旋转台上鉴定An30-70斜长石成分与结构状态的新鉴定图

卡斯巴-钠长律(简称卡-钠律)是一种复合双晶律,又名罗克·图尔奈律(Roc Tournélaw),双晶结合面CP=(010),双晶轴TA=⊥[001]/(010),常见于中基性斜长石中,特别是在中性和中基性的火山岩中的斜长石斑晶里更为常见。笔者在旋转台鉴定工作中发现,当被测的An_30-70斜长石具有卡-钠律双晶时,联合运用欧拉角Ⅱ(Euler angleⅡ)中的Ⅰ角,即Nm∧[001],与卡-钠双晶寇勒角(Khler angle)中的Nm₁∧Nm₂来鉴定其成分和结构状态,效果甚好,优于传统的双晶法。     

消光角曲线法鉴定斜长石

当斜长石双晶片十分纤细时,在旋转台上用常规的双晶法、欧拉角法等进行鉴定是比较困难的,这时必须采用其它方法。常用的方法有:垂直(010)晶带最大消光角法、垂直a轴消光角法、卡斯巴双晶及卡钠复合双晶消光角法。在工作中笔者利用诹访兼位等日本学者根据BPW数据在斜长石的消光角鉴定法研究方面取得的成果,采用了又一种确定斜长石结构状态与成分     

旋转台法鉴别斜长石双晶律

用旋转台法鉴别斜长石双晶律,在A.C.马富宁“斜长石主要双晶鉴别图的基础上。把11种⊥a切面增为17种,并绘制了立体图.对比斜长石双晶律和系统研究斜长石特征,应分别采用A.李德曼法和D.B.斯利蒙斯法,并举例详述了后者的应用.     

小秦岭地区一些中酸性岩斜长石双晶的特征

斜长石双晶的种类较多,在中酸性岩中出现频繁,多年来人们通过对双晶类型与斜长石组分(An值)、岩石类型、晶出环境之间的关系和规律的研究,得出了一些结论。作者对小秦岭地区五个中酸性浅成岩体及四个中酸性深成岩体中的斜长石双晶进行了测定,并获得了一     

斜切[010]晶带切片上直接测定斜长石⊥[010]晶带Np′∧[010]_(max)角的新方法

本文作者研究出来的测定Np′∧[010]_(max)的新方法,以测定斜长石斜切[010]晶带切片中钠长石面律双晶结合面(010)的倾角(θ)为手段,按a=90°-θ公式求出斜切[010]晶带切面的倾角(a)。然后,根据视消光角(φ′)和⊥(010)晶带最大消光角(φ)与a角三者间的三角函数关系求出φ角。最后,依φ角查有关图表定出斜长石成分(An％)。     

大别山朱家冲二云石英片岩中石英双晶及交生特征

为揭示岩石中石英晶体之间的结晶学取向关系,采用光学显微镜和电子背散射衍射(EBSD)技术对大别山朱家冲二云母石英片岩进行研究。结果显示石英普遍发育双晶,其中道芬双晶律产出的概率最高(57.8%),日本律(3.2%)、Esterel(3.2%)、Breithaupt(4.8%)、Cornish(2.4%)等双晶律均有少量产出。除双晶外,相邻石英之间多为交生关系。各单形交生的相对概率为:{11■1}{11■2}{11■0}{20■1}{10■0}{10■1}{10■2}{00■1}。无结晶学取向关系的概率相对较低(7%)。石英具较强的择优取向,其C轴组构表现为靠近Z轴的简单点极密。石英变形机制以底面a滑移为主,变形温度约350℃~550℃。     

松辽盆地南部片钠铝石形成与碎屑长石的成因联系

含片钠铝石砂岩通常以富长石类型为主(岩屑长石砂岩,长石岩屑砂岩,长石砂岩)。为揭示片钠铝石与长石之间的主要赋存关系及长石在片钠铝石形成过程中所做的贡献,通过偏光显微镜、扫描电镜及阴极发光等镜下观察方法对松辽盆地南部红岗地区含片钠铝石砂岩进行了岩石学系统研究。本区片钠铝石主要以充填孔隙及交代颗粒的形式产出,其中片钠铝石交代斜长石的现象明显多于交代钾长石,片钠铝石交代斜长石初期优先沿其双晶缝向内生长,有些甚至完全交代斜长石而呈现交代假象。整体上片钠铝石含量与长石含量呈负相关关系。长石的溶蚀溶解为片钠铝石的形成提供Na+、Al 3+,由于各类长石的热力学性质存在差异,钾长石发生溶蚀溶解的速率及程度会明显低于斜长石,因此斜长石对形成片钠铝石的离子贡献大于钾长石。     

斜长石双晶律光学鉴定的一种新方法——消光曲线法

本文提出的消光曲线法可以迅速而准确地判断双晶结合面为(010)的斜长石双晶律,并提出测定a轴和c轴的方法。斜长石光学常数的精确测定,历来都是费氏台的专利,其中许多鉴定方法对矿物切面都有特殊要求,需设计相应的鉴定图表。作者设计的晶体光性测试仪可以完成与费氏台相同的,甚至更多的工作,而且只需一个碎屑颗粒即能使用几乎所有的光学龄定方法及鉴定图表。     

小秦岭地区一些中酸性岩斜长石双晶的特征

斜长石双晶的种类较多,在中酸性岩中出现频繁,多年来人们通过对双晶类型与斜长石组分(An值),岩石类型、晶出环境之间的关系和规律的研究,得出了一些结论.作者对小秦岭地区五个中酸性浅成岩体及四个中酸性深成岩体中的斜长石双晶进行了测定,并获得了一些资料,这些资料,与前人研究结论,有的相同或相似,有一些则不相一致.现整理成文,供参考.根据原西北地质科学研究所小秦岭研究组资料,本文共研究了九个岩体,其中华山、     

文象花岗岩的成分、结构和成因机制

文象花岗岩具有特殊文象结构,研究其三维拓扑结构和形成过程有助于了解花岗质岩石的结晶作用.以北京周口店房山岩体和湖北罗田蕙兰山的文象花岗岩为研究对象,综合利用光学显微镜、扫描电镜、电子探针和电子背散射衍射等技术方法,对岩石矿物组成、结晶学取向和拓扑结构进行了系统研究.结果表明:(1) 文象花岗岩的矿物组成与其形成地质环境有关,石英和长石的含量变化范围很大,其中石英含量通常在20%~45%,但是相同地区同期形成的文象花岗岩具有相对稳定的矿物组成;(2) 长石作为寄主矿物通常呈半自形－自形粗大晶体,可以是碱性长石或斜长石,其端元组分以钾长石和钠长石为主,低温下常分解为条纹长石;(3) 石英在长石寄主矿物中规则穿插生长,在三维空间通常呈近似平行板状、长条状/柱状或非连通枝杈状,并只在特定岩石断面形似象形文字;(4) 正交偏光显微镜下,石英可以具有多种消光位,但是通常在一定范围内同时消光;(5) 石英普遍发育道芬双晶,偶见日本双晶;(6) 条纹长石中钾长石与钠长石对应(100)、(010)、(001) 面和[001]轴近似平行;(7) 多数石英颗粒与寄主长石之间具有密切结晶学取向关系,即石英[1123]轴近似平行长石c[001]轴.该研究证实文象花岗岩是石英和长石同时生长的结果,而长石作为寄主矿物影响并控制着石英的成核与生长方向.      

Plagioclase twin laws and fabrics in three specimens of anorthosite

Twinning patterns and petrofabrics of plagioclases are examined in three specimens of anorthosite from the Bushveld Complex, the Quebec Massif, and the Fiskenaesset Complex. Their plagioclases have petrographical characteristics exhibiting their different petrogeneses.In an anorthosite from the Bushveld Complex, plagioclase grains are twinned after the albite-Carlsbad, pericline, albite and Carlsbad laws. Frequency percentage of the albite-Carlsbad and Carlsbad laws reaches 43% Plagioclase grains in the adcumulate layers are developed with their composition plane (010) subparallel to the cumulate plane, whereas those in the heteradcumulate layers are developed with their composition plane (010) subperpendicular to the cumulate plane.In an equigranular anorthosite from the Quebec Massif, plagioclase grains are polysynthetically twinned after the albite and pericline laws with rare examples of the albite-Carlsbad and Carlsbad laws. Frequency percentage of the latter two laws is only 1% together. Some regularities are recognized in the petrofabrics of c-axis and (010) plane.In a calcic anorthosite from the Fiskenaesset Complex, plagioclase grains are polysynthetically twinned, exclusively according to the pericline law or a combination of pericline and albite laws. The pericline law is predominant and reaches 64% and this twinning pattern cleaarly differs from that of the former two anorthosites.     

Electron microscopy study of domain structure due to phase transitions in natural perovskite

Transmission electron microscopy on natural calcium metatitanate perovskite (dysanalyte) reveals the following twin laws in the orthorhombic (space group Pbnm) phase: reflection twins on the {110} and {112} planes, and 90° rotation twins about the [001] axis (referred to as [001]_90° twin). Single crystals that were heattreated and quenched from above 1585 K exhibit a dramatic change in domain structure compared with the starting material and specimens quenched from T < 1470=" k.=" mutually=" perpendicular=" {110}=" and=">_90° twins are observed throughout the crystal, forming a cross-hatched domain texture. 1/2[001] antiphase domains, which are very rarely observed in the starting material, also become dominant in the crystal. This change in domain structure is interpreted as due to a structural phase transition in perovskite at a temperature below 1585 K. From the point symmetry elements that describe the twin laws and the translational elements that relate the antiphase domains, the most likely phase near 1585 K is tetragonal with space group P4/mbm. These results are consistent with high-temperature powder X-ray diffraction study. On the other hand, density of the {112} twins is increased significantly in the crystal quenched from 1673 K. Twin domains are either bound by mutually perpendicular {110} and (001) walls, or by {112} walls with {110} twin domains within the polygonal {112} domains. Both twin density variation and domain morphology suggest that the crystal may be cubic at this temperature. Microstructure of a single crystal deformed at 1273 K and 3.5 GPa (within the orthorhombic stability field) is morphologically quite distinct from that of the heat-treated specimens. Dislocations dominate the microstructure and often interact with twin domain boundaries.A National Science Foundation Science and Technology Center     

Transformation Trillings in Cordierite

Cordierite sector trillings, which are found well developedin some A1-rich volcanic rocks and pelitic buchites, are thoughtto have formed initially as hexagonal high cordierite crystals.Subsequent ordering of the (Al, Si) configuration in the crystalstructure would have produced the present orthorhombic modificationand simultaneously the sector trilling, preserving in the processthe hexagonal habit of form. The predominance of the regularsixfold sector pattern in the composition plane configurationof the resulting trilling is best explained by assuming thatits formation is kinetically more advantageous than that ofother configurations because it mimics the hexagonal trend setby the initial crystal. The three orthorhombic orientations in the cordierite trillingshave parallel c-axes and each can be transformed into eitherof the other two by operation of a threefold axis (rotationthrough 120°) parallel to the common c-axis and coincidentwith the main axis of the original hexagonal form. The compositionplanes in the sector trilling pattern are shown to be essentiallyirregular in the present orthorhombic form; they do not belongto {110} or {130}. The traditional explanation that the trillings are multipletwins with repeated twin and composition planes of {110} or{130} is rejected since elementary geometrical considerationsshow that this model is only feasible if (110) (110) of orthorhombiccordierite equals 120°. X-ray work shows conclusively thatthis is not the case. In fact (110) (110) = 120° woulddefine a hexagonal symmetry.     

大别山超高压变质岩的显微构造与有效黏度

超高压变质岩提供了研究大陆俯冲隧道中岩石的变形机制和流变差异性的窗口。文章使用电子背散射衍射技术分析了大别山超高压变质带的榴辉岩和长英质片麻岩的显微构造。榴辉岩中的石榴子石基本呈无序分布,绿辉石发育较强烈的晶格优选定向,[001]轴的极密平行或近平行于拉伸线理,(100)面的法线近垂直于面理,退变榴辉岩中角闪石的(100)[001]组构可能继承了绿辉石的晶格优选定向。退变榴辉岩和长英质片麻岩中的石英记录了(0001)低温底面滑移和{1010}中温 柱面滑移,反映了超高压变质岩折返到中地壳的韧性变形;而斜长石的(001)<110>和(010)[100]组构形成于折返到下地壳的角闪岩相变质条件（>600℃）。根据主要矿物的流变律计算了俯冲与折返过程中无水矿物的有效黏度变化。俯冲过程中,钠长石=硬玉+石英的分解反应以及石英-柯石英相变导致长英质片麻岩的有效黏度和密度都显著增高,有利于陆壳深俯冲。但是折返过程中由于温度较高,这两个反应带来的有效黏度变化较小。>80 km深度,石榴子石的流变强度>硬玉>绿辉 石>柯石英,俯冲上地壳的流变由柯石英和硬玉控制,下地壳的流变由绿辉石和石榴子石控制。超高压变质岩流变强度的差异有助于上—下地壳力学解耦,使相对低密度、低黏度的上地壳物质在俯冲隧道内快速折返。     

论石英双晶的复杂性

石英双晶的复杂性远远超出了人们的想象。首先介绍了石英的11种双晶律,然后介绍测试鉴定石英双晶律的各种方法及存在的局限性,综述了近年来石英双晶与温压条件关系、晶格结构匹配理论方面的研究成果,最后结合我们近期用EBSD对岩石中石英双晶的观察、测试结果,指出存在的问题及今后的研究方向。     

湖北大冶铁山矿区构造的岩组分析

本文采用了方解石光轴优选方位、e双晶C—T图法、以及两种用e双晶页理估算应力大小的动力学方法,对鄂东大冶铁山矿区的大理岩进行了岩组学的研究,根据所得资料的分析及相互印证,得出了若干结论。是一次运用岩组分析配合地区构造研究的尝试。     

Analysis of dislocations in some naturally deformed plagioclase feldspars

Dislocations in intermediate plagioclase feldspars, which were deformed under granulite facies conditions, have been analysed. The study reveals extensive ductile deformation by intracrystalline slip and by twinning. Six out of the seven possible Burgers vectors were identified: \(b = \left[ {001} \right],\tfrac{1}{2}\left[ {110} \right],\tfrac{1}{2}\left[ {1\bar 10} \right],\left[ {101} \right],\tfrac{1}{2}\left[ {112} \right]and\tfrac{1}{2}\left[ {1\bar 12} \right]\) . Most, perhaps all, dislocations are dissociated by up to 200 Å. The microstructure is dominated by [001] screw dislocations, most of which appear to be dissociated in (010). The dominant slip system appears to be (010) [001]. Large grain-to-grain variations in the density of free dislocations indicate that the plastic strain in individual grains depended upon the Schmid factor for (010) [001]. The microstructure suggests that the rate-controlling step for high-temperature creep of plagioclase is cross-slip of extended [001] screw dislocations. The rheological contrast between feldspar and quartz is partly due to a difference in stacking fault energy.     

Grain boundary plane populations in minerals: the example of wet NaCl after low strain deformation

Many physical properties of rocks are sensitive to grain size and hence to the structure of grain boundaries. Depending on their properties, such as deformation and transport behaviour, boundaries may be divided into two broad types, namely special and general grain boundaries. Electron backscattered diffraction (EBSD) is used to investigate the misorientation distributions of grain boundaries and, more recently, to determine the population of grain boundary planes. Studies on metals and ceramics suggest that the grain boundary plane, rather than the misorientation, is the key parameter when defining special and general grain boundaries. In this study, the distribution of grain boundary plane orientations has been successfully determined using EBSD for a slightly deformed, synthetic NaCl material containing 22 ppm water. Boundaries showed a preference for {100} planes, which occurred with twice the frequency of a random distribution. The grain boundary plane distributions found in NaCl were largely in agreement with studies on MgO. Grain boundaries, with a coincident site lattice (CSL) misorientation, also showed a preference for {100} planes, rather than the planes of high coincident density associated with the CSL. Three main types of boundary were identified, namely {100} twist boundaries, boundaries with {100}{hkl} planes and general {hkl}{hkl} boundaries. As the properties of these three types of boundary differ, then the transport and creep properties in wet NaCl will depend on the fraction of the different boundary types found in the grain boundary population.     

Stress-induced natural transformation of ortho- to clinohypersthene in metagabbros of the Ivrea Zone,Northern Italy

Summary Orthopyroxenes of a high temperature protomylonite of the Ivrea Zone, Northern Italy show twin like polysynthetic lamellae parallel to {210} of the hypersthene host. The transformation is caused by plastic deformation under high metamorphic conditions which has resulted in dynamic recrystallization of pyroxene and plagioclase. The lamellae consist of clinohypersthene. The twin plane and the lamellar clino-ortho-inversion of hypersthene due to natural deformation have not been described hitherto.

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Stressinduzierte natürliche Transformation von ortho- zu Klinohypersthen in Metagabbros der Ivrea-Zone, Norditalien

Zusammenfassung Orthopyroxene aus hoch temperierten Protomyloniten der Ivrea-Zone, Nord Italien zeigen polysynthetische Lamellen parallel {210} des Wirtes. Ihr Erscheinungsbild entspricht Deformationszwillingen. Die Lamellen sind invertiert zu Klinohypersthen. Die Ortho-Klino-Transformation ist auf eine Hochtemperaturdeformation zurückzuführen, wie dies anhand der dynamischen Rekristallisation der Pyroxene und Plagioklase bewiesen werden kann. Weder die speziellen Verwachsungsflächen noch die Ortho-Klino-Inversion durch natürliche Deformation wurden bisher beschrieben.

     

Olivine xenocrysts in picritic magmas

Experimental partial melting of plagioclase lherzolite at 0.7 MPa confining pressure has produced euhedral olivine crystals by corrosion and overgrowth during cooling. The particular conditions of this experiment allow observation of both processes recorded in the crystal shape: corrosion boundaries are rounded, or straight when parallel to [001] intersection of {110} planes; (010) and {110} facets are developed by fast overgrowth during quenching. These observations support the contention that phenocrysts in basaltic or picritic magmas are, in part, xenocrysts. The possible mantle origin of olivine crystals in two natural occurrences of ultramafic magmas; the picritic pillow lavas of the Troodos, and a wehrlitic intrusion of the oman ophiolite, is investigated. In both cases discriminant characteristics are deduced from detailed microstructural study. The mantle origin of olivine megacrysts in the investigated picrites raises the question about the existence of picritic magmas in the mantle.