, it did not affect its overall velocity dependence behavior. We suggest that the foliation resulted from competing shear localization and frictional slip hardening and that the velocity dependence of natural fault gouge depends upon compositional as well as microstructural evolution of the gouge.  相似文献   

Flank spreading and collapse of weak-cored volcanoes   总被引：1，自引：1，他引：0  

Emmanuelle?CecchiEmail author  Benjamin?van?Wyk de Vries  Jean-Marc?Lavest 《Bulletin of Volcanology》2004,67(1):72-91

Volcanoes subjected to hydrothermal activity develop weak cores as a result of alteration and due to elevated pore pressures. Edifices constructed at the angle of repose of volcanoclastics, or at even more gentle slopes, respond to internal weakening by initially deforming slowly, but may then collapse catastrophically. Such a process has so far been described for only a few volcanoes, such as Casita, Nicaragua; however, the conditions for flank spreading are widespread and many, if not most volcanoes should suffer some alteration-related flank spreading. We provide analogue models that characterise the structure — surface deformation fields and internal structures — of a spreading flank. Deformation creates a characteristic concave-convex-concave flank profile producing structures such as basal thrusts, summit normal faults, grabens and strike-slip relay faults. Three deformation regimes are found: a pit collapse regime is associated with very small volumes of ductile material located far from the edifice surface. This would not appear in nature, as time for deformation is greater than the lifetime of a volcano, unless very low rock viscosities are present. The other two regimes are flank spreading regimes, one symmetric and one asymmetric. The latter is the most common, as most volcanic structures are asymmetrical in form and in distribution of physical properties. The deformation is controlled by altered region dimensions, volume and position relative to the edifice, and to a lesser extent by its shape. As the flanks spread, landslides are created, initially on the steepened portion, but also from fault scarps. Major flank collapse may occur leading to explosive hydrothermal decompression and to a debris avalanche rich in hydrothermally altered material. We provide several new examples of volcanoes that have structures and morphologies compatible with flank spreading. We suggest that it is a common feature, important in the tectonics and hazards of many volcanoes.Editorial Responsibility: J. Gilbert  相似文献   

应用反射波法对基桩完整性进行定量评估   总被引：2，自引：0，他引：2  

黄文清 《矿产与地质》2001,15(Z1):610-620

利用应力波在一维杆中传播的机理对应力波在不同介面和变截面状态下的反射、透射与能量耗散之间的关系进行分析的基础上,用反射系数、透射系数、波幅衰减比等参数之间的关系及计算公式,对振动测桩中的实测波幅进行定量计算,得出面积削减率,以此值为依据进行桩身缺陷程度的判断.  相似文献