石香肠构造研究进展

100多年来，石香肠构造的研究取得了巨大的进展。出现了骨节状石香肠、不对称鱼嘴构造、复合石香肠等新的构造样式。在石香肠构造形成理论研究上，关于断裂石香肠构造形成的理论推导、肿缩石香肠构造形成的流变参数的限制、多层石香肠构造在大地构造研究中的应用、石香肠构造控矿以及石香肠构造流变计的研究已经展开并取得了较大进展。理论研究的深入和应用研究的拓展还需要借助其他学科的研究成果。     

湖北铁山与北京西山复合石香肠的初步研究

湖北铁山地区发育接触热动力变质带，叠加了热动力和构造变形作用，这使该区岩体附近互层的灰岩和泥岩变质为大理岩和角岩；而且这两种之间存在有较大的粘度差，这就为石香肠构造的发育提供了充要条件，所以在湖北铁山地区形成了形式多样的石香肠，北京西山地区震旦系互层的灰岩和白云岩也存在明显的粘度差异，在构造变形作用下，也广泛发育有石香肠构造，结合湖北铁山和北京西山地区的复合石香肠，依据石香肠横断面形态把复合石香肠分为I，Ⅱ，Ⅲ三类，并分析了每种类型的成因，复合石香肠是一种有特殊意义的石香肠构造，其特点是具有复合的形态特征，复合的构造成因，研究复合石香肠对了解其发育过程有重要的研究价值，对区域构造运动方向和期次的判定也有重要的指示意义。     

湖北银洞沟银金矿床石香肠构造样式及形成机制

该矿床中以平行陡倾的含矿石英脉为特征的矿体，在构造变形过程中常产生石香肠化，由于局部应力环境的差异，所形成的石香肠构造样式也各不相同，并控制了矿体形态及有用矿物组分的分布，以不同样式石香肠构造在矿区的分布特点进行了构造分区，并对其形成机理作初步探讨。     

湖北铁山与川西北地区发现不对称鱼嘴构造

早在１９世纪中叶，人们就已经开始了对石香肠构造的描述与研究。随着资料的不断积累以及观测和实验手段的不断提高，其理论研究也越来越深入。但是，新的构造样式的出现，总是迫使人们突破原有的理论格架，重新认识、探讨其成因及构造意义。     

鄂东南铁山不对称骨节状石香肠构造基质层中的应变测量与分析

鄂东南铁山是亚洲首个发现骨节状石香肠构造的地区。以该区不对称骨节状石香肠构造为研究对象,利用惯量椭圆法对其基质层进行有限应变测量,获得真应变差、运动学涡度等相关参数及有限应变椭圆长轴展布方位的分布图。对所获数据资料研究表明:该不对称骨节状石香肠构造基质层的应变受其能干层控制,有限应变值与其离能干层的距离趋于负相关,且与其矿物颗粒粒径呈负相关,在平行于石香肠构造伸展方向上基质层有限应变分布不均;石香肠体附近与之相近规模的变形构造可使其相应基质中的应变分布紊乱;该不对称骨节状石香肠构造是由早期平行于层面简单剪切叠加晚期平行层面伸长、垂直层面压缩的纯剪切作用形成。与不对称鱼嘴状石香肠构造对比研究表明,两者基质层中简单剪切与纯剪切的分布均分别与其相对增厚与减薄区段对应,而两者形态的不同主要与石香肠体不连续处充填物的能干性不同有关,再次表明两者均是较好的岩石流变学标志。     

鄂东南铁山梯形石香肠构造基质层中的应变测量与分析

鄂东南铁山是全球第二个梯形石香肠构造的发现点。以该区成层分布、形态相近的梯形石香肠构造为研究对象,利用惯量椭圆法对其基质层进行有限应变测量,获得真应变差、岩层厚度比、运动学涡度分布等。结合梯形石香肠几何形态学、岩石学特征,对所得数据综合分析研究表明:剪切带中垂直剪切方向的厚度比值与其所受真应变差趋于负相关;该梯形石香肠构造是由其上、下相邻基质层厚度差异,基质层中总体上的纯剪切,局部相对集中的简单剪切及相对富集于张裂隙处角岩层中的热液流体等综合作用形成的;发育成层分布且形态相近的梯形石香肠构造所需特征性条件是能干层上、下相邻基质层厚度相差较大,且受总体上持续的平行层面拉伸、垂直层面压缩的纯剪切与局部的简单剪切共同作用。该类石香肠构造是较好的岩石流变学标志。     

北京西山和湖北铁山发现骨节状石香肠构造

人们对于石香肠构造的普遍性及其意义早就有所认识。 Lohest于 1 90 9年最早对石香肠构造进行了描述。但直到 Cloos于 1 947年和 Ramberg于1 95 5年对石香肠构造的成因进行初步探讨后 ,人们才逐渐的注意这种构造。根据石香肠构造的连续性 ,将其可分为膨缩石香肠构造 (或藕节状石香肠构造 ) [1]和断裂石香肠构造 [2 ] 。经典的膨缩石香肠都是双凸形。而 Malavieille等 [3] 发现了一种双凹形石香肠 ,并称之为骨节状石香肠。此后不久他们的文章被介绍到中国 ,但这十多年来 ,国内并未见骨节状石香肠的进一步报道。笔者在进行“石香肠构造流变计研究”项目的过程中 ,对北京西山和湖北铁山的石香肠构造进行了研究 ,分别在两地发现了骨节状石香肠构造。北京西山的骨节状石香肠构造发育于震旦系碳酸盐岩建造中。由灰质白云岩组成香肠体 ,白云质灰岩组成基质 ,石英脉充填于香肠体裂口处 (图 1 )。反映出两期垂直层面的压缩和平行层面拉伸的纯剪切变形的叠加。图 1　北京西山第一类骨节状石香肠1石英脉 ;2灰质白云岩 ;3白云质灰岩湖北铁山的骨节状石香肠构造发育于狮子山岩体与围岩的接触热动力变质带上...     

菱形石香肠简单剪切成因模式及其构造流变计

菱形石香肠虽常被作为指示剪切作用的标志,但其形成过程和流变学意义并未完全清楚。纯剪切模式作为一种已被认可的成因模式表明菱形石香肠也可能在简单剪切作用下形成。本文从石香肠与基质的流变差异出发,提出了菱形石香肠的简单剪切成因模式,建立了简单直观的平面模型,即方形石香肠置于方形基质中,后将其简单剪切变形分解为旋转和纯剪变形两步,并利用有限变形几何学知识,计算出理论的菱形石香肠剪切角和层面转动角,其与有限元数字模拟的实验结果还是较接近的。进一步的理论分析给出了利用菱形石香肠几何学参数(剪切角和层面转动角)求取石香肠与基质粘度比的方法,即菱形石香肠构造流变计,并运用它在湖北铁山地区获得石香肠的粘度是基质的4.76倍,菱形石香肠构造流变计扩展了香肠构造流变计的适用范围,提供了在野外快捷测算岩石粘度比的途径。     

鱼嘴构造流变计研究与基于流变学的分类方案

如同膨缩型香肠构造一样,鱼嘴石香肠构造是存在岩石流变性差异的能干层与基质在纯剪切作用机制下形成的构造形迹。在深入研究鱼嘴构造形态与能干层基质流变性差异的基础上,运用物理模拟的方法,模拟出不同形态的鱼嘴香肠构造,反演出能干层基质粘度比与香肠形态之间的关系,进而得出一种关于鱼嘴香肠构造的经验流变计。 认识到鱼嘴构造的纯剪切作用机制及其平面应变的特点,通过对香肠现有的几何参数的测量和计算以及对香肠构造演化初始阶段几何参数的恢复,在合理假设的理想状况下,推导出鱼嘴构造的应变差折射流变计。 鱼嘴构造是流变行为下应变的结果,因此这种构造行迹不仅有几何学意义,更折射出流变学意义。在模拟实验与野外考察的基础上提出了一种基于流变学与剪切作用机制的鱼嘴构造分类方案。     

利用两种天然构造变形估算岩石古流变参数

肿缩石香肠构造和能干层褶皱作为自然构造有的产物，其几何形态理所当然地能够反映构造变形时温压条件下岩石的流变性质，在力学分析的基础上，对北京西北部分肿缩石香肠构造进行了测量，得以方解石石英脉的应力指数为３．６１～７．６９，与云母大理岩的粘度比为８．７４～１８．３２；板岩中的石英脉的应力指数为２．５７～４．７５，与板岩的粘度比为９４．８～１７５．８，白云岩中硅质条带的应力指数为２．２５～３．９３，对白     

A stress-transfer model for the development of extension fracture boudinage

The term boudinage is used to describe a wide variety of extensional structures in deformed rocks. This paper is mainly concerned with boudinage resulting from through-layer extension fractures followed by separation of the layer segments, thus forming boudins with more or less rectangular cross-sections. In principle, this process is similar to the break up of fibres in fibre-reinforced composite materials extended parallel to the fibre direction. Both processes are controlled by the transfer of stress from the matrix to the fibre (or layer) and a mathematical model for fibre-matrix stress transfer (the ‘fibre-loading’ model) is well established. We have used this as a basis for developing a stress transfer model for boudinage. The only difference in the basic mathematical formulation results from geometric differences between the two systems; the geometric expressions in the fibre-loading model have, therefore, been rederived for the layer-matrix case.Stress-transfer theory predicts that the tensile stress in a layer segment rises from a minimum at the end of a segment to a maximum at the centre. This behaviour, which is clearly shown by finite-element models of boudinage structure, suggests that extension fracture boudinage develops by successive ‘mid-point’ fracturing. According to stress-transfer theory, the process will continue until a layer is reduced to segments (boudins) all of which are shorter than some critical length (for which the tensile fracture strength of the layer is equal to the tensile stress at the mid-point). In practice, successive fracturing will be influenced by two other factors: (1) in nature the controlling material properties (tensile fracture strength, elastic moduli) will not be single-valued but will have a distribution reflecting local variations in lithology and microstructure and (2) major pre-deformation flaws may be present in a layer which will control the ‘starting length’ of layer segments. These factors are incorporated with the stress-transfer theory into a statistical (Monte Carlo) model for extension fracture boudinage which results in a prediction of boudin aspect ratios. The predicted distribution compares very closely with the observed distribution of 91 quartzite boudins within Lower Carboniferous slates at Tintagel, Cornwall.The stress-transfer model implies that boudin-defining fractures occur sequentially so that inter-boudin gap lengths will be unequal. Strain estimates based on boudinage structure will vary according to which part and how much of a layer is sampled. A much improved strain estimate is possible based on sequentially closing the inter-boudin gaps. The stress-transfer theory also leads to the possibility of estimating palaeostress from boudinage structure and is the only model available which predicts an aspect ratio distribution of boudins formed by extension fracture. Other than our own, we know of no published data on boudin aspect ratio distributions. Hence, further elaboration of the model is not possible until more field data is available. We hope that our work will encourage the systematic measurement of boudinage as well as the development of alternative models.     

骨节状香肠构造形成机制研究——以湖北铁山为例

以湖北大冶铁山地区骨节状香肠构造为对象,根据其骨节缝形态、香肠层的剖面形态以及骨节缝填充脉体与香肠形成的期次关系,划分出13种骨节状香肠构造类型;通过对其物质组成的镜下鉴定,认为其形成过程中至少发生两期变形作用,并总结出三种力学机制①两期递进的垂直层面压缩变形叠加;②早期垂直层面压缩与后期平行层面剪切的叠加;③早期垂直层面压缩与后期平行层面挤压的叠加。     

浅论伸展构造在基岩中的表现型式

伸展构造在基岩中的表现,取决于其形成时的变形相及岩石的变形行为,可以归纳为五种主要型式:高角度正断层系组成的地堑或盆岭式构造;剥离断层;岩层的普遍变薄与糜棱岩化;相对强硬层的香肠化和缺失;褶叠层的普遍存在。文中比较详细地讨论了剥离断层与冲断推覆构造的差异及糜棱岩的识别,尤其是对碳酸盐糜棱岩识别的主要标准。     

Extensional structures in anisotropic rocks

A distinct class of structures can form as a result of extension along a plane of anisotropy (foliation). The effect of the foliation is to decrease the ductility of the material in this orientation so that brittle fractures or shear-bands develop. Foliation boudinage is caused by brittle failure; extensional fractures cause symmetric boudinage, and shear fractures cause asymmetric boudinage.Extensional crenulation cleavage is defined by sets of small-scale ductile shear-bands along the limbs of very open microfolds in the foliation. The sense of movement on the shear-bands is such as to cause a component of extension along the older foliation. Conjugate cleavage sets indicate coaxial shortening normal to the foliation; the shortening axis bisects the obtuse angle between the sets. A single set indicates oblique or non-coaxial deformation.Extensional crenulation cleavage is microstructurally and genetically distinct from other types of cleavage. It does not occur as an axial plane structure in folds, and has no fixed relationship to the finite strain axes. It is common in mylonite zones, and may be favoured by crystal-plastic and cataclastic deformational mechanisms. These cause grain-size reduction, and hence softening, which favour the development of shear-bands.     

Lithospheric boudinage in the Western Mediterranean back-arc basin

The western Mediterranean is composed of irregular troughs formed as back-arc basins in the hanging wall of the W-directed Apenninic subduction which retreated eastward during Neogene and Quaternary times. The basins are progressively younger toward the east, ageing from late Oligocene–early Miocene (Valencia, Provençal, Alboran and Algerian basins), to middle Miocene–Pleistocene (Tyrrhenian Sea). The basins isolated boudins of continental lithosphere, the Sardinia–Corsica block representing the largest. The boudinage has a wavelength of 100–400 km and facilitated stretching of the continental lithosphere with formation of new oceanic crust in the Provençal, Algerian, Vavilov and Marsili basins. The boudins developed both in the earlier Alpine–Betic orogen (Alboran basin) and in its foreland (Provençal and Valencia troughs). The extension appears clearly asymmetric due to its eastward polarity, accommodated by E-dipping master low-angle normal faults. Moreover the thinning shows variations in boudinage wavelength and is characterized by several along-strike transfer zones and heterogeneities. The western Mediterranean back-arc setting is comparable with Atlantic and western Pacific back-arc basins associated with W-directed subduction zones that show similar large-scale lithospheric boudinage.     

Character,extent and significance of broken formation for the Tabberabbera Zone,central Lachlan Orogen

Restoration of fault displacements on a section through the Lunnon Shoot is made in accordance with the general importance, noted by others, of flexural slip and ductile flow in the growth of the Kambalda Anticline. Coupled with the interpretation here that ‘normal’ and ‘reverse’ faults at Kambalda may simply be opposite walls of the same dilated fracture (one movement instead of two) this restoration allows the prism of anomalous stratigraphic sequence confined by faults and hosting the ores to be interpreted structurally‐metamorphically (‐metasomatically) rather than magmatically. The movement picture may be synoptically described as ‘boudinage on radial fractures or axial‐plane cleavage’, the structure being close to that for which the term ‘boudinage’ was originally coined. A model is proposed whereby flattening and commensurate pullapart due to tangential longitudinal strain between the footwall Lunnon Basalt and the overlying Upper (ultramafic) Sequence is focused within the contact zone occupied by the Lower (ultramafic‐sediment) Sequence (the ore sequence). Sulfur‐halogen‐rich volatiles expressed from the shales and ductile interlayered ultramafics are mobilised intraformationally commensurate with flattening, and are juxtaposed in the gaps created as the sediment units are pulled apart over the tightening anticline (the ‘zones of missing sediments'—ore zones). A boudinage model that allows for the juxtaposition of ore constituents (sulfur‐halogen‐rich volatiles and silicate nickel) in the sites that are now ore, supports the view that metamorphism has been important in the formation of the orebody, and provides scope for interpreting the entire orebody as having been structurally‐metamorphically‐metasomatically emplaced. A boudinage model is arguably simpler than magmatic models, accounting not only for all the features supporting magmatic models but also for features that magmatic models cannot explain adequately. As the Lunnon Shoot is typical of Kambalda ores, and Kambalda is the type for stratiform ultramafic‐hosted nickel deposits in Archaean greenstone belts worldwide, the currently widely accepted magmatic model could usefully be reappraised.     

Stress and displacement analysis of boudinages by the finite-element method

The paper deals with the displacement and stress distribution in boudinage structures. To analyze this, the finite-element method is used. Four models are examined.The first model treats three homogeneous bands. The displacement of the central band produces a barrel-shaped structure. The tension is greatest in the central part of this band and decreases almost continuously towards the shorter edges. If the band ruptures, the rupture will occur in the central part.The second model treats a quarter of a total structure that is already in part a developed boudinage. This development is followed through 19 iterative steps. The displacement analysis demonstrates that the boudin is displaced towards the free short edge and becomes more barrel-shaped, thinner and wider. The mean stress has two, local, tensilestress maxima inside the boudin at the upper boundary: one in the gap area and the other in the matrix at the outer, short edge of the boudin.The third model treats a quarter of a developed boudinage with two materials in the matrix. Displacement analyses demonstrate that the barrel shape of the boudin becomes more pronounced when the competence contrast between boudin and matrix decreases.One axis of principal stress has a direction in every element close to the x-axis of the model. In the area marked PbS (model 6A), this axis shows a local tensile-stress maximum and a local compressive-stress maximum. In model 6B, these points are still extreme points, but the local compressive-stress maximum has changed to a local tensile-stress maximum.The fourth model treats a boudinage in which one boudin is rotated. Displacement analyses demonstrate that the boudins tend to rotate to a position in which they are parallel, diverging a little from a right angle to the angle of the applied pressure. The mean stress demonstrates a pressure shadow in the PbS area, with a slight displacement downwards in the area beside the rotated boudin.The stress distribution corresponds to the mineral distribution of the boudinage from the Udden Mine. The investigation indicates a direct relationship between grain size and stress distribution.     

北京西山膨缩石香肠流变性质构造研究初探

本文探索了利用膨缩石香肠构造定量估测古岩石流变参数的方法,获得北京西山云母大理岩中的方解石石英脉的应力指数在3.06-7.69之间,与云母大理岩的粘度比在8.74-20.27之间;板岩中的石英脉的应力指数在2.57-4.75之间,与板岩的粘度比在94.8-175.8之间;白云岩中硅质条带的应力指数在2.25-3.93之间,与白云岩的粘度比在2.38-4.26之间.