Variation of rare earth concentrations in pigeonitic and hypersthenic rock series from Izu-Hakone region,Japan

The abundances of rare earth elements in 5 each of aphyric volcanic rocks of pigeonitic and hypersthenic rock series from Izu-Hakone region have been determined by neutron activation analysis. Pigeonitic rock series show rare earth patterns with relative depletion of lighter rare earths (low lanthanum type) and large increase in rare earth abundances with differentiation. Hypersthenic rock series show higher lanthanum abundances (high lanthanum type) compared with pigeonitic rock series. The differences in rare earth patterns between two rock series are compatible with the theory of independent magmatic generation of these two series. Variation of rare earth patterns in both series have been examined by a model of magmatic differentiation based on the observed rare earth partition coefficients.     

川西呷村超大黑矿型矿床成矿流体烯土元素组成

本文用ＩＣＰ－ＭＳ首次测定了呷村银多金属黑矿型矿床矿石流体包裹体中的稀土元素含量,研究表明,主成矿期流体稀土元素配分模式均为轻稀土富集,Ｅｕ具明显正异常,通过初步对比,本区主成矿期流体与东太平洋脊、大西洋脊等现代高温酸性地热系统热液具有相似的稀土模式,反映了它们物化条件的相似性;但前者∑ＰＥＥ高于后者,且两者Ｅｕ／Ｅｕ＾＊值不同,经过分析,本区成矿流体Ｅｕ正异常主要为Ｔ、ｐＨ、ｆｏ２控制,另外,围     

Geochemistry of red residua underlying dolomites in karst terrains of Yunnan-Guizhou Plateau: II. The mobility of rare earth elements during weathering

The aim of this study is to characterize the evolution of the rare earth elements (REE) in the Pingba red residua on karst terrain of Yunnan-Guizhou Plateau. The in-situ weathering and the two-stage development of the profile had been inferred from REE criterions. The REE were significantly fractionated, and Ce was less mobilized and separated from the other REEs at the highly enriched top of the profile. This is consistent with the increase of oxidation degree in the regolith. And it is also suggested that the wet/dry climate change during chemical weathering caused Ce alternative change between enrichment and invariance in the upper regolith. Chondrite-normalized REE distribution patterns for samples from dolomites and the lower regolith are characteristic of MREE enrichment and remarkable negative Ce-anomalies patterns (similar to the convex-up REE patterns). The following processes are interpreted for the patterns in this study: (1) the accumulation of MRRE-rich minerals in dolomite dissolution, (2) water–rock interaction in the weathering front, and (3) more leaching MREE from the upper part of the profile. The latter two explanations are considered as the dominant process for the formation of the REE patterns. Samples from the soil horizon exhibit typical REE distribution patterns of the upper crust, i.e., La_N/Yb_N=10 and Eu/Eu*=0.65. All data indicate that the leaching process is very important for pedogenesis in this region. The experiments demonstrating that abnormal enrichment of REE at the upper regolith–bedrock interface is caused by a combination of volume change, accumulation of REE-bearing minerals, leaching of REE from the upper regolith, and water–rock interaction during rock–soil alteration processes. Our results support the conclusion that the weathering profile represents a large, continental elemental storage reservoir, whereas REE enrichment occurs under favorable conditions in terms of stable tectonics, low erosion and rapid weathering over sufficiently long time.     

类节理岩石直剪试验力学特性的数值模拟研究

节理岩体的剪切特性是主导岩体工程稳定性的关键因素。基于PFC2D离散元颗粒流程序,结合室内试验结果对比分析,选取合理的细观参数进行数值模拟,分别从细观角度研究了节理岩石的裂纹发展、能量转化及声发射现象等特性,从宏观角度研究了节理岩石的强度模型和破坏形态。结果表明：节理岩体主要呈现磨损和剪断两种破坏形态,不同的破坏形态对应不同的强度模型;随着剪切变形增加,岩体沿节理面发生破坏,弹性阶段以法向裂纹为主,而塑性阶段切向裂纹起主导作用,滑移区R、P裂纹贯通形成破碎带,节理面产生较大滑移;在应力达到峰值强度前,边界能主要转化为应变能,法向裂纹生成较多;越过峰值强度后,摩擦能快速增长,并伴随大量切向裂纹产生。与室内试验结果相比,PFC2D较好地模拟了节理岩体剪切力学特性,弥补了室内试验中无法进行细观特性研究的缺陷,对于节理岩体后期研究提供了一些参考。     

Tortoises,hares and the evolution of the Irish landscape

Across Ireland there is a striking topographical contrast between predominantly limestone-floored lowlands and uplands developed on silicate-dominated rock types. This arises from the fundamentally different way in which limestone and other rocks are removed. Limestone is removed through dissolution, a low-energy process enhanced by vegetation. Other rock types are removed by erosion, a high energy process that is inhibited by vegetation. In Ireland countless ‘soft days’ over the last 60 Ma have been more effective at removing limestone than other rock types. Limestone uplands have survived only where they were protected by a cover of insoluble rock, such as sandstone or mudstone, which has been stripped away relatively recently by glacial erosion. The large-scale removal of considerable thicknesses of limestone across Ireland has increased the relief of non-limestone uplands through the effects of isostatic uplift. Denudation across the Irish landscape has led to changing outcrop patterns of limestone and other rocks, resulting in profound long-term changes in topography and drainage patterns.     

Effects of the micro-structure and micro-parameters on the mechanical behaviour of transversely isotropic rock in Brazilian tests

Based on the Brazilian test results of 23 kinds of transversely isotropic rocks, five trends are obtained for the variation of normalized failure strength (NFS) as a function of the weak plane-loading angles. For each angle, three kinds of fracture patterns are obtained. Furthermore, a new numerical approach based on the particle discrete element method is put forward to systematically investigate the influence of the micro-structure of rock matrix and strength of weak plane on NFS and fracture patterns. The results reveal that the trend of NFS and fracture patterns are slightly influenced by coordination number of rock particles and tensile strength of weak plane, but greatly influenced by percentage of pre-existing cracks and shear strength of weak plane. Micro-parameters of the numerical approach are calibrated to reproduce behaviours of transversely isotropic rocks with different trends, and the simulation results are well matched with experimental results in terms of NFS and fracture patterns. Finally, the numerical approach is applied to study the failure process of layered surrounding rock after tunnel excavation. The simulation results also agree well with observation results of engineering projects.     

工准噶尔库布苏金矿床岩脉与金矿成因关系的研究

库布苏金矿床的三个金矿带均产于闪长玢岩和花岗闪长斑岩内。为了研究这些岩脉与金矿的成因关系,测定了含金石英脉中英流体包裹体均一温度、成分、盐度和Ｈ２Ｏ的氢氧同位素,分析了含英脉和相关脉岩及围岩的稀土元素及微量元素,发现石英流体包裹体属有较高的均一温度、低盐度、富ＣＯ２的还原性流体,其阳离子组合为Ｃａ＾２＋〉Ｎａ＾＋〉Ｋ＾＋或Ｎａ＾＋〉Ｋ＾＋〉Ｍｇ＾２＋,阴离子组合属Ｃｌ＾１〉ＳＯ４＾２－〉Ｆ＾－型,     

江西相山潜火山岩中淬冷包体的发现及其成因机制探讨

在江西相山大型塌陷式火山盆地北部的潜火山岩岩墙中，笔者发现了闪长质的岩石包体，这种包体具典型的反向脉及淬冷边，且淬冷边内含有大量针状磷灰石。在包体内部或包体与寄主岩的边界均见有钾长石及斜长石捕虏晶，这种捕虏晶是包体岩浆从寄主岩岩浆中捕获的，常被熔蚀成筛状或浑圆状。包体与寄主岩（次斑状花岗闪长岩）的稀土元素曲线和不相容元素蛛网图的形态非常相似。因此，相山潜火山岩岩墙中的闪长质岩石包体是不同成分、不同温度的岩浆经对流及不均一岩浆混合作用而形成，在成因类型上属淬冷包体。     

唐古拉山北坡中新世霓辉石正长岩的地球化学特征、时代及构造意义

阿多霓辉石正长岩是分布在唐古拉山北坡的碱性侵入岩,岩石中含有大量的霓辉石、白榴石、霞石等碱性矿物。侵入体具有明显的分带性,其中心的白榴石霓辉石正长岩为典型的碱性岩,而边部或呈岩脉状出现的霓辉石正长斑岩为酸性程度较高的霓辉石正长岩,岩石具有富钾、高硅和低铁镁的特点,稀土元素配分型式呈轻稀土元素富集型,无Eu异常。霓辉石正长岩侵入于早—中侏罗世雁石坪群中,上新世曲果组不整合于其上。在黑云母霓辉石正长斑岩中获得了10.71Ma±0.08Ma和11.26Ma±0.16Ma正长石和黑云母的Ar39/Ar40坪年龄,其侵位时代为中新世。构造环境分析结果显示其形成于后造山构造环境。这表明在10Ma左右青藏高原处在构造体制转换时期,这些碱性岩是造山带崩塌早期阶段的产物。     

多节理岩体裂纹扩展及变形破坏试验研究

为了研究不同倾角下多节理岩体力学行为,采用10 MN微机控制电液伺服大型多功能动静力三轴仪,开展包含较多预制非贯通节理类岩石试件的单轴压缩试验,研究了多节理岩体裂纹的特征、贯通模式、破坏模式、应力-应变特征等与节理倾角之间的关系。试验结果表明,（1）多节理岩体的裂纹类型主要有翼裂纹和次生共面裂纹,翼裂纹的扩展路径与单个节理情况下的扩展路径差异较大,翼裂纹起裂后沿起裂方向存在较长的扩展长度,直接与相邻节理或翼裂纹形成贯通,并且裂纹的贯通表现出四种不同的模式;（2）多节理岩体的破坏模式归纳为3种类型：平面破坏、块体转动式破坏和台阶式破坏;（3）根据多节理岩体的应力-应变曲线在应变软化阶段所表现出的不同非线性变形行为特征,可以将曲线归纳为4种类型;（4）多节理岩体的强度和变形各向异性特征非常显著,强度和弹性模量均在节理倾角30°时最小,90°时最大。     

岩体力学试验的理论分析

本文通过对岩石力学试验中岩石试件破坏方式的分析, 在理论上解释了岩体力学试验中经常遇到的一些力学现象并且作出了定量的回答, 同时还建立了岩石的各种破坏模式的判据。     

四川石棉大水沟碲矿床稀土元素地球化学特征

通过对大水沟碲矿床矿体与围岩稀土元素地球化学组成及特征研究表明,矿体与围岩的稀土元素特征截然不同,表明它们形成于同一地质时期和地质环境。大水沟碲矿床受岩浆作用改造,成矿物质应源于岩浆岩,且围岩与矿体存在氧化还原地球化学界面;稀土元素球粒陨石标准化分配模式图显示,大水沟赋矿围岩、贫碲矿石稀土元素具有大陆拉斑玄武岩的稀土元素特征,表明该碲矿床成因与峨眉山玄武岩有关。     

岩石各向异性实验研究及对工程勘探的影响

以不同的砂岩和大理岩为标本,对岩石的各向异性在应力应变关系、波速、动静杨氏模量、动静泊松比、抗压强度等方面的各向异性问题进行了测试和研究。通过实验得到岩石标本在平行层理和垂直层理方向上述物理性质存在着的差异情况和变化规律,分析和探讨了岩层的各向异性对工程勘探工作带来的影响情况。指出地壳介质的岩体各向异性对地球物理勘探来说是不能忽视的,尤其是各向异性会导致横波分裂,影响横波勘探的精度,但同时也有助于了解岩体中裂纹结构的信息,做出工程事故的准确预报。     

Analysis of spatial order in sandstones. I. Basic principles

The spatial arrangement of sedimentary rock components is a fundamental property of sedimentary rocks. If we assume that the size, shape, and composition of sedimentary rock components (mineral grains, pores) carry useful petrologic information, there is no reason to assume that their spatial arrangement does not. Spatial arrangement has been discussed in terms of texture and fabric, but it has had little objective measurement or classification. This deficiency is primarily due to the difficulties associated with the quantification of spatial phenomena. However, using digital-imaging techniques it is possible to generate petrographic images from thin-sections and quantify the spatial arrangement of selected rock components using a two-dimensional (2D) Fourier transform. A Fourier transform creates a spectral representation of the image similar to an x-ray diffraction pattern. This paper presents the fundamental framework of 2D Fourier analysis in petrology. This type of analysis provides a means to quantify and analyze the spatial arrangement of rock components in an objective, mathematical framework. 2D Fourier power spectra can be used to characterize the type and degree of spatial order in an image, both in terms of the classical concepts of long-range and short-range order and in terms of spatial patterns characteristic of sedimentary rock. The clearly defined mathematical relationship between an image and its Fourier power spectrum provide the opportunity to define the 2D structure of an image in the same manner that x-ray diffraction patterns are used to map 3D structure in minerals. In addition, a 2D Fourier power spectrum is easily transformed into a radial power spectrum. Radial power spectra can be used to characterize the density of objects in an image. They also provide a valid means to compare and contrast images in a multivariate framework, regardless of the type of order. One of the most desirable properties of a Fourier transform is its reversibility. Using selected components of the power spectrum, the inverse transform can be used to build synthetic images, which highlight those petrologic components that most affect the power spectrum. The inverse transform provides the means to translate the results of analysis into meaningful petrologic characteristics.     

Transbaikal Mesozoic granites: Mode of crystallization and subsequent metasomatic transformations

Crystallization conditions and early post-magmatic rock alteration have been studied for three orebearing granite massifs using the method of stochastic modeling. These Mesozoic granites were crystallized from a relatively dry melt, whose barren (ore-free) parts were crystallized from a volatile-enriched magma under sealed conditions. Surface zones of weak rock alteration over subsurface mineralization reflect the subsurface structural patterns controlling the mineralization.     

青海鄂拉山地区陆相火山岩地球化学特征及构造环境

鄂拉山岩浆岩带晚三叠世火山岩为中-中酸性火山岩组合,由玄武安山岩、安山岩、英安岩、流纹岩及少量火山碎屑岩等组成,岩石蚀变强烈,成层性差,柱状节理发育,具典型的陆相喷发特点.火山岩属铝饱和类型,里特曼指数(δ)及岩石学等显示具钙碱性特征,(FeO/MgO)、K2O/Na2O显示可能具有陆缘岛弧环境的特性;轻稀土元素分馏程度高且富集,δEu小于1,为弱负异常,稀土元素配分模式曲线与岛弧型稀土元素配分模式图相似;微量元素Rb、Ba、Th等元素明显富集,而Ti、Y、Yb、Sc、Cr等元素较亏损.Nb/Zr、La/Nb、Th/Ta、Th×Ta/Hf2等特征反映鄂拉山组火山岩产于陆缘火山弧环境.结合区域地质背景、岩石地球化学及构造环境等特征,认为鄂拉山地区晚三叠世火山岩产于大陆碰撞与陆缘弧并存的环境.     

岩石质量指标(RQD)的各向异性分析

各向异性是工程岩体的重要工程特性, 岩石质量指标RQD具明显的各向异性。本文运用结构面网络模拟技术, 通过结构面间距、倾角、相对夹角以及结构面组数的敏感性分析, 探讨了RQD的各向异性规律。结合实际工程应用, 提出正确引用RQD指标的建议。     

压力型锚杆力学性能模型试验研究

为了研究在软质沉积岩条件下压力型锚杆的力学性能,进行了缩尺模型试验。设计的试验锚杆构造良好,模拟的承载体和无黏结形式简单可靠。通过设计不同的锚固段长度,试验获得了岩石条件下压力型锚杆的荷载-位移全曲线。与相同条件的普通拉力型锚索对比,压力型锚杆体现出优秀的抗拔极限承载力、良好的位移延性特征和残余强度;在归纳压力型锚杆破坏模式的基础上提出最佳锚固长度的基本范围,并按理论解进行了算例验证,计算结果与试验结果吻合良好。模型试验对压力型锚杆的力学性能进行了较深入探索,可供相关理论研究、科学试验和工程实践参考。     

西秦岭台乌龙一带晚三叠世华日组火山机构及演化

西秦岭地区的构造演化是许多地质学家普遍关注的问题。三叠纪以来西秦岭发生了复杂的俯冲碰撞造山作用,这一时期发育的火山岩,便是这一地质事件的重要记录。本文选取西秦岭甘青交界处台乌龙一带华日组火山岩为研究对象,运用"火山旋回—火山构造—火山地层—岩性岩相"的火山岩区填图方法,在华日组火山岩中识别出喷溢相、爆发相、侵出相、喷发—沉积相、火山通道相和次火山岩相等6个岩相;台乌龙层状火山机构、色日欠破火山机构等11个火山机构;两个组合样式(台乌龙—年支北串珠式组合、下毛娘北—色日欠镶嵌式组合);划分出1个火山喷发旋回,3个亚旋回。较合理地建立起地层层序、岩相相序和演化模式。华日组火山岩的出现标志着西秦岭地区在晚三叠世已进入陆相演化阶段。     

REE示踪沉积物物源研究进展

ＲＥＥ作为一种重要的沉积物物源示踪剂运用很广。在介绍了ＲＥＥ性质的基础上，对海水、河水、沉积岩、河流及边缘海沉积物中的ＲＥＥ元素丰度与配分模式特征进行了深入综述，概述了影响和控制ＲＥＥ丰度、模式及分馏特征的主要因素；论述了ＲＥＥ的物泊示踪意义以及在国内外应用情况与存在问题：源岩风化对ＲＥＥ分馏的影响；颗粒运及沉积时水动力分选对ＲＥＥ分馏可能造成的影响，即不同粒级中的ＲＥＥ不同的丰度与配分模式和碎屑