地壳不同构造层次岩石变形机制及其构造岩类型

构造岩记录地壳构造变形演化重要信息,其成因、分类与命名一直没有统一认识。本文对构造岩变形机制、控制因素和构造岩分类进行系统总结。认为构造岩形成受物质成分、变形机制、应变速率、流体、温度、压力等因素控制,是物质成分与物理化学条件、变形机制等众多变量的函数。变形机制包括破裂作用、碎裂流动、晶质塑性、物质扩散、重结晶作用和超塑性流动,不同变形机制出现在不同地壳构造层次中,形成不同的显微组构。依据成因机制、物质组成和组构等标志对构造岩分类与命名进行重新修订,将构造岩划分为碎裂岩系列和变质构造岩系列,前者发育在地壳浅构造层次上,以破裂作用和碎裂流动变形机制为主;后者发育在中深部构造层次上,以晶质塑性、重结晶作用、物质扩散作用和超塑性流动作用为主。碎裂岩系列划分碎裂岩、角砾岩、微角砾岩、超碎裂岩、断层泥和假玄武玻璃;变质构造岩系列划分为构造片岩、糜棱岩和构造片麻岩。依据岩石流变性质、变形机制和构造岩分布,地壳构造层次划分为:脆性域,变形机制以碎裂作用和碎裂流动为主,发育碎裂岩系列;脆-韧性转换域,以晶质塑性、物质扩散和重结晶作用为主,并伴随有碎裂作用,形成糜棱岩、千糜岩和构造片岩;低温韧性域,以晶质塑性、物质扩散和重结晶作为主,发育糜棱岩与构造片岩;高温韧性域,以超塑性蠕变和重结晶作用为主,形成构造片麻岩。     

Superplastic flow in finegrained limestone

Creep of Solnhofen limestone at temperatures between 600° and 900° C was found to fall into three different flow regimes: regime 1 with an exponential stress-dependence of strain rate, regime 2 with power-law creep and n ~ 4.7 and finally a superplastic regime 3 with n ~ 1.7. Within the superplastic regime the creep behaviour is strongly grain-size dependent, the strain rate increasing markedly with decrease in grain size at a given stress. Microstructural observations indicate that in regimes 1 and 2 intracrystalline plasticity is dominant whereas the superplastic regime is characterized by grain-boundary sliding. The crystallographic preferred orientation within the superplastic regime is weaker and of different geometry when compared with that in flow regimes 1 and 2. In a discussion on the deformation mechanisms it is suggested that flow regimes 1 and 2 are regimes of dis location creep in which the rate controlling step is diffusion assisted; for the superplastic regime existing models of grain-boundary sliding are compared with the observations Finally, the tectonophysical importance of superplasticity is discussed and by extra polating the observed creep behaviour to geological strain rates it is found that super plasticity in rocks is to be expected under a wide range of conditions, particularly at smal grain sizes.     

Plagioclase microfabrics in a ductile shear zone from the Jotun Nappe,Norway

Gabbroic and anorthositic rocks from the Jotun Nappe are transected by small ductile shear zones in which a high-grade paragenesis and a new foliation are formed. Most plagioclase grains show evidence of plastic deformation, and have recrystallized by subgrain rotation and ‘bulge’ processes to fine-grained mylonite. During these processes a plagioclase grain-shape fabric was destroyed, and with increasing strain a pre-existing plagioclase crystal fabric was successively modified, enhanced and finally obliterated. This could be evidence of superplastic flow. Inverse pole figure analysis of the typical plagioclase crystal fabric in the shear zone indicates that (021) ⊥ 〈a〉 could be an operative slip system, and planes close to (132) could be possible slip planes.     

Evidence for dominant grain-boundary sliding deformation in greenschist- and amphibolite-grade polymineralic ultramylonites from the Redbank Deformed Zone, Central Australia

Microstructural and textural investigations by scanning (SEM) and transmission electron microscopy (TEM) techniques have been performed on samples taken across two quartzo-feldspathic mylonite zones from the Redbank Deformed Zone, Central Australia. One has been deformed at greenschist-facies (GS), the second at amphibolite-facies (Am), conditions. With increasing strain the rock type changes from protomylonite to mylonite to ultramylonite. The protomylonites and mylonites consist of alternating quartz and polymineralic quartz-feldspar bands. At the highest strains a homogeneous, fine-grained polymineralic ultramylonite occurs. Shear-zone geometry and microscale structures indicate that these ultramylonites experienced higher strains and were weaker than the encapsulating protomylonites and mylonites. TEM and SEM studies of the ultramylonites reveal a rectangular to square grain shape, a continuous alignment of grain and interphase boundaries across several grain diameters, a grain size (GS 0.5 μm; Am 5–11 μm) less than the equilibrium subgrain size, and open and void-containing grain and interphase boundaries. Analysis of local textures by electron back-scatter diffraction (EBSD) in the SEM showed a very weak crystallographic preferred orientation (CPO) for the quartz. The grain misorientation relationships are not consistent, with dislocation creep being the dominant deformation mechanism. All structures are of the type expected if grain-boundary sliding processes had contributed significantly to the deformation. Consequently, the deformation of such quartzo-feldspathic rocks, and by implication the rheology of the Redbank Deformed Zone, must have been controlled by the mechanical properties of these fine-grained polymineralic ultramylonites, deforming by grain-boundary sliding processes. This is in contrast to the pure quartz bands which deformed by dislocation-creep mechanisms and were less important in the rheology of the Redbank Deformed Zone.     

糜棱岩型金矿金元素丰度与构造变形的关系

蚀变糜棱岩型金矿是一种成矿机制与放因素都与韧性剪切带及其糜棱岩密切相关的金矿床类型。研究表明：①深部韧性剪切变形是元素分异迁出区,未叠加蚀变矿化的糜棱岩变形越强,Ａｕ丰度就越低;②中浅层次变形域是Ａｕ元素聚集区,矿化发生于韧性剪切带糜棱岩抬升至较浅部位叠加了韧脆性变形阶段。构造变形超强的糜棱岩,越易叠加矿化,Ａｕ元素丰度越高;③强变形或者大构造并应力不仅是促使Ａｕ元素活化分异、形成含Ａｕ热液、使Ａ     

Petrology of a portion of the Eastern Peninsular Ranges mylonite zone,Southern California

Peraluminous and metaluminous plutonic rocks of the Peninsular Ranges batholith near Borrego Springs in southern California were mylonitized in the large shear zone known as the eastern Peninsular Ranges mylonite zone (EPRMZ). Accompanying mylonitization in this portion of the EPRMZ was metamorphism at intermediate-low-pressure amphibolite-facies conditions. Deformation in the zone overlapped in time with Cretaceous intrusion of the batholith. In the San Ysidro Mountain — Pinyon Ridge area, four north-south trending zones of differing intensity of deformation have been defined; from east to west the degree and style of deformation gradually change from undeformed or weakly deformed rocks to strongly mylonitized rocks. Electron microprobe analysis shows that recrystallized hornblende, biotite, and plagioclase are variable in composition, probably reflecting a range of metamorphic conditions accompanying deformation. Comparison of mineral compositions with those from mafic schists of Vermont suggests conditions ranged from andalusite-staurolite through sillimanite-muscovite grades as defined for pelitic rocks. Stability of muscovite+quartz in mylonite assemblages and lack of remelting of granitic rocks indicate that temperature did not exceed about 650° C during mylonitization and lithostatic pressure did not exceed about 5 kbar. Over time, any given rock volume experienced a range of temperature, lithostatic pressure, and perhaps fluid pressure and differential stress. Mineral reactions in the zone involved hydration, requiring introduction of water. The possibility of large-scale migration of K and Fe is suggested by whole-rock chemical data. Brittle and ductile deformation features are closely associated in one part of the EPRMZ. The combined evidence suggests the presence of a pore fluid with fluid pressure close to lithostatic pressure. Short periods of low fluid pressure and possible high differential stress cannot be ruled out.     

The role of deformation partitioning in the deformation and recrystallization of plagioclase and K-feldspar in the Woodroffe Thrust mylonite zone, central Australia

ABSTRACT In the Woodroffe Thrust mylonite zone, central Australia, recrystallization in plagioclase and K-feldspar involved subgrain rotation, assisted by grain-boundary or kink band boundary bulging, without contribution from a change in the chemical composition from host grains to new grains. The size of subgrains and new grains changes across the mylonite zone, apparently as a function of the strain rate and the H2O content of the rock. The partitioning of deformation into zones of progressive shearing and progressive shortening controls the sites of recovery and recrystallization in feldspar during mylonitization. The size of feldspar porphyroclasts in well developed mylonites is governed by the scale of deformation partitioning reached in the earlier stages of mylonitization, before the formation of a large proportion of fine-grained matrix that can accommodate the progressive shearing component of the deformation. Recrystallization occurs in microcline, apparently without involving a translation to a monoclinic structure, as microcline-twinned new grains are common adjacent to microcline-twinned host grains. K-feldspar triclinicity values calculated from XRD traces increase from the margins to the interior of the mylonite zone, in conjunction with deformation intensity. K-feldspar host grains locally have cores of orthoclase or untwinned microcline, surrounded by mantles of twinned microcline, suggesting a relationship between the presence of microcline twinning and the degree of K-feldspar triclinicity.     

Superplastic flow and changes in crystal chemistry of feldspars

Comparison of observed microstructures and deduced physical parameters of natural deformations with those encountered in superplastic metals permits identification of superplastic behaviour in rocks. From microstructural evidence, superplastic flow of feldspar is inferred to have occurred in the deformation of a granite from Miéville, Aiguilles-Rouges massif, Switzerland. The original igneous orthoclase and oligoclase phenocrysts have both recrystallised to fine-grained albite which has deformed by superplastic flow. This change in crystal chemistry was associated with a large negative change in free energy, enabling recrystallised grains of a very small size to be stable under the prevailing conditions, thereby producing the pre-requisite conditions for superplastic behaviour.     

胶东焦家断裂带韧性变形特征

焦家断裂带晚期表现为强烈的脆性变形,但其早期则表现以糜棱岩组合、对称组构等为特征的韧性变形。应变测量和差应力估算表明:从焦家主断裂到望儿山支断裂的糜棱岩变形标志体有主轴比变小、K值增大、古应力值逐渐变小的趋势,韧性变形阶段差应力方向为NWW-SEE.焦家断裂带早期是在中温(300℃~500℃)、中等围压(0.27 GPa~0.49 GPa)条件下形成的以压扁作用为主的左行韧性变形带。      

秦岭岩群古生代构造变形分析

秦岭岩群是秦岭造山带中最古老的地体之一,其强烈的构造变形记录了秦岭造山带的形成和演化信息。本文在野外构造调查的基础上、结合显微构造变形分析和锆石U?Pb定年,对秦岭岩群进行了构造变形解析及年代学研究,结果显示秦岭岩群古生代构造变形表现为由东向西的斜向挤出抬升,其构造变形时间为426.7±5.8 Ma~395.7±7.4 Ma。该期构造变形温度为480℃~560℃,对应变质相为高绿片岩相—低角闪岩相,差异应力为20.19~56.54 MPa,应变速率为1.82281×10^-13s^-1~5.62102×10^-13s^-1,付林参数为0.29~0.47,涡度值为0.57~0.75。综合前人研究及本次构造变形分析,认为秦岭岩群在扬子板块与华北板块斜向汇聚背景下经历了由东向西的斜向挤出抬升。     

An experimental study of effect of pre‐existing fabric on deformation of foliated mylonite at high temperature and pressure

We performed deformation experiments on a foliated mylonite under high temperature and pressure conditions in this study. To investigate the effect of pre‐existing fabric on the rheology of rocks, our samples were drilled from natural mylonite with the cylinder axis parallel to the foliation (PAR) and perpendicular to the foliation (PER). We performed 25 tests on seven PAR samples and 21 tests on seven PER samples at temperatures ranging from 600 to 890 °C, confining pressures ranging from 800 to 1400 MPa, and steady‐state strain rates of 1 × 10⁻⁴, 1 × 10⁻⁵ and 2.5 × 10⁻⁶ s⁻¹. In the temperatures of 600–700 °C, the deformation is accommodated by semi‐brittle flow, with the average stress exponent being 6–7 assuming power law flow; in the temperature range of 800–890 °C, deformation is mainly by plastic flow, with an average stress exponent of n = 3 and activation energies of Q = 354 ± 52 kJ/mol (PER and PAR samples). The experimental results show that the strengths of PER samples are higher than those of PAR samples. Deformation microstructures have been studied by optical and electron microscopy. The original foliation of PER samples is destroyed by deformation and replaced by a new foliation, but the deformation of PAR samples followed the original foliation. Electron backscatter diffraction (EBSD) measurements show a strong lattice preferred orientation (LPO) of the quartz c axis fabrics of the starting samples and deformed PER and PAR samples. However, the c axis fabric of quartz in experimentally deformed PER and PAR samples varied with temperature and strain rate is different from that seen in the starting mylonite sample. The initial quartz c axis fabric of the starting mylonite sample has been transformed into a new fabric during experimental deformation. Dehydration melting of biotite and hornblende occurred in both PER and PAR samples at temperatures of 800–890 °C. Copyright © 2014 John Wiley & Sons, Ltd.     

Fluid flow,metasomatism and amphibole deformation in an imbricated ophiolite,North Cascades,Washington

Metasomatic tremolite-rich mylonites are widespread in imbricate thrust slices of ultramafic rocks of the ophiolitic Ingalls Complex in Washington State. Protoliths for these amphibolite-facies mylonites were peridotite and serpentinite. Abundant syntectonic tremolite veins in the ultramafites record narrowly channelized flow of infiltrating fluids, whereas metasomatic mylonite zones record more pervasive flow. Fluids were probably released mainly by prograde devolatization reactions within serpentinite and mafic ophiolitic rocks that experienced earlier hydrothermal metamorphism.Olivine apparently deformed by dislocation creep in the mylonites. In the tremolite-rich rocks, locally preserved amphibole porphyroclasts deformed mainly by microfracturing. Acicular tremolites, which dominate the mylonites, form syntectonic overgrowths on porphyroclasts and probably record diffusive mass transfer which may have accompanied cataclasis. Acicular tremolites subsequently were folded and define both post-crystalline crenulations and polygonal arcs.Fluid flow, deformation and metamorphism were apparently complexly interrelated in the imbricate zone. Thrusts juxtaposed contrasting rock types that were sources and sinks for fluids, and shear zones focused fluid flow. Metamorphism probably facilitated deformation through the release of fluids during dehydration reactions. High fluid pressure may have led to hydraulic fracturing and may have controlled strain softening in the tremolitic mylonite zones as it favored microcracking and diffusive mass transfer over dislocation creep. Infiltrating metasomatic fluids probably play an important role in the evolution of shear zones in many ultramafic bodies during medium-grade metamorphism.     

郯庐断裂南段主断裂韧性剪切带形成历时时限的探索

为求得此前未曾测得过的郯庐断裂韧性构造事件的过程时间 ,选定居于安徽省肥东县桴槎山隶属郯庐断裂南段主断裂韧性剪切带糜棱岩为研究对象。运用显微构造物理化学方法 ,首先测算形成糜棱岩的差异流动应力 ,以进行应变速率 ( ε)的求算 ;然后 ,用等浓度线法和晶胞参数法分别测算糜棱岩化过程中岩石体积应变量 (fV) ;再根据公式t =-lnfV/ ε ,计算出糜棱岩化过程时间 (t)。结果得出该糜棱岩带的形成时限为几十万年 (0 19～ 0 94Ma)的时间跨度 ,不同方法测定时限的精度差值在半个量级左右。     

多相糜棱岩内第二相对应变局部化的影响——以秦岭群花岗质糜棱岩为例

糜棱岩韧性变形发生的应变局部化过程,尤其是多相糜棱岩第二相对基质相变形的影响一直是显微构造研究难点.研究表明糜棱岩借助颗粒边界滑移实现多相混合,形成多矿物相集合体.在多相糜棱岩内,第二相在基质相颗粒边界施加齐纳阻力,牵制基质相颗粒边界的迁移速率,破坏基质相颗粒的动态平衡过程,使基质相颗粒位于古应力计对应的颗粒粒度以下,...     

构造形变类型与金矿化类型的关系

含金构造形变类型决定或控制金矿化类型,深层次的韧性超韧性变莆为元素迁出区,一般不利于金矿化;韧性含金构造控制蚀变糜棱岩型金矿化,韧脆性变形含金构造控制构造蚀变岩型金矿化,脆性含金构造控制石英脉型金矿化。对于韧性剪切带和未来发生叠加蚀变矿化的糜棱岩来说,往往是构造变形越强,金元素含量越低。但在蚀变糜棱岩型金矿床中,已经叠加蚀变矿化的糜棱岩若幅度,石英变形机制与金矿富集程度都有密切的关系,而且含金构造     

Fluid-assisted fracturing,cataclasis, and resulting plastic flow in mylonites from the Moresby Seamount detachment,Woodlark Basin

The Moresby Seamount detachment (MSD) in the Woodlark Basin (offshore Papua New Guinea) is a large active low-angle detachment excellently exposed at the seafloor, and cutting through mafic metamorphic rocks. Hydrothermal infiltration of quartz followed by that of calcite occurred during cataclastic deformation. Subsequent deformation of these a priori softer minerals leads to mylonite formation in the MSD. This study aims at a better understanding of the deformation mechanism switch from cataclastic to plastic flow. Deformation fabrics of the fault rocks were analyzed by light-optical microscopy. Rheologically critical phases were mapped to determine distributions and area proportions, and EBSD was used to measure crystallographic preferred orientation (CPO). Strong calcite CPOs indicate dominant dislocation creep. Quartz CPOs, however, are weak and more difficult to interpret, suggesting at least some strain accommodation by diffusion creep mechanisms. When quartz aggregates are intermixed with the polymineralic mylonite matrix diffusion creep grain boundary sliding may be dominant. The syntectonic conversion from mafic cataclasites to more siliceous and carbonaceous mylonites induced by hydrothermal processes is a critical weakening mechanism enabling the MSD to at least intermittently plastic flow at low shear stresses. This is probably a crucial process for the operation of low-angle detachments in hydrated and dominantly mafic crust.     

Marble mylonites in the Bancroft shear zone, Ontario, Canada: microstructures and deformation mechanisms

Mylonitization of medium-grade marbles in the Bancroft shear zone, Ontario, Canada, is characterized by decreasing grain-size of both calcite and graphite, and a variety of textures. Calcite grain-sizes vary from several millimeters in the protolith, to 50–200 μm in mylonite, to <30 μm in ultramylonite. Corresponding calcite grain shapes are equant in the protolith, elongate in protomylonite (first-developed dimensional preferred orientation), equant in coarse mylonite, elongate in fine mylonite (second-developed dimensional preferred orientation) and generally equant in ultramylonite, which suggests that external energy (applied stress) that tends to elongate grains competed with internal energy sources (e.g. distortional strain) that favor equant shapes. Graphite grain-size changes from several millimeters to centimeters in the protolith to submicroscopic in ultramylonite. In the mylonitic stages, graphite is present as dark bands, while in the ultramylonitic stage it is preserved as a fine coating on calcite grains.Based on textural evidence, twinning (exponential creep; regime I), dynamic recrystallization (power law creep; regime II) and possibly grain boundary sliding superplasticity (regime III) are considered the dominant deformation mechanisms with increasing intensity of mylonitization; their activity is largely controlled by calcite grain-size. Calcite grain-size reduction occurred predominantly by the process of rotation recrystallization during the early stages of mylonitization, as indicated by the occurrence of core and mantle or mortar structures, and by the grain-size of subgrains and recrystallized grains. Grain elongation in S-C structures indicates the activity of migration recrystallization; these structures are not the result of flattening of originally equant grains. Differential stress estimates in coarse mylonites and ultramylonites, based on recrystallized grain-size, are 2–5 and 14–38 MPa, respectively. Initial grain-size reduction of graphite occurred by progressive separation along basal planes, analogous to mica fish formation in quartzo-feldspathic mylonites.Calcite-graphite thermometry on mylonitic and ultramylonitic samples shows that the metamorphic conditions during mylonitization were 475 ± 50°C, which, combined with a differential stress value of 26 MPa, gives a strain rate of 1.2 x 10⁻¹⁰s⁻¹ based on constitutive equations; corresponding displacement rates are <38 mmyr⁻¹.     

Deformation mechanisms and flow regimes in limestones from the Helvetic zone of the Swiss Alps

This paper is based on a combined field, transmission-electron (TEM) and transmission-optical (TOM) microscope study of limestones from the Helvetic zone (Swiss Alps) and discusses the deformation mechanisms and flow regimes that governed the deformation of these rocks.During pre-metamorphic regional ductile deformations the limestones deformed by power-law dislocation creep with differential stresses probably not exceeding 1 kbar. Dynamic recrystallization with grain-boundary sliding and grain-boundary migration allowed the grains to be less elliptical than the strain ellipse. A characteristic of the structure is the existence of dislocation-free subgrains. In the footwall of and approaching the Lochseiten calc-mylonite along the Glarus overthrust, grain-boundary sliding becomes more important (shift to diffusional creep or superplastic flow).During a syn- and post-metamorphic deformation, dynamic recovery seems to have become less competitive (no dislocation-free sub-grains), and along thrust faults twinning indicates a shift to higher differential stresses at the close of the deformation.It was not possible to separate these deformation phases on the basis of the dislocation debris. Sub-grain sizes as observed in TEM and TOM were identical.In limestones that underwent cataclastic deformation the rocks seem to have started breaking up along the grain boundaries. The new grain fragments are very small (0.1–0.3 μm) and are heavily twinned. In TEM the old large grains show very long straight glide dislocations, cleavage and, when shattered, ring patterns in diffraction.     

应变软化在甘肃红柳河辉长质糜棱岩形成中的作用

本文论述的辉长质糜棱岩发现于甘肃北山红柳河蛇绿岩套中。在简单说明了糜棱岩的地质背景及特征、描述了变形岩石的显微构造特征之后，重点对糜棱岩形成过程中的应变软化机制作了论述。探讨了软化岩的存在、组构调整、粒度缩小，长石的动态重结晶，水以及主导变形机制的不断调整与转化等应变软化机制，在应力作用下使岩石逐步软化过程中所起的作用，得出这种糜棱岩是在拆离剪切作用下，应力在蛇绿岩中的软化岩石辉长岩中集中，从而形