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1.
含水对富铁橄榄石流变性的影响   总被引：3，自引：2，他引：3  
橄榄石是下地壳上地幔最丰富的造岩矿物,橄榄石集合体的高温高压流变性对地幔动力学过程有着很大的影响。以往对橄榄石单晶和集合体进行过的流变性实验研究,涉及了温度、压力、氧逸度、含铁量以及含水等因素的影响,本文研究了含水对富铁橄榄石集合体流变性能的影响,首先,利用高精度 Paterson 气体介质变形装置对含水富铁橄榄石集合体(Mg_(0.9),Fe_(0.1))_2SiO_4、(Mg_(0.7),Fe_(0.3))_2SiO_4和(Mg_(0.5),Fe_(0.5))_2SiO_4进行了高温三轴压缩蠕变试验,变形试验条件为:温度1323～1473K,围压300MPa,差应力10～300MPa,应变率10~(-7)～10~(-4)s~(-1),每个试件的最大变形量为20%。利用三维非线性拟合方法对蠕变试验数据进行分析,结果表明,含水富铁橄榄石集合体的微观变形机制为扩散域和位错域,对三种铁含量,扩散域的应力指数为1。位错蠕变域中,Fo_(50)应力指教为3.8,活化能为444kJ/mol;Fo_(70)应力指数为3.7,活化能为479kJ/mol,Fo_(90)应力指数为3.6,活化能为514kJ/mol。将实验结果与不含水富铁橄榄石集合体的强度进行对比,发现含水使富铁橄榄石的强度明显下降,舍铁量相同时,含水橄榄石集合体的流变强度比干燥时小至少一个数量级。从而得到了含水对含铁量不同的橄榄石集合体粘性(强度)影响的初步试验结果。  相似文献   

2.
The validity of the thermodynamic cBΩ model is tested in terms of the experimentally determined diffusion coefficients of He in a natural Fe-bearing olivine (Fo90) and a synthetic end-member forsterite (Mg2SiO4) over a broad temperature range (250–950 °C), as reported recently by Cherniak and Watson (Geochem Cosmochim Acta 84:269–279, 2012). The calculated activation enthalpies for each of the three crystallographic axes were found to be (134 ± 5), (137 ± 13) and (158 ± 4) kJ mol?1 for the [100], [010] and [001] directions in forsterite, and (141 ± 9) kJ mol?1 for the [010] direction in olivine, exhibiting a deviation of <1 % with the corresponding reported experimental values. Additional point defect parameters such as activation volume, activation entropy and activation Gibbs free energy were calculated as a function of temperature. The estimated activation volumes (3.2–3.9 ± 0.3 cm3 mol?1) of He diffusion in olivine are comparable with other reported results for hydrogen and tracer diffusion of Mg cations in olivine. The pressure dependence of He diffusion coefficients was also determined, based on single experimental diffusion measurements at 2.6 and 2.7 GPa along the [001] direction in forsterite at 400 and 650 °C.  相似文献   

3.
High temperature creep of single crystal gadolinium gallium garnet (GGG) was studied in the temperature range of 1723–1853 K (0.86–0.94 Tm, Tm: melting temperature) and strain rate from 9 · 10?7 s?1 to 2 · 10?5 s?1. The compression tests were made along the 〈100〉 and 〈111〉 orientations. We have performed both constant strain-rate and stress-dip tests. For the 〈100〉 orientation, deformation occurs via the 〈111〉 slip systems. For the 〈111〉 orientation, both the 〈100〉 {010} and the 〈111〉 slip systems can be activated. GGG garnet is very strong under these conditions: σ/μ=(1–3)×10?3 (σ: creep strength, μ: shear modulus). The creep behavior is characterized by a power law with stress exponent n=2.9–3.3 and high activation energies E*=612–743 kJ/mol (E*～45×RTm, at zero stress which decrease with the increase of stress). Stress-dip tests suggest a small internal stress (σi/σ～0.62; σi: internal stress, σ: applied stress) compared to other materials. These results suggest that the high creep strength of GGG is mainly due to difficulty of dislocation glide rather than dislocation climb.  相似文献   

4.
Eclogite plays an important role in mantle convection and geodynamics in subduction zones. An improved understanding of processes in the deeper levels of subduction zones and collision belts requires information on eclogite rheology. However, the deformation processes and associated fabrics in eclogite are not well understood. Incompatible views of deformation mechanism have been proposed for both garnet and omphacite. We present here deformation behaviour of eclogite at temperatures of 1027–1427 °C, confining pressures of 2.5–3.5 GPa, and strain rates of 1 × 10?5 s?1 to 5 × 10?4 s?1. We obtained a power‐law creep for the high temperature and pressure deformation of a ‘dry’ eclogite (50 vol.% garnet, 40% omphacite and 10% quartz) with A = 103.3 ± 1.0, n = 3.5 ± 0.4, ΔE =403 ± 30 KJ mol?1 and ΔV = 27.2 cm3 mol?1. The two principal minerals of eclogite have greatly different strengths. Progressive increase of garnet results in a smooth increase in strength. Analysis by electron back‐scattered diffraction shows that: (1) garnet displays pole figures with near random distributions of misorientation angle under both dry and wet conditions; (2) omphacite shows pronounced lattice preferred orientations (LPOs), suggesting a dominant dislocation creep mechanism. Further investigation into the water effects on eclogite show: (3) water content does not influence the style of omphacite fabric but increases slightly the fabric strength; (4) grain boundary processes dominate the deformation of garnet under high water fugacity or high shear‐strain conditions, yielding a random LPO similar to that of non‐deforming garnet, despite the strong shape preferred orientation (SPO) observed. {110} [001] slip may dominate the deformation of rutile. Quartz displays complicated and inconsistent LPOs in eclogite. These results are remarkably similar to observations from deformed eclogites in nature.  相似文献   

5.
In an extensional shear zone in the Talea Ori, Crete, quartz veins occur in high-pressure low-temperature metamorphic sediments at sites of dilation along shear band boundaries, kink band boundaries and boudin necks. Bent elongate grains grown epitactically from the host rock with abundant fluid inclusion trails parallel to the vein wall indicate vein formation by crack-seal increments during dissolutionprecipitation creep of the host rock. The presence of sutured high-angle grain boundaries and subgrains shows that temperatures were sufficiently high for recovery and strain-induced grain boundary migration, i.e. higher than 300 -350℃, close to peak metamorphic conditions. The generally low amount of strain accumulated by dislocation creep in quartz of the host rock and most veins indicates low bulk stress conditions of a few tens of MPa on a long term. The time scale of stress-loading to cause cyclic cracking and sealing is assumed to be lower than the Maxwell relaxation time of the metasediments undergoing dissolution-precipitation creep at high strain rates(10-10 s-1 to 10-9 s-1), which is on the order of hundred years. In contrast, some veins discordant or concordant to the foliation show heterogeneous quartz microstructures with micro-shear zones, sub-basal deformation lamellae, shortwavelength undulatory extinction and recrystallized grains restricted to high strain zones. These microstructures indicate dislocation glide-controlled crystal-plastic deformation(low-temperature plasticity) at transient high stresses of a few hundred MPa with subsequent recovery and strain-induced grain boundary migration at relaxing stresses and temperatures of at least 300 -350℃. High differential stresses in rocks at greenschist-facies conditions that relieve stress by creep on the long term, requires fast stress-loading rates, presumably by seismic activity in the overlying upper crust. The time scale for stress loading is controlled by the duration of the slip event along a fault, i.e. a few seconds to minutes.This study demonstrates that microstructures can distinguish between deformation at internal low stress-loading rates(to tens of MPa on a time scale of hundred years) and high(coseismic) stress-loading rates to a few hundred MPa on a time scale of minutes.  相似文献   

6.
The role of aqueous fluid in fracturing in subducting slabs was investigated through a series of deformation experiments on dunite that was undersaturated (i.e., fluid-free) or saturated with water (i.e., aqueous-fluid bearing) at pressures of 1.0–1.8 GPa and temperatures of 670–1250 K, corresponding to the conditions of the shallower regions of the double seismic zone in slabs. In situ X-ray diffraction, radiography, and acoustic emissions (AEs) monitoring demonstrated that semi-brittle flow associated with AEs was dominant and the creep/failure strength of dunite was insensitive to the dissolved water content in olivine. In contrast, aqueous fluid drastically decreased the creep/failure strength of dunite (up to ~?1 GPa of weakening) over a wide range of temperatures in the semi-brittle regime. Weakening of the dunite by the aqueous fluid resulted in the reduction of the number of AE events (i.e., suppression of microcracking) and shortening of time to failure. The AE hypocenters were located at the margin of the deforming sample while the interior of the faulted sample was aseismic (i.e., aseismic semi-brittle flow) under water-saturated conditions. A faulting (slip rate of ~?10?3 to 10?4 s?1) associated with a large drop of stress (Δσ?~?0.5 to 1 GPa) and/or pressure (ΔP?~?0.5 GPa) was dominant in fluid-free dunite, while a slow faulting (slip rate?<?8?×?10?5 s?1) without any stress/pressure drop was common in water-saturated dunite. Aseismic semi-brittle flow may mimic silent ductile flow under water-saturated conditions in subducting slabs.  相似文献   

7.
The Anita Peridotite, in southwestern New Zealand, is a ∼1 × 20 km ultramafic massif that was rapidly extruded from beneath a Cretaceous arc within the 4 km wide mylonitic Anita Shear Zone. The peridotitic body contains a spectacular array of textures that preserve evidence for changing temperature, stress, and deformation mechanisms during the exhumation process. Olivine and orthopyroxene microstructures and lattice-preferred orientations (LPO) record a three-phase deformation history. Dislocation glide on the C- and E-type slip systems is recorded by coarse pre-mylonitised olivine grains, and occurred under hydrous conditions at T ∼650 °C, stress ∼200–700 MPa and strain rate ∼10−15 s−1, probably within hydrated sub-arc mantle lithosphere. Rare protomylonite pods record deformation by dislocation creep in porphyroclasts and dislocation-accommodated grain boundary sliding in the matrix on {0kl}[100] in olivine and (100)[001] in orthopyroxene, under conditions of T ∼730–770 °C, stress ∼52–700 MPa and strain rate ∼10−15 s−1. The massif, however, is dominated by mylonite and ultramylonite that wrap the protomylonite pods, comprising mostly fine-grained olivine neoblasts that lack internal distortions and have uniform LPOs. These textures indicate deformation occurred by grain-size sensitive (GSS) creep at T ∼650 °C, stress ∼69–137 MPa and strain rate ∼10−15 s−1, and thus during conditions of cooling and decreasing stress. GSS creep became more dominant with time, as the proportion of randomly-oriented neoblasts increased and formed interlinked networks that accommodated much of the strain. Grain boundary pinning allowed GSS creep to be maintained in polyphase regions, following mixing of olivine and orthopyroxene, which may have occurred by grain boundary transport in a fluid phase during a “creep cavitation” process. The results indicate that the Anita Peridotite recrystallised and underwent rheological weakening at a constant strain rate, with strain distributed across the entire section. This widespread deformation caused rapid exhumation of the peridotite from the lithospheric mantle into the overlying arc crust. The massif therefore records multiple overprinting phases of deformation under mantle and crustal conditions associated with the rapid exhumation of a large orogenic peridotite.  相似文献   

8.
The dehydration kinetics of serpentine was investigated using in situ high-temperature infrared microspectroscopy. The analyzed antigorite samples at room temperature show relatively sharp bands at around 3,655–3,660 cm?1 (band 1), 3,570–3,595 cm?1 (band 2), and 3,450–3,510 cm?1 (band 3). Band 1 corresponds to the Mg–OH bond, and bands 2 and 3 correspond to OH associated with the substitution of Al for Si. Isothermal kinetic heating experiments at temperatures ranging from 625 to 700 °C showed a systematic decrease of the OH band absorbance with heating duration. The one-dimensional diffusion was found to provide the best fit to the experimental data, and diffusion coefficients were determined with activation energies of 219 ± 37 kJ mol?1 for the total water band area, 245 ± 46 kJ mol?1 for band 1, 243 ± 57 kJ mol?1 for band 2, and 256 ± 53 kJ mol?1 for band 3. The results indicate that the dehydration process is controlled by one-dimensional diffusion through the tetrahedral geometry of serpentine. Fluid production rates during antigorite dehydration were calculated from kinetic data and range from 3 × 10?4 to 3 × 10?5  $ {\text{m}}_{\text{fluid}}^{ 3} \,{\text{m}}_{\text{rock}}^{ - 3} \,{\text{s}}^{ - 1} $ . The rates are high enough to provoke hydraulic rupture, since the relaxation rates of rocks are much lower than these values. The results suggest that the rapid dehydration of antigorite can trigger an intermediate-depth earthquake associated with a subducting slab.  相似文献   

9.
Calcium-free carbonate cancrinite with formula unit Na8.28[Al5.93Si6.07O24](CO3)0.93(OH)0.49·3.64H2O (CAN) has been synthesized under hydrothermal conditions. The product has been characterized by the methods of scanning electronic microscopy and energy dispersive X-ray analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis with FTIR of evolved gases (TGA–FTIR), and X-ray powder diffraction. The heat capacity of CAN has been measured from 6 to 259 K via low-temperature adiabatic calorimetry. A linear combination of Einstein functions has been used to approximate the obtained data on the heat capacity. The thermal contributions to the entropy and enthalpy of CAN in the temperature range 0–300 K have been calculated from these data. The heat capacity and third-law absolute entropy of CAN at 298.15 K are 1,047 ± 30 and 1,057 ± 35 J mol?1 K?1, respectively. High-temperature oxide-melt solution calorimetry has been used to determine the enthalpy of formation from elements of CAN at 298.15 K; the value equals ?14,684 ± 50 kJ mol?1. The Gibbs energy of formation from elements at 298.15 K has been calculated and totaled ?13,690 ± 51 kJ mol?1.  相似文献   

10.
This paper discusses in detail the deformation textures, glide system, petrofabrics and olivine dislocation microstructures of mantle peridotites at Yushigou in the North Qilian Mountains, northwestern China. The peridotites have undergone high-pressure, high-temperature and low-strain rate plastic flow deformation. According to the dynamic recrystallized-grain size of olivine and the average spacing between the dislocation walls as well as the chemical composition of enstatite, the authors calculated the rheological parameters of the ancient upper mantle in the study area as follows: temperatures 1025-1093℃; pressures 3043-4278 MPa; depths 95-132 km; deviatoric stress 28-32 MPa; strain rates 0.2×10-14-2.13×10-14s-1 and equivalent viscosities 0.45×1020-4.65×1020 Pa · s. These parameters suggest that the position where plastic flow took place was correspondent to the low-velocity zone beneath the oceanic lithosphere and that oceanization characterized by middle-velocity (1-3 cm/a) sea-floor spreadi  相似文献   

11.
The interdiffusion coefficient of Mg–Fe in olivine (D Mg–Fe) was obtained at 1,400–1,600 °C at the atmospheric pressure with the oxygen fugacity of 10?3.5–10?2 Pa using a diffusion couple technique. The D Mg–Fe shows the anisotropy (largest along the [001] direction and smallest along the [100] direction), and its activation energy (280–320 kJ/mol) is ~80–120 kJ/mol higher than that estimated at lower temperatures. The D Mg–Fe at temperatures of >1,400 °C can be explained by the cation-vacancy chemistry determined both by the Fe3+/Fe2+ equilibrium and by the intrinsic point defect formation with the formation enthalpy of 220–270 kJ/mol depending on the thermodynamical model for the Fe3+/Fe2+ equilibrium in olivine. The formation enthalpy of 220–270 kJ/mol for the point defect (cation vacancy) in olivine is consistent with that estimated from the Mg self-diffusion in Fe-free forsterite. The increase in the activation energy of D Mg–Fe at >1,400 °C is thus interpreted as the result of the transition of diffusion mechanism from the transition metal extrinsic domain to the intrinsic domain at the atmospheric pressure.  相似文献   

12.
Acacia nilotica was used for the adsorption of Reactive Black 5 (RB5) dye from an aqueous solution. Both the raw and activated (with H3PO4) carbon forms of Acacia nilotica (RAN and ANAC, respectively) were used for comparison. Various parameters (including dye concentration, contact time, temperature, and pH) were optimized to obtain the maximum adsorption capacity. RAN and ANAC were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The maximum experimental adsorption capacities for RAN and ANAC were 34.79 and 41.01 mg g?1, respectively, which agreed with the maximum adsorption capacities predicted by the Langmuir, Freundlich, and Dubinin–Radushkevich equilibrium isotherm models. The adsorption data of ANAC showed a good fit to the isotherm models based on the coefficient of determination (R 2): Langmuir type II (R 2 = 0.99) > Freundlich (R 2 = 0.9853) > Dubinin–Radushkevich (R 2 = 0.9659). This result suggested monolayer adsorption of RB5 dye. The adsorption of RB5 dye followed pseudo-second-order kinetics. The RAN adsorbent reflected an exothermic reaction (enthalpy change, ΔH = ?0.006 kJ mol?1) and increased randomness (standard entropy change, ΔS = 0.038 kJ mol?1) at the solid–solution interface. In contrast, ANAC reflected both exothermic [?0.011 kJ mol?1 (303–313 K)] and endothermic [0.003 kJ mol?1 (313–323 K)] reactions. However, the ΔS value of ANAC was lower when the RB5 adsorption increased from 313 to 323 K. The negative values for the Gibbs free energy change at all temperatures indicated that the adsorption of RB5 dye onto RAN and ANAC was spontaneous in the forward direction.  相似文献   

13.
Enthalpies and entropies of transition for the Mg2GeO4 olivine-spinel transformation have been determined from self-consistency analyses of Dachille and Roy's (1960), Hensen's (1977) and Shiota et al.'s (1981) phase boundary studies. When all three data sets are analyzed simultaneously,ΔH 973 andΔS 973 are constrained between ?14000 to ?15300 J mol?1 and ?13.0 to ?14.1·J mol?1 K?1, respectively. High-temperature solution calorimetric experiments completed on both polymorpha yield a value of ?14046±1366 J mol?1 forΔH 973. Kieffer-type lattice vibrational models of Mg2GeO4 olivine and spinel based on newly-measured infrared and Raman spectra predict a value of ?13.3±0.6 J mol?1 K?1 forΔS 1000. The excellent agreement between these three independent determinations ofΔH andΔS suggests that the synthesis runs of Shiota et al. (1981) at high pressures and temperatures bracket equilibrium conditions. In addition, no configurational disorder of Mg and Ge was needed to obtain the consistent parameters quoted. The Raman spectrum and X-ray diffractogram show that little disorder, if any, is present in Mg2GeO4 spinel synthesized at 0.2 GPa and 973–1048 K.  相似文献   

14.
We present new partition coefficients for various trace elements including Cl between olivine, pyroxenes, amphibole and coexisting chlorine-bearing aqueous fluid in a series of high-pressure experiments at 2 GPa between 900 and 1,300 °C in natural and synthetic systems. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA–ICP–MS. The chlorine and fluorine contents in mantle minerals were measured by electron microprobe, and the nature of OH defects was investigated by infrared spectroscopy. Furthermore, a fluorine-rich olivine from one selected sample was investigated by TEM. Results reveal average Cl concentrations in olivine and pyroxenes around 20 ppm and up to 900 ppm F in olivine, making olivine an important repository of halogens in the mantle. Chlorine is always incompatible with Cl partition coefficients D Cl olivine/fluid varying between 10?5 and 10?3, whereas D Cl orthopyroxene/fluid and D Cl clinopyroxene/fluid are ~10?4 and D Cl amphibole/fluid is ~5 × 10?3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered as D amph/fluid ≈ D cpx/fluid > D opx/fluid > D ol/fluid but that D mineral/fluid for Li and P is very similar for all observed silicate phases. Infrared spectra of olivine synthesized in a F-free Ti-bearing system show absorption bands at 3,525 and ~3,570 cm?1. In F ± TiO2-bearing systems, additional absorption bands appear at ~3,535, ~3,595, 3,640 and 3,670 cm?1. Absorption bands at ~3,530 and ~3,570 cm?1, previously assigned to humite-like point defects, profit from low synthesis temperatures and the presence of F. The presence of planar defects could not be proved by TEM investigations, but dislocations in the olivine lattice were observed and are suggested to be an important site for halogen incorporation in olivine.  相似文献   

15.
《International Geology Review》2012,54(10):1226-1245
Monzogabbro stocks including felsic enclaves (monzosyenite) around the Bafra (Samsun) area at the western edge of the Eastern Pontides cut Eocene-aged volcanic and sedimentary units. The monzogabbros contain plagioclase, alkali feldspar, clinopyroxene, olivine, hornblende, biotite, apatite, and iron-titanium oxides, whereas the felsic enclaves contain alkali feldspar, plagioclase, hornblende, biotite, clinopyroxene, and iron-titanium oxides. Mineral chemistry data suggest that magmas experienced hydrous and anhydrous crystallization in deep and shallow crustal magma chambers. Several thermobarometers were used to estimate temperatures of crystallization and emplacement for the mafic and felsic magmas. Clinopyroxene thermobarometry yielded 1100–1232 C and 5.9–8.1 kbar for monzogabbros, and 931–1109 C and 1.8–6.9 kbar for felsic enclaves. Hornblende thermobarometry and oxygen fugacity estimates reveal 739–971°C, 7.0–9.2 kbar and 10?9.71 for monzogabbros and 681–928°C, 3.0–6.1 kbar and 10?11.34 for felsic enclaves. Biotite thermobarometry shows elevated oxygen fugacity varying from 10?18.9–10?11.07 at 632–904°C and 1.29–1.89 kbar for monzogabbros, to 10?15.99 –10?11.82 at 719–873°C and 1.41–1.77 kbar for felsic enclaves. The estimated zircon and apatite saturation temperatures are 504–590°C and 693–730°C for monzogabbros and 765–775°C and 641–690°C for felsic enclaves, respectively. These data imply that several phases in the gabbroic and syenitic magmas did not necessarily crystallize simultaneously and further indicate that the mineral compositions may register intervals of disequilibrium crystallization. Besides, thermobarometry contrasts between monzogabbro and felsic enclave may be partly a consequence of extended interactions between the mafic and felsic magmas by mixing/mingling and diffusion. Additionally, the hot felsic magma was close to liquidus conditions (crystallinity < 30%) when injected into cooler mafic magma (crystallinity > 50%), and thus, the monzogabbro stocks reflect hybrid products from the mingling and incomplete mixing of these two magmas.  相似文献   

16.
Wadsleyite (β-(Mg,Fe)2SiO4) is a major constituent of the Earth's transition zone and is known to accommodate OH. The portion of the transition zone between 400–550 km could be an important source or sink for hydroxyl in plumes and slabs intersecting this region. Micro-infrared spectroscopy has been carried out on the β-phase and coexisting metastable olivine synthesized in a multianvil apparatus at 14 GPa and 1550–1650 K under hydrous conditions. Single-crystal and polycrystal specimens of both phases were analyzed in the 1800–8500 cm?1 frequency region to determine the speciation, abundances, and partitioning behavior of the hydrous components in coexisting β-phase and olivine. β-phase spectra consistently show three distinct OH bands at 3329, 3580, and 3615 cm?1. OH concentrations range from 10000–65000 H/106 Si. A strong positive correlation of grain size and extent of transformation with OH concentration in the β-phase indicates that grain-growth and transformation rates are enhanced in a hydrous environment. Olivine spectra are variable, but consistently show a prominent broad-band absorbance representing molecular H2O, consistent with the infrared signature of the starting material. OH concentrations in olivine range from <300–1400 H/106 Si. The highest OH concentrations measured for olivine and the β-phase may represent solubility limits, in which case the OH solubility ratio between these two phases is approximately 1∶40. Where both phases coexist and are undersaturated with OH, the partitioning ratio of OH between them is about 1∶100. The large solubility contrast between olivine and the β-phase suggests a mechanism for hydrating the transition zone via olivine carried down in subducting slabs. Plumes impinging on an OH-rich upper transition region could cause H2 or H2O to be released upon transformation of the β-phase to olivine, resulting in initiation of secondary upwellings. If dissolution of OH weakens the β-phase, and if OH is present in the mantle, the region between 400–550 km could be a zone of low viscosity.  相似文献   

17.
Electrical conductivity measurements on dry polycrystalline K-feldspar were performed at 1.0 to 3.0 GPa and 873 to 1,173 K with a multi-anvil high-pressure apparatus and the Solartron-1260 Impedance/Gain Phase Analyzer in the frequency range of 10?1 to 106 Hz. At each temperature the complex impedance displays a perfect semi-circular arc that represents the grain-interior conduction. Under the experimental conditions, electrical conductivity exponentially increases with increasing temperature and slightly decreases with increasing pressure; however, the effect of pressure on the conductivity is less pronounced than that of temperature. The activation enthalpy decreases slightly from 0.99 to 1.02 eV with increasing pressure, and the activation energy and activation volume for K-feldspar are 0.98 eV and 1.46?±?0.17 cm3/mol, respectively. According to these Arrhenius parameters, ionic conduction is proposed to be the dominant conduction mechanism in K-feldspar at high temperatures and pressures, and potassium ions are the charge carriers transporting by an interstitial mechanism. The diffusion coefficient of potassium at high temperatures was calculated from our conductivity data on K-feldspar using Nernst–Einstein equation, and the results were compared with the previous experimental results.  相似文献   

18.
Stress relaxation experiments were performed on hot-pressed cylinders of synthetic, polycrystalline galena at temperatures of 500°, 600°, 700° and 800°C at atmospheric pressure after various levels of axial strain, in the range from 2% to 25%, had been imposed at a constant strain rate (?) of 3×10?4 s?1. For this study a new apparatus was built which can measure small changes in applied stress (σ), better than ±0.5 × 105 Pa, and which incorporates a facility whereby the composition of the test specimen can be fixed through equilibration with a gas atmosphere of controlled composition. Deformation mechanism maps constructed largely on theoretical grounds predict that, under the conditions studied here, high-temperature dislocation creep, for which ?∝σ5, gives way on lowering the applied stress to diffusion creep, for which ?∝σ. The experimental results agree in large measure with these theoretical predictions. However, it is not possible in this preliminary study to conclusively identify the dominant deformation mechanisms.  相似文献   

19.
Carbon subsurface concentration profiles in olivine single crystals from San Carlos, Arizona, and the Sergebet Island. Red Sea, containing total carbon between 60–180 wt.-ppm, were analyzed by means of the 12C(d. p)13C nuclear reaction and by x-ray induced photoelectron spectroscopy (XPS) in combination with acid etching and with Ar+ ion sputtering respectively, between 200–930 K. The (d, p) analysis reveals equilibrium subsurface C profiles extending 1–2 μm or more into the bulk. Their steepness is a function of temperature. Typical mean C concentrations at 300 K in the resolvable layers, 0–0.6, 0.6–1.2, and 1.2–1.8 μm. are 1.8, and 0.6 wt.-%, corresponding to enrichment factors over the mean bulk C concentration of the order of 100, 40 and 30 respectively. In the topmost atomic layers analyzed by XPS the carbon is enriched by a factor of the order of 1000, decreasing with increasing temperature. The results suggest that the carbon is in a truly dissolved state and highly mobile, subject to a reversible subsurface segregation. Most probably local lattice strain associated with the solute C species provide the driving force for this diffusional process. The C diffusion coefficient was determined from the (d, p) data below 300 K: D= 10?13 exp(?7.8/RT) [m2· sec?1; KJ · mole?1] and from XPS data between 450–925 K: D = 10?14 exp(-6/RT) [m2 · sec?1; KJ · mole?1] The estimated error of the preexponential factors is ± one order of magnitude, that of the activation energies ±3.5 and ±2 KJ mole?1 respectively.  相似文献   

20.
The effect of alumina and water solubility on the development of fabric in orthopyroxene in response to simple shear deformation has been investigated at a pressure of 1.5 GPa and a temperature of 1,100 °C using the D-DIA apparatus. The microstructure observations at these conditions indicate that dislocation glide is the dominant deformation mechanism. In MgSiO3 enstatite and hydrous aluminous enstatite, partial dislocations bounding the stacking faults in [001] glide parallel to the (100) (or) the (100) [001] slip system. Electron backscattered diffraction analysis of anhydrous aluminous enstatite, however, indicates operation of the (010) [001] slip system, and microstructure analysis indicates dislocation movement involving [001] on both (100) and {210} planes. The strong covalent bonding induced by the occupation of M1 and T2 sites by Al could have restricted the glide on (100), activating slip on {210}. The resulting seismic anisotropies (~2 %) in orthopyroxene are weaker compared to olivine (~9.5 %), and reduced anisotropy can be expected if orthopyroxene coexists with olivine. Weak anisotropy observed in stable cratonic regions can be explained by the relatively high abundance of orthopyroxene in these rocks.  相似文献   

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