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1.
The comment of Green et al. debates the interpretation of the temperature of the H2O-saturated peridotite solidus and presence of silicate melt in the experiments of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) at <1,000?°C. The criticisms presented in their comment do not invalidate any of the most compelling observations of Till et al. (Contrib Mineral Petrol 163:669–688, 2012) as discussed in the following response, including the changing minor element and Mg# composition of the solid phases with increasing temperature in our experiments with 14.5?wt% H2O at 3.2?GPa, as well as the results of our chlorite peridotite melting experiments with 0.7?wt% H2O. The point remains that Till et al. (Contrib Mineral Petrol 163:669–688, 2012) present data that call into question the H2O-saturated peridotite solidus temperature preferred by Green (Tectonophysics 13(1–4):47–71, 1972; Earth Planet Sci Lett 19(1):37–53, 1973; Can Miner 14:255–268, 1976); Millhollen et al. (J Geol 82(5):575–587, 1974); Mengel and Green (Stability of amphibole and phlogopite in metasomatized peridotite under water-saturated and water-undersaturated conditions, Geological Society of Australia Special Publication, Blackwell, pp 571-581, 1989); Wallace and Green (Mineral Petrol 44:1–19, 1991) and Green et al. (Nature 467(7314):448–451, 2010).  相似文献   

2.
Three-dimensional, elastic and elasto-plastic finite element (FE) programs have permitted calculation of the displacements and the factor of safety (FOS) for the excavation for a tower, 132.70 m high (above foundation) on the island of Tenerife. The tower is supported by a 2 m thick reinforced concrete slab on jointed, vesicular and weathered basalt and scoria. The installation of rod extensometers at different depths below the slab has permitted comparison between measured and calculated displacements and the estimation of in situ deformation modulus. The moduli deduced from the simple empirical equations proposed by Hoek et al. (In: NARMS-TAC, 2002) and Gokceoglu et al. (Int J Rock Mech Min Sci 40:701–710, 2003) as a function of GSI, and Nicholson and Bieniawski (Int J Min Geol Eng 8:181–202, 1990) as a function of RMR, provide an acceptable fit with the measured settlements in this type of rock. Good correlation is also obtained with the empirical equation presented by Verman et al. (Rock Mech Rock Eng 30(3):121–127, 1997) that incorporates the influence of confining stress in the deformation modulus. The FOS obtained from different correlations with geomechanical classifications is within a relatively narrow range. These results increase our confidence in the use of classification schemes to estimate the deformation and stability in jointed rock.  相似文献   

3.
A total of 163 free-field acceleration time histories recorded at epicentral distances of up to 200 km from 32 earthquakes with moment magnitudes ranging from M w 4.9 to 7.4 have been used to investigate the predictive capabilities of the local, regional, and next generation attenuation (NGA) ground-motion prediction equations and determine their applicability for northern Iran. Two different statistical approaches, namely the likelihood method (LH) of Scherbaum et al. (Bull Seismol Soc Am 94:341–348, 2004) and the average log-likelihood method (LLH) of Scherbaum et al. (Bull Seismol Soc Am 99:3234–3247, 2009), have been applied for evaluation of these models. The best-fitting models (considering both the LH and LLH results) over the entire frequency range of interest are those of Ghasemi et al. (Seismol 13:499–515, 2009a) and Soghrat et al. (Geophys J Int 188:645–679, 2012) among the local models, Abrahamson and Silva (Earthq Spectra 24:67–97, 2008) and Chiou and Youngs (Earthq Spectra 24:173–215, 2008) among the NGA models, and finally Akkar and Bommer (Seism Res Lett 81:195–206, 2010) among the regional models.  相似文献   

4.
The imbrication’s area in northern Tunisia is the most external segment of Alpine range, where several associated folds types with thrust ramps are recognized within imbricate units beneath Numidian front slope. Their presence help to understand thrusting mechanisms installation through studied area. In fact, this zone was considered as a result of Paleogene gravitary slop (Kujawski (Ann Miner Géol Tunis (24):281, 1969); Caire (Ann Min Géol Tunis 26:87–110, 1973); Rouvier 1977), which is proved to be affected by major deep decollement, given rise to various structures, some are propagation folds, specific of foreland front, limited to this area, and those in more external position: Tunisian Atlas (Creusot et al. (C R Acad Sci Paris 314(Sér II):961–965, 1992); Ouali and Mercier (PII: S0191-8141(97):00048-5, 1997); Ouali 1984; Ahmadi et al. (J Struct Geol 28:721–728, 2006)). Various categories of fold ramps could be identified: frontal folds ramp NE–SW and others as lateral or oblique ramp with NW–SE trend (Aridhi et al. (C R Geosci 343:360–369, 2011)). The relation between various structures has been used as recognition tools of thrusting sequences and to propose a new deformation chronology. Delimited outcropping of these structures between two both parallel faults strikes with regional displacement, leads to interpret these faults as cogenetic tear faults of propagation thrusts; this fault separates two domains with different deformation styles from each other side.  相似文献   

5.
We believe the hypothesis presented by Maier et al. (Miner Deposita 48:1–56, 2012) for the formation of the various ore bodies in the Bushveld Complex to be overly simplistic, and we raise concerns that some of our work, used in support of this hypothesis, has been misrepresented. The formation of both diverse metalliferous layers (platinum-group element (PGE) reefs and Ti-magnetite layers) and some discordant (pipe) ore deposits has been ascribed by Maier et al. to the single unifying process of hydrodynamic sorting. The problem faced by authors of universal hypotheses for the Bushveld Complex is the sheer size and complexity of the intrusion. We disagree with many aspects of the overall Maier et al. model and have also identified several minor errors on maps and photographs, although some of these do not have a material effect on the model. The nature and origin of the layering is, however, too complex a topic to deal with in the context of this commentary, and we restrict ourselves to noting that our preferred hypothesis, namely the incremental buildup of layering from numerous episodes of replenishment, by different magma lineages, is consistent with field relationships. Our hypothesis for the origin of the ultramafic-hosted PGE-rich reefs, i.e., lateral mixing, is applicable to economically mineralized reefs (Mitchell and Scoon, Econ Geol 102:971–1009, 2007) and poorly mineralized layers such as the Pseudoreef harzburgite (Scoon and De Klerk, Canad Mineral 25:51–77, 1987) and the chromitite layers below the UG2 (Scoon and Teigler, Econ Geol 89:1094–1121, 1994).  相似文献   

6.
Phenocryst assemblages of lavas from the long-lived Aucanquilcha Volcanic Cluster (AVC) have been probed to assess pressure and temperature conditions of pre-eruptive arc magmas. Andesite to dacite lavas of the AVC erupted throughout an 11-million-year, arc magmatic cycle in the central Andes in northern Chile. Phases targeted for thermobarometry include amphibole, plagioclase, pyroxenes, and Fe–Ti oxides. Overall, crystallization is documented over 1–7.5 kbar (~25 km) of pressure and ~680–1,110 °C of temperature. Pressure estimates range from ~1 to 5 kbar for amphiboles and from ~3 to 7.5 kbar for pyroxenes. Pyroxene temperatures are tightly clustered from ~1,000–1,100 °C, Fe–Ti oxide temperatures range from ~750–1,000 °C, and amphibole temperatures range from ~780–1,050 °C. Although slightly higher, these temperatures correspond well with previously published zircon temperatures ranging from ~670–900 °C. Two different Fe–Ti oxide thermometers (Andersen and Lindsley 1985; Ghiorso and Evans 2008) are compared and agree well. We also compare amphibole and amphibole–plagioclase thermobarometers (Ridolfi et al. 2010; Holland and Blundy 1994; Anderson and Smith 1995), the solutions from which do not agree well. In samples where we employ multiple thermometers, pyroxene temperature estimates are always highest, zircon temperature estimates are lowest, and Fe–Ti oxide and amphibole temperature estimates fall in between. Maximum Fe–Ti oxide and zircon temperatures are observed during the middle stage of AVC activity (~5–3 Ma), a time associated with increased eruption rates. Amphibole temperatures during this time are relatively restricted (~850–1,000 °C). The crystal record presented here offers a time-transgressive view of an evolving, multi-tiered subvolcanic reservoir. Some crystals in AVC lavas are likely to be true phenocrysts, but the diversity of crystallization temperatures and pressures recorded by phases in individual AVC lavas suggests erupting magma extensively reams and accumulates crystals from disparate levels of the middle to upper crust.  相似文献   

7.
We perform a strong ground motion simulation using a modified semi-empirical technique (Midorikawa in Tectonophysics 218:287–295, 1993), with frequency-dependent radiation pattern model. Joshi et al. (Nat Hazards 71:587–609, 2014) have modified the semi-empirical technique to incorporate the modeling of strong motion generation areas (SMGAs). A frequency-dependent radiation pattern model is applied to simulate high-frequency ground motion more precisely. Identified SMGAs (Kurahashi and Irikura in Earth Planets Space 63:571–576, 2011) of the 2011 off the Pacific coast of Tohoku earthquake (M w  = 9.0) were modeled using this modified technique. We analyzed the effect of changing seismic moment values of SMGAs on the simulated acceleration time series. Final selection of the moment values of SMGAs is based on the root-mean-square error (RMSE) of waveform comparison. Records are simulated for both frequency-dependent and constant radiation pattern function. Simulated records for both cases are compared with observed records in terms of peak ground acceleration, peak ground velocity and pseudo-acceleration response spectra at different stations. Comparison of simulated and observed records in terms of RMSE suggests that the method is capable of simulating record, which matches in a wide frequency range for this earthquake and bears realistic appearance in terms of shape and strong motion parameters. The results confirm the efficacy and suitability of rupture model defined by five SMGAs for the developed modified technique.  相似文献   

8.
Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) investigated a double capsule assembly for use in piston-cylinder experiments that would allow hydrous, high-temperature, and high-pressure experiments to be conducted under controlled oxygen fugacity conditions. Using a platinum outer capsule containing a metal oxide oxygen buffer (Ni–NiO or Co–CoO) and H2O, with an inner gold–palladium capsule containing hydrous melt, this study was able to compare the oxygen fugacity imposed by the outer capsule oxygen buffer with an oxygen fugacity estimated by the AuPdFe ternary system calibrated by Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010). H2O loss or gain, as well as iron loss to the capsule walls and carbon contamination, is often observed in piston-cylinder experiments and often go unexplained. Only a few have attempted to actually quantify various aspects of these changes (Brooker et al. in Am Miner 83(9–10):985–994, 1998; Truckenbrodt and Johannes in Am Miner 84:1333–1335, 1999). It was one of the goals of Jakobsson (Contrib Miner Petrol 164(3):397–407, 2012) to address these issues by using and testing the AuPdFe solution model of Barr and Grove (Contrib Miner Petrol 160(5):631–643, 2010), as well as to constrain the oxygen fugacity of the inner capsule. The oxygen fugacities of the analyzed melts were assumed to be equal to those of the solid Ni–NiO and Co–CoO buffers, which is incorrect since the melts are all undersaturated in H2O and the oxygen fugacities should therefore be lower than that of the buffer by 2 log $a_{{{\text{H}}_{ 2} {\text{O}}}}$ .  相似文献   

9.
Sixteen rock samples of outcrop of Chia Gara Formations from the type locality area, south of Amadia, North Iraq showed evidences for hydrocarbon generation potential by palynological studies. These analyses include age assessment of Upper Jurassic (Tithonian) to Lower Cretaceous (Berriasian) age based on assemblages of mainly dinoflagellate cyst constituents. Qualitative studies are done in this study by textural microscopy used in assessing amorphous organic matter for palynofacies type belong to kerogen type A of Thompson and Dembiki (Int J Coal Geol 6:229–249, 1986) which contain brazinophyte algae, Tasmanites, and foraminifera test linings, as well as the dinoflagellate cysts and spores, deposited in dysoxic–anoxic environment. The palynomorphs are of dark orange and light brown, on the spore species Cyathidites australis, that indicate mature organic matters with thermal alteration index of 2.7–3.0 by Staplin’s scale. These characters and total organic carbon of 0.5–8.5 wt% have rated the succession as a source rock for high efficiency for generation and expulsion of oil with ordinate gas that charged mainly oil fields of Tawqi. Some oil is released from the Chia Gara Formation to charge the Cretaceous–Tertiary total petroleum system.  相似文献   

10.
Melting experiments were conducted on a mica–clinopyroxenite xenolith brought up in a minette dyke in southern Alberta, Canada, near Milk River. Both the minettes and mica–clinopyroxenite xenoliths were studied by Buhlmann et al. (Can J Earth Sci 37:1629–1650, 2000), who hypothesized that the minettes formed by partial melting of a mantle source containing clinopyroxene + phlogopite ± olivine, at pressures ≥1.7 GPa. In liquidus experiments performed on the most primitive minette in our previous study (Funk and Luth in Contrib Mineral Petrol 164:999–1009, 2012), we found a multiple saturation point where olivine and orthopyroxene coexisted with liquid at 1.77 GPa and 1,350 °C. We argued that the minette originally formed by partial melting of clinopyroxene + phlogopite, but had re-equilibrated with a harzburgite during ascent. In the current study, we wanted to test both the source region hypothesis of Buhlmann et al. and our re-equilibration hypothesis by studying the near-solidus phase equilibria of a mica + clinopyroxene assemblage. We found the solidus for our xenolith has a steep slope in P–T space and lies at temperatures above those of a normal cratonic geotherm, implying that this mica–clinopyroxenite is stable in the cratonic mantle. Melting could occur at greater depths, where the solidus is extrapolated to cross the geotherm or must be induced either by raising the temperatures of the surrounding rocks or by introducing hydrous fluids into the source. Our melts are in equilibrium with clinopyroxene and olivine. The compositions of the liquids derived from melting this xenolith are similar to madupitic lamproites from the Leucite Hills, Wyoming, studied by Carmichael (Contrib Mineral Petrol 15:24–66, 1967) and Barton and Hamilton (Contrib Mineral Petrol 66:41–49, 1978; Contrib Mineral Petrol 69:133–142, 1979). Barton and Hamilton (Contrib Mineral Petrol 69:133–142, 1979) proposed that the madupitic lamproites may have come from a source containing mica and pyroxene. This study supports their hypothesis. The composition of the most primitive minette from southern Alberta lies between our experimental melt and a population of representative mantle orthopyroxenes. We conclude from our study that the Milk River minettes were likely derived from a source containing phlogopite, clinopyroxene and trace amounts of apatite, which formed olivine upon melting. During ascent, the melts changed composition by reacting with orthopyroxene.  相似文献   

11.
In this paper, we study solving iteratively the coupling of flow and mechanics. We demonstrate the stability and convergence of two widely used schemes: the undrained split method and the fixed stress split method. To our knowledge, this is the first time that such results have been rigorously obtained and published in the scientific literature. In addition, we propose a new stress split method, with faster convergence rate than known schemes. These results are specially important today due to the interest in hydraulic fracturing (Dean and Schmidt SPE J. 14:707–714, 2009; Ji et al. SPE J. 14:423–430, 2009; Samier and De Gennaro 2007; Settari and Maurits SPE J. 3:219–226, 1998), in oil and gas shale reservoirs.  相似文献   

12.
Despite a missing definition of equivalence of mathematical models or methods by Zhang et al. (Math Geosci, 2013), an “equivalence” (Zhang et al., Math Geosci, 2013, p. 6,7,8,14) of modified weights-of-evidence (Agterberg, Nat Resour Res 20:95–101, 2011) and logistic regression does not generally exist. Its alleged proof is based on a previously conjectured linear relationship between weights of evidence and logistic regression parameters (Deng, Nat Resour Res 18:249–258, 2009), which does not generally exist either (Schaeben and van den Boogaart, Nat Resour Res 20:401–406, 2011). In fact, an extremely simple linear relationship exists only if the predictor variables are conditionally independent given the target variable, in which case the contrasts, i.e., the differences of the weights, are equal to the logistic regression parameters. Thus, weights-of-evidence is the special case of logistic regression if the predictor variables are binary and conditionally independent given the target variable.  相似文献   

13.
Constraining magnitudes of mechanical and thermo-mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics (Talbot in J Struct Geol 21:949–957, 1999). Such parameters aid dynamic scaling of analogue tectonic models (Ramberg in Gravity, deformation and the Earth’s crust in theory, experiments and geological applications, 2nd edn. Academic Press, London, 1981), which are useful to unravel tectonics in further details (Schultz-Ela and Walsh in J Struct Geol 24:247–275, 2002). The channel flow extrusion of the Higher Himalayan Shear Zone (HHSZ, = Higher Himalaya) can be explained by a top-to-S/SW simple shear (i.e. the D2 deformation) in combination with a pressure gradient induced flow against gravity. Presuming its Newtonian incompressible rheology with parallel inclined boundaries, the viscosity (μ) of this shear zone along a part of the Himalayan chain through India, Nepal and Bhutan is estimated to vary widely between ~1016 and 1023 Pa s, and its Prandtl number (P r ) within ~1021–1028. The estimates utilized ranges of known thickness (6–58 km) of the HHSZ, that of its top subzone of ductile shear of normal shear sense (STDSU: 0.35–9.4 km), total rate of slip of its two boundaries (0.7–131 mm year?1), pressure gradient (0.02–6 kb km?1), density (2.2–3.1 g cm?3) and thermal diffusivity (0.5 × 10?6–2.1 × 10?6 m s?2) along the orogenic trend. Considering most of the parameters specifically for the Sutlej section (India), the calculated viscosity (μ) and the Prandtl number (P r ) of the HHSZ are deduced to be μ: ~1017–1023 Pa s and P r  ~ 1022–1028. The upper limits of the estimated viscosity ranges are broadly in conformity with a strong Tibetan mid-crust from where a part of the HHSZ rocks extruded. On the other hand, their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure. The estimated mechanical and thermo-mechanical parameters of the HHSZ will help to build dynamically scaled analogue models for the Himalayan deformation of the D2–phase.  相似文献   

14.
Determination of the peak thermal condition is vital in order to understand tectono-thermal evolution of the Himalayan belt. The Lesser Himalayan Sequence (LHS) in the Western Arunachal Pradesh, being rich in carbonaceous material (CM), facilitates the determination of peak metamorphic temperature based on Raman spectroscopy of carbonaceous material (RSCM). In this study, we have used RSCM method of Beyssac et al. (J Metamorph Geol 20:859–871, 2002a) and Rahl et al. (Earth Planet Sci Lett 240:339–354, 2005) to estimate the thermal history of LHS and Siwalik foreland from the western Arunachal Pradesh. The study indicates that the temperature of 700–800 °C in the Greater Himalayan Sequence (GHS) decreases to 650–700 °C in the main central thrust zone (MCTZ) and decreases further to <200 °C in the Mio-Pliocene sequence of Siwaliks. The work demonstrates greater reliability of Rahl et al.’s (Earth Planet Sci Lett 240:339–354, 2005) RSCM method for temperatures >600 and <340 °C. We show that the higher and lower zones of Bomdila Gneiss (BG) experienced temperature of ~600 °C and exhumed at different stages along the Bomdila Thrust (BT) and Upper Main Boundary Thrust (U.MBT). Pyrolysis analysis of the CM together with the Fission Track ages from upper Siwaliks corroborates the RSCM thermometry estimate of ~240 °C. The results indicate that the Permian sequence north of Lower MBT was deposited at greater depths (>12 km) than the upper Siwalik sediments to its south at depths <8 km before they were exhumed. The 40Ar/39Ar ages suggest that the upper zones of Se La evolved ~13–15 Ma. The middle zone exhumed at ~11 Ma and lower zone close to ~8 Ma indicating erosional unroofing of the MCT sheet. The footwall of MCTZ cooled between 6 and 8 Ma. Analyses of P–T path imply that LHS between MCT and U.MBT zone falls within the kyanite stability field with near isobaric condition. At higher structural level, the temperatures increase gradually with P–T conditions in the sillimanite stability field. The near isothermal (700–800 °C) condition in the GHS, isobaric condition in the MCTZ together with T–t path evidence of GHS that experienced relatively longer duration of near peak temperatures and rapid cooling towards MCTZ, compares the evolution of GHS and inverted metamorphic gradient closely to channel flow predictions.  相似文献   

15.
The trace element signatures of fluids were investigated by leaching experiments on natural samples of partly altered mafic igneous rocks recovered from the drilling site 1,256 of ODP Leg 206 on the Cocos plate (Central America). Experiments with ultrapure water were performed at 400 °C/0.4 GPa and 500 °C/0.7 GPa. Both fluids and residual solids were examined to obtain the partition coefficients (Dfluid/rock) of various trace elements. Element partition coefficients (Dfluid/rock) obtained at 500 °C/0.7 GPa are significantly lower compared to results obtained at 400 °C/0.4 GPa, which is in contrast to observations at higher pressures (2.2–6 GPa) and temperatures between 700 and 1,400 °C (Kessel et al. in Earth Planet Sci Lett 237: 873–892, 2005a; Spandler et al. in Chem Geol 239: 228–249, 2007). This finding may indicate a considerable pressure effect on the leaching processes and strongly divergent fluid–rock interactions in the upper part of a subduction zone at 0.4–0.7 GPa compared to deeper subduction areas with higher pressures. Furthermore, this may be interpreted as one of the earliest fractionation processes during the subduction of crustal material.  相似文献   

16.
Polarized optical absorption spectra of natural olivine, Fa10Fo90, were measured before and after annealing/quenching experiments performed at 650, 800, 1,000 and 1,200°C under controlled oxygen fugacity. It was found that the annealing induces weak but definite changes in the olivine spectra. The intensity of the spin-allowed Z > X-polarized band at 9,560 cm?1 and shoulder at ～8,300 cm?1 attributed to Fe2+(M2), continuously decreases with annealing temperature, whereas a weaker band at ～11,600 cm?1 assigned to electronic spin-allowed transitions of Fe2+(M1), increases. This evidently shows that annealing treatments cause a redistribution of Fe2+ from M2 to M1. The fractionation increases with increasing temperature. This observation is in good correspondence with many diffraction structural studies of natural and synthetic olivines, as well as with recent Raman and Mössbauer investigations by Kolesov and Geiger (Mitt Österr Mineral Ges 149:48, 2004) and Morozov et al. (Eur J Mineral 17:495–500, 2005) evidencing a weak tendency of Fe to order into the M1 site with increasing temperature. However, this deduction is incompatible with the results of the in situ neutron power diffraction study of synthetic FeMgSiO4 by Redfern et al. (Phys Chem Minerals 27:630–637, 2000). Polarization properties of the UV absorption edge, attributed to ligand-to-metal charge-transfer transitions in Fe3+, changes from Y > X ? Z in natural samples to a weak Y ≥ X ≥ Z-pleochroism in annealed ones. This may be due to redistribution of a small content of Fe3+ among M1 and M2 structural sites.  相似文献   

17.
The concentrations of uranium, iron and the major constituents were determined in groundwater samples from aquifer containing uranyl phosphate minerals (meta-autunite, meta-torbernite and torbernite) in the Köprüba?? area. Groundwater samples from wells located at shallow depths (0.5–6 m) show usually near neutral pH values (6.2–7.1) and oxidizing conditions (Eh = 119–275 mV). Electrical conductivity (EC) values of samples are between 87 and 329 μS/cm?1. They are mostly characterized by mixed cationic Ca dominating bicarbonate types. The main hydrogeochemical process is weathering of the silicates in the shallow groundwater system. All groundwater in the study area are considered undersaturated with respect to torbernite and autunite. PHREEQC predicted UO2(HPO4) 2 2? as the unique species. The excellent positive correlation coefficient (r = 0.99) between U and PO4 indicates the dissolved uranium in groundwater would be associated with the dissolution of uranyl phosphate minerals. The groundwater show U content in the range 1.71–70.45 μg/l but they are mostly lower than US EPA (2003) maximum contaminant level of 30 μg/l. This low U concentrations in oxic groundwater samples is attributed to the low solubility of U(VI) phosphate minerals under near neutral pH and low bicarbonate conditions. Iron closely associated with studied sediments, were also detected in groundwater. The maximum concentration of Fe in groundwater samples was 2837 μg/l, while the drinking water guidelines of Turkish (TSE 1997) and US EPA (2003) were suggested 200 and 300 μg/l, respectively. Furthermore, iron and uranium showed a significant correlation to each other with a correlation coefficient (r) of 0.94. This high correlation is probably related to the iron-rich sediments which contain also significant amounts of uranium mineralization. In addition to pH and bicarbonate controlling dissolution of uranyl phosphates, association of uranyl phosphates with iron (hydr) oxides seems to play important role in the amount of dissolved U in shallow groundwater.  相似文献   

18.
Cylinders of synthetic periclase single crystals were annealed at 0.15–0.5 GPa and 900–1200 °C under water-saturated conditions for 45 min to 72 h. Infrared spectra measured on the quenched products show bands at 3,297 and 3,312 cm?1 indicating V OH ? centers (OH-defect stretching vibrations in a half-compensated cation vacancy) in the MgO structure as a result of proton diffusion into the crystal. For completely equilibrated specimens, the OH-defect concentration, expressed as H2O equivalent, was calculated to 3.5 wt ppm H2O at 1,200 °C and 0.5 GPa based on the calibration method of Libowitzky and Rossmann (Am Min 82:1111–1115, 1997). This value was confirmed via Raman spectroscopy, which shows OH-defect-related bands at identical wavenumbers and yields an H2O equivalent concentration of about 9 wt ppm using the quantification scheme of Thomas et al. (Am Min 93:1550–1557, 2008), revised by Mrosko et al. (Am Mineral 96:1748–1759, 2011). Results of both independent methods give an overall OH-defect concentration range of 3.5–9 (+4.5/?2.6) ppm H2O. Proton diffusion follows an Arrhenius law with an activation energy E a = 280 ± 64 kJ mol?1 and the logarithm of the pre-exponential factor logDo (m2 s?1) = ?2.4 ± 1.9. IR spectra taken close to the rims of MgO crystals that were exposed to water-saturated conditions at 1,200 °C and 0.5 GPa for 24 h show an additional band at 3,697 cm?1, which is related to brucite precipitates. This may be explained by diffusion of molecular water into the periclase, and its reaction with the host crystal during quenching. Diffusion of molecular water may be described by logDH2O (m2 s?1) = ?14.1 ± 0.4 (2σ) at 1,200 °C and 0.5 GPa, which is ~ 2 orders of magnitude slower than proton diffusion at identical P-T conditions.  相似文献   

19.
The key mineralogical features of the Newania carbonatites, that illustrate their derivation from primary mantle melts (Gruau et al. Terra Nova, Abstract Suppl 1:336, 1995; Viladkar Petrology 6(3):272–283, 1998; Basu and Murty Abstracts of Goldschmidt Conference A40, 2006), are the presence of magnesite, graphite and Cr-rich magnetite. Magnesite is an early crystallizing phase. Cr-rich magnetite and graphite coexist with carbonatite minerals and precipitated from carbonate magma. Graphite, as well as gaseous CO2 and carbonate minerals such as dolomite and magnesite, can be stable in peridotite mantle. Coexistence of these minerals is controlled by fO 2 and PT-conditions. Mineral geothermometers for the Newania carbonatite give temperatures from 463 to 950°C. The parental source for Newania carbonatites was characterized by a relatively high log (fHF/fH2O) level which increased during the crystallization history of Newania. The estimated oxygen fugacity (for ilmenite–magnetite pairs) varies from ?1.5 to +3.5 (log-bar unit deviation from FMQ buffer), which is supported by the presence of Fe-columbite, and the composition of phlogopite, amphibole and pyroxene that have an elevated concentration of Fe3+. However, the oxygen fugacity range represented by co-existing early-crystallized graphite and magnesite is below that of the FMQ buffer and lies on the CCO buffer.  相似文献   

20.
The flow rule used in the high-cycle accumulation (HCA) model proposed by Niemunis et al. (Comput Geotech 32: 245, 2005) is examined on the basis of the data from approximately 350 drained long-term cyclic triaxial tests (N = 105 cycles) performed on 22 different grain-size distribution curves of a clean quartz sand. In accordance with (Wichtmann et al. in Acta Geotechnica 1: 59, 2006), for all tested materials, the “high-cyclic flow rule (HCFR)”, i.e., the ratio of the volumetric and deviatoric strain accumulation rates \(\dot{\varepsilon}_{\rm{v}}^{{\rm acc}}/\dot{\varepsilon}_{\rm{q}}^{{\rm acc}}\) , was found dependent primarily on the average stress ratio η av = q av/p av and independent of amplitude, soil density and average mean pressure. The experimental HCFR can be fairly well approximated by the flow rule of the modified Cam-clay (MCC) model. Instead of the critical friction angle \(\varphi_{\rm{c}}\) which enters the flow rule for monotonic loading, the HCA model uses the MCC flow rule expression with a slightly different parameter \(\varphi_{\rm{cc}}\) . It should be determined from cyclic tests. \(\varphi_{\rm{cc}}\) and \(\varphi_{\rm{c}}\) are of similar magnitude but not always identical, because they are calibrated from different types of tests. For a simplified calibration in the absence of cyclic test data, \(\varphi_{\rm{cc}}\) may be estimated from the angle of repose \(\varphi_{\rm{r}}\) determined from a pluviated cone of sand (Wichtmann et al. in Acta Geotechnica 1: 59, 2006). However, the paper demonstrates that the MCC flow rule with \(\varphi_{\rm{r}}\) does not fit well the experimentally observed HCFR in the case of coarse or well-graded sands. For an improved simplified calibration procedure, correlations between \(\varphi_{\rm{cc}}\) and parameters of the grain-size distribution curve (d 50,   C u) have been developed on the basis of the present data set. The approximation of the experimental HCFR by the generalized flow rule equations proposed in (Wichtmann et al. in J Geotech Geoenviron Eng ASCE 136: 728, 2010), considering anisotropy, is also discussed in the paper.  相似文献   

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