Fractal distribution of particle size in carbonate cataclastic rocks from the core of a regional strike-slip fault zone

We present particle size data from 31 samples of carbonate cataclastic rocks collected across the 26 m thick fault core of the Mattinata Fault in the foreland of the Southern Apennines, Italy. Particle size distributions of incoherent samples were determined by a sieving-and-weighting technique. The number of weight-equivalent spherical particles by size is well fitted by a power-law function on a log–log space. Fractal dimensions (D) of particle size distributions are in the 2.091–2.932 range and cluster around the value of 2.5. High D-values pertain to gouge in shear bands reworking the bulk cataclastic rocks of the fault core. Low D-values characterise immature cataclastic breccias. Intermediate D-values are typical of the bulk fault core. Analysis of the ratio between corresponding equivalent particle numbers from differently evolved cataclastic rocks indicates that the development of particle size distributions with D>2.6–2.7 occurred by a preferential relative increase of fine particles rather than a selective decrement of coarse particles. This preferentially occurred in shear bands where intense comminution enhanced by slip localisation progressed by rolling of coarse particles whose consequent smoothing produced a large number of fine particles. Our data suggest that during the progression of cataclasis, the fragmentation mode changed from the Allègre et al.'s [Nature 297 (1982) 47] “pillar of strength” mechanism in the early evolutionary stages, to the Sammis et al.'s [Pure and Applied Geophysics 125 (1987) 777] “constrained comminution” mechanism in the subsequent stages of cataclasis. Eventually, localised shear bands developed mainly by abrasion of coarse particles.     

Alteration and mass transfer in cataclasites and mylonites in 6.6 km of granitic crust at the Siljan impact structure,central Sweden

Granitic rocks deformed by cataclasis and mylonitization on macro- (a few meters) and micro- (thin section) scales are found at depths down to 6.6km in the Siljan impact structure in central Sweden. Granites near fault planes exhibit: (1) fracturing, kinking, fragmentation, and recrystallization of feldspars into pure K and Na endmember varieties, (2) fragmentation, polygonization and development of undulose extinction in quartz, and (3) kinking, appearance of wavy extinction and alteration of biotite, chlorite, amphibole, and alteration of ilmenite and magnetite. Whole-rock chemical analyses of deformed and undeformed rocks show that deformed rocks are enriched in SiO₂ (by about 5 wt.%) and depleted in other oxides by variable percentages. Apart from Rb and Co, the concentrations of other trace elements (including Ba, Sr, Zn, Zr, Pb, Cd, Cu, Cr, Ni, V, U, Th, La, and Li) are lower in deformed relative to undeformed rocks. Mass-balance calculations for a 1000 cm³ model granite which were based on modal mineralogy, whole-rock chemistry, and mineral analyses suggest that the break down of primary biotite, chlorite, and amphibole in deformed zones released elements to circulating fluids. These calculations also indicate liberation of water and a doubling of porosity (from 1 to 2%) during the deformation episodes. Later precipitation of minerals in shear and tension fractures reduced this porosity. Within the upper 2000 m of the Gravberg-1 well, the formation of fracture-filling minerals (smectite, calcite, hematite, chlorite, and albite) is impact-related, and was favored by active circulation of meteoric water. Fracture-filling minerals in the upper 2000 m of the borehole formed at temperatures of 70° to 200°C. Between depths of 2000 and 3500 m, fracture-filling mineral assemblages (dominated by Fe–Mg chlorite, sphene and epidote) suggest formation temperatures in the range of 150° to 300°C. Occurrence of pumpellyite and prehnite in some altered biotite and chlorite of the deformed zones between 3500 and 5500 m suggest preimpact metamorphism and formation temperature above 150°C. Below 5500 m, the mineral assemblages in the fractures are dominated by quartz, sphene, epidote, and some muscovite and chlorite, indicating a temperature range between 300° and 450°C. One of the possible origins for the CH₄ and H₂ gases detected in the Gravberg-1 well is a combination of hydrogen ions released by decomposition of hydrated silicates (biotite, chlorite, hornblende) with carbon. The presence of iron in the deformed granitic rocks prevented the resulting CH₄ from being oxidized.     

S–C fabrics developed in cataclastic rocks from the Nojima fault zone,Japan and their implications for tectonic history

S–C fabrics similar to those found in mylonites are observed in foliated cataclastic granitic rocks from the Nojima fault zone, southwest Japan. The foliated cataclastic rocks comprise cataclasite, fault breccia, gouge, and crushing-originated pseudotachylyte. The S–C fabrics observed in these cataclastic rocks involve S-surfaces defined by shape preferred orientation of biotite fragments or aggregates of quartz and feldspar fragments, and C-and C′-surfaces defined by microshears and shear bands, respectively, where fine-grained material is concentrated. Striations on the main fault plane are oriented parallel to the cataclasite lineations. A significant microstructural difference between the foliated cataclastic rocks and S–C mylonites is the absence of dynamically recrystallized grains in the foliated cataclasites. The striations, cataclastic lineations, and the S–C fabrics in the cataclastic rocks formed from the late Tertiary to the late Holocene indicate that the Nojima fault zone has moved as a dextral strike-slip fault, with a minor reverse component since it formed. S–C fabrics in cataclastic rocks provide important information on the tectonic history and are reliable kinematic indicators of the shear sense in brittle shear zones or faults.     

矿物成因族的演化及其地质找矿信息

基于对胶东、晋北寒武纪变质岩系、超基性岩、基性岩、花岗岩类、火山岩类、硅铁建造铁矿、金矿蚀变带内 1 1个不同地质产状的 34个角闪石、 2 51个绿泥石、 60个黑云母单矿物的提纯 ,矿物的共生组合、物理性质、化学成分、X光衍射分析、热分析、红外吸收光谱分析、双矿物地质温度计、矿物压力计的测定 ,提出了角闪石、绿泥石、黑云母矿物成因族的地壳物质演化、成岩成矿作用、变质岩原岩恢复、地层对比、变质相、蚀变带的演化规律和地质找矿信息。     

Metamorphism of the Basement of the Qilian Fold Belt in the Minhe-Ledu Area, Qinghai Province, NW China

The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on me     

Particle shape evolution in natural carbonate granular wear material

A fundamental yet still unresolved puzzle provided by cataclasis is whether particle size reduction mostly progresses through time by the same fragmentation mechanism or not. Available field, laboratory and numerical modelling results on the evolution of cataclastic rocks are still controversial. The evidence that cataclastic rocks exert a primary control on the frictional strength, stability, seismic velocity and permeability properties of fault zones encourages further research on cataclasis. Here, we report data on particle shape from natural cataclastic rocks in poorly layered carbonates in the Apulian foreland of the Southern Apennines of Italy. Particle shape analyses show that particle angularity decreases with increasing size and, for a given size class, it decreases with increasing fractal dimension of the particle size distribution. These results offer support to the temporally and spatially variable nature of rock comminution.     

Fluid behaviors from the seismogenic region of Longmenshan fault zone,eastern Tibetan PlateauSCIEI北大核心CSCD

震间期、同震期和震后期流体对断裂带物质的强度和运动性质起到重要作用。前人已识别出断裂带浅部区域流体对断层的弱化以及矿物沉淀导致的断层愈合,然而对于断裂带深部流体的研究鲜有报道。为深入了解孕震区流体行为以及地震成核过程中流体对断层的影响,本文以龙门山断裂带的映秀-北川断裂南段虹口乡八角庙村附近碎裂岩滑动带中石英和方解石脉为研究对象,通过对断裂带脉体的显微构造、碳氧同位素和主量元素含量等分析,开展地震相关脉体的特征结构、流体来源和矿物沉淀环境的研究。结果表明,碎裂岩主滑移带由颜色结构不同的三层断层泥和细小的方解石条带组成,在主滑动带边部和上盘碎裂岩中则分别发育了指示震间期、同震期和震后期三个阶段断层活动的脉体:(1)沿阶步生长的纤维状方解石脉和拉伸型柱状颗粒方解石脉;(2)断层泥楔入脉;(3)近等粒状方解石脉以及具有横向竞争生长结构的非等粒状方解石脉和石英脉。它们分别代表了震间期封闭的还原环境下的微滑动、同震外源高压流体注入以及震后开放的氧化环境至还原环境下的矿物沉淀。碳氧同位素结果表明主滑动带和碎裂岩方解石脉δ^(18)O V-PDB值为-20.5‰~-20.3‰,低于围岩碳酸钙胶结物,表明方解石脉具有大气水来源特征。方解石沉淀温度结合地温梯度表明方解石脉的形成深度大于4km,与碎裂岩形成深度及龙门山断裂带震源深度一致。该地区方解石脉和石英脉的研究深化了关于龙门山断裂带孕震区流体行为的理解,并且对进一步认识震间期、同震期和震后期断层的强度变化机制具有重要意义。     

Particle size distributions of fault rocks and fault transpression: are they related?

ABSTRACT Laboratory experiments on rock faulting show that processes of particle comminution in fault rocks are influenced by several parameters, including fault strike and normal stress across faults. In nature, normal stress across faults increases with increasing transpressional strike of faults. Accordingly, different structural fabrics and particle size distributions are expected for cataclastic rocks that have developed along faults with different transpressional orientations and comparable displacements within regional-scale strike-slip fault zones. Adjacent bands of cataclastic gouge and breccia were analysed from four small-scale fault zones. All have comparable displacements and very similar protolith (i.e. shallow-water limestone), structure, kinematics, size, and tectonic environment, but different transpressional strikes within the regional-scale left-lateral Mattinata strike-slip fault, Italy. An inverse linear relationship is found between fault transpressional angles and fractal dimensions of particle size distributions from cataclastic rock samples.     

Patterns of mineral transformations in clay gouge,with examples from low-angle normal fault rocks in the western USA

Neoformed minerals in shallow fault rocks are increasingly recognized as key to the behavior of faults in the elasto-frictional regime, but neither the conditions nor the processes which wall-rock is transformed into clay minerals are well understood. Yet, understanding of these mineral transformations is required to predict the mechanical and seismogenic behavior of faults. We therefore present a systematic study of clay gouge mineralogy from 30 outcrops of 17 low-angle normal faults (LANF's) in the American Cordillera to demonstrate the range and type of clay transformations in natural fault gouges. The sampled faults juxtapose a wide and representative range of wall rock types, including sedimentary, metamorphic and igneous rocks under shallow-crustal conditions. Clay mineral transformations were observed in all but one of 28 faults; one fault contains only mechanically derived clay-rich gouge, which formed entirely by cataclasis.Clay mineral transformations observed in gouges show four general patterns: 1) growth of authigenic 1M_d illite, either by transformation of fragmental 2M₁ illite or muscovite, or growth after the dissolution of K-feldspar. Illitization of fragmental illite–smectite is observed in LANF gouges, but is less common than reported from faults with sedimentary wall rocks; 2) ‘retrograde diagenesis’ of an early mechanically derived chlorite-rich gouge to authigenic chlorite–smectite and saponite (Mg-rich tri-octahedral smectite); 3) reaction of mechanically derived chlorite-rich gouges with Mg-rich fluids at low temperatures (50–150 °C) to produce localized lenses of one of two assemblages: sepiolite + saponite + talc + lizardite or palygorskite +/− chlorite +/− quartz; and 4) growth of authigenic di-octahedral smectite from alteration of acidic volcanic wall rocks. These transformation groups are consistent with patterns observed in fault rocks elsewhere. The main controls for the type of neoformed clay in gouge appear to be wall-rock chemistry and fluid chemistry, and temperatures in the range of 60–180 °C.     

Microstructures and their implications for faulting processes –Insights from DGLab core samples from the Gulf of Corinth

We have examined microstructures, mineralogical composition, geochemical alteration, and texture of four selected fault rock samples from the Deep Geodynamical Laboratory (DGLab) Gulf of Corinth project using optical microscopy, cathodoluminescence microscopy (CL), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and synchrotron X-ray diffraction measurements. The fault core is composed of red and gray clayey gouge material and surrounded by a damage zone of brecciated limestones. Pressure solution features, calcite veins and calcite clasts in the breccia and gouge material attest the presence of paleo-fluids and fluid-driven mass transfer during deformation. Differences in CL-colors between the matrix and calcite vein cement and inside the vein cement suggest repeated infiltration of fluids with different composition from various sources (formation water and meteoric water). Twin lamellae densities estimated in calcite veins are used as paleo-piezometer. The deduced differential stress is ∼140 ± 70 MPa for the older vein generation and appears to be higher than stress for the youngest veins (45 ± 23 MPa). In spite of the relatively small clay content in both samples, newly formed clay minerals have been observed in gray as well as red clayey gouge material. Differences between gray and red clay gouge material are found in fault rock composition, porosity and clay fabric. The proportion of chlorite in the red gouge is significantly less than that in the gray gouge whereas the initial porosity is significantly higher than in the gray gouge material. The detection of a well-oriented clay fabric in red clay gouge samples is unique in comparison to other major fault zones.     

A case for hornblende dominated fractionation of arc magmas: the Chelan Complex (Washington Cascades)

Amphibole fractionation in the deep roots of subduction-related magmatic arcs is a fundamental process for the generation of the continental crust. Field relations and geochemical data of exposed lower crustal igneous rocks can be used to better constrain these processes. The Chelan Complex in the western U.S. forms the lowest level of a 40-km thick exposed crustal section of the North Cascades and is composed of olivine websterite, pyroxenite, hornblendite, and dominantly by hornblende gabbro and tonalite. Magmatic breccias, comb layers and intrusive contacts suggest that the Chelan Complex was build by igneous processes. Phase equilibria, textural observations and mineral chemistry yield emplacement pressures of ∼1.0 GPa followed by isobaric cooling to 700°C. The widespread occurrence of idiomorphic hornblende and interstitial plagioclase together with the lack of Eu anomalies in bulk rock compositions indicate that the differentiation is largely dominated by amphibole. Major and trace element modeling constrained by field observations and bulk chemistry demonstrate that peraluminous tonalite could be derived by removing successively 3% of olivine websterite, 12% of pyroxene hornblendite, 33% of pyroxene hornblendite, 19% of gabbros, 15% of diorite and 2% tonalite. Peraluminous tonalite with high Sr/Y that are worldwide associated with active margin settings can be derived from a parental basaltic melt by crystal fractionation at high pressure provided that amphibole dominates the fractionation process. Crustal assimilation during fractionation is thus not required to generate peraluminous tonalite.     

福建岱前山辉长岩体的地球化学特征与成因探讨

岱前山辉长岩体沿福建长乐一南澳大断裂带分布，侵位于沿海的绿片岩相和角闪岩相的变质岩中及内陆的中生代火山岩中，对其成因存在较多分歧。该岩体表现为与俯冲有关的岛弧地球化学特点，但在时间上又与古太平洋板块低角度歪斜俯冲、晚中生代的变质事件、平潭一东山变质带抬升和长乐一南澳剪切带运动在时间上基本一致。对于其成因不能简单的用拉张或碰撞加以解释，是受俯冲流体交代的上地幔，经部分熔融沿长乐一南澳断裂．应力转换带侵入。它与中国东南部出露的其它基性岩同源，但并未受到地壳的混染作用。计算结果表明，岱前山岩体经7％的部分熔融形成，其Sm、Nd含量高于原始地幔。     

The low temperature brittle-ductile transition in a quartzite and the occurrence of cataclastic flow in nature

The paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite (Oughtibridge Ganister), and compares its microstructural development with features of cataclastic deformation of rocks in nature. The brittle to ductile transition in dry ganister occurs at about 600 MPa at room temperature. At lower pressures shear oriented grain boundary cracks form both pre and post peak strength, loosening the microstructure to the point at which axial transgranular cracks develop. Fault zone localization then occurs. At high pressures fault localization is suppressed by friction, and cataclastic flow occurs by the formation of ultracataclasite shear zones around each grain boundary, Rhomb shaped, relatively intact grain cores survive to high (greater than 20%) strains. Hardening mechanisms responsible for the ductility are discussed. It is shown that natural zones of intense cataclasis (fault zones) often develop microstructures comparable with those seen in these experiments, but the less intense cataclastic flow often associated with folding of rocks at high crustal levels in the external zones of orogenic belts is not comparable inasmuch as grain-scale catalaclasis does not normally occur. It is emphasised that finite strain microstructural similarity does not necessarily point to comparable deformation paths and stress history.     

Contact metamorphism of pelitic,psammitic and calcareous sediments in the Southern Highlands of New South Wales

Contact metamorphism has been recognized along a 4 km wide belt adjacent to the shallow‐dipping eastern margin of the Arthursleigh Tonalite, an Early Devonian pluton of the Marulan Batholith, eastern New South Wales. In Ordovician psammitic and pelitic rocks three zones of progressive contact metamorphism range from muscovite + biotite + chlorite assemblages in the outer zone to K‐feldspar + cordierite assemblages adjacent to the pluton and in metasedimentary xenoliths. Retrograde phenomena include extensive replacement of metamorphic minerals by ‘sericite’ and chlorite. Calcareous metasediments adjacent to the tonalite typically contain assemblages of quartz + calcic plagioclase + ferrosalite + sphene, or wollastonite + calcite + diopside with minor grossularite and vesuvianite. Thermal effects in volcanic rocks along the western margin of the pluton are confined to recrystallization of the groundmass.

The regional geology indicates confining pressures of approximately 1 kbar at the time of emplacement of the tonalite. Contact metamorphic temperatures were estimated from two‐feldspar geothermometry to attain a maximum of approximately 590°C for rocks in the innermost zone of the aureole and 700°C for the xenoliths. Fluid compositions attending progressive contact metamorphism were water‐rich (Xco₂<0.2) and, during cooling, these fluids probably account for the extensive retrograde hydration observed in the aureole.     

A two-stage fluid history for the Orocopia Schist and associated rocks related to flat subduction and exhumation,southeastern California

ABSTRACT

Stable isotopes combined with pre-existing ⁴⁰Ar/³⁹Ar thermochronology at the Gavilan Hills and Orocopia Mountains in southeastern California record two stages of fluid–rock interaction: (1) Stage 1 is related to prograde metamorphism as Orocopia Schist was accreted to the base of the crust during late Cretaceous–early Cenozoic Laramide flat subduction. (2) Stage 2 affected the Orocopia Schist and is related to middle Cenozoic exhumation along detachment faults. There is no local evidence that schist-derived fluids infiltrated structurally overlying continental rocks. Mineral δ¹⁸O values from Orocopia Schist in the lower plate of the Chocolate Mountains fault and Gatuna normal fault in the Gavilan Hills are in equilibrium at 490–580°C with metamorphic water (δ¹⁸O = 7–11‰). Phengite and biotite δD values from the Orocopia Schist and upper plate suggest metamorphic fluids (δD ~ –40‰). In contrast, final exhumation of the schist along the Orocopia Mountains detachment fault (OMDF) in the Orocopia Mountains was associated with alteration of prograde biotite and amphibole to chlorite (T ~ 350–400°C) and the influx of meteoric-hydrothermal fluids at 24–20 Ma. Phengites from a thin mylonite zone at the top of the Orocopia Schist and alteration chlorites have the lowest fluid δD values, suggesting that these faults were an enhanced zone of meteoric fluid (δD < –70‰) circulation. Variable δD values in Orocopia Schist from structurally lower chlorite and biotite zones indicate a lesser degree of interaction with meteoric-hydrothermal fluids. High fluid δ¹⁸O values (6–12‰) indicate low water–rock ratios for the OMDF. A steep thermal gradient developed across the OMDF at the onset of middle Cenozoic slip likely drove a more vigorous hydrothermal system within the Orocopia Mountains relative to the equivalent age Gatuna fault in the Gavilan Hills.     

弓长岭鞍山群太古代基底岩石特征

弓长岭鞍山群呈北西至南东方向分布，位于中朝陆块东端，该群各类型岩石构成华北陆块古老的变质结晶基底。文中详细地记述了岩浆岩及混合岩、硅质板岩和长英质变粒岩、交超基性岩、交基性火山岩、变泥质岩、铁矿床、变辉长辉绿岩岩墙群的岩石特征和产出特征及成岩时代。本区为低压区域浅变质类型，演化与成岩时代约在太古代的中、晚期(3400～2500Ma)。     

断裂在纯净砂岩中的变形机制及断裂带内部结构

以纯净砂岩为对象,考虑了影响断裂变形的主要因素,包括成岩阶段、孔隙度、温度和围压,系统剖析了不同性质砂岩的断裂变形机制、微构造特征及形成断裂带的内部结构,对研究砂岩内断裂封闭性具有重要的指导意义。研究表明：纯净的砂岩在未固结-半固结成岩阶段发生断裂,变形机制为颗粒边界摩擦滑动,导致颗粒旋转和滚动,即为颗粒流,形成的微构造为解聚带,孔渗性同母岩比没有明显降低,断裂带尽管具有断层核和破碎带二分结构,但渗透率比母岩高,为流体垂向运移的通道;在固结成岩阶段（孔隙度大于15%）发生断裂,变形机制为碎裂作用,颗粒边界摩擦滑动导致颗粒旋转,即为碎裂流,形成的微构造为碎裂带,渗透率同母岩比一般降低1～3个数量级,形成侧向有一定封闭能力、垂向渗透的断裂带;固结阶段（孔隙度小于15%）发生断裂,开始由于破裂作用,形成断层角砾岩,伴随着碎裂流发生,形成碎裂岩,因此早期形成高渗透断裂带,后期断层逐渐封闭。固结成岩的砂岩在抬升过程发生断裂,变形机制为破裂作用,形成无内聚力的角砾岩,为高渗透断裂带。在不同成岩阶段发生变形,形成多类型变形构造的叠加,对于一条晚期形成的断层而言,由于不同深度变形机制及微构造类型不同,导致油气选择性充注,碎裂带和压溶胶结碎裂带阻止油气向高孔隙度砂岩中充注,解聚带会成为油气运移的通道,裂缝有利于油气优先充注。因此,高孔隙性砂岩中孔隙度较低的储集层由于碎裂带不发育常常含油气性最好,而低孔隙性砂岩由于裂缝产生含油气性较好。     

Principal fault zone width and permeability of the active Neodani fault, Nobi fault system, Southwest Japan

The internal structure and permeability of the Neodani fault, which was last activated at the time of the 1891 Nobi earthquake (M8.0), were examined through field survey and experiments. A new exposure of the fault at a road construction site reveals a highly localized feature of the past fault deformation within a narrow fault core zone. The fault of the area consists of three zone units towards the fault core: (a) protolith rocks; (b) 15 to 30 m of fault breccia, and (c) 200 mm green to black fault gouge. Within the fault breccia zone, cataclastic foliation oblique to the fault has developed in a fine-grained 2-m-wide zone adjacent to the fault. Foliation is defined by subparallel alignment of intact lozenge shaped clasts, or by elongated aggregates of fine-grained chert fragments. The mean angle of 20°, between the foliation and the fault plane suggests that the foliated breccia accommodated a shear strain of γ<5 assuming simple shear for the rotation of the cataclastic foliation. Previous trench surveys have revealed that the fault has undergone at least 70 m of fault displacement within the last 20,000 years in this locality. The observed fault geometry suggests that past fault displacements have been localized into the 200-mm-wide gouge zone. Gas permeability analysis of the gouges gives low values of the order of 10⁻²⁰ m². Water permeability as low as 10⁻²⁰ m² is therefore expected for the fault gouge zone, which is two orders of magnitude lower than the critical permeability suggested for a fault to cause thermal pressurization during a fault slip.     

碳酸盐岩内断裂带结构及其与油气成藏

以野外观察描述为手段,系统研究了碳酸盐岩断裂变形机制的影响因素及断裂带结构演化过程,剖析了碳酸盐岩地层中断裂带结构与流体运移的关系。研究表明,影响碳酸盐岩内断裂变形机制的因素包括岩性、孔隙度、变形深度、温度、胶结作用、先存裂缝等,控制断裂带结构形成的因素包括滑动位移和破裂模式等。低孔隙度碳酸盐岩以裂缝发育为主,高孔隙度碳酸盐岩变形早期产生变形带,带内裂缝联接逐渐发育成断层带。随着埋藏深度的增加,断裂带结构不同：埋藏深度小于3 km,断层核主要发育无内聚力的断层角砾岩和断层泥;埋藏深度大于3 km,断层核普遍发育有内聚力的断层角砾岩和碎裂岩,破碎带发育多种成因的裂缝。随着位移的增加,破裂模式从早期的破裂作用变为后期的碎裂作用,最终形成碎裂流。断裂带演化是一个四维过程,断层核和破碎带发育情况直接影响断层对油气的运移和封闭的作用。断裂变形机制、断裂带内部结构以及与流体运移关系的研究,都可为封闭性提供重要的理论依据。     

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。