Radial Fracturing Research Articles

Tectonics and Evolution of Coronae on Venus: Preliminary Results of Tectonophysical Modeling

The formation of annular features on Venus, the so-called coronae, is modeled. It is common practice to associate their formation with the uplift and relaxation of hot mantle diapirs. We managed to partially reproduce the topography and structural pattern of the initial stage of corona evolution, a radially fractured dome, by lifting and lowering a piston under a layer of sand with consistent oil or moist clay. We failed to model a dense radial fracturing, which is typical of the earliest stage of corona evolution. We were able to reproduce the necessary attribute of coronae, concentric structures, which are commonly assumed to be formed at the stage of dome relaxation. Their formation mechanism in our experiments can serve only as a partial analog of the processes that produce corona rims. There is an obvious need to use more accurate models. Nevertheless, our modeling shows that the brittle deformations manifest themselves more clearly than do the plastic ones in the formation of dome-shaped uplift during the generation of natural coronae. The modeling also shows that the pattern of deformation within the dome-shaped uplift depends to some extent on the relationship between the layer thickness and the cross-sectional piston sizes. The latter can be a model for the relationship between the lithosphere thickness and the cross-sectional sizes of the mantle diapir that form a corona.

Present-day ultrahigh-pressure conditions of coesite inclusions in zircon and garnet: Evidence from laser Raman microspectroscopy

Research Article| November 01, 1999 Present-day ultrahigh-pressure conditions of coesite inclusions in zircon and garnet: Evidence from laser Raman microspectroscopy C. D. Parkinson; C. D. Parkinson 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan Search for other works by this author on: GSW Google Scholar I. Katayama I. Katayama 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information C. D. Parkinson 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan I. Katayama 1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo 152-8551, Japan Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (11): 979–982. https://doi.org/10.1130/0091-7613(1999)027<0979:PDUPCO>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation C. D. Parkinson, I. Katayama; Present-day ultrahigh-pressure conditions of coesite inclusions in zircon and garnet: Evidence from laser Raman microspectroscopy. Geology 1999;; 27 (11): 979–982. doi: https://doi.org/10.1130/0091-7613(1999)027<0979:PDUPCO>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Coesite (the dense, high-pressure polymorph of quartz) occurs as inclusions in mechanically strong minerals in deeply subducted, metamorphosed crustal rocks in a number of Eurasian collisional orogens. It is the primary indicator mineral of ultrahigh-pressure (P) metamorphism. Whereas some coesite inclusions are untransformed, most exhibit partial transformation to palisade quartz and a concomitant increase in volume (resulting in rupture and radial fracturing of the host grain). Coesite can be identified by its diagnostic Raman spectrum; the strongest band (at atmospheric pressure, room temperature) is at 521 cm−1. Laser Raman microspectroscopic analyses of coesite inclusions within garnet and zircon in ultrahigh-P metamorphic rocks from Kazakhstan, Indonesia, and China reveal consistent differences in the Raman spectra of (1) partially transformed coesite + quartz (main Raman band at 521 cm−1) and (2) untransformed monomineralic coesite grains (main band at 525–526 cm−1). Applying the room-temperature calibration of pressure dependence of the coesite Raman spectrum, we conclude that the latter coesite inclusions are subject to a remarkable pressure differential of 19–23 kbar with the host grains, and are still undergoing pressure-temperature conditions on or close to the quartz-coesite equilibrium boundary. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Cement Sheath Stress Failure

Summary Observation of the sudden appearance of annular pressure in wells exposed to high temperature changes or excessive internal casing pressure prompted a laboratory investigation to simulate conditions under which cement sheath failure could occur and thereby define the causes, characteristics, and limits of the problem. Cement sheath failure is manifested by interzonal problem. Cement sheath failure is manifested by interzonal annular-fluid movement and abnormally high annular pressure at some point behind the casing up to and at the surface. Cement sheath point behind the casing up to and at the surface. Cement sheath failure can be observed in any producing area where excessive flowing temperatures exist at the surface or where excessive internal casing test pressures are used. The detrimental effects of cement sheath failure are numerous and may include lost revenue from lost production, potentially hazardous rig operations (especially when annular isolation loss creates shallow-water sands supercharged with gas), and potentially hazardous producing operations. Exposure of steel casing to excessive temperature increases or internal test pressures causes diametrical and circumferential casing expansion. This circumferential force creates a shearing force at the cement/casing interface, causing failure at the cement/casing interface or radial fracturing of the cement sheath from the inner casing surface to the outer casing (or borehole) surface.

YAG Laser Demonstration of the Anatomy of the Lens Nucleus

I used YAG laser energy to demonstrate the position and surface of the core of the lens nucleus and to prove the existence of the radial structure of the lens nucleus. Not only does hydrodissection of the epinuclear layers from the nuclear core demonstrate the existence of an anatomical substrate, but also radial fracturing of the nucleus both in phacoemulsification and planned extracapsular surgery can make use of these anatomical features to achieve smaller incisions and thereby smaller wounds.

The effect of rock mass confinement on the bond strength of fully grouted cable bolts

A laboratory and field research programme was conducted to investigate the major factors influencing the bond capacity of grouted cable bolts. All tests were conducted on standard 5 8 ″ (15.9 mm) 7-strand cable groted using type 10 Portland cement pastes. The results indicate that cable bolt capacity most critically depends on: 1. (i) the cement properties, which are primarily controlled by water; cement ratio; 2. (ii) the embedment length; and 3. (iii) the radial confinement acting on the outer surface of the cement annulus 4. (iii) the radial confinement acting on the outer surface of the cement annulus. The material properties of cement paste vary with the water: cement ratio of the mix. The use of low water: cement ratio grouts (<0.40 by wt) can increase peak cable bolt capacities by 50–75%. This can be attributed to both their high uniaxial compressive strengths and their high Young's moduli. The effect is maximized under conditions of high radial confinement. However, the use of super-thick pastes (0.30 and less) may be both impractical and undesirable, first because of their limited pumpability and second because of their inconsistency in strength. Tests at different embedment lengths indicated that cable bolt capacity increased with embedment length although not in direct proportionality. All tests were conducted with embedment length: cable diameter ratios in excess of 15 (below 5 the decay in shear stress along the cable can be ignored). Consequently, failure is non-simultaneous in nature, with one section having failed while another is approaching peak capacity. In the laboratory “split-pipe” tests were conducted using PVC, Al and steel pipes to provide radial confinement, and in the field, surface test sites were chosen in granite, limestone and shale rock masses, as well as an underground case study at the Golden Giant Mine. In general, higher capacities were obtained under conditions of higher radial confinement. A correlation between the laboratory and the field test results was obtained through a comparison of the radial stiffness of the laboratory pipes with that of the field boreholes as measured using a high-pressure dilatometer. As the degree of radial confinement increased the failure mechanism changed from radial fracturing and lateral displacement of the grout annulus under low confinement, to shear of the cement flutes and pull out along a cylindrical frictional surface under high confinement.

Regional topographic rises on Venus: Geology of Western Eistla Regio and comparison to Beta Regio and Atla Regio

Regional topographic rises in the equatorial region of Venus (Western Eistla Regio, Beta Regio, and Atla Regio) form a unique class of structures which on the basis of geologic mapping and geophysical data are interpreted to be sites of mantle upwelling or plumes. The geologically least complex of these regions is Western Eistla Regio, an elongated domical rise that contains the volcanoes Sif and Gula montes. Sif Mons is a large volcano (diameter &gt; 100 km) whose local stratigraphy indicates that it has undergone a history marked by initial radial fracturing, widespread outpouring of lava, additional fracturing along its northern flank, and extrusion of lava that is either extremely fluid or was erupted at a high rate of effusion. Sif contains a 40‐km‐diameter summit caldera within which are nested smaller calderas and pit structures. Theoretical considerations suggest multiple levels of magma emplacement within the volcano, with the primary reservoir residing in the crust below the edifice. Gula Mons is made up of multiple volcanic source regions and is associated with Guor Linea, a zone of lithospheric stretching, faulting, and rifting. The geologically complex highland of Beta Regio is a tectonic junction with three arms of Devana Chasma intersecting at Theia Mons. Magellan data reveal (1) the details of rifting and volcanism concentrated at Theia Mons, (2) that Rhea Mons is highly deformed and possesses characteristics of tesserae and whose origin as a volcano is placed in question, (3) that tesserae are a major unit, arrayed in a pattern around Theia from east to west starting on the eastern flank of Beta and continuing westward to the northern part of Asteria Regio, (4) that the northern periphery of the highland contains coronae connected by fractures forming chains, and (5) the presence of a deformed crater within Devana Chasma, split and extended in an east‐west direction, indicating that part of the rift has undergone as much as 20–30% extension. Like Beta, Atla Regio is a complex area of converging rifts (five separate arms) that are centered on the volcano Ozza Mons. The Magellan images show that volcanism and rifting have occurred contemporaneously at Ozza, with lava flows both covering and being crosscut by faults. A second volcano, Maat Mons, contributes to the infilling of the rift Dali Chasma and does not appear to be deformed by faulting. Two of the rifts at Atla contain chains of coronae, suggesting that upwelling along linear zones of extension has occurred. Beta, Atla, and Western Eistla are similar in that they are broad regional rises, are associated with major rift zones, have large apparent depths of isostatic compensation, and contain large volcanoes. Their associations with features mapped as coronae and tesserae are quite variable, suggesting that the detailed characteristics of the individual highlands are most likely linked to each areas local geologic environment.

Primary fractures within a tuff cone, North Menan Butte, Idaho, U.S.A.

Abstract North Menan Butte is a tuff cone near Idaho Falls, Idaho. It is a result of the eruption of basaltic magma through shallow water-saturated river alluvium of the Snake River. The cone is characterized by primary fractures that can be classified into four groups on the basis of their physical properties and their orientations relative to the symmetry elements of the cone. Type I fractures are short, closely spaced and usually confined to individual beds. They strike approximately at right angles to cone radii and always dip toward the rim of the tuff cone. Bed segments separated by these fractures have undergone rotation, resulting in normal displacements. Type II fractures have similar attitudes but are more continuous, less frequent, and show no shear displacement. Type III fractures also strike at right angles to cone radii, but they dip away from the cone rim. They cut across several beds and reveal inconsistent senses of shear displacement. Type IV fractures are radial, steeply dipping and tend to be the most continuous of all fracture types. Type I fractures were the earliest to develop; age relationships otherwise are uncertain. Examples of all four types of fractures are exposed on the inner and outer eroded slopes of the cone. Evidence from the cone indicates that the fractures developed in an unconsolidated aggregate of tuff with low cohesion; therefore, analysis of fracture genesis should be constrained by principles of soil mechanics. Type I fractures originated as tension fractures related to early downslope mass movement. Later movement on Type I fractures accompanied the development of Type III shear fractures and possible bedding plane displacements, all caused by overloading the crest of the cone by late-stage eruptive products. The origin of Type II fractures is unknown; shrinkage due to desiccation or large-scale creep are possible explanations. The radial Type IV fractures may be a consequence of desiccation shrinkage or possibly of subcone processes such as magma doming or radial hydraulic fracturing.

Comparison of multiple radial fracturing enhancement techniques - laboratory investigation : Zeigler, B; Schatz, J; Nudd, E Key Questions in Rock Mechanics: Proc 29th US Symposium, Minneapolis, 13–15 June 1988P143–150. Publ Rotterdam: A A Balkema, 1988

Comparison of multiple radial fracturing enhancement techniques - laboratory investigation : Zeigler, B; Schatz, J; Nudd, E Key Questions in Rock Mechanics: Proc 29th US Symposium, Minneapolis, 13–15 June 1988P143–150. Publ Rotterdam: A A Balkema, 1988

Field Tests of the Stem-Induced Explosive Fracturing Technique

Summary The explosive stem-induced fracturing technique has been field tested in over 20 producing oil wells in western Pennsylvania. The technique basically involves the placement of a primary explosive charge in an expendable rathole below the pay zone(s) to be fractured and of a solid gravel stem near the top of the pay zone to cause local fracturing through the dynamic reflection of the explosive gases. In the best cases, production increases realized with the technique are comparable to those obtained with conventional hydraulic fracturing in the area. A 35-mm downhole camera was developed and used to obtain photographs that show the absence of any vertical fracturing before the explosive treatments and well-developed vertical fractures in all zones designed to be fractured. This vertical fracturing is developed despite the fact that the in-situ stresses favor horizontal fracturing. The photographs also show that multiple radial fracturing, which might be expected with the high rates of the explosive loading, does not usually occur and that wellbore damage is less than predicted.

Relationship of zones of buckling crushing, fragmentation, and radial fracturing with critical microfracturing

Zones of buckling crushing (fine pulverization) and fragmentation appear around a borehole when the pressure pulse of the detonation products (DP) is quite strong. The initial radial cracks, which may grow further on quasistatic expansion of the DP, are formed at the fragmentation zone boundary. Based on the kinetic concepts of the nature of destruction, and in developing what has been elucidated elsewhere, the authors present here, in reference to granite, the theoretical evaluations of the amplitude stresses at the boundaries of the buckling crushing and fragmentation zones, the dimensions of these zones, and the possible dimensions and number of the radial cracks.

Calculation of the zone of intense radial fracturing accompanying an explosion

Calculation of the zone of intense radial fracturing accompanying an explosion

Morphology and Structure of the Western Galápagos Volcanoes and a Model for Their Origin

The two westernmost Galapagos Islands, Isabela and Fernandina, comprise six large, active, basaltic shield volcanoes, which are closely related in space and in the time of their formation. The volcanoes have marked morphological and structural similarities, but gradational differences exist which show relative volcano ages. These features also indicate the mechanisms of volcano origin and development. The unusual subaerial profiles are typified by steep upper slopes and a broad, flat top. Profiles, including submarine portions, show that all six volcanoes have four slope segments: two submarine and two subaerial. Distinct profile differences provide evidence for various formational processes; the subaerial upper segments are sensitive indicators of these processes. Superimposed profiles show that erupted lavas move far down the volcano slopes to be deposited on the subaerial lower segment and especially on the submarine segments. Relative slope maturities on a volcano can be determined that depend upon the volume of lava added to different profile directions. Different ranges of slope maturities indicate the relative volcano ages. Subaerial profiles are influenced by the submarine base which formed prior to subaerial accumulation. The “flattish” volcano tops are mostly large calderas, although some calderas are surrounded by a wide, flat rim area. Caldera characteristics, such as diameter, circularity, and depth, show trends which agree with the age sequence determined from the profiles. Volcano elevations decrease regularly with increasing caldera diameter. A radial fissure pattern is well developed on the younger volcanoes but becomes less well defined with age. When present, this pattern is restricted to the subaerial upper segment of the volcano. Fissures on subaerial lower segments have a linear nature; they extend upslope to the calderas and downslope to link adjacent volcanoes. A circumferential fissure pattern around the caldera is well displayed by some volcanoes. The diameter of the circumferential fissure pattern increases with age; on the youngest volcano, circumferential fissures have a strong linear nature. Coalescence of circumferential and linear fissures, caldera elongation, and eruption locations define dominant, throughgoing lineaments which cross each volcano and link the six volcanic centers. Subordinate lineaments can also be defined which intersect dominant lineaments at each caldera. Two lineament orientations are present which correspond to previously proposed trends for the Galapagos Islands. A model for the origin and development of the volcanoes outlines five main periods: (1) submarine base construction, (2) subaerial construction, (3) tumescence and radial fracturing, (4) caldera development, and (5) morphological decline. A key concept in the model is the formation of a dome by tumescence and associated radial fracturing. The dome is supported by radial dikes so that a steep upper slope segment is formed and maintained during caldera development. Circumferential fissures are viewed as “passive” features which form during collapse of the central part of the dome. Calderas are initially grabenlike because of the control of the throughgoing dominant lineament. Caldera growth is accompanied by increasing circumferential fissure diameter; radial fissures become less distinct as tumescence decreases in importance. During morphological decline, the caldera consumes the upper portion of the volcano while eruptions broaden and flatten the profile. The resulting landform is similar to shield volcanoes of other areas and to the older Galapagos Islands.