花岗岩风化程度的化学指标及微观特征对比——以香港九龙地区为例

据香港九龙3个不同工程场地取得的149件不同级别的风化花岗岩样品的化学分析结果,用统计学方法,从反映岩石风化程度的18项化学指标中选取9项进行了分析计算.对其结果及其与风化程度分级的关系的研究表明有4种指标比较理想.通过对样品微观特征的观察研究和矿物成分、微孔隙率以及综合显微岩石指标(I_p)进行了描述和定量分析,发现其中一些指标有一定相关性.这些化学指标和微观特征相关的统计值在一定程度上可定量表征花岗岩的风化程度,即:随风化作用进行,碱、碱土金属组分逐渐淋失,脱硅、富铝铁化作用逐渐加强;相应地,先是钠长石风化成高岭石,其次为云母和钾长石的风化.粘土矿物所占体积百分比随风化程度增高而变大,至残积土(Ⅵ级)时已达50%左右;I_p指标值下降,微孔隙率增高.文章综合出各个风化级别的指标变化范围及平均值供花岗岩分布区花岗岩风化野外调查和研究工作参考.     

深圳地区花岗岩风化球成因探讨及勘察对策

通过对深圳地区花岗岩的成因，区域构造，风化作用等因素的对比分析，探讨了风化球成因与它们的内在联系。燕山晚期混染花岗岩，蚀变花岗岩是风化球形成的内在原因，断裂构造带及次生裂隙为风化球形成提供了有利条件；风化带特征与风化球形态有密切关系。由此提出圈定花岗岩风化球发育地段的几点原则和勘察对策。列工程实例予以说明。     

亚热带小流域花岗岩化学风化及CO2消耗速率研究

文章选择深圳市的亚热带典型小流域作为研究对象,通过定期采集流域内降水、泉水、岩石及风化残积土样品,分析所有样品的常量元素和微量元素,探讨流域水体的化学成分组成和主要成分来源以及岩石化学风化程度和风化趋势,结合流域水文气象数据估算了花岗岩化学风化速率及CO2消耗速率.结果表明,研究区地下水化学类型为HCO3-Na型,主要...     

闽南风化花岗岩类的点荷载试验及声学特性研究

点荷载强度指数I_(S_(56))对花岗岩类的风化程度反映灵敏,各风化带的数值较稳定,因此,提出以其降低率作为闽南花岗岩类各风化带划分指标。同时,为了消除试样面积大小的影响,便于对比,对I_(S_(56))与室内常规试验(劈裂法及单轴抗压强度试验)结果通过统计分析,找出它们间的幂次曲线关系和回归方程,并提出相应的强度换算系数,以便于点荷载试验的推广和使用。根据典型风化花岗岩类地质剖面的综合研究及大量岩芯的声波测定及钻孔声波测井资料,综合得出闽南地区风化花岗岩类的声学特性。在此基础上,初步探讨其风化机理,提出以纵波速度降低率作为风化分带指标,并按不同岩性分别找出其强度——纵波速度经验关系式。     

基于坡度特征的花岗岩风化程度划分方法研究

针对目前遥感技术手段难以快速划分岩石风化程度的问题,以花岗岩为研究对象,通过分析风化程度与坡度的耦合关系,提出了一种基于坡度特征的花岗岩风化程度划分方法。该方法首先利用卫星遥感数据解译区域地层岩性,通过立体像提取区域坡度信息; 然后对坡度分级并统计花岗岩地质体内各级坡度的面积百分比; 最后根据坡度分级特征曲线判断花岗岩风化程度。野外验证表明,该方法可以准确划分花岗岩风化程度,可为工程设计和施工作业提供参考。     

基于单轴压缩试验的不同风化程度花岗岩分形特征分析

风化花岗岩物理力学性质的弱化给工程稳定性带来很大影响,因此,研究不同风化程度花岗岩的破坏特性具有重要意义。利用河南五岳抽水蓄能电站库区采集的风化花岗岩,结合现场岩芯特征的定性描述及波速比定量评价指标,划分出了微、弱、强3种不同风化程度的花岗岩;对单轴压缩破坏后产生的碎屑进行质量和尺度的特征分析,在此基础上建立了碎屑分形维数值与波速比之间的对应关系,并利用MATLAB对花岗岩破坏后主破裂表面裂缝进行分形维数计算。结果表明：风化试样产生的碎屑以粗粒组为主,且随风化程度增强,粗粒组碎屑质量占比逐渐增大;强风化岩石碎屑长厚比分布范围小,块状碎屑占比低,破坏动力学特性不明显,其形状更单一,主要以板状为主;随着风化程度的降低,块状碎屑含量增多,岩石动力学破坏特征增强,碎屑分形维数随着表征风化程度波速比的增大而呈增大趋势;相较于碎屑质量、宽度和厚度,碎屑数量和长度是影响碎屑分形维数的主控因素,是反映不同风化程度花岗岩破碎分形特征的主要参量;强风化类组花岗岩表面裂缝分形随波速比变化不明显,而弱风化、微风化花岗岩的裂缝分形维数随波速比增大而呈显著增大趋势,说明其自相似程度更高,形状更复杂,而在裂缝形成过...     

花岗岩中黑云母风化的矿物变化机制

对采自广东阳江花岗岩风化剖面的黑云母及其风化产物进行了Ｘ射线衍射,扫描电子显微镜及能谱,高分辨率透射电子显微镜等分析,并探讨了黑云母风化过程中成分的变化及矿物的转化机制。研究结果表明：阳江地区花岗岩中黑云母的风化系列为黑云母→蛭石,绿泥石→伊利石／绿泥石,高岭石,黑云母风化初期的蛭石和绿泥石是独立的矿物相,而不是通常认为的水黑云母,而混层矿物伊利石／绿泥石的出现则表明了以黑云母风化程度为指标的深度     

北京怀柔云蒙山地区花岗岩风化过程的地球化学基因

地球化学基因是近两年提出的一种新的地球化学示踪技术,本文选择北京怀柔云蒙山地区两个邻近的花岗岩风化剖面(编号为B和C)来分析岩性地球化学基因和金矿化地球化学基因的属性特征.剖面B样品的化学蚀变指数CIA变化为51.3～58.9,WIG的范围为89.4～68.6,属于初始风化程度;剖面C样品的CIA变化为52.4～78....     

花岗岩风化带的现场确定及定量划分

本文通过八达岭高速公路工程实例，对野外花岗岩风化现场定量划分方法进行探讨，并总结出花岗岩类风化岩的统一划分标准的初步意见。     

我国热带亚热带部分地区花岗岩和片麻岩中黑云母风化研究

综合应用Ｘ射线衍射、扫描电镜、透射电镜及偏光显微镜等技术手段研究了我国热带、亚热带部分地区花岗岩和片麻岩中黑云母的风化现象。结果表明，化学风化产物主要有黑云母／蛭石不规则间层矿物、水黑云母、蛭石、０．７ｎｍ埃洛石及铁的氢氧化物（氧化物）等。影响黑云母风化及次生产物形成的主要因素包括黑云母的晶体结构和化学成分、气候、风化壳母岩的矿物成分等。     

Assessment of weathering processes effect on engineering properties of Alvand granitic rocks (west of Iran), based on weathering indices

The Alvand batholith is one of the largest plutonic bodies in the west of Iran. In this research, several physico-mechanical tests have been performed on granodiorite and porphiroid monzogranite consisting of five degrees of weathering in Hamedan area, west of Iran. Furthermore, weathering process of Alvand granitoid is studied by chemical analysis and petrographical studies. The results indicated that engineering properties of weathered granodiorite and monzogranite vary over the wide range depending on the degree of weathering. On the other hand, this research is focused on the assessment of relationship between weathering indices and uniaxial compressive strength. For this reason, some of the most important weathering indices are reviewed. It should be noted that, application of these chemical, engineering and petrographical indices are good quantitative indicators for describing the degree of weathering. Using these indices for the assessment of uniaxial compressive strength of granodiorite and monzogranite rocks, yields suitable and meaningful results.     

An application of lithogeochemistry to the evaluation of the Ni-sulphide ore potential of weathered serpentinites in the Fortaleza de Minas Greenstone Belt,Minas Gerais,Brazil

A practical application of lithogeochemistry to the classification of weathered serpentinites as to whether or not serpentinites are host rocks to Ni-sulphide ore is presented. An effort is made to apply existing concepts used to distinguish between fertile and sterile unweathered ultramafics to explain the observed chemical differences between fertile and sterile weathered serpentinites in southwestern Minas Gerais, Brazil.The data comprise total-attack chemical analyses for Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Ti, V, and partial-attack determinations of Cu and Ni as ascorbic acid, hydrogen peroxide-soluble metal. Student's t-tests are used to identify element concentration differences between the two serpentinite groups. Discriminant analysis is used to classify the weathered fertile and sterile serpentinites. Non-linear mapping and fuzzy c-means clustering help to assess the validity of the discriminant analysis. Finally, chemical element associations provide extra information on geological and mineralogical causes that can be responsible for the identified differences.It is found that a clear separation and classification of weathered serpentinites is possible using the procedures presented. The observed chemical differences between fertile and sterile serpentinites are interpreted in terms of original magmatic differentiation, the degree of sulphur saturation of the original magma and the behavior of the derived ultramafic rocks in a tropical weathering environment.     

Structurally controlled landslides in saprolitic soils in Hong Kong

A number of large slope failures which have occurred in Hong Kong have highlighted the important influence that discontinuities in saprolitic soils can have on slope stability. Conventional stability analyses normally adopted for such soils, which assume failure through intact materials of uniform shear strength, are not appropriate if discontinuity-controlled failures can be postulated. Stress history and present-day weathering effects should also be taken into consideration in the assessment of the long-term stability of slopes in weathered rocks in tropical and subtropical regions. © Rapid Science Ltd. 1998     

A new chemical index of weathering for metamorphic silicate rocks in tropical regions: A study from Sri Lanka

Weathered and fresh samples of metamorphic rocks from Sri Lanka were collected from various localities and analysed for major elements by XRF method (RIGAKU, KG-X System, Japan). The content of water was determined by the ignition method.

The XRF results, obtained from these samples form the basis of a new index of chemical weathering, particularly for Sri Lanka, which is named the Silica-Titania Index, and is calculated as follows: Silica-Titania Index = {(SiO₂/TiO₂)/[(SiO₂/TiO₂) × (Al₂O₃/TiO ₂) × (SiO₂/Al₂O₃)]} × 100(molecular proportions).

The index can be used to determine the degree of weathering in chemically weathered silicate rocks of other countries in tropical regions. A triangular diagram plots the position of this index. The point load strengths of fresh rocksand weathered rocks with different degrees of weathering were correlated with the values of this new chemical index. The relative variation in strengths of fresh rocks and weathered rocks clearly indicates its suitability and usefulness for engineering geologists.     

黄河拉西瓦水电站坝区花岗岩风化研究

风化作用对于岩体工程地质性能的降低不言而喻。研究探讨重大水电工程岩石风化作用机理对于工程区岩体风化带划分、风化渐进性分析、表征岩体风化特征指标的选择及力学性质参数取值等具有重要意义。文章从风化作用本质、化学元素迁移、风化作用类型等角度,对拉西瓦水电站坝区花岗岩风化作用机理进行了探讨。结合本区气候演化、岩石性质、地形条件等综合分析认为:在浅表河谷范围内,风化形式以岩石胀缩作用和冰劈作用为主,而化学风化作用并不强烈。论文采用量化指标对岩体进行风化带划分,选取的定量指标有平硐纵波速度Vp、钻孔RQD、裂隙间距与单元面积节理数等。在此基础上,利用电站20余a来丰富详实的地质、物探、岩体测试等大量资料,采用定性分析与定量划分相结合的研究方法,对黄河拉西瓦坝基花岗岩体进行风化分带,得出坝基岩体风化带总体空间布局。     

风化过程中硒背景值的定量表征

硒是人和动物必需的微量元素,基于58件标准物质的化学风化指标和硒的认定值,采用微量元素地球化学背景值的经验方程形式拟合得到表征全国范围内硒背景值的经验方程：lgc=0822×(12-WIG/100)-1061×lg(K2O/SiO2)-2704,式中c为Se的含量(单位为μg/g),风化指标WIG的变化范围为43~1116,风化指标K2O/SiO2变化范围为0020~0137。该方程所表征的是样品因风化程度不同所呈现出的硒地球化学背景值,风化程度强的样品总体上具有较高的Se地球化学背景值。将该经验方程式在广东河台和广东南昆山两个研究区进行应用,认为寻找富硒区应当优先将风化程度较强的地区视为备选区,依据全国区域化探扫面数据可以方便地确定风化程度较强的地区。在环境质量评价中可以利用Se实测值确定足硒和富硒区,利用实测值扣除背景值获得的元素含量剩余值可以有效确定残积层土壤下伏的足硒和富硒岩石,即依据全国多目标地球化学调查数据可以有效地确定足硒和富硒地质体(残积层土壤及其下伏岩石)的分布区。广东南昆山岩体中西部的岩石应属于足硒和富硒地质体。     

Weathering indices for rhyolitic tuff and granite in Hong Kong

A series of chemical analyses and dry density tests of rhyolitic tuff and granitic samples have been carried out. The test results have been interpreted using a newly developed theoretical weathering model for calculating a mobility index of major elements in rock and soil. It is found that this index is useful for describing changes of rock and soil during weathering and classifying the degrees of weathering. Based on the theoretical model, a new parameter called the volume index, which combines chemical and physical data, is suggested. This index appears to be a good indicator for classifying the degree of weathering in Hong Kong. A quantitative classification scheme is suggested.     

发育完整的灰岩风化壳及其矿物学和地球化学特征

对于碳酸盐岩土覆土壤成因、尽管碳酸盐岩风化残积成土说被多数学者认同,但由于碳酸盐岩中酸不溶物含量极低,在风化成土过程中会伴随着巨大的体积缩小变化,原岩结构和半风化带无法保留,从而缺失了探索上覆土壤物质来源的重要中间环节,使得这种观点缺乏野外宏观证据的支持。最近,我们在贵州、湖南等地发现了数个以泥质灰岩和泥质白云岩为基岩的碳酸盐岩风化壳剖面,尚保留有较好的原岩结构,具有明显的风化壳分带和过渡现象。这些风化壳剖面的发现为深入研究碳酸盐岩风化成土过程提供了良好的研究场所。本文选取了较为典型的吉首泥灰岩风化壳剖面,从矿物学地球化学的角度来探讨碳酸盐岩风化壳的形成过程和发育特征,结果表明该风化壳既遵循非碳酸盐岩（主要是结晶岩类）风化壳的发育特征,也具有自己独特的地球化学演化规律。风化壳总体特点受碳酸盐中的酸不溶物矿物组合及化学成分的影响甚至控制,风化非碳酸盐风壳相似的发育特征。吉首泥灰岩风化壳剖面的发育特征和作者早先提出 的碳酸盐岩风化成土的两阶段模式是一致的,即以碳酸盐矿物大量淋失、酸不溶物逐渐堆积或残积为特征的早期阶段和残积物进一步风化成土的阶段,后一阶段的演化类似非碳酸盐岩类的风化过程。