The initiation of brittle faults in crystalline rock

Faults in the upper crust initiate from pre-existing (inherited) or precursory (early-formed) structures and typically grow by the mechanical interaction and linkage of these structures. In crystalline rock, rock architecture, composition, cooling, and exhumation influence the initiation of faults, with contrasting styles observed in plutonic rocks, extrusive igneous rocks, and foliated metamorphic rocks. Brittle fault growth in granitic rock is commonly controlled by the architecture of inherited joints or preexisting dikes. In basalt, abundant joints control the surface expression of faulting, and enhanced compliance due to abundant joints leads to folding and deformation asymmetry in the fault zone. Highly reactive mafic minerals likely become rapidly evolving fault rocks. In foliated metamorphic rocks, fault initiation style is strongly influenced by strength anisotropy relative to the principal stress directions, with fracturing favored when the foliation is aligned with the directions of principal stress. The continuity of micas within the foliation also influences the micromechanics of fault initiation. Brittle kink bands are an example of a strain-hardening precursory structure unique to foliated rock. Each of these fault initiation processes produces different initial fault geometry and spatial heterogeneity that influence such properties as fault permeability and seismogenesis.     

Determination of the elastic modulus set of foliated rocks from ultrasonic velocity measurements

Ultrasonic measurements of compressional and shear wave velocities under hydrostatic pressure up to 70 MPa were carried out on cylindrical specimens cored across and along the foliation planes. Our measurements revealed that the foliation of the metamorphic rocks induces a clear velocity anisotropy between two orthogonal directions; faster along the foliation plane and slower across the plane in most rock types. All velocity components monotonically increase with the confining pressure, probably due to the closure of microcracks distributed in rock specimens. We determined the complete set of dynamic moduli of foliated metamorphic rocks with two assumptions; transverse isotropy due to the foliation and ellipsoidal seismic energy propagation from a point source. The calculated elastic moduli referring to different directions could be valuable for the design of various engineering structures in planar textured rock mass.     

Development of shear zone-related lozenges in foliated rocks

Tectonic lozenges are elongate bodies bounded by relatively more deformed rocks. The focus of this study is on the 2-D structure of tectonic lozenges developed during ductile shear in rocks with a pre-existing mechanical anisotropy. On the basis of a detailed analysis of shear zones in foliated rocks from the Cap de Creus area (Variscan of the eastern Pyrenees), five mechanisms to explain the development of different types of lozenges in foliated rocks are suggested. These mechanisms are explained on the basis of the orientation of the previous foliation relative to the bulk shearing direction. It is shown that the prevailing mechanism does not majorly depend on the bulk kinematics but on the angular relationship between the pre-existing foliation and the bulk kinematic axes, and on shear zone interaction. This has implications on the use of lozenge shapes in tectonic interpretations. The fact that there is a wide range of initial orientations, propagation modes and coalescence types implies that the final lozenge geometry is not univocally related neither to the type of strain nor to the kinematic regime.     

Characterisation of rock aggregate breakage properties using realistic texture‐based modelling

Realistic texture‐based modelling methods, that is microstructural modelling and micromechanical modelling, are developed to simulate the rock aggregate breakage properties on the basis of the rock actual microstructure obtained using microscopic observations and image analysis. The breakage properties of three types of rocks, that is Avja, LEP and Vandle taken from three quarries in Sweden, in single aggregate breakage tests and in inter‐aggregate breakage tests are then modelled using the proposed methods. The microstructural modelling directly integrates the microscopic observation, image analysis and numerical simulation together and provides a valuable tool to investigate the mechanical properties of rock aggregates on the basis of their microstructure properties. The micromechanical modelling takes the most important microstructure properties of rock aggregates into consideration and can model the major mechanical properties. Throughout this study, it is concluded that in general, the microstructure properties of rock aggregate work together to affect their mechanical properties, and it is difficult to correlate a single microstructure property with the mechanical properties of rock aggregates. In particular, for the three types of rock Avja, LEP and Vandle in this study, crack size distribution, grain size and grain perimeter (i.e. grain shape and spatial arrangement) show good correlations with the mechanical properties. The crack length and the grain size negatively affect the mechanical properties of Avja, LEP and Vandle, but the perimeter positively influences the mechanical properties. Besides, the modelled rock aggregate breakage properties in both single aggregate and inter‐aggregate tests reveal that the aggregate microstructure, aggregate shape and loading conditions influence the breakage process of rock aggregate in service. For the rock aggregate with the same microstructure, the quadratic shape and good packing dramatically improve its mechanical properties. During services, the aggregate is easiest to be fragmented under point‐to‐point loading condition, and then in the sequence of multiple‐point, point‐to‐plane and plane‐to‐plane loading conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Difference in petrophysical properties between foliated and dilatant fault rocks in deeply buried clastics: The case of the Grès d'Annot Formation,SW French Alps

This study describes normal fault zones formed in foreland arkosic turbidites (the Grès d'Annot Formation, SW French Alps) under deep diagenesis conditions (~200 °C) and highlights the occurrence of two markedly different fault‐rock types: (1) the foliated fault rocks of the Moutière‐Restefond area; and (2) the dilatant fault rocks of the Estrop area. The deformation of (1) is dominated by intra‐ and transgranular fracturing, pressure solution of quartz and feldspar grains and syn‐kinematic phyllosilicate precipitation resulting from feldspar alteration. The combination of these mechanisms results in a strongly anisotropic strain with intense shortening normal to the foliation (pressure solution) and extension parallel to the foliation (quartz‐ and calcite‐sealed extension veins). This deformation implies local mass transfer that may be achieved without (or with limited) volume change. The deformation of (2) is expressed as dilatant quartz‐sealed veins and breccia textures in which the main mechanisms are transgranular fracturing and quartz precipitation. Type (2) implies fault volume increase, isotropy of deformation and mass transfer at distances larger than in type (1). This study discusses the origins of (1) and (2) and shows that the permeability of (1) is anisotropic, with higher values than the host rocks parallel to the Y main deformation axis (i.e. perpendicular to the slip vector), whereas the permeability of (2) is isotropic and equivalent to that of the host rocks.     

Textural characterisation of rocks

Textural characteristics are a major factor in determining the mechanical behaviour of rocks and in the prediction of performance of rock cutting and drilling equipment. The principal textural characteristics of rocks are grain size, grain shape, grain orientation, relative proportion of grains and matrix material which were herein quantitatively measured using a modern image analysis system. These features resulted in a texture coefficient represented by a single number for each rock specimen. In this study a range of both textural and mechanical data for a range of rock types are given with some of the textural determination methodology. Correlation between textural and physical properties are also highlighted. The results of drilling tests using polycrystalline diamond compact (pin and hybrid) and impregnated diamond core bits in the rocks are presented which demonstrate the influence of rock texture on drillability. The rock texture can be used as a predictive factor for assessing the drillability and cuttability, mechanical and wear performance of rocks.     

Triassic Collisional Structures and Post—Collisional Deformation of Bixiling UHP Rock Stack： Insights for Tectonic Evolution of UHP Metamorphic Belt in Dabie Massif, Central China

Detailed three-dimensional structural studies indicate that the Bixiling area,Dabie massif,central Chian shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze0Sino-Korean continental collision.New1:10000 scale structural mapping,combined with detailed petrological analysis in this area,has enabled us to accurately distinguish structures related to the Trias-sic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit.The collisional or compressional structures include the massive eclogite with a weak foliation,foliated eclogite or UHP ductile shear zones,as well as upper amphibolite facies shear zones,whereas the post-collisional deformation is characterized by a regionally,flat-lying foliation con-taining stretching lineations and common reclined folds .The former is present exclusively in the eclogite lenses and their margins,representing orogenic thickening or syn-collisional events,while the latter was best occurred on variable scales under amphibolite facies conditions,showing sub-vertical,extreme short-ening and ductile thinning of the metamorphic rock stack.The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common.It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was,at least partly,responsible for exhumation of the UHP metamorphic rocks in the Dabie massif.A new tec-tionic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif.The Bixiling area thus provides a window,from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed.Regional studies in the Dabie Mountains have confirmed this interpretation.     

Relationships between texture and mechanical properties of hybrid rocks from the Jaala–Iitti complex, southeastern Finland

The relationships between petrographical and mechanical properties of rock aggregate raw materials from the hybridised, subvolcanic Jaala–Iitti complex, southeastern Finland, were investigated. Petrography was quantified from polished thin sections with a polarising microscope to determine the modal composition and grain size distribution, and resistance to fragmentation and abrasion were determined. Abundance of fine-grained minerals (especially of hornblende), fine grain size-dominated grain size distribution, uniform spatial dispersion of hornblende crystals, and intense micrographic intergrowth texture with interlocking grain boundaries were found to have the greatest positive influence on the mechanical properties. The results showed the potentiality of hybridised rocks as raw materials for high quality aggregates that can resist fragmentation and abrasion.     

Assessments of Strength Anisotropy and Deformation Behavior of Banded Amphibolite Rocks

Assessment of strength anisotropy in transversely isotropic rocks has been one of the most challenging subjects in rock engineering. However, far too little attention has been paid to banded amphibolite rocks. This study aim to evaluate strength and deformation anisotropy behavior of banded amphibolite rocks. The dynamic mechanical tests including ultrasonic pulse test, uniaxial compressive strength, Brazilian test and deformability test were performed on drilled rock samples as a function of foliation plane angle (β = 0°, 30°, 60° and 90°). The results obtained have shown that the dynamic mechanical properties of amphibolite rocks have different values concerning banding plane. Compression and shear waves taken parallel to the foliation plane show highest values than those obtained in the other directions. Under uniaxial test, the banded amphibolite has a U-shaped anisotropy with maximum strength at β = 90° and minimum strength is obtained when β = 30°. Strength anisotropic index ranges between 0.96 and 1.47. It seems that the high range value of anisotropic index is mainly due to slight undulation of foliation planes, that being not perfectly straight. The results of elastic deformation test show that there is no clear dependence on microstructures characteristics of subtype-amphibolite rocks that controlling modulus “shape-anisotropy”. However, in this study, Young modulus values of amphibolite rocks with β follow both types of shape-anisotropy, “U-shape” and “decreased order-shaped”. Thus, this study recommended that further research be undertaken regarding the role of modulus “shape-anisotropy” within the same lithotype.     

Mechanical quality of bedrock with increasing ductile deformation

Most of the rocks in Precambrian shield areas have experienced a complex structural and metamorphic evolution, processes which have a strong influence on bedrock quality. The properties vary on both a local and a regional scale. It is highly beneficial to know the variations in detail when exploiting the rocks for industrial purposes. The main objective of the investigation was to study the variation of rock mechanical properties in an originally more or less isotropic rock at various stages of ductile deformation. The rocks investigated were Paleoproterozoic and with ages of ca. 1.80-1.88 Ga, and the areas chosen for sampling were situated north-east of Lake Vänern (Kristinehamn; 10 samples), south of the city of Eskilstuna, South Central Sweden (5 samples) and south of Ödeshög, near Lake Vättern in southern Sweden (7 samples). The 12 samples from the latter two areas are described in this investigation, while the 10 samples from Kristinehamn have been published earlier (Göransson et al., 2004). A comprehensive study of various parameters of importance for bedrock quality has been performed on all samples, e.g. studded tyre test (STT) and Los Angeles test (LA), uniaxial compressive strength (UCS), ultrasonic velocity, perimeter measurements of mineral phases, and petrographic and chemical analyses. The weakly deformed and massive (more or less isotropic) rocks show a tendency towards better properties of abrasion (STT) than the strongly deformed rocks and this can also be said for UCS, reflecting the greater ability of rocks to split along foliation planes. This is not entirely unambiguous, as the more deformed rocks, such as the mylonites, may have varying properties. This depends on the combined effects of, e.g. grain size, recrystallisation and foliation. However, the brittleness (LA) shows somewhat better values with increased deformation. This may depend on higher amounts of dark minerals, as their existence does not affect this test as much as in the case of abrasion tests. The perimeter values of the mineral phases display generally higher values, i.e. grain boundaries for the more strongly deformed rocks are more complicated. However, the values for the investigated mylonites may vary between low and high. The lower value may be due to dynamic recrystallisation and the creation of triple points (static recrystallisation) making the rock weaker. Besides, the development of a strong foliation may decrease rock strength despite the usually finer grain size. The results show that it is extremely important to consider all possible variations of bedrock before classification and exploitation, as the bedrock material in fact is highly heterogeneous.     

Fabric and seismic properties of carrara marble mylonite

Shear deformation in calcite-rich rocks can produce strong lattice preferred orientations (LPO), which result in a high anisotropy of bulk seismic properties because of the high elastic anisotropy of calcite (32% Vp anisotropy). Deformed rocks often show also strong shape preferred orientations (SPO). Theories for averaging the elastic properties have not yet satisfactorily predicted the contribution to the seismic anisotropy caused by the SPO alone.A calcite mylonite from Carrara (Italy) was investigated, which is characterised by a strong SPO and a weak LPO. It was composed of about 80% calcite, then white mica, quartz and hematite. Flattening of mica and of calcite grains defined the mylonitic foliation, and elongation of calcite grains defined the lineation. On average calcite grains have aspect ratios of about 2.5:1.6:1, and grain sizes of about 10 μm. At 400 MPa confining pressure, the measured Vp (km/s) parallel to the lineation (X direction) was highest (6.63), lower in the intermediate Y direction (6.47); the Vp normal to the foliation (Z direction) was lowest (6.30). This yielded a Vp anisotropy of 5%. The LPO, determined by automated electron backscatter diffraction (EBSD), was very weak (texture index 1.1), with intensities between 0.6 and 1.6 m.r.d. in the c-axis pole figure. Extrapolation of the texture index to an infinite number of orientation measurements indicated that the observed variations were mostly random noise in the orientation distributions and that the bulk rock texture was random. The Vp anisotropy of the Voigt, Reuss and Hill averages calculated from this calcite LPO is predicted to be close to zero. Adding 5% of muscovite with (001) perfectly aligned parallel to the foliation, we calculated a total anisotropy of 2.8%. The anisotropy calculated for the special directions X, Y and Z remained at 2.6% only.It was concluded that the measured seismic anisotropy cannot be explained by the LPO of calcite and by 5% of mica alone. It is also attributed to the strong SPO and to further grain boundary effects.     

中国大陆科学钻探主孔100～2000m岩石弹性波速度：对地震深反射的约束

在常温常压条件对中国大陆科学钻CCSD主孔岩心的700样品进行了弹性波速度测量,并建立了主孔2000m的波速(Vp和Vs)连续剖面,为检验地球物理模型的合理解释提供了岩石物理学方面的宝贵资料。主孔中新鲜榴辉岩纵波速度(Vp)最大(7.86km／s),正副片麻岩波速最小,又分别为5.53km／s和5．71km／s,榴辉岩的波速随着退变质作用的增强而明显减小。主孔2000m总平均Vp速度为6．2km／s,它与地球物理探测方法获得的大别-苏鲁造山带上地壳具有6.2-6．3km／s高速层结论是一致的。大部分岩石具有明显地震波各向异性。水饱和度使岩石纵波(Vp)速度和剪切波速度(Vs)分别增加19％和6％,而使Vp的各向异性降低3％～4％。不同岩性界面的反射系数(Rc)是产生地震反射的主要原因。金红石榴辉岩与片麻岩之间具有很高的反射系数(0.24-0．31)。韧性剪切带中糜棱岩化片麻岩和面理化榴辉岩使岩石各向异性和反射强度明显增加。岩石微裂隙与主孔原位波速变化有密切关系。饱水岩石速度(Vp和Vs)可以代表CCSD主孔原位状态的地震波速度。上述成果为本区地震反射体成因提供了重要的岩石物理性质约束。     

The influence of the characteristics of quartz and mineral deterioration on the strength of granitic dimensional stones

It is important to have a thorough knowledge of the petrographic characteristics of rocks to evaluate and understand their mechanical behavior. This paper deals with the influence of the texture and the mineral characteristics of nine Portuguese granites employed as dimensional stones. This study evaluates different mineral characteristics, such as mineral deterioration, grain size, quartz fissuration and the contacts between quartz and others mineral groups. The main differences in the studied granites were identified, clarifying the relationship between the petrographic characteristics. The consequences on their respective mechanical behavior were subsequently evaluated. The physical and textural characteristics of quartz in the studied granites have proven to be very important for understanding the behavior of granitic rocks under compressive stress. Uniaxial compressive strength values are not proportional to the quartz–feldspar ratio or quartz content and there is a tendency for strength to decrease with the increase in quartz. This could be related to the increase in quartz-quartz contacts and the decrease in the rock capacity for accommodating the deformation.     

Plagioclase preferred orientation by TOF neutron diffraction and SEM-EBSD

The lattice preferred orientation (LPO) of an anorthosite (composed of andesine) sampled from a highly deformed anorthositic mylonite (Grenville Province, Quebec) was measured by TOF neutron diffraction and SEM-EBSD. The quantitative texture analysis of neutron data was accomplished by using the Rietveld texture analysis with the WIMV algorithm, implemented in the program package Materials Analysis Using Diffraction (MAUD). The texture calculations of the EBSD data were performed by using the program BEARTEX. Analyses from neutron and electron diffraction data gave similar results if EBSD data are smoothed to account for grain statistics. The principal pole figures show (010) roughly parallel to the rock foliation, (001) poles exhibiting a low angle (25°) to the pole to foliation, and (100) poles close to the Y-direction (perpendicular to the lineation and foliation pole). The [100] crystallographic direction shows a maximum in the lineation direction, [010] directions concentrate near the foliation pole. The geological deformation conditions and the constructed pole figure patterns indicate that the preferred orientation could be attributed to intracrystalline slip dominantly on (010) with [100] as slip direction. Elastic properties, calculated by averaging, document weak anisotropy that has implications for the seismic structure of the lower crust.     

水压影响岩石渐进破裂过程的试验研究

岩石的压缩过程伴随着裂纹扩展,在低、中围压条件下扩展的裂纹主要受到张拉作用而产生,张拉破坏是首要的作用机制。研究发现,岩石的渐进破裂过程受岩石的结构和构造影响,比如矿物成分、颗粒大小以及胶结情况等,另外,围压以及开挖扰动等外界因素对岩石的渐进破裂过程也有重要影响。基于试验方法探讨水压对岩石渐进破坏过程的影响,首先,阐述岩石渐进破裂过程各个阶段的特征;然后,对岩石渐进破裂指标--岩石的启裂强度 和损伤强度 的确定方法进行总结;最后,选取细粒的石英砂岩为研究对象,通过试验研究水压对岩石渐进破坏过程的影响。试验结果表明,相同围压条件下,随着岩样两端水压的增大,岩石的 有逐渐增大的趋势,而岩石的 和峰值强度 逐渐变小;随着围压逐渐增大,岩石的启裂强度 、损伤强度 及峰值强度 均逐渐增大。     

高喜马拉雅晚新生代富铁火山岩的发现及其构造意义

本文首次报道了在藏南高喜马拉雅变质带新发现的一种特殊的晚新生代超基性富铁火山岩,主要由铁橄榄石、氧化铁、及富钾玻璃基质组成,铁橄榄石中含有少量自形铁尖晶石,玻璃基质中含有少量铁石榴石雏晶。岩石具玻基斑状结构,气孔构造发育,具有典型鬣刺构造。全岩成分具有强烈硅不饱和(全岩SiO_2含量为18.8%~29.7%)和极端富铁(全岩Fe2OT3含量为56.2%~74.2%)的特征。地球化学分析表明其大离子亲石元素Th和U等强烈富集,高场强元素Nb和Ta及Ti元素相对亏损,Sr元素具有明显的负异常,显示与板块消减俯冲有关的地球化学特征。该火山岩切割区域片麻理,说明其形成于碰撞后的陆内伸展环境,而其富铁和硅极不饱和的特征表示其有可能属于不混溶作用的产物,也可能属于后期热液蚀变作用,以及由富铁原岩在深部发生熔融并在伸展环境沿裂隙喷发而形成。该火山岩的K/Ar年龄介于4.76~7.25Ma,被熔浆包裹的围岩的磷灰石裂变径迹(AFT)分析结果是2.04±0.21Ma,指示该火山岩可能是上新世-更新世喷发的(2～4Ma)。这些超基性富铁火山岩首次提供了高喜马拉雅构造带在新生代经历碰撞后发生伸展作用的火山岩证据,为认识青藏高原南部大地构造格局及其形成演化过程提供了新的依据。     

Quantitative assessment of rock texture and correlation with drillability and strength properties

Summary A dimensionless quantitative measure of rock texture, describing grain: —shape, orientation, degree of grain interlocking and relative proportions of grains and matrix (packing density) has been developed. Data required for the model are obtained by image analysis of thin sections and concerns percentage areas of grains and matrix, length, breadth, perimeter, orientation and area of each grain in the viewing window. The results of rock strength, diamond and percussion drillability tests in eleven sandstones, marbles and igneous rocks are reported, and correlated with the developed texture coefficient. The texture coefficient returns highly statistically significant correlations with rock strength and drillability data. Sandstones have low texture coefficients and high drillability whereas igneous rocks have high texture coefficients and low drillability. With particular reference to percussive drillability it is suggested that extensional crack propagation in the sandstones in an energy efficient process since fracture paths propagate through the weak phyllosilicate matrix. Extensional crack propagation in the igneous rocks is an energy intensive process since a significant proportion of the available drilling energy is consumed in the formation of intra-granular fracture paths. Observational and correlated data are supportive of the suggestion that the texture coefficient is a measure of the resistance of the microstructure of a rock to crack propagation, whether it be inter-or intra-granular. The texture coefficient can be used as a predictive tool for the assessment of drillability and rock strength properties. The technique offers a useful approach in understanding fracture initiation and growth as controlled by the texture of intact rock samples.     

Late Cryogenian arc-related volcaniclastic metasediment successions at Wadi Hammuda,Central Eastern Desert,Egypt: geology and geochemistry

Wadi Hammuda is dominated by a variety of low grade regionally metamorphosed volcaniclastic metasediments pertaining to two different geotectonic settings and intruded by arc and late collision granitic rocks. Thus, the volcaniclastic metasediments which form extensive outcrops are considered as a member of island arc assemblages. This paper deals with the petrography, geochemistry, and tectonic setting of the island arc volcaniclastic metasediment rock units. The volcaniclastic metasediments consist of interbedded metagreywackes, metasiltstones, metamudstones, and schists as well as metapyroclastics. They are well foliated, crenulated and tightly folded, metamorphosed, and intruded by granitic rocks. Geochemical data support the petrographic classification and reveal that these volcaniclastic metasediments are generally low-K, essentially tholeiitic in character, with the exception of some metasediments and metapyroclastics which exhibits calc-alkaline and tholeiitic affinities and represent the first stage of island arc volcanism. The overthrusted oceanic lithosphere blocks with fragments of the fore arc and/or back-arc marginal basins volcaniclastic metasediments were incorporated among the island arc volcanics which supported by tectonically relationship between the different rock units in the study area. Contemporaneous with this deformation event, Wadi Hammuda was subjected to low grade regional metamorphism and the rocks document an early phase of shearing and/or foliation. Occasionally minor folds were developed particularly in the metasediments and schists. The subsequent emplacement of the syn-tectonic granites (tonalites and granodiorites) resulted in minor local thrusts. During the regional thrusting event which preceded the emplacement of the late-tectonic granites (alkali feldspar granites) and affected the whole region, low grade successions cover the study area similar to the Meatiq volcaniclastic metasediments.     

Cumulatic Diorites Related to Post-Collisional,Brasiliano/Pan-African Mafic Magmatism in the Vila Nova Belt,Southern Brazil

The Capivaras Diorite, in the Vila Nova region, NW of the Sul-rio-grandense Shield, is composed of six NE- to NNE-oriented rock bodies of late-tectonic emplacement relative to the D3 deformation phase which forms subvertical high-strain zones in basement gneiss sequences. Within these intrusive bodies, a shape foliation is present, generally parallel to contacts and displaying a local solid-state deformational component. The internal structure of the Capivaras Diorite main intrusion is marked by a zone of intense flow and mingling, characterized by strong shape foliation and layers of variable texture and composition, which result from cumulative processes, heterogeneous flow and interaction of coeval, compositionally contrasting magmas. The central part of this intrusion is texturally homogeneous and slightly foliated, even though cumulative processes have remained important during its formation. Along the contact with basement gneisses, fine-grained diorites are found, which are considered to be compositionally close to the parental magma of the Capivaras Diorite. This magma has a mildly alkaline affinity and shows moderate to high contents of Zr, Ti and P. Highly-fractionated REE patterns, low Nb contents, as well as high contents of K, Sr, Ba, and Rb, are suggestive of its provenance from mantle sources which have been previously affected by subduction processes, such as those of mature magmatic arcs or post-collisional settings. Magmatic evolution was controlled by cumulative processes and gave origin to pyroxene orthocumulates, plagioclase-pyroxene orthocumulates, pyroxene adcumulates, and more rarely plagioclase adcumulates. The cumulative origin of these rocks is indicated by field, textural and geochemical features, which are distinct from those of crystallized liquids. The compositional diversity of cumulates has led to the generation of compositionally different melts. The early-formed pyroxene cumulates have caused Ca, Al, Na, Ba, and Sr enrichment in the magmatic liquid, leading to plagioclase crystallization and accumulation. Coarse-grained mafelsic cumulates were formed during the late stages of magmatic crystallization, due to volatile enrichment of the intercumulus liquid. Considering geological relations, as well as tectonic and compositional features of the Capivaras Diorite, it is interpreted as part of Neoproterozoic magmatism related to the post-collisional stage of Brasiliano/Pan-African Orogenic Cycle in southern Brazil.     

A Review of General Considerations for Assessing Rock Mass Blastability and Fragmentation

Blasting is the primary comminution process in most mining operations. This process involves the highly complex and dynamic interaction between two main components. The first is the detonating explosive and the second is the rock mass into which the explosive is loaded. The mechanical properties of the rock material (such as dynamic strength, tensile strength, dynamic modulus and fracture toughness) are important considerations in understanding the blasting process. However, it is the characteristics of the geological defects (joints, foliation planes, bedding planes) within the rock mass that ultimately determine how effectively a blast performs in terms of fragmentation, all else being equal. The defect characteristics include, but are not limited to, their orientation, spacing, and mechanical properties. During the blasting process, some of the geotechnical characteristics of the rock mass are substantially changed. From the blasting outcome point of view, the most notable and important is the change in fragment size distribution that the rock mass undergoes. The pre-blast in situ defect-bounded block size distribution is transformed into the post-blast muckpile fragment size distribution. Consequently, it is fundamental to our understanding of and ability to predict the blasting process that both the blastability of a rock mass and its transformation into the fragment size distribution can be appropriately quantified.