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Sample records for disturbed rock zone

  1. The disturbed rock zone at the Waste Isolation Pilot Plant.

    SciTech Connect

    Hansen, Francis D.

    2003-12-01

    The Disturbed Rock Zone constitutes an important geomechanical element of the Waste Isolation Pilot Plant. The science and engineering underpinning the disturbed rock zone provide the basis for evaluating ongoing operational issues and their impact on performance assessment. Contemporary treatment of the disturbed rock zone applied to the evaluation of the panel closure system and to a new mining horizon improves the level of detail and quantitative elements associated with a damaged zone surrounding the repository openings. Technical advancement has been realized by virtue of ongoing experimental investigations and international collaboration. The initial portion of this document discusses the disturbed rock zone relative to operational issues pertaining to re-certification of the repository. The remaining sections summarize and document theoretical and experimental advances that quantify characteristics of the disturbed rock zone as applied to nuclear waste repositories in salt.

  2. WIPP air-intake shaft disturbed-rock zone study

    SciTech Connect

    Dale, T.; Hurtado, L.D.

    1996-12-01

    The disturbed-rock zone surrounding the air-intake shaft at the Waste Isolation Pilot Plant (WIPP) site was investigated to determine the extent and the permeability of the disturbed-rock zone as a function of radial distance from the 6.1 m diameter shaft, at different elevations within the Salado. Gas- and brine-permeability tests were performed in the bedded halite of the Salado formation at two levels within the air-intake shaft. The gas- and brine-permeability test results demonstrated that the radial distance to an undisturbed formation permeability of 1 {times} 10{sup {minus}21} m{sup 2} was less than 3.0 m.

  3. Discrete fracture hydromechanical model for the disturbed rock zone in a clay rock

    NASA Astrophysics Data System (ADS)

    Asahina, D.; Houseworth, J. E.; Birkholzer, J. T.

    2013-12-01

    We have developed a coupled thermal-hydrological-mechanical (THM) fracture damage model, TOUGH-RBSN, to investigate the behavior of fracture generation and evolution in rock in the presence of perturbations to THM conditions. This model combines the capabilities of the TOUGH2 simulator to represent thermal-hydrological processes with a rigid-body-spring-network (RBSN) model, a type of discrete modeling, to treat geomechanical and fracture-damage processes. In particular, the development and evolution of fractures in the excavation damaged zone (EDZ) of a clay rock, with application to high-level nuclear waste disposal, is a focus for this model development. Previously, the TOUGH-RBSN approach has been used to model fracture damage under tensile conditions as a result of desiccation shrinkage. The next phase of model testing will be application to the HG-A test being conducted at the Mont Terri underground research laboratory (URL) near Saint-Ursanne, Switzerland. This test is being conducted in a 13-m long, 1-m diameter microtunnel in the Opalinus clay rock in which a test section at the far end of the microtunnel is isolated using a packer. The test is specifically targeted to observe how fluids injected into the test section penetrate into the rock, with particular emphasis on the EDZ. The HG-A microtunnel was excavated in 2005 and subsequent mapping of the tunnel surface shows preferential fracturing and tunnel breakouts along zones where bedding planes are tangential to the tunnel wall and where faults intercept the tunnel. It appears that the EDZ fracture damage can be attributed to both tensile and shear fracturing mechanisms. A series of injection tests with water and gas have been performed which also show preferential invasion of the fluid pressure along the observed damage zones, as well as fracture self-sealing over time. The TOUGH-RBSN approach has been successfully applied to modeling fracture driven by predominately tensile loading, whereas only

  4. Prediction of the Extent of the Disturbed Rock Zone around a WIPP Disposal Room, USA

    SciTech Connect

    Park, B.Y.; Herrick, C.G.; Holcomb, D.J.

    2008-07-01

    This paper is one of a series of papers outlining the recent performance assessment for the Waste Isolation Pilot Plant repository conducted by Sandia National Laboratories. The disturbed rock zone (DRZ) is an important feature that is included in the performance assessment process models to predict future repository conditions and brine flow to the accessible environment. Furthermore, the properties of the DRZ control a significant portion of the brine that can flow into the waste rooms. Extensive laboratory salt creep data demonstrate that damage can be assessed in terms of volumetric strain and principal stresses. Stress states that cause dilation are defined in terms of stress invariants, which allow reasonable models of DRZ evolution and devolution. In this paper, the change of DRZ extent with time is calculated based on a dilatant damage potential criterion. The constant C in the dilatancy criterion is determined by comparing the numerical analysis results of the Room Q access drift with the field data obtained at the same location for the analysis. The most extensive DRZ exists during early times, within the first ten years after an opening is mined. As the back stresses from the waste stack resist deformation, the damage to the salt decreases. The maximum extents of the DRZ calculated below and above the room reach approximately 2.24 m and 4.74 m, respectively. The maximum lateral DRZ extent in the side of the room is calculated to be roughly 2 m. (authors)

  5. Extent of the Disturbed Rock Zone Around a WIPP Disposal Room

    NASA Astrophysics Data System (ADS)

    Herrick, C. G.; Park, B. Y.; Holcomb, D. J.

    2008-12-01

    The Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico, is operated by the U.S. Department of Energy (DOE) as the underground disposal facility for transuranic (TRU) nuclear waste. It is located in a bedded salt formation at a depth of about 650 m. Salt at this depth behaves as a viscous material having an initially lithostatic state of stress. Mining of an opening disturbs the static equilibrium to a degree where fracturing of the rock surrounding a room occurs, changing its mechanical and hydrologic properties. This disturbed rock zone (DRZ) is an important geomechanical feature included in the performance assessment process models used to predict future repository conditions as a part of certification by the EPA as meeting regulatory compliance. Based on ongoing scientific investigations and evaluation of published data since the original certification in 1998, our understanding of the DRZ has continued to progress. Three deformation processes are activated as deviatoric stresses are induced upon excavation of a room in a salt formation: (1) elastic response, (2) inelastic viscoplastic flow, and (3) inelastic- damage induced flow. Damage, the least understood of these processes, is manifested by the time- dependent initiation, growth, coalescence, and healing of microfractures with a deviatoric stress state. Since the ability to model the spatial and temporal changes in salt damage is not available at this time, various means to measure it have been attempted. At the WIPP, for this study, we used sonic velocity measurements obtained over a 12 year period as the principal field method to describe the extent of the DRZ. Predictions of the DRZ extent based on these experimental results are substantiated by permeability measurements and microfracture density analysis from other places in the repository. Extensive laboratory salt creep data demonstrate that damage can be assessed in terms of volumetric strain and principal stresses. Stress states

  6. Coupled Biological-Geomechanical-Geochemical Effects of the Disturbed Rock Zone on the Performance of the Waste Isolation Pilot Plant

    NASA Astrophysics Data System (ADS)

    Dunagan, S. C.; Herrick, C. G.; Lee, M. Y.

    2008-12-01

    The Waste Isolation Pilot Plant (WIPP) is located at a depth of 655 m in bedded salt in southeastern New Mexico and is operated by the U.S. Department of Energy as a deep underground disposal facility for transuranic (TRU) waste. The WIPP must comply with the EPA's environmental regulations that require a probabilistic risk analysis of releases of radionuclides due to inadvertent human intrusion into the repository at some time during the 10,000-year regulatory period. Sandia National Laboratories conducts performance assessments (PAs) of the WIPP using a system of computer codes representing the evolution of underground repository and emplaced TRU waste in order to demonstrate compliance. One of the important features modeled in a PA is the disturbed rock zone (DRZ) surrounding the emplacement rooms in the repository. The extent and permeability of DRZ play a significant role in the potential radionuclide release scenarios. We evaluated the phenomena occurring in the repository that affect the DRZ and their potential effects on the extent and permeability of the DRZ. Furthermore, we examined the DRZ's role in determining the performance of the repository. Pressure in the completely sealed repository will be increased by creep closure of the salt and degradation of TRU waste contents by microbial activity in the repository. An increased pressure in the repository will reduce the extent and permeability of the DRZ. The reduced DRZ extent and permeability will decrease the amount of brine that is available to interact with the waste. Furthermore, the potential for radionuclide release from the repository is dependent on the amount of brine that enters the repository. As a result of these coupled biological-geomechanical-geochemical phenomena, the extent and permeability of the DRZ has a significant impact on the potential radionuclide releases from the repository and, in turn, the repository performance. Sandia is a multi program laboratory operated by Sandia

  7. RATDAMPER - A Numerical Model for Coupling Mechanical and Hydrological Properties within the Disturbed Rock Zone at the Waste Isolation Pilot Plant

    SciTech Connect

    RATH,JONATHAN S.; PFEIFLE,T.W.; HUNSCHE,U.

    2000-11-27

    A numerical model for predicting damage and permeability in the disturbed rock zone (DRZ) has been developed. The semi-empirical model predicts damage based on a function of stress tensor invariant. For a wide class of problems hydrologic/mechanical coupling is necessary for proper analysis. The RATDAMPER model incorporates dilatant volumetric strain and permeability. The RATDAMPER model has been implemented in a weakly coupled code, which combines a finite element structural code and a finite difference multi-phase fluid flow code. Using the development of inelastic volumetric strain, a value of permeability can be assigned. This flexibility allows empirical permeability functional relationships to be evaluated.

  8. Determination of near field excavation disturbance in crystalline rock

    SciTech Connect

    Koopmans, R.; Hughes, R.W.

    1986-01-01

    The computerized dilatometer system has rapidly and economically provided deformation moduli of low and high modulus rock, determined the extent of excavation disturbance surrounding an underground opening and located open fracture within a rock mass. Results from both test sites indicate that the moduli obtained were influenced by the in situ tangential stress field. It has been shown that the near field excavation disturbance is kept to a minimum through the use of careful excavation techniques such as the tunnel boring machine. In turn, the in situ tangential stress levels and deformation moduli are maximized while the corresponding permeability is minimized.

  9. Test plan: Sealing of the Disturbed Rock Zone (DRZ), including Marker Bed 139 (MB139) and the overlying halite, below the repository horizon, at the Waste Isolation Pilot Plant. [Cementitious grout into fractured WIPP rock

    SciTech Connect

    Ahrens, E.H.

    1992-05-01

    This test plan describes activities intended to demonstrate equipment and techniques for producing, injecting, and evaluating microfine cementitious grout. The grout will be injected in fractured rock located below the repository horizon at the Waste Isolation Pilot Plant (WIPP). These data are intended to support the development of the Alcove Gas Barrier System (AGBS), the design of upcoming, large-scale seal tests, and ongoing laboratory evaluations of grouting efficacy. Degradation of the grout will be studied in experiments conducted in parallel with the underground grouting experiment.

  10. Brine and Gas Flow Patterns Between Excavated Areas and Disturbed Rock Zone in the 1996 Performance Assessment for the Waste Isolation Pilot Plant for a Single Drilling Intrusion that Penetrates Repository and Castile Brine Reservoir

    SciTech Connect

    ECONOMY,KATHLEEN M.; HELTON,JON CRAIG; VAUGHN,PALMER

    1999-10-01

    The Waste Isolation Pilot Plant (WIPP), which is located in southeastern New Mexico, is being developed for the geologic disposal of transuranic (TRU) waste by the U.S. Department of Energy (DOE). Waste disposal will take place in panels excavated in a bedded salt formation approximately 2000 ft (610 m) below the land surface. The BRAGFLO computer program which solves a system of nonlinear partial differential equations for two-phase flow, was used to investigate brine and gas flow patterns in the vicinity of the repository for the 1996 WIPP performance assessment (PA). The present study examines the implications of modeling assumptions used in conjunction with BRAGFLO in the 1996 WIPP PA that affect brine and gas flow patterns involving two waste regions in the repository (i.e., a single waste panel and the remaining nine waste panels), a disturbed rock zone (DRZ) that lies just above and below these two regions, and a borehole that penetrates the single waste panel and a brine pocket below this panel. The two waste regions are separated by a panel closure. The following insights were obtained from this study. First, the impediment to flow between the two waste regions provided by the panel closure model is reduced due to the permeable and areally extensive nature of the DRZ adopted in the 1996 WIPP PA, which results in the DRZ becoming an effective pathway for gas and brine movement around the panel closures and thus between the two waste regions. Brine and gas flow between the two waste regions via the DRZ causes pressures between the two to equilibrate rapidly, with the result that processes in the intruded waste panel are not isolated from the rest of the repository. Second, the connection between intruded and unintruded waste panels provided by the DRZ increases the time required for repository pressures to equilibrate with the overlying and/or underlying units subsequent to a drilling intrusion. Third, the large and areally extensive DRZ void volumes is a

  11. Properties of Flow Zones in Fractured Rock

    NASA Astrophysics Data System (ADS)

    Salve, R.

    2004-12-01

    Observations over the last 25 years from various field studies suggest that preferential flow is common in soils and rocks. Despite this realization, very little is known about the large-scale properties (e.g., structure, distribution, continuity) of such flow regimes. This information is important for predictive models, but it remains elusive, mainly because of the difficulties involved in characterizing flow that has substantial spatial (both vertical and horizontal) and temporal variability. To better understand preferential flow in fractured rock, we carried out an in situ field experiment in the Topopah Spring tuff found in Exploratory Studies Facility at Yucca Mountain, Nevada. This experiment involved the release of ~22 m3 of ponded water (at a pressure head of ~0.04 m) over a period of 7 months, directly onto a 12 m2 infiltration plot. As water was released, changes in moisture content were monitored along horizontal boreholes located in the formation ~19-22 m below. Distinct flow zones, with significant differences in flow velocity, size, and extent of lateral movement, intercepted the 6-9 m long monitoring boreholes. Further, in some flow zones saturation levels persisted for the time period in which water was released, while in others there were periodic fluctuations. There was also evidence of water being diverted above the ceiling of a cavity in the immediate vicinity of the monitoring boreholes. Observations from this field experiment suggested that inconsistencies exist in present conceptual models of flow in fractured rock. Particularly, these observations suggest that isolated conduits within the fractured rock formation encompass a large number of fractures to form preferential flow paths that persist if there is a continuous supply of water. It appears that in fractured welded tuffs, the propensity for vertical dispersion and fracture-matrix interactions may be significantly greater than suggested by existing conceptual models. These observations

  12. Geohydromechanical Processes in the Excavation Damaged Zone in Crystalline Rock, Rock Salt, and Indurated and Plastic Clays

    SciTech Connect

    Tsang, Chin-Fu; Bernier, Frederic; Davies, Christophe

    2004-06-20

    The creation of an excavation disturbed zone or excavation damaged zone is expected around all man-made openings in geologic formations. Macro- and micro-fracturing, and in general a redistribution of in situ stresses and rearrangement of rock structures, will occur in this zone, resulting in drastic changes of permeability to flow, mainly through the fractures and cracks induced by excavation. Such an EDZ may have significant implications for the operation and long-term performance of an underground nuclear waste repository. Various issues of concern need to be evaluated, such as processes creating fractures in the excavation damaged zone, the degree of permeability increase, and the potential for sealing or healing (with permeability reduction) in the zone. In recent years, efforts along these lines have been made for a potential repository in four rock types-crystalline rock, salt, indurated clay, and plastic clay-and these efforts have involved field, laboratory, and theoretical studies. The present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on EDZ in these four rock types at a CLUSTER Conference and Workshop held in Luxembourg in November, 2003. First, definitions of excavation disturbed and excavation damaged zones are proposed. Then, an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the EDZ for the four rock types (crystalline rock, salt, indurated clay, and plastic clay). Comparison tables of relevant processes, associated factors, and modeling and testing techniques are developed. A discussion of the general state-of-the-art and outstanding issues are also presented. A substantial bibliography of relevant papers on the subject is supplied at the end of the paper.

  13. Excavation Damaged Zones In Rock Salt Formations

    SciTech Connect

    Jockwer, N.; Wieczorek, K.

    2008-07-01

    Salt formations have long been proposed as potential host rocks for nuclear waste disposal. After the operational phase of a repository the openings, e.g., boreholes, galleries, and chambers, have to be sealed in order to avoid the release of radionuclides into the biosphere. For optimising the sealing techniques knowledge about the excavation damaged zones (EDZ) around these openings is essential. In the frame of a project performed between 2004 and 2007, investigations of the EDZ evolution were performed in the Stassfurt halite of the Asse salt mine in northern Germany. Three test locations were prepared in the floor of an almost 20 year old gallery on the 800-m level of the Asse mine: (1) the drift floor as existing, (2) the new drift floor shortly after removing of a layer of about 1 m thickness of the floor with a continuous miner, (3) the new drift floor 2 years after cutting off the 1-m layer. Subject of investigation were the diffusive and advective gas transport and the advective brine transport very close to the opening. Spreading of the brine was tracked by geo-electric monitoring in order to gain information about permeability anisotropy. Results obtained showed that EDZ cut-off is a useful method to improve sealing effectiveness when constructing technical barriers. (authors)

  14. Disturbed zones; indicators of deep-seated subsurface faults in the Valley and Ridge and Appalachian structural front of Pennsylvania

    USGS Publications Warehouse

    Pohn, Howard A.; Purdy, Terri L.

    1982-01-01

    Field studies of geologic structures in the Valley and Ridge and adjacent parts of the Appalachian Plateau provinces in Pennsylvania have shown a new type of structure, formerly poorly understood and frequently unmapped, is a significant indicator of deep-seated subsurface faulting. These structures, herein called disturbed zones, are formed by movement between closely spaced pairs of thrust faults. Disturbed zones are characterized at the surface by long, narrow, intensely folded and faulted zones of rocks in a relatively undisturbed stratigraphic sequence. These zones are frequently kilometers to tens of kilometers long and tens to hundreds of meters wide. Although disturbed zones generally occur in sequences of alternating siltstone and shale beds, they can also occur in other lithologies including massively-bedded sandstones and carbonates. Disturbed zones are not only easily recognized in outcrop but their presence can also be inferred on geologic maps by disharmonic fold patterns, which necessitates a detachment between adjacent units that show the disharmony. A number of geologic problems can be clarified by understanding the principles of the sequence of formation and the method of location of disturbed zones, including the interpretation of some published geologic cross sections and maps. The intense folding and faulting which accompanies the formation of a typical disturbed zone produces a region of fracture porosity which, if sealed off from the surface, might well serve as a commercially-exploitable hydrocarbon trap. We believe that the careful mapping of concentrations of disturbed zones can serve as an important exploration method which is much less expensive than speculation seismic lines.

  15. Test plan: Sealing of the Disturbed Rock Zone (DRZ), including Marker Bed 139 (MB139) and the overlying halite, below the repository horizon, at the Waste Isolation Pilot Plant. Small-scale seal performance test-series F

    SciTech Connect

    Ahrens, E.H.

    1992-05-01

    This test plan describes activities intended to demonstrate equipment and techniques for producing, injecting, and evaluating microfine cementitious grout. The grout will be injected in fractured rock located below the repository horizon at the Waste Isolation Pilot Plant (WIPP). These data are intended to support the development of the Alcove Gas Barrier System (AGBS), the design of upcoming, large-scale seal tests, and ongoing laboratory evaluations of grouting efficacy. Degradation of the grout will be studied in experiments conducted in parallel with the underground grouting experiment.

  16. Study on the Characteristic Energy Factor of the Deep Rock Mass Under Weak Disturbance

    NASA Astrophysics Data System (ADS)

    Wang, Mingyang; Li, Jie; Ma, Linjian; Huang, Houxu

    2016-08-01

    This study aims to investigate the characteristic energy factor of the deep rock mass deformation subjected to the disturbance induced by excavation or explosion. Based on the well-known rock hierarchical structure, the equivalent average kinetic energy of the deep rock mass under weak disturbance is first introduced. The characteristic energy factor that reflects the instable deformation of the deep rock mass is derived using the principle of variation. The relationship between the characteristic energy factor and the energy hierarchical sequence of the deep rock mass deformation and failure has also been illustrated. We believe that the characteristic energy factor is closely related to the characteristic scientific phenomena of deep rock mass in essence, which can provide a new approach for the study of deep rock mass in the fields of nonlinear mechanics, statistic physical mechanics, and mechanics of explosion and geophysics.

  17. Bioprotection and disturbance: Seaweed, microclimatic stability and conditions for mechanical weathering in the intertidal zone

    NASA Astrophysics Data System (ADS)

    Coombes, Martin A.; Naylor, Larissa A.; Viles, Heather A.; Thompson, Richard C.

    2013-11-01

    As well as their destructive roles, plants, animals and microorganisms contribute to geomorphology and ecology via direct and indirect bioprotection, which can reduce weathering and erosion. For example, indirect bioprotection can operate via biotic influences on microclimate whereby physical decay processes associated with fluctuations in temperature and moisture (salt crystallization, thermal fatigue and wetting-drying), are limited. In the intertidal zone, the spatial and temporal distribution of macroalgae (seaweeds) is patchy, related to physical and ecological conditions for colonization and growth, and the nature and frequency of natural and anthropogenic disturbance. We examined the influence of seaweed canopies (Fucus spp.) on near-surface microclimate and, by implication, on conditions for mechanical rock decay and under-canopy ecology. Monitoring on hard artificial coastal structures in South West England, UK, built from limestone and concrete showed that both the range and maxima of daily summertime temperatures were significantly lower, by an average of 56% and 25%, respectively, in areas colonized by seaweed compared to experimentally cleared areas. Short-term microclimatic variability (minutes-hours) was also significantly reduced, by an average of 78% for temperature and 71% for humidity, under algal canopies during low-tide events. Using seaweed as an example, we develop a conceptual model of the relationship between biological cover and microclimate in the intertidal zone. Disturbance events that remove or drastically reduce seaweed cover mediate shifts between relatively stable and unstable states with respect to mechanical decay and ecological stress associated with heat and desiccation. In urban coastal environments where disturbance may be frequent, facilitating the establishment and recovery of canopy-forming species on rocks and engineered structures could enhance the durability of construction materials as well as support conservation

  18. Fluid-rock reaction weakening of fault zones

    SciTech Connect

    Wintsch, R.P.; Christoffersen, R.; Kronenberg, A.K.

    1995-07-10

    The presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well-developed fabrics. The growth of phyllosilicates is favored in meteoric water-dominated granitic fault systems, where mineral-aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions. In deeper, more alkaline, rock-dominated regimes, the reactions reverse, and feldspars tend to replace phyllosilicates. In Mg-rich mafic rocks, however, phyllosilicates (chlorite, biotite) can replace stronger framework and chain silicates in both shallower (<{approximately}10 km) meteoric H{sub 2}O-dominated and in deeper, alkaline, rock-dominated regimes. Where these phyllosilicates precipitate in active fault zones, they contribute directly to reaction softening. Because low-temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure-independent dislocation glide, the strength of phyllosilicate-rich fault rocks can be low at all depths. Low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites. Where preferred orientations are strong and contiguity of phyllosilicates is large, strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals. Fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well-defined folia can exhibit aseismic slip, especially where mafic Mg-rich rocks occur along the fault (like parts of the San Andreas Fault). 104 refs., 6 figs., 1 tab.

  19. DISTURBED ZONE AND PISTON SHOCK AHEAD OF CORONAL MASS EJECTION

    SciTech Connect

    Eselevich, V.; Eselevich, M.

    2012-12-10

    The 2010 June 13 coronal mass ejection (CME) propagating toward the position angle P.A. Almost-Equal-To 245 Degree-Sign (measured counterclockwise from the Sun's north pole) was studied from the SDO/AIA and SOHO/LASCO C2, C3 data. We show that ahead of the CME frontal structure, as a result of its interaction with the undisturbed solar wind, a disturbed region (with an increased and disturbed plasma density), whose size increases as the CME travels away from the Sun, emerges gradually. Discontinuity formation at the disturbed zone front is observed in the narrow P.A. Almost-Equal-To 245 Degree-Sign -250 Degree-Sign range. Its characteristics satisfy the properties of a piston collision shock. In the other directions relative to the CME motion axis (P.A. > 250 Degree-Sign and P.A. < 245 Degree-Sign ), there exists only the disturbed zone, whose density gradually decreases with distance. The discontinuity that was always observed at all distances where measurements were made is absent. The analysis of this CME and several other limb CMEs with different velocities from the MK4, LASCO C2, C3, and STEREO/COR2 data confirmed the previously established laws of piston shock formation ahead of a CME, which are as follows: (1) Shock formation ahead of a CME in a vicinity along its propagation axis may occur at various distances R = R{sub u} from the Sun's center. Its formation is determined by fulfilling a local inequality u(R) > V{sub A} (R), where u(R) is a CME velocity relative to the surrounding solar wind and V{sub A} (R) is a local Alfven velocity that is approximately equal to the velocity of fast magnetic sound in the solar corona. (2) At R < 6 R{sub Sun }, the shock front width {delta}{sub F} is on the order of the proton mean free path {lambda}{sub p}, and the mechanism for energy dissipation at the front is, apparently, collisional. (3) At R {approx}> 10-15 R{sub Sun }, one observes the formation of a new discontinuity {delta}{sup *}{sub F} << {lambda}{sub p} wide

  20. Simulation of hydraulic disturbances caused by the underground rock characterization facility in Olkiluoto, Finland

    NASA Astrophysics Data System (ADS)

    Löfman, Jari; Mészáros, Ferenc

    A final repository for spent nuclear fuel is sought in Finland by Posiva (the company responsible for the construction and operation of the final nuclear-waste disposal facility in Finland, http://www.posiva.fi). A part of this project involves an underground rock characterization facility (ONKALO), which will consist of an 8,500 m long and 520 m deep system of tunnels, to be potentially extended with the drifts of the repository. The maximum hydraulic disturbance (water table drawdown, deep saline-water upconing and tunnel inflow) that might result from the construction and operation of the ONKALO facility were assessed by site-scale finite-element simulations. The drawdown was calculated by employing the free-surface approach. Tunnel inflows were obtained from the state of equilibrium, while the evolution of the salinity distribution was simulated using a time-dependent and coupled flow and salt transport model. The simulations showed that without engineering measures to limit inflow of groundwater into the ONKALO facility, the hydraulic disturbances would be significantly greater than with these measures implemented. Most of the inflow (330-1,100 L/min) would come from the conductive subhorizontal fracture zones intersected by the drifts. The water table could sink to a depth of about 200 m, and the depressed area could extend over the Olkiluoto Island. Groundwater salinity (expressed as total dissolved solids [TDS]) could locally rise from 22 g/L to over 50 g/L at the tunnel depth of 520 m. With tight grouting, the simulations showed that the depression in the water table can be confined to the immediate vicinity of the ONKALO, the maximum draw-down of the water table remained around 10 m, and the total inflow to the tunnels was about 20 L/min. Moreover, upconing of the saline water remained moderate.

  1. Coupled diffusion and abiotic reaction of trichlorethene in minimally disturbed rock matrices.

    PubMed

    Schaefer, Charles E; Towne, Rachael M; Lippincott, David R; Lazouskaya, Volha; Fischer, Timothy B; Bishop, Michael E; Dong, Hailiang

    2013-05-01

    Laboratory experiments were performed using minimally disturbed sedimentary rocks to measure the coupled diffusion and abiotic reaction of trichloroethene (TCE) through rock core samples. Results showed that, for all rock types studied, TCE dechlorination occurred, as evidenced by generation of acetylene, ethene, and/or ethane daughter products. First-order bulk reaction rate constants for TCE degradation ranged from 8.3 × 10(-10) to 4.2 × 10(-8) s(-1). Observed reaction rate constants showed a general correlation to the available ferrous iron content of the rock, which was determined by evaluating the spatial distribution of ferrous iron relative to that of the rock porosity. For some rock types, exposure to TCE resulted in a decrease in the effective diffusivity. Scanning electron microscopy (SEM) indicated that the decrease in the effective diffusivity was due to a decrease in the porosity that occurred after exposure to TCE. Overall, these coupled diffusion and reaction results suggest that diffusion of TCE into rock matrices as well as the rate and extent of back-diffusion may be substantially mitigated in rocks that contain ferrous iron or other naturally occurring reactive metals, thereby lessening the impacts of matrix diffusion on sustaining dissolved contaminant plumes in bedrock aquifers. PMID:23590334

  2. Internal structure of fault zones in geothermal reservoirs: Examples from palaeogeothermal fields and potential host rocks

    NASA Astrophysics Data System (ADS)

    Leonie Philipp, Sonja; Reyer, Dorothea; Meier, Silke; Bauer, Johanna F.; Afşar, Filiz

    2014-05-01

    characterized by increased fracture densities and higher percentages of fractures with large apertures. In the Upper Rhine Graben (2) damage zones in Muschelkalk limestones (Middle Triassic) are well developed even in fault zones with dm-scale displacements. Their fault cores, however, are narrow compared with that of fault zones with larger displacements and comprise brecciated material, clay smear, host rock lenses or zones of mineralization. Fracture apertures are larger parallel or subparallel to fault zone strike. A large fault zone footwall in Triassic Bunter sandstone shows a clearly developed fault core with fault gouge, slip zones, deformation bands and host rock lenses, a distal fault core with disturbed layering and high fracture density and a damage zone with increased fracture density compared with the host rock. In the study areas of palaeogeothermal fields in the Bristol Channel (3), all the mineral veins are clearly related to the faults and occur almost exclusively in the damage zones, indicating that geothermal water was transported along the then-active faults into the host rocks. Field measurements indicate that in all the localities, a large majority of the fractures in the fault damage zones are extension fractures, fewer are shear fractures. In the Jurassic Blue Lias there is evidence that the veins were injected as hydrofractures from fault planes into the limestone layers. In the Triassic Mercia Mudstone most veins were arrested during their propagation by layers with contrasting mechanical properties (stress barriers). Some veins, however, propagated through the barriers along faults to shallower levels. Our studies contribute to understanding and modelling of hydromechanical behaviour of fault zones and fluid transport in geothermal reservoirs. For successful exploration and exploitation, fault zones must be studied in detail regarding their likely internal structure, fracture parameters and orientation in relation to the current stress field. We show

  3. Subduction-zone cycling of nitrogen in serpentinized mantle rocks

    NASA Astrophysics Data System (ADS)

    Halama, R.; Bebout, G. E.; John, T.; Scambelluri, M.

    2010-12-01

    Nitrogen (N) has shown great potential as a geochemical tracer of volatiles recycling, in part because of large differences in the N isotope composition of the various Earth reservoirs. The subduction flux of N in serpentinized oceanic mantle could be as important as N input flux in oceanic crust and even sediment because, although its N concentrations are lower, its volume is potentially far greater than that of the crust/sediment. However, recycling of oceanic mantle rocks is still poorly constrained for the N cycle, and N isotope data for subduction-related ultramafic rocks are scarce [1]. The primary goal of this study is to characterize the subduction flux of N in subducting altered oceanic mantle by documenting concentrations and isotopic compositions of N in mantle rocks that reflect different stages of the metamorphic subduction zone cycle. The results are crucial to assess the composition of N recycled into the mantle, to determine the extent to which N can be retained in subducted mantle rocks to depths approaching those beneath arcs, and to balance N subduction-zone inputs with outputs in arc volcanic gases. Moreover, information has been gained regarding the redistribution and isotope fractionation of N via ultramafic dehydration and metamorphic fluid-rock interaction. The samples analyzed in this study are ultramafic rocks from shallow oceanic environments to increasing P-T conditions up to depths of ~70 km. Three distinct metamorphic grades, reflecting seafloor fluid uptake, water release due to brucite breakdown and the final antigorite breakdown, were investigated: 1. Pre-subduction serpentinized mantle peridotite from non-subducted ophiolite sequences from the Northern Apennines, Italy (Monte Nero). 2. Eclogite-facies antigorite serpentinites from the Ligurian Alps, Italy (Erro Tobbio). 3. Eclogite-facies chlorite harzburgites derived from dehydration of serpentinites from the Betic Cordillera, Spain (Cerro de Almirez). The pre

  4. Rock mechanics. Superplastic nanofibrous slip zones control seismogenic fault friction.

    PubMed

    Verberne, Berend A; Plümper, Oliver; de Winter, D A Matthijs; Spiers, Christopher J

    2014-12-12

    Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis. PMID:25504714

  5. A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice

    USGS Publications Warehouse

    Clow, Gary D.

    2015-01-01

    A knowledge of subsurface temperatures in sedimentary basins, fault zones, volcanic environments and polar ice sheets is of interest for a wide variety of geophysical applications. However, the process of drilling deep boreholes in these environments to provide access for temperature and other measurements invariably disturbs the temperature field around a newly created borehole. Although this disturbance dissipates over time, most temperature measurements are made while the temperature field is still disturbed. Thus, the measurements must be ‘corrected’ for the drilling-disturbance effect if the undisturbed temperature field is to be determined. This paper provides compact analytical solutions for the thermal drilling disturbance based on 1-D (radial) and 2-D (radial and depth) Green's functions (GFs) in cylindrical coordinates. Solutions are developed for three types of boundary conditions (BCs) at the borehole wall: (1) prescribed temperature, (2) prescribed heat flux and (3) a prescribed convective condition. The BC at the borehole wall is allowed to vary both with depth and time. Inclusion of the depth dimension in the 2-D solution allows vertical heat-transfer effects to be quantified in situations where they are potentially important, that is, near the earth's surface, at the bottom of a well and when considering finite-drilling rates. The 2-D solution also includes a radial- and time-dependent BC at the earth's surface to assess the impact of drilling-related infrastructure (drilling pads, mud pits, permanent shelters) on the subsurface temperature field. Latent-heat effects due to the melting and subsequent refreezing of interstitial ice while drilling a borehole through ice-rich permafrost can be included in the GF solution as a moving-plane heat source (or sink) located at the solid–liquid interface. Synthetic examples are provided illustrating the 1-D and 2-D GF solutions. The flexibility of the approach allows the investigation of thermal

  6. A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice

    NASA Astrophysics Data System (ADS)

    Clow, Gary D.

    2015-12-01

    A knowledge of subsurface temperatures in sedimentary basins, fault zones, volcanic environments and polar ice sheets is of interest for a wide variety of geophysical applications. However, the process of drilling deep boreholes in these environments to provide access for temperature and other measurements invariably disturbs the temperature field around a newly created borehole. Although this disturbance dissipates over time, most temperature measurements are made while the temperature field is still disturbed. Thus, the measurements must be `corrected' for the drilling-disturbance effect if the undisturbed temperature field is to be determined. This paper provides compact analytical solutions for the thermal drilling disturbance based on 1-D (radial) and 2-D (radial and depth) Green's functions (GFs) in cylindrical coordinates. Solutions are developed for three types of boundary conditions (BCs) at the borehole wall: (1) prescribed temperature, (2) prescribed heat flux and (3) a prescribed convective condition. The BC at the borehole wall is allowed to vary both with depth and time. Inclusion of the depth dimension in the 2-D solution allows vertical heat-transfer effects to be quantified in situations where they are potentially important, that is, near the earth's surface, at the bottom of a well and when considering finite-drilling rates. The 2-D solution also includes a radial- and time-dependent BC at the earth's surface to assess the impact of drilling-related infrastructure (drilling pads, mud pits, permanent shelters) on the subsurface temperature field. Latent-heat effects due to the melting and subsequent refreezing of interstitial ice while drilling a borehole through ice-rich permafrost can be included in the GF solution as a moving-plane heat source (or sink) located at the solid-liquid interface. Synthetic examples are provided illustrating the 1-D and 2-D GF solutions. The flexibility of the approach allows the investigation of thermal drilling

  7. Evolving subduction zones in the Western United States, as interpreted from igneous rocks

    USGS Publications Warehouse

    Lipman, P.W.; Prostka, H.J.; Christiansen, R.L.

    1971-01-01

    Variations in the ratio of K2O to SiO4 in andesitic rocks suggest early and middle Cenozoic subduction beneath the western United States along two subparallel imbricate zones dipping about 20 degrees eastward. The western zone emerged at the continental margin, but the eastern zone was entirely beneath the continental plate. Mesozoic subduction apparently occurred along a single steeper zone.

  8. Multiple-code benchmark simulation study of coupled THMC processesin the excavation disturbed zone associated with geological nuclear wasterepositories

    SciTech Connect

    Rutqvist, J.; Feng, X-T.; Hudson, J.; Jing, L.; Kobayashi, A.; Koyama, T.; Pan, P-Z.; Lee, H-S.; Rinne, M.; Sonnenthal, E.; Yamamoto, Y.

    2006-05-10

    An international, multiple-code benchmark test (BMT) studyis being conducted within the international DECOVALEX project to analysecoupled thermal, hydrological, mechanical and chemical (THMC) processesin the excavation disturbed zone (EDZ) around emplacement drifts of anuclear waste repository. This BMT focuses on mechanical responses andlong-term chemo-mechanical effects that may lead to changes in mechanicaland hydrological properties in the EDZ. This includes time-de-pendentprocesses such as creep, and subcritical crack, or healing of fracturesthat might cause "weakening" or "hardening" of the rock over the longterm. Five research teams are studying this BMT using a wide range ofmodel approaches, including boundary element, finite element, and finitedifference, particle mechanics, and elasto-plastic cellular automatamethods. This paper describes the definition of the problem andpreliminary simulation results for the initial model inception part, inwhich time dependent effects are not yet included.

  9. A computational model of pile vertical vibration in saturated soil based on the radial disturbed zone of pile driving

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Shi, Qian; Wang, Kuihua

    2010-06-01

    In this study, a simplified computational model of pile vertical vibration was developed. The model was based on the inhomogeneous radial disturbed zone of soil in the vicinity of a pile disturbed by pile driving. The model contained two regions: the disturbed zone, which was located in the immediate vicinity of the pile, and the undisturbed region, external to the disturbed zone. In the model, excess pore pressure in the disturbed zone caused by pile driving was assumed to follow a logarithmic distribution. The relationships of stress and strain in the disturbed zone were based on the principle of effective stress under plain strain conditions. The external zone was governed by the poroelastic theory proposed by Biot. With the use of a variable separation method, an analytical solution in the frequency domain was obtained. Furthermore, a semi-analytical solution was attained by employing a numerical convolution method. Numerical results from the frequency and time domain indicated that the equivalent radius of the disturbed zone and the ratio of excess pore pressure had a significant effect on pile dynamic response. However, actual interactions between pile and soil will be weaker due to the presence of the radial disturbed zone, which is caused by pile driving. Consequently, the ideal undisturbed model overestimates the interaction between pile and soil; however, the proposed model reflects the interaction of pile and soil better than the perfect contact model. Numerical results indicate that the model can account for the time effect of pile dynamic tests.

  10. 78 FR 53243 - Safety Zone; TriRock San Diego, San Diego Bay, San Diego, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-29

    ... Acronyms DHS Department of Homeland Security FR Federal Register NPRM Notice of Proposed Rulemaking A... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; TriRock San Diego, San Diego Bay, San Diego... Safety Zone; TriRock San Diego, San Diego Bay, San Diego, CA. (a) Location. The limits of the safety...

  11. Deformation of footwall rock of Phulad Shear Zone, Rajasthan: Evidence of transpressional shear zone

    NASA Astrophysics Data System (ADS)

    Choudhury, Manideepa Roy; Das, Subhrajyoti; Chatterjee, Sadhana M.; Sengupta, Sudipta

    2016-07-01

    Phulad Shear Zone (PSZ) of Delhi Fold Belt in Rajasthan is a northeasterly striking ductile shear zone with a well developed mylonitic foliation (035/70E) and a downdip stretching lineation. The deformation in the PSZ has developed in a transpressional regime with thrusting sense of movement. The northeastern unit, i.e., the hanging wall contains a variety of rocks namely calc-silicates, pelites and amphibolites and the southwestern unit, i.e., the footwall unit contains only granitic rocks. Systematic investigation of the granites of the southwestern unit indicate a gradual change in the intensity of deformation from a distance of about 1 km west of the shear zone to the shear zone proper. The granite changes from weakly deformed granite to a mylonite/ultramylonite as we proceed towards the PSZ. The weakly deformed granite shows a crude foliation with the same attitude of mylonitic foliation of the PSZ. Microscopic study reveals the incipient development of C and S fabric with angle between C and S varying from 15 ∘ to 24 ∘. The small angle between the C and S fabric in the least deformed granite variety indicates that the deformation has strong pure shear component. At a distance of about 1 m away from the PSZ, there is abrupt change in the intensity of deformation. The granite becomes intensely foliated with a strong downdip lineation and the rock becomes a true mylonite. In mesoscopic scale, the granite shows stretched porphyroclasts in both XZ and YZ sections indicating a flattening type of deformation. The angle between the C and S fabric is further reduced and finally becomes nearly parallel. In most places, S fabric is gradually replaced by C fabric. Calculation of sectional kinematic vorticity number ( W n) from the protomylonitic and mylonite/ultramylonite granites varies from 0.3 ± 0.03 to 0.55 ± 0.04 indicating a strong component of pure shear. The similarity of the geometry of structures in the PSZ and the granites demonstrates that the

  12. Effect of simulated sampling disturbance on creep behaviour of rock salt

    NASA Astrophysics Data System (ADS)

    Guessous, Z.; Gill, D. E.; Ladanyi, B.

    1987-10-01

    This article presents the results of an experimental study of creep behaviour of a rock salt under uniaxial compression as a function of prestrain, simulating sampling disturbance. The prestrain was produced by radial compressive loading of the specimens prior to creep testing. The tests were conducted on an artifical salt to avoid excessive scattering of the results. The results obtained from several series of single-stage creep tests show that, at short-term, the creep response of salt is strongly affected by the preloading history of samples. The nature of this effect depends upon the intensity of radial compressive preloading, and its magnitude is a function of the creep stress level. The effect, however, decreases with increasing plastic deformation, indicating that large creep strains may eventually lead to a complete loss of preloading memory.

  13. Example Building Damage Caused by Mining Exploitation in Disturbed Rock Mass

    NASA Astrophysics Data System (ADS)

    Florkowska, Lucyna

    2013-06-01

    Issues concerning protection of buildings against the impact of underground coal mining pose significant scientific and engineering challenges. In Poland, where mining is a potent and prominent industry assuring domestic energy security, regions within reach of mining influences are plenty. Moreover, due to their industrial character they are also densely built-up areas. Because minerals have been extracted on an industrial scale in majority of those areas for many years, the rock mass structure has been significantly disturbed. Hence, exploitation of successive layers of multi-seam deposits might cause considerable damage - both in terms of surface and existing infrastructure networks. In the light of those facts, the means of mining and building prevention have to be improved on a regular basis. Moreover, they have to be underpinned by reliable analyses holistically capturing the comprehensive picture of the mining, geotechnical and constructional situation of structures. Scientific research conducted based on observations and measurements of mining-induced strain in buildings is deployed to do just that. Presented in this paper examples of damage sustained by buildings armed with protection against mining influences give an account of impact the mining exploitation in disturbed rock mass can have. This paper is based on analyses of mining damage to church and Nursing Home owned by Evangelical Augsburg Parish in Bytom-Miechowice. Neighbouring buildings differ in the date they were built, construction, building technology, geometry of the building body and fitted protection against mining damage. Both the buildings, however, have sustained lately significant deformation and damage caused by repeated mining exploitation. Selected damage has been discussed hereunder. The structures have been characterised, their current situation and mining history have been outlined, which have taken their toll on character and magnitude of damage. Description has been supplemented

  14. Disturbance, A Mechanism for Increased Microbial Diversity in a Yellowstone National Park Hot Spring Mixing Zone

    NASA Astrophysics Data System (ADS)

    Howells, A. E.; Oiler, J.; Fecteau, K.; Boyd, E. S.; Shock, E.

    2014-12-01

    The parameters influencing species diversity in natural ecosystems are difficult to assess due to the long and experimentally prohibitive timescales needed to develop causative relationships among measurements. Ecological diversity-disturbance models suggest that disturbance is a mechanism for increased species diversity, allowing for coexistence of species at an intermediate level of disturbance. Observing this mechanism often requires long timescales, such as the succession of a forest after a fire. In this study we evaluated the effect of mixing of two end member hydrothermal fluids on the diversity and structure of a microbial community where disturbance occurs on small temporal and spatial scales. Outflow channels from two hot springs of differing geochemical composition in Yellowstone National Park, one pH 3.3 and 36 °C and the other pH 7.6 and 61 °C flow together to create a mixing zone on the order of a few meters. Geochemical measurements were made at both in-coming streams and at a site of complete mixing downstream of the mixing zone, at pH 6.5 and 46 °C. Compositions were estimated across the mixing zone at 1 cm intervals using microsensor temperature and conductivity measurements and a mixing model. Qualitatively, there are four distinct ecotones existing over ranges in temperature and pH across the mixing zone. Community analysis of the 16S rRNA genes of these ecotones show a peak in diversity at maximal mixing. Principle component analysis of community 16S rRNA genes reflects coexistence of species with communities at maximal mixing plotting intermediate to communities at distal ends of the mixing zone. These spatial biological and geochemical observations suggest that the mixing zone is a dynamic ecosystem where geochemistry and biological diversity are governed by changes in the flow rate and geochemical composition of the two hot spring sources. In ecology, understanding how environmental disruption increases species diversity is a foundation

  15. Chlorine Behavior in Metasedimentary Rocks during Subduction Zone Metamorphism

    NASA Astrophysics Data System (ADS)

    Barnes, J.; Selverstone, J.; Bebout, G. E.; Penniston-Dorland, S.

    2014-12-01

    Chlorine concentrations and isotopic compositions were measured in two well-characterized metasedimentary suites from the Catalina Schist and the Western Alps to determine Cl behavior during prograde metamorphism. The Catalina Schist is a subduction zone metamorphic complex in California, USA containing lawsonite-albite (LA) to amphibolite grade rocks recording temperatures of 350 to 750°C and depths of 15 to 45 km. Previous work has shown a decrease in N, B, Cs, As, and Sb concentrations from the LA to the epidote-blueschist facies, with relatively little loss at higher metametamorphic grade [1], and limited Li loss across all grades [2]. Metapelitic rocks from the Western Alps (Schistes Lustres and Lago di Cignana) record temperatures of 350 to 550°C and depths up to 90 km. In contrast to Catalina, N, B, Cs, Ba, and Rb concentrations are relatively uniform across grade [3]. In the Catalina Schist, Cl concentration shows a pattern of loss similar to B and N, from ~100-500 ppm Cl in the LA facies to ~100 ppm in the lawsonite-blueschist facies to relatively uniform concentrations of ~10-25 ppm at higher grades. This loss is likely not due to the breakdown of apatite as P2O5 concentrations remain constant across grade. In the Alps, Cl concentrations are overall lower and show moderate loss from ~10 ppm in the lowest grade to <5 ppm in the highest grade. δ37Cl values range from -1 to +1.6‰ and -1.7 to -0.7‰ in Catalina and the Alps, respectively. Both suites show significant isotopic heterogeneities within a single metamorphic grade and no systematic change in δ37Cl value with increasing grade. We interpret these heterogeneities to be inherited from the protolith. Despite large Cl losses, limited Cl isotope fractionation at high temperatures minimizes variations in δ37Cl value with increasing metamorphic grade. [1] Bebout et al, 1999, EPSL, 171, 53-81 [2] Penniston-Dorland et al, 2012, GCA, 77, 530-545 [3] Bebout et al, 2013, Chem Geol, 342, 1-20

  16. Decimeter Scale Ultra-Fine Fault Rocks (Possible Pseudotachylites) in an Ancient Subduction Thrust Zone

    NASA Astrophysics Data System (ADS)

    Rowe, C. D.; Moore, J. C.; Meneghini, F.; McKiernan, A. W.

    2004-12-01

    Large bodies of ultrafine fault rock (possible pseudotachylite or frictional melt) occur within cataclastic thrust zones in the Ghost Rocks Formation, Kodiak Accretionary Complex, Alaska. The Paleocene Ghost Rocks Formation includes map-scale mélange belts formed by flattening and shearing of seafloor sediments and volcanic rocks at about 250 degrees C and 325 MPa (~13 km depth) during subduction between 65-60Ma. Ten to 15-meter thick cataclastite zones crosscut the mélange fabric at a low angle, representing a stage of increasingly localized shear during subduction thrusting. Ultrafine fault rocks occur as thick (10-25cm) continuous planar beds along the boundaries of cataclastites, or in discontinuous accumulation bodies within cataclastite zones. The boundaries of the ultrafine fault rocks are intrusive, sharp but irregular and deform the cataclastite host fabric. Single pulse intrusions of the ultrafine fault rock range up to 0.5m in intrusive dimension and form complex morphologies resembling both upward and downward directed flame structures and dike-sill complexes, as well as sheath folds and disharmonic flow banding and folding. These field characteristics indicate fluidization and perhaps frictional melting of the ultrafine fault rocks. Ultrafine fault rock bodies can be traced laterally for meters to tens of meters at individual outcrops and occur for about 2 km along strike. Preliminary SEM analysis reveals that the primary matrix material is physically and chemically homogenous down to few-micron scale, consistent with the field identification of pseudotachylite. Thin sections show rounded remnant quartz aggregates, typical of pseudotachylytes. Although some thin sections show suggest melting others may represent ultracataclastite. Some ultrafine fault rock material is rebrecciated and cataclastized to a fine scale, indicating reactivation of previous fault rock generation surfaces. These ultrafine fault rock zones represent the most highly deformed

  17. Acoustic emission and ultrasonic-velocity methods used to characterise the excavation disturbance associated with deep tunnels in hard rock

    NASA Astrophysics Data System (ADS)

    Falls, Stephen D.; Young, R. Paul

    1998-04-01

    Acoustic emission (AE) and ultrasonic-velocity monitoring studies have been undertaken at both the Atomic Energy of Canada Limited (AECL) Underground Research Laboratory (URL) and at the Swedish Nuclear Fuel Waste Management Company (SKB) Hard Rock Laboratory (HRL). At both locations the excavations were tunnels in granitic material at approximately 420 m depth. However, the stress regime was more severe at the URL Mine-by tunnel site than the HRL ZEDEX tunnel. Different parts of the ZEDEX tunnel were created using different excavation techniques. Using AE and ultrasonic techniques to study these tunnels we have been able to examine the nature of the excavation-disturbed zone around the tunnel, as well as examining the effects of different stress regimes and excavation techniques. Studies were undertaken both during and after the Mine-by tunnel excavation and during excavation in the ZEDEX tunnel. AE monitoring in the wall of the Mine-by tunnel during excavation showed that some activity occurred in the sidewall regions, but the spatial density of AE hypocentres increased toward the regions in the floor and roof of the tunnel where breakout notches formed. This sidewall activity was clustered primarily within 0.5 m of the tunnel wall. AE monitoring in the floor of the tunnel showed that small numbers of AE continued to occur in the notch region in the floor of the tunnel over 2 years after excavation was completed. This activity became more acute as the rock was heated, imposing thermally induced stresses on the volume. Ultrasonic-velocity studies both in the floor and the wall of the tunnel showed that the velocity is strongly anisotropic with the direction of slowest velocity orthogonal to the tunnel surface. The velocity increased with distance into the rock from the tunnel surface. In the floor, this effect was seen up to 2 m from the tunnel surface. Most of the change occurred within the first 0.5 m from the tunnel perimeter. At the lower-stress HRL, most of

  18. Peculiarities of ULF electromagnetic disturbances before strong earthquakes in seismic active zone of Kamchatka peninsula

    NASA Astrophysics Data System (ADS)

    Kopytenko, Y. A.; Ismagilov, V. S.; Schekotov, A.; Molchanov, O.; Chebrov, V.; Raspopov, O. M.

    2006-12-01

    Regular observations of ULF electromagnetic disturbances and acoustic emissions at st. Karymshino in seismic active zone of Kamchatka peninsula were carried out during 2001-2003 years. Five seismic active periods with strong earthquakes (M>5) were displayed during this period. These EQs occurred at the Pacific at 20-60 km depth at 100-140 km distances to the East from the st. Karymshino. Analysis of normalized dynamic power spectra of data of high-sensitive (0.2 pT/sqrt(Hz)) three-component induction magnetometer achieved a significant disorder of daily variation and increasing of the magnetic disturbance intensities (from 0.2 to ~1 pT) in the whole investigated frequency range (0.2-5 Hz). The anomaly intensity increasing was observed during the 12-18 hours before main seismic shocks. Maximum of the increasing occurred during 4-6 hours before the EQs. An increasing of acoustic emissions (F=30 Hz) was observed during the same period. A sharp decreasing of the magnetic disturbance intensities was observed 2-4 hours before the EQs. We suppose that physical processes in a hearth of forthcoming EQ lead to an irreversible avalanche-like formation of cracks and stimulation of the acoustic and ULF electromagnetic disturbances.

  19. 43 CFR 6302.15 - When and how may I collect or disturb natural resources such as rocks and plants in wilderness...

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... natural resources such as rocks and plants in wilderness areas? 6302.15 Section 6302.15 Public Lands... disturb natural resources such as rocks and plants in wilderness areas? (a) You may remove or disturb natural resources for non-commercial purposes in wilderness areas, including prospecting, provided—...

  20. 43 CFR 6302.15 - When and how may I collect or disturb natural resources such as rocks and plants in wilderness...

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... natural resources such as rocks and plants in wilderness areas? 6302.15 Section 6302.15 Public Lands... disturb natural resources such as rocks and plants in wilderness areas? (a) You may remove or disturb natural resources for non-commercial purposes in wilderness areas, including prospecting, provided—...

  1. 43 CFR 6302.15 - When and how may I collect or disturb natural resources such as rocks and plants in wilderness...

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... natural resources such as rocks and plants in wilderness areas? 6302.15 Section 6302.15 Public Lands... disturb natural resources such as rocks and plants in wilderness areas? (a) You may remove or disturb natural resources for non-commercial purposes in wilderness areas, including prospecting, provided—...

  2. 43 CFR 6302.15 - When and how may I collect or disturb natural resources such as rocks and plants in wilderness...

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... natural resources such as rocks and plants in wilderness areas? 6302.15 Section 6302.15 Public Lands... disturb natural resources such as rocks and plants in wilderness areas? (a) You may remove or disturb natural resources for non-commercial purposes in wilderness areas, including prospecting, provided—...

  3. Where microorganisms meet rocks in the Earth's Critical Zone

    NASA Astrophysics Data System (ADS)

    Akob, D. M.; Küsel, K.

    2011-12-01

    The Critical Zone (CZ) is the Earth's outer shell where all the fundamental physical, chemical, and biological processes critical for sustaining life occur and interact. As microbes in the CZ drive many of these biogeochemical cycles, understanding their impact on life-sustaining processes starts with an understanding of their biodiversity. In this review, we summarize the factors controlling where terrestrial CZ microbes (prokaryotes and micro-eukaryotes) live and what is known about their diversity and function. Microbes are found throughout the CZ, down to 5 km below the surface, but their functional roles change with depth due to habitat complexity, e.g. variability in pore spaces, water, oxygen, and nutrients. Abundances of prokaryotes and micro-eukaryotes decrease from 1010 or 107 cells g soil-1 or rock-1, or ml water-1 by up to eight orders of magnitude with depth. Although symbiotic mycorrhizal fungi and free-living decomposers have been studied extensively in soil habitats, where they occur up to 103 cells g soil-1, little is known regarding their identity or impact on weathering in the deep subsurface. The relatively low abundance of micro-eukaryotes in the deep subsurface suggests that they are limited in space, nutrients, are unable to cope with oxygen limitations, or some combination thereof. Since deep regions of the CZ have limited access to recent photosynthesis-derived carbon, microbes there depend on deposited organic material or a chemolithoautotrophic metabolism that allows for a complete food chain, independent from the surface, although limited energy flux means cell growth may take tens to thousands of years. Microbes are found in all regions of the CZ and can mediate important biogeochemical processes, but more work is needed to understand how microbial populations influence the links between different regions of the CZ and weathering processes. With the recent development of "omics" technologies, microbial ecologists have new methods that

  4. 77 FR 54811 - Safety Zone; TriRock San Diego, San Diego Bay, San Diego, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-06

    .... SUPPLEMENTARY INFORMATION: Table of Acronyms DHS Department of Homeland Security FR Federal Register NPRM Notice... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; TriRock San Diego, San Diego Bay, San Diego... Competitor Group is sponsoring the TriRock Triathlon, consisting of 2000 swimmers swimming a...

  5. 77 FR 50916 - Safety Zone; Boston Harbor's Rock Removal Project, Boston Inner Harbor, Boston, MA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-23

    ... INFORMATION: Table of Acronyms DHS Department of Homeland Security FR Federal Register NPRM Notice of Proposed... SECURITY Coast Guard 33 CFR Part 165 RIN 1625-AA00 Safety Zone; Boston Harbor's Rock Removal Project... Engineers rock removal project. Entering into, transiting through, mooring or anchoring within this...

  6. Multiscale model for predicting shear zone structure and permeability in deforming rock

    NASA Astrophysics Data System (ADS)

    Cleary, Paul W.; Pereira, Gerald G.; Lemiale, Vincent; Piane, Claudio Delle; Clennell, M. Ben

    2016-04-01

    A novel multiscale model is proposed for the evolution of faults in rocks, which predicts their internal properties and permeability as strain increases. The macroscale model, based on smoothed particle hydrodynamics (SPH), predicts system scale deformation by a pressure-dependent elastoplastic representation of the rock and shear zone. Being a continuum method, SPH contains no intrinsic information on the grain scale structure or behaviour of the shear zone, so a series of discrete element method microscale shear cell models are embedded into the macroscale model at specific locations. In the example used here, the overall geometry and kinematics of a direct shear test on a block of intact rock is simulated. Deformation is imposed by a macroscale model where stresses and displacement rates are applied at the shear cell walls in contact with the rock. Since the microscale models within the macroscale block of deforming rock now include representations of the grains, the structure of the shear zone, the evolution of the size and shape distribution of these grains, and the dilatancy of the shear zone can all be predicted. The microscale dilatancy can be used to vary the macroscale model dilatancy both spatially and temporally to give a full two-way coupling between the spatial scales. The ability of this model to predict shear zone structure then allows the prediction of the shear zone permeability using the Lattice-Boltzmann method.

  7. Deformation and fluid flow during fault zone development in granitic rocks

    SciTech Connect

    Pollard, D.D.; Buergmann, R.; Christiansen, P.P. . Geology Dept.); Martel, S.J. )

    1992-01-01

    Fault zone development in crystalline rock of the Lake Edison granodiorite, Sierra Nevada, California, is characterized by five stages with distinct physical mechanisms, each identified by outcrop mapping, and understood through mechanical analysis. Because fluid flow through the developing fault system can influence the rock properties and loading, and because rock fracturing can influence the fluid pathways, the phenomena of deformation and fluid flow are closely coupled. Both the faulting mechanisms and the evolution of permeability in crystalline rocks are demonstrably different from fault zones in porous sedimentary rocks. The paper describes the five stages of fault development. Deformation of the adjacent granodiorite at each stage of growth for a particular fault zone depended on the distribution of slip. This distribution is a function of the remote stress state, the constitutive rock properties, the geometry of the fault surfaces, and their frictional properties. Simple forward models, using elasticity theory, illustrate how the displacement distributions can vary with remote loading, friction, and geometry. Inverse methods provide the analytical tools to deduce these variables from outcrop data, but their implementation awaits a credible model that couples the fluid flow and rock deformation.

  8. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    USGS Publications Warehouse

    Sweetkind, Donald S.; Drake II, Ronald M.

    2007-01-01

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  9. Characteristics of Fault Zones in Volcanic Rocks Near Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    Donald Sweetkind; Ronald M. Drake II

    2007-11-27

    During 2005 and 2006, the USGS conducted geological studies of fault zones at surface outcrops at the Nevada Test Site. The objectives of these studies were to characterize fault geometry, identify the presence of fault splays, and understand the width and internal architecture of fault zones. Geologic investigations were conducted at surface exposures in upland areas adjacent to Yucca Flat, a basin in the northeastern part of the Nevada Test Site; these data serve as control points for the interpretation of the subsurface data collected at Yucca Flat by other USGS scientists. Fault zones in volcanic rocks near Yucca Flat differ in character and width as a result of differences in the degree of welding and alteration of the protolith, and amount of fault offset. Fault-related damage zones tend to scale with fault offset; damage zones associated with large-offset faults (>100 m) are many tens of meters wide, whereas damage zones associated with smaller-offset faults are generally a only a meter or two wide. Zeolitically-altered tuff develops moderate-sized damage zones whereas vitric nonwelded, bedded and airfall tuff have very minor damage zones, often consisting of the fault zone itself as a deformation band, with minor fault effect to the surrounding rock mass. These differences in fault geometry and fault zone architecture in surface analog sites can serve as a guide toward interpretation of high-resolution subsurface geophysical results from Yucca Flat.

  10. Swirling flow can suppress monocyte adhesion in the flow disturbance zones of the endovascular stent.

    PubMed

    Chen, Zengsheng; Zhang, Xiwen; Deng, Xiaoyan

    2012-01-01

    Adhesion of monocytes (U-937 cells) along a silicone tube deployed with circular ring stents was studied to test the hypothesis that by intentionally inducing swirling flow in an endovascular stent, the adhesion of monocytes would be suppressed. The results revealed that under a normal flow condition, the flow disturbance created by the circular ring stents enhanced the adhesion of U-937 cells in the silicone tube. By inducing a swirling flow in the silicone tube, the average wall shear stress (WSS) in the tube with the circular ring stents was elevated and significantly suppressed the adhesion density of U-937 cells to the surface in the disturbed flow zones to a level equal to that when no stents were deployed in the tube. The results also showed that, due to the attenuation of the swirling flow along the tube, the adhesion density of U-937 cells increased monotonically along the tube, indicating that the adhesion density was negatively correlated with the strength of the swirling flow. Thus, the present study suggests that intentionally introducing swirling flow in an artery deployed with stents may be a solution to solve the problem of stent restenosis by restraining the adhesion of monocytes. PMID:23380900

  11. Thermo-physical rock properties of greywacke basement rock and intrusive lavas from the Taupo Volcanic Zone, New Zealand

    NASA Astrophysics Data System (ADS)

    Mielke, P.; Weinert, S.; Bignall, G.; Sass, I.

    2016-09-01

    Greywacke of the Waipapa and Torlesse (Composite) Terrane form the basement of the Taupo Volcanic Zone (TVZ), New Zealand. Together with inferred buried lavas, domes and igneous complexes they are likely to be the dominant rock type prevailing at depths > 4 km beneath the TVZ. A fundamental understanding of the rock properties of the deep formations is of utmost importance for the exploration of deep unconventional geothermal resources. An outcrop analogue study was conducted to improve the understanding of the thermo-physical rock properties of likely deep buried rock formations beneath the TVZ. A total of 145 core samples were taken at 10 locations inside and outside the TVZ and their grain and bulk density, porosity, matrix permeability, bulk thermal conductivity and specific heat capacity, and the compressional and shear wave velocities measured on oven-dry samples. Additional tests of the unconfined compressive strength were conducted for selected greywacke samples to quantify their mechanical rock strength. The obtained data indicates that the thermo-physical rock properties are mainly controlled by porosity, and minor by mineralogy, texture and grain size. Samples from Waipapa-type and Torlesse-type greywacke exhibit minor rheological differences, with Waipapa-type greywacke having lowest porosity (about 1% vs. 3%) and highest bulk thermal conductivity (2.5 W m- 1 K- 1 vs. 1.7 W m- 1 K- 1) and specific heat capacity (0.8 kJ kg- 1 K- 1 vs. 0.7 kJ kg- 1 K- 1). Matrix permeability is < 1E-16 m2 for all greywacke samples. Tested lavas exhibit heterogeneous rock properties due to their wide range of porosity (< 1% up to 32%). The thermo-physical rock properties were tested at laboratory conditions (ambient temperature and pressure), which do not reflect the in situ conditions at greater depth. With depth, thermal conductivity and acoustic wave velocity are likely to decrease caused by micro fractures resulting from thermal cracking of the rock, while specific

  12. Saturated Zone Plumes in Volcanic Rock: Implications for Yucca Mountain

    SciTech Connect

    S. Kelkar; R. Roback; B. Robinson; G. Srinivasan; C. Jones; P. Reimus

    2006-02-14

    This paper presents a literature survey of the occurrences of radionuclide plumes in saturated, fractured rocks. Three sites, Idaho National laboratory, Hanford, and Oak Ridge are discussed in detail. Results of a modeling study are also presented showing that the length to width ratio of a plume starting within the repository footprint at the Yucca Mountain Project site, decreases from about 20:1 for the base case to about 4:1 for a higher value of transverse dispersivity, indicating enhanced lateral spreading of the plume. Due to the definition of regulatory requirements, this lateral spreading does not directly impact breakthrough curves at the 18 km compliance boundary, however it increases the potential that a plume will encounter reducing conditions, thus significantly retarding the transport of sorbing radionuclides.

  13. Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

    NASA Astrophysics Data System (ADS)

    Ujiie, Kohtaro; Kimura, Gaku

    2014-12-01

    Subduction earthquakes on plate-boundary megathrusts accommodate most of the global seismic moment release, frequently resulting in devastating damage by ground shaking and tsunamis. As many earthquakes occur in deep-sea regions, the dynamics of earthquake faulting in subduction zones is poorly understood. However, the Integrated Ocean Drilling Program (IODP) Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) and fault rock studies in accretionary prisms exhumed from source depths of subduction earthquakes have greatly improved our understanding of earthquake faulting in subduction zones. Here, we review key advances that have been made over the last decade in the studies of fault rocks and in laboratory experiments using fault zone materials, with a particular focus on the Nankai Trough subduction zone and its on-land analog, the Shimanto accretionary complex in Japan. New insights into earthquake faulting in subduction zones are summarized in terms of the following: (1) the occurrence of seismic slip along velocity-strengthening materials both at shallow and deep depths; (2) dynamic weakening of faults by melt lubrication and fluidization, and possible factors controlling coseismic deformation mechanisms; (3) fluid-rock interactions and mineralogical and geochemical changes during earthquakes; and (4) geological and experimental aspects of slow earthquakes.

  14. Alleghanian development of the Goat Rock fault zone, southernmost Appalachians: Temporal compatibility with the master decollement

    SciTech Connect

    Steltenpohl, M.G. ); Goldberg, S.A. ); Hanley, T.B. ); Kunk, M.J. )

    1992-09-01

    The Goat Rock and associated Bartletts Ferry fault zones, which mark the eastern margin of the Pine Mountain Grenville basement massif, are controversial due to the suggestion that they are rare exposed segments of the late Paleozoic southern Appalachian master decollement. The controversy in part stems from reported middle Paleozoic (Acadian) radiometric dates postulated as the time of movement along these fault zones. Ultramylonite samples from the type area at Goat Rock Dam yield a 287 [plus minus] 15 Ma Rb-Sr isochron interpreted as the time of Sr isotopic rehomgenization during mylonitization. This date is corroborated by Late Pennsylvanian-Early Permian [sup 40]Ar/[sup 39]Ar mineral ages on hornblende (297-288 Ma) and muscovite (285-278 Ma) from neomineralized and dynamically recrystallized rocks within and straddling the fault zone. These Late Pennsylvanian-Early Permian dates indicate the time of right-slip movement (Alleghenian) along the Goat Rock fault zone, which is compatible with the timing suggested by COCORP for thrusting along the southern Appalachian master decollement.

  15. Significance of fracture rim zone heterogeneity for tracer transport in crystalline rock

    NASA Astrophysics Data System (ADS)

    Cvetkovic, V.

    2010-03-01

    Conducting fractures of crystalline rock are typically altered over long periods of time. The fracture rim zone, a result of these alterations, will as a rule have different physical and chemical properties from the unaltered ("fresh") rock, depending on various microscopic and macroscopic factors of the alterations. In this paper, we study the impact of rim zone heterogeneity, exemplified by a decreasing porosity trend as inferred from the Äspö Hard Rock Laboratory site (Sweden), on short- and long-term tracer transport. Our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales. The findings of this work lend further support to the interpretation of the relatively strong retention reported by Cvetkovic et al. The fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent.

  16. Mapping of hydrothermal alternation zones and regional rock types using computer enhanced ERTS MSS images. [Nevada

    NASA Technical Reports Server (NTRS)

    Rowan, L. C.; Wetlaufer, P. H.; Billingsley, F. C.; Goetz, A. F. H.

    1974-01-01

    A combination of digital computer processing and color compositing of ERTS MSS images has been used to map hydrothermal alternation zones and regional rock types in south-central Nevada. The technique is based on enhancement of subtle visible and near infrared reflectivity differences between mineralogically dissimilar rocks, especially unaltered and altered rocks. MSS spectral bands are ratioed, pixel by pixel, in the computer and subsequently stretched. These ratio values are used to produce a new black and white image which shows the subtle spectral reflectivity differences. Additional enhancement is achieved by preparing color composites of two or more stretched ratio images. The choice of MSS bands for rationing depends on the spectral reflectance properties of the rocks to be discriminated. Although this technique is in the initial stage of development and is untested in other areas, it already appears to have considerable potential for targeting mineral prospects and for regional geologic mapping.

  17. Synthesis of Concepts in Disturbance Hydrology and the Importance for Hydrologic Response to Extreme Hydroclimatic Events in the Critical Zone

    NASA Astrophysics Data System (ADS)

    Ebel, B. A.; Mirus, B. B.

    2014-12-01

    The watersheds we rely on for water resources, ecosystem services, and protection from hydrologically driven natural hazards are increasingly impacted by landscape disturbance. Abrupt alterations of hydrologic processes resulting from wildfires, urban development, resource extraction, deforestation, hurricanes, tsunamis, and landslides change the storage or buffering capacity as well as the hydrologic functional connectivity in watersheds. We highlight some of the critical issues and major challenges to predicting disturbance impacts on water resources and natural hazards and outline some of the opportunities for improved mechanistic understanding of how disturbances propagate through landscape hydrological processes. In particular, we emphasize synthesis of conceptual commonalities and opportunities from other disciplines, primarily ecologic sciences, which are well versed in the study of disturbed landscapes. Cross scale interactions and complex adaptive systems theory are examples of useful concepts for synthesis across different disturbance effects. We also highlight the importance of improved understanding of disturbance hydrology for predicting the effects of extreme hydroclimatic events on the hydrologic response of the Critical Zone. An example from the Front Range of the Rocky Mountains, USA of a watershed with multiple disturbances subjected to a low frequency extreme rainfall event is presented to show the diversity of runoff generation mechanisms and the implications for watershed scale impacts.

  18. Multiple-Code BenchMaek Simulation Stidy of Coupled THMC Processes IN the EXCAVATION DISTURBED ZONE Associated with Geological Nuclear Waste Repositories

    SciTech Connect

    J. Rutqvist; X. Feng; J. Hudson; L. Jing; A. Kobayashi; T. Koyama; P.Pan; H. Lee; M. Rinne; E. Sonnenthal; Y. Yamamoto

    2006-05-08

    An international, multiple-code benchmark test (BMT) study is being conducted within the international DECOVALEX project to analyze coupled thermal, hydrological, mechanical and chemical (THMC) processes in the excavation disturbed zone (EDZ) around emplacement drifts of a nuclear waste repository. This BMT focuses on mechanical responses and long-term chemo-mechanical effects that may lead to changes in mechanical and hydrological properties in the EDZ. This includes time-dependent processes such as creep, and subcritical crack, or healing of fractures that might cause ''weakening'' or ''hardening'' of the rock over the long term. Five research teams are studying this BMT using a wide range of model approaches, including boundary element, finite element, and finite difference, particle mechanics, and elasto-plastic cellular automata methods. This paper describes the definition of the problem and preliminary simulation results for the initial model inception part, in which time dependent effects are not yet included.

  19. Where microorganisms meet rocks in the Earth's Critical Zone

    NASA Astrophysics Data System (ADS)

    Akob, D. M.; Küsel, K.

    2011-03-01

    The Earth's Critical Zone (CZ) is the critical, outer shell of the Earth that provides an arena for the interplay of diverse physical, chemical, and biological processes that are fundamental for sustaining life. As microbes are the principle drivers of biogeochemical cycles, it is necessary to understand the biodiversity of the CZ unseen majority and their impact on life-sustaining processes. This review aims to summarize the factors controlling where microbes (prokaryotes and micro-eukaryotes) live within the CZ and what is known to date about their diversity and function. Microbes live in all regions of the CZ down to 5 km depth, but due to changing habitat complexity, e.g., variability in pore spaces, water, oxygen, and nutrients, their functional role changes with depth. The abundance of prokaryotes and micro-eukaryotes decreases from a maximum of 1010 or 107 cells g soil-1 up to eight orders of magnitude with depth. Symbiotic mycorrhizal fungi and free-living decomposers are best understood in soil habitats, where they are up to 103 cells g soil-1. However, little is known about their identity and impact on weathering in the deep subsurface. The relatively low abundance of micro-eukaryotes in the deep subsurface suggests that these organisms are either limited in space or nutrients or unable to cope with oxygen limitations. Since deep regions of the CZ are limited in the recent input of photosynthesis-derived carbon, microbes are dependent on deposited organic material or on chemolithoautotrophic metabolism that allows for the establishment of a complete food chain independent from the surface. However, the energy flux available might only allow cell growth over tens to thousands of years. The recent development of "omics" technologies has provided microbial ecologists with methods to link the composition and function of in situ microbial communities. We should expect new metabolic discoveries as we have a closer look utilizing a polyphasic approach into the

  20. Characterising and modelling the excavation damaged zone (EDZ) in crystalline rock in the context of radioactive waste disposal

    SciTech Connect

    Hudson, J.A.; Backstrom, A.; Rutqvist, J.; Jing, L.; Backers, T.; Chijimatsu, M.; Christiansson, R.; Feng, X.-T.; Kobayashi, A.; Koyama, T.; Lee, H.-S.; Neretnieks, I.; Pan, P.Z.; Rinne, M.; Shen, B.-T.

    2008-10-01

    This paper describes current knowledge about the nature of and potential for thermo-hydro-mechanical-chemical modelling of the Excavation Damaged Zone (EDZ) around the excavations for an underground radioactive waste repository. In the first part of the paper, the disturbances associated with excavation are explained, together with reviews of Workshops that have been held on the subject. In the second part of the paper, the results of a DECOVALEX research programme on modelling the EDZ are presented. Four research teams used four different models to simulate the complete stress-strain curve for Avro granite from the Swedish Aespoe Hard Rock Laboratory. Subsequent research extended the work to computer simulation of the evolution of the repository using a 'wall block model' and a 'near-field model'. This included assessing the evolution of stress, failure and permeability and time dependent effects during repository evolution. As discussed, all the computer models are well suited to sensitivity studies for evaluating the influence of their respective supporting parameters on the complete stress-strain curve for rock and for modelling the EDZ.

  1. Possible detachment zone in Precambrian rocks of Kanjamalai Hills, Cauvery Suture Zone, Southern India: Implications to accretionary tectonics

    NASA Astrophysics Data System (ADS)

    Mohanty, D. P.; Chetty, T. R. K.

    2014-07-01

    Existence of a possible detachment zone at Elampillai region, NW margin of Kanjamalai Hills, located in the northern part of Cauvery Suture Zone (CSZ), Southern India, is reported here for the first time. Detailed structural mapping provides anatomy of the zone, which are rarely preserved in Precambrian high grade terranes. The detachment surface separates two distinct rock units of contrasting lithological and structural characters: the upper and lower units. The detachment zone is characterized by a variety of fold styles with the predominance of tight isoclinal folds with varied plunge directions, limb rotations and the hinge line variations often leading to lift-off fold like geometries and deformed sheath folds. Presence of parasitic folding and associated penetrative strains seem to be controlled by differences in mechanical stratigraphy, relative thicknesses of the competent and incompetent units, and the structural relief of the underlying basement. Our present study in conjunction with other available geological, geochemical and geochronological data from the region indicates that the structures of the detachment zone are genetically related to thrust tectonics forming a part of subduction-accretion-collision tectonic history of the Neoproterozoic Gondwana suture.

  2. Ultrasonic probing of the fracture process zone in rock using surface waves

    NASA Technical Reports Server (NTRS)

    Swanson, P. L.; Spetzler, H.

    1984-01-01

    A microcrack process zone is frequently suggested to accompany macrofractures in rock and play an important role in the resistance to fracture propagation. Attenuation of surface waves propagating through mode I fractures in wedge-loaded double-cantilever beam specimens of Westerly granite has been recorded in an attempt to characterize the structure of the fracture process zone. The ultrasonic measurements do not support the generally accepted model of a macroscopic fracture that incrementally propagates with the accompaniment of a cloud of microcracks. Instead, fractures in Westerly granite appear to form as gradually separating surfaces within a zone having a width of a few millimeters and a length of several tens of millimeters. A fracture process zone of this size would necessitate the use of meter-sized specimens in order for linear elastic fracture mechanics to be applicable.

  3. Of Rock Damage and the Regolith Conveyor Belt: A Geomorphologist's View of the Critical Zone

    NASA Astrophysics Data System (ADS)

    Anderson, R. S.; Anderson, S. P.; Tucker, G. E.

    2011-12-01

    Models of hillslope evolution require rules for the rate of detachment of rock into the mobile regolith layer, for the rate of mobile regolith transport, and for channel incision or aggradation rates that serve as boundary conditions. The evolution of material as it passes through the weathered zone is typically ignored, making it difficult to cast proper rules for production of mobile regolith. The current rules are therefore insufficient to address critical zone evolution, in which the chemical, mechanical, and hydrologic properties of the rock and the regolith matter. These properties evolve as rock is weathered during exhumation, and they continue to evolve as particles ride the conveyor belt of mobile regolith downslope. Models that honor specific processes involved in the evolution of rock as it passes through the CZ will both advance models of landscape evolution, and provide context for ecological and hydrological investigations. Physical processes responsible for progressive damage of rock during exhumation in the current CZOs include frost cracking and tree root cracking. If we define damage as the density of flaws within the rock, we require rules governing the rate of generation of new flaws, which will vary with climate, depth, and the present state of damage. We envision a "damage-limited system" in which the likelihood of release of rock fragments into mobile regolith depends on the accumulated damage in the subjacent rock. In most temperate and alpine settings relevant to the present CZOs, the ratio of a rock's residence time in the damage zone to the duration of a climate oscillation is such that a rock parcel will experience the full spectrum of Quaternary climates. This requires that we address both climate history and the damage and transport rates associated with all Quaternary climates. We present numerical models for rock damage, mobile regolith production, and hillslope profile evolution. These models are motivated by the Boulder Creek CZO

  4. The Bolivian source rocks: Sub Andean Zone-Madre de Dios-Chaco

    SciTech Connect

    Moretti, I.; Montemurro, G.; Aguilera, E.; Perez, M.; Martinez, E.Diaz

    1996-08-01

    A complete study of source rocks has been carried out in the Bolivian foothills and foreland (Sub Andean Zone, Chaco and Madre de Dios) in order to quantify the petroleum potential of the area. Besides the classical mid-Devonian source rocks (Tequeje Formation in the north, Limoncito Formation in the center and Los Monos Formation in the south), others are important: the Tomachi Formation (late Devonian) in the north and the Copacabana Formation (Upper Carboniferous-lower Permian) in the northern Sub Andean Zone. Both show an excellent potential with S{sub 2} over 50 mg HC/g and average values higher than 10 mg HC/g over few hundred meters. The Latest Cretaceous Flora Formation present locally a high potential but is very thin. Almost all the source rocks matured during the Neogene due to the subsidence in the Andean foreland and in the piggyback basins, and are thus involved on the current petroleum system. Silurian and Lower Paleozoic units also contain thick shale beds, but these source rocks were mature before the Jurassic in the south of the country. In the center, the Silurian is not nowadays overmature and may play an important role. The different zones are compared based on their Source Potential Index which indicates that the richest areas are the northern Sub Andean Zone and the Madre de Dios basin with SPI greater than 10 t/m{sup 2}. Since these two areas remain almost unexplored, these results allow us to be optimistic about the possibilities for future exploration.

  5. Possible emplacement of crustal rocks into the forearc mantle of the Cascadia Subduction Zone

    USGS Publications Warehouse

    Calvert, A.J.; Fisher, M.A.; Ramachandran, K.; Trehu, A.M.

    2003-01-01

    Seismic reflection profiles shot across the Cascadia forearc show that a 5-15 km thick band of reflections, previously interpreted as a lower crustal shear zone above the subducting Juan de Fuca plate, extends into the upper mantle of the North American plate, reaching depths of at least 50 km. In the extreme western corner of the mantle wedge, these reflectors occur in rocks with P wave velocities of 6750-7000 ms-1. Elsewhere, the forearc mantle, which is probably partially serpentinized, exhibits velocities of approximately 7500 ms-1. The rocks with velocities of 6750-7000 ms-1 are anomalous with respect to the surrounding mantle, and may represent either: (1) locally high mantle serpentinization, (2) oceanic crust trapped by backstepping of the subduction zone, or (3) rocks from the lower continental crust that have been transported into the uppermost mantle by subduction erosion. The association of subparallel seismic reflectors with these anomalously low velocities favours the tectonic emplacement of crustal rocks. Copyright 2003 by the American Geophysical Union.

  6. Rock Magnetic Study in the Methanogenesis Zone, Site U1437, IODP Exp 350, Izu Rear Arc

    NASA Astrophysics Data System (ADS)

    Kars, M. A. C.; Musgrave, R. J.; Kodama, K.; Jonas, A. S.

    2015-12-01

    In 2014, IODP Expedition 350 drilled a 1806.5 m deep hole at Site U1437 in the Izu Bonin rear arc. The Site presents an unusual deep methanogenesis zone because of a release of sulfate below the sulfate reduction zone (27-83 mbsf) which may buffer methanogenesis by anaerobic methanogens. Methane abundance gradually increases with depth, with significant abundance at ~750-1459 mbsf with a maximum value at 920 mbsf. The rock magnetic study carried out in Hole U1437D from ~775 to ~1000 mbsf shows a drastic change of the magnetic properties at ~850 mbsf coincidently with a stronger release of methane from < 60 ppm at 841 mbsf to ~300 ppm at 854 mbsf. That also corresponds to a depth interval where no core was recovered (~846-854 mbsf). For the sake of clarity, we call hereafter zone A the depth interval above this non-recovered interval (775-846 mbsf) and zone B the interval below (854-1000 mbsf). Both belong to the same lithostratigraphic unit composed of tuffaceous mudstones intercalated with volcanoclastics. In the zone A, NRM, magnetic susceptibility, ARM, SIRM, HIRM display high values. In the zone B, these parameters show much lower values of one order of magnitude less, except for the interval 936-950 mbsf that corresponds to a local maximum (but still lower values than the zone A). Besides, the rock magnetic parameters for grain size and coercivity, such as ARM/χ, S-ratio and Bcr do not show any variations throughout the entire studied interval, although S-ratio displays slightly lower values from ~850 to ~930 mbsf. Grains are low coercivity pseudo-single domain sized. According to the present data, two preliminary hypotheses can be proposed to explain the observations. 1) The non-recovered interval between the zones A and B can be caused by the presence of a sedimentary hiatus and/or a fault, which may be consistent with the observed change in sedimentation rate. 2) No hiatus in the sedimentation. The changes in the magnetic properties can be explained by a

  7. Physical property characterization of a damage zone in granitic rock - Implications for geothermal reservoir properties

    NASA Astrophysics Data System (ADS)

    Wenning, Quinn; Madonna, Claudio; Amann, Florian; Gischig, Valentin; Burg, Jean-Pierre

    2016-04-01

    Geothermal energy offers a viable alternative to mitigate greenhouse gas emitting energy production. A tradeoff between less expensive drilling costs and increased permeability at shallow depths versus increased heat production at deeper depths stipulates the economic energy potential of a given reservoir. From a geological perspective, successful retrieval of geothermal energy from the subsurface requires sufficient knowledge of the structural and stratigraphic relationship of the target formations, which govern the thermal conditions, physical properties, and fluid flow properties of reservoir rocks. In Switzerland, deep basement rocks (~5 km) with fluid conducting damage zones and enhanced fractured systems stimulated by hydraulic shearing are seen as a potential geothermal reservoir system. Damage zones, both natural and induced, provide permeability enhancement that is especially important for creating fluid conductivity where the matrix permeability is low. This study concentrates on characterizing the elastic and transport properties entering into a natural damage zone penetrated by a borehole at the Grimsel underground research laboratory. The borehole drilled from a cavern at 480 m below ground surface penetrates approximately 20 m of mostly intact Grimsel granodiorite before entering the first phyllosilicate-rich shear zone (~0.2 m thick). The borehole intersects a second shear zone at approximately 23.8m. Between the two shear zones the Grimsel granodiorite is heavily fractured. The minimum principle stress magnitude from in-situ measurements decreases along the borehole into the first shear zone. Two mutually perpendicular core samples of Grimsel granodiorite were taken every 0.1 m from 19.5 to 20.1 m to characterize the physical properties and anisotropy changes as a gradient away from the damage zone. Measurements of ultrasonic compressional (Vp) and shear (Vs) velocities at 1 MHz frequency are conducted at room temperature and hydrostatic pressures

  8. Geochemical evolution of a fractured zone in the cap rock of an underground carbon storage site

    NASA Astrophysics Data System (ADS)

    Vialle, S.; Druhan, J. L.; Maher, K.

    2013-12-01

    Assessment and management of environmental risks associated with underground storage of CO2 in geological systems is essential for the commercial deployment of this technology. A major risk is leakage of the CO2 from its storage reservoir, through wellbores, and along faults and fractures in the cap rock. The geochemical reactions likely to take place as CO2 leaks through a damage zone and their impact on cap rock integrity still need to be better understood and quantified. Should CO2 leakage occur, geochemical reactions would govern the environmental impact on shallow groundwater aquifers and could provide an indication of the leak prior to surface-based monitoring techniques. We used the reactive transport code TOUGH2/TOUGHREACT to model a leakage scenario through a fractured cap rock. Since geochemical reactions will strongly depend upon the local hydrodynamics of the CO2 leak, the first step of the study is to provide an appropriate physical representation of fluid flow through the system. Typically, for a low porosity rock formation, a fault/damaged zone system is composed of a core of low permeability and a damage zone with second-order fractures whose density decreases with distance from the fault core. Permeability is thus increased along the fault plane and laterally decreases down to the permeability value of the undamaged cap rock. Appropriate scaling relationships (e.g., and analytical expression of for permeability as a function of fracture aperture and fracture density), effective physical parameters as well as constitutive relationships are carefully chosen to model the fractured system, treated as an equivalent porous medium. The cap rock is initially saturated with brine (salinity of 0.15 in mass fraction) and due to overpressure in the lower storage reservoir, CO2 migrates through the damage zone. Geochemical reactions involve both salt precipitation due to the partitioning of H2O and CO2 between liquid and gas phases as well as well reactions

  9. Ultramafic rocks of the western Idaho suture zone: Asbestos Peak and Misery Ridge

    SciTech Connect

    Godchaux, M.M. . Dept. of Geology); Bonnichsen, B. )

    1993-04-01

    The Western Idaho Ultramafic Belt extends northward from the town of Weiser to the northern end of Dworshak Reservoir; in its northern portion most of the ultramafic bodies are localized along the suture zone where the Mesozoic oceanic accreted terranes meet the continental craton. Of the twenty bodies investigated, all are small, all are in fault contact with their metavolcanic and metasedimentary host rocks, all have been metamorphosed, and all display deformational fabrics in at least some portion of the outcrop area, suggesting that deformation continued after peak metamorphism. The degree of metamorphism ranges from incipient serpentinization to attainment of equilibrium in the upper amphibolite facies. Some bodies have been intruded by granitic dikes or pegmatite veins after emplacement, and have locally undergone contact metasomatism. Two particularly complex bodies, Asbestos Peak and Misery Ridge, were chosen for detailed petrographic and chemical study. Asbestos Peak is composed mostly of decussate anthophyllite-talc rock containing isolated patches of harzburgite protolith, and has blackwall border zones. Misery Ridge is composed mostly of coarse-grained sheared tremolite-talc schist without remnant protolith, and lacks true blackwall zones. Both bodies exhibit an unusual and enigmatic hornblende-poikiloblastic garnet-green spinel-skeletal ilmenite assemblage, present in some places as well-defined border zones and in other places as cross-cutting bodies.

  10. Groundwater compatibility with formation water and pay zone rocks in Pervomaysk oil-gas-condensate field to maintain formation pressure

    NASA Astrophysics Data System (ADS)

    Trifonov, N.; Nazarov, A.; Alekseev, S.

    2016-03-01

    The paper describes the research results in determining the compatibility of groundwater from Aptain-Albian-Cenomanian aquifer with formation water and pay zone rocks in U1 layer sediments, Pervomaysk oil field.

  11. Characterizing fractures and shear zones in crystalline rock using seismic and GPR methods

    NASA Astrophysics Data System (ADS)

    Doetsch, Joseph; Jordi, Claudio; Laaksonlaita, Niko; Gischig, Valentin; Schmelzbach, Cedric; Maurer, Hansruedi

    2016-04-01

    Understanding the natural or artificially created hydraulic conductivity of a rock mass is critical for the successful exploitation of enhanced geothermal systems (EGS). The hydraulic response of fractured crystalline rock is largely governed by the spatial organization of permeable fractures. Defining the 3D geometry of these fractures and their connectivity is extremely challenging, because fractures can only be observed directly at their intersections with tunnels or boreholes. Borehole-based and tunnel-based ground-penetrating radar (GPR) and seismic measurements have the potential to image fractures and other heterogeneities between and around boreholes and tunnels, and to monitor subtle time-lapse changes in great detail. We present the analysis of data acquired in the Grimsel rock laboratory as part of the In-situ Stimulation and Circulation (ISC) experiment, in which a series of stimulation experiments have been and will be performed. The experiments in the granitic rock range from hydraulic fracturing to controlled fault-slip experiments. The aim is to obtain a better understanding of coupled seismo-hydro-mechanical processes associated with high-pressure fluid injections in crystalline rocks and their impact on permeability creation and enhancement. GPR and seismic data have been recorded to improve the geological model and characterize permeable fractures and shear zones. The acquired and processed data include reflection GPR profiles measured from tunnel walls, single-borehole GPR images, and borehole-to-borehole and tunnel-to-tunnel seismic and GPR tomograms. The reflection GPR data reveal the geometry of shear zones up to a distance of 30 m from the tunnels and boreholes, but the interpretation is complicated by the geometrical ambiguity around tunnels and boreholes and by spurious reflections from man-made structures such as boreholes. The GPR and seismic traveltime tomography results reveal brittle fractured rock between two ductile shear zones. The

  12. Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure

    NASA Astrophysics Data System (ADS)

    Jeppson, Tamara N.; Bradbury, Kelly K.; Evans, James P.

    2010-12-01

    We examine the relationships between borehole geophysical data and physical properties of fault-related rocks within the San Andreas Fault as determined from data from the San Andreas Fault Observatory at Depth borehole. Geophysical logs, cuttings data, and drilling data from the region 3- to 4-km measured depth of the borehole encompass the active part of the San Andreas Fault. The fault zone lies in a sequence of deformed sandstones, siltstone, shale, serpentinite-bearing block-in-matrix rocks, and sheared phyllitic siltstone. The borehole geophysical logs reveal the presence of a low-velocity zone from 3190 to 3410 m measured depth with Vp and Vs values 10-30% lower than the surrounding rocks and a 1-2 m thick zone of active shearing at 3301-3303 m measured depth. Seven low-velocity excursions with increased porosity, decreased density, and mud-gas kick signatures are present in the fault zone. Geologic data on grain-scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data. In places, Vp and Vs increase with grain-scale deformation and alteration and decrease with porosity in the fault zone. The low-velocity zone is associated with a significant lithologic and structural transition to low-velocity rocks, dominated by phyllosilicates and penetratively foliated, sheared rocks. The zone of active shearing and the regions of low sonic velocity appear to be associated with clay-rich rocks that exhibit fine-scale foliation and higher porosities that may be a consequence of the fault-related shearing of foliated and fine-grained sedimentary rocks.

  13. 77 FR 59551 - Safety Zone, Changes to Original Rule; Boston Harbor's Rock Removal Project, Boston Inner Harbor...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-09-28

    ... Zone; Boston Harbor's Rock Removal Project, Boston Inner Harbor, Boston, MA'' (77 FR 50916). This new... Department of Homeland Security FR Federal Register NPRM Notice of Proposed Rulemaking COTP Captain of the... Rock Removal Project, Boston Inner Harbor, Boston, MA AGENCY: Coast Guard, DHS. ] ACTION:...

  14. 3-D study of texture and elastic anisotropy on rocks from NW Italy Ivrea zone

    NASA Astrophysics Data System (ADS)

    Pros, Z.; Lokajicek, T.; Prikryl, R.; Klima, K.; Nikitin, A. N.; Ivankina, T. I.; Martinkova, M.

    2003-04-01

    The direct measurement of physical properties of lower crustal and upper mantle rocks, which can be found on the Earth's surface, could be used for the improving of our knowledge of deep rocks. These results could be used mainly for the correction of geological and geophysical models based on the indirect data. Elastic properties of rocks are one of the most important parameters studied and could be applied in many fields of Earth sciences. In this study several quite different methods were applied to determine elastic properties. P-wave ultrasonic sounding of mafic and ultrabasic rock samples in 132 independent directions at several levels of confining pressure enable to determine elastic anisotropy of P-wave velocity. The samples were collected in nearby of Balmuccia ultra basic massif (Ivrea zone, southern Alps, NW Italy). This method revealed large directional variance of maximum P-wave velocity and different symmetric (orthorhombic vs. transversal isotropic) of elastic waves 3-D distribution, that has not been found on these rocks before. Identical samples were studied by means of neutron diffraction. Neutron diffraction provide data on CPO orientation in identical spherical samples, on which was measured P-wave velocity. Laboratory 3-D measurement of P-wave velocity thus present powerful method for detection of magmatic fabric features not visible by naked eye. One dunite sample exhibits P-wave velocity approaching to that of olivine crystal 9.8 km/s due to the strong CPO of olivine in this sample. Such observation was not done before on the natural olivine-rich rocks. It follows from the comparison of measured and calculated P-wave velocities, that these values are more reliable than data obtained from measurement in few directions only. This project was supported by Grant Agency of the Czech Republic No.: 205/01/1430.

  15. Pilot study on tracing the rapidly buried rock avalanche deposits within the accumulation zone of glacier

    NASA Astrophysics Data System (ADS)

    Reznichenko, Natalya; Dunning, Stuart; Rosser, Nick; McColl, Sam

    2015-04-01

    Recent studies shown that large mass failure events significantly contribute to the glacial sediment budget and affect its final deposition. However, in accumulation zone these events are exceptionally fast subsumed by snowfall and become ingested into the glacier with no evident surface expression. This leads to poor understanding of the magnitude-frequency of these events and their contribution to the sediment budget of the glaciers. The buried rock avalanches travel as englacial load within the ice that becomes the unique geomorphic horizon, which may constitute a major fraction of total glacial debris supplied to supraglacial cover of many debris-covered glaciers, but usually re-emerging in ablation zones not in a form usable to reconstruct the magnitude-frequency of these events. Here we present a first attempt to detect the rock avalanche deposit within the ice that becomes the unique geomorphic horizon or isochrones. Ground Penetrating Radar (GPR) was applied over the large deposit of well documented in January 2013 Mt. Haast/Dixon rock avalanche in Southern Alps of New Zealand, one year after emplacement. The large deposit 2 x 106 m3 of rock, snow and ice travelled 2.9 km over the northern margins of the Grand Plateau, just 200 m west of Plateau Hut, stalling close to the top of the Hochstetter Icefall, Aoraki/ Mt. Cook. The large deposit was lost to conventional remote sensing within 3 month after the event. In April 2014, at the time of the survey the deposit was entirely buried beneath the snow/firn cover, leaving no topographic expression of the deposit at the snow surface. The buried deposit was visible in crevasses, in the Hochstetter Ice Fall, in the Grand Plateau, and the icefall beneath Mt Haast, at depths estimated to be in the order of 5-10 m. Our subsurface data shows a good preservation of a rock avalanche deposit under about 3-5 m of snow and firn with the thickness broadly consistent along the length of the transect (1-2 m), with a thicker (5

  16. Dissecting Oceanic Detachment Faults: Fault Zone Geometry, Deformation Mechanisms, and Nature of Fluid-Rock Interactions

    NASA Astrophysics Data System (ADS)

    Bonnemains, D.; Escartin, J.; Verlaguet, A.; Andreani, M.; Mevel, C.

    2015-12-01

    To understand the extreme strain localization at long-lived oceanic detachment faults rooting deeply below the axis, we present results of geological investigations at the 13°19'N detachment along the Mid-Atlantic Ridge, conducted during the ODEMAR cruise (Nov-Dec13, NO Pourquoi Pas?) with ROV Victor6000 (IFREMER). During this cruise we investigated and sampled the corrugated fault to understand its geometry, nature of deformation, and links to fluid flow. We identified and explored 7 fault outcrops on the flanks of microbathymetric striations subparallel to extension. These outcrops expose extensive fault planes, with the most prominent ones extending 40-90m laterally, and up to 10 m vertically. These fault surfaces systematically show subhorizontal striations subparallel to extension, and define slabs of fault-rock that are flat and also striated at sample scale. Visual observations show a complex detachment fault zone, with anastomosing fault planes at outcrop scale (1-10 m), with a highly heterogeneous distribution of deformation. We observe heterogeneity in fault-rock nature at outcrop scale. In situ samples from striated faults are primarily basalt breccias with prior green-schist facies alteration, and a few ultramafic fault-rocks that show a complex deformation history, with early schistose textures, brittlely reworked as clasts within the fault. The basalt breccias show variable silicification and associated sulfides, recording important fluid-rock interactions during exhumation. To understand the link between fluid and deformation during exhumation, we will present microstructural observation of deformation textures, composition, and distribution and origin of quartz and sulfides, as well as constraints on the temperature of silicifying fluids from fluid inclusions in quartz. These results allow us to characterize in detail the detachment fault zone geometry, and investigate the timing of silicification relative to deformation.

  17. Ultramafic rocks of a fracture-zone ophiolite, North Cascades, Washington

    NASA Astrophysics Data System (ADS)

    Miller, Robert B.; Mogk, David W.

    1987-11-01

    The Ingalls Complex was deformed in a Late Jurassic oceanic fracture zone. An unusually diverse group of ultramafic tectonites comprise three units in this ophiolite. Unit 1 consists mostly of poorly to moderately foliated harzburgite and dunite characterized by porphyroclastic textures. Irregular-shaped and tabular dunite bodies probably represent intrusive bodies or residues of partial melting. Voluminous Unit 2 consists mostly of poorly to strongly foliated Iherzolite and clinopyroxene-bearing harzburgite, plagioclase peridotite is present locally. Olivine and enstatite generally define equigranular mosaics or weakly porphyroclastic textures. Clinopyroxene, however, in some samples displays only weak deformation, compositional zoning, simple (growth?) twins and interstitial, commonly poikilitic texture. Clinopyroxene and plagioclase in these samples probably formed from a melt after recrystallization of olivine and enstatite, indicating that these Iherzolites are impregnated peridotites. Other Iherzolites and clinopyroxene-bearing harzburgites may represent weakly depleted mantle. Pods of metagabbroic gneiss within Unit 2 probably are small intrusions that were deformed as they cooled. Unit 3 represents a major high-temperature ( 700 °≥ 900 ° C) shear zone that separates Units 1 and 2, and consists of strongly foliated, commonly mylonitic Iherzolites and hornblende peridotites. The latter are the most strongly foliated ultramafites, and olivine in them records stresses as high as 275 MPa. The abundance of hornblende implies a genetic relationship between mylonitization and the hydration and metasomatism necessary to form such rocks from Iherzolites. Mineral chemistry and geothermometry are typical of mantle tectonites in many ophiolites and oceanic fracture zones. There is a particularly strong similarity between the spinels in the Ingalls Complex and the spinels from the Owen and Vema fracture zones. Hornblende in Unit 3 ranges from edenite to edenitic

  18. Geoelectric characteristics of portions of the Raha fault zone and surrounding rocks, Jabal As Silsilah Quadrangle, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Zablocki, Charles J.; Hajnour, M.O.

    1987-01-01

    Telluric-electric and auto-magnetotelluric measurements obtained in and around the Raha fault zone in the Buqaya area indicate that it dips steeply to the southwest. Large contrasts in the electrical properties of Qarnayn and Maraghan metasedimentary rocks located on either side of the fault are characteristic of the rocks within the fault zone. However, no large electrical contrasts were detected along several segments of a southern branch of the main fault in the Shiaila area, indicating that the rocks on either side of the fault are of similar composition. Extremely low resistivity readings in the Buqaya and Shiaila areas are associated with fracturing and clay-bearing gouge that accompany known shear zones. The locations of several shallow plutons have been inferred from these studies, one of which is probably a source of gold-bearing quartz veins in the metasedimentary rocks of the Shiaila area.

  19. Sedimentation, zoning of reservoir rocks in W. Siberian basin oil fields

    SciTech Connect

    Kliger, J.A. )

    1994-02-07

    A line pattern of well cluster spacing was chosen in western Siberia because of taiga, marshes, etc., on the surface. The zoning of the oil pools within productive Upper Jurassic J[sub 3] intervals is complicated. This is why until the early 1990s almost each third well drilled in the Shaimsky region on the western edge of the West Siberian basin came up dry. The results of development drilling would be much better if one used some sedimentological relationships of zoning of the reservoir rocks within the oil fields. These natural phenomena are: Paleobasin bathymetry; Distances from the sources of the clastic material; and Proximity of the area of deposition. Using the diagram in this article, one can avoid drilling toward areas where the sandstone pinch out, area of argillization of sand-stones, or where the probability of their absence is high.

  20. Flow dynamics and potential for biodegradation of organic contaminants in fractured rock vadose zones

    NASA Astrophysics Data System (ADS)

    Geller, J. T.; Holman, H.-Y.; Su, G.; Conrad, M. E.; Pruess, K.; Hunter-Cevera, J. C.

    2000-04-01

    We present an experimental approach for investigating the potential for bioremediation of volatile organic compounds (VOCs) in fractured rock vadose zones. The experimental work was performed with rock samples and indigenous microorganisms from the site of the United States Department of Energy's Idaho National Engineering and Environmental Laboratory (INEEL), located in a basalt flow basin where VOC contamination threatens the Snake River Aquifer. Our approach has four components: (1) establishing a conceptual model for fluid and contaminant distribution in the geologic matrix of interest; (2) identification of important features of liquid distribution by means of seepage experiments in the fracture plane; (3) identification of the presence and activity of microorganisms by non-destructive monitoring of biotransformations on rock surfaces at the micron-scale; and (4) integration of flow and biological activity in natural rock "geocosms". Geocosms are core-scale flow cells that incorporate some aspects of natural conditions, such as liquid seepage in the fracture plane and moisture content. Fluid flow and distribution within fracture networks may be a significant factor in the ability of microorganisms to degrade VOCs, as they affect the availability of substrate, moisture and nutrients. Flow visualization and tracer breakthrough curves in transparent fracture replicas for unsaturated inlet conditions exhibited the channelized and intermittent nature of liquid seepage. The seepage of water and non-aqueous phase liquids (NAPLs) of varying physical and chemical properties into an initially dry replica showed only subtle differences in liquid distribution. In contrast, the seepage of a NAPL into the fracture replica containing residual water resulted in complex trapping of NAPL along the solid/water/air contact lines and diversion of NAPL to previously dry parts of the fracture. We found that a mixed culture of viable bacteria exists on the natural rock surfaces

  1. Dynamics of mantle rock metasomatic transformation in permeable lithospheric zones beneath Siberian craton

    NASA Astrophysics Data System (ADS)

    Sharapov, Victor; Sorokin, Konstantin; Perepechko, Yury

    2015-04-01

    The numerical descriptions of hydrodynamic model of two - velocity heat and mass transfer in permeable zones above the asthenospheric lenses was formulated and solved basing on the study the composition of inclusions in minerals of low crust ultra metamorphic rocks and lithospheric mantle metasomatites and estimation of thermodynamic conditions of the processes. Experimental study of influence of the simulated hot reduced gas flows on the minerals of low crust and mantle xenolith of the Siberian craton platform (SP) give the basic information for this processes. In detail: 1. Thermobarometric study of composition of inclusions in granulite and lithospheric mantle rocks beneath the diamondiferous cratons allowed to estimate the gas phase compositions during the metamorphism and metasomatism as well as products of their re equilibration during decompression. 2. Results of the pilot study of the influence of hot gas impact flows on minerals of mantle xenoliths are taken into account. This allowed to reproduce the elements and heterophase kinetics of interactions within a temperature range of about 300 to 1300o on relative to the interactions between the solid, liquid and gas phases. 3. Correct mathematical two-velocities model of fluid dynamics for compressible multiphase fluid -rock systems. 4. Numerical schemes are simulated and solved for the problems of quantitative description of 2D dynamics behavior of P and T within the permeable zone above the asthenospheric lens. 5. Quantitative description of heterophase non isothermal fluid-rock interaction within the framework of the approximation was obtained on the basis of the parallel solutions of the exchange between the ideal gas flow and solid phase according to the model of multi-reservoir reactors based on minimization of the Gibbs potential. Qualitatively the results of numerical simulation are as follows: 1) appearance in permeable zones of the any composition fluid flows from the upper mantle magma chambers

  2. P-waves imaging of the FRI and BK zones at the Grimsel Rock Laboratory

    SciTech Connect

    Majer, E.L.; Peterson, J.E. Jr. ); Blueming, P.; Sattel, G. )

    1990-08-01

    This report is one of a series documenting the results of the Nagra-DOE Cooperative (NDC-I) research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a rock mass as a geological repository for nuclear waste. Tomographic imaging studies using a high frequency (10 Khz.) piezoelectric source and a three component receiver were carried out in two different regions of the underground Nagra Grimsel test facility in Switzerland. Both sites were in fractured granite, one being in a strongly foliated granite (FRI site), and the other being in a relatively homogeneous granite (BK zone). The object of the work was to determine if the seismic techniques could be useful in imaging the fracture zones and provide information on the hydrologic conditions. Both amplitude and velocity tomograms were obtained from the Data. The results indicate that the fracture zones strongly influenced the seismic wave propagation, thus imaging the fracture zones that were hydrologically important. 11 refs., 24 figs.

  3. Hydraulic sealing due to pressure solution contact zone growth in siliciclastic rock fractures

    NASA Astrophysics Data System (ADS)

    Lang, P. S.; Paluszny, A.; Zimmerman, R. W.

    2015-06-01

    Thermo-hydro-mechanical-chemical simulations at the pore scale are conducted to study the hydraulic sealing of siliciclastic rock fractures as contact zones grow driven by pressure dissolution. The evolving fluid-saturated three-dimensional pore space of the fracture results from the elastic contact between self-affine, randomly rough surfaces in response to the effective confining pressure. A diffusion-reaction equation controls pressure solution over contact zones as a function of their emergent geometry and stress variations. Results show that three coupled processes govern the evolution of the fracture's hydraulic properties: (1) the dissolution-driven convergence of the opposing fracture walls acts to compact the pore space; (2) the growth of contact zones reduces the elastic compression of the pore space; and (3) the growth of contact zones leads to flow channeling and the presence of stagnant zones in the flow field. The dominant early time compaction mechanism is the elastic compression of the fracture void space, but this eventually becomes overshadowed by the irreversible process of pressure dissolution. Growing contact zones isolate void space and cause an increasing disproportion between average and hydraulic aperture. This results in the loss of hydraulic conductivity when the mean aperture is a third of its initial value and the contact ratio approaches the characteristic value of one half. Convergence rates depend on small-wavelength roughness initially and on long-wavelength roughness in the late time. The assumption of a characteristic roughness length scale, therefore, leads to a characteristic time scale with an underestimation of dissolution rates before and an overestimation thereafter.

  4. Petrological and geochemical studies of ultramafic-mafic rocks from the North Puruliya Shear Zone (eastern India)

    NASA Astrophysics Data System (ADS)

    Mandal, Aditi; Ray, Arijit

    2015-12-01

    Ultramafic and mafic rocks occur within a linear belt, trending nearly E-W along North Puruliya Shear Zone of the Chhotanagpur Gneissic Complex (CGC). These rocks are classified as gabbro, norite, gabbro-norite, dolerite, diorite, olivine-websterite and lherzolite. Mafic rocks (Group 1) often occur in association with ultramafic variants (Group 2) and sometimes in isolation. A genetic link has been established between these mafic and ultramafic rocks using disposition of ultramafic and mafic rocks in the outcrop, systematic variation in modal mineralogy, co-linearity of plots in biaxial chemical variation diagram. Chemical composition of biotite and clinopyroxene reveal calc-alkaline nature and arc signature in these mafic-ultramafic rocks and whole rock geochemical characters indicate similarity with arc magma in subduction zone setting. The high values of Mg no. (47-81) and Al 2 O 3 (5.5-17.9) of mafic rocks indicate primitive, aluminous nature of the parental melt and presence of amphibole and biotite indicate its hydrous nature. The parent mafic melt evolved through fractionation of olivine, spinel, clinopyroxene and plagioclase. The crystal cumulates gave rise to the ultramafic rocks and the associated mafic rocks formed from residual melt. Crustal contamination played an important role in magmatic evolution as evident from variation in abundance of Rb in different lithomembers. Mafic-ultramafic rocks of the present study have been compared with intra-cratonic layered complexes, mafic-ultramafic rocks of high grade terrain, Alaskan type ultramafic-mafic complex and ophiolites. It is observed that the ultramafic-mafic rocks of present study have similarity with Alaskan type complex.

  5. Metasomatic reaction bands at the Mt. Hochwart gneiss-peridotite contact (Ulten Zone, Italy): insights into fluid-rock interaction in subduction zones

    NASA Astrophysics Data System (ADS)

    Marocchi, M.; Mair, V.; Tropper, P.; Bargossi, G. M.

    2009-03-01

    We investigated the contact zone between peridotite lenses and host gneisses located on the northern side of the Hochwart peak, also known as Vedetta Alta (Ulten Zone, Alto Adige -Südtirol) where metasomatic contact bands occur. The country rocks are gneisses consisting mainly of quartz, K-feldspar, garnet, kyanite, biotite and muscovite. The ultramafic body consists of a hectometre-sized garnet peridotite and harzburgite lens. The reaction zone shows mineralogic zoning from phlogopite-rich to tremolite-anthophyllite-talc-rich rocks from the host gneiss towards the peridotite. In some cases, lenses of serpentine and talc in association with chlorite, and trondhjemitic pods develop at the ultramafic rocks border to the gneisses. Trondhjemite dikes with pegmatoid texture also crosscut the peridotite body. Phlogopite aggregates with accessory zircon, Cl-apatite and tourmaline and phlogopite-hornblende aggregates also occur. The combination of petrography, mineral chemistry and mass balance calculations constrains the gains and losses of elements during metasomatism. Reaction zone formation involved extensive addition of H2O, K2O and LILE from the fluid, whereas MgO, CaO and Al2O3 were removed from the peridotite. Thus, the formation of the reaction zones between the mantle rocks and the gneisses was triggered by considerable fluid/melt circulation, causing crystallisation of mainly phlogopite, anthophyllite and talc, and the release of a trondhjemitic residual melt. Field mapping provides evidence that the internal structures of the host migmatites (folds) and those of the peridotites (foliation, fluid texture) are discordant. Pseudosection calculations give insights into the P-T conditions (T 660-700°C; P 0.5-0.7 GPa) of metasomatism responsible for the formation of reaction zones, which is related to the retrograde path of the Ulten Zone peridotites. Our results suggest that the redistribution of major and trace elements in subduction zones is strongly influenced

  6. Comparative mineral chemistry and textures of SAFOD fault gouge and damage-zone rocks

    USGS Publications Warehouse

    Moore, Diane E.

    2014-01-01

    Creep in the San Andreas Fault Observatory at Depth (SAFOD) drillhole is localized to two foliated gouges, the central deforming zone (CDZ) and southwest deforming zone (SDZ). The gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-smectite clays that formed as a result of shearing-enhanced reactions between the serpentinite and quartzofeldspathic rocks. The CDZ takes up most of the creep and exhibits differences in mineralogy and texture from the SDZ that are attributable to its higher shearing rate. In addition, a ∼0.2-m-wide sector of the CDZ at its northeastern margin (NE-CDZ) is identical to the SDZ and may represent a gradient in creep rate across the CDZ. The SDZ and NE-CDZ have lower clay contents and larger porphyroclasts than most of the CDZ, and they contain veinlets and strain fringes of calcite in the gouge matrix not seen elsewhere in the CDZ. Matrix clays in the SDZ and NE-CDZ are saponite and corrensite, whereas the rest of the CDZ lacks corrensite. Saponite is younger than corrensite, reflecting clay crystallization under declining temperatures, and clays in the more actively deforming portions of the CDZ have better equilibrated to the lower-temperature conditions.

  7. Deciphering groundwater potential zones in hard rock terrain using geospatial technology.

    PubMed

    Dar, Imran A; Sankar, K; Dar, Mithas A

    2011-02-01

    Remote sensing and geographical information system (GIS) has become one of the leading tools in the field of groundwater research, which helps in assessing, monitoring, and conserving groundwater resources. This paper mainly deals with the integrated approach of remote sensing and GIS to delineate groundwater potential zones in hard rock terrain. Digitized vector maps pertaining to chosen parameters, viz. geomorphology, geology, land use/land cover, lineament, relief, and drainage, were converted to raster data using 23 m×23 m grid cell size. Moreover, curvature of the study area was also considered while manipulating the spatial data. The raster maps of these parameters were assigned to their respective theme weight and class weights. The individual theme weight was multiplied by its respective class weight and then all the raster thematic layers were aggregated in a linear combination equation in Arc Map GIS Raster Calculator module. Moreover, the weighted layers were statistically modeled to get the areal extent of groundwater prospects with respect to each thematic layer. The final result depicts the favorable prospective zones in the study area and can be helpful in better planning and management of groundwater resources especially in hard rock terrains. PMID:20364317

  8. Comparative mineral chemistry and textures of SAFOD fault gouge and damage-zone rocks

    NASA Astrophysics Data System (ADS)

    Moore, Diane E.

    2014-11-01

    Creep in the San Andreas Fault Observatory at Depth (SAFOD) drillhole is localized to two foliated gouges, the central deforming zone (CDZ) and southwest deforming zone (SDZ). The gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-smectite clays that formed as a result of shearing-enhanced reactions between the serpentinite and quartzofeldspathic rocks. The CDZ takes up most of the creep and exhibits differences in mineralogy and texture from the SDZ that are attributable to its higher shearing rate. In addition, a ∼0.2-m-wide sector of the CDZ at its northeastern margin (NE-CDZ) is identical to the SDZ and may represent a gradient in creep rate across the CDZ. The SDZ and NE-CDZ have lower clay contents and larger porphyroclasts than most of the CDZ, and they contain veinlets and strain fringes of calcite in the gouge matrix not seen elsewhere in the CDZ. Matrix clays in the SDZ and NE-CDZ are saponite and corrensite, whereas the rest of the CDZ lacks corrensite. Saponite is younger than corrensite, reflecting clay crystallization under declining temperatures, and clays in the more actively deforming portions of the CDZ have better equilibrated to the lower-temperature conditions.

  9. Rock strength and fault rheology at the Nankai subduction zone: Insight from laboratory experiments

    NASA Astrophysics Data System (ADS)

    Kitajima, H.; Saffer, D. M.; Takahashi, M.; Otsubo, M.

    2015-12-01

    Understanding the wide spectrum of fault slip behaviors observed in continental and subduction faults zones requires investigation of absolute fault strength and fault rheology that are controlled by in-situ stress, strain, pressure, temperature, and chemical conditions. Because the deformation mode and strength of porous rocks are dependent on porosity and effective stress, rapid reduction of sediment porosity from 60-70% to less than 5% should strongly affect deformation style in the shallow portion of subduction zones. Here, we present the results of laboratory experimental studies on modern clay-rich sediments subducting at the Nankai Trough and rocks from the exhumed Shimanto accretionary complex near the Nobeoka thrust, which is an ancient out-of-sequence-thrust, to constrain porosity, rock strength and fault rheology in the Nankai subduction zone. Based on uniaxial and triaxial experiments on mudstones, combined with seismic velocity data from geophysical surveys in the Nankai Trough, estimated porosity along the plate boundary decreases from ~40% at the trench, to ~5% at 50 km from the trench (~8 km depth). This porosity reduction is faster than that expected in a basinal environment, and can be attributed to the effects of horizontal tectonic loading. The phyllites and cataclasites (2-5% porosity) across the Nobeoka thrust fault deform brittlely with a peak strength of 80-90 MPa, followed by strain weakening to residual strengths of 40-60 MPa at effective pressure of 20 MPa and temperature of 250°C. At effective pressure of 120 MPa, on the other hand, they exhibit strain hardening and their strength at 10% strain reaches ~300 MPa. The extrapolation of a brittle-ductile transition for the Nankai mudstones as a function of porosity and confining stress is consistent with the behavior of the ancient prism samples, which serve as an analog for the mechanical behavior of rocks at seismogenic depth in the modern Nankai Trough. These results suggest that as the

  10. Gouge-zone or solid-rock: An experimental view on fault frictional behavior

    NASA Astrophysics Data System (ADS)

    Reches, Z.

    2015-12-01

    Natural faults always include zone(s) of breccia, gouge or cataclasite that localize the slip. In contrast, many rock mechanics experiments are conducted on experimental faults made of rough, solid blocks without fault-rock zones. We experimentally compare the frictional strength of solid experimental faults with fault-zones made of granular material in high-velocity/long-distance runs. The frictional evolution of solid and granular dolomite fault was tested in a rotary apparatus at slip velocity up to 1 m/s and normal stress up to 7 MPa. The granular samples were composed of the 125-250 microns fraction of the crushed dolomite. They were sheared in a confined, rotary cell with continuous monitoring of CO2 and H2O and mechanical data. The tests showed that the granular samples required longer slip-distances and higher velocities to evolve to a frictional strength similar to the solid samples. Yet, both sample types display similar evolution trends, including slip-weakening at velocities above ~0.05 m/s, and drastic velocity-weakening as slip velocity approached 1 m/s. At velocity above 0.3 m/s, a shining principal-slip-zone developed spontaneously with identical microstructure in both solid and granular sample: thickness < 1 micron and sintered, 20-40 nm nano-grains. This development was associated with intense emission of CO2 (Fig. 1). In a similar testing approach and conditions, we tested the friction evolution of granular granite from the San-Andreas fault-zone at Tejon-Pass, CA. These samples remained strong, μ =0.8-0.9, at velocities up to 0.8 m/s and slip-distances up to 3 m, in contrast to known frictional evolution of solid faults made of granite and tonalite. We envision that at the present slip-velocity/normal-stress, the dolomite samples reached a stage of thermally activated phase-transition and associated weakening, whereas the granitic samples were below such transition. Fig. 1. Evolotion of slip-velocity, friction, temperature and CO2 emission in

  11. Rheologic evolution of low-grade metasedimentary rocks and granite across a large strike-slip fault zone: A case study of the Kellyland fault zone, Maine, USA

    NASA Astrophysics Data System (ADS)

    Sullivan, W. A.; Monz, M. E.

    2016-05-01

    We examine a large strike-slip fault zone that juxtaposes low-grade clastic metasedimentary rocks with coarse-grained granite near the brittle-ductile transition. The load-bearing matrixes in granite-derived ultramylonites and pelite and wacke metasedimentary intervals are texturally similar, and all deformed by diffusion-assisted granular flow. Granite underwent rapid strengthening as the pluton cooled followed by rapid weakening driven by brittle grain-size reduction and mixing that catalyzed ultramylonite formation. The textural and mineralogical similarity of pelitic intervals across the zone indicates they experienced little textural and reaction weakening. Wacke intervals record progressive textural and reaction weakening in an open system. Quartz recrystallized grain sizes in granite-derived ultramylonites record ∼2-times more differential stress than those in metasedimentary rocks in the interior of the zone. The relative weakness of metasedimentary rocks is correlated with fluid influx that likely enhanced diffusion and grain-boundary sliding in pelitic and wacke intervals and catalyzed textural and reaction weakening in wacke intervals. The lack of evidence for fluid and ionic communication with granitic rocks indicates that fluid movement was restricted to foliation-parallel pathways within single rock units. This localized fluid influx is the best explanation for the strength contrasts between texturally similar fault rocks deformed by similar mechanisms.

  12. Evaluation of Coseismic Fluid-Rock Interaction in Fault Zones on the Basis of Geochemistry of Fault Rocks in Accretionary Prisms

    NASA Astrophysics Data System (ADS)

    Ishikawa, T.; Hirono, T.; Honda, G.

    2011-12-01

    Recent studies revealed that concentration and isotopic composition of fluid-mobile trace elements such as Li, Rb, Cs and Sr in slip-zone rocks can change significantly during coseismic fluid-rock interaction at high temperatures (e.g., Ishikawa et al., 2008). In this study, we summarize the results obtained for fault-zone rocks recovered from various depths of the subduction zones. Analysis of a slip-zone sample recovered from shallow portion (0.27 km bsf) of the magasplay fault at Site C0004, IODP Exp. 316, Nankai Trough showed no clear fluid-induced geochemical signals, although a peak temperature over 300 deg. C is estimated on the basis of vitrinite reflectance data (Sakaguchi et al., 2011). In contrast, a major reverse fault in a fossil accretionary prism, the Emi Group (burial depth, 1-2 km) exhibited marked decreases of Li, Rb and Cs relative to adjacent host rocks, suggesting coseismic fluid-rock interactions at >350 deg. C. Geochemical signals observed in the Emi slip zone have a strong resemblance to those observed in the Taiwan chelungpu fault at comparable depths (1.1-1.2 km). Slip-zone samples collected from a fossil out-of-sequence thrust at greater depth (2.5-5.5 km) adjacent to the Kure Melange in the Shimanto accretionary prism showed unique geochemical characteristics, in which effects from disequilibrium flash melting to generate pseudotachylyte coexist with those from fluid-rock interactions at >350 deg. C. In the cases of Emi and Chelungpu, it is possible that the fluid-induced geochemical signatures, together with fluidization structures observed in these samples, resulted from thermal pressurization. On the other hand, the Kure data suggest a slip process in which high-temperature pore fluids were generated by frictional slip, but the thermally-enhanced pressure might not have reached a sufficient level to cause thermal pressurization, and the temperature continued to increase to attain melting. Kinetic estimation suggests that fluid

  13. Deformation Mechanisms of Antigorite Serpentinite at Subduction Zone Conditions Determined from Experimentally and Naturally Deformed Rocks

    NASA Astrophysics Data System (ADS)

    Auzende, A. L.; Escartin, J.; Walte, N.; Guillot, S.; Hirth, G.; Frost, D. J.

    2014-12-01

    The rheology of serpentinite, and particularly that of antigorite-bearing rocks, is of prime importance for understanding subduction zone proceses, including decoupling between the downwelling slab and the overriding plate, exhumation of high-pressure rocks, fluids pathways and, more generally, mantle wedge dynamics. We present results from deformation-DIA experiments on antigorite serpentinite performed under conditions relevant of subduction zones (1-3.5 GPa ; 400-650°C). We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400°C (Chernak and Hirth, EPSL, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Our observations on experimental samples of antigorite deformed within its stability field show that deformation is dominated by cataclastic flow; we can only document a minor contribution of plastic deformation. In naturally deformed samples, deformation-related plastic structures largely dominate strain accommodation, but we also document a minor contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases, and is coupled to local embrittlement attributed to hydraulic fracturating due to the migration of dehydration fluids. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. We also document that the corrugated structure of antigorite has a control on the strain accommodation mechanisms under subduction conditions, with preferred inter and intra-cracking along (001) and gliding along both a and b. Deformation dominated by brittle processes, as observed in experiments, may occur during deformation at elevated (seismic?) strain rates, while plastic deformation, as observed in naturally deformed rocks, may correspond instead to low strain rates instead (aseismic creep?). We also discuss the role of antigorite rheology and mode of deformation on fluid transport.

  14. Rocks.

    ERIC Educational Resources Information Center

    Lee, Alice

    This science unit is designed for limited- and non-English speaking students in a Chinese bilingual education program. The unit covers rock material, classification, characteristics of types of rocks, and rock cycles. It is written in Chinese and simple English. At the end of the unit there is a list of main terms in both English and Chinese, and…

  15. Fault damage zones in mechanically layered rocks: The effects of planar anisotropy

    NASA Astrophysics Data System (ADS)

    Misra, Santanu; Ellis, Susan; Mandal, Nibir

    2015-08-01

    This study shows how inherited strength anisotropy influences damage localization at both the tip and wall regions of a fault or fracture. We performed analogue and numerical compression experiments on transversely isotropic models with single and multiple cuts of finite length, simulating the propagation of preexisting faults and cracks in layered rock. The stress-strain curves from the analogue experiments show a change in bulk yield behavior with fault inclination and anisotropy orientation with respect to the stress direction. Earlier isotropic models demonstrated a brittle (wing fracturing) to ductile (shear-zone formation) transition as the fault angle (α) to the principal compression direction increased. The experiments with anisotropic models show patterns of damage localization change dramatically with the orientation of transversely isotropic planes (θ, measured with respect to principal extension direction). Under layer-normal (θ = 0°) and layer-parallel compression (θ = 90°), preexisting faults undergo significant reactivation when 0 < α < 90°, and fault slip eventually leads to mechanical instabilities within the anisotropic layering, causing damage zones in the tip regions. For layer-normal (θ = 0°) compression, the damage processes involve intense extensional shear localization, whereas for layer-parallel compression, contractional shear localization and tensile opening result in characteristic internal shear-band structures. In contrast, for 0 < θ < 90°, the faults undergo little or no reactivation, irrespective of α. In this case, bulk compression leads to an interlayer slip-mediated global deformation. Obliquely anisotropic models thus produce weak or no fault damage zones. We also show that the fault-parallel principal damage localized at the tips can be coupled with transversely oriented, antithetic secondary damage in the wall regions. However, secondary damage develops predominantly when θ = 90°. Field examples of fault damage

  16. The application of a neural network to map clay zones in crystalline rock

    NASA Astrophysics Data System (ADS)

    Meller, Carola; Genter, Albert; Kohl, Thomas

    2014-02-01

    The appearance of clay in fractures is an important issue of applied geoscience as it not only affects the stability but also the flow paths through rocks. Forming a link between hydraulic, geochemical and mechanical processes, clay structures need to be thoroughly investigated. The growing importance of clay for waste disposal, petroleum research, geothermal exploration and geotechnical engineering necessitates tools to find and to characterize clay structures and clay minerals indirectly from geophysical measuring methods. Particularly, there is need for a technique enabling to map clay-rich zones from geophysical well logs acquired on-site in order to assess the mechanical and hydraulic properties of rocks. In this study, we present a neural network based method to map clay bearing fracture zones in crystalline facies. The study has been performed on the basis of geophysical and geological data acquired at the geothermal site of Soultz-sous-Forêts (France), in the granitic reservoir. A neural network was trained on geophysical logs from the fully cored exploration well EPS1. Calibration of the network was done on reference logs derived from the drill core. The effective calibration enabled the creation of synthetic clay content logs, which predict the clay amount in fractures along the well with >74 per cent accordance with a reference log. High clay contents could be located in faults, on which aseismic movements have been identified. The validation of this relationship destines the synthetic logs to help identifying potentially weak zones from geophysical logging methods. With application on non-cored wells, this tool can become a powerful means for assessing the probability of aseismic movements on faults caused by the presence of clay and estimating the hydraulic properties of fractures.

  17. Fluid Flow and Fault Zone Damage in Crystalline Basement Rocks (Ore Mountains Saxony)

    NASA Astrophysics Data System (ADS)

    Achtziger-Zupančič, P.; Loew, S.; Hiller, A.; Mariethoz, G.

    2015-12-01

    Groundwater flow in fractured basement rocks on aquifer scale and processes involved in the creation of fracture network permeability are poorly understood even though they have been studied for decades. A unique hydrogeological dataset consisting of 1030 discrete inflows (corresponding to preferential groundwater pathways) to the Poehla Ore Mine (Ore Mountains) of the SDAG Wismut has been compiled and quantitatively interpreted. Transmissivities and permeabilities were calculated from discrete and cumulative inflows using analytical equations and numerical groundwater flow models. The Variscan basement at Poehla Mine was modelled in 3-D, covering a volume of 14x4x1 km3 with 14 metamorphosed litho-stratigraphic units and 131 faults separated in 6 main strike directions. Mesoscale fractures mapped at inflows points, i.e. locally conductive fractures, show a weak correlation with fault orientation, and a large orientation scattering, which could be related to small scale stress heterogeneities. Inflow points were spatially correlated with major faults considering two distance criteria. This correlation suggests that mainly NW-SE and NE-SW striking faults are transmissive, which should be critically stressed considering all available data about the regional stress field. The trace length (extent) and width of the core and damage zones of the modelled faults were compiled in order to investigate the flow distribution and permeability profiles in directions perpendicular to fault strike. It can be shown that 90% of all inflows are located in damage zones. The inflows are usually situated within multiple fault zones which overlap each other. Cumulative flow distribution functions within damage zones are non-linear and vary between faults with different orientation. 75-95% of the flow occurs in the inner 50% of the damage zone. Significantly lower flow rates were recognized within most fault cores.

  18. The use of trace element zoning patterns in garnet to infer reaction paths of metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Konrad-Schmolke, Matthias; Witte, Clemens; Dohmen, Ralf; O'Brien, Patrick; Erpel, Lars; Halama, Ralf; Schmidt, Alexander; Ditterova, Hana

    2015-04-01

    Garnet is one of the most versatile minerals in metamorphic petrology. It is stable over a large pressure and temperature range and thus occurs in many metamorphic environments. Garnet has a wide range of chemical compositions and its major and trace element composition well reflects the pressure (P), temperature (T) and chemical conditions (X) as well as the element transport kinetic properties of the host rock during growth. Hence, compositional growth zonations in garnet contain information about most geochemical, mineralogical and petrological properties of metamorphic rocks. However, detailed interpretation of complex zoning patterns in metamorphic garnet was hindered mainly by the lack of knowledge about the various contributions of kinetic and equilibrium effects to the trace element incorporation into garnet. In this contribution we combine thermodynamic equilibrium calculations together with mass balanced trace element distribution among coexisting phases with diffusion models that simulate kinetically controlled element transport in a reacting host rock. Comparison of the model results with natural garnets enables detailed interpretation of commonly observed major and trace element patterns in high-pressure (HP) and ultra-high pressure (UHP) garnets in terms of reaction paths and physico-chemical properties of the host rock. The comparison of our numerical models with a series of well-investigated (U)HP samples shows that the kinetic influence on rare earth element incorporation into garnet is limited in most rocks at the early stages of garnet growth and increases with increasing grade of rock transformation. We show that REE zoning patterns can be used to distinguish between cold (lawsonite-stable) and warm (epidote-stable) prograde reaction paths. REE liberation along a warm P-T trajectory occurs in three breakdown reactions involving chlorite, epidote and amphibole. All three reactions result in characteristic heavy (HREE) and medium (MREE) REE growth

  19. Lessons from a Disturbance Experiment in the Intertidal Zone of an Exposed Sandy Beach

    NASA Astrophysics Data System (ADS)

    Schoeman, D. S.; Mclachlan, A.; Dugan, J. E.

    2000-06-01

    Exposed sandy beaches are important, sensitive and widespread coastal habitats. Although they have been studied for more than 50 years, investigators have been reluctant to attempt manipulative experiments due to the dynamic nature of these environments. Consequently, the ecology of exposed sandy beaches remains relatively poorly understood. We conducted a community-level, manipulative experiment involving a simulated anthropogenic disturbance on an exposed microtidal sandy beach in the Eastern Cape, South Africa; the first of its kind and scale. This study comprised pre- and post-impact sampling at an experimental site and two control sites. The impact involved excavating and removing a 200 m2quadrat of sand from the mid-intertidal of the experimental site to a depth of 0·3 m. The intention was to address the prediction that anthropogenic disturbances would be detectable if appropriate spatial and temporal scales were investigated. The following variables were monitored: transect gradient; species richness; macrofaunal abundance; and both the abundance and biomass of the dominant infaunal species, the beach clam Donax serra Röding. Analyses revealed significant differences in temporal patterns of all response variables amongst sites. Some evidence linked these changes to the experimental disturbance, although impacts appear temporary, being ameliorated within, at most, one semi-lunar cycle. This confirms that it is possible to successfully conduct manipulative experiments on exposed sandy beaches. However, the uncontrollable, natural dynamics of the beach face, as expressed by intertidal gradient, contributed significantly to the description of spatio-temporal variation in biotic response variables. It is concluded that to isolate treatment effects from those of natural variation, two advances are necessary on the current research approach. First, experimental designs must take cognizance of the fact that exposed, microtidal sandy beaches have little in common

  20. The global range of subduction zone thermal structures from exhumed blueschists and eclogites: Rocks are hotter than models

    NASA Astrophysics Data System (ADS)

    Penniston-Dorland, Sarah C.; Kohn, Matthew J.; Manning, Craig E.

    2015-10-01

    The maximum-pressure Psbnd T conditions (Pmax- T) and prograde Psbnd T paths of exhumed subduction-related metamorphic rocks are compared to predictions of Psbnd T conditions from computational thermal models of subduction systems. While the range of proposed models encompasses most estimated Pmax- T conditions, models predict temperatures that are on average colder than those recorded by exhumed rocks. In general, discrepancies are greatest for Pmax < 2 GPa, where only a few of the highest-T model paths overlap petrologic observations and model averages are 100-300 °C colder than average conditions recorded by rocks. Prograde Psbnd T paths similarly indicate warmer subduction than typical models. Both petrologic estimates and models have inherent biases. Petrologic analysis may overestimate temperatures at Pmax where overprinting occurs during exhumation, although Psbnd T paths suggest that relatively warm conditions are experienced by rocks on the prograde subduction path. Models may underestimate temperatures at depth by neglecting shear heating, hydration reactions and fluid and rock advection. Our compilation and comparison suggest that exhumed high-P rocks provide a more accurate constraint on Psbnd T conditions within subduction zones, and that those conditions may closely represent the subduction geotherm. While exhumation processes in subduction zones require closer petrologic scrutiny, the next generation of models should more comprehensively incorporate all sources of heat. Subduction-zone thermal structures from currently available models appear to be inaccurate, and this mismatch has wide-reaching implications for our understanding of global geochemical cycles, the petrologic structure of subduction zones, and fluid-rock interactions and seismicity within subduction zones.

  1. Sediment Dynamics Within Buffer Zone and Sinkhole Splay Areas Under Extreme Soil Disturbance Conditions

    NASA Astrophysics Data System (ADS)

    Schoonover, Jon E.; Crim, Jackie F.; Williard, Karl W. J.; Groninger, John W.; Zaczek, James J.; Pattumma, Klairoong

    2015-09-01

    Sedimentation dynamics were assessed in sinkholes within training areas at Ft. Knox Military Installation, a karst landscape subjected to decades of tracked vehicle use and extreme soil disturbance. Sinkholes sampled were sediment-laden and behaved as intermittent ponds. Dendrogeomorphic analyses were conducted using willow trees ( Salix spp.) located around the edge of 18 sinkholes to estimate historical sedimentation rates, and buried bottles were installed in 20 sinkholes at the center, outer edge, and at the midpoint between the center and edge to estimate annual sedimentation rates. Sedimentation data were coupled with vegetation characteristics of sinkhole buffers to determine relationships among these variables. The dendrogeomorphic method estimated an average accumulation rate of 1.27 cm year-1 translating to a sediment loss rate of 46.1 metric ton year-1 from the training areas. However, sediment export to sinkholes was estimated to be much greater (118.6 metric ton year-1) via the bottle method. These data suggest that the latter method provided a more accurate estimate since accumulation was greater in the center of sinkholes compared to the periphery where dendrogeomorphic data were collected. Vegetation data were not tightly correlated with sedimentation rates, suggesting that further research is needed to identify a viable proxy for direct measures of sediment accumulation in this extreme deposition environment. Mitigation activities for the sinkholes at Ft. Knox's tank training area, and other heavily disturbed karst environments where extreme sedimentation exists, should consider focusing on flow path and splay area management.

  2. Sediment Dynamics Within Buffer Zone and Sinkhole Splay Areas Under Extreme Soil Disturbance Conditions.

    PubMed

    Schoonover, Jon E; Crim, Jackie F; Williard, Karl W J; Groninger, John W; Zaczek, James J; Pattumma, Klairoong

    2015-09-01

    Sedimentation dynamics were assessed in sinkholes within training areas at Ft. Knox Military Installation, a karst landscape subjected to decades of tracked vehicle use and extreme soil disturbance. Sinkholes sampled were sediment-laden and behaved as intermittent ponds. Dendrogeomorphic analyses were conducted using willow trees (Salix spp.) located around the edge of 18 sinkholes to estimate historical sedimentation rates, and buried bottles were installed in 20 sinkholes at the center, outer edge, and at the midpoint between the center and edge to estimate annual sedimentation rates. Sedimentation data were coupled with vegetation characteristics of sinkhole buffers to determine relationships among these variables. The dendrogeomorphic method estimated an average accumulation rate of 1.27 cm year(-1) translating to a sediment loss rate of 46.1 metric ton year(-1) from the training areas. However, sediment export to sinkholes was estimated to be much greater (118.6 metric ton year(-1)) via the bottle method. These data suggest that the latter method provided a more accurate estimate since accumulation was greater in the center of sinkholes compared to the periphery where dendrogeomorphic data were collected. Vegetation data were not tightly correlated with sedimentation rates, suggesting that further research is needed to identify a viable proxy for direct measures of sediment accumulation in this extreme deposition environment. Mitigation activities for the sinkholes at Ft. Knox's tank training area, and other heavily disturbed karst environments where extreme sedimentation exists, should consider focusing on flow path and splay area management. PMID:25975438

  3. Strain localisation in mechanically layered rocks beneath detachment zones: insights from numerical modelling

    NASA Astrophysics Data System (ADS)

    Le Pourhiet, L.; Huet, B.; Labrousse, L.; Yao, K.; Agard, P.; Jolivet, L.

    2013-04-01

    We have designed a series of fully dynamic numerical simulations aimed at assessing how the orientation of mechanical layering in rocks controls the orientation of shear bands and the depth of penetration of strain in the footwall of detachment zones. Two parametric studies are presented. In the first one, the influence of stratification orientation on the occurrence and mode of strain localisation is tested by varying initial dip of inherited layering in the footwall with regard to the orientation of simple shear applied at the rigid boundary simulating a rigid hanging wall, all scaling and rheological parameter kept constant. It appears that when Mohr-Coulomb plasticity is being used, shear bands are found to localise only when the layering is being stretched. This corresponds to early deformational stages for inital layering dipping in the same direction as the shear is applied, and to later stages for intial layering dipping towards the opposite direction of shear. In all the cases, localisation of the strain after only γ=1 requires plastic yielding to be activated in the strong layer. The second parametric study shows that results are length-scale independent and that orientation of shear bands is not sensitive to the viscosity contrast or the strain rate. However, decreasing or increasing strain rate is shown to reduce the capacity of the shear zone to localise strain. In the later case, the strain pattern resembles a mylonitic band but the rheology is shown to be effectively linear. Based on the results, a conceptual model for strain localisation under detachment faults is presented. In the early stages, strain localisation occurs at slow rates by viscous shear instabilities but as the layered media is exhumed, the temperature drops and the strong layers start yielding plastically, forming shear bands and localising strain at the top of the shear zone. Once strain localisation has occured, the deformation in the shear band becomes extremely penetrative but

  4. Transformations in shallow fault zones; evidence from fault rocks in young strike-slip systems.

    NASA Astrophysics Data System (ADS)

    van der Pluijm, B. A.; Schleicher, A. M.; Warr, L. N.

    2008-12-01

    cataclasis creates nucleation sites for neomineralization or produces localized melting in upper-crustal strike-slip fault systems (< 5 km depth), which is coupled to slip rate. Transformations in shallow fault rock involve the localization of clay neomineralization along slip surfaces in creeping segments, controlling strength in the shallowest segment of fault zones. During sudden, large displacements, the energy can be sufficient to produce friction melts that are similarly generated at small slip surfaces. Thus, shallow faults rocks preserve mineral and state transformations during faulting, and provide information on the history of fluid activity, mass transport and mechanical behavior. Additionally, dating of neocrystallized mineral phases by radiogenic techniques provides the age of faulting and can constrain rates of crustal deformation.

  5. Geochemistry and Geochronology of Oceanic Rock Assemblages in the Izmir-Ankara-Erzincan Suture Zone, Turkey

    NASA Astrophysics Data System (ADS)

    Sarifakioglu, Ender; Dilek, Yildirim; Sevin, Mustafa

    2013-04-01

    We report here new data from the Izmir-Ankara-Erzincan Suture Zone (IAESZ), which connects the Vardar Suture Zone in the west with the Sevan-Akera Suture Zone in the east. It occurs between the Sakarya Continent and the Anatolide-Tauride ribbon continent in Turkey, and consists mainly of ophiolitic thrust sheets emplaced into a subduction-accretion mélange. The ophiolites include upper mantle peridotites, cumulate to massive gabbros, sheeted doleritic dykes, plagiogranite dykes and stocks, and basalt-chert-radiolarite as in a complete Penrose-type ophiolite pseudostratigraphy. They display a geochemical progression in their magmatic evolution from initially MORB-like to island arc tholeiites (IAT) to boninites, similar to many other Tethyan ophiolites in the eastern Mediterranean region. Boninitic dykes and volcanic rocks have very low TiO2 (0.03-0.50 wt.%), Nb (0.03-1.9 ppm), Y (1,9-10.7ppm) and Zr (4.10-42 ppm) values. IAT-type doleritic dykes and basaltic lavas contain low TiO2 (0.42-1.04 wt.%), Nb (0.90-2.7 wt.%), Y (9.7-33.3 ppm) and Zr (12.7-85 ppm). The TiO2 (0.81-2.60 wt.%), Nb (3.30-4.8 ppm), Y (22.6-63.8 ppm) and Zr (36.01-179.33 ppm) contents of the MORB-like basaltic rocks are higher than those in the IAT and boninitic lavas. The subduction-accretion mélange (Ankara Mélange) in the central part of the IAESZ, includes volcanic mega-blocks derived from seamounts and/or an oceanic plateau that have OIB and P-MORB geochemical characteristics. This subduction-accretion complex also contains blocks of MORB- and/or IAT-like ophiolite fragments within a matrix composed of serpentinite, altered volcanics-volcaniclastics and/or pelitic sedimentary rocks. Pegmatitic gabbros in the ophiolites in the western and eastern IAESZ reveal 40Ar-39Ar hornblende ages of 168.9Ma and 195.7±2.7Ma, respectively. Plagiogranite dykes in the central and eastern parts of the IAESZ are 180 Ma and 179±2 Ma to 180.1±2.4 Ma in age as determined from U-Pb from zircon dates. The

  6. Areal extent, hydrogeologic characteristics, and possible origins of the carbonate rock Newburg Zone (Middle-Upper Silurian) in Ohio

    USGS Publications Warehouse

    Strobel, M.L.; Bugliosi, E.F.

    1991-01-01

    The zone occurs in carbonate rocks of Middle to Late Silurian age across much of Ohio. Known also to well drillers as the "Second Water' in the "Big Lime' carbonate sequence, the Newburg zone is a source of hydrocarbons in northeast Ohio, brines in southeast Ohio, and a widespread source of water over much of west-central Ohio. Close to recharge areas, the quality of the water is comparable to that of the overlying carbonate rocks; thus, the Newburg zone warrants further investigation as a source of water for domestic use. Theories for the porosity and permeabilty of the Newburg zone include: 1) deposition of carbonate or quartz sand along an erosional surface and later lithified to porous and permeable sandstone; 2) dissolution of fossils within Silurian reef complexes; 3) fracture-induced porosity along thrust faults developed during the Alleghenian orogeny; and 4) a combination of these processes. -from Authors

  7. Disturbed basal ice seen in radio echo images coincide with zones of big interlocking ice crystals.

    NASA Astrophysics Data System (ADS)

    Dahl-Jensen, Dorthe; Gogineni, Sivaprasad; Panton, Christian

    2014-05-01

    Improvement of the depth sounding radio echo sounding (RES) over Antarctica and Greenland Ice Sheet has made it possible to map the near basal layers that have not been 'seen' earlier due to the very high demand of attenuation needed to reach through more than 3000m of ice. The RES internal reflectors show that the near basal ice at many locations has disturbed layering. At the locations where ice cores reach the bedrock both in Greenland and Antarctica studies of the ice crystal size and orientation show that the near basal ice has big and interlocking ice crystals which suggests the ice is not actively deforming. These observations challenge the often used constitutive equations like Glens flow law in ice sheet modelling. A discussion of the impact of the RES findings on ice sheet modeling and the quest to find the oldest ice in Antarctic based on the anisotropy of the basal ice will follow.

  8. Anisotropy of electrical conductivity of the excavation damaged zone in the Mont Terri Underground Rock Laboratory

    NASA Astrophysics Data System (ADS)

    Nicollin, Florence; Gibert, Dominique; Lesparre, Nolwenn; Nussbaum, Christophe

    2010-04-01

    Electrical resistivity measurements were performed to characterize the anisotropy of electrical resistivity of the excavation damaged zone (EDZ) at the end-face of a gallery in the Opalinus clay of the Mont Terri Underground Rock Laboratory (URL). The data were acquired with a combination of square arrays in 18 zones on the gallery's face and in two series of four boreholes perpendicular to the face. Each data set is independently inverted using simulated annealing to recover the resistivity tensor. Both the stability and the non-uniqueness of the inverse problem are discussed with synthetic examples. The inversion of the data shows that the face is split in two domains separated by a tectonic fracture, with different resistivity values but with a common orientation. The direction of the maximum resistivity is found perpendicular to the bedding plane, and the direction of minimum resistivity is contained in the face's plane. These results show that the geo-electrical structure of the EDZ is controlled by a combination of effects due to tectonics, stratigraphy, and recent fracturing produced by the excavation of the gallery.

  9. 75 FR 31321 - Fisheries of the Exclusive Economic Zone Off Alaska; Rock Sole, Flathead Sole, and “Other...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-03

    ... the BSAI (75 FR 11778, March 12, 2010). In accordance with Sec. 679.21(e)(3)(vi)(B) and Sec. 679.21(e... Economic Zone Off Alaska; Rock Sole, Flathead Sole, and ``Other Flatfish'' by Vessels Participating in the... ``other flatfish'' by vessels participating in the Amendment 80 limited access fishery in the Bering...

  10. Carbonation by fluid-rock interactions at high-pressure conditions: Implications for carbon cycling in subduction zones

    NASA Astrophysics Data System (ADS)

    Piccoli, Francesca; Vitale Brovarone, Alberto; Beyssac, Olivier; Martinez, Isabelle; Ague, Jay J.; Chaduteau, Carine

    2016-07-01

    Carbonate-bearing lithologies are the main carbon carrier into subduction zones. Their evolution during metamorphism largely controls the fate of carbon, regulating its fluxes between shallow and deep reservoirs. Recent estimates predict that almost all subducted carbon is transferred into the crust and lithospheric mantle during subduction metamorphism via decarbonation and dissolution reactions at high-pressure conditions. Here we report the occurrence of eclogite-facies marbles associated with metasomatic systems in Alpine Corsica (France). The occurrence of these marbles along major fluid-conduits as well as textural, geochemical and isotopic data indicating fluid-mineral reactions are compelling evidence for the precipitation of these carbonate-rich assemblages from carbonic fluids during metamorphism. The discovery of metasomatic marbles brings new insights into the fate of carbonic fluids formed in subducting slabs. We infer that rock carbonation can occur at high-pressure conditions by either vein-injection or chemical replacement mechanisms. This indicates that carbonic fluids produced by decarbonation reactions and carbonate dissolution may not be directly transferred to the mantle wedge, but can interact with slab and mantle-forming rocks. Rock-carbonation by fluid-rock interactions may have an important impact on the residence time of carbon and oxygen in subduction zones and lithospheric mantle reservoirs as well as carbonate isotopic signatures in subduction zones. Furthermore, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.

  11. Ductile shear zone rheology: the viewpoint of experimentally crept lower crustal rocks and analogues

    NASA Astrophysics Data System (ADS)

    Dimanov, Alexandre; Raphanel, Jean; Bornert, Michel; Bourcier, Mathieu; Gaye, Ababacar; Ludwig, Wolfgang

    2015-04-01

    With respect to lithosphere rheology, we are especially interested in the mechanical behavior and evolution of ductile shear zones at depth, which present polyphase and heterogeneous character and multi-scale strain localization patterns. According to structural geology, most strain concentrates in ultramylonitic layers, which exhibit along with metamorphism overprinted or concomitant microstructural signatures from several deformation mechanisms. The latter are either active in volume (crystal slip plasticity and dislocation recovery processes), or in the vicinity and along interfaces (grain sliding, phase transformations and solution mass transfer). Because all of these contribute to the drastic evolution of microstructures with respect to the wall rock and the protomylonite, and because the chronology of their activation and their interactions are unclear, inference of the overall rheology from these microstructural records seems illusory. Therefore, since more than a decade we investigate experimentally and numerically the rheology of synthetic rocks representative of lower crustal mineralogy (namely plagioclases and clinopyroxenes). Samples are elaborated with different microstructures and with variable phases, fluid and melt contents for the purpose of being representative of diverse geodynamical contexts. Experiments were performed either at constant stress or strain rate, in co-axial compression or in torsion. For macroscopic non-Newtonian flow we clearly identified dislocation glide and creep mechanisms. That is to say that power law rheology relates to dominant crystal slip plasticity accommodated by recovery processes, including dislocation climb and pile-up, sub-grain rotation and marginal recrystallization. We further refer to this regime as RCSP (recovery crystal slip plasticity). Conversely, Newtonian (linear viscous) behavior mostly involves grain boundary sliding (GBS) accommodated by diffusional mass transfer and grain boundary dislocation

  12. Origin and accumulation mechanisms of petroleum in the Carboniferous volcanic rocks of the Kebai Fault zone, Western Junggar Basin, China

    NASA Astrophysics Data System (ADS)

    Chen, Zhonghong; Zha, Ming; Liu, Keyu; Zhang, Yueqian; Yang, Disheng; Tang, Yong; Wu, Kongyou; Chen, Yong

    2016-09-01

    The Kebai Fault zone of the West Junggar Basin in northwestern China is a unique region to gain insights on the formation of large-scale petroleum reservoirs in volcanic rocks of the western Central Asian Orogenic Belt. Carboniferous volcanic rocks are widespread in the Kebai Fault zone and consist of basalt, basaltic andesite, andesite, tuff, volcanic breccia, sandy conglomerate and metamorphic rocks. The volcanic oil reservoirs are characterized by multiple sources and multi-stage charge and filling history, characteristic of a complex petroleum system. Geochemical analysis of the reservoir oil, hydrocarbon inclusions and source rocks associated with these volcanic rocks was conducted to better constrain the oil source, the petroleum filling history, and the dominant mechanisms controlling the petroleum accumulation. Reservoir oil geochemistry indicates that the oil contained in the Carboniferous volcanic rocks of the Kebai Fault zone is a mixture. The oil is primarily derived from the source rock of the Permian Fengcheng Formation (P1f), and secondarily from the Permian Lower Wuerhe Formation (P2w). Compared with the P2w source rock, P1f exhibits lower values of C19 TT/C23 TT, C19+20TT/ΣTT, Ts/(Ts + Tm) and ααα-20R sterane C27/C28 ratios but higher values of TT C23/C21, HHI, gammacerane/αβ C30 hopane, hopane (20S) C34/C33, C29ββ/(ββ + αα), and C29 20S/(20S + 20R) ratios. Three major stages of oil charge occurred in the Carboniferous, in the Middle Triassic, Late Triassic to Early Jurassic, and in the Middle Jurassic to Late Jurassic periods, respectively. Most of the oil charged during the first stage was lost, while moderately and highly mature oils were generated and accumulated during the second and third stages. Oil migration and accumulation in the large-scale stratigraphic reservoir was primarily controlled by the top Carboniferous unconformity with better porosity and high oil enrichment developed near the unconformity. Secondary dissolution

  13. Semi-automatic mapping of fault rocks on a Digital Outcrop Model, Gole Larghe Fault Zone (Southern Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Vho, Alice; Bistacchi, Andrea

    2015-04-01

    A quantitative analysis of fault-rock distribution is of paramount importance for studies of fault zone architecture, fault and earthquake mechanics, and fluid circulation along faults at depth. Here we present a semi-automatic workflow for fault-rock mapping on a Digital Outcrop Model (DOM). This workflow has been developed on a real case of study: the strike-slip Gole Larghe Fault Zone (GLFZ). It consists of a fault zone exhumed from ca. 10 km depth, hosted in granitoid rocks of Adamello batholith (Italian Southern Alps). Individual seismogenic slip surfaces generally show green cataclasites (cemented by the precipitation of epidote and K-feldspar from hydrothermal fluids) and more or less well preserved pseudotachylytes (black when well preserved, greenish to white when altered). First of all, a digital model for the outcrop is reconstructed with photogrammetric techniques, using a large number of high resolution digital photographs, processed with VisualSFM software. By using high resolution photographs the DOM can have a much higher resolution than with LIDAR surveys, up to 0.2 mm/pixel. Then, image processing is performed to map the fault-rock distribution with the ImageJ-Fiji package. Green cataclasites and epidote/K-feldspar veins can be quite easily separated from the host rock (tonalite) using spectral analysis. Particularly, band ratio and principal component analysis have been tested successfully. The mapping of black pseudotachylyte veins is more tricky because the differences between the pseudotachylyte and biotite spectral signature are not appreciable. For this reason we have tested different morphological processing tools aimed at identifying (and subtracting) the tiny biotite grains. We propose a solution based on binary images involving a combination of size and circularity thresholds. Comparing the results with manually segmented images, we noticed that major problems occur only when pseudotachylyte veins are very thin and discontinuous. After

  14. Deformation of Sedimentary Rock Across the San Andreas Fault Zone: Mesoscale and Microscale Structures Displayed in Core From SAFOD

    NASA Astrophysics Data System (ADS)

    Chester, J. S.; Chester, F. M.; Kirschner, D. L.; Almeida, R.; Evans, J. P.; Guillemette, R. N.; Hickman, S.; Zoback, M.; Ellsworth, W.

    2007-12-01

    Sedimentary rocks captured in cores taken at the San Andreas Fault Observatory at Depth (SAFOD) provide an unparalleled sampling of deformation in the transition zone between creeping and locked segments of a major transform fault at 2.5-3.1 km vertical depth. These samples provide the unique opportunity to study deformation processes and the development of brittle structures within porous and granular rocks that have been subjected to variable loading rates and chemically reactive fluids while residing at the top of the seismogenic zone. The samples provide a transect from relatively undeformed host rock through highly fractured and sheared rock, and capture the two prominent zones of active, aseismic slip. Core recovery was almost complete. Wrap-around 1:1 map tracings of the outer surfaces of all cores characterize the lithology and mesoscale deformation. Cores from 3056-3067 m and 3141-3153 m measured depth (MD) sample moderately deformed rock at the western boundary of the fault zone. The cores display massive to finely laminated, pebbly arkosic sandstones with lesser amounts of fine-grained sandstone and siltstone. Numerous shear fractures and cm-thick cataclastic shear zones form a conjugate geometry indicating contraction at high angles to the San Andreas fault. Both intervals display minor faults that juxtapose different lithologies consistent with meters or greater of slip. Fracture density is variable but tends to increase with proximity to the minor faults. Cross-cutting relationships between shear fractures and cataclastic zones indicate a general progression from early faulting along thicker shear zones to later, more localized slip within shear zones and along fractures. Microstructures provide ample evidence for densification of the sandstones through grain-scale fracture and crushing, as well as fluid assisted processes of crack-sealing, dissolution-precipitation, and alteration-neocrystallization. Grain-scale features are consistent with these

  15. The ammonium content in the Malayer igneous and metamorphic rocks (Sanandaj-Sirjan Zone, Western Iran)

    NASA Astrophysics Data System (ADS)

    Ahadnejad, Vahid; Hirt, Ann Marie; Valizadeh, Mohammad-Vali; Bokani, Saeed Jabbari

    2011-04-01

    The ammonium (NH4+) contents of the Malayer area (Western Iran) have been determined by using the colorimetric method on 26 samples from igneous and metamorphic rocks. This is the first analysis of the ammonium contents of Iranian metamorphic and igneous rocks. The average ammonium content of metamorphic rocks decreases from low-grade to high-grade metamorphic rocks (in ppm): slate 580, phyllite 515, andalusite schist 242. In the case of igneous rocks, it decreases from felsic to mafic igneous types (in ppm): granites 39, monzonite 20, diorite 17, gabbro 10. Altered granitic rocks show enrichment in NH4+ (mean 61 ppm). The high concentration of ammonium in Malayer granites may indicate metasedimentary rocks as protoliths rather than meta-igneous rocks. These granitic rocks (S-types) have high K-bearing rock-forming minerals such as biotite, muscovite and K-feldspar which their potassium could substitute with ammonium. In addition, the high ammonium content of metasediments is probably due to inheritance of nitrogen from organic matter in the original sediments. The hydrothermally altered samples of granitic rocks show highly enrichment of ammonium suggesting external sources which intruded additional content by either interaction with metasedimentary country rocks or meteoritic solutions.

  16. Water-rock interactions in the Median Tectonic Line fault zone, SW Japan revealed by core sample analysis

    NASA Astrophysics Data System (ADS)

    Fujimoto, K.; Tanaka, N.; Shigematsu, N.

    2012-12-01

    Alteration minerals along the fault zone of the Median Tectonic Line (MTL), the Japan's largest onshore fault, are characterized to understand the crustal faulting at various depth conditions by describing a borehole penetrating the MTL. The borehole was drilled by the Geological Survey of Japan, AIST (GSJ, AIST) to predict the forthcoming Nankai-Tonankai Earthquake at Matsusaka-Iitaka (ITA), SW Japan. The drilling length is 600m. It penetrates the MTL at the depth of 473.9m. The fault plane has an almost E-W strike and dips at 56° to the north. Hangingwall of the MTL consists of Ryoke-derived tonalitic mylonite and footwall of the MTL consists of fractured rocks derived from Sanbagawa metamorphic rocks. Ryoke-derived tonalitic mylonite in the hangingwall suffered more or less later cataclastic deformations. X-ray diffraction patterns of powdered samples derived from ITA borehole were obtained to identify alteration mineral assemblages and estimate alteration conditions. Chlorite, laumontite, white-mica, prehnite and calcite are main alteration minerals in the Ryoke belt above 400m depth, while analcine and stilbite occur as zeolite minerals instead of laumontite between 400m and 473.9m depth. Laumontite is preferentially occurred in the cataclastically deformed zones and calcite often fills fractures and cavities. The fault plane and fractures in the fault zone provide fluid conduit. The presence of laumontite and prehnite indicates that the alteration temperature was more than 200°C, while analcime and stilbite formed at lower temperature than laumontite. These suggest that the zone of hydrothermal alteration less than 200°C was restricted below 400m depth in the ITA borehole. We also applied chlorite geothermometry (Inoue et al., 2009), which yeileds temperatures of about 300°C for mylonitic rocks and those of about 200°C for cataclastic rocks. Immediately beneath the MTL, approximately 40m thick fractured rocks form the major strand of the MTL fault zone

  17. Delineating a shallow fault zone and dipping bed rock strata using multichannal analysis of surface waves with a land streamer

    USGS Publications Warehouse

    Ivanov, J.; Miller, R.D.; Lacombe, P.; Johnson, C.D.; Lane, J.W., Jr.

    2006-01-01

    The multichannel analysis of surface waves (MASW) seismic method was used to delineate a fault zone and gently dipping sedimentary bedrock at a site overlain by several meters of regolith. Seismic data were collected rapidly and inexpensively using a towed 30-channel land streamer and a rubberband-accelerated weight-drop seismic source. Data processed using the MASW method imaged the subsurface to a depth of about 20 m and allowed detection of the overburden, gross bedding features, and fault zone. The fault zone was characterized by a lower shear-wave velocity (Vs) than the competent bedrock, consistent with a large-scale fault, secondary fractures, and in-situ weathering. The MASW 2D Vs section was further interpreted to identify dipping beds consistent with local geologic mapping. Mapping of shallow-fault zones and dipping sedimentary rock substantially extends the applications of the MASW method. ?? 2006 Society of Exploration Geophysicists.

  18. Hydrogen sulfide gas emissions in the human-occupied zone during disturbance and removal of stored spent mushroom compost.

    PubMed

    Velusami, B; Curran, T P; Grogan, H M

    2013-10-01

    Hydrogen sulfide (H2S) gas levels were monitored in the human-occupied zone at four spent mushroom compost (SMC) storage sites during removal of SMC for application on agricultural land. During SMC removal operations, H2S gas monitors were mounted on the outside of the tractor positioned at the SMC periphery, and worn by individual tractor drivers. The highest H2S concentrations (10 s average) detected outside the tractor, at the SMC periphery, and for the tractor driver were, respectively, 454, 249, and 100 ppm for the outdoor sites and 214, 75, and 51 ppm for the indoor sites. The highest short-term exposure values (STEV over a 15 min period) outside the tractor at the SMC periphery, and for the tractor driver were 147, 55, and 86 ppm for the outdoor sites and 19, 9, and 10 ppm for the indoor sites. The values exceeded the current maximum permissible concentration limit of 10 ppm for all the sites except for the SMC periphery and tractor driver at the indoor sites. Results suggest that H2S levels detected at indoor storage sites during SMC removal are lower compared to outdoor storage sites. Results indicate that there is a substantial health and safety risk associated with working in the vicinity of stored SMC when it is being disturbed and removed for land application, and that the risk is great for the tractor driver. This article discusses possible control measures and lists recommendations to reduce the risks. PMID:24673036

  19. High temperature pseudotachylytes and ductile shear zones in dry rocks from the continental lower crust (Lofoten, Norway)

    NASA Astrophysics Data System (ADS)

    Menegon, Luca; Pennacchioni, Giorgio; Harris, Katherine; Wood, Elliot

    2014-05-01

    Understanding the mechanisms of initiation and growth of shear zones under lower crustal conditions is of fundamental importance when assessing lithosphere rheology and strength. In this study we investigate brittle-ductile shear zones developed under lower crustal conditions in anorthosites from Nusfjord, Lofoten (northern Norway). Steep ductile shear zones trend E-W to ESE-WSW and have a stretching lineation plunging steeply to the SSW or SSE. The shear sense is normal (south block down to the south) as indicated by SC and SC' fabrics and sigmoidal foliations. The shear zone show a mylonitic to ultramylonitic fabric, sharp boundaries to the host anorthosites, and abundant anastomosing dark fine-grained layers along the main foliation. The fine-grained layers localized much of the strain. Relatively lower strain domains within or adjacent to shear zones indicate that the fine dark bands of mylonites represent transposed pseudotachylyte which still locally preserve the pristine structures such as chilled margins, breccia textures with angular clasts of the host rock and injection veins; intersecting veins of pseudotachylyte record multiple stages of seismic slip. The orientation of injection veins and marker offset along the most preserved pseudotachylyte fault veins indicate approximately a sinistral strike slip kinematic during faulting event responsible for the friction-induced melting. These observations indicate that ductile shear zones exploited pre-existing brittle fault zones including a network of pseudotachylytes, and that the fine-grained "ultramylonites" derive from former fine-grained pseudotachylytes. The pseudotachylyte microstructure is dominated by plagioclase microlites dispersed in a groundmass of fine-grained clinopyroxene. Clinopyroxene recrystallizes in the damage zone flanking the pseudotachylytes, indicating high metamorphic grade during pseudotachylyte formation. Small idioblastic or cauliflower garnet are scattered through the matrix and

  20. Reconstruction of the Magnetkoepfl rockfall event - Detecting rock fall release zones using terrestrial laser scanning, Hohe Tauern, Austria

    NASA Astrophysics Data System (ADS)

    Hartmeyer, I.; Keuschnig, M.; Delleske, R.; Schrott, L.

    2012-04-01

    Instability of rock faces in high mountain areas is an important risk factor for man and infrastructure, particularly within the context of climate change. Numerous rock fall events in the European Alps suggest an increasing occurrence of mass movements due to rising temperatures in recent years. Within the MOREXPERT project ('Monitoring Expert System for Hazardous Rock Walls') a new long-term monitoring site for mass movement and permafrost interaction has been initiated in the Austrian Alps. The study area is located at the Kitzsteinhorn (Hohe Tauern), a particularly interesting site for the investigation of glacier retreat and potential permafrost degradation and their respective consequences for the stability of alpine rock faces. To detect and quantify changes occurring at the terrain surface an extensive terrestrial laser scanning (TLS) monitoring campaign was started in 2011. TLS creates three-dimensional high-resolution images of the scanned area allowing precise quantification of changes in geometry and volume in steep rock faces over distances of up to several hundreds of meters. Within the TLS monitoring campaign at the Kitzsteinhorn a large number of differently dimensioned rock faces is examined (varying size, slope inclination etc.). Scanned areas include the Kitzsteinhorn northwest and south face, the Magnetkoepfl east face as well as a couple of small rock faces in the vicinity of the summit station. During the night from August 27th to August 28th 2011 a rock fall event was documented by employees of the cable car company. The release zone could not immediately be detected. The east face of the Magnetkoepfl covers approximately 70 meters in height and about 200 meters in width. It is made up of calcareous mica-schist and displays an abundance of well-developed joint sets with large joint apertures. Meteorological data from a weather station located at the same altitude (2.950m) and just 500m away from the release zone show that the rock fall event

  1. Application of the TitaniQ Geothermobarometer to metamorphic rocks of the Santa Rosa Mylonite Zone in southern California

    NASA Astrophysics Data System (ADS)

    Canada, T.; Behr, W. M.; Stockli, L.; Stockli, D. F.

    2014-12-01

    In order to study the behavior of the crust in different regions and over time, it remains important to be able to quantify the pressure (P) and temperature (T) conditions of metamorphism in exhumed rocks. The recently developed technique, known as "Titanium-in-quartz" (TitaniQ) shows particular promise as both a geothermometer and geobarometer, because it focuses on one of the most abundant minerals on Earth—quartz—and it can thus be applied to a very wide range of rock types. Despite the potential of TitaniQ, two aspects of the technique remain poorly understood. Firstly, the two most recently developed calibrations predict Ti concentrations that differ by close to a factor of three at the same temperature. Secondly, the effect of deformation on Ti re-equilibration at temperatures where static diffusion is sluggish is debated. We address these aspects of the TitaniQ thermobarometer by applying the technique to a suite of rocks in the Santa Rosa mylonite zone of eastern California that were deformed and metamorphosed at known P-T conditions. The Santa Rosa mylonite zone is a 100-km-long Cretaceous ductile thrust system that juxtaposes deformed metasedimentary rocks (P = 3-5 kbar, T = 600-800 C) known as the Palm Canyon Series in the hanging wall against mylonitized granodiorites (P 4-5 kbar, T = 400-550) of the Peninsular Ranges Batholith in the footwall. The Palm Canyon series includes quartzites, amphibolites and garnet-mica schists, most of which contain titanite as the primary Ti-bearing phase. We measure Ti concentrations in several samples from this unit to see whether they are consistent among different rock types and whether calibrations of the TitaniQ thermobarometer match the P-T conditions constrained by mineral assemblages. The granodiorites show a distinct strain gradient developed over approximately one kilometer as they are incorporated into the Santa Rosa mylonite zone; they range from weakly deformed at the shear zone margin to ultramylonitic

  2. Nanoscale Properties of Rocks and Subduction Zone Rheology: Inferences for the Mechanisms of Deep Earthquakes

    NASA Astrophysics Data System (ADS)

    Riedel, M. R.

    2007-12-01

    Grain boundaries are the key for the understanding of mineral reaction kinetics. More generally, nanometer scale processes involved in breaking and establishing bonds at reaction sites determine how and at which rate bulk rock properties change in response to external tectonic forcing and possibly feed back into various geodynamic processes. A particular problem is the effects of grain-boundary energy on the kinetics of the olivine-spinel phase transformation in subducting slabs. Slab rheology is affected in many ways by this (metastable) mineral phase change. Sluggish kinetics due to metastable hindrance is likely to cause particular difficulties, because of possible strong non-linear feedback loops between strain-rate and change of creep properties during transformation. In order to get these nanoscale properties included into thermo-mechanical models, reliable kinetic data is required. The measurement of grain-boundary energies is, however, a rather difficult problem. Conventional methods of grain boundary surface tension measurement include (a) equilibrium angles at triple junction (b) rotating ball method (c) thermal groove method, and others (Gottstein & Shvindlerman, 1999). Here I suggest a new method that allows for the derivation of grain-boundary energies for an isochemical phase transformation based on experimental (in-situ) kinetic data in combination with a corresponding dynamic scaling law (Riedel and Karato, 1997). The application of this method to the olivine-spinel phase transformation in subducting slabs provides a solution to the extrapolation problem of measured kinetic data: Any kinetic phase boundary measured at the laboratory time scale can be "scaled" to the correct critical isotherm at subduction zones, under experimentelly "forbidden" conditions (Liou et al., 2000). Consequences for the metastability hypothesis that relates deep seismicity with olivine metastability are derived and discussed. References: Gottstein G, Shvindlerman LS (1999

  3. Evaluation of Methods for Delineating Zones of Transport for Production Wells in Karst and Fractured-Rock Aquifers of Minnesota

    USGS Publications Warehouse

    Jones, Perry M.

    2010-01-01

    Assessment of groundwater-flow conditions in the vicinity of production wells in karst and fractured-rock settings commonly is difficult due in part to the lack of detailed hydrogeologic information and the resources needed to collect it. To address this concern and to better understand the hydrogeology and aquifer properties of karst and fractured-rock aquifers in Minnesota, the U.S. Geological Survey, in cooperation with the Minnesota Department of Health, conducted a study to evaluate methods for delineating zones of transport for 24 production wells in karst and fractured-rock aquifers in Minnesota. Two empirical methods for delineating zones of transport around wells were applied to the 24 production wells that extract groundwater from karst and fractured-rock aquifers in nine Minnesota communities. These methods were the truncated-parabola and modified-ellipse methods, and both methods assume porous-media flow conditions. The 24 wells extracted water from a karst aquifer (Prairie du Chien-Jordan aquifer), porous aquifers interspersed with solution-enhanced fractures (Jordan and Hinckley aquifers), or fractured-bedrock aquifers (Biwabik Iron-Formation and Sioux Quartzite aquifers). Zones of transport delineated using these two empirical methods were compared with zones of transport previously delineated by Minnesota Department of Health hydrologists for the wells using the calculated-fixed-radius method and groundwater-flow models. Large differences were seen in the size and shapes of most zones of transport delineated using the truncated-parabola and modified-ellipse methods compared with the zones of transport delineated by the Minnesota Department of Health. In general, the zones of transport delineated using the truncated-parabola and modified-ellipse methods were smaller in area than those delineated by the Minnesota Department of Health and included only small parts of the Minnesota Department of Health zones of transport. About two-thirds(67 percent) of

  4. Joint seismic, hydrogeological, and geomechanical investigations of a fracture zone in the Grimsel Rock Laboratory, Switzerland

    SciTech Connect

    Majer, E.L.; Myer, L.R.; Peterson, J.E. Jr.; Karasaki, K.; Long, J.C.S.; Martel, S.J. ); Bluemling, P.; Vomvoris, S. )

    1990-06-01

    This report is one of a series documenting the results of the Nagra-DOE Cooperative (NDC-I) research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a rock mass as a geologic repository for nuclear waste. From 1987 to 1989 the United States Department of Energy (DOE) and the Swiss Cooperative for the Storage of Nuclear Waste (Nagra) participated in an agreement to carryout experiments for understanding the effect of fractures in the storage and disposal of nuclear waste. As part of this joint work field and laboratory experiments were conducted at a controlled site in the Nagra underground Grimsel test site in Switzerland. The primary goal of these experiments in this fractured granite was to determine the fundamental nature of the propagation of seismic waves in fractured media, and to relate the seismological parameters to the hydrological parameters. The work is ultimately aimed at the characterization and monitoring of subsurface sites for the storage of nuclear waste. The seismic experiments utilizes high frequency (1000 to 10,000 Hertz) signals in a cross-hole configuration at scales of several tens of meters. Two-, three-, and four-sided tomographic images of the fractures and geologic structure were produced from over 60,000 raypaths through a 10 by 21 meter region bounded by two nearly horizontal boreholes and two tunnels. Intersecting this region was a dominant fracture zone which was the target of the investigations. In addition to these controlled seismic imaging experiments, laboratory work using core from this region were studied for the relation between fracture content, saturation, and seismic velocity and attenuation. In-situ geomechanical and hydrologic tests were carried out to determine the mechanical stiffness and conductivity of the fractures. 20 refs., 90 figs., 6 tabs.

  5. Physical rock properties in and around a conduit zone by well-logging in the Unzen Scientific Drilling Project, Japan

    USGS Publications Warehouse

    Ikeda, R.; Kajiwara, T.; Omura, K.; Hickman, S.

    2008-01-01

    The objective of the Unzen Scientific Drilling Project (USDP) is not only to reveal the structure and eruption history of the Unzen volcano but also to clarify the ascent and degassing mechanisms of the magma conduit. Conduit drilling (USDP-4) was conducted in 2004, which targeted the magma conduit for the 1990-95 eruption. The total drilled length of USDP-4 was 1995.75??m. Geophysical well logging, including resistivity, gamma-ray, spontaneous potential, sonic-wave velocity, density, neutron porosity, and Fullbore Formation MicroImager (FMI), was conducted at each drilling stage. Variations in the physical properties of the rocks were revealed by the well-log data, which correlated with not only large-scale formation boundaries but also small-scale changes in lithology. Such variations were evident in the lava dike, pyroclastic rocks, and breccias over depth intervals ranging from 1 to 40??m. These data support previous models for structure of the lava conduit, in that they indicate the existence of alternating layers of high-resistivity and high P-wave velocity rocks corresponding to the lava dikes, in proximity to narrower zones exhibiting high porosity, low resistivity, and low P-wave velocity. These narrow, low-porosity zones are presumably higher in permeability than the adjacent rocks and may form preferential conduits for degassing during magma ascent. ?? 2008 Elsevier B.V.

  6. Physical properties of fault zone rocks from SAFOD: Tying logging data to high-pressure measurements on drill core

    NASA Astrophysics Data System (ADS)

    Jeppson, T.; Tobin, H. J.

    2013-12-01

    In the summer of 2005, Phase 2 of the San Andreas Fault Observatory at Depth (SAFOD) borehole was completed and logged with wireline tools including a dipole sonic tool to measure P- and S-wave velocities. A zone of anomalously low velocity was detected from 3150 to 3414 m measured depth (MD), corresponding with the subsurface location of the San Andreas Fault Zone (SAFZ). This low velocity zone is 5-30% slower than the surrounding host rock. Within this broad low-velocity zone, several slip surfaces were identified as well as two actively deforming shear zones: the southwest deformation zone (SDZ) and the central deformation zone (CDZ), located at 3192 and 3302 m MD, respectively. The SAFZ had also previously been identified as a low velocity zone in seismic velocity inversion models. The anomalously low velocity was hypothesized to result from either (a) brittle deformation in the damage zone of the fault, (b) high fluid pressures with in the fault zone, or (c) lithological variation, or a combination of the above. We measured P- and S-wave velocities at ultrasonic frequencies on saturated 2.5 cm diameter core plug samples taken from SAFOD core obtained in 2007 from within the low velocity zone. The resulting values fall into two distinct groups: foliated fault gouge and non-gouge. Samples of the foliated fault gouge have P-wave velocities between 2.3-3.5 km/s while non-gouge samples lie between 4.1-5.4 km/s over a range of effective pressures from 5-70 MPa. There is a good correlation between the log measurements and laboratory values of P-and S wave velocity at in situ pressure conditions especially for the foliated fault gouge. For non-gouge samples the laboratory values are approximately 0.08-0.73 km/s faster than the log values. This difference places the non-gouge velocities within the Great Valley siltstone velocity range, as measured by logs and ultrasonic measurements performed on outcrop samples. As a high fluid pressure zone was not encountered during

  7. Climate change and human disturbance can lead to local extinction of Alpine rock ptarmigan: new insight from the western Italian Alps.

    PubMed

    Imperio, Simona; Bionda, Radames; Viterbi, Ramona; Provenzale, Antonello

    2013-01-01

    Alpine grouses are particularly vulnerable to climate change due to their adaptation to extreme conditions and to their relict distributions in the Alps where global warming has been particularly marked in the last half century. Grouses are also currently threatened by habitat modification and human disturbance, and an assessment of the impact of multiple stressors is needed to predict the fate of Alpine populations of these birds in the next decades. We estimated the effect of climate change and human disturbance on a rock ptarmigan population living in the western Italian Alps by combining an empirical population modelling approach and stochastic simulations of the population dynamics under the a1B climate scenario and two different disturbance scenarios, represented by the development of a ski resort, through 2050.The early appearance of snow-free ground in the previous spring had a favorable effect on the rock ptarmigan population, probably through a higher reproductive success. On the contrary, delayed snowfall in autumn had a negative effect possibly due to a mismatch in time to molt to white winter plumage which increases predation risk. The regional climate model PROTHEUS does not foresee any significant change in snowmelt date in the study area, while the start date of continuous snow cover is expected to be significantly delayed. The net effect in the stochastic projections is a more or less pronounced (depending on the model used) decline in the studied population. The addition of extra-mortality due to collision with ski-lift wires led the population to fatal consequences in most projections. Should these results be confirmed by larger studies the conservation of Alpine populations would deserve more attention. To counterbalance the effects of climate change, the reduction of all causes of death should be pursued, through a strict preservation of the habitats in the present area of occurrence. PMID:24260581

  8. Climate Change and Human Disturbance Can Lead to Local Extinction of Alpine Rock Ptarmigan: New Insight from the Western Italian Alps

    PubMed Central

    Imperio, Simona; Bionda, Radames; Viterbi, Ramona; Provenzale, Antonello

    2013-01-01

    Alpine grouses are particularly vulnerable to climate change due to their adaptation to extreme conditions and to their relict distributions in the Alps where global warming has been particularly marked in the last half century. Grouses are also currently threatened by habitat modification and human disturbance, and an assessment of the impact of multiple stressors is needed to predict the fate of Alpine populations of these birds in the next decades. We estimated the effect of climate change and human disturbance on a rock ptarmigan population living in the western Italian Alps by combining an empirical population modelling approach and stochastic simulations of the population dynamics under the a1B climate scenario and two different disturbance scenarios, represented by the development of a ski resort, through 2050.The early appearance of snow-free ground in the previous spring had a favorable effect on the rock ptarmigan population, probably through a higher reproductive success. On the contrary, delayed snowfall in autumn had a negative effect possibly due to a mismatch in time to molt to white winter plumage which increases predation risk. The regional climate model PROTHEUS does not foresee any significant change in snowmelt date in the study area, while the start date of continuous snow cover is expected to be significantly delayed. The net effect in the stochastic projections is a more or less pronounced (depending on the model used) decline in the studied population. The addition of extra-mortality due to collision with ski-lift wires led the population to fatal consequences in most projections. Should these results be confirmed by larger studies the conservation of Alpine populations would deserve more attention. To counterbalance the effects of climate change, the reduction of all causes of death should be pursued, through a strict preservation of the habitats in the present area of occurrence. PMID:24260581

  9. Mount St. Augustine volcano fumarole wall rock alteration: mineralogy, zoning, composition and numerical models of its formation process

    NASA Astrophysics Data System (ADS)

    Getahun, Aberra; Reed, Mark H.; Symonds, Robert

    1996-05-01

    Intensely altered wall rock was collected from high-temperature (640 °C) and low-temperature (375 °C) vents at Augustine volcano in July 1989. The high-temperature altered rock exhibits distinct mineral zoning differentiated by color bands. In order of decreasing temperature, the color bands and their mineral assemblages are: (a) white to grey (tridymite-anhydrite); (b) pink to red (tridymite-hematite-Fe hydroxide-molysite (FeCl 3) with minor amounts of anhydrite and halite); and (c) dark green to green (anhydrite-halite-sylvite-tridymite with minor amounts of molysite, soda and potash alum, and other sodium and potassium sulfates). The alteration products around the low-temperature vents are dominantly cristobalite and amorphous silica with minor potash and soda alum, aphthitalite, alunogen and anhydrite. Compared to fresh 1986 Augustine lava, the altered rocks exhibit enrichments in silica, base metals, halogens and sulfur and show very strong depletions in Al in all alteration zones and in iron, alkali and alkaline earth elements in some of the alteration zones. To help understand the origins of the mineral assemblages in altered Augustine rocks, we applied the thermochemical modeling program, GASWORKS, in calculations of: (a) reaction of the 1987 and 1989 gases with wall rock at 640 and 375 °C; (b) cooling of the 1987 gas from 870 to 100 °C with and without mineral fractionation; (c) cooling of the 1989 gas from 757 to 100 °C with and without mineral fractionation; and (d) mixing of the 1987 and 1989 gases with air. The 640 °C gas-rock reaction produces an assemblage consisting of silicates (tridymite, albite, diopside, sanidine and andalusite), oxides (magnetite and hercynite) and sulfides (bornite, chalcocite, molybdenite and sphalerite). The 375 °C gas-rock reaction produces dominantly silicates (quartz, albite, andalusite, microcline, cordierite, anorthite and tremolite) and subordinate amounts of sulfides (pyrite, chalcocite and wurtzite), oxides

  10. Modeling Spatial Structure of Rock Fracture Surfaces Before and After Shear Test: A Method for Estimating Morphology of Damaged Zones

    NASA Astrophysics Data System (ADS)

    Babanouri, Nima; Karimi Nasab, Saeed

    2015-05-01

    This paper deals with the structural analysis of rock fracture roughness, and accordingly, a method is developed for estimating/predicting the post-shearing 3D geometry of the fracture surface. For this purpose, surfaces of three natural rock fractures were digitized and studied before and after the direct shear test. The variogram analysis of the surfaces indicated a strong non-linear trend in the topography data. Hence, the spatial variability of the rock fracture surfaces was decomposed to: one deterministic component, characterized by a high-order polynomial representing the large-scale undulations, and one stochastic component, described by the variogram of residuals representing the small-scale roughness. Using an image-processing technique, a total of 343 damage zones with different sizes, shapes, initial roughness characteristics, local stress fields, and/or asperity strength values were spatially located and clustered. In order to characterize the overall spatial structure of the degraded zones, the concept of the `pseudo-zonal variogram' was introduced. The results showed that the spatial continuity at the damage zones increases due to the asperity degradation. The increase in the variogram range is anisotropic and tends to be higher along the shearing. Consequently, the direction of maximum continuity rotates towards the shear direction. After modeling the evolution of the spatial structure with shearing and detecting boundaries of the degraded areas, a methodology was presented to provide a regression-kriging estimate of the morphology of sheared surfaces. The proposed method can be considered as a cost-free and reasonably accurate alternative to expensive techniques of scanning the rock fracture surface after the shear test.

  11. Profile of a modern coastal mixing zone in Tertiary carbonate rocks of the Floridan aquifer, Pasco County, Florida

    SciTech Connect

    Jee, J.L.; Randazzo, A.F. ); Wicks, C.M.; Herman, J.S. )

    1991-03-01

    Rock-core and ground-water samples from the Floridan aquifer mixing zone water were studied to assess diagenesis and porosity and permeability development. This zone occurs in the Ocala Limestone (Eocene) and Suwannee Limestone (Oligocene); shallow-marine lithofacies thereof are grouped into eight informal lithologic units, five in the Ocala and three in the Suwannee. Most diagenetic features relate to episodic sea-level fluctuations throughout the {le} 50 my post depositional history. Paragenesis includes marine micritization and cementation, meteoric mineralogic stabilization, dissolution enhancement of porosity, and phreatic, equant calcite cements and echinoderm overgrowths. Dolomitization of selected intervals occurred relatively late in the paragenetic sequence and dolomite crystals show no evidence of subsequent alteration. Calcite cements are noncathodoluminescent and have {delta}{sup 13}C and {delta}{sup 18}O values higher in the Ocala and lower in the Suwannee. Dolomite crystals are nonstoichiometric and thinly zoned, alternating noncathodoluminescent and red-orange cathodoluminescent. Microprobe analysis revealed no systematic variations in Ca and Mg and concentrations of Mn, Fe, Sr and Na below reliable limits. Dolomite stable isotope value ranges are {minus}1.30 to +0.85 {delta}{sup 13}C (PDB) and +0.274 to +2.651 {delta}{sup 18}O (PDB). The modern regional meteoric aquifer is a mature, mineralogically stable carbonate sequence. Aqueous geochemical data indicate supersaturation with respect to stoichiometric calcite and dolomite, and slight supersaturation with respect to aragonite. Bulk solubility measurements show that observed water compositions are in approximate equilibrium with respect to aquifer rocks and there is little evidence of water/rock interaction in this modern mixing zone.

  12. Relations of zoned pegmatites to other pegmatites, granite, and metamorphic rocks in the southern Black Hills, South Dakota

    USGS Publications Warehouse

    Norton, J.J.; Redden, J.A.

    1990-01-01

    The pegmatite field and the Harney Peak Granite of the southern Black Hills, South Dakota, form an igneous system that progresses from slightly biotitic muscovite granite through layered pegmatitic granite, with alternating sodic and potassic rocks, to simple plagioclase-quartz-perthite pegmatites, and on to zoned pegmatites. Most of the country rocks are Lower Proterozoic mica schists. At 1700 Ga, intrusion of the Harney Peak Granite created a large dome in these rocks, a thermal aureole with a staurolite, a first sillimanite isograd, and a small area of metamorphism above the second sillimanite isograd. The zoned pegmatites have a strong tendency to occur in clusters, and the types of pegmatites are different in different clusters. A less obvious tendency is a regional zonation in which rare-mineral pegmatites become more abundant and muscovite pegmatites less abundant toward the outskirts of the region. The composition of the granite indicates that its magma originated by partial melting of metasedimentary mica schists similar to those at the present surface. The pegmatitic nature of most of the granite probably reflects exsolution of an aqueous phase. -from Authors

  13. Abnormal Activation of RhoA/ROCK-I Signaling in Junctional Zone Smooth Muscle Cells of Patients With Adenomyosis.

    PubMed

    Wang, S; Duan, H; Zhang, Y; Sun, F Q

    2016-03-01

    Adenomyosis (ADS) is a common estrogen-dependent gynecological disease with unknown etiology. The RhoA/Rho-kinase (ROCK) signaling pathway is involved in various cellular functions, including migration, proliferation, and smooth muscle contraction. Here we examined the potential role of this pathway in junctional zone (JZ) contraction in women with and without ADS. We demonstrated that in the normal JZ, RhoA and ROCK-I messenger RNA (mRNA) and protein expression was significantly higher in the proliferative phase of the menstrual cycle than in the secretory phase. Expression of RhoA and ROCK-I in the JZ from women with ADS was significantly higher than in the control women and showed no significant differences across the menstrual cycle. Treatment of JZ smooth muscle cells (JZSMCs) with estrogen at 0, 1, 10, or 100 nmol/L for 24 hours resulted in increased expression of RhoA, ROCK-I, and myosin light-chain (MLC) phosphorylation (p-MLC) in a dose-dependent manner. In parallel to its effects on p-MLC, estrogen-mediated, dose-dependent contraction responses in JZSMCs. Estrogen-mediated contraction in the ADS group was significantly higher than in the controls and also showed no significant differences across the menstrual cycle. These effects were suppressed in the presence of ICI 182780 or Y27632, supporting an estrogen receptor-dependent and RhoA activation-dependent mechanism. Our results indicate that the level of RhoA and ROCK-I increases in patients with ADS and the cyclic change is lost. Estrogen may affect uterine JZ contraction of ADS by enhancing RhoA/ ROCK-I signaling. PMID:26335177

  14. Rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones

    USGS Publications Warehouse

    Kirby, S.H.

    1985-01-01

    Emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures, conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones. Much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock-mechanics-based yield criteria for the inelastic deformations at the top and base. At mid-plate depths, stresses are likely to be supported elastically because bending strains and elastic stresses are low. The collisional tectonic regime, however, is far more complex because very large permanent strains are sustained at mid-plate depths and this requires us to include the broad transition between brittle and ductile flow. Moreover, important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid-plate depths. Two specific contributions of laboratory rock rheology research are considered in this paper. First, the high-temperature steady-state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks. Rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere. The thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm Tc above which (at geologic strain rates) the high-temperature ductile strength falls below some arbitrary strength isobar (e.g., 100 MPa). For olivine Tc is about 700??-800??C but for other crustal silicates, Tc may be as low as 400??-600??C, suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the Moho, as suggested by a number of workers on independent grounds. Put another way, the Moho is a rheological discontinuity. A second class of laboratory observations pertains to

  15. Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves

    USGS Publications Warehouse

    Ellsworth, William L.; Malin, Peter E.

    2011-01-01

    Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by Fg, can propagate. Here we show with core samples, well logs and Fg-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (FL) and Rayleigh-type- (FR) guided waves, but also a new fault-guided wave, which we name FF. As recorded 2.7 km underground, FF is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that FF travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, FF at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site.

  16. Fabric-related velocity anisotropy and shear wave splitting in rocks from the Santa Rosa Mylonite Zone, California

    SciTech Connect

    Kern, H. ); Wenk, H.R. )

    1990-07-10

    The directional dependence of P and S wave velocities have been measured at pressures (up to 600 MPa) and temperatures (up to 700C) in rocks from the Santa Rosa Mylonite Zone (southern California). During tectonism, these were progressively deformed from granodiorite protolith to mylonite and ultimately phyllonite. The mineralogical and chemical composition of protolith and mylonite is nearly identical. Thus these rocks provide excellent material for documenting the effect of microstructural and textural changes on rock anisotropy. Velocity anisotropy increases significantly with the degree of deformation, whereas average velocities and densities do not change. At low pressure (50 MPa) the velocity anisotropy ranges from 1.7% in granodiorite up to 19% in phyllonite and is due to both oriented microfractures and crystallographic preferred orientation. At high pressure (600 MPa), the residual anisotropy up to 12% is mainly due to preferred mineral orientation, in particular of biotite. Significant shear wave splitting is measured parallel to the foliation plane and shows a good correlation with the biotite texture. These observations confirm that oriented microcracks and preferred orientation of minerals should be taken into account in the interpretation of seismic reflection and refraction data in terranes with deformed rocks.

  17. Mount St. Augustine volcano fumarole wall rock alteration: Mineralogy, zoning, composition and numerical models of its formation process

    USGS Publications Warehouse

    Getahun, A.; Reed, M.H.; Symonds, R.

    1996-01-01

    Intensely altered wall rock was collected from high-temperature (640??C) and low-temperature (375??C) vents at Augustine volcano in July 1989. The high-temperature altered rock exhibits distinct mineral zoning differentiated by color bands. In order of decreasing temperature, the color bands and their mineral assemblages are: (a) white to grey (tridymite-anhydrite); (b) pink to red (tridymite-hematite-Fe hydroxide-molysite (FeCl3) with minor amounts of anhydrite and halite); and (c) dark green to green (anhydrite-halite-sylvite-tridymite with minor amounts of molysite, soda and potash alum, and other sodium and potassium sulfates). The alteration products around the low-temperature vents are dominantly cristobalite and amorphous silica with minor potash and soda alum, aphthitalite, alunogen and anhydrite. Compared to fresh 1986 Augustine lava, the altered rocks exhibit enrichments in silica, base metals, halogens and sulfur and show very strong depletions in Al in all alteration zones and in iron, alkali and alkaline earth elements in some of the alteration zones. To help understand the origins of the mineral assemblages in altered Augustine rocks, we applied the thermochemical modeling program, GASWORKS, in calculations of: (a) reaction of the 1987 and 1989 gases with wall rock at 640 and 375??C; (b) cooling of the 1987 gas from 870 to 100??C with and without mineral fractionation; (c) cooling of the 1989 gas from 757 to 100??C with and without mineral fractionation; and (d) mixing of the 1987 and 1989 gases with air. The 640??C gas-rock reaction produces an assemblage consisting of silicates (tridymite, albite, diopside, sanidine and andalusite), oxides (magnetite and hercynite) and sulfides (bornite, chalcocite, molybdenite and sphalerite). The 375??C gas-rock reaction produces dominantly silicates (quartz, albite, andalusite, microcline, cordierite, anorthite and tremolite) and subordinate amounts of sulfides (pyrite, chalcocite and wurtzite), oxides (magnetite

  18. Characterisation and monitoring of the Excavation Disturbed Zone (EDZ) in fractured gneisses of the Roselend underground laboratory: permeability measurements, transport property changes and related radon bursts

    NASA Astrophysics Data System (ADS)

    Wassermann, Jérôme; Sabroux, Jean-Christophe; Richon, Patrick; Pontreau, Sébastien; Guillon, Sophie; Pili, Eric

    2010-05-01

    pressure measurements between an obturated borehole and the tunnel is conducted to monitor the possible modifications of the transport properties of the EDZ due to hydraulical and/or mechanical sollicitations of the nearby Roselend reservoir lake. As radon level is controlled by emanation and transport path through the medium. The observed bursts of radon should be due to changes of the radon transport properties (Trique et al. 1999) of the EDZ. A correlation between the differential pressure variations and radon bursts is clearly observed. Radon bursts seem to be related to overpressure events that take place in the instrumented borehole. Which external sollicitations, hydraulical or mechanical, or both, induce such a behaviour? References Bossart, P., Meier, P. M., Moeri, A., Trick, T., and J.-C. Mayor (2002). Geological and hydraulic characterisation of the excavation disturbed zone in the Opalinus Clay of the Mont Terri Rock Laboratory, Engineering Geology, 66, 19-38. Dezayes, C., and T. Villemin (2002). Etat de la fracturation dans la galerie CEA de Roselend et analyse de la déformation cassante dans le massif du Méraillet, technical report, Lab. de Geodyn. de Chaisnes Alp., Univ. de Savoie, Savoie, France. Jakubick, A. T., and T. Franz (1993). Vacuum testing of the permeability of the excavation damaged zone, Rock Mech. Rock Engng., 26(2), 165-182. Patriarche, D., Pili, E., Adler, P. M., and J.-F. Thovert (2007). Stereological analysis of fractures in the Roselend tunnel and permeability determination, Water Resour. Res., 43, W09421. Richon, P., Perrier, F., Sabroux, J.-C., Trique, M., Ferry, C., Voisin, V., and E. Pili (2004). Spatial and time variations of radon-222 concentration in the atmosphere of a dead-end horizontal tunnel, J. Environ. Radioact., 78, 179-198. Richon, P., Perrier, F., Pili, E., and J.-C. Sabroux (2009). Detectability and significance of the 12hr barometric tide in radon-222 signal, dripwater flow rate, air temperature and carbon dioxide

  19. Rift-zone magmatism: Petrology of basaltic rocks transitional from CFB to MORB, southeastern Brazil margin

    NASA Astrophysics Data System (ADS)

    Fodor, R. V.; Vetter, S. K.

    1984-12-01

    Compositions of basaltic samples from the southeastern Brazil passive margin (18° 24° S) depict the change from continental to oceanic lithosphere during the opening of the South Atlantic Ocean. Samples studied range from 138 to 105 m.y. old and are from 12 Petrobrás drill cores recovered from the coastline to about 150 km offshore in the Espirito Santo, Campos, and Santos basins. Compositions vary, ranging, for example, from 49 54 wt.% SiO2, 0.5 3.0 wt.% TiO2, 0.6 5.0 FeO*/MgO, and <1->6 La/ Yb(n), but can be grouped: (i) basalts enriched in incompatible elements, such as K (some K2O>2.0 wt.%), Rb (>18 ppm), Zr (>120 ppm), and LREE (some FeO* 16 wt.%; most with SiO2 51 54 wt.%), and resembling Serra Geral continental flood basalts (SG-CFB) of southern Brazil; (ii) basalts less enriched, or transitional, in incompatible elements, having K2O <0.40 wt.% and flat REE patterns, and resemble N. Atlantic diabases and FAMOUS basalts; and (iii) one depleted sample, Ce/Yb(n)=0.7, where Ce(n)=4. Expressed in oceanic-basalt terminology and Zr-Nb-Y abundances, ‘enriched’ samples are P- and T-type MORB (e.g., Zr/Nb ˜4 25), ‘transitional’ samples are T-type (Zr/ Nb ˜8 27), and the ‘depleted’ sample is N-type MORB (Zr/Nb>30). Trace-element ratios (e.g., Zr/Nb, Zr/Y) link the Brazil margin basalts to a heterogeneous mantle (attributed to metasomatic veining) of variably proportioned mixtures of depleted-mantle (N-MORB) and plume (P-MORB, e.g., Tristan hotspot) materials. The various compositions therefore reflect, in part, different zones of melting during the separation of Gondwanaland, where gradual decompression during rifting enabled concurrent melting of upper, more depleted (non- or sparsely-veined) mantle and enriched (densely-veined) mantle. Within the time represented, melting produced enriched, transitional, and depleted magmas that were emplaced subaerially, hypabyssally, and subaqueously; they mark the transition from CFB before rifting and separation

  20. Assessing the disturbed rock zone (DRZ) around a 655 meter vertical shaft in salt using ultrasonic waves: An update

    SciTech Connect

    HARDY,ROBERT D.; HOLCOMB,DAVID J.

    2000-03-14

    An array of ultrasonic transducers was constructed consisting of three identical arrays at various depths in an air intake shaft at the Waste Isolation Pilot Plant (WIPP). Each array consists of transducers permanently installed in three holes arranged in an L shape. An active array, created by appropriate arrangement of the transducers and selection of transmitter-receiver pairs, allows the measurement of transmitted signal velocities and amplitudes (for attenuation studies) along 216 paths parallel, perpendicular and tangential to the shaft walls. Transducer positions were carefully surveyed, allowing absolute velocity measurements. Installation occurred over a period of about two years beginning in early 1989, with nearly continuous operation since that time, resulting in a rare, if not unique, record of the spatial and temporal variability of damage development around an underground opening. This paper reports results from the last two years of operation, updating the results reported by Holcomb, 1999. Results will be related to the damage, due to microcracking, required to produce the observed changes. It is expected that the results will be useful to other studies of the long-term deformation characteristics of salt.

  1. Linking Weathering, Rock Moisture Dynamics, Geochemistry, Runoff, Vegetation and Atmospheric Processes through the Critical Zone: Graduate Student led Research at the Eel River Critical Zone Observatory

    NASA Astrophysics Data System (ADS)

    Dietrich, W. E.

    2014-12-01

    In the Eel River Critical Zone Observatory lies Rivendell, a heavily-instrumented steep forested hillslope underlain by nearly vertically dipping argillite interbedded with sandstone. Under this convex hillslope lies "Zb", the transition to fresh bedrock, which varies from less than 6 m below the surface near the channel to 20 m at the divide. Rempe and Dietrich (2014, PNAS) show that the Zb profile can be predicted from the assumption that weathering occurs when drainage is induced in the uplifting fresh bedrock under hillslopes by lateral head gradients driven by channel incision at the hillslope boundary. Infiltrating winter precipitation is impeded at the lower conductivity boundary at Zb, generating perched groundwater that dynamically pulses water laterally to the channel, controlling stream runoff. Below the soil and above the water table lies an unsaturated zone through which all recharge to the perched groundwater (and thus all runoff to channels) occurs. It is this zone and the waters in them that profoundly affect critical zone processes. In our seasonally dry environment, the first rains penetrate past the soil and moisten the underlying weathered bedrock (Salve et al., 2012, WRR). It takes about 200 to 400 mm of cumulative rain, however, before the underlying groundwater rises significantly. Oshun et al (in review) show that by this cumulative rainfall the average of the wide-ranging isotopic signature of rain reaches a nearly constant average annual value. Consequently, the recharging perched groundwater shows only minor temporal isotopic variation. Kim et al, (2014, GCA) find that the winter high-flow groundwater chemistry is controlled by relatively fast-reacting cation exchange processes, likely occurring in transit in the unsaturated zone. Oshun also demonstrates that the Douglas fir rely on this rock moisture as a water source, while the broadleaf trees (oaks and madrone) use mostly soil moisture. Link et al (2014 WRR) show that Doug fir declines

  2. Petrogenesis of cataclastic rocks within the San Andreas fault zone of Southern California U.S.A.

    NASA Astrophysics Data System (ADS)

    Lawford Anderson, J.; Osborne, Robert H.; Palmer, Donald F.

    1980-08-01

    This paper petrologically characterizes cataclastic rocks derived from four sites within the San Andreas fault zone of southern California. In this area, the fault traverses an extensive plutonic and metamorphic terrane and the principal cataclastic rock formed at these upper crustal levels is unindurated gouge derived from a range of crystalline rocks including diorite, tonalite, granite, aplite, and pegmatite. The mineralogical nature of this gouge is decidedly different from the "clay gouge" reported by Wu (1975) for central California and is essentially a rock flour with a quartz, feldspar, biotite, chlorite, amphibole, epidote and oxide mineralogy representing the milled-down equivalent of the original rock. Clay development is minor (less than 4 wt. %) to nonexistent and is exclusively kaolinite. Alterations involve hematitic oxidation, chlorite alteration on biotite and amphibole, and local introduction of calcite. Electron microprobe analysis showed that in general the major minerals were not reequilibrated with the pressure—temperature regime imposed during cataclasis. Petrochemically, the form of cataclasis that we have investigated is largely an isochemical process. Some hydration occurs but the maximum amount is less than 2.2% added H 2O. Study of a 375 m deep core from a tonalite pluton adjacent to the fault showed that for Si, Al, Ti, Fe, Mg, Mn, K, Na, Li, Rb, and Ba, no leaching and/or enrichment occurred. Several samples experienced a depletion in Sr during cataclasis while lesser number had an enrichment of Ca (result of calcite veining). Texturally, the fault gouge is not dominated by clay-size material but consists largely of silt and fine sand-sized particles. An intriguing aspect of our work on the drill core is a general decrease in particulate size with depth (and confining pressure) with the predominate shifting sequentially from fine sand to silt-size material. The original fabric of these rocks is commonly not disrupted during the

  3. Intrusive rocks of the Holden and Lucerne quadrangles, Washington; the relation of depth zones, composition, textures, and emplacement of plutons

    USGS Publications Warehouse

    Cater, Fred W.

    1982-01-01

    serpentine. These occur either as included irregular masses in later intrusives or as tectonically emplaced lenses in metamorphic rocks. Also of uncertain age but probably much younger, perhaps as young as Eocene, are larger masses of hornblendite and hornblende periodotite that grade into hornblende gabbro. These are exposed on the surface and in the underground workings of the Holden mine. Oldest of the granitoid intrusives are the narrow, nearly concordant Dumbell Mountain plutons, having a radiometric age of about 220 m.y. They consist of gneissic hornblende-quartz diorite and quartz diorite gneiss. Most contacts consist of lit-par-lit zones, but some are gradational or more rarely sharp. The plutons are typically catazonal. Closely resembling the Dumbell Mountain plutons in outcrop appearance, but differing considerably in composition, are the Bearcat Ridge plutons. These consist of gneissic quartz diorite and granodiorite. The Bearcat Ridge plutons are not in contact with older dated plutons, but because their textural and structural characteristics so closely resemble those of the Dumbell Mountain plutons, they are considered to be the same age. Their composition, however, is suggestive of a much younger age. Cutting the Dumbell Mountain plutons is the Leroy Creek pluton, consisting of gneissic biotite-quartz diorite and trondjhemite. The gneissic foliation in the Leroy Creek is characterized by a strong and pervasive swirling. Cutting both the Dumbell Mountain and Leroy Creek plutons are the almost dikelike Seven-fingered Jack plutons. These range in composition from gabbro to quartz diorite; associated with them are contact complexes of highly varied rocks characterized by gabbro and coarse-grained hornblendite. Most of the rocks are gneissic, but some are massive and structureless. Radiometric ages by various methods range from 100 to 193 m.y. Dikes, sills, small stocks, and irregular clots of leucocratic quartz diorite and granodiorite are abundant in t

  4. Isotopic evidence (B, C, O) of deep fluid processes in fault rocks from the active Woodlark Basin detachment zone

    NASA Astrophysics Data System (ADS)

    Kopf, Achim; Behrmann, Jan H.; Deyhle, Annette; Roller, Sybille; Erlenkeuser, Helmut

    2003-03-01

    We report results from boron, carbon and oxygen stable isotope analyses of faulted and veined rocks recovered by scientific ocean drilling during ODP Leg 180 in the western Woodlark Basin, off Papua New Guinea. In this area of active continental extension, crustal break-up and incipient seafloor spreading, a shallow-dipping, seismically active detachment fault accommodates strain, defining a zone of mylonites and cataclasites, vein formation and fluid infiltration. Syntectonic microstructures and vein-fill mineralogy suggest frictional heating during slip during extension and exhumation of Moresby Seamount. Low carbon and oxygen isotope ratios of calcite veins indicate precipitation from hydrothermal fluids (δ 13C PDB down to -17‰; δ 18O PDB down to -22‰) formed by both dehydration and decarbonation. Boron contents are low (<7 ppm), indicating high-grade metamorphic source rock for the fluids. Some of the δ 11B signatures (17-35‰; parent solutions to calcite vein fills) are low when compared to deep-seated waters in other tectonic environments, likely reflecting preferential loss of 11B during low-grade metamorphism at depth. Pervasive devolatilization and flux of CO 2-rich fluids are evident from similar vein cement geochemistry in the detachment fault zone and splays further updip. Multiple rupture-and-healing history of the veins suggests that precipitation may be an important player in fluid pressure evolution and, hence, seismogenic fault movement.

  5. Maine Pseudotachylyte Localities and the Role of Host Rock Anisotropy in Fault Zone Development and Frictional Melting

    NASA Astrophysics Data System (ADS)

    Swanson, M. T.

    2004-12-01

    Three brittle strike-slip fault localities in coastal Maine have developed pseudotachylyte fault veins, injection veins and other reservoir structures in a variety of host rocks where the pre-existing layering can serve as a controlling fabric for brittle strike-slip reactivation. Host rocks with a poorly-oriented planar anisotropy at high angles to the shear direction will favor the development of R-shears in initial en echelon arrays as seen in the Two Lights and Richmond Island Fault Zones of Cape Elizabeth that cut gently-dipping phyllitic quartzites. These en echelon R-shears grow to through-going faults with the development of P-shear linkages across the dominantly contractional stepovers in the initial arrays. Pseudotachylyte on these faults is very localized, typically up to 1-2 mm in thickness and is restricted to through-going fault segments, P-shear linkages and some sidewall ripouts. Overall melt production is limited by the complex geometry of the multi-fault array. Host rocks with a favorably-oriented planar anisotropy for reactivation in brittle shear, however, preferentially develop a multitude of longer, non-coplanar layer-parallel fault segments. Pseudotachylyte in the newly-discovered Harbor Island Fault Zone in Muscongus Bay is developed within vertical bedding on regional upright folds with over 50 individual layer-parallel single-slip fault veins, some of which can be traced for over 40 meters along strike. Many faults show clear crosscuts of pre-existing quartz veins that indicate a range of coseismic displacements of 0.23-0.53 meters yielding fault vein widths of a few mm and dilatant reservoirs up to 2 cm thick. Both vertical and rare horizontal lateral injection veins can be found in the adjoining wall rock up to 0.7 cm thick and 80 cm in length. The structure of these faults is simple with minor development of splay faults, sidewall ripouts and strike-slip duplexes. The prominent vertical flow layering within the mylonite gneisses of

  6. Oxygen and hydrogen isotope compositions of eclogites and associated rocks from the Eastern Sesia zone (Western Alps, Italy)

    USGS Publications Warehouse

    Desmons, J.; O'Neil, J.R.

    1978-01-01

    Oxygen and hydrogen isotope analyses have been made of mineral separates from eclogites, glaucophanites and glaucophane schists from the eastern Sesia zone (Italian Western Alps). Regularities in (1) hydrogen isotope compositions, (2) order of 18O enrichment among coexisting minerals, and (3) ?? 18O (quartz-rutile) and ?? 18O (quartz-phengite) imply attainment of a high degree of isotopic equilibrium. However, some scattering of ??18O values of individual minerals indicates that the eclogitic assemblage did not form in the presence of a thoroughly pervasive fluid. Minerals from an eclogitic lens enclosed in marble have ??18O values distinctly different from those measured in the other rocks. The ??18O values are high in comparison with other type C eclogites of the world, and it is proposed that the fluid present during the high pressure metamorphism has to a large extent been inherited from the precursor rocks of amphibolite facies. An average formation temperature of 540 ?? C is inferred from the oxygen isotope fractionations between quartz and rutile and between quartz and white mica. This temperature is in accordance with petrologic considerations and implies subduction of the precursor rocks into the upper mantle to achieve the high pressures required. ?? 1978 Springer-Verlag.

  7. Stratigraphic and structural relations of Lower Triassic rocks within the frontal fold-and-thrust zone of southwestern Montana

    SciTech Connect

    Paull, R.K.; Paull, R.A. )

    1991-06-01

    New sections of Lower Triassic rocks were measured within the frontal fold-and-thrust zone of southwestern Montana at Garfield Canyon, Horse Prairie Creek, Kennison Spring, and Birch Creek to clarify stratigraphic and structural relations. Triassic rocks disconformably overlie Upper Permian units and unconformably underlie younger rocks. From oldest to youngest, they include the Dinwoody, Woodside, and Thaynes formations. The Dinwoody consists of shale, siltstone, and limestone; thickness varies from 152 to 273 m. Red beds of the Woodside thin northward to zero in the northern Tendoy Mountains. The Thaynes is comprised of limestone, siltstone, and sandstone; thickness varies from 244 m in the south, zero in the central area, to 51 m in the north. North of the Woodside termination, recognition of the Thaynes depends upon recovery of Smithian conodonts. Conodonts provide correlation and biofacies information for this study. From Birch Creek northward, conodonts are basinal, consistent with lithofacies data. This area is within the McCartney Mountain salient, a depositional basin which may have existed on the craton margin prior to thrusting. However, there is no evidence to support basinal conditions in the Blacktail Mountain salient to the south. Although thermal alteration values for most conodonts are within the range of oil and condensate production, those from Birch Creek north exceed the stability regime for hydrocarbons.

  8. Direct measurement of 3D elastic anisotropy on rocks from the Ivrea zone (Southern Alps, NW Italy)

    NASA Astrophysics Data System (ADS)

    Pros, Z.; Lokajíček, T.; Přikryl, R.; Klíma, K.

    2003-07-01

    Lower crustal and upper mantle rocks exposed at the earth's surface present direct possibility to measure their physical properties that must be, in other cases, interpreted using indirect methods. The results of these direct measurements can be then used for the corrections of models based on the indirect data. Elastic properties are among the most important parameters studied in geophysics and employed in many fields of earth sciences. In laboratory, dynamic elastic properties are commonly tested in three mutually perpendicular directions. The spatial distribution of P- and S-wave velocities are then computed using textural data, modal composition, density and elastic constants. During such computation, it is virtually impossible to involve all microfabric parameters like different types of microcracking, micropores, mineral alteration or quality of grain boundaries. In this study, complete 3D ultrasonic transmission of spherical samples in 132 independent directions at several levels of confining pressure up to 400 MPa has been employed for study of selected mafic and ultrabasic rocks sampled in and nearby Balmuccia ultrabasic massif (Ivrea zone, Southern Alps, NW Italy). This method revealed large directional variance of maximum P-wave velocity and different symmetries (orthorhombic vs. transversal isotropic) of elastic waves 3D distribution that has not been recorded on these rocks before. Moreover, one dunite sample exhibits P-wave velocity approaching to that of olivine single crystal being interpreted as influence of CPO.

  9. What's so critical about the critical zone?: New insights at the boundaries between hydrology, pedology, geomorphology, rocks and life (Invited)

    NASA Astrophysics Data System (ADS)

    Grant, G.

    2013-12-01

    understanding of feedbacks among vegetation growth and water uptake, soil moisture regimes, snowpack dynamics, and overall forest health are challenging previous assumptions about how best to manage forest environments in the face of a warming atmosphere and increased frequencies of disturbance. Time will tell whether these new perspectives represent incremental or fundamental shifts in our thinking about the critical zone, but it is clearly an exciting time for critical zone science and scientists.

  10. Genesis of rare-metal pegmatites and alkaline apatite-fluorite rocks of Burpala massi, Northern Baikal folded zone

    NASA Astrophysics Data System (ADS)

    Sotnikova, Irina; Vladykin, Nikolai

    2015-04-01

    Burpalinsky rare metal alkaline massif in the Northern Baikal folded zone in southern margin of Siberian Platform, is a of intrusion central type, created 287 Ma covering area of about 250 km2. It is composed of nepheline syenites and pulaskites grading to quartz syenites in the contacts. Veines and dykes are represented by shonkinites, sodalite syenite, leucocratic granophyres, alkali granites and numerous rare metal alkaline syenite pegmatites and two dykes of carbonatites. All rocks except for granites are cut by a large apatite-fluorite dyke rocks with mica and magnetite, which in turn is cut by alaskite granites dyke. The massif has been studied by A.M. Portnov, A.A. Ganzeev et al. (1992) Burpalinsky massif is highly enriched with trace elements, which are concentrated in pegmatite dykes. About 70 rare-metal minerals we found in massif. Zr-silicates: zircon, eudialyte, lovenite, Ti-lovenite, velerite, burpalite, seidozerite, Ca- seidozerite, Rosenbuschite, vlasovite, katapleite, Ca-katapleite, elpidite. Ti- minerals:- sphene, astrophyllite, ramsaite, Mn-neptunite bafertisite, chevkinite, Mn-ilmenite, pirofanite, Sr-perrerit, landauite, rutile, anatase, brookite; TR- minerals - loparite, metaloparite, britolite, rinkolite, melanocerite, bastnesite, parisite, ankilite, monazite, fluocerite, TR-apatite; Nb- minerals - pyrochlore, loparite. Other rare minerals leucophanite, hambergite, pyrochlore, betafite, torite, thorianite, tayniolite, brewsterite, cryolite and others. We have proposed a new scheme massif: shonkinites - nepheline syenites - alkaline syenite - quartz syenites - veined rocks: mariupolites, rare-metal pegmatites, apatite, fluorite rock alyaskite and alkaline granites and carbonatites (Sotnikova, 2009). Apatite-fluorite rocks are found in the central part of massif. This is a large vein body of 2 km length and a 20 m width cutting prevailing pulaskites. Previously, these rocks were regarded as hydrothermal low-temperature phase. New geological and

  11. Integrating GIS-based geologic mapping, LiDAR-based lineament analysis and site specific rock slope data to delineate a zone of existing and potential rock slope instability located along the grandfather mountain window-Linville Falls shear zone contact, Southern Appalachian Mountains, Watauga County, North Carolina

    USGS Publications Warehouse

    Gillon, K.A.; Wooten, R.M.; Latham, R.L.; Witt, A.W.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.

    2009-01-01

    Landslide hazard maps of Watauga County identify >2200 landslides, model debris flow susceptibility, and evaluate a 14km x 0.5km zone of existing and potential rock slope instability (ZEPRSI) near the Town of Boone. The ZEPRSI encompasses west-northwest trending (WNWT) topographic ridges where 14 active/past-active rock/weathered rock slides occur mainly in rocks of the Grandfather Mountain Window (GMW). The north side of this ridgeline is the GMW / Linville Falls Fault (LFF) contact. Sheared rocks of the Linville Falls Shear Zone (LFSZ) occur along the ridge and locally in the valley north of the contact. The valley is underlain principally by layered granitic gneiss comprising the Linville Falls/Beech Mountain/Stone Mountain Thrust Sheet. The integration of ArcGIS??? - format digital geologic and lineament mapping on a 6m LiDAR (Light Detecting and Ranging) digital elevation model (DEM) base, and kinematic analyses of site specific rock slope data (e.g., presence and degree of ductile and brittle deformation fabrics, rock type, rock weathering state) indicate: WNWT lineaments are expressions of a regionally extensive zone of fractures and faults; and ZEPRSI rock slope failures concentrate along excavated, north-facing LFF/LFSZ slopes where brittle fabrics overprint older metamorphic foliations, and other fractures create side and back release surfaces. Copyright 2009 ARMA, American Rock Mechanics Association.

  12. Lateral variations in mylonite zone thickness as influenced by fluid-rock interactions, Linville falls fault, North Carolina

    NASA Astrophysics Data System (ADS)

    Newman, J.; Mitra, G.

    1993-07-01

    Over a distance of approximately 20 km, along strike, the Linville Falls mylonite varies in thickness from 1 m at Linville Falls to >60 m at Banner Elk. Along strike, pressure, temperature and displacement variations are minimized, allowing this study to focus on the influences of fluid behavior and protolith mineralogy on fault zone development. The protolith at Linville Falls contains mainly K-feldspar, perthite and quartz, while at Banner Elk the protolith contains plagioclase and quartz. At Linville Falls, quartz deformed by dynamic recrystallization, feldspar by intragranular fracturing and alteration to quartz and mica, and mica by sliding along cleavage planes. Modal mineralogies change from the protolith to the mylonite with quartz decreasing from 39 to 19% and feldspar from 59 to 1.5%; muscovite increases from <1 to 80%. Mean grain size of the quartz and feldspar also decreased, from 30 to 20 μm and from 110 to 50 μm, respectively. At Banner Elk, deformation occurred predominantly by dynamic recrystallization within the quartz and by sliding along cleavage planes in mica; no feldspar remains within the mylonite zone. Modal mineralogies change from the protolith to the mylonite with quartz and muscovite increasing from 21 to 50% and from < 1 to 44%, respectively. Mean grain size of quartz decreases from 60 to 24 μm. Mass-balance calculations, based on major- and trace-element geochemistry, indicate approximately 75% volume loss at Linville Falls and 20% at Banner Elk. Fluid-rock ratios estimated from the calculated depletions of Si are an order of magnitude higher at Linville Falls than at Banner Elk. Fluids infiltrated the fault zone over a thicker zone at Banner Elk than at Linville Falls because the plagioclase altered more readily than K-feldspar, creating new pathways for fluids. Fluids migrated preferentially through channels along the fault zone, creating a three-dimensional network of higher fluid flow.

  13. Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

    NASA Astrophysics Data System (ADS)

    Ghamgosar, M.; Erarslan, N.

    2016-03-01

    The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

  14. Integrating geospatial and ground geophysical information as guidelines for groundwater potential zones in hard rock terrains of south India.

    PubMed

    Rashid, Mehnaz; Lone, Mahjoor Ahmad; Ahmed, Shakeel

    2012-08-01

    The increasing demand of water has brought tremendous pressure on groundwater resources in the regions were groundwater is prime source of water. The objective of this study was to explore groundwater potential zones in Maheshwaram watershed of Andhra Pradesh, India with semi-arid climatic condition and hard rock granitic terrain. GIS-based modelling was used to integrate remote sensing and geophysical data to delineate groundwater potential zones. In the present study, Indian Remote Sensing RESOURCESAT-1, Linear Imaging Self-Scanner (LISS-4) digital data, ASTER digital elevation model and vertical electrical sounding data along with other data sets were analysed to generate various thematic maps, viz., geomorphology, land use/land cover, geology, lineament density, soil, drainage density, slope, aquifer resistivity and aquifer thickness. Based on this integrated approach, the groundwater availability in the watershed was classified into four categories, viz. very good, good, moderate and poor. The results reveal that the modelling assessment method proposed in this study is an effective tool for deciphering groundwater potential zones for proper planning and management of groundwater resources in diverse hydrogeological terrains. PMID:21901310

  15. Characteristics of the Lithology, Fault-related Rocks and Fault Zone Structures in the TCDP Hole-A

    NASA Astrophysics Data System (ADS)

    Song, S.; Kou, L.; Yeh, E.

    2005-12-01

    Probing a fault zone of recently major activity at depth to study the physical, mechanical and chemical properties is the one of main purposes of the Taiwan Chelungpu-fault Drilling Project (TCDP). We have finished drilling the hole-A which it has the cuttings from 0 to 430 m and cores from 430 to 2003.67 m deep in the end of 2004. Stratigraphically, from surface to 1029 m deep is the Pliocene to Pleistocene Cholan Formation which is dominantly composed of sandstone and sandstone-siltstone alternation with weak to heavy bioturbations. The Pliocene Chinshui Shale occurs from 1029 to 1303 m deep and predominantly consists of siltstone with weak bioturbation. From 1303 to 1712 m deep is the late Miocene to early Pliocene Kueichulin Formation and is dominantly composed of massive sandstone with minor siltstone. Below the 1712 m deep, the Formation is back to the younger Cholan Formation with mollusca-rich thick layered shale and heavy bioturbated sandstone. Four kinds of fault rocks can be identified in the cores. They are the fault breccia, gouge, foliated and non-foliated cataclasites and pseudotachylyte. At least six major fault zones can be found in the cores: FZ1111, FZ1153, FZ1222, FZ1580, FZ1712 and FZ1818. In those fault zones, the FZ1111 may be correlative to the surface rupture of Chi-Chi earthquake,1999, while the FZ1712 may be the Sanyi fault.

  16. 76 FR 55796 - Safety Zone; TriRock Triathlon, San Diego Bay, San Diego, CA

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-09-09

    ... participants, crew, spectators, participating vessels, and other vessels and users of the waterway. Persons and... other users of the waterway. Discussion of Rule The Coast Guard is establishing a safety zone that will... standards are technical standards (e.g., specifications of materials, performance, design, or...

  17. Rock magnetic properties in the sulfate reduction zone in IODP 350 Hole 1437B, Izu Bonin rear arc: preliminary results

    NASA Astrophysics Data System (ADS)

    Musgrave, R. J.; Kars, M. A. C.; Kodama, K.

    2014-12-01

    During the northern Spring 2014 (April-May), IODP Expedition 350 drilled a 1806.5 m deep hole at Site U1437 in the Izu-Bonin rear arc, in order to understand, among other objectives, the compositional evolution of the arc since the Miocene and track the missing half of the subduction factory. The good recovery of mostly fine grained sediments at this site enables a high resolution paleomagnetic and rock magnetic study. Particularly, variations in magnetic properties and mineralogy are well documented. The onboard magnetostratigraphy established from the study of the archive halves highlighted remagnetized intervals that produced "ghost" repetitions of geomagnetic reversals ~10's meters below their actual stratigraphic position in specific intervals. Onboard paleo- and rock magnetic analyses showed that remagnetization is probably due to a chemical remanence carried by iron sulfides (putatively identified as greigite). The rock magnetic parameters, SIRM/k and the S-ratio are consistent with the presence of ferromagnetic iron sulfides in Site U1437. A mixture of iron oxides and iron sulfides was found within the sulfate reduction zone, which was identified by onboard pore water analyses at ~50-60 meters below sea floor (mbsf) by a minimum in sulfate (~5 mM) coupled with a maximum in alkalinity. Below 50 mbsf, the sulfate content increases up to ~29 mM at ~460 mbsf. The particular downhole profile of the sulfate content in Site U1437 is probably triggered by fluid circulation. Evolution of sulfate content, pyritization process and fluid circulation are closely linked. Onshore research is focusing on further downhole characterization of the iron sulfides including their abundance, grain size and composition. Routine magnetic properties (NRM, magnetic susceptibility) and rock magnetic analyses at high resolution (every ~20-50 cm), including hysteresis properties and low temperature magnetic measurements, have been conducted on about 400 discrete samples in the first 200

  18. Stability of sharp reaction fronts in porous rocks and implications for non-sharp reaction zones

    NASA Astrophysics Data System (ADS)

    Wangen, Magnus

    2014-05-01

    The flow of reactive fluids in the subsurface, like for instance acids, may create reaction fronts. A sharp reaction front is an idealization of the narrow zone where the reaction takes place. Narrow reaction zones are studied with a one-component reaction transport model, where a first order reaction changes the porosity. The porosity field is coupled to the permeability field, where an increasing porosity leads to an increasing permeability. Therefore, the reaction has a feed-back on the flow field. We have derived 1D approximate solutions for the change in concentration and porosity across the reaction zone. These solutions are used to derive a condition for reaction fronts to be narrow. The condition gives a minimum reaction rate necessary for 90% of the reaction to be restricted to the given area. Sharp fronts are idealizations of narrow fronts that are more amendable for analytical treatment. A condition has recently been derived for the stability of sharp reaction fronts in homogeneous porous medium using linear stability analysis. The condition gives that a perturbation of a flat reaction front of any wave-length becomes unstable if the permeability behind the front increases. The front instability grows faster for short wave lengths than for long wave lengths. Similarly, the perturbations of the front will die out if the permeability behind the front decreases, and short wave length perturbations will die out faster than long wave length perturbations. It is a condition that applies for both 2D and 3D porous media. Numerical experiments are shown that demonstrate the front stability criterion, when the fronts are narrow, but not sharp. The sharp front approximation turns out to be useful for the interpretation of reactions that are not sufficiently fast to give narrow reaction zones, when the reaction alters the porosity- and the permeability fields. Dissolution is an important example of reactions that increase the porosity and therefore the permeability

  19. Geochronological and geochemical constraints on the mafic rocks along the Luang Prabang zone: Carboniferous back-arc setting in northwest Laos

    NASA Astrophysics Data System (ADS)

    Qian, Xin; Feng, Qinglai; Wang, Yuejun; Chonglakmani, Chongpan; Monjai, Denchok

    2016-02-01

    The key to gaining a better understanding of Paleotethyan tectonic evolution is to determine the tectonic setting of the main suture/tectonic zones and their relationships in SE Asia. The Luang Prabang tectonic zone in NW Laos lies in the area that aligns with the Jinshajiang-Ailaoshan suture zone to the north and the Nan suture zone to the south. Correlations among them have been debated. Samples from a diabase dyke and coarse-grained basalt in the Luang Prabang tectonic zone yield zircon U-Pb weighted mean ages of 335.5 ± 3.3 Ma and 304.9 ± 3.9 Ma, respectively, suggesting that these mafic rocks formed in the Carboniferous rather than in the Permian, as previously inferred. The zircon in-situ εHf (t) values range from 11.6 to 13.3. Their initial 87Sr/86Sr ratios range from 0.70318 to 0.70522, and εNd (t) ranges from + 5.16 to + 6.93. The diabase samples have E-MORB-like characteristics with an addition of a subduction-related component, and the basalt samples were derived from the same type of source as N-MORB magmas newly modified by a slab-derived component. The ages of the mafic rocks along the Luang Prabang tectonic zone are similar to the mafic rocks from the Jinshajiang-Ailaoshan, Song Ma and Nan suture zones in SE Asia. A synthesis of available data suggests the development of a Carboniferous continental back-arc basin separating the Sukhothai Terrane and the Indochina Block. The Luang Prabang tectonic zone represents a remnant of a series of synchronous back-arc basins to the northeast of the Paleotethyan Main Ocean. It is proposed that the Luang Prabang tectonic zone links with the Nan suture zone to the southwest and with the Jinshajiang-Ailaoshan suture zone to the north.

  20. The effect of stagnant water zones on retarding radionuclide stransport in fractured rocks: An extension to the Channel Network Model

    NASA Astrophysics Data System (ADS)

    Shahkarami, Pirouz; Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2016-09-01

    An essential task of performance assessment of radioactive waste repositories is to predict radionuclide release into the environment. For such a quantitative assessment, the Channel Network Model and the corresponding computer program, CHAN3D, have been used to simulate radionuclide transport in crystalline bedrocks. Recent studies suggest, however, that the model may tend to underestimate the rock retarding capability, because it ignores the presence of stagnant water zones, STWZs, situated in the fracture plane. Once considered, the STWZ can provide additional surface area over which radionuclides diffuse into the rock matrix and thereby contribute to their retardation. The main objective of this paper is to extend the Channel Network Model and its computer implementation to account for diffusion into STWZs and their adjacent rock matrices. In the first part of the paper, the overall impact of STWZs in retarding radionuclide transport is investigated through a deterministic calculation of far-field releases at Forsmark, Sweden. Over the time-scale of the repository safety assessments, radionuclide breakthrough curves are calculated for increasing STWZ width. It is shown that the presence of STWZs enhances the retardation of most long-lived radionuclides except for 36Cl and 129I. The rest of the paper is devoted to the probabilistic calculation of radionuclide transport in fractured rocks. The model that is developed for transport through a single channel is embedded into the Channel Network Model and new computer codes are provided for the CHAN3D. The program is used to (I) simulate the tracer test experiment performed at Äspö HRL, STT-1 and (II) investigate the short- and long-term effect of diffusion into STWZs. The required data for the model are obtained from detailed hydraulic tests in boreholes intersecting the rock mass where the tracer tests were made. The simulation results fairly well predict the release of the sorbing tracer 137Cs. It is found that

  1. Semi-automatic mapping of fault rocks on a Digital Outcrop Model, Gole Larghe Fault Zone (Southern Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Mittempergher, Silvia; Vho, Alice; Bistacchi, Andrea

    2016-04-01

    A quantitative analysis of fault-rock distribution in outcrops of exhumed fault zones is of fundamental importance for studies of fault zone architecture, fault and earthquake mechanics, and fluid circulation. We present a semi-automatic workflow for fault-rock mapping on a Digital Outcrop Model (DOM), developed on the Gole Larghe Fault Zone (GLFZ), a well exposed strike-slip fault in the Adamello batholith (Italian Southern Alps). The GLFZ has been exhumed from ca. 8-10 km depth, and consists of hundreds of individual seismogenic slip surfaces lined by green cataclasites (crushed wall rocks cemented by the hydrothermal epidote and K-feldspar) and black pseudotachylytes (solidified frictional melts, considered as a marker for seismic slip). A digital model of selected outcrop exposures was reconstructed with photogrammetric techniques, using a large number of high resolution digital photographs processed with VisualSFM software. The resulting DOM has a resolution up to 0.2 mm/pixel. Most of the outcrop was imaged using images each one covering a 1 x 1 m2 area, while selected structural features, such as sidewall ripouts or stepovers, were covered with higher-resolution images covering 30 x 40 cm2 areas.Image processing algorithms were preliminarily tested using the ImageJ-Fiji package, then a workflow in Matlab was developed to process a large collection of images sequentially. Particularly in detailed 30 x 40 cm images, cataclasites and hydrothermal veins were successfully identified using spectral analysis in RGB and HSV color spaces. This allows mapping the network of cataclasites and veins which provided the pathway for hydrothermal fluid circulation, and also the volume of mineralization, since we are able to measure the thickness of cataclasites and veins on the outcrop surface. The spectral signature of pseudotachylyte veins is indistinguishable from that of biotite grains in the wall rock (tonalite), so we tested morphological analysis tools to discriminate

  2. Analysis of the hydraulic data from the MI fracture zone at the Grimsel Rock Laboratory, Switzerland

    SciTech Connect

    Davey, A.; Karasaki, K.; Long, J.C.S.; Landsfeld, M.; Mensch, A.; Martel, S.J.

    1989-10-01

    One of the major problems in analyzing flow and transport in fractured rock is that the flow may be largely confined to a poorly connected network of fractures. In order to overcome some of this problem, Lawrence Berkeley Laboratory (LBL) has been developing a new type of fracture hydrology model called an equivalent discontinuum model. In this model the authors represent the discontinuous nature of the problem through flow on a partially filled lattice. A key component in constructing an equivalent discontinuum model from this lattice is removing some of the conductive elements such that the system is partially connected in the same manner as the fracture network. This is done through a statistical inverse technique called simulated annealing. The fracture network model is annealed by continually modifying a base model, or template such that the modified systems behave more and more like the observed system. In order to see how the simulated annealing algorithm works, the authors have developed a series of synthetic real cases. In these cases, the real system is completely known so that the results of annealing to steady state data can be evaluated absolutely. The effect of the starting configuration has been studied by varying the percent of conducting elements in the initial configuration. Results have shown that the final configurations converge to about the same percentage of conducting elements. An example using Nagra field data from the Migration Experiment (MI) at Grimsel Rock Laboratory in Switzerland is also analyzed. 24 refs., 33 figs., 3 tabs.

  3. Monitoring of fluid-rock interaction in active fault zones: a new method of earthquake prediction/forecasting?

    NASA Astrophysics Data System (ADS)

    Claesson, L.; Skelton, A.; Graham, C.; Dietl, C.; Morth, M.; Torssander, P.

    2003-12-01

    We propose a new method for earthquake forecasting based on the "prediction in hindsight" of a Mw 5.8 earthquake on Iceland, on September 16, 2002. The "prediction in hindsight" is based on geochemical monitoring of geothermal water at site HU-01 located within the Tj”rnes Fracture Zone, northern Iceland, before and after the earthquake. During the 4 weeks before the earthquake exponential (<800%) increases in the concentration of Cu, Zn and Fe in the fluid, was measured, together with a linear increase of Na/Ca and a slight increase of δ 18O. We relate the hydrogeochemical changes before the earthquake to influx of fluid which interacted with the host rock at higher temperatures and suggest that fluid flow was facilitated by stress-induced modification of rock permeability, which enabled more rapid fluid-rock interaction. Stepwise increases (13-35 %) in the concentration of, Ba, Ca, K, Li, Na, Rb, S, Si, Sr, Cl, Br and SO4 and negative shifts in δ 18O and δ D was detected in the fluid immediately after the earthquake, which we relate to seismically-induced source switching and consequent influx of older (or purer) ice age meteoric waters. The newly tapped source reservoir has a chemically and isotopically distinct ice-age meteoric water signature, which is the result of a longer residence in the crust. The immediancy of these changes is consistent with experimentally-derived timescales of fault-sealing in response to coupled deformation and fluid flow, interpreted as source-switching. These precursory changes may be used to "predict" the earthquake up to 2 weeks before it occurs.

  4. Measurement of the optical properties of lunar rocks in the transition zone, resulting from observations made by Lunokhod 2

    NASA Technical Reports Server (NTRS)

    Lipskiy, Y. N.; Shevchenko, V. V.

    1977-01-01

    Photometric measurements were carried out directly on the lunar surface with the aid of a calibration device, a plate with fields of different brightness, placed in the field of view of the panoramic telephotometers. The brightness of the fields of the calibration plate were measured in preliminary studies, relative to the brightness of a magnesia screen. This permitted determination of the reflectance features of the surficial lunar material relative to the standard most widely used in brightness studies of natural substances. The total brightness of sections a few centimeters across was recorded in direct proximity to the apparatus. The total area investigated in one panorama was about one square meter. Several areas in the mare and highland regions were studied. The albedos of various surface objects were obtained. A comparison of the brightness measurements with data from the RIFMA-M instrument discloses a correlation of the albedo change with change in chemical composition of the surface rock. Direct photometric studies of the lunar surface in the "mare-highland" transition zone assist in tracing the transition from one type of rock to another, and in obtaining information on the processes of material exchange between these two types of lunar landscape.

  5. Tunneling Analyst: A 3D GIS extension for rock mass classification and fault zone analysis in tunneling

    NASA Astrophysics Data System (ADS)

    Choi, Yosoon; Yoon, Seo-Youn; Park, Hyeong-Dong

    2009-06-01

    In this study, an extension called Tunneling Analyst (TA) has been developed in ArcScene 3D GIS software, part of the ArcGIS software package. It dramatically extends the functionalities of ArcScene because it allows: (1) estimation of the 3D distribution of rock mass rating (RMR) values using borehole and geophysical exploration data, (2) the modeling of 3D discontinuity planes such as faults from field-based structural measurements, and (3) analysis of 3D intersections and 3D buffer zones between proposed tunnel alignments and some discontinuities. Because TA can handle and visualize both 2D and 3D geological data in a single GIS environment, the tedious tasks required for data conversion between various software packages can be reduced significantly. The application to the Daecheong tunneling project in Korea shows that TA could present a rational solution to evaluating the rock mass classes along a proposed tunnel alignment and can also provide specific 3D spatial query tools to support the tunnel design work. This paper describes the concept and details of the development and implementation of TA.

  6. Physicochemical changes of aluminium in mixing zones: Mortality and physiological disturbances in brown trout (Salmo trutta L.)

    SciTech Connect

    Witters, H.E.; Van Puymbroeck, S.; Stouthart, A.J.H.X.; Bonga, S.E.W.

    1996-06-01

    A standardized laboratory setup, simulating field mixing zones that originate at the confluence of limed rivers with acidic, aluminium-rich, tributaries, has been developed. Detailed analyses of the chemical speciation of aluminium (Al) in relation to the biological response of brown trout were performed to identify the mechanism of unexpected high fish mortality in the above-mentioned mixing zones with pH levels above 6.0. Brown trout experienced an acute cumulative mortality (98% in 48 h) immediately after neutral and acidic, Al-rich, water had mixed. Mortality was only 60% within 48 h of exposure to the acid water with Al (pH 4.6 + 6.8 {micro}mol Al/L), although the Al concentration in the mixing zone was less (2.8 {micro}mol Al/L) at a nonharmful pH level (pH 6.4). Chemical speciation and ultrafiltration studies demonstrated that the transformation of low-molecular weight Al (<10 kD) into high-molecular weight Al (>10 kD), defined as Al polymerization, could better be related to the toxic response of fish, than the total Al concentration. The aging of polymerized Al forms (for 480 s) resulted in reduced fish mortality and less pronounced physiological stress. Brown trout in the initial mixing zone showed significantly increased plasma glucose and cortisol levels. Light and electron microscopy studies demonstrated serious damage to the skin: increased mucous secretion, a high ratio of acid to neutral glycoprotein-containing mucous cells, increased apoptosis, and infiltration of leucocytes and macrophages between the epithelial cells. Ionoregulatory parameters, which showed minor changes in fish in the initial mixing zone, did not allow explanation of acute fish mortality. Data on the ventilation frequency and the blood hematocrit, which both increased, gave support for the hypothesis that acute fish mortality in mixing zones could be caused by respiratory dysfunction.

  7. Determination of geochemical affinities of granitic rocks from the Aue-Schwarzenberg zone (Erzgebirge, Germany) by multivariate statistics

    USGS Publications Warehouse

    Forster, H.-J.; Davis, J.C.

    2000-01-01

    Variscan granites of the Erzgebirge region can be effectively classified into five genetically distinct major groups by canonical analysis of geochemical variables. The same classification procedure, when applied to small plutons in the Aue-Schwarzenberg granite zone (ASGZ), shows that all ASGZ granites have compositional affinities to low-F biotite or low-F two-mica granite groups. This suggests that the ASGZ granites were emplaced during the first, late-collisional stage of silicic magmatism in the region, which occurred between about 325 and 318 Ma. The numerous biotite granite bodies in the zone are geochemically distinct from both the neighboring Kirchberg granite pluton and the spatially displaced Niederbobritzsch biotite granite massif. Instead, these bodies seem to constitute a third sub-group within the low-F biotite granite class. The ASGZ biotite granites represent three or more genetically distinct bodies, thus highlighting the enormous compositional variability within this group of granites. Least evolved samples of two-mica granites from the ASGZ apparently reflect the assimilation of low-grade metamorphic country rocks during emplacement, altering the original composition of the melts by enhancing primary Al content. The same genesis is implied for the rare "cordierite granite" facies of the Bergen massif, the type pluton for the low-F two-mica granite group in the Erzgebirge.

  8. Application of Geographical Information System for Identification of Potential Groundwater Artificial Recharge Zones in Hard Rock Terrain

    NASA Astrophysics Data System (ADS)

    Prasad, R. K.; Banerjee, Pallavi; Singh, V. S.

    2010-05-01

    There are several methods which are employed to delineate the groundwater artificial recharge potential zones. Remote sensing and geographical information system (GIS) technique provides an advantage of having access to large coverage, even in inaccessible areas. It is rapid and cost-effective tool in producing valuable data on geology, geomorphology, lineaments, slope etc. Detail analysis of drainage, geology, lineament, geomorphology and slope has been carried out in the hard rock terrain in Andhra Pradesh, India. These data have been digitized and finally integrated through the application of GIS to decipher groundwater potential zones in the study area. These various data are prepared in the form of thematic map using geographical information system (GIS) software tool. In order to get all these information in the form of thematic map unified, it is essential to integrate these data with appropriate factor. Therefore, all information are integrated through the application of GIS. Various thematic maps are reclassified on the basis of weightage assigned and brought into the "Raster Calculator" function of Spatial Analysist tool for integration. In the recent years digital technique is used to integrate various data to solve problems related to groundwater. In the present study approach of remote sensing and GIS technique is used for ground water exploration and identification of artificial recharge sites.

  9. Seismic heating signatures in the Japan Trench subduction plate-boundary fault zone: evidence from a preliminary rock magnetic `geothermometer'

    NASA Astrophysics Data System (ADS)

    Yang, Tao; Dekkers, Mark J.; Zhang, Bo

    2016-04-01

    Frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation. The amount of annealing varies widely and is, as yet, poorly constrained. Here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced. The case study comprises sheared clay cored from the Japan Trench subduction plate-boundary fault zone (décollement), which accommodated the large slip of the 2011 Mw 9.0 Tohoku-oki earthquake. The décollement was cored during the Integrated Ocean Drilling Program (IODP) Expedition 343, the Japan Trench Fast Drilling Project (JFAST). Heating signatures with estimated maximum temperatures ranging from ˜300 to over 500 °C are determined close to the multiple slip surfaces within the décollement. Since it is impossible to tie a specific slip surface to a certain earthquake, thermal evidence for the cumulative effect of several earthquakes is unveiled. This as yet preliminary rock magnetic `geothermometer' would be a useful tool to detect seismic heating along faults that experienced medium temperature rise, a range which is difficult to assess with other approaches.

  10. A long-term rock uplift rate for eastern Crete and geodynamic implications for the Hellenic subduction zone

    NASA Astrophysics Data System (ADS)

    Strobl, M.; Hetzel, R.; Fassoulas, C.; Kubik, P.

    2014-12-01

    The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with a local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island (e.g. Lambeck, 1995). These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have recently affected Crete (Stiros, 2001). Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ˜600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ˜100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ca. 68 and ca. 76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level high-stands (Siddall et al., 2003) indicates sustained rock uplift at a rate of ˜0.5 m/ka since at least ˜600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete. Lambeck, 1995, Geophys. J. Int. 122, 1022

  11. Deformation mechanisms of antigorite serpentinite at subduction zone conditions determined from experimentally and naturally deformed rocks

    NASA Astrophysics Data System (ADS)

    Auzende, Anne-Line; Escartin, Javier; Walte, Nicolas P.; Guillot, Stéphane; Hirth, Greg; Frost, Daniel J.

    2015-02-01

    We performed deformation-DIA experiments on antigorite serpentinite at pressures of 1-3.5 GPa and temperatures of between 400 and 650 °C, bracketing the stability of antigorite under subduction zone conditions. For each set of pressure-temperature (P-T) conditions, we conducted two runs at strain rates of 5 ×10-5 and 1 ×10-4 s-1. We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400 °C (Chernak and Hirth, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Optical and transmission electron microscopies were used for microstructural characterization and determination of deformation mechanisms. Our observations on experimentally deformed antigorite prior to breakdown show that deformation is dominated by cataclastic flow with observable but minor contribution of plastic deformation (microkinking and (001) gliding mainly expressed by stacking disorder mainly). In contrast, in naturally deformed samples, plastic deformation structures are dominant (stacking disorder, kinking, pressure solution), with minor but also perceptible contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases and is coupled to local embrittlement that we attribute to antigorite dehydration. In dehydrating samples collected in the Alps, embrittlement is also observed suggesting that dehydration may contribute to intermediate-depth seismicity. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. However, the plastic deformation recorded by naturally deformed samples was likely acquired at low strain rates. We also document that the corrugated structure of antigorite controls the strain accommodation mechanisms under subduction conditions, with preferred inter- and intra-grain cracking along (001) and gliding along both a and b. We also show that antigorite rheology in subduction zones is partly controlled

  12. Mechanical properties and processes of deformation in shallow sedimentary rocks from subduction zones: An experimental study

    NASA Astrophysics Data System (ADS)

    Gadenne, Leslie; Raimbourg, Hugues; Champallier, Rémi; Yamamoto, Yuzuru

    2014-12-01

    better constrain the mechanical behavior of sediments accreted to accretionary prism, we conducted triaxial mechanical tests on natural samples from the Miura-Boso paleo-accretionary prism (Japan) in drained conditions with confining pressures up to 200 MPa as well as postexperiments P-wave velocity (Vp) measurements. During experiments, deformation is principally noncoaxial and accommodated by two successive modes of deformation, both associated with strain-hardening and velocity-strengthening behavior: (1) compaction-assisted shearing, distributed in a several mm-wide shear zone and (2) faulting, localized within a few tens of μm-wide, dilatant fault zone. Deformation is also associated with (1) a decrease in Young's modulus all over the tests, (2) anomalously low Vp in the deformed samples compared to their porosity and (3) an increase in sensitivity of Vp to effective pressure. We interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation. When applied to natural conditions, these results suggest that the deformation style (localized versus distributed) of shallow (z < a few km) sediments is mainly controlled by the variations in stress/strain rate during the seismic cycle and is therefore independent of the porosity of sediments. Finally, we show that the effect of strain, through cement breakage and microcracks formation, may lower Vp for effective pressure up to 40 MPa. As a consequence, the low Vp anomalies observed in Nankai accretionary prisms by seismic imaging between 2 and 4 km depth could reflect sediment deformation rather than porosity anomalies.

  13. High-pressure mafic oceanic rocks from the Makbal Complex, Tianshan Mountains (Kazakhstan & Kyrgyzstan): Implications for the metamorphic evolution of a fossil subduction zone

    NASA Astrophysics Data System (ADS)

    Meyer, Melanie; Klemd, Reiner; Konopelko, Dmitry

    2013-09-01

    The Makbal Complex in the western Tianshan Mountains of Kazakhstan and Kyrgyzstan consists of HP/UHP metasedimentary host rocks which enclose various HP mafic blocks or boudins. These mafic rocks comprise rare eclogites (sensu stricto and sensu lato), garnet amphibolites (retrograded eclogites) and a newly discovered glaucophanite (glaucophane-garnet-omphacite bearing rock). So far the Makbal Complex has been interpreted to predominantly consist of continental lithologies and the mafic rocks were considered as dismembered dikes intruding continental metasediments. This interpretation is mainly based on the geological relationship and bulk rock chemistry of the different rock types. It was further suggested that the continental lithologies of the Makbal Complex underwent eclogite-facies metamorphism in a former subduction zone. In the present study we combined conventional geothermometry, P-T pseudosection modeling and major and trace element whole rock geochemistry for different mafic samples (glaucophanite and eclogites (sensu lato)) in order to shed light on both the metamorphic evolution and the protoliths of the mafic HP rocks in the Makbal Complex. Prograde to peak-pressure clockwise P-T paths of glaucophanite and eclogites (sensu lato) were modeled using garnet isopleth thermobarometry. The results show that the glaucophanite and eclogite (sensu lato) samples experienced similar prograde P-T paths and slightly different peak metamorphic conditions at ~ 560 °C at 2.4 GPa for the former and between ~ 520 °C at 2.2 GPa and ~ 555 °C at ~ 2.5 GPa for the latter, corresponding to burial depths between 70 and 85 km. Whole rock major and trace element analyses and petrological evidence imply that the various rock types at the Makbal Complex most likely originated from different precursor rocks. Eclogites (sensu lato) are believed to represent strongly retrogressed former eclogite-facies rocks that had never been eclogites (sensu stricto, i.e. > 70 vol.% garnet and

  14. Studies of microstructures of deformed charnockitic rocks in Telsiai deformation zone, Lithuania

    NASA Astrophysics Data System (ADS)

    Vejelyte, Irma

    2010-05-01

    The Telsiai Deformation Zone (TDZ), a regional scale Precambrian deformation zone in the crystalline basement of Lithuania, transects the WLGD in the E-W direction and is approximately 15-20 km wide as mirrored by a belt of gravity and magnetic lows. As indicated by petrological and geophysical data the TDZ crosscuts a 1.82 Ga charnockitic pluton in a ductile manner. In turn, the TDZ appears to have been intruded by or accommodated a 1.46 Ga granitoid intrusion, defining at least its age in-between of these two magmatic events. The mesoanalyses and microanalyses of drillcores have been carried out on augen mylonite and ultramylonite, which were formed at upper amphibolite facies. The temperature during the deformation was 650-750 C° at pressure between 3.0 and 4.7 kbar. The deformed charnockites have a prominent foliation marked mainly by feldspar, biotite, quartz, orthopyroxene, garnet and ± clinopyroxene. Porphyroclasts of plagioclase are elongated and banded. They are partly recrystallized to fine-grained polygonal aggregates as a result of high temperature deformation. In places, plagioclase has been truncated by plagioclase-rich microshears. Quartz grains are in three manners: large old grains with deeply indented boundaries and undulate extinction; medium polygonal grains and ribbons grains. Large biotite grains are locally kinked, some of them have been partly neocrystallized to much smaller new grains of biotite parallel to the foliation. Garnet crystals are elongated and oriented to the foliation. Individual grains of them in the highest strain areas have been recrystallized to many small garnet grains. Large crystals of orthopyroxene are deformed and elongated, on their sheared rims tails of fine grained orthopyroxene and clinopyroxene have been formed. The subgrain rotation, grain-boundary migration recrystallization and recovery processes predominate in all minerals. Near residual plagioclase also are visible myrmekites. They formed along those sides

  15. Climate change induced effects on the predisposition of forests of the water protection zone Wildalpen to disturbances by bark beetles

    NASA Astrophysics Data System (ADS)

    Baier, P.; Pennerstorfer, J.; Schopf, A.

    2012-04-01

    The provision of drinking water of high quality is a precious service of forests. Large-scale disturbances like forest fires, wind throws, pest outbreaks and subsequent clear cutting may lead to changes in hydrology (runoff as well as percolation). Furthermore, water quality can be negatively influenced by increased erosion, increased decomposition of litter and humus and leaching of nitrate. Large-scale epidemics of forest pests may induce forest decline at landscape scale with subsequent long-lasting negative effects on water quality. The European spruce bark beetle, Ips typographus (L.), is one of the most significant sources of mortality in mature spruce forest ecosystems in Eurasia. The objective of this study was to apply a complex predisposition assessment system for hazard rating and for the evaluation of climate change impacts for the water protection forests of the City of Vienna in Wildalpen. The following steps have been done to adapt/apply the bark beetle phenology model and the hazard rating system: -application, adaptation and validation of the bark beetle phenology model PHENIPS concerning start of dispersion, brood initiation, duration of development, beginning of sister broods, voltinism and hibernation - spatial/temporal modelling of the phenology and voltinism of I. typographus using past, present as well as projected climate data - application and validation of the stand- and site related long-term predisposition assessment system using forest stand/site data, annual damage reports and outputs of phenology modelling as data input - mapping of endangered areas and assessment of future susceptibility to infestations by I. typographus and other disturbing agents based on climate scenarios using GIS. The assessment of site- and stand-related predisposition revealed that the forest stands in Wildalpen are highly susceptible to bark beetle infestation. More than 65% of the stands were assigned to the predisposition classes high/very high. Only 10% of

  16. Geochronology and geochemistry of a dyke host rock association and implications for the formation of the Bavarian Pfahl shear zone, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Siebel, Wolfgang; Blaha, Ulrich; Chen, Fukun; Rohrmüller, Johann

    2005-02-01

    To place constraints on the formation and deformation history of the major Variscan shear zone in the Bavarian Forest, Bavarian Pfahl zone, SW Bohemian Massif, granitic dykes and their feldspar-phyric massive host rock (so-called “palite”), zircons were dated by the U Pb isotope dilution and Pb-evaporation methods. The dated samples comprise two host rocks and four dykes from a K-rich calc-alkaline complex adjoining the SW part of the Bavarian Pfahl shear zone. The palites, which appear to be the oldest magmatic rocks emplaced in the shear zone, yield ages of 334±3, 334.5±1.1 Ma (average 207Pb/206Pb-evaporation zircon ages) and 327 342 Ma (range of U/Pb zircon ages) suggesting a Lower Carboniferous age for the initiation of the Pfahl zone. Absence of inherited older cores in all investigated zircons indicates that incorporation of crustal zircon material has played virtually no role or that the melting temperature was very high. Determination of the dyke emplacement age is complicated by partial Pb-loss in most of the fractions analysed. This Pb-loss can be ascribed to higher U content of the dyke zircons compared to those from host rock. Upper discordia intercept ages of the different dykes range from 322±5 to 331±9 Ma. The dykes are pre- to synkinematic with respect to penetrative regional mylonitisation along the Pfahl zone, and the upper intercept ages provide a maximum age for this tectonic event.

  17. Compositional variations in spinel-hosted pargasite inclusions in the olivine-rich rock from the oceanic crust-mantle boundary zone

    NASA Astrophysics Data System (ADS)

    Tamura, Akihiro; Morishita, Tomoaki; Ishimaru, Satoko; Hara, Kaori; Sanfilippo, Alessio; Arai, Shoji

    2016-05-01

    The crust-mantle boundary zone of the oceanic lithosphere is composed mainly of olivine-rich rocks represented by dunite and troctolite. However, we still do not fully understand the global variations in the boundary zone, and an effective classification of the boundary rocks, in terms of their petrographical features and origin, is an essential step in achieving such an understanding. In this paper, to highlight variations in olivine-rich rocks from the crust-mantle boundary, we describe the compositional variations in spinel-hosted hydrous silicate mineral inclusions in rock samples from the ocean floor near a mid-ocean ridge and trench. Pargasite is the dominant mineral among the inclusions, and all of them are exceptionally rich in incompatible elements. The host spinel grains are considered to be products of melt-peridotite reactions, because their origin cannot be ascribed to simple fractional crystallization of a melt. Trace-element compositions of pargasite inclusions are characteristically different between olivine-rich rock samples, in terms of the degree of Eu and Zr anomalies in the trace-element pattern. When considering the nature of the reaction that produced the inclusion-hosting spinel, the compositional differences between samples were found to reflect a diversity in the origin of the olivine-rich rocks, as for example in whether or not a reaction was accompanied by the fractional crystallization of plagioclase. The differences also reflect the fact that the melt flow system (porous or focused flow) controlled the melt/rock ratios during reaction. The pargasite inclusions provide useful data for constraining the history and origin of the olivine-rich rocks and therefore assist in our understanding of the crust-mantle boundary of the oceanic lithosphere.

  18. Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

    USGS Publications Warehouse

    Abbott, Jeffrey T.

    1970-01-01

    Rocks within the Big Narrows and Poudre Park quadrangles located in the northern Front Range of Colorado are Precambrian metasedimentary and metaigneous schists and gneisses and plutonic igneous rocks. These are locally mantled by extensive late Tertiary and Quaternary fluvial gravels. The southern boundary of the Log Cabin batholith lies within the area studied. A detailed chronology of polyphase deformation, metamorphism and plutonism has been established. Early isoclinal folding (F1) was followed by a major period of plastic deformation (F2), sillimanite-microcline grade regional metamorphism, migmatization and synkinematic Boulder Creek granodiorite plutonism (1.7 b.y.). Macroscopic doubly plunging antiformal and synformal structures were developed. P-T conditions at the peak of metamorphism were probably about 670?C and 4.5 Kb. Water pressures may locally have differed from load pressures. The 1.4 b.y. Silver Plume granite plutonism was post kinematic and on the basis of petrographic and field criteria can be divided into three facies. Emplacement was by forcible injection and assimilation. Microscopic and mesoscopic folds which postdate the formation of the characteristic mineral phases during the 1.7 b.y. metamorphism are correlated with the emplacement of the Silver Plume Log Cabin batholith. Extensive retrograde metamorphism was associated with this event. A major period of mylonitization postdates Silver Plume plutonism and produced large E-W and NE trending shear zones. A detailed study of the Rb/Sr isotope geochemistry of the layered mylonites demonstrated that the mylonitization and associated re- crystallization homogenized the Rb87/Sr 86 ratios. Whole-rock dating techniques applied to the layered mylonites indicate a probable age of 1.2 b.y. Petrographic studies suggest that the mylonitization-recrystallization process produced hornfels facies assemblages in the adjacent metasediments. Minor Laramide faulting, mineralization and igneous activity

  19. Cenozoic volcanic rocks of North Kamchatka: In search of subduction zones

    NASA Astrophysics Data System (ADS)

    Shapiro, M. N.; Solov'ev, A. V.

    2011-05-01

    Two belts of subaerial volcanic rocks—the Eocene Kinkil belt and the Neogene belt of the Sredinny Range—extend along the Kamchatka Isthmus. It is suggested that their formation is related to subduction of the oceanic lithosphere beneath the continental margin of North Kamchatka. The oceanic lithosphere consumed in the subduction zones could have been formed as a result of active spreading in the Komandorsky Basin. In the simplest case, both spreading and subduction reflect the northwestward motion of the lithosphere of the Komandorsky Plate relative to Kamchatka, the Shirshov Ridge, and the Aleutian Basin combined into one relatively immobile plate conventionally called the North American Plate. The authors perform a simulation of conjugate spreading and subduction. The most important parameter determining the regional geodynamics—the velocity of the Komandorsky Plate moving relative to the North American Plate—is taken as 2.5, 5.0, and 7.5 cm/yr. The calculated ages of the onset and end of volcanic activity in the aforementioned belts are compared with the dates obtained with the isotopic and paleontological methods. For the Eocene Kinkil belt, where volcanism started 44 Ma ago, the model age of the onset of subduction depends on the accepted velocity of the motion of the Komandorsky Plate and varies from 54 Ma at the velocity of 2.5 cm/yr to 47.5 Ma at the velocity of 7.5 cm/yr. It can be assumed that the model of fast subduction in this age interval is most consistent with the geological data. For the Miocene-Pliocene belt of the Sredinny Range, assuming the velocity of the motion of the Komandorsky Plate at 5.0 and 7.5 cm/yr, multiple rifting at the boundary with the Shirshov Ridge should be assumed. Therefore, for the end of the Neogene, a model with low velocity (2.5-5.0 cm/yr, i.e., about 4.0 cm/yr) is preferable.

  20. Rock and mineral transformations in a fault zone leading to permanent creep: Interactions between brittle and viscous mechanisms in the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Richard, Julie; Gratier, Jean-Pierre; Doan, Mai-Linh; Boullier, Anne-Marie; Renard, François

    2014-11-01

    Creep processes may relax part of the tectonic stresses in active faults, either by continuous or episodic processes. The aim of this study is to obtain a better understanding of these creep mechanisms and the manner in which they change in time and space. Results are presented from microstructural studies of natural samples collected from San Andreas Fault Observatory at Depth borehole drilled through the San Andreas Fault, which reveal the chronology of the deformation within three domain types. (i) A relatively undeformed zone of the host rock reflects the first step of the deformation process with fracturing and grain indentations showing the coupling between fracturing and pressure solution. (ii) Shear deformation development that associates fracturing and solution cleavage processes leads to profound changes in rock composition and behavior with two types of development depending on the ratio between the amount of dissolution and deposition: abundant mineral precipitation strengthens some zones while pervasive dissolution weakens some others, (iii) zones with mainly dissolution trended toward the present-day creeping zones thanks to both the passive concentration of phyllosilicates and their metamorphic transformation into soft minerals such as saponite. This study shows how interactions between brittle and viscous mechanisms lead to widespread transformation of the rocks and how a shear zone may evolve from a zone prone to earthquakes and postseismic creep to a zone of steady state creep. In parallel, the authors discuss how the creeping mechanism, mainly controlled by the very low friction of the saponite in the first 3-4 km depth, may evolve with depth.

  1. Seismic tomography of the Excavation Damaged Zone of the Gallery 04 in the Mont Terri Rock Laboratory

    NASA Astrophysics Data System (ADS)

    Nicollin, F.; Gibert, D.; Bossart, P.; Nussbaum, Ch.; Guervilly, C.

    2008-01-01

    An endoscopic antenna is used to perform a seismic cross-hole tomography in the Excavation Damaged Zone (EDZ) of the new G04 gallery of the Mont Terri Underground Rock Laboratory (Switzerland) excavated in Opalinus clay. More than 800 seismic traces were recorded between two vertical boreholes by combining 22 source and 48 receiver locations. A vertical area of 1.2 × 3.4 m under the floor of the gallery is investigated with a high-resolution tomography. Data with a very good quality allow to determine the traveltimes and the amplitudes of a 40kHz source wavelet propagating between the two boreholes. The analysis of the traveltimes shows that the wave velocity is homogeneous but anisotropic with a minimum value of 2490 +/- 45ms-1 in the direction normal to the bedding and a maximum of 3330 +/- 90ms-1 parallel to the bedding. The amplitude of the first arrivals strongly varies depending on the source-receiver locations, and suggesting an heterogeneous distribution of the attenuation coefficient of the seismic waves. A Bayesian inversion provides likely models of attenuation that are compared with geological observations. The areas where fractures or cracks exist in the Opalinus clay appear as highly absorbing the seismic waves.

  2. The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

    NASA Astrophysics Data System (ADS)

    Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

    2016-04-01

    The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

  3. Integrating gamma log and conventional electrical logs to improve identification of fracture zones in hard rocks for hydrofracturing: a case study from Ghana

    NASA Astrophysics Data System (ADS)

    Amartey, E. O.; Akiti, T. T.; Armah, T.; Osae, S.; Agyekum, W. A.

    2016-07-01

    Hydrofracturing of low-yielding boreholes in hard rocks is a widely used technique in Africa for improvement of yield, thus making them qualified for installation of a hand-pump for domestic water supply. However, the success rate of the hydrofracturing campaigns seems not to be that high as generally claimed by contractors. One reason amongst others might be that the selection of zones for hydrofracturing in the individual borehole is based on pre-hydrofracturing investigation using conventional electrical logs only. Thereby, the zones selected are the occurring resistivity minima interpreted as weak zones with some fracturing. However, resistivity minima can also be caused solely by lithological reasons, which then in most cases could have been seen on a gamma log as corresponding increased gamma radiation. The advantages of using gamma logging in combination with conventional electrical logging technique for prediction of fractured zones in basement rocks is illustrated by investigations of three low-yielding boreholes located in different geological environments in crystalline basement rocks in Ghana.

  4. Structural and petrographic analysis of hypabyssal rocks in the central Menderes Massif: implications for the role of transfer zones during detachment faulting

    NASA Astrophysics Data System (ADS)

    Erkül, Fuat; Gürboǧa, Şule; Tatar Erkul, Sibel; Deveci, Zehra

    2014-05-01

    Structural and petrographic analysis of hypabyssal rocks in the central Menderes Massif: implications for the role of transfer zones during detachment faulting Fuat ERKÜL(1), Şule GÜRBOǧA(2), Sibel TATAR ERKÜL(3), Zehra DEVECİ(4) The central Menderes Massif is formed by complex assemblages of transfer zones, detachment faults and associated syn-extensional granitoids in western Turkey. Syn-extensional Salihli and Turgutlu granitoids were widely recognized in the footwall rocks of the Gediz detachment fault, but their hypabyssal equivalents were not described in detail. Hypabyssal rocks discovered during this study include substantial structural data that may shed light into the development of transfer zones during detachment faulting. Hypabyssal rocks are mafic and felsic in compositions. Mafic rocks, which are located to the SW of the Turgutlu granitoid, were emplaced into the phyllites as sills and dykes that were surrounded by a narrow hornfelsic halo. Dykes are subvertical and trend N20oW, intersecting the phyllites of the Menderes Massif. They include abundant xenoliths of phyllite and gneiss and are mainly characterized by ophitic texture formed by plagioclase, tremolite/actinolite, biotite, and pyroxene crystals. Felsic dykes, which are located in the SE of the Salihli granitoid, are defined as three subparallel, N10oW-trending dykes that intrude into the mica schists. Felsic dykes consist of quartz, sanidine and plagioclase and zircon, apatite and allanite as accessory phases. They display holocrystalline hypidiomorphic porphyritic texture, suggesting their typical shallow-seated and hypabyssal emplacement. Microcrystalline matrix surrounds embayed quartz and locally corroded crystals. Alteration mineral assemblages of chlorite, epidote and sericite and carbonatization are also common. Their mineral constituents appear to be similar to those of the Salihli granitoid. Felsic dykes have well-preserved two sets of slip surfaces striking NE and NW in

  5. Mountain permafrost and recent Alpine rock-fall events: a GIS-based approach to determine critical factors and runout zones

    NASA Astrophysics Data System (ADS)

    Noetzli, J.; Hoelzle, M.; Haeberli, W.:

    2003-04-01

    Glacier retreat and permafrost changes, as related to climate change, are supposed to affect stability conditions of steep rock walls in cold mountain ranges. Several rock-fall events that have occurred in the European Alps during the 20th century (for example, the Brenva Glacier rock avalanches of 1920 and 1997 in the Aosta Valley or the recently developed instability in the Monte-Rosa east wall in the Anzasca Valley, both in the Italian Alps) are possibly related to warm permafrost. The presence of unfrozen water in partially ice-filled bedrock fissures is likely to lead to reduced shearing resistance. However, available knowledge about thermal, topographic and geological conditions under which such instabilities develop remains limited and needs quantitative investigation. Corresponding data can be used as a basis for GIS-based spatial modeling of critical factors or of combinations of factors. Such spatial models of critical rock-fall factors then serve as a basis for assessing hazard potentials that may evolve from periglacial rock falls in case of continued or even accelerated atmospheric temperature rise. In order to proceed into this direction, parameters are determined in a systematic study of known rock-fall events in the Alps. Surface temperatures of historically documented starting zones are estimated either by applying the ärules of thumb“ earlier developed for the Swiss Alps, by applying GIS-based spatial models such as PERMAMAP or by using the data of a 2001/2002 rock-temperature measurement campaign. Topographic factors such as slope, altitude or aspect are derived from DTMs. Altitude difference, length, overall slope and surface characteristics (glacier, moraines, turns etc.) of runout paths are also inventoried. Despite the relatively small number of events documented (around 20), first results can be given and first model runs of spatial patterns and potential runout zones can be presented from a selected test area in the Valais Alps

  6. Plume-proximal mid-ocean ridge origin of Zhongba mafic rocks in the western Yarlung Zangbo Suture Zone, Southern Tibet

    NASA Astrophysics Data System (ADS)

    He, Juan; Li, Yalin; Wang, Chengshan; Dilek, Yildirim; Wei, Yushuai; Chen, Xi; Hou, Yunling; Zhou, Aorigele

    2016-05-01

    The >2000 km-long Yarlung Zangbo Suture Zone (YZSZ) in southern Tibet includes the remnants of the Mesozoic Neotethyan oceanic lithosphere, and is divided by the Zhada-Zhongba microcontinent into northern and southern branches in its western segment. Zircon U-Pb dating of a doleritic rock from the northern branch has revealed a concordant age of 160.5 ± 1.3 Ma. All of the doleritic samples from the northern branch and the pillow basalt and gabbro samples from the southern branch display consistent REE and trace element patterns similar to those of modern OIB-type rocks. The geochemical and Sr-Nd-Pb isotopic signatures of these OIB-type rocks from the western segment are identical with those of OIB-type and alkaline rocks from other ophiolite massifs along the central and eastern segments of the YZSZ, suggesting a common mantle plume source for their melt evolution. The enriched Sr-Nd-Pb isotopic character of the gabbroic dike rocks from the southern branch points to a mantle plume source, contaminated by subducted oceanic crust or pelagic sediments. We infer that the mafic rock associations exposed along the YZSZ represent the remnants of a Neotethyan oceanic lithosphere, which was developed as part of a plume-proximal seafloor-spreading system, reminiscent of the seamount chains along-across the modern mid-ocean ridges in the Pacific Ocean.

  7. Record of Variscan Low-P/High-T metamorphism in Alpine medium-P rocks of the Pelagonian Zone, Greece

    NASA Astrophysics Data System (ADS)

    Mposkos, E.; Krohe, A.; Perraki, M.

    2003-04-01

    In the Early Cretaceous, obduction of the ophiolites from the Vardar ocean over the eastern Pelagonian continental margin caused medium-P metamorphism in the pre-Alpine basement and the Alpine volcanosedimentary cover series of the Pelagonian Zone (Yarwood &Dixon, 1977, Schermer et al., 1990, Perraki et al., 2003). Representative mineral assemblages are garnet-chloritoid-chlorite-kyanite-white K-mica-paragonite-rutile in Permo-Triassic pelitic metasediments from Voras and Vermion Mountains (Western Macedonia) and hornblende-garnet-clinozoisite-albite-quartz-rutile in metabasites. Pervasive deformation associated with this metamorphism completely converted Variscan granitoids and pelitic migmatites into mylonites with the syn-mylonitic mineral assemblage quartz-albite-microcline-phengite (Si up to 3.5 atoms p.f.u.)-garnet-clinozoisite-biotite on granitoid mylonites. Pelitic migmatites from Voras and Vernon Massifs are converted to garnet-chlorite-biotite-muscovite schists, garnet-chloritoid-kyanite-chlorite-muscovite schists and garnet-kyanite-staurolite-chlorite-muscovite schists. Less deformed domains of pelitic migmatites locally preserve Pre-Alpine mineral assemblages characteristic for a low-P/high-T metamorphism. In the NE Vernon Massif, SE Othris and N. Euboea island sillimanite-biotite-garnet-muscovite-K-feldspar-plagioclase-quartz indicate P~4.5 kbar and T~640 0C. In western Vernon and Voras Massifs the mineral assemblages andalusite-cordierite-biotite-muscovite-sillimanite-plagioclase-quartz, andalusite-sillimanite-cordierite-K-feldspar-plagioclase-muscovite-quartz evidence even lower pressures of 2.5 kbar and ~600-620 0C. This metamorphism reflects heat transfer by intrusion of large volumes of granitoid magmas in a Variscan magmatic arc setting. Klippen and tectonic slivers of LP/HT metamorphic rocks, also, occur in the Cyclades and the ophiolite melange of Crete, where they are conventionally considered as Upper Cretaceous magmatic arc. In contrast we

  8. Rock pulverization and localization of a strike-slip fault zone in dolomite rocks (Salzach-Ennstal-Mariazell-Puchberg fault, Austria)

    NASA Astrophysics Data System (ADS)

    Schröckenfuchs, Theresa; Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

    2015-09-01

    Detailed investigations of dolomite fault rocks, formed at shallow crustal depths along the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps, revealed new insights into cataclasite formation. The examined Miocene, sinistral strike-slip faults reveal grain size reduction of dolomite host rocks by tensile microfracturing at a large range of scales, producing rock fragments of centimetre to micrometre sizes. In situ fracturing leads to grain size reduction down to grain sizes <25 μm, producing mosaic breccias and fault rocks which have previously been described as "initial/embryonic" and "intermediate" cataclasites. At all scales, grain fragments display little to no rotation and no or minor evidence of shear deformation. The observed microstructures are similar to those previously described in studies on pulverized rocks. Microstructural investigations of cataclasites and mosaic breccias revealed aggregations of small dolomite grains (<50 μm) that accumulated on top of large fragments or as infillings of V-shaped voids between larger grains and show constant polarity throughout the investigated samples. Fabrics indicate deposition in formerly open pore space and subsequent polyphase cementation. The newly described tectonic geopetal fabrics (geopetal-particle-aggregates, GPA) prove that these faults temporarily passed through a stage of extremely high porosity/permeability prior to partial cementation.

  9. Effect of petrophysical properties and deformation on vertical zoning of metasomatic rocks in U-bearing volcanic structures: A case of the Strel'tsovka caldera, Transbaikal region

    NASA Astrophysics Data System (ADS)

    Petrov, V. A.; Andreeva, O. V.; Poluektov, V. V.

    2014-03-01

    The development of vertical zoning of wall-rock metasomatic alteration is considered with the Mesozoic Strel'tsovka caldera as an example. This caldera hosts Russia's largest uranium ore field. Metasomatic rocks with the participation of various phyllosilicates, carbonates, albite, and zeolites are widespread in the ore field. In the eastern block of the caldera, where the main uranium reserves are accommodated, hydromica metasomatic alteration gives way to beresitization with depth. Argillic alteration, which is typical of the western block, is replaced with hydromica and beresite alteration only at a significant depth. Postore argillic alteration is superposed on beresitized rocks in the lower part of the section. Two styles of vertical metasomatic zoning are caused by different modes of deformation in the western and eastern parts of the caldera. Variations of the most important petrophysical properties of host rocks—density, apparent porosity, velocities of P- and S-waves, dynamic Young's modulus, and Poisson coefficient—have been determined by sonic testing of samples taken from different depths. It is suggested that downward migration of the brittle-ductile transition zone could have been a factor controlling facies diversity of metasomatic rocks. Such a migration was caused by a new phase of tectonothermal impact accompanied by an increase in the strain rate or by emplacement of a new portion of heated fluid. Transient subsidence of the brittle-ductile boundary increases the depth of the hydrodynamically open zone related to the Earth's surface and accelerates percolation of cold meteoric water to a greater depth. As a result, the temperature of the hydrothermal solution falls down, increasing the vertical extent of argillic alteration. High-grade uranium mineralization is also localized more deeply than elsewhere.

  10. The significance of geological and zircon age data derived from the wall rocks of the Ailao Shan-Red River Shear Zone, NW Vietnam

    NASA Astrophysics Data System (ADS)

    Żelaźniewicz, Andrzej; Hòa, Trần Trọng; Larionov, Alexander N.

    2013-09-01

    This paper offers new evidence on whether the Ailao Shan-Red River Shear Zone of NW Vietnam is part of a suture zone between two continental blocks (the IndoChina Block and the South China Block) or whether it is itself of intracontinental origin, developed within the South China margin. To help clarify the role that the Ailao Shan-Red River Shear Zone plays in South China tectonic reconstructions, we gathered new whole-rock geochemistry, structural field data, and zircon U-Pb (SHRIMP) ages from granites, rhyodacites, and migmatites that occur within geological units adjacent to both the SW and NE sides of the Red River Fault Zone, a segment of the larger shear zone. The new zircon ages show that both walls of the Red River Fault Zone contain metamorphic and intraplate A-type granitoid rocks of Late Permian-Early Triassic age (263-240 Ma) and are of Indosinian origin. In the SW wall, the Fan Si Pan complex is a Neoproterozoic basement of metagranites and metasediments that was intruded by Late Permian (˜260 Ma), peralkaline, A-type granites and by subalkaline, A-type, biotite granite of Eocene age (˜35 Ma), containing xenoliths of gneissified Permian granitoids. The two intrusive episodes were separated by regional tectonic deformations occurring within a transpressional regime of a NW/W-vergent thrusting with a left-lateral oblique component, that was associated with greenschist to amphibolite facies metamorphism, presumably also of Eocene age (˜50-35 Ma), and that may have been related to the left-lateral movement on the Ailao Shan-Red River Shear Zone. In the NE wall, the Lo Gam complex is a Neoproterozoic basement (˜767 Ma) that was repeatedly subjected to tectonothermal activity throughout the Palaeozoic (at ˜450-420 Ma, ˜350 Ma, ˜265 Ma), ending in the Early Triassic (˜248 Ma). There was no thermal overprint during the Cenozoic. In this wall, a significant part of the Permo-Triassic thermotectonism was ductile shearing that was concentrated along

  11. Spatial and temporal variability of rock fall in a (peri)glacial environment: a LiDAR-based, multi-year investigation of rock fall release zones and volumes, Kitzsteinhorn, Austria

    NASA Astrophysics Data System (ADS)

    Delleske, Robert; Hartmeyer, Ingo; Keuschnig, Markus; Götz, Joachim

    2014-05-01

    October). All scans (n = 41) were conducted using a RIEGL LMS-Z620. The resulting spatial resolution varies between 0.1 and 0.5 m and object distance (i.e. distance between scanner and rock face) ranges from 250 to 500 m. Post-processing of TLS data enabled to precisely identify rock fall release zones, rock fall volumes and surface changes of the Schmiedingerkees glacier (lowering rate of approximately 1.5 m per year). Since 2011 a total number of nine rock fall events with a volume exceeding 100 m³ have been recorded - with the largest reaching a volume of approx. 500 m³. All were triggered from areas that have been exposed by the retreating Schmiedingerkees glacier over the last 1-2 decades. Thus, glacial debuttressing and subsequent exposure to atmospheric influences might be considered as the dominant destabilizing factors. Temporal clustering of rock fall events over the first three seasons (2011 to 2013) tentatively indicates a bimodal occurrence pattern with a first maximum during snowmelt (May/June) and a second distinct peak during the warmest period of the year (August).

  12. Pressure solution in rocks: focused ion beam/transmission electron microscopy study on orthogneiss from South Armorican Shear Zone, France

    NASA Astrophysics Data System (ADS)

    Bukovská, Zita; Wirth, Richard; Morales, Luiz F. G.

    2015-09-01

    In order to characterize the µm-to-nm structures related to operation of pressure solution on phase boundaries in naturally deformed rocks, we have performed a detailed focused ion beam/transmission electron microscopy study in ultramylonite samples from South Armorican Shear Zone (France) that focused on grain boundary scale. We have studied phase boundaries between quartz, K-feldspar and white mica in both 2D and 3D and compare our evidences with theoretical dissolution precipitation models in the current literature. The dissolution (re)precipitation processes lead to the development of different features at different phase boundaries. In both quartz-white mica and quartz-K-feldspar phase boundaries, voids were ubiquitously observed. These voids have different shapes, and the development of some of them is crystallographically controlled. In addition, part of these voids might be filled with vermiculite. Amorphous leached layers with kaolinite composition were observed at the boundaries of K-feldspar-quartz and K-feldspar-white mica. The development of different features along the phase boundaries is mainly controlled by the crystallography of the phases sharing a common interface, together with the presence of fluids that either leaches or directly dissolve the mineral phases. In addition, the local dislocation density in quartz may play an important role during pressure solution. We suggest that the nanoscale observations of the quartz-white mica phase boundaries show direct evidence for operation of island-and-channel model as described in Wassmann and Stockhert (Tectonophysics 608:1-29, 2013), while K-feldspar-quartz phase boundaries represents amorphous layers formed via interface-coupled dissolution reprecipitation as described by Hellmann et al. (Chem Geol 294-295:203-216, 2012).

  13. Final closure of the Paleo-Asian Ocean along the Solonker Suture Zone: Constraints from geochronological and geochemical data of Permian volcanic and sedimentary rocks

    NASA Astrophysics Data System (ADS)

    Eizenhöfer, Paul R.; Zhao, Guochun; Zhang, Jian; Sun, Min

    2014-04-01

    There is a broad consensus that the Solonker Suture Zone marks the final closure of the Paleo-Asian Ocean, which led to the formation of the eastern segment of the Central Asian Orogenic Belt. However, when and how the final closure occurred still remains controversial. To address this issue, provenance analysis of Permian sedimentary rocks of arc basins along the Xar Moron River was carried out. Geochemical analysis revealed a close relationship between the sedimentary and volcanic rock suite in the study region suggesting short transport distances and a complex convergent arc setting. Detrital zircon U-Pb analysis identified two major age provenances: (1) the Precambrian basement of the North China Craton (~2497 Ma and ~1844 Ma) and (2) the Paleozoic Southern Accretionary Orogen along the northern margin of North China (~436 Ma and ~269 Ma). The present locations of identified age provenances indicate southward subduction beneath the northern margin of North China. A comparison of the youngest age population in the sedimentary rocks with U-Pb ages obtained for subduction-related volcanic rocks implies that the Solonker Suture Zone formed from the Late Permian to Early Triassic. The results of our study advocate a complex Permian arc system which was probably similar to present-day Southeast Asia.

  14. Crystal preferred orientations of minerals from mantle xenoliths in alkali basaltic rocks form the Catalan Volcanic Zone (NE Spain)

    NASA Astrophysics Data System (ADS)

    Fernández-Roig, Mercè; Galán, Gumer; Mariani, Elisabetta

    2015-04-01

    Mantle xenoliths in alkali basaltic rocks from the Catalan Volcanic Zone, associated with the Neogene-Quaternary rift system in NE Spain, are formed of anhydrous spinel lherzolites and harzburgites with minor olivine websterites. Both peridotites are considered residues of variable degrees of partial melting, later affected by metasomatism, especially the harzburgites. These and the websterites display protogranular microstructures, whereas lherzolites show continuous variation between protogranular, porphyroclastic and equigranular forms. Thermometric data of new xenoliths indicate that protogranular harzburgites, lherzolites and websterites were equilibrated at higher temperatures than porphyroclastic and equigranular lherzolites. Mineral chemistry also indicates lower equilibrium pressure for porphyroclastic and equigranular lherzolites than for the protogranular ones. Crystal preferred orientations (CPOs) of olivine and pyroxenes from these new xenoliths were determined with the EBSD-SEM technique to identify the deformation stages affecting the lithospheric mantle in this zone and to assess the relationships between the deformation fabrics, processes and microstructures. Olivine CPOs in protogranular harzburgites, lherzolites and a pyroxenite display [010]-fiber patterns characterized by a strong point concentration of the [010] axis normal to the foliation and girdle distribution of [100] and [001] axes within the foliation plane. Olivine CPO symmetry in porphyroclastic and equigranular lherzolites varies continuously from [010]-fiber to orthorhombic and [100]-fiber types. The orthorhombic patterns are characterized by scattered maxima of the three axes, which are normal between them. The rare [100]-fiber patterns display strong point concentration of [100] axis, with normal girdle distribution of the other two axes, which are aligned with each other. The patterns of pyroxene CPOs are more dispersed than those of olivine, especially for clinopyroxene, but

  15. A new stent with streamlined cross-section can suppress monocyte cell adhesion in the flow disturbance zones of the endovascular stent.

    PubMed

    Chen, Zengsheng; Zhan, Fan; Ding, Jun; Zhang, Xiwen; Deng, Xiaoyan

    2016-01-01

    We proposed a new stent with streamlined cross-sectional wires, which is different from the clinical coronary stents with square or round cross-sections. We believe the new stent might have better hemodynamic performance than the clinical metal stents. To test the hypothesis, we designed an experimental study to compare the performance of the new stent with the clinical stents in terms of monocyte (U-937 cells) adhesion. The results showed that when compared with the clinical stents, the adhesion of U-937 cells were much less in the new stent. The results also showed that, when Reynolds number increased from 180 (the rest condition for the coronary arteries) to 360 (the strenuous exercise condition for the coronary arteries), the flow disturbance zones in the clinical stents became larger, while they became smaller with the new stent. The present experimental study therefore suggests that the optimization of the cross-sectional shape of stent wires ought to be taken into consideration in the design of endovascular stents. PMID:25434694

  16. Mantle wedge peridotites: Fossil reservoirs of deep subduction zone processes: Inferences from high and ultrahigh-pressure rocks from Bardane (Western Norway) and Ulten (Italian Alps)

    NASA Astrophysics Data System (ADS)

    Scambelluri, Marco; Van Roermund, Herman L. M.; Pettke, Thomas

    2010-11-01

    The garnet websterites from Bardane (Western Gneiss Region, Norway) derive from cold Archean subcontinental lithosphere involved in Scandian continental subduction to ultrahigh-pressures. Subduction zone metamorphism was promoted by slab fluid infiltration into the cold overlying mantle wedge. The earliest subduction transformation (M3-1) consists of garnet/clinopyroxene exsolution from old pre-subduction orthopyroxene. This stage was likely coeval with fluid input and formation of phlogopite and dolomite rods in the exsolution structures. Magnesite formation after dolomite and entrapment of fluid-related diamond-bearing polyphase inclusions in corona structures around the exsolved orthopyroxenes point to pressure increase to 4.5 GPa (M3-2). Peak pressures of 6.5-7 GPa (c.a. 200 km depth) are witnessed by crystallization of majoritic garnet (M3-3), mostly in veins cutting all the above microstructures. When such veins infiltrate the corona domains, formation of majoritic garnet in coronas is enhanced. This multistage evolution thus envisages episodic fluid influx, favouring rock recrystallization and formation of microdiamond-bearing inclusions and of majoritic garnet veins. These mantle rocks thus record fluid circulation along grain boundaries and microfractures down to 200 km depth in subduction environments. The Ulten Zone peridotites are slices of Variscan mantle wedge. Infiltration of metasomatic subduction fluids favoured transition from spinel-facies to garnet + amphibole ± dolomite parageneses at pressures below 3 GPa. Formation of metasomatized garnet-bearing peridotite mylonites suggest channelled influx of subduction fluids. The incompatible element-enriched signature of all subduction minerals in Bardane indicate that previously depleted websterites have been refertilized by COH subduction fluids. Comparison with the Ulten Zone garnet + amphibole ± dolomite peridotites outlines striking similarities in the metasomatic style and in the COH fluid phase

  17. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    NASA Astrophysics Data System (ADS)

    Solum, John G.; Davatzes, Nicholas C.; Lockner, David A.

    2010-12-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ˜1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon.

  18. Fault-related clay authigenesis along the Moab Fault: Implications for calculations of fault rock composition and mechanical and hydrologic fault zone properties

    USGS Publications Warehouse

    Solum, J.G.; Davatzes, N.C.; Lockner, D.A.

    2010-01-01

    The presence of clays in fault rocks influences both the mechanical and hydrologic properties of clay-bearing faults, and therefore it is critical to understand the origin of clays in fault rocks and their distributions is of great importance for defining fundamental properties of faults in the shallow crust. Field mapping shows that layers of clay gouge and shale smear are common along the Moab Fault, from exposures with throws ranging from 10 to ???1000 m. Elemental analyses of four locations along the Moab Fault show that fault rocks are enriched in clays at R191 and Bartlett Wash, but that this clay enrichment occurred at different times and was associated with different fluids. Fault rocks at Corral and Courthouse Canyons show little difference in elemental composition from adjacent protolith, suggesting that formation of fault rocks at those locations is governed by mechanical processes. Friction tests show that these authigenic clays result in fault zone weakening, and potentially influence the style of failure along the fault (seismogenic vs. aseismic) and potentially influence the amount of fluid loss associated with coseismic dilation. Scanning electron microscopy shows that authigenesis promotes that continuity of slip surfaces, thereby enhancing seal capacity. The occurrence of the authigenesis, and its influence on the sealing properties of faults, highlights the importance of determining the processes that control this phenomenon. ?? 2010 Elsevier Ltd.

  19. Fault-rock magnetism from the earth surface trench closed to the Wenchuan Earthquake Surface Rupture Zone imply the different slip dynamics

    NASA Astrophysics Data System (ADS)

    Liu, D.; Li, H.; Lee, T. Q.; Sun, Z.

    2014-12-01

    The 2008 Mw 7.9 Wenchuan Earthquake had induced two major earthquake surface rupture zones, including the Yingxiu-Beichuan earthquake fault (Y-B F.) and Guanxian-Anxian earthquake fault (G-A F.) earthquake surface rupture zones. This giant earthquake had caused great human and financial loss. After main shock, the Wenchuan earthquake Fault Scientific Drilling project (WFSD) was co-organized by the Ministry of Science and Technology, Ministry of Land and Resources and China Bureau of Seismology, and this project focused on earthquake fault mechanics, earthquake slip process, fault physical and chemical characteristics, mechanical behavior, fluid behavior, fracture energy, and so on. In this study, the fault-rocks in the two trenches close to the two Wenchuan Earthquake surface rupture zone were used to discuss the earthquake slip dynamics, including the Bajiaomiao and Jiulong trenches along the Y-B F. and G-A F. earthquake surface rupture zones, respectively. This study also combined with the recent fault-rock magnetism from the earth surface and WFSD-1. The rock magnetism, from the Bajiaomiao trench and other previous researches, shows that the high susceptibility of the fault gouge along the Yingxiu-Beichuan earthquake fault zone was caused by the new-formed ferrimagnetic minerals, such as magnetite and hematite, so the Y-B F. had experienced high temperature and rapid speed thermal pressurization earthquake slip mechanism. The rock magnetism from the Jiulong trench implied that the slightly low average susceptibility of fault gouge was caused by high content of Fe-sulfides than that of fault breccia and Jurassic sandstones, which was possibly induced by earthquake process or earth surface process after the fault rocks exposed to the surface. If the high content of Fe-sulfides was induced by earthquake process, the G-A F. had experienced the low temperature and slow speed machanical lubrication earthquake slip mechanism. The different earthquake slip mechanism was

  20. Extensional Detachment faulting in melange rocks. Plurikilometres migration by W the External Zone (Cordillera Bética, Spain)

    NASA Astrophysics Data System (ADS)

    Roldán, Francisco Javier; Azañon, Jose Miguel; Rodríguez, Jose; Mateos, Rosa Maria

    2014-05-01

    The synthesis and correlation of units carried out in the continuous geological map (Roldán et al., 2012), has revealed a fragmentation of the carbonate outcrops belong to the Subbetic Domain (García-Hernández et al., 1980). Subbetic NW verging thrust and fold axial traces have not lateral continuity and Jurassic carbonate outscrops appear as klippes on the olistotromic unit. These ductile structures that can be observed in the internal structure of these jurassic blocks are unrelated to the brittle-ductile deformation bands observed at the basal pelitic levels. Basal detachments are rooted in: a) the Olistostromic unit, a Upper Langhian-Lower Serravallian breccia constituted by gypsum-bearing clay and marls; b) Cretaceous-Tertiary marly sedimentary rocks (Rodríguez-Fernández, et al., 2013) . In both kind of rocks, cataclastic structures allows to infer a top-to-the WSW displacement. Paleostress measurements, made on these detachments levels, are compatible with a extensional regime (Roldán et al., 2012). At the same time, the analysis and interpretation of subsurface data (seismic surveys and borehole testing) shows that the Subbetic Domain (External Subbetic, Molina 1987) are affected by westward low-angle normal faults. A balanced cross-section, based on morphological and cartographic data in the area between Sierra de Cabra and Sierra de Alta Coloma (Valdepeñas de Jaén), shows plurikilometric displacements which has been produced during Late Serravallian-Early Tortonian times. References: García-Hernández, M., López-Garrido, A.C., Rivas, P., Sanz de Galdeano, C., Vera, J.A. (1980): Mesozoic paleogeographic evolution of the zones of the Betic Cordillera. Geol. Mijnb. 59 (2). 155-168. Molina, J.M. (1987). Análisis de facies del Mesozoico en el Subbético. Tesis Doctoral, Univ. Granada. 518 p. Rodríguez-Fernández, J., Roldán, F. J., Azañón, J.M. y García-Cortés, A. (2013). El colapso gravitacional del frente orogénico a lpino en el Dominio Subb

  1. Teaching Marine Geoscience at Sea: Integrated Ocean Drilling Program's School of Rock Explores Cascadia Subduction Zone - Cores, Logs, and ACORKs

    NASA Astrophysics Data System (ADS)

    Reagan, M.; Collins, J.; Ludwig, K. A.; Slough, S.; Delaney, M. L.; Hovan, S. A.; Expedition 328 Scientists

    2010-12-01

    For twelve days this past September, seventeen formal and informal educators from the US, UK, and France joined six instructors and a small science party on the scientific drillship JOIDES Resolution for the Integrated Ocean Drilling Program (IODP)’s Cascadia ACORK Expedition. The educators were part of the annual “School of Rock (SOR)” education program. SOR is coordinated by the U.S. Implementing Organization (USIO) of IODP and is designed to engage participants in seagoing Earth systems research and education workshops onboard the JOIDES Resolution and on shore at the Gulf Coast Core Repository in Texas. The scientific objective of the Cascadia ACORK expedition was to install a new permanent hydrologic observatory at ODP Site 889 to provide long-term monitoring of the pressure at the frontal part of the Cascadia accretionary prism. This year’s SOR workshop focused on how cores, logs, and ACORKs shed light on the hydrology and geology of the Cascadia subduction zone in the Northeast Pacific. In addition to observing the deployment of the ACORK, the SOR participants conducted daily hands-on analyses of archived sediment and hard-rock cores with scientists and technicians who specialize in IODP research using the lab facilities on the ship. Throughout the expedition, participants engaged in different activities and lessons designed to explore the deep biosphere, methane hydrates, paleoceanography, sedimentology, biostratigraphy, seafloor spreading, and drilling technology. The workshop also provided participants with “C3” time; time to communicate their experience using the successful joidesresolution.org website and other tools, make connections to their prior knowledge and expertise, and to be creative in developing and planning new education and outreach activities based on their new knowledge and research. As part of participating in the expedition, participants committed to further developing and testing their education and outreach products after

  2. Influence of host lithofacies on fault rock variation in carbonate fault zones: A case study from the Island of Malta

    NASA Astrophysics Data System (ADS)

    Michie, E. A. H.

    2015-07-01

    Relatively few studies have examined fault rock microstructures in carbonates. Understanding fault core production helps predict the hydraulic behaviour of faults and the potential for reservoir compartmentalisation. Normal faults on Malta, ranging from <1 m to 90 m displacement, cut two carbonate lithofacies, micrite-dominated and grain-dominated carbonates, allowing the investigation of fault rock evolution with increasing displacement in differing lithofacies. Lithological heterogeneity leads to a variety of deformation mechanisms. Nine different fault rock types have been identified, with a range of deformation microstructures along an individual slip surface. The deformation style, and hence type of fault rock produced, is a function of host rock texture, specifically grain size and sorting, porosity and uniaxial compressive strength. Homogeneously fine-grained micrtie-dominated carbonates are characterised by dispersed deformation with large fracture networks that develop into breccias. Alternatively, this lithofacies is commonly recrystallised. In contrast, in the coarse-grained, heterogeneous grain-dominated carbonates the development of faulting is characterised by localised deformation, creating protocataclasite and cataclasite fault rocks. Cementation also occurs within some grain-dominated carbonates close to and on slip surfaces. Fault rock variation is a function of displacement as well as juxtaposed lithofacies. An increase in fault rock variability is observed at higher displacements, potentially creating a more transmissible fault, which opposes what may be expected in siliciclastic and crystalline faults. Significant heterogeneity in the fault rock types formed is likely to create variable permeability along fault-strike, potentially allowing across-fault fluid flow. However, areas with homogeneous fault rocks may generate barriers to fluid flow.

  3. The Moho as a transition zone: A revisit from seismic and electrical properties of minerals and rocks

    NASA Astrophysics Data System (ADS)

    Wang, Qin; Bagdassarov, Nickolai; Ji, Shaocheng

    2013-12-01

    The seismic Moho discontinuity is not always consistent with a chemical boundary (the “petrological Moho”) that separates the mafic lower crust from the ultramafic upper mantle. We summarize the effects of pressure, temperature and metamorphism on seismic and electrical properties of lower crustal and mantle rocks. The sharpness of the Moho discontinuity is generally related with the petrological transition from olivine-poor to olivine-rich compositions. Due to serpentinizat]ion, the seismic Moho may not correspond with the petrological Moho beneath the oceanic crust and forearcs. More precise velocity-density relationships are established for typical oceanic and continental crust-mantle boundaries, as well as for serpentinization of peridotites at low and high temperatures. Combined with Poisson's ratio, the occurrence of continental lowest crust with Vp > 7.2 km/s may reflect pyroxenites and garnet gabbros by magma underplating, or eclogitization of gabbros and mafic granulites by crustal thickening. On the other hand, the “electrical Moho” is defined as the bottom of the relatively conductive continental lower crust (10- 4 to 10- 1 S/m). Electrical conductivity of granulites and peridotites is mainly controlled by temperature, composition (iron content and water content) and oxygen fugacity, but weakly depends on pressure. Even a small amount of hydrogen can significantly enhance electrical conductivity of olivine, pyroxene and garnet. Although amphibole and serpentine are resistive under their stability conditions, their electrical conductivity will be remarkably increased by dehydration reaction at temperature > 600 °C. Granulites and eclogites show similar conductivity of 10- 4 to 10- 2 S/m at 500-1000 °C, about one order more conductive than water-poor garnet pyroxenites and spinel peridotites. Therefore the depth of the electrical Moho varies with temperature and water content at the crust-mantle boundary. The discrepancy between the seismic

  4. Accessory and rock forming minerals monitoring the evolution of zoned mafic ultramafic complexes in the Central Ural Mountains

    NASA Astrophysics Data System (ADS)

    Krause, J.; Brügmann, G. E.; Pushkarev, E. V.

    2007-04-01

    This study describes major and trace element compositions of accessory and rock forming minerals from three Uralian-Alaskan-type complexes in the Ural Mountains (Kytlym, Svetley Bor, Nizhnii Tagil) for the purpose of constraining the origin, evolution and composition of their parental melts. The mafic-ultramafic complexes in the Urals are aligned along a narrow, 900 km long belt. They consist of a central dunite body grading outward into clinopyroxenite and gabbro lithologies. Several of these dunite bodies have chromitites with platinum group element mineralization. High Fo contents in olivine (Fo 92-93) and high Cr/(Cr + Al) in spinel (0.67-0.84) suggest a MgO-rich (> 15 wt.%) and Al 2O 3-poor ultramafic parental magma. During its early stages the magma crystallized dominantly olivine, spinel and clinopyroxene forming cumulates of dunite, wehrlite and clinopyroxenite. This stage is monitored by a common decrease in the MgO content in olivine (Fo 93-86) and the Cr/(Cr + Al) value of coexisting accessory chromite (0.81-0.70). Subsequently, at subsolidus conditions, the chromite equilibrated with the surrounding silicates producing Fe-rich spinel while Al-rich spinel exsolved chromian picotite and chromian titanomagnetite. This generated the wide compositional ranges typical for spinel from Uralian-Alaskan-type complexes world wide. Laser ablation analyses (LA-ICPMS) reveal that clinopyroxene from dunites and clinopyroxenite from all three complexes have similar REE patterns with an enrichment of LREE (0.5-5.2 prim. mantle) and other highly incompatible elements (U, Th, Ba, Rb) relative to the HREE (0.25-2.0 prim. mantle). This large concentration range implies the extensive crystallization of olivine and clinopyroxene together with spinel from a continuously replenished, tapped and crystallizing magma chamber. Final crystallization of the melt in the pore spaces of the cooling cumulate pile explains the large variation in REE concentrations on the scale of a thin

  5. The systematics of chlorine, fluorine, and water in Izu arc front volcanic rocks: Implications for volatile recycling in subduction zones

    NASA Astrophysics Data System (ADS)

    Straub, Susanne M.; Layne, Graham D.

    2003-11-01

    We studied the systematics of Cl, F and H 2O in Izu arc front volcanic rocks using basaltic through rhyolitic glass shards and melt inclusions (Izu glasses) from Oligocene to Quaternary distal fallout tephra. These glasses are low-K basalts to rhyolites that are equivalent to the Quaternary lavas of the Izu arc front (Izu VF). Most of the Izu glasses have Cl ˜400-4000 ppm and F ˜70-400 ppm (normal-group glasses). Rare andesitic melt inclusions (halogen-rich andesites; HRA) have very high abundances of Cl (˜6600-8600 ppm) and F (˜780-910 ppm), but their contents of incompatible large ion lithophile elements (LILE) are similar to the normal-group glasses. The preeruptive H 2O of basalt to andesite melt inclusions in plagioclase is estimated to range from ˜2 to ˜10 wt% H 2O. The Izu magmas should be undersaturated in H 2O and the halogens at their preferred levels of crystallization in the middle to lower crust (˜3 to ˜11 kbar, ˜820° to ˜1200°C). A substantial portion of the original H 2O is lost due to degassing during the final ascent to surface. By contrast, halogen loss is minor, except for loss of Cl from siliceous dacitic and rhyolitic compositions. The behavior of Cl, F and H 2O in undegassed melts resembles the fluid mobile LILE (e.g.; K, Rb, Cs, Ba, U, Pb, Li). Most of the Cl (>99%), H 2O (>95%) and F (>53%) in the Izu VF melts appear to originate from the subducting slab. At arc front depths, the slab fluid contains Cl = 0.94 ± 0.25 wt%, F = 990 ± 270 ppm and H 2O = 25 ± 7 wt%. If the subducting sediment and the altered basaltic crust were the only slab sources, then the subducted Cl appears to be almost entirely recycled at the Izu arc (˜77-129%). Conversely, H 2O (˜13-22% recycled at arc) and F (˜4-6% recycled) must be either lost during shallow subduction or retained in the slab to greater depths. If a seawater-impregnated serpentinite layer below the basaltic crust were an additional source of Cl and H 2O, the calculated percentage of

  6. Rock magnetism constrain response thickness on earth surface to large earthquake: Evidence from the Bajiaomiao Outcrop of the Wenchuan Earthquake Rupture Zone, China

    NASA Astrophysics Data System (ADS)

    Liu, D.; Li, H.; Lee, T.; Song, S.; Sun, Z.; Wang, X.; Chou, Y.; Chevalier, M.; Si, J.; Wang, H.

    2013-12-01

    The 2008 Mw 7.9 Wenchuan Earthquake has raptured along two fault zones, the Yingxiu-Beichuan f and the Anxian-Guanxian fault zones. The Wenchuan earthquake Fault Scientific Drilling project (WFSD) funded by the Chinese government, drilled five holes close to the two seismic fault zones. Fault gouge with various thicknesses were found in the drill holes and at the earth surface outcrops. In general, one such large earthquake creates several centimeters-thick fault gouge, i.e. the repeated large earthquakes must have taken place in the Longmen Shan region in order to accumulate the amount of gouge observed here. Rock magnetism is an economic, easy-access and non-destructive method for deciphering the magnetic mineral assemblage during large earthquake slip process, which can give us more information about this intercontinental earthquake dynamics, thanks to the occurrence of many large earthquakes as well as to the thick fault gouge present here. The Bajiaomiao outcrop, crossing to the Yingxiu-Beichuan seismic fault rapture zone, consisted of fault breccia and gouge in the hanging wall and Quaternary conglomerate in the footwall. The samples from the hanging wall of this outcrop were used to study rock magnetic porperties. Basing on the in-situ field magnetic susceptibility measurement, high magnetic susceptibility values were found in the fault gouge, possibly induced by more new-formed ferrimagnetic minerals. We apply other rock magnetic methods (such as Isothermal Remanent Magnetization (IRM), high-temperature thermomagnetism (K-T)) to the samples from the Bajiaomiao outcrop. The IRM results show that the magnetite was present in the gouge and fault breccia of the hand hall of the Yingxiu-Beichuan seismic fault rapture zone. Basing on the K-T results, magnetite and other ferromagnetic minerals existed in the gouge and fault breccia; the <2 cm thick gouge close to the fault rapture zone had existed the only magnetic mineral of magnetite. This < 2cm gouge was most

  7. Snow-cover dynamics monitored by automatic digital photography at the rooting zone of an active rock glacier in the Hinteres Lantal Cirque, Austria

    NASA Astrophysics Data System (ADS)

    Kellerer-Pirklbauer, Andreas; Rieckh, Matthias; Avian, Michael

    2010-05-01

    Knowledge regarding snow-cover dynamics and climatic conditions in the rooting zone of active rock glaciers is still limited. The number of meteorological stations on the surface of or close to active rock glaciers is increasing. However, areal information on snow-cover distribution and its spatial dynamics caused by different processes on rock glaciers surfaces with a high temporal resolution from such remote alpine areas are mostly difficult to obtain. To face this problem an automatic remote digital camera (RDC) system was proprietary developed. The core parts of the RDC system are a standard hand-held digital camera, a remote control, a water proof casing with a transparent opening, a 12V/25Ah battery and solar panels with a charge controller. Three such devices were constructed and installed at different sites in the Central Alps of Austria. One RDC system is used to monitor the rooting zone of the highly active rock glacier in the Hinteres Langtal Cirque (46°59'N, 12°47'E), Central Schober Mountains, Austria. The 0.15 km² large NW-facing rock glaciers is tongue-shaped with a fast moving lower part (>1m/a) and a substantially slower upper part, ranging in elevation between 2455-2700 m a.s.l. The RDC system was set up in September 2006 and is located since than at 2770 m a.s.l. on a pronounced ridge crest that confines the Hinteres Langtal Cirque to the SW. The water proof casing was attached to a 1.5 m high metal pole which itself was fixed to the bedrock by screws and concrete glue. The viewing direction of the camera is NE. Hence, the image section of the RDC focuses on the rooting zone of the rock glacier and its headwalls up to c. 3000 m a.s.l. Photographs were taken daily at 3 pm providing the optimal lighting conditions in the relevant part of the cirque. 720 photographs were taken continuously in the period 12.09.2006 to 31.08.2008. These optical data were analysed by applying GIS and remote sensing techniques regarding snow-cover distribution

  8. Geological setting and geochemical signatures of the mafic rocks from the Intra-Pontide Suture Zone: implications for the geodynamic reconstruction of the Mesozoic Neotethys

    NASA Astrophysics Data System (ADS)

    Sayit, Kaan; Marroni, Michele; Göncüoglu, M. Cemal; Pandolfi, Luca; Ellero, Alessandro; Ottria, Giuseppe; Frassi, Chiara

    2016-01-01

    A number of suture zones exist in Turkey, which is believed to represent the closure of Paleo and NeoTethyan oceanic basins. Regarding the development of the latter oceanic entity, namely Neotethys, the geodynamic evolution of the Intra-Pontide branch, the northernmost one of a number of oceanic basins remains enigmatic. The Intra-Pontide Suture Zone in Northwest Turkey includes several tectonic units most of which are characterized by the occurrence of mafic rocks with distinct geochemical signatures. In this paper, the mafic rocks collected from four of these units (the Domuz Dağ Unit, the Saka Unit, the Daday Unit and the Arkot Dağ Mèlange) have been studied in detail along two selected transects. The Domuz Dağ Unit is characterized by amphibolites, micaschists and marbles, which have been overprinted by low-grade metamorphism.The Saka Unit is in turn represented by an assemblage of slices of amphibolites, marbles and micaschists metamorphosed under upper amphibolite facies metamorphic conditions in the Late Jurassic time. In these units, the amphibolites and their retrograded counterparts display E-MORB-, OIB- BABB- and IAT-type signatures. The Daday Unit is characterized by metasedimentary and metamafic rocks metamorphosed under blueschist to sub-greenschist facies conditions. The metamafic rocks comprise actinolite-bearing schists and Na-amphibole-bearing varieties possibly derived from basaltic and gabbroic protoliths. They have a wide range of chemical compositions, displaying N-MORB-, E-MORB-, OIB- BABB- and IAT-type signatures. The Arkot Dağ Mèlange consists of a Late Santonian assemblage of slide-blocks mainly represented by basaltic lithologies showing affinities ranging from N-MORB- and IAT- to BABB-type magmas. The geochemical signature of the studied mafic rocks indicates that the tectonic units documented along the two studied transects of the Intra-Pontide Suture Zone have been derived from a supra-subduction zone. This hypothesis

  9. Burial and exhumation of high- and ultra high-pressure (U) HP rocks: some lessons on orogenic root-zone dynamics from the Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Andersen, T. B.

    2011-12-01

    The Caledonides of southern Norway have some of the best-exposed examples of (U) HP rocks in the world. A regional southeast to northwest metamorphic gradient in eclogite bearing rocks from ~550-600C; 1.8 GPa, to ~800C; >2.8-3GPa is documented in several studies. In addition there are several examples of diamond and majorite-bearing extreme UHP rocks indicating pressures up to 5.5 to 6 GPa (e.g. Van Roermund, 2009). The Proterozoic protoliths of the Western Gneiss Region (WGR) and trailing ends of Caledonian allochthons were deeply buried during the Scandian continental collision at 430-400 Ma. The initial response of the down-going Fennoscandian crust below the Caledonian floor-thrust was brittle failure and coseismic deformation as recorded by eclogite pseudotachylytes and localized high-strain zones (e.g. Austrheim & Boundy 1994). The co-facial brittle and ductile high-strain zones provide important lessons about the mechanism controlling deformation, particularly intermediate depth earthquakes in collision zones (e.g. Labrousse et al. 2010). Restorations of regional SE-NW cross-sections show that burial- and exhumation of coesite eclogites from 90-100 km can be reconciled with the observable structures. The exhumation can be explained by: 1) >50% pure shear vertical shortening at eclogite to amphibolite facies, 2) large-scale (>100 km) rotational deformation along extensional detachments at amphibolite to greenschist facies, 3) upper crustal normal faulting and 4) an average of 15 km erosion (e.g., Andersen et al. 1991). Preservation of the regional metamorphic gradient strongly suggests that the WGR was buried and exhumed as a mostly coherent unit. Within the coesite UHP-domains some occurrences of diamond, majorite and extreme-UHP opx-eclogites suggest pressure anomalies of up to 6 GPa, perturbing the regional metamorphic gradient by very local doubling of the regional P-max. Radiometric ages from the majorite-diamond UHP, coesite UHP and normal eclogites are

  10. Processes controlling the migration and biodegradation of Non-aqueous phase liquids (NAPLs) within fractured rocks in the vadose zone FY97 annual report

    SciTech Connect

    Geller, J.T.; Holman, Hoi-Ying; Conrad, M.

    1998-02-01

    Subsurface contamination from volatile organic compounds (VOCs) has been found at many Department of Energy (DOE), Department of Defense (DoD) and industrial sites due to the widespread use of organic solvents and hydrocarbon fuels. At ambient pressures and temperatures in the shallow subsurface, these substances are liquids that are immiscible with water; hence they are commonly designated as non-aqueous phase liquids (NAPLs). At some DOE sites, NAPLs are the presumed source of groundwater contamination in fractured rocks, such as basalts (at Hanford and Idaho National Engineering and Environmental Laboratory (INEEL)), shales (Oak Ridge Y-12 Plant), and welded tuffs (Los Alamos National Laboratory (LANL)). The flow, transport and biodegradation processes controlling NAPL behavior in the vadose zone must be understood in order to establish the possible extent of contamination, the risk to groundwater supplies, and appropriate remediation action. This is particularly important in and sites with deep water tables (such as at Hanford, INEEL and LANL). In fractured rock aquifers, NAPL migration is likely to be dominated by the highly permeable pathways provided by rock fractures and joints. Two- and three-phase fluid phases may be present in vadose zone fractures, including NAPL-gas, NAPL-water (in regions of perched water) and NAPL-water-gas.

  11. Fluid-mediated mass transfer from a paleosubduction channel to its mantle wedge: Evidence from jadeitite and related rocks from the Guatemala Suture Zone

    NASA Astrophysics Data System (ADS)

    Harlow, George E.; Flores, Kennet E.; Marschall, Horst R.

    2016-08-01

    Jadeitites in serpentinite mélanges are the product of crystallization from and/or metasomatism by aqueous fluids that transfer components from and within a subduction channel-the slab-mantle interaction volume-into discrete rock units, most commonly found within the serpentinized or serpentinizing portion of the channel or the overlying mantle rocks at high pressure (1 to > 2 GPa). Two serpentinite mélanges on either side of the Motagua fault system (MFS) of the Guatemala Suture Zone contain evidence of this process. Whole rock compositional analyses are reported here from 86 samples including jadeitites and the related rocks: omphacitites, albitites and mica rocks. The predominance of a single phase in most of these rocks is reflected in the major element compositions and aspects of the trace elements, such as REE abundances tracking Ca in clinopyroxene. Relative to N-MORB all samples show relative enrichments in the high field strength elements (HFSE) Hf, Zr, U, Th, and the LILE Ba and Cs, contrasted by depletions in K and in some cases Pb or Sr. Most jadeitites are also depleted in the highly compatible elements Cr, Sc and Ni despite their occurrence in serpentinite mélange; however, some omphacitite samples show the opposite. Trace elements in these jadeitite samples show a strong similarity with GLOSS (globally subducted oceanic sediment) and other terrigenous sediments in terms of their trace-element patterns, but are offset to lower abundances. Jadeitites thus incorporate a strong trace-element signature derived from sediments mixed with that from fluid derived from altered oceanic crust. Enrichment in the HFSE argues for mobility of these elements in aqueous fluids at high P/T conditions in the subduction channel and a remarkable lack of fractionation that might otherwise be expected from dissolution and fluid transport.

  12. Critical zone co-evolution: evidence that weathering and consequent seasonal rock moisture storage leads to a mixed forest canopy of conifer and evergreen broadleaf trees

    NASA Astrophysics Data System (ADS)

    Oshun, J.; Dietrich, W. E.; Dawson, T. E.; Rempe, D. M.; Fung, I. Y.

    2014-12-01

    Despite recent studies demonstrating the importance of rock moisture as a source of water to vegetation, much remains unknown regarding species-specific and seasonal patterns of water uptake in a Mediterranean climate. Here, we use stable isotopes of water (d18O, dD) to define the isotope composition of water throughout the subsurface critical zone of Rivendell, within the Eel River Critical Zone Observatory. We find that a structured heterogeneity of water isotope composition exists in which bulk saprolite is chronically more negative than bulk soil, and tightly held moisture is more negative than the mobile water that recharges the saturated zone and generates runoff. These moisture reservoirs provide a blueprint from which to measure the seasonal uptake patterns of different species collocated on the site. Douglas-firs use unsaturated saprolite and weathered bedrock moisture (i. e. rock moisture) throughout the year. Contrastingly, hardwood species (madrone, live oak, tanoak) modify their source water depending on which moisture is energetically favorable. Hardwoods use freely mobile water in the wet season, and rely on unsaturated zone soil moisture in the dry season. When soil water tension decreases on the drier south-facing slope, hardwood species use saprolite moisture. Although adjacent hardwoods and Douglas-firs partition water based on matric pull on the north side, there is competition for saprolite moisture in late summer on the south side. These results reveal the eco-hydrological importance of moisture derived from weathered bedrock, and show that the hardwoods have a competitive advantage under the drier conditions predicted in many climate models. Finally, the data emphasize that isotope measurements of all subsurface reservoirs and potential water sources are necessary for a complete and accurate characterization of the eco-hydrological processes within the critical zone.

  13. Anthropogenic disturbance as a driver of microspatial and microhabitat segregation of cytotypes of Centaurea stoebe and cytotype interactions in secondary contact zones

    PubMed Central

    Mráz, Patrik; Španiel, Stanislav; Keller, Andreas; Bowmann, Gillianne; Farkas, Alexandre; Šingliarová, Barbora; Rohr, Rudolf P.; Broennimann, Olivier; Müller-Schärer, Heinz

    2012-01-01

    Background and Aims In a mixed-ploidy population, strong frequency-dependent mating will lead to the elimination of the less common cytotype, unless prezygotic barriers enhance assortative mating. However, such barriers favouring cytotype coexistence have only rarely been explored. Here, an assessment is made of the mechanisms involved in formation of mixed-ploidy populations and coexistence of diploid plants and their closely related allotetraploid derivates from the Centaurea stoebe complex (Asteraceae). Methods An investigation was made of microspatial and microhabitat distribution, life-history and fitness traits, flowering phenology, genetic relatedness of cytotypes and intercytotype gene flow (cpDNA and microsatellites) in six mixed-ploidy populations in Central Europe. Key Results Diploids and tetraploids were genetically differentiated, thus corroborating the secondary origin of contact zones. The cytotypes were spatially segregated at all sites studied, with tetraploids colonizing preferentially drier and open microhabitats created by human-induced disturbances. Conversely, they were rare in more natural microsites and microsites with denser vegetation despite their superior persistence ability (polycarpic life cycle). The seed set of tetraploid plants was strongly influenced by their frequency in mixed-ploidy populations. Triploid hybrids originated from bidirectional hybridizations were extremely rare and almost completely sterile, indicating a strong postzygotic barrier between cytotypes. Conclusions The findings suggest that tetraploids are later immigrants into already established diploid populations and that anthropogenic activities creating open niches favouring propagule introductions were the major factor shaping the non-random distribution and habitat segregation of cytotypes at fine spatial scale. Establishment and spread of tetraploids was further facilitated by their superior persistence through the perennial life cycle. The results highlight

  14. Effect of length-scale on localization of shear zones along precursor fractures and layers during deformation of middle to lower crustal rocks

    NASA Astrophysics Data System (ADS)

    Mancktelow, Neil; Pennacchioni, Giorgio; Hawemann, Friedrich; Wex, Sebastian; Camacho, Alfredo

    2016-04-01

    Deformation of high grade rocks at middle to lower crustal levels involves both distributed and more highly localized ductile strain, with localized shear zones developing on elongate near-planar rheological precursors. These planar heterogeneities may be compositional layers (e.g. dykes) or pre-existing or newly developed fractures, with or without pseudotachylyte. Usual rheological models for viscous rock deformation are scale independent. The geometry of developing localized shear zones should therefore be scalable and depend only on the pre-existing geometry and imposed boundary conditions, as shown in numerical and analogue models. However, this is not what is observed in natural examples. Shear zones preferentially or exclusively develop on long fractures and dykes, typically on the scales of many (tens of) metres to (tens of) kilometres, whereas smaller-scale healed fractures, basic enclaves and short layers or inclusions are less prone to reactivation and locally may be largely ignored. Preferential localization of strain on these longer structures means that the intervening rock volumes remain low-strain domains, so that the smaller-scale planar heterogeneities are effectively shielded during progressive deformation. Any localized deformation of these intervening low-strain domains requires the formation of new elongate fractures acting as a necessary precursor for subsequent localization. These field observations suggest that ductile shear zone localization is more effective with increasing length of the approximately planar precursor. Localized shear zones do not develop by propagation away from an initial small heterogeneity. Instead, their length is largely predetermined by the length of the controlling precursor structure and in-plane propagation of the tips appears to be very limited. Preferential shear reactivation of longer precursors introduces a length-scale dependence from the very initiation of localized "viscous" or "ductile" shear zones

  15. Lichen Persistence and Recovery in Response to Varied Volcanic Disturbances

    NASA Astrophysics Data System (ADS)

    Nelson, P.; Wheeler, T. B.

    2015-12-01

    Volcanic eruptions produce many ecological disturbances that structure vegetation. While lichens are sensitive to disturbances, little is known about their responses to volcanic disturbances, except for colonization of lava. We examined lichen community responses through time to different disturbances produced by the May 1, 2008 eruption of Volcan Chaiten in south-central Chile. Pre-eruption vegetation near the volcano was old-growth Valdivian temperate rainforest dominated by closed-canopy Nothofagus sp... In 2012, we installed thirteen 1-acre plots across volcanic disturbance zones on which a time-constrained search was done for all macrolichen species, each of which was assigned an approximate log10 categorical abundance. We also installed a 0.2 m2 quadrat on two representative trees per plot for repeat photography of lichen cover. We remeasured at least one plot per disturbance zone in 2014 and re-photographed tree quadrats in 2013 and 2014. We then analyzed species composition and abundance differences among disturbance zones. In 2012, the blast (pyroclastic density flow), scorch (standing scorched forest at the edge of the blast) and deep tephra (>10 cm) zones had the lowest lichen species richness (5-13 species), followed by reference (unimpacted) and shallow (<10 cm) tephra (17-20 species). Gravel rain (preexisting rock ejected by eruption initiation), gravel rain + pumice and flooded forests (fluvially reworked volcanic material entrained by heavy rains) were species-rich (25-42 species). In 2014, the blast and deep tephra had regained 2-3 times the number of lichen species since 2012 while the light tephra and reference were essentially unchanged. Gravel rain, gravel rain + pumice and flooded forest plots all had about the same number of species in 2014 as 2012. Lichen colonization and growth in tree quadrats varied widely, from very little colonization in the blast to prolific colonization in the gravel rain + pumice zone. Lichen's varied responses to

  16. Petrofabrics of high-pressure rocks exhumed at the slab-mantle interface from the "point of no return" in a subduction zone (Sivrihisar, Turkey)

    NASA Astrophysics Data System (ADS)

    Whitney, Donna L.; Teyssier, Christian; Seaton, Nicholas C. A.; Fornash, Katherine F.

    2014-12-01

    The highest pressure recorded by metamorphic rocks exhumed from oceanic subduction zones is ~2.5 GPa, corresponding to the maximum decoupling depth (MDD) (80 ± 10 km) identified in active subduction zones; beyond the MDD (the "point of no return") exhumation is unlikely. The Sivrihisar massif (Turkey) is a coherent terrane of lawsonite eclogite and blueschist facies rocks in which assemblages and fabrics record P-T-fluid-deformation conditions during exhumation from ~80 to 45 km. Crystallographic fabrics and other features of high-pressure metasedimentary and metabasaltic rocks record transitions during exhumation. In quartzite, microstructures and crystallographic fabrics record deformation in the dislocation creep regime, including dynamic recrystallization during decompression, and a transition from prism slip to activation of rhomb and basal slip that may be related to a decrease in water fugacity during decompression (~2.5 to ~1.5 GPa). Phengite, lawsonite, and omphacite or glaucophane in quartzite and metabasalt remained stable during deformation, and omphacite developed an L-type crystallographic fabric. In marble, aragonite developed columnar textures with strong crystallographic fabrics that persisted during partial to complete dynamic recrystallization that was likely achieved in the stability field of aragonite (P > ~1.2 GPa). Results of kinematic vorticity analysis based on lawsonite shape fabrics are consistent with shear criteria in quartzite and metabasalt and indicate a large component of coaxial deformation in the exhuming channel beneath a simple shear dominated interface. This large coaxial component may have multiplied the exhuming power of the subduction channel and forced deeply subducted rocks to flow back from the point of no return.

  17. Thermal Evolution of Juvenile Subduction Zones ' New Constraints from Lu-Hf Geochronology on HP oceanic rocks (Halilbaǧi, Central Anatolia)

    NASA Astrophysics Data System (ADS)

    Pourteau, Amaury; Scherer, Erik; Schmidt, Alexander; Bast, Rebecca

    2015-04-01

    The thermal structure of subduction zones plays a key role on mechanical and chemical processes taking place along the slab-mantle interface. Until now, changes through time of this thermal structure have been explored mostly by the means of numerical simulations. However, both "warm" (i.e., epidote-bearing), and "cold" (i.e., lawsonite-bearing) HP oceanic rocks have been reported in some fossil subduction complexes exposed at the Earth's surface (e.g., Franciscan Complex, California; Rio San Juan Complex, Hispañola; Halilbağı Unit, Central Anatolia). These a-priori "incompatible" rocks witness different thermal stages of ancient subduction zones and their study might provide complementary constraints to numerical models. To decipher the meaning of these contrasting metamorphic rocks in the Halilbağı Unit, we are carrying out Lu-Hf geochronology on garnet (grt) and lws from a variety of HP oceanic rocks, as well as the metamorphic sole of the overlying ophiolite. We selected five samples that are representative of the variety of metamorphic evolutions (i.e. peak conditions and P-T paths) encountered in this area. Preliminary analyses yielded 110 Ma (grt-hbl isochron) for a sub-ophiolitic grt amphibolite; 92 Ma (grt-omp) for an eclogite with prograde and retrograde ep; 90 Ma (grt-omp) for an eclogitic metabasite with prograde ep and retrograde ep+lws; 87 Ma (grt-gln) for a lws eclogite with prograde ep; and 86 Ma (grt-gln) for a blueschist with prograde and retrograde lws. These ages are mainly two-point isochrons. Further-refined data will be presented at the EGU General Assembly 2015, in Vienna. The consistent younging trend from "warm" to "cold" metamorphic rocks revealed by these first-order results points to metamorphic-sole formation during the initiation of intra-oceanic subduction at ~110 Ma, and subsequent cooling of the slab-mantle interface between 92 and 86 Ma. Therefore, the contrasting metamorphic evolutions encountered in the Halilbağı Unit

  18. Mechanics of slip and fracture along small faults and simple strike-slip fault zones in granitic rock

    NASA Astrophysics Data System (ADS)

    Martel, Stephen J.; Pollard, David D.

    1989-07-01

    We exploit quasi-static fracture mechanics models for slip along pre-existing faults to account for the fracture structure observed along small exhumed faults and small segmented fault zones in the Mount Abbot quadrangle of California and to estimate stress drop and shear fracture energy from geological field measurements. Along small strike-slip faults, cracks that splay from the faults are common only near fault ends. In contrast, many cracks splay from the boundary faults at the edges of a simple fault zone. Except near segment ends, the cracks preferentially splay into a zone. We infer that shear displacement discontinuities (slip patches) along a small fault propagated to near the fault ends and caused fracturing there. Based on elastic stress analyses, we suggest that slip on one boundary fault triggered slip on the adjacent boundary fault, and that the subsequent interaction of the slip patches preferentially led to the generation of fractures that splayed into the zones away from segment ends and out of the zones near segment ends. We estimate the average stress drops for slip events along the fault zones as ˜1 MPa and the shear fracture energy release rate during slip as 5 × 102 - 2 × 104 J/m2. This estimate is similar to those obtained from shear fracture of laboratory samples, but orders of magnitude less than those for large fault zones. These results suggest that the shear fracture energy release rate increases as the structural complexity of fault zones increases.

  19. Origin of the ca. 90 Ma magnesia-rich volcanic rocks in SE Nyima, central Tibet: Products of lithospheric delamination beneath the Lhasa-Qiangtang collision zone

    NASA Astrophysics Data System (ADS)

    Wang, Qing; Zhu, Di-Cheng; Zhao, Zhi-Dan; Liu, Sheng-Ao; Chung, Sun-Lin; Li, Shi-Min; Liu, Dong; Dai, Jin-Gen; Wang, Li-Quan; Mo, Xuan-Xue

    2014-06-01

    Bulk-rock major and trace element, Sr-Nd-Hf isotope, zircon U-Pb age, and zircon Hf isotopic data of the Late Cretaceous Zhuogapu volcanic rocks in the northern Lhasa subterrane provide a new insight into tectonic processes following the collision of the terrane with the Qiangtang zone. SHRIMP zircon U-Pb dating reveals that the Zhuogapu volcanic rocks crystallized at ca. 91 Ma, postdating the development of a regional angular unconformity between the Upper Cretaceous and the underlying strata in the Lhasa-Qiangtang collision zone. Compared to the Andean arc-type andesites and dacites, the Zhuogapu volcanic rocks are characterized by higher MgO of 2.78-5.86 wt.% and Mg# of 54-64 for andesites and MgO of 2.30-2.61 wt.% and Mg# of 55-58 for dacites. Eight andesite samples have whole-rock (87Sr/86Sr)i of 0.7054-0.7065, εNd(t) of - 3.2 to - 1.7, and εHf(t) of + 3.8-+ 6.4, similar to those of the three dacite samples with (87Sr/86Sr)i = 0.7056-0.7060, εNd(t) of - 2.7 to - 2.2, and εHf(t) of + 5.6-+ 7.0. Thirteen analyses from a dacite sample give positive zircon εHf(t) of + 5.6 to + 8.7. These signatures indicate that the Zhuogapu Mg-rich andesites were most likely derived from partial melting of a delaminated mafic lower crust (including the lowermost crust straddling the northern and central Lhasa subterranes) that led to the generation of the Zhuogapu primary melts with adakitic signatures and small negative εNd(t). Such melts subsequently experienced interaction of melt-asthenospheric mantle peridotite followed by the modification of highly fractionated magmas in shallow crustal magma chamber. Hornblende-controlled fractionation results in the change of geochemical composition from Mg-rich andesitic to Mg-rich dacitic magmas. Field observations, together with geochronological and geochemical data, indicate that the Zhuogapu Mg-rich volcanic rocks and coeval magmatism in the northern Lhasa subterrane may be the result of thickened lithospheric delamination

  20. Effects of fluid-rock interactions on faulting within active fault zones - evidence from fault rock samples retrieved from international drilling projects

    NASA Astrophysics Data System (ADS)

    Janssen, C.; Wirth, R.; Kienast, M.; Yabe, Y.; Sulem, J.; Dresen, G. H.

    2015-12-01

    Chemical and mechanical effects of fluids influence the fault mechanical behavior. We analyzed fresh fault rocks from several scientific drilling projects to study the effects of fluids on fault strength. For example, in drill core samples on a rupture plane of an Mw 2.2 earthquake in a deep gold mine in South Africa the main shock occurred on a preexisting plane of weakness that was formed by fluid-rock interaction (magnesiohornblende was intensively altered to chlinochlore). The plane acted as conduit for hydrothermal fluids at some time in the past. The chemical influence of fluids on mineralogical alteration and geomechanical processes in fault core samples from SAFOD (San Andreas Fault Observatory at Depth) is visible in pronounced dissolution-precipitation processes (stylolites, solution seams) as well as in the formation of new phases. Detrital quartz and feldspar grains are partially dissolved and replaced by authigenic illite-smectite (I-S) mixed-layer clay minerals. Transmission Electron Microscopy (TEM) imaging of these grains reveals that the alteration processes and healing were initiated within pores and small intra-grain fissures. Newly formed phyllosilicates growing into open pore spaces likely reduced the fluid permeability. The mechanical influence of fluids is indicated by TEM observations, which document open pores that formed in-situ in the gouge material during or after deformation. Pores were possibly filled with formation water and/or hydrothermal fluids suggesting elevated fluid pressure preventing pore collapse. Fluid-driven healing of fractures in samples from SAFOD and the DGLab Gulf of Corinth project is visible in cementation. Cathodoluminescence microscopy (CL) reveals different generations of calcite veins. Differences in CL-colors suggest repeated infiltration of fluids with different chemical composition from varying sources (formation and meteoric water).

  1. Variscan terrane boundaries in the Odenwald-Spessart basement, Mid-German Crystalline Zone: New evidence from ocean ridge, intraplate and arc-derived metabasaltic rocks

    NASA Astrophysics Data System (ADS)

    Will, T. M.; Lee, S.-H.; Schmädicke, E.; Frimmel, H. E.; Okrusch, M.

    2015-04-01

    The Mid-German Crystalline Zone is part of a large Variscan suture and consists of various basement complexes that are exposed in central Germany. New lithogeochemical and Sr-Nd-Pb isotope data obtained on various amphibolites from the Odenwald-Spessart basement show that their protoliths formed in different tectonic settings and were subsequently incorporated into a subduction zone prior to Variscan continental collision. Metabasic rocks from the northernmost Spessart and the western Odenwald are geochemically almost identical and their protoliths are interpreted to have formed in an extensional, possibly, a back-arc setting. The tholeiitic and calc-alkaline rocks have intermediate TiO2 concentrations and high Th/Nb ratios, typical of volcanic arc-type and/or subduction-fluid modified rocks. The Nd initial ratios are depleted (εNd330 Ma = 5.0-5.8) and Nd model ages range from 660 to 610 Ma, which points at juvenile crustal addition towards the end of the Neoproterozoic. The samples define a linear array in 206Pb/204Pb versus 207Pb/204Pb space. In contrast, the protoliths of the metabasic rocks from the southern and central Spessart formed either in an intraplate oceanic island or a continental arc setting. The alkaline intraplate rocks from the southern Spessart basement are very TiO2-rich and have very low Th/Nb ratios. The rocks have weakly depleted Nd initals (εNd330 Ma = 2.6-3.3) and Nd model ages between 870 and 810 Ma. In contrast, the central Spessart within-plate rocks have considerably lower TiO2 concentrations but higher Th/Nb ratios. In addition, these rocks are isotopically enriched (εNd330 Ma = - 13.1 to - 9.5) and have Palaeoproterozoic Nd model ages. The continental arc rocks from the central and southern Spessart basement have low TiO2 concentrations and variable Th/Nb ratios. Mostly negative Nd initials (εNd330 Ma = - 2.6 to + 0.9) and late Mesoproterozoic Nd model ages indicate that recycling of older crust or mixing of crustal components of

  2. Middle Miocene nepheline-bearing mafic and evolved alkaline igneous rocks at House Mountain, Arizona Transition Zone, north-central Arizona

    SciTech Connect

    Wittke, J.; Holm, R.F.; Ranney, W.D.R. . Dept. of Geology)

    1993-04-01

    The Middle Miocene House Mountain shield volcano is located on the northern margin of the Arizona Transition Zone, about 7 km SW of Sedona, AZ. Deep erosion has exposed internal structural and stratigraphic relationships of the volcano. Mapping documents two igneous suites: (1) alkali basalt to trachyte and alkali-feldspar syenite, and (2) olivine melanephelinite, nepheline monzodiorite, nepheline monzosyenite and nepheline syenite. The rocks of the first suite occur as dikes and flows, which, with a thick pyroclastic section, are the principal units of the volcano. The melanephelinite is nonvesicular and intruded as a large irregular dike and several smaller dikes. The nepheline-bearing syenitic rocks, which are phaneritic with nepheline and clinopyroxene crystals up to 1 cm in diameter, occur as pods and sheets within the melanephelinite. Also within the melanephelinite are wispy leucocratic segregations, syenitic fracture-fillings, and ocelli. The largest phaneritic sheet is [approx]18 m thick; it displays crude subhorizontal compositional banding and vuggy surfaces. The latter indicate that the magmas were fluid-rich. Compositions intermediate between the melanephelinite and syenitic rocks have not been found. Although the syenitic rocks are coarse-grained, mapping indicates the they are near the summit of the volcano and were probably emplaced at a depth of less than 1 km, possibly of only a few hundred meters. The field relationships of the phaneritic rocks can be explained by ascent and coalescence of immiscible syenitic liquids within the melanephelinite dike. Calculated density contrasts between melanephelinite and syenitic liquids exceed 0.2 g/cm[sup 3].

  3. Key role of Upper Mantle rocks in Alpine type orogens: some speculations derived from extensional settings for subduction zone processes and mountain roots

    NASA Astrophysics Data System (ADS)

    Müntener, Othmar

    2016-04-01

    Orogenic architecture and mountain roots are intrinsically related. Understanding mountain roots largely depends on geophysical methods and exhumed high pressure and high temperature rocks that might record snapshots of the temporal evolution at elevated pressure, temperatures and/or fluid pulses. If such high pressure rocks represent ophiolitic material they are commonly interpreted as exhumed remnants of some sort of 'mid-ocean ridge' processes. Mantle peridotites and their serpentinized counterparts thus play a key role in understanding orogenic architecture as they are often considered to track suture zones or ancient plate boundaries. The recognition that some mantle peridotites and their serpentinized counterparts are derived from ocean-continent transition zones (OCT's) or non-steady state (ultra-)slow plate separation systems question a series of 'common beliefs' that have been applied to understand Alpine-type collisional orogens in the framework of the ophiolite concept. Among these are: (i) the commonly held assumption of a simple genetic link between mantle melting and mafic (MORB-type) magmatism, (ii) the commonly held assumption that mélange zones represent deep subduction zone processes at the plate interface, (iii) that pre-collisional continental crust and oceanic crust can easily be reconstructed to their original thickness and used for reconstructions of the size of small subducted oceanic basins as geophysical data from rifted margins increasingly indicate that continental crust is thinned to much less than the average 30-35 kilometers over a large area that might be called the 'zone of hyperextension', and (iv) the lack of a continuous sheet of mafic oceanic crust and the extremely short time interval of formation results in a lack of 'eclogitization potential' during convergence and hence a lack of potential for subsequent slab pull and, perhaps, a lack of potential for 'slab-breakoff'. Here we provide a synopsis of mantle rocks from the

  4. UNDERSTANDING HARD ROCK HYDROGEOLOGY THROUGH AN EXPERIMENTAL HYDROGEOLOGICAL PARK IN SOUTH INDIA: Site development and investigations on the major role of the fractured zone in crystalline aquifers

    NASA Astrophysics Data System (ADS)

    Ahmed, S.; Guiheneuf, N.; Boisson, A.; Marechal, J.; Chandra, S.; Dewandel, B.; Perrin, J.

    2012-12-01

    In water stressed south India most of the groundwater used for irrigation is pumped from crystalline rocks aquifers. In those structures groundwater flow dominantly occur in a shallow higher-permeability zone that overlies a deeper lower-permeability zone hosting little flow. The fractured zone of the weathering profile plays an important role for groundwater. In order to understand clearly this impact on water availability and quality changes the Experimental Hydrogeological Park at Choutuppal, Andhra Pradesh, India is developed in the framework of the SORE H+ network. Several hydraulic tests (injection, flowmeter profiles, single-packer tests…) and geophysical measurements (ERT, Borehole logging…) are carried out on the site in order to characterize the depth-dependence of hydrodynamic parameters in the Indian Archean granite. Specific investigation on a borewell through packer tests demonstrate that the most conductive part of the aquifer corresponds to the upper part of the fractured layer, located just below the saprolite bottom, between 15 meters and 20 meters depth. There is no highly conductive fracture beyond 20 meters depth and no indication for any conductive fracture beyond 25 meters depth. Packer tests show that the upper part of the fractured layer (15-20 m depth) is characterized by a good vertical connectivity. On the contrary, the tests carried out below 20 m depth show no vertical connectivity at all. The geometry of the fracture network and associated hydrodynamic parameters are in agreement with the conceptual model of hard-rock aquifers that derive its properties from weathering processes. The general existence of such a highly conductive structure at the top of the fractured zone has a great impact on water prospection and exploitation in such crystalline aquifers.

  5. Exploitation of high-yields in hard-rock aquifers: downscaling methodology combining GIS and multicriteria analysis to delineate field prospecting zones.

    PubMed

    Lachassagne, P; Wyns, R; Bérard, P; Bruel, T; Chéry, L; Coutand, T; Desprats, J F; Le Strat, P

    2001-01-01

    Based on research work in the Truyère River catchment of the Massif Central (Lozère Department, France), a methodology has been developed for delineating favorable prospecting zones of a few square kilometers within basement areas of several hundred, if not thousand, square kilometers for the purpose of sitting high-yield water wells. The methodology adopts a functional approach to hard-rock aquifers using a conceptual model of the aquifer structure and of the functioning of the main aquifer compartments: the alterites (weathered and decayed rock), the underlying weathered-fissured zone, and the fractured bedrock. It involves an economically feasible method of mapping the thickness and spatial distribution of the alterites and the weathered-fissured zone, on which the long-term exploitation of the water resource chiefly depends. This method is used for the first time in hydrogeology. The potential ground water resources were mapped by GIS multicriteria analysis using parameters characterizing the structure and functioning of the aquifer, i.e., lithology and hydrogeological properties of the substratum, nature and thickness of the alterites and weathered-fissured zone, depth of the water table, slope, fracture networks and present-day tectonic stresses, and forecasted ground water quality. The methodology involves a coherent process of downscaling that, through applying methods that are increasingly precise but also increasingly costly, enables the selection of sites with diminishing surface areas as the work advances. The resulting documents are used for ground water exploration, although they can also be applied to the broader domain of land-use management. PMID:11447857

  6. Subsurface Rock Damage Structure of the Mw7.1 Darfield and Mw6.3 Christchurch Earthquake Sequence Viewed with Fault-Zone Trapped Waves

    NASA Astrophysics Data System (ADS)

    Li, Y.; De Pascale, G. P.; Quigley, M. C.; Gravley, D.

    2012-12-01

    In order to document the subsurface structure of the damage zones caused by multiple slips in the 2010 Mw7.1 Darfield - 2011 Mw6.3 Christchurch earthquake sequence in NZ's South Island, we deployed two short linear seismic arrays in the Canterbury region to record aftershocks in middle 2011. Array 1 was deployed across the central Greendale fault (GF) where right-lateral slip of ~4.5 m was measured across the surface rupture of the 2010 Darfield mainshock. Array 2 was located at the surface projection of an aftershock zone along the blind Port Hills fault (PHF) which ruptured in the 2011 Christchurch earthquake. We have examined the data for 853 aftershocks and identified prominent fault-zone trapped waves (FZTWs) with large amplitude and long wavetrains following S-arrivals at stations of Array 1 within the ~200-m-wide rupture zone for aftershocks occurring along the GF and the PHF. The post-S durations of these FZTWs increase as event depth and epicentral distance increase, showing an effective low-velocity waveguide formed by severely damaged rocks extending along the GF and PHF at seismogenic depth, but with variations in its geometry and velocity reduction along multiple rupture segments. The FZTWs suggest that the Darfield rupture zone extends eastward as bifurcating blind fault segments an additional ~5-8 km beyond the mapped ~30-km extent of the GF surface rupture, consistent with aftershock distributions and geodetic models. On the other hand, the main rupture of the Mw6.3 Christchurch earthquake is ~15-km in length on the blind PHF dipping to SSE, but it likely extends westward along the aftershock lineament approaching the east blind extension of the GF/Darfield rupture. These two main rupture segments might connect through a weak portion of the low-velocity waveguide formed by rocks along blind faults that experienced milder damage beneath the dilatational fault step-over where accumulated seismic energy release was lower than adjacent rupture zones in

  7. Meteoric water-rock interaction and clay-gouge formation during higher temperature brittle faulting on the Silltal-Brenner Fault Zone, Eastern Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Mancktelow, Neil; Zwingmann, Horst; Campani, Marion; Fügenschuh, Bernhard; Mulch, Andreas

    2015-04-01

    The Silltal Fault is the northern brittle continuation of the Brenner Fault Zone, with a normal, down-to-west sense of movement. It is marked by a narrow zone of cataclasis and, in three sampled locations, clay-rich fault gouges. The clay mineral composition of these gouges is dominated by higher temperature 2M1 polytype illite/muscovite, with no 1M/1Md illite or mixed layer illite/smectite detected. Smectite is limited to the northern samples from the Stephansbrücke location, whereas chlorite is present in all samples. New growth of 2M1 polytype illite in the finest size fractions indicates temperatures > 200-250° C and therefore fault gouge development at depths and temperatures close to the ductile-brittle transition in quartz rich rocks (~280-300° C). Hydrogen stable isotope (δD) analyses show that gouge formation was associated with the influx of meteoric water, which was strongly focused within the fault zone itself, without significant interchange with the adjacent footwall and hanging wall rocks. K-Ar ages from the different sample grain size fractions (< 0.1 to 6-10 μm and 'whole rock gouge') show a wide spread, from ca. 115 to 12 Ma, with ages consistently decreasing with grain size. Although the ranges overlap, ages from the northern Stephansbrücke samples are generally older (115-36 Ma) than those from the south near Matrei (55-12 Ma), possibly reflecting increasing regional metamorphic temperatures to the south. The well-defined linear relationship between apparent age and hydrogen stable isotope (δD) values establishes a direct correlation between rejuvenation of the K-Ar system and increased interaction with meteoric water. The dependence of both apparent age and δD on grain size also indicates that radiogenic and stable isotope exchange was controlled by grain size, reflecting new 2M1 illite growth, mechanical grinding of protolith muscovite during cataclastic faulting, or both. The results demonstrate the advantages of combining radiogenic

  8. Phengite-hosted LILE enrichment in eclogite and related rocks: Implications for fluid-mediated mass transfer in subduction zones and arc magma genesis

    USGS Publications Warehouse

    Sorensen, Sorena S.; Grossman, J.N.; Perfit, M.R.

    1997-01-01

    Geochemical differences between island arc basalts (LAB) and ocean-floor basalts (mid-ocean ridge basalts; MORB) suggest that the large-ion lithophile elements (LILE) K, Ba, Rb and Cs are probably mobilized in subduction zone fluids and melts. This study documents LILE enrichment of eclogite, amphibolite, and epidote ?? garnet blueschist tectonic blocks and related rocks from melanges of two subduction complexes. The samples are from six localities of the Franciscan Complex, California, and related terranes of Oregon and Baja California, and from the Samana Metamorphic Complex, Samana Peninsula, Dominican Republic. Most Franciscan blocks are MORB-like in their contents of rare earth elements (REE) and high field strength elements (HFSE); in contrast, most Samana blocks show an LAB signature of these elements. The whole-rock K2O contents of both groups range from 1 to 3 wt %; K, Ba, Rb, and Cs are all strongly intercorrelated. Many blocks display K/Ba similar to melasomatized transition zones and rinds at their outer margins. Some transition zones and rinds are enriched in LILE compared with host blocks; others are relatively depleted in these elements. Some LILE-rich blocks contain 'early' coarse-grained muscovite that is aligned in the foliation defined by coarse-grained omphacite or amphibole grains. Others display 'late' muscovite in veins and as a partial replacement of garnet; many contain both textural types. The muscovite is phengite that contains ???3??25-3??55 Si per 11 oxygens, and ???0??25-0??50 Mgper 11 oxygens. Lower-Si phengite has a significant paragonite component: Na per 11 oxygens ranges to ???0??12. Ba contents of phengite range to over 1 wt % (0??027 per 11 oxygens). Ba in phengite does not covary strongly with either Na or K. Ba contents of phengite increase from some blocks to their transition zones or rinds, or from blocks to their veins. Averaged KlBa ratios for phengite and host samples define an array which describes other subsamples of

  9. Geochronological and geochemical constraints on the petrogenesis of late Cretaceous volcanic rock series from the eastern Sakarya zone, NE Anatolia-Turkey

    NASA Astrophysics Data System (ADS)

    Aydin, Faruk; Oǧuz, Simge; Şen, Cüneyt; Uysal, İbrahim; Başer, Rasim

    2016-04-01

    New SHRIMP zircon U-Pb ages and whole-rock geochemical data as well as Sr-Nd-Pb and δ18O isotopes of late Cretaceous volcanic rock series from the Giresun and Artvin areas (NE Anatolia, Turkey) in the northern part of the eastern Sakarya zone (ESZ) provide important evidence for northward subduction of the Neo-Tethyan oceanic lithosphere along the southern border of the ESZ. In particular, tectonic setting and petrogenesis of these subduction-related volcanites play a critical role in determining the nature of the lower continental crust and mantle dynamics during late Mesozoic orogenic processes in this region. The late Cretaceous time in the ESZ is represented by intensive volcanic activities that occurred in two different periods, which generally consist of alternation of mafic-intermediate (basaltic to andesitic) and felsic rock series (dacitic to rhyolitic) within each period. Although there is no geochronological data for the lower mafic-intermediate rock series of the first volcanic period, U-Pb zircon dating from the first cycle of felsic rocks yielded ages ranging from 88.6±1.8 to 85.0±1.3 Ma (i.e. Coniacian-Early Santonian). The first volcanic period in the region is generally overlain by reddish biomicrite-rich sedimentary rocks of Santonian-Early Campanian. U-Pb zircon dating for the second cycle of mafic-intermediate and felsic rocks yielded ages varying from 84.9±1.7 to 80.8±1.5Ma (i.e. Early to Middle Campanian). The studied volcanic rocks have mostly transitional geochemical character changing from tholeiitic to calc-alkaline with typical arc signatures. N-MORB-normalised multi-element and chondrite-normalised rare earth element (REE) patterns show that all rocks are enriched in LILEs (e.g. Rb, Ba, Th) and LREEs (e.g. La, Ce) but depleted in Nb and Ti. In particular, the felsic samples are characterised by distinct negative Eu anomalies. The samples are characterized by a wide range of Sr-Nd-Pb isotopic compositions (initial ɛNd values from -7

  10. Diagenesis of the Oligocene-Miocene rocks of the Upper Floridan and Intermediate aquifer systems by meteoric and mixing-zone waters in southwest Florida

    SciTech Connect

    Weedman, S.D. ); McCartan, L. )

    1993-03-01

    Optical and SEM of samples from 6 cores of Oligocene and Miocene rocks that compose portions of the Florida and Intermediate aquifers and the intervening semiconfining unit documents meteoric and mixing-zone (seawater and fresh carbonate ground water) diagenesis inferred to have occurred over several cycles of sea level change. Dolomite, limestone, sandstone, and claystone of the Suwannee Formation and the Arcadia Formation (Hawthorn Group) were examined. Core samples from time-equivalent strata in two E--W transects in Manatee, Hardee, Highlands, Sarasota, and DeSoto Counties are estimated to be 16--33 Ma on the basis of [sup 87]Sr/[sup 86]Sr ratios from unaltered mollusk shells and by molluscan biostratigraphy. Lithostratigraphic correlations are based on examination of 19 cores, 62 thin sections, 60 geophysical logs, and mineralogy determined by X-ray diffraction. Diagenetic indicators that the authors tracked petrographically include shell micritization, shell dissolution, equant and (or) fibrous CaCO[sub 3] cement, neomorphism, dolomite, etched phosphate grains, echinoderm fragment syntaxial overgrowths, and amorphous silica pore lining. Infiltration of meteoric water caused dissolution of carbonate minerals, especially aragonite, and precipitation of equant calcite crystals in voids of dissolved fossils and in pore spaces between grains. The silica was precipitated as pore linings in zones having soil textures. Observed replacement of calcite by limpid dolomite is consistent with modeling predictions of mixing-zone diagenesis. Etched crystals of limpid dolomite may indicate freshwater dissolution of a mixing-zone precipitate. Mapping of regional unconformities revealed pronounced thickening and thinning of some units. Evidence of meteoric water diagenesis is observed in the upper 600 ft of the transects examined. Evidence of mixing-zone diagenesis is observed at varying depths, but appears to increase in abundance and thickness toward the west.

  11. The effects of rock type and landscape position on solution chemistry of soils in the Biosphere 2 Desert Site of the Santa Catalina Mountains Critical Zone Observatory

    NASA Astrophysics Data System (ADS)

    Penprase, S. B.; Abramson, N.; LaSharr, K.; Chorover, J.

    2014-12-01

    The interaction of near surface soil water with surrounding rock and soil matter plays a crucial role in determining the chemical composition of biogeological systems. This interaction drives subsurface processes such as erosion, mineralization, and depletion. However, how and why soil pore water chemistry fluctuates based on localized conditions such as rock type and landscape position is not fully understood. This study examines the role these two factors play in altering soil water chemistry by analyzing samples collected from schist and granite field sites within the Biosphere 2 Desert Site of the Santa Catalina Mountains Critical Zone Observatory. We hypothesized that soil water from the schist site would have higher solute concentrations than the granite site because schist is a more weatherable rock and, thus, is more susceptible to chemical erosion. We also hypothesized that soil water from convergent positions would have higher solute concentrations than those from divergent positions due to a longer upgradient flow path. Each field site was situated within a Zero Order Basin (ZOB) with seven Zero Tension Lysimeters (ZTL). At the schist site, there were 3 convergent (SC 1-3) and 4 divergent (SD 1-4) ZTL positions. For the granite site, there were 4 convergent (GC 1-2, 4-5) and 3 divergent (GD 1-3) ZTLs. Samples were collected following rainstorms from July 2011-July 2013. Each solution sample was analyzed for major and trace cations, anions, pH, EC, and organic and inorganic carbon. Comparisons between SC and GC and all schist and all granite are consistent with the hypotheses for multiple elements. Results also indicate higher solute levels for SC relative to SD. Thus, our analyses suggest that rock type and landscape position influence the chemical composition of soil water at these two sites.

  12. New Magnetostratigraphic Results From Sedimentary Rocks of IODP's Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) Expedition 322

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Oda, H.; Wu, H.; Yamamoto, Y.; Underwood, M.; Saito, S.; Kubo, Y.; Iodp Expedition 322 Shipboard Scientific Party

    2010-12-01

    We report new magnetostratigraphic and rock magnetic results from our post-expedition studies on the Nankai sedimentary rocks recovered by Integrated Ocean Drilling Program (IODP) Expedition 322. Shore-based studies confirm that stable characteristic remanent magnetization (ChRM) components are observed throughout the majority of the recovered cores of the two subduction input sites (Sites C0011and C0012), following removal of a low stability drilling-induced remanence. Inclination values of ChRM are moderate downward or upward, consistent with the expected inclination for the site. Rock magnetic study demonstrates that the ChRM components of both polarities are mostly carried by fine grains of magnetite. Positive results from mean-inclination reversal test indicate that the ChRM is a record of the paleomagnetic field close to the time of formation of these sediments, and most of the observed magnetostratigraphy from the characteristic directions is in excellent agreement with that to be expected from the stratigraphic position of the sequence deduced from the biostratigraphic data. The new magnetic results support the shipboard discovery that an abrupt decrease in the rate of sedimentation occurs at about 11 Ma, suggesting that some fundamental paleoenvironmental change in the Shikoku Basin and/or the significant tectonic event may have occurred in Late Miocene.

  13. Reaction zone between pre-UHP titanite and host rock: insights into fluid-rock interaction and deformation mechanisms during exhumation of deeply subducted continental crust (Dabie Shan UHP unit, China)

    NASA Astrophysics Data System (ADS)

    Wawrzenitz, N.; Romer, R. L.; Grasemann, B.; Morales, L. F. G.

    2012-04-01

    Exhumed crustal UHP rocks may occur as relict blocks in strongly metasomatized matrix rocks. Due to variations in competence between the mm to km sized blocks and their ductile matrix, the largely undeformed blocks may preserve the pre-subduction and the prograde history, whereas the matrix rocks have been ductilely deformed to high magnitudes and record successive stages of deformation. The reaction zones between blocks and matrix, however, provide insights into the fluid-rock interaction, deformation and the deformation mechanisms active during the exhumation of deeply subducted continental crust in the subduction channel. We investigate a titanite megacryst (3 cm in diameter) in a calc-silicate marble from the UHP unit in the Dabie Shan, China. The core of the titanite megacryst grew prograde during subduction. Its U-Pb system remained closed and yields a maximum age for UHP metamorphism. Sr and Nd isotope compositions in the core demonstrate that the titanite megacryst precipitated from a homogeneous fluid source. During metamorphism in the subduction zone, infiltration of external fluids resulted first in Sr-loss from the marbles and then introduction of Sr with unusually low 87Sr/86S values (Romer et al., 2003), leading to the contrasting 87Sr/86Sr values in the titanite megacryst and the hosting UHP marbles (Wawrzenitz et al., 2006). Related to deformation in the calc-silicate marble matrix, the rim of the titanite megacryst has been replaced during the following dissolution-precipitation reactions: (i) Pseudomorphic replacement of the old titanite megacryst by coupled dissolution-reprecipitation. Fluid migrated into the old grain producing a sharp boundary of the replacement front. (ii) New small titanite grains grew with their long axes parallel to the foliation of the marble matrix, reflecting the activation of dissolution precipitation creep. In the matrix, the foliation is defined by the orientation of the basal planes of phengitic white mica. The new

  14. Ductile shear zones can induce hydraulically over-pressured fractures in deep hot-dry rock reservoirs: a new target for geothermal exploration?

    NASA Astrophysics Data System (ADS)

    Schrank, C. E.; Karrech, A.; Regenauer-Lieb, K.

    2014-12-01

    It is notoriously difficult to create and maintain permeability in deep hot-dry rock (HDR) geothermal reservoirs with engineering strategies. However, we predict that long-lived, slowly deforming HDR reservoirs likely contain hydraulically conductive, over-pressured fracture systems, provided that (a) the underlying lower crust and/or mantle are not entirely depleted of fluids and (b) the fracture system has not been drained into highly permeable overlying rocks. Such fracture systems could be targeted for the extraction of geothermal energy. Our prediction hinges on the notion that polycrystalline creep through matter transfer by a liquid phase (dissolution-precipitation creep) is a widespread mechanism for extracting fluids from the lower crust and mantle. Such processes - where creep cavities form during the slow, high-temperature deformation of crystalline solids, e.g., ceramics, metals, and rocks - entail the formation of (intergranular) fluid-assisted creep fractures. They constitute micron-scale voids formed along grain boundaries due to incompatibilities arising from diffusion or dislocation creep. Field and laboratory evidence suggest that the process leading to creep fractures may generate a dynamic permeability in the ductile crust, thus extracting fluids from this domain. We employed an elasto-visco-plastic material model that simulates creep fractures with continuum damage mechanics to model the slow contraction of high-heat-producing granites overlain by sedimentary rocks in 2D. The models suggest that deformation always leads to the initiation of a horizontal creep-damage front in the lower crust. This front propagates upwards towards the brittle-ductile transition (BDT) during protracted deformation where it collapses into highly damaged brittle-ductile shear zones. If the BDT is sufficiently shallow or finite strain sufficiently large, these shear zones trigger brittle faults emerging from their tips, which connect to the sub-horizontal damage

  15. Velocity Structure of the Alpine Fault Zone, New Zealand: Laboratory and Log-Based Fault Rock Acoustic Properties at Elevated Pressures

    NASA Astrophysics Data System (ADS)

    Jeppson, T.; Graham, J. L., II; Tobin, H. J.; Paris Cavailhes, J.; Celerier, B. P.; Doan, M. L.; Nitsch, O.; Massiot, C.

    2015-12-01

    The elastic properties of fault zone rocks at seismogenic depth play a key role in rupture nucleation, propagation, and damage associated with fault slip. In order to understand the seismic hazard posed by a fault we need to both measure these properties and understand how they govern that particular fault's behavior. The Alpine Fault is the principal component of the active transpressional plate boundary through the South Island of New Zealand. Rapid exhumation along the fault provides an opportunity to study near-surface rocks that have experienced similar histories to those currently deforming at mid-crustal depths. In this study, we examine the acoustic properties of the Alpine Fault in Deep Fault Drilling Project (DFDP)-1 drill core samples and borehole logs from the shallow fault zone, DFDP-2 borehole logs from the hanging wall, and outcrop samples from a number of field localities along the central Alpine Fault. P- and S-wave velocities were measured at ultrasonic frequencies on saturated 2.5 cm-diameter core plugs taken from DFDP-1 core and outcrops. Sampling focused on mylonites, cataclasites, and fault gouge from both the hanging and foot walls of the fault in order to provide a 1-D seismic velocity transect across the entire fault zone. Velocities were measured over a range of effective pressures between 1 and 68 MPa to determine the variation in acoustic properties with depth and pore pressure. When possible, samples were cut in three orthogonal directions and S-waves were measured in two polarization directions on all samples to constrain velocity anisotropy. XRD and petrographic characterization were used to examine how fault-related alteration and deformation change the composition and texture of the rock, and to elucidate how these changes affect the measured velocities. The ultrasonic velocities were compared to sonic logs from DFDP to examine the potential effects of frequency dispersion, brittle deformation, and temperature on the measured

  16. Behavior of major and trace elements upon weathering of peridotites in New Caledonia : A possible site on ultramafic rocks for the Critical Zone Exploration Network (CZEN) ?

    NASA Astrophysics Data System (ADS)

    Juillot, Farid; Fandeur, D.; Fritsch, E.; Morin, G.; Ambrosi, J. P.; Olivi, L.; Cognigni, A.; Hazemann, J. L.; Proux, O.; Webb, S.; Brown, G. E., Jr.

    2010-05-01

    ). However, these high concentration of potentially toxic elements can represent a serious hazard for the environmental quality of the Caledonian ecosystem which is a '' biodiversity hotspot' (Myers, 2000), which emphasize the strong need for characterizing the natural cycling of these elements upon weathering of ultramafic rocks. To reach this goal, we have studied the mineralogical distribution, crystal-chemistry and mass balance modelling of major (Si, Mg, Al, Fe, Mn) and trace elements (Ni, Cr and Co) in the freely-drained weathering profile developed in the serpentinized harzburgites of Mt Koniambo (West Coast of New Caledonia). Results show that both hydrothermal and meteoric processes contributed to the vertical differentiation of this freely drained weathering profiles in serpentinized ultramafic rocks. Finally, they also emphasize the importance of both redox reactions and interactions with Mn- and Fe-oxyhydroxydes (Fandeur et al., 2009a; 2009b) to explain the opposite behavior observed between very mobile Ni and almost immobile Cr (Fandeur et al., 2010). These results bring new insights on the geochemical behavior of trace elements upon weathering of ultramafic rocks under tropical conditions leading to the formation of supergene ore deposits. They also emphasize the interest of such a weathering site on ultramafic rocks under tropical climate to complemente the reference sites of the Critical Zone Exploration Network (CZEN). References Cluzel D., Aitchinson J.C. and Picard C. (2001) Tectonic accretion and underplating of mafic terranes in the Late Eocene intraoceanic fore-arc of New-Caledonia (Southwest Pacific): geodynamic implications. Tectonophysics, 340, 23-59. Coleman, R.G. (1977) Ophiolites: Ancient oceanic lithosphere?: Berlin, Germany, Springer-Verlag, 229p. Fandeur D., Juillot F., Morin G., Olivi L., Cognigni A., Fialin M., Coufignal F., Ambrosi J.P., Guyot F. and Fritsch E. (2009a). Synchrotron-based speciation of chromium in an Oxisol from New

  17. Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite

    USGS Publications Warehouse

    Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.

    2006-01-01

    High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

  18. Non-disturbing characterization of natural organic matter (NOM) contained in clay rock pore water by mass spectrometry using electrospray and atmospheric pressure chemical ionization modes.

    PubMed

    Huclier-Markai, Sandrine; Landesman, Catherine; Rogniaux, Hélène; Monteau, Fabrice; Vinsot, Agnes; Grambow, Bernd

    2010-01-01

    We have investigated the composition of the mobile natural organic matter (NOM) present in Callovo-Oxfodian pore water using electrospray ionization mass spectrometry (ESI-MS), atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and emission-excitation matrix (EEM) spectroscopy. The generation of knowledge of the composition, structure and size of mobile NOM is necessary if one wants to understand the interactions of these compounds with heavy metals/radionuclides, in the context of environmental studies, and particularly how the mobility of these trace elements is affected by mobile NOM. The proposed methodology is very sensitive in unambiguously identifying the in situ composition of dissolved NOM in water even at very low NOM concentration, due to innovative non-disturbing water sampling and ionization (ESI/APCI-MS) techniques. It was possible to analyze a quite exhaustive inventory of the small organic compounds of clay pore water without proceeding to any chemical treatment at naturally occurring concentration levels. The structural features observed were mainly acidic compounds and fatty acids as well as aldehydes and amino acids. PMID:20013952

  19. Oxygen isotope zoning in garnets from Franciscan eclogite blocks: evidence for rock-buffered fluid interaction in the mantle wedge

    NASA Astrophysics Data System (ADS)

    Errico, J. C.; Barnes, J.; Strickland, A.; Valley, J. W.

    2012-12-01

    The oxygen isotope composition of Franciscan Complex eclogite garnets and actinolite rind encasing the high-grade blocks have been analyzed to place constraints on the fluid history of these blocks. In situ SIMS oxygen isotope analysis of single garnet crystals from three eclogite blocks (Ring Mountain, Jenner Beach, Mt. Hamilton) shows an abrupt decrease in the δ18O value by ~1-3‰ from core to rim at ~120 ± 50 μm from the rim at all locations. The δ18O values of two Ring Mountain eclogite garnets decrease from 6.0 ± 0.3‰ to 3.8 ± 0.6‰ from core to rim. Four Mt. Hamilton eclogite garnets decrease from 8.6 ± 0.5‰ to 5.9 ± 0.6‰ from core to rim and two decrease from 7.1 ± 0.2‰ in the core to 5.7 ± 0.5‰ at the rim. Two Jenner Beach eclogite garnets decrease from ~11.0 to ~10‰, whereas two others show little to no variation at 9.9 ± 0.3‰ and 11.4 ± 0.2‰. δ18O values of eclogite garnet cores likely inherit the original oxygen isotope composition of the altered MORB protolith, whereas the abrupt and >1‰ change in the δ18O values of the garnet rims suggest interaction with a lower δ18O value fluid during the final stages of growth. Equilibrium calculations indicate that the temperature change associated with Franciscan eclogite metamorphism (400-600°C) is not likely to account for >~1‰ change in the δ18O value of the growing garnet. Previous work suggests sediments as a potential source of metasomatic fluid during blueschist facies metamorphism (300-350°C); however, these temperatures are too low for garnet growth and sedimentary derived fluids would have high δ18O values. Instead, mantle wedge peridotite is a significant source of lower δ18O material. We suggest that the oxygen composition of infiltrating slab derived fluids is buffered by surrounding ultramafic rock since the volume of ultramafic rock is much greater than that of the fluids. The oxygen isotope composition is recorded in the garnet during final stages of

  20. H2O-fluid-saturated melting of subducted continental crust facilitates exhumation of ultrahigh-pressure rocks in continental subduction zones

    NASA Astrophysics Data System (ADS)

    Labrousse, L.; Duretz, T.; Gerya, T.

    2015-10-01

    We present two-dimensional numerical models of plate subduction and collision inspired by the Scandinavian Caledonian orogeny to investigate the possible impact of continental crust partial melting on the exhumation of ultra-high pressure metamorphic rocks. Three possible reactions were tested: low temperature solidus representing H2O-fluid-saturated partial melting, and two end-member reaction curves for dehydration melting. Thermo-mechanical effects of partial melting were implemented as (1) a viscosity decrease as a determined rheologically critical melt percentage was reached (here 0.1), (2) a change in effective heat capacity and adiabatic heating/cooling accounting for a latent heat term in the heat equation. Among the 3 tested reactions, only H2O-fluid-saturated partial melting drastically modifies the collision dynamics from the non-melting reference model holding all other parameters constant. A substantially low general viscosity truncation (here 1017 Pa s) is needed to properly resolve the effect of partial melting on deep collision processes. Low temperature melting indeed induces the development of a low viscosity buoyant plume prior to slab detachment, where migmatites exhume from UHP conditions at rates and with pressure-temperature paths similar to the natural values acknowledged for the Norwegian Caledonides. High temperature melting has no drastic influence on early collision dynamics. While positive buoyancy remains the first order driver for the exhumation of buried continental rocks, exhumation initiates in these cases with eduction subsequent to slab detachment. Melting and formation of a migmatite plume can later occur along decompression path while continental crust undergoes thermal reequilibration at temperatures above 900 °C. Some of the partially molten material can also relaminate in the overriding plate rather than exhume within the collision zone. Even if minor in terms of amount of magma produced, H2O-fluid-saturated partial melting

  1. Diffusional modification of prograde chemical zoning in garnet and its bearing on the estimates of prograde metamorphic conditions in medium to high grade rocks

    NASA Astrophysics Data System (ADS)

    Konopásek, Jiří; Caddick, Mark J.

    2016-04-01

    Preserved prograde chemical zoning in metamorphic garnet is often used for quantification of pressure and temperature conditions during its growth. However, from the time that zoning is established during growth, intra-crystalline diffusion continually acts to modify it. This operates at various rates throughout the entire metamorphic cycle and causes progressive deviation of garnet compositional profiles from those established during growth, potentially leading to large errors if these compositions are used to estimate pressure-temperature (P-T) conditions. To illustrate, we quantify the extent of compositional changes due to intra-crystalline diffusion occurring during 20 Ma of burial along 16-19°C/km geotherms followed by 1, 15 and 30 Ma of exhumation, for a pelitic sample. Typically, garnet growth in our modelling starts at c. 420°C and 5.5-7 kbar and is terminated at Tmax (600-750°C at c. 10-10.5 kbar). Calculations involve development of growth zoning (inferred from equilibrium thermodynamic modelling) and its simultaneous modification due to intra-crystalline multi-component diffusion along these prescribed paths. This allows us to quantify the extent to which zoning modification depends on crystal growth rate and size, maximum temperature achieved, and garnet composition. The use of diffusionally modified garnet compositions for thermobarometry leads to shortening of the inferred prograde pressure-temperature paths (relative to the actual path experienced) and can introduce significant errors in estimates of P-T conditions at different stages of a rock's evolution. In our model example, the conditions of earliest garnet growth would be overestimated by c. 1.5-2 kbar and c. 40-70°C for garnet crystal diameters of c. 3-5 mm in samples eventually reaching mid-amphibolite facies temperatures (or by 2-4 kbar and c. 130-180°C for crystal diameters of c. 0.2-0.5 mm). The conditions of earliest garnet growth in crystals reaching 1 mm in diameter can be

  2. Correlation of coal beds, coal zones, and key stratigraphic units in the Pennsylvanian rocks of eastern Kentucky

    USGS Publications Warehouse

    Rice, Charles L.; Smith, J. Hiram

    1980-01-01

    The Pennsylvanian rocks of the eastern Kentucky coal field unlderlie an area of about 27,000 square kilometers (see index map). Largely because of the size and stratigraphic complexity of the area, Huddle and others (1963, p. 31) divided it into six coal reserve districts (unofficial), utilizing state and county lines as well as geologic features, drainage areas, and cola producing areas. This division is followed herein because, in general, each of these districts has a characteristic stratigraphic nomenclature, particularly as related to coal bed names. The six districts shown on the index mat, are the Princess, Licking River, Big Sandy, Hazard, Southwestern, and Upper Cumberland River; the Upper Cumberland River district has been divided into the Harlan and Middlesboro subdistricts. 

  3. Carbon deposition during brittle rock deformation: Changes in electrical properties of fault zones and potential geoelectric phenomena during earthquakes

    SciTech Connect

    Mathez, E A; Roberts, J J; Duba, A G; Kronenberg, A K; Karner, S L

    2008-05-16

    To investigate potential mechanisms for geoelectric phenomena accompanying earthquakes, we have deformed hollow cylinders of Sioux quartzite to failure in the presence of carbonaceous pore fluids and investigated the resulting changes in electrical conductivity and carbon distribution. Samples were loaded at room temperature or 400 C by a hydrostatic pressure at their outer diameter, increasing pressure at a constant rate to {approx}290 MPa. Pore fluids consisted of pure CO, CO{sub 2}, CH{sub 4} and a 1:1 mixture of CO{sub 2} and CH{sub 4}, each with pore pressures of 2.0 to 4.1 MPa. Failure occurred by the formation of mode II shear fractures transecting the hollow cylinder walls. Radial resistivities of the cylinders fell to 2.9 to 3.1 M{Omega}-m for CO tests and 15.2 to 16.5 M{Omega}-m for CO{sub 2}:CH{sub 4} tests, compared with >23 M{Omega}-m for dry, undeformed cylinders. Carbonaceous fluids had no discernable influence on rock strength. Based on mapping using electron microprobe techniques, carbon occurs preferentially as quasi-continuous films on newly-formed fracture surfaces, but these films are absent from pre-existing surfaces in those same experiments. The observations support the hypothesis that electrical conductivity of rocks is enhanced by the deposition of carbon on fracture surfaces and imply that electrical properties may change in direct response to brittle deformation. They also suggest that the carbon films formed nearly instantaneously as the cracks formed. Carbon film deposition may accompany the development of microfracture arrays prior to and during fault rupture and thus may be capable of explaining precursory and coseismic geoelectric phenomena.

  4. Deciphering P-T paths in metamorphic rocks involving zoned minerals using quantified maps (XMapTools software) and thermodynamics methods: Examples from the Alps and the Himalaya.

    NASA Astrophysics Data System (ADS)

    Lanari, P.; Vidal, O.; Schwartz, S.; Riel, N.; Guillot, S.; Lewin, E.

    2012-04-01

    Metamorphic rocks are made by mosaic of local thermodynamic equilibria involving minerals that grew at different temporal, pressure (P) and temperature (T) conditions. These local (in space but also in time) equilibria can be identified using micro-structural and textural criteria, but also tested using multi-equilibrium techniques. However, linking deformation with metamorphic conditions requires spatially continuous estimates of P and T conditions in least two dimensions (P-T maps), which can be superimposed to the observed structures of deformation. To this end, we have developed a new Matlab-based GUI software for microprobe X-ray map processing (XMapTools, http://www.xmaptools.com) based on the quantification method of De Andrade et al. (2006). XMapTools software includes functions for quantification processing, two chemical modules (Chem2D, Triplot3D), the structural formula functions for common minerals, and more than 50 empirical and semi-empirical geothermobarometers obtained from the literature. XMapTools software can be easily coupled with multi-equilibrium thermobarometric calculations. We will present examples of application for two natural cases involving zoned minerals. The first example is a low-grade metapelite from the paleo-subduction wedge in the Western Alps (Schistes Lustrés unit) that contains only both zoned chlorite and phengite, and also quartz. The second sample is a Himalayan eclogite from the high-pressure unit of Stak (Pakistan) with an eclogitic garnet-omphacite assemblage retrogressed into clinopyroxene-plagioclase-amphibole symplectite, and later into amphibole-biotite during the collisional event under crustal conditions. In both samples, P-T paths were recovered using multi-equilibrium, or semi-empirical geothermobarometers included in the XMapTools package. The results will be compared and discussed with pseudosections calculated with the sample bulk composition and with different local bulk rock compositions estimated with XMap

  5. Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada

    USGS Publications Warehouse

    Lowery, Claiborne L.E.; Miller, C.F.; Walker, B.A.; Wooden, J.L.; Mazdab, F.K.; Bea, F.

    2006-01-01

    Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ???35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/ Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/ Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (TTiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ???30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and TTiZ (>100??C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone. ?? 2006 The Mineralogical Society.

  6. Sensors and Monitoring Techniques for the Deep Unsaturated Zone: Reducing Uncertainty Related to Seepage and Transport in Fractured Rock

    NASA Astrophysics Data System (ADS)

    Dinwiddie, C. L.; Or, D.; Stothoff, S. A.; Fedors, R. W.; Pohle, J. A.; Tuller, M.

    2007-12-01

    Planning for performance confirmation of hydrologic properties and processes in a potential geologic repository for high-level radioactive waste at Yucca Mountain is a requirement stated in Subpart F of 10 CFR Part 63. An important goal of performance confirmation is to acquire information indicating whether natural and engineered barriers are functioning as intended, and whether the conditions encountered are within the limits assumed during a licensing review. Long-term monitoring of hydrologic properties and processes and in situ confirmation of design assumptions will play a key role in the safe operation of the potential geologic radioactive waste repository and in the decision to close the repository. Despite remarkable advances in cyberinfrastructure for linking sensors into spatially distributed environmental networks, the extended time horizon (decades to hundreds of years) for long-term monitoring activities, the harsh thermal and radiative conditions in the near-field environment, the deep fractured unsaturated rock environment at Yucca Mountain, the potential scope of observations, and restricted access to observation ports for maintenance and upgrades each present unprecedented challenges to the design of hydro-environmental monitoring networks. Activities for performance confirmation could include the use of pore water samplers and sensors for measuring water content, matric potential, temperature, relative humidity, and water and gas fluxes. Current sensor technology for deep fractured rock systems (i) lags behind environmental observatory network solutions for surface and near-surface processes, (ii) lags behind analogous technology for unconsolidated porous media, (iii) cannot be reliably deployed without ongoing maintenance or replacement at relatively frequent intervals, and (iv) is not designed to withstand harsh thermal and radiative conditions. Long-term monitoring could require special design considerations, such as measurement redundancy

  7. Phase-equilibrium geobarometers for silicic rocks based on rhyolite-MELTS. Part 2: application to Taupo Volcanic Zone rhyolites

    NASA Astrophysics Data System (ADS)

    Bégué, Florence; Gualda, Guilherme A. R.; Ghiorso, Mark S.; Pamukcu, Ayla S.; Kennedy, Ben M.; Gravley, Darren M.; Deering, Chad D.; Chambefort, Isabelle

    2014-11-01

    Constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems; however, it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems. In this study, we use the recently developed rhyolite-MELTS geobarometer to constrain the crystallisation pressures of rhyolites from the Taupo Volcanic Zone (TVZ). As sanidine is absent from the studied deposits, we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass (the quartz +1 feldspar constraint of Gualda and Ghiorso, Contrib Mineral Petrol 168:1033. doi:10.1007/s00410-014-1033-3. 2014). We use glass compositions (matrix glass and melt inclusions) from seven eruptive deposits dated between ~320 and 0.7 ka from four distinct calderas in the central TVZ, and we discuss advantages and limitations of the rhyolite-MELTS geobarometer in comparison with other geobarometers applied to the same eruptive deposits. Overall, there is good agreement with other pressure estimates from the literature (amphibole geobarometry and H2O-CO2 solubility models). One of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions—regardless of volatile saturation. The examples presented also emphasise the utility of this method to filter out spurious glass compositions. Pressure estimates obtained with the new rhyolite-MELTS geobarometer range between ~250 to ~50 MPa, with a large majority at ~100 MPa. These results confirm that the TVZ hosts some of the shallowest rhyolitic magma bodies on the planet, resulting from the extensional tectonic regime and thinning of the crust. Distinct populations with different equilibration pressures are also recognised, which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and

  8. Neotectonic deformation in the Eurasia-Arabia collision zone, the East Anatolian Plateau, E Turkey: evidence from palaeomagnetic study of Neogene-Quaternary volcanic rocks

    NASA Astrophysics Data System (ADS)

    Hisarlı, Z. Mümtaz; Çinku, Mualla Cengiz; Ustaömer, Timur; Keskin, Mehmet; Orbay, Naci

    2016-01-01

    Palaeomagnetic studies of the Neogene-Quaternary rocks of Anatolia have been mostly interpreted in the light of its westward escape as a result of the collision between the Arabian and Eurasian plates along the Bitlis-Zağros suture during the Neotectonic period. However, within the collision zone, in East Anatolia, palaeomagnetic data are not available. In order to help understand the deformational history of Eastern Anatolia during the Neotectonic period, we have carried out a palaeomagnetic study of Miocene-Quaternary volcanic rocks from 100 sites, selected on the basis of their geographical position and known age. The results indicate that the study area can be divided into five principal tectonic blocks, based on earthquake activity and the rotation that the blocks underwent. These blocks are the Van Block (VB), the Kars Block (KB), the Anatolian Block (AB), the Pontide Block (PB), and the Arabian Block (ARB). The largest counterclockwise (CCW) tectonic rotations were encountered in the AB and PB, whereas the largest clockwise (CW) rotations were recorded in the VB. The sinistral East Anatolian Fault and the Erzurum Fault Zone form the present boundary of these two contrasting, CW and CCW-rotating domains. Both the AB and the PB exhibit similar amount of rotation until the Quaternary, during which the AB rotated 13° CCW while the PB remained stable. The Quaternary rotation of the AB is attributed to the activity of the North Anatolian Fault. The KB shows the smallest amount of CW rotation during all of the time intervals studied. All of the blocks studied indicate an acceleration in the amount of rotations during the Quaternary, which was preceded by a period of relative tectonic stability during the Late Pliocene. Following the collision of the Arabian Plate with the Eurasian Plate during the Mid-Miocene, the crust was initially thickened by thrusting and folding. This was followed by lateral extrusion and differential rotation of the crustal blocks during

  9. Identification and characterization of hydrothermally altered zones in granite by combining synthetic clay content logs with magnetic mineralogical investigations of drilled rock cuttings

    NASA Astrophysics Data System (ADS)

    Meller, Carola; Kontny, Agnes; Kohl, Thomas

    2014-10-01

    Clay minerals as products of hydrothermal alteration significantly influence the hydraulic and mechanical properties of crystalline rock. Therefore, the localization and characterization of alteration zones by downhole measurements is a great challenge for the development of geothermal reservoirs. The magnetite bearing granite of the geothermal site in Soultz-sous-Forêts (France) experienced hydrothermal alteration during several tectonic events and clay mineral formation is especially observed in alteration halos around fracture zones. During the formation of clay minerals, magnetite was oxidized into hematite, which significantly reduces the magnetic susceptibility of the granite from ferrimagnetic to mostly paramagnetic values. The aim of this study was to find out if there exists a correlation between synthetic clay content logs (SCCLs) and measurements of magnetic susceptibility on cuttings in the granite in order to characterize their alteration mineralogy. Such a correlation has been proven for core samples of the EPS1 reference well. SCCLs were created from gamma ray and fracture density logs using a neural network. These logs can localize altered fracture zones in the GPK1-4 wells, where no core material is available. Mass susceptibility from 261 cutting samples of the wells GPK1-GPK4 was compared with the neural network derived synthetic logs. We applied a combination of temperature dependent magnetic susceptibility measurements with optical and electron microscopy, and energy dispersive X-ray spectroscopy to discriminate different stages of alteration. We found, that also in the granite cuttings an increasing alteration grade is characterized by an advancing oxidation of magnetite into hematite and a reduction of magnetic susceptibility. A challenge to face for the interpretation of magnetic susceptibility data from cuttings material is that extreme alteration grades can also display increased susceptibilities due to the formation of secondary magnetite

  10. A transmissivity model for deformation zones in fractured crystalline rock and its possible correlation to in situ stress at the proposed high-level nuclear waste repository site at Forsmark, Sweden

    NASA Astrophysics Data System (ADS)

    Follin, Sven; Stigsson, Martin

    2014-03-01

    The Forsmark site was recently proposed by the Svensk Kärnbränslehantering AB (SKB) to serve as the potential site for construction of a future geological repository for spent high-level nuclear fuel at about 470 m depth in fractured crystalline rock. The considerations included, among other things, distance from regionally significant deformation zones with highly strained rock, lithological homogeneity, low hydraulic conductivity, groundwater salinity with an acceptable range, and lack of potential mineral resources. This report describes the calculation of transmissivity of deduced deformation zones at Forsmark and the transmissivity model used in the regional groundwater flow modeling carried out in support of the integrated site description. Besides significant decrease with increasing depth (more than four orders of magnitude over a depth of about 1 km), the calculated transmissivity values also reveal considerable spatial variability along the strikes of the zones, i.e. lateral heterogeneity (more than two orders of magnitude). A hydro-mechanical coupling is discussed, based on presented models for the tectonic evolution and the principal stress tensor. Tentatively, laboratory-scale relationships developed from normal stress experiments on a single fracture in crystalline rock can be used to estimate the maximum values of transmissivity of deduced deformation zones at Forsmark.