Brittle Stage Research Articles

The Experiments of Coalbed Methane Penetration Law in Zhaogu Mine

Set the raw coal samples of zhaogu mine in Jiaozuo as the object of study, with a self-developed equipment for thermo-fluid-solid-stress coupling of coal containing methane, analyse the relationship between permeability of raw coal samples and the change of effective stress, resultant stress strain process of raw coal samples. Experimental results show that The permeability of coal samples have stress sensitivity, permeability represents nonlinear decreasing relationship with effective stress increasing, Possess the law of negative exponent,This is consistent with the results of previous studies. During the full stress-strain process, strain increases with the stress increasing, penetration rate changed with the strain of the coal sample Increase after reducing ,on compaction stage stage and elastic deformation stage, transfusion decreased with stress increased , on yield deformation stage, permeability of coal samples reached minimum and began to overtake, on brittle break stage and residual strength stage, permeability increased by a large margin, mainly due to the coal macroscopic fissures.

Mixed-Mode Fracture Characteristics of Cold Recycling Mixes with Emulsified Asphalt

In order to study the Mixed-Mode cracking behavior of cold recycling mixes with emulsified asphalt, the Arcan test configuration was chosen to perform the fracture characteristics of cold recycling mixes in five levels of Mixed-Mode (100, 75, 50, 25 and 0% Mode I) at three loading rates (1.0mm/min, 0.5mm/min, 0.1mm/min). The load and load-line displacement, peak load, crack angle and fracture energy were all used for further analysis. The process of cracking can be divided into three stages: the stage of crack arises, expand stage, and the brittle break stage; 0% Mode I has a significant difference from the others; the loading rates and levels of Mixed-Mode both have great influence on peak load; the higher level of Mode I usually gets lower crack angle; the fracture energy of 100% Mode I ranges from 168 J/m2 to 308 J/m2 and the specimen in 0.5mm/min has greater fracture energy.

Hundred years after the first triaxial test

It was more than hundred years ago, when Theodore von Kármán (born as Tódor Kármán) designed and developed the first triaxial cell for investigation of brittle rocks behavior. His first research was based on Carrara marble and Mutenberg sandstone with varying confining pressures up to 600 MPa, demonstrating changes from brittle stages to ductile behavior in addition to hardening. The target of this paper is to give tribute to his development and work on this topic, having inspired and influenced many people in rock engineering and geophysical sciences, among others. After a short historical overview of this research the published data are recalculated using different empirical failure criteria which are widely used in the rock mechanics and rock engineering practice. For the recalculation and description of Kármán´s triaxial tests the original Hungarian paper was used.

Metadolomitos talcificados do Grupo Itaiacoca, Paraná: regime de fluidos e implicações genéticas

Brazil's largest talc deposits occur in the Itaiacoca Group, which is a low-grade metasedimentary belt composed mainly of dolomitic rocks. Fluid inclusions from three geological settings in which talc was formed differently were analysed. Talc schist ore occur along transcurrent shear zones. These talc schists are host to quartz veins, which indicates prolonged circulation of hydrothermal fluids at high water:rock ratios. The fluid inclusions in the quartz veins contain predominantly low-salinity (< 5 wt % NaCl equiv.) and CO2-free aqueous inclusions. The wide range of Thtot values in the primary fluid inclusions in the veins, mainly from 110 to 230ºC, is related to several episodes of fluid percolation during the shear zone evolution. As a contrast, outward of the shear zones, fractured metadolomites with lower concentrations of talc contain quartz veins with CO2-rich fluid inclusions (X CO2 from 0.17 to 0.81) and Thtot ranging mainly from 250 to 300ºC, which indicates restricted fluid circulation during the trapping of these inclusions, shortly after the peak of talcification, in a later brittle stage. Density-salinity relationships for these inclusions suggest supersolvus mixing in variable proportions of aqueous-carbonic fluids. In the contact aureole between the metadolomites and the Cunhaporanga granite complex, where talc was formed in minor amounts by retrometamorphism of high temperature magnesium silicates, fluid inclusions are mainly carbonic to aqueous-carbonic, suggesting restricted fluid circulation. Fluid inclusions in this setting show a wide range of measured and calculated parameters, such as salinity (0 to 20 wt % NaCl equiv.), dCO2 (0.13 to 1.0 g/cm³), dtot (0.2 to 1.0 g/cm³), and Thtot (between 130 and 574ºC). Results obtained in this study did not allow precise determination of the talc-ore forming conditions, considering that the inclusions contain fluids which were trapped after the peak of talcification. Conditions similar to those of talcification are suggested by the Thtot values obtained for the inclusions in quartz-veins from fractured metadolomites, although from a later, brittle stage.

Epigenetic formation of amethyst-bearing geodes from Los Catalanes gemological district, Artigas, Uruguay, southern Paraná Magmatic Province

Giant geodes (up to 4 m long) in the massive central portions of altered basalt lavas from the Paraná Magmatic Province, southern Brazil and Uruguay, form a world-class source of amethyst and agate. Although the origin of the cavities has been ascribed to degassing of the lava at > 1150 °C, field evidence is conclusive that the giant amethyst-agate-filled geodes were formed by hydrothermal processes at low temperatures. We propose an epigenetic and hydrothermal model for the origin of giant geodes. This model includes hydrothermal brecciation during an early brittle stage and the late formation of the cavities (geodes). In the brittle stage an overpressured aqueous fluid affected the basalt in a P, T field delimited by temperatures between 100 and 150 °C and vapor pressures between 1.2 and 5.5 bar. The fluids were capable of lifting the roof and fracturing the host rock along new subhorizontal and subvertical fractures and breccias in the massive lava. The formation of these structures occurred at shallow depths, unit-by-unit. To open the cavities, dissolution of the now altered basalt to clay minerals is necessary. The process is closely linked to the highest alteration grade of mineralized lavas in Los Catalanes gemological district. Dissolution processes are observed in micrometer-scale in the studied basalts. The primary mineralogy, consisting of labradorite (± andesine) +augite + pigeonite + mesostasis (K-rich), was altered during the interaction of large volumes of hot aqueous fluid with the rock. The alteration of pigeonite and its replacement by smectite is observed around the cavities, followed by the precipitation of amorphous silica and microcrystalline quartz in clay-rich sites. Associated zeolites (heulandite + clinoptilolite) fill the newly formed cavities in progressive stages of hydrothermal alteration. Our data indicate that the temperatures were less than 200 °C and probably less than 150 °C; cavity formation occurred after alteration of the basalt to more than 60 vol.% clay minerals. We thus suggest that cavities related to geode formation are of epigenetic origin.

Epoxy nanocomposites containing mercaptopropyl polyhedral oligomeric silsesquioxane: Morphology, thermal properties, and toughening mechanism

AbstractA novel polyhedral oligomeric silsesquioxane (POSS) containing a mercaptopropyl group [mercaptopropyl polyhedral oligomeric silsesquioxane (MPOSS)] was synthesized via the hydrolytic condensation of γ‐mercaptopropyl triethoxysilane in an ethanol solution catalyzed by concentrated hydrochloric acid and was used to modify epoxy–amine networks by a cocuring reaction with diglycidyl ether of bisphenol A (DGEBA). The structure, morphology, and thermal and mechanical properties of these MPOSS/DGEBA epoxy nanocomposites were studied and investigated with thermogravimetric analysis/differential thermal analysis (TGA–DTA), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). From SEM analysis, we observed that the miscibility between epoxy and POSS occurred at a relatively high POSS content, which characterized this mixture as a polymer nanocomposite system. The impact test showed that MPOSS reinforced the epoxy effectively, and the SEM study of the impact fracture surface showed that the fibrous yielding phenomenon observed was an indication of the transition of the brittle stage to a ductile stage and correlated well with the large increases in the impact strength; this was in agreement with the in situ reinforcing and toughening mechanism. The TGA–DTA analysis indicated that the MPOSS/DGEBA epoxy hybrids exhibited lower thermostability at a lower temperature but higher thermostability and higher efficiency in char formation at an elevated temperature. Differential scanning calorimetry showed that the glass transition temperature (Tg) of the MPOSS/epoxy hybrids were lower than that of the neat epoxy. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Impact properties of acrylate rubber-modified PVC: Influence of temperature

The enhancement of the impact resistance of plastics through the introduction of a rubbery dispersed phase is one of the means to develop high impact strength polymers and has been exploited commercially on a large scale. Rubber-toughened PVC-U or high impact PVC-U is one such important class of rubber-toughened plastics material which has been developed and has a wide application in the building and furniture industries. The type of impact modifiers most commonly used for window frame applications are chlorinated polyethylene, ethylene-vinyl acetate and acrylate modifiers. The current trend shows the importance and popularity of high impact-acrylate-modified PVC. The objective of this research is to extend the existing understanding of toughness enhancement in rubber-toughened polymer materials to acrylate rubber-modified PVC. This paper reports on the effect of temperature on the impact strength of acrylate rubber-modified PVC-U using the instrumented falling weight impact test (IFWI) method. Toughening and fracture mechanism in acrylate-modified PVC were also investigated. The results show that all the acrylate rubber-toughened PVC blends have successfully shifted the ductile–brittle transition points to a lower temperature. However, the impact modifiers were found to differ in their efficiency to shift the ductile to brittle transition. The findings from the SEM study shows that the fibrous yielding phenomenon observed is an indication of the transition of the brittle stage to ductile stage and correlates well with the large increases of the impact strength.

Showa Shell reduces CO 2 produced in hydrogen generation

The La Bellière gold district, in the Ligerian domain of the Armorican Massif is the third one of France in term of production. It shows gold-bearing quartz veins neighboring with a complex network of Sb veins, hosted in the Neoproterozoic metasedimentary basement of the Mauges Nappe. New structural data, mineralogical, textural and geochemical assays have been carried out to clarify the gold and Sb veins relationships. Our results favor of two-step hydrothermal event with an early deep-seated gold event followed by a late shallower Sb event. The gold-bearing quartz veins are hosted by N60°E to N90°E sinistral strike-slip faults. These veins exhibit a four-stage paragenesis: 1) early barren quartz filling, 2) arsenopyrite-pyrite with minor scheelite assemblage, 3) gold and base metal sulfides crystallized after a ductile/brittle deformation stage, and 4) pyrite-carbonate coeval with a late brittle stage. These results support a continuous evolution model from a deep emplacement level (12 to 9 km) to a shallow one (7 to <5 km) with a brutal change in the P/T conditions that triggered the deposition of gold (stage 2) controlled by a seismic-valve mechanism. On the contrary, Sb veins correspond to open space vein types, hosted in a N20°W to N20°E conjugated strike-slip fault network arranged in a Riedel shear model, controlled by N130-140°E regional dextral strike-slip shear zone associated to the South Armorican Shear Zone system. A two-stage evolution is recognized, the first one consists of early pyrite-arsenopyrite with microcrystalline quartz, followed by a late stibnite stage formed after geodic quartz deposition. Quartz texture argues for a shallow emplacement (<5 km) of veins controlled by a suction-pump mechanism. Chronologically, the gold vein opening complies with a NE-SW maximum shortening direction different from the late-Variscan stress field responsible for the dextral Armorican shear zone during late Carboniferous, and constrains an indirect dating. Thus, a Visean age is proposed for the formation of gold veins. The overall features of gold deposits are close to those of mesozonal orogenic gold deposits in Europe. Conversely, Sb-bearing veins are generated by a N-S shortening during the late Carboniferous. The Sb event, distinct in time from the earlier gold one, might correspond to a different expression of the so-called “epizonal” type in the orogenic gold model. It is proposed that the Late Carboniferous “Or 300” event is not the unique metallogenic period for gold deposition in the French Variscan domain. Our study highlights the role of the sinistral strike-slip shearing of possible Visean age, in the gold metallogenesis of the Ligerian domain.

Fault systems and Paleo-stress tensors in the Indus Suture Zone (NW Pakistan)

Analysis of fault-striations measured in the Kohistan part of the Indus Suture Zone (NW Himalaya, Pakistan) has been carried out to document dynamic evolution during the brittle stage of the collision of India and Asia. Processing of the data with a direct inversion method identified four stress fields which were chronologically ordered from field evidence as SSE–NNW compression, E–W compression, radial extension and SSW–NNE compression. The last corresponds to the present-day stress field defined from seismic activity. The earlier stress fields are related to times during the Miocene, when convergence-related stresses were disturbed by the formation of the nearby Nanga Parbat and Indus syntaxes.

Geology and structural evolution of pre-Caledonian rocks and the ?Devonian Sutorfjella conglomerate, northern Prins Karls Forland (Svalbard)

On northern Prins Karls Forland, Early Vendian metasediments (Glenbegdalen and Taylorfjellet units) were thrust over conglomerates, quartz-carbonate schists, quartzites and phyllites of the Macnairrabbane unit. Remnants of microfossils in dolomite clasts of the conglomerates indicate an Early Paleozoic age of the Macnairrabbane unit. The Glenbegdalen, Taylorfjellet and Macnairrabbane units were affected by two ductile phases of isoclinal folding (D1, D2), followed by a third ductile to brittle stage (D3) of NE-vergent folding. This polyphase deformation post-dated the deposition of the Early Paleozoic Macnairrabbane unit, indicating a Caledonian age of D1 to D3. The Sutorfjella conglomerate on the west-coast of Prins Karls Forland contains clasts which are characterized by two stages of ductile folding and foliation (D1, D2), whereas the matrix is unaffected by any ductile deformation. The Sutorfjella conglomerate unconformably overlies the vertical short limb of a F3-fold. These observations suggest that the Sutorfjella conglomerate represents a post-Caledonian sediment which could be related to the ?Late Silurian to Early Devonian molasse basins in NW Spitsbergen. The occurrences of some reddish beds and red-weathered clasts indicate an ?Early Devonian age. The youngest convergent deformation (D4) is characterized by thrust-faulting and nappe-stacking in the basement rocks and by the formation of a F4-fold in the Sutorfjella conglomerate. Compared with the structures on Brøggerhalvøya, this deformation could be assigned to the formation of the Tertiary West Spitsbergen Fold-and-Thrust Belt.

Tectonics of the Red Sea region reassessed

The brittle upper level of the continental crust had been rifted with or without ocean opening many times in many places during the geological past and the process is still happening. Since the advent of plate tectonic theory in the early 1960s, the formation of such rifts has been viewed in the context of plate tectonic processes that caused the repeated dispersal of supercontinents. Several researchers focused on the mechanisms of formation of continental rifts because some rifts, like the Red Sea and Gulf of Aden, are precursors to ocean basins and many hydrocarbons yet to be located which are either directly or indirectly related to rift structures. The East African Rift System and the Red Sea-Gulf of Aden young oceans have been considered as prime examples of the early stage of continental separation that has long been a testing ground for classical hypotheses of continental drift. The Red Sea separates the once contiguous Neoproterozoic Arabian–Nubian Shields and started opening about 25 Ma ago. Geophysics and geochronology of dredged basaltic rocks indicate that sea-floor spreading began at only about 4–5 Ma. Numerous multidisciplinary investigations have been carried out in this region. However, several questions remain unresolved. Examples pertain to the nature of the crust that underlies the shelves, the extent of the ocean floor, the interplay between sea-floor spreading, crustal extension and plutonic activity and mechanisms of rifting. Several mechanisms of rifting have been proposed for the formation of the Red Sea. Examples include extension by prolonged steep normal faulting (horst–graben terrain), early diffuse ductile extension followed by brittle deformation, low-angle lithospheric simple shear, low-angle shear and magmatic expansion, lithospheric thinning by faulting and dike injection, northeastward migration of asymmetric rifting over a fixed mantle plume and the formation of pull-apart basin(s) by transtension. The major differences between the various models center on the relative timing of updoming, rifting and magmatism and whether the rifting was active and driven by a mantle plume or passive and due to lateral extension of the lithosphere leading to reactive effects in the mantle. New geological field data from the western margin of the Southern Red Sea in Eritrea reveal two main stages of NE–SW extension history. The first semi-brittle stage (⩾30 Ma) was dominantly characterized by top-to-east low-angle detachments. The second brittle stage of extension (since ∼22 Ma) occurred on a new system of dominantly down-to-southwest planar normal faults and dikes with NW–SE strikes. The earlier semi-brittle stage of extension corresponds to the predicted low-angle simple shear zone through the lithosphere and the later gives some support to the models that invoke graben–horst formation along steep normal faults that ultimately soled out to detachments at intermediate crustal level or merge with the Moho.

The slip-fiber chrysotile asbestos deposit in the Zidani area, northern Greece

The chrysotile asbestos deposit of Zidani in northern Greece is an example of a slip-fiber deposit associated with alpine-type peridotites. The deposit occurs in the northern part of an antigorite serpentinite and peridotite body, tectonically emplaced on the Pelagonian basement of the area. A continuous retrograde alteration event is recognizable along the thrust fault between a metaclastic and carbonate sequence and the serpentinite body. A phase of ductile deformation that formed antigorite mylonites was followed by a brittle one, which formed schistose serpentinite. The sense of shear of the overthrusting metaclastic mylonite coincides with that of the immediate underlying schistose and mylonite serpentinites; thus retrogression of both groups of rocks is assumed to be the result of the thrust event. The numerous altered amphibolite dikes crosscutting the ore created planar anisotropies during the thrust-related deformation. These planar anisotropies localized the deformation and consequently the formation of the schistose serpentinite and the asbestos ore in the northern part of the serpentinite body. Slip-fiber chrysotile asbestos was formed along anastomosing non-penetrating shear surfaces in the schistose serpentinite. The chrysotile fibers replaced antigorite “in situ” in shear planes, most likely at a transitional stage of deformation exhibiting both ductile and brittle fabrics. However, syntectonic filling of “shear veins” at the brittle stage is the major cause of the origin of the asbestos deposit.

Late Orogenic extension in mountain belts: Insights from the basin and range and the Late Paleozoic Variscan Belt

From two examples of orogenic domains, some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized. The Basin and Range province and the Variscan belt in the French Massif Central have both suffered important compressional orogenic crustal thickening, and the results of late orogenic processes can be observed in the field. Both areas are covered by deep seismic profiling providing constraints on the geometry of a crust which has been restored to a normal thickness. Late orogenic features from the two domains are compared at different scales and their tectonic significance for extension mechanisms is discussed. At the scale of the orogenic domains, the most prominent tectonic features are the metamorphic core complexes (MCC) which expose deformed rocks from the middle crust generally affected by high‐temperature, low to medium pressure metamorphism, partial melting, and widespread granite emplacement. In these MCC, large‐scale extensional shear zones present an intense mylonitic deformation characterized by low dipping foliations and pervasive stretching lineations. They show a complete evolution from early deep‐seated ductile deformation (generally achieved under high‐temperature, low to medium pressure metamorphism) to a late shallow brittle stage characterized by cataclastic deformation. The late detachment stage generally controls the development of asymmetrical extensional sedimentary basins filled by continental deposits. Two main geometries of MCC are defined that are characterized by differing geometry and kinematics of low‐angle shear zones. In the first case, two low‐angle shear zones with opposite vergence develop along the flanks of a roughly symmetrical MCC (often one system is dominant over the other). The second geometry characterizes asymmetrical MCC bounded by a single normal shear zone which is upwarped during uplift and doming of the core caused by tectonic denudation. Detailed strain analysis performed in several extensional shear zones shows that the deformation regime is heterogeneous and results from general noncoaxial flow. Deformation along the shear zones evolves progressively from slight homogeneous pure shear strain to intense heterogeneous noncoaxial shear strain. Strain distribution within the lower crust is less well constrained by field observation; however, analogies between COCORP and ECORS deep seismic reflection profiles give important constraints on crustal structure. Wide zones of highly subhorizontally layered lower crust and a flat high‐amplitude reflection Moho characterize both evolved orogenic domains suggesting that major deformations and flow occur within the lower crust during extension. A kinematic model involving heterogeneous crustal deformation and regional scale flow fits relatively well with late orogenic structures observed in continental domains. A weak, hot upper mantle allows large‐scale flow of lower crust material from zones of deep ductile extension to uplifted domains of upper crustal denudation. Heterogeneous strain is accommodated by low‐angle extensional shear zones from localized zones of extension in the brittle crust to ductile lower crust. Combined pure and simple shear occurs along localized shear zones, whereas at the scale of the whole lithosphere, deformation nearly corresponds to a vertical pure shear. Such deformation processes which affect a thick and hot crust seem to be common in both compared domains suggesting that late orogenic extensional processes are slightly dependent of the type of contractional tectonics. Thus, as much in the Andean‐type west American Cordilleran belt as in the collision‐type Variscan belt, late orogenic processes produced similar extensional features.

Metallogenesis in the French part of the Variscan orogen. Part I: U preconcentrations in pre-Variscan and Variscan formations — a comparison with Sn, W and Au

In the French part of the Variscan orogen, the pre-Variscan metamorphic rocks and the Variscan granites resulting from pure crustal recycling are enriched in uranium and tin. Data on tungsten and gold are too scarce for a reasonable estimation of the average concentrations of these elements to be obtained. The spatial distribution of uranium preconcentrations is transverse to the main Variscan structural domains, and the distribution of the Sn-W mineralizations prompts the same conclusions. U, Sn, W and Au metal enrichment in crustal domains in Europe seems to result from late Proterozoic to early Palaeozoic basic and acid magmatism. For uranium, at least two main stages of partial melting, early Palaeozoic and Late Carboniferous, lead to enrichment of the metal in peraluminous leucogranites; these leucogranites represent the main source of late Variscan uranium and tin. Within the peraluminous granitic complexes, the main metal source is related to the late intrusion of small granitic cupolas strongly enriched in metals. In the case of uranium the efficiency of the hydrothermal remobilization depends on the proportion of metal located in uraninite, which is easily leachable by hydrothermal solutions. The emplacement of these cupolas is structurally controlled in well-defined areas by large shear zones. These shear zones are continuously active during the successive emplacement of the granitic magmas. Most of the hydrothermal uranium mineralization is related to the Permian reactivation of the shear zones in a brittle stage. These zones then channel the hydrothermal fluids involved in the last metal concentration step, leading to the formation of the orebodies. The efficiency of metal remobilization is dependent on a close spatial relationship between magmatic structures enriched in uranium and brittle structures channeling the hydrothermal fluids.

Embrittlement of Cu&amp;ndash;Zn Alloys in the Solidification Process

Tensile strength and apparent deformation of solidifying binary Cu–Zn alloy castings were studied at various fractions of solid by use of a tensile test apparatus newly developed. The alloys complete solidification through four stages with increase in fraction of solid. The alloys at stage I with fractions of solid up to fa have significant deformation. Those at stage II with fractions of solid fa to fb rapidly lower the deformation. Those at stage III with fractions of solid fb to fc minimize the deformation and have noticeable strength. Those at stage IV with fraction of solid fc or more show rapid increase of both deformation and strength (fa<fb<fc). The α-phase solid solution alloys containing Zn up to 30% have less deformation in the extended brittle stage III than the β-phase solid solution alloys containing Zn 40 to 45%. The peritectic alloy has the maximum apparent deformation. Interdendritic fluid flow plays a significant role in the embrittlement during solidification. Changes in tensile properties with increase in fraction of solid and difference in properties among alloys are explainable by the solid growing proess and interdendritic liquid behavior.

Aureole Deformation by Flattening around a Diapir during in Situ Ballooning: The Cannibal Creek Granite

The Cannibal Creek Granite, a foliated pluton within a strongly deformed aureole, shows several diagnostic features of a diapir: the intensity of the aureole deformation diminished away from the contact; the aureole foliation is continuous with that of the granite and forms closed, elliptical trend lines; and the contact metamorphic minerals are synkinematic with regard to the aureole foliation. The pluton deformed its aureole in three stages, involving initially brittle, then ductile, and finally brittle deformation styles. Initial intrusion of a low strength magma stoped, kinked and flexed aside its overburden. Crystallization of the magma prevented further rise, and it ballooned and deformed its aureole evidently entirely by ductile bulk shortening perpendicular to the contact. This, the major stage of aureole deformation, records no evidence of vertical movement of the pluton, or of progressive simple shear along its margin. During this stage, the magma may have been Theologically a high-strength Bingham body, with a melt content probably less than 30%. Ballooning probably accounts for at least 70% of the pluton's present volume. The second brittle stage of deformation involved the fracturing of the complex and inner aureole rocks, possibly in response to thermal contraction. Three external dykes formed a sheath around the pluton, and three ring dykes were injected about a subsiding central block.

Cu-Zn 2元合金の凝固の進行に伴う脆化

Tensile strength and apparent deformation of solidifying binary Cu-Zn alloy castings were studied at various fractions of solid by use of a tensile test apparatus newly designed. The alloys complete solidification through four stages with increasing fraction of solid. The alloys in stage I with fraction of solid up to fa have significant deformation and negligible strength. Those in stage II with fraction of solid fa to fb rapidly lower the deformation. Those in stage III with fraction of solid fb to fc minimize the deformation and have noticeable strength. Those in stage IV with fraction of solid fc or more show rapid increase in both of deformation and strength (fa<fb<fc). The α-phase alloys containing Zn up to 30 mass% have less apparent deformation in the extended brittle stage III than the β-phase alloys. The peritectic alloy has the maximum apparent deformation. Interdendritic fluid flow plays a significant role in the embrittlement during solidification. Changes in the tensile properties with increase of fraction of solid are explainable by the solid forming process and interdendritic fluid behavior.

Internal structure of the Buckboard Mesa basalt

Engineering studies on Buckboard Mesa in Nevada have included extensive coring and borchole photographing in a late Cenozoic basalt flow. The basalt was evidently extruded from a fissure, now marked by a cinder cone, localized in the moat of the Timber Mountain caldera. It is an olivine-bearing andesitic basalt with a moderately high potassium content. Away from complications near the vent only a single flow is present. Distributaries from the main channel branch to clusters of lava toes at the flow terminus. A vesicular facies overlies a dense facies in general, but alternating layers formed in an early flow stage complicate the stratigraphy. Structures formed in a transitional stage are flattened vesicles, layers of vesicles, and lineated vesicles. These flow structures commonly parallel concentric flattened cylinders of the various rock types. The cylindrical structure is apparently fundamental to lava flow mechanics. In the brittle stage, an orthogonal system of three sets of fractures developed in the lava parallel and perpendicular to the flow layering. Similar flow channels with cylindrical flow structure and related fractures are present in Columbia River basalt and elsewhere.

ORIGIN OF A SCAPOLITE METAGABBRO IN BUCKS COUNTY, PENNSYLVANIA

In Bucks County, Pennsylvania, a body of limestone was invaded by pre-Cambrian gabbro with practically no contact action. Much later, dynamic metamorphism transformed the gabbro into a metagabbro, composed chiefly of andesine and hornblende, which replaced the original augite. Lighter bands in the metagabbro, containing oligoclase feldspar, indicate the introduction of hydrothermal solutions. Within the quarry some of the metagabbro is interbanded with a scapolite metagabbro, consisting mainly of diopside and scapolite. The chemical composition of the two rock types is similar despite their distinct mineral suites. The scapolite metagabbro is considered the result of recrystallization of the metagabbro which took place at the time of dynamic metamorphism, aided by the introduction of small amounts of hydrothermal solutions. Coarse-grained, crosscutting bands of scapolite and diopside, isolated masses of scapolite and diopside, and oligoclase-diopside masses are also present within the limestone. Throughout, the composition of the scapolite is the same. All the rock masses within the limestone are boudins which lie along three parallel zones. This indicates that the original gabbro intruded the limestone in dikes, which, during later dynamic metamorphism, were drawn out into boudins and rotated in the limestone during a plastic stage of the deformation. Joints and a fault, roughly perpendicular to the regional foliation, suggest a still later brittle stage in the deformation, but the uniformity of the scapolite composition implies that the plastic and brittle stages of the deformation were connected, and both were generally contemporaneous with the hydrothermal activity.