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1.
To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10− 3 mm/s and 1.22 × 10− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes.  相似文献   

2.
D. Arcay  M.-P. Doin  E. Tric  R. Bousquet   《Tectonophysics》2007,441(1-4):27-45
At continental subduction initiation, the continental crust buoyancy may induce, first, a convergence slowdown, and second, a compressive stress increase that could lead to the forearc lithosphere rupture. Both processes could influence the slab surface P–T conditions, favoring on one side crust partial melting or on the opposite the formation of ultra-high pressure/low temperature (UHP-LT) mineral. We quantify these two effects by performing numerical simulations of subduction. Water transfers are computed as a function of slab dehydration/overlying mantle hydration reactions, and a strength decrease is imposed for hydrated mantle rocks. The model starts with an old oceanic plate ( 100 Ma) subducting for 145.5 Myr with a 5 cm/yr convergence rate. The arc lithosphere is thermally thinned between 100 km and 310 km away from the trench, due to small-scale convection occuring in the water-saturated mantle wedge. We test the influence of convergence slowdown by carrying on subduction with a decreased convergence rate (≤ 2 cm/yr). Surprisingly, the subduction slowdown yields not only a strong slab warming at great depth (> 80 km), but also a significant cooling of the forearc lithosphere at shallower depth. The convergence slowdown increases the subducted crust temperature at 90 km depth to 705 ± 62 °C, depending on the convergence rate reduction, and might thus favor the oceanic crust partial melting in presence of water. For subduction velocities ≤ 1 cm/yr, slab breakoff is triggered 20–32 Myr after slowdown onset, due to a drastic slab thermal weakening in the vicinity of the interplate plane base. At last, the rupture of the weakened forearc is simulated by imposing in the thinnest part of the overlying lithosphere a dipping weakness plane. For convergence with rates ≥ 1 cm/yr, the thinned forearc first shortens, then starts subducting along the slab surface. The forearc lithosphere subduction stops the slab surface warming by hot asthenosphere corner flow, and decreases in a first stage the slab surface temperature to 630 ± 20 °C at 80 km depth, in agreement with P–T range inferred from natural records of UHP-LT metamorphism. The subducted crust temperature is further reduced to 405 ± 10 °C for the crust directly buried below the subducting forearc. Such a cold thermal state at great depth has never been sampled in collision zones, suggesting that forearc subduction might not be always required to explain UHP-LT metamorphsim.  相似文献   

3.
Frictional sliding of gabbro gouge under hydrothermal conditions   总被引：12，自引：0，他引：12  
We investigated the frictional sliding behaviour of gabbro gouge under hydrothermal conditions. Experiments were performed on 1-mm-thick gabbro gouge sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) in a triaxial testing system with argon gas as the confining medium. In the first series, experiments were conducted under effective normal stresses of 200 MPa and 300 MPa respectively, with pore pressure of 10 MPa. For temperature over 400 °C, pore pressure of 30 MPa was also applied to implement supercritical water conditions. At temperatures up to 615 °C, slip rate steps ranging from 0.0488 μm/s to 1.22 μm/s were applied to obtain the rate dependence of friction.At 200 MPa effective normal stress and a pore pressure of 10 MPa, the steady state rate dependence a–b shows velocity-weakening behaviour for temperatures between  200 and  310 °C. The higher temperature limit for velocity-weakening behaviour to occur extends up to  510 °C under supercritical water conditions with a pore pressure of 30 MPa. For the limited sliding distance in our experiments, only velocity-strengthening behaviour occurred at 300 MPa effective normal stress. Considering the limited displacement (< 3.5 mm), velocity-weakening behaviour may not be excluded in the high effective normal stress case for temperature below  510 °C.The coefficient of friction shows an increasing trend with increasing temperature in the low temperature range. The cut-off temperatures for the increasing trend are  250 °C and  440 °C, respectively for the 200 MPa and 300 MPa effective normal stress cases. Above the cut-off temperatures, the coefficient of friction at 1.83 mm permanent displacement varies around an average of 0.73, which is identical to the average for the oven-dried case [He, C., Yao, W., Wang, Z., Zhou, Y., 2006. Strength and stability of frictional sliding of gabbro gouge at elevated temperatures. Tectonophysics 427, 217–229, doi:10.1016/j.tecto.2006.05.023]. Together with the small value of rate dependence (a–b < 0.0073) for the whole temperature range, these results indicate the absence of fluid-assisted creep.With the result of our experiments as a constraint on strength of frictional sliding, comparison between converted strength for strike–slip faults and creep strength of gabbro-like rocks implies fracturing and faulting behaviours in the lower crust of a cool area (Zhangbei) in North China.  相似文献   

4.
Apatite fission-track analysis was applied to Triassic and Cretaceous sediments from the South-Iberian Continental Margin to unravel its thermal history. Apatite fission-track age populations from Triassic samples indicate partial annealing and point to a maximum temperature of around 100–110 °C during their post-depositional evolution. In certain apatites from Cretaceous samples, two different fission-track age populations of 93–99 and around 180 Ma can be distinguished. Track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms. These thermal models indicate that the post-depositional thermal evolution attained temperatures ≤ 70 °C, which is consistent with available vitrinite-reflectance data. Thermal modelling for the Cretaceous samples makes it possible to decipher a succession of cooling and heating periods, consisting of (a) a late Carboniferous–Permian cooling followed by (b) a progressive heating episode that ended approximately 120 Ma at a maximum T of around 110 °C. The first cooling episode resulted from a combination of factors such as: the relaxation of the thermal anomaly related to the termination of the Hercynian cycle; the progressive exhumation of the Hercynian basement and the thermal subsidence related to the rifting of the Bay of Biscay, reactivated during the Late Permian. Jurassic thermal evolution deduced from the inherited thermal signal in the Cretaceous sediments is characterized by progressive heating that ended around 120 Ma. This heating episode is related to thermal subsidence during Jurassic rifting, in agreement with the presence of abundant mantle-derived tholeiitic magmas interbedded in the Jurassic rocks. The end of the Jurassic rifting is well marked by a cooling episode apparently starting during Neocomiam times and ending at surface conditions by Albian times.  相似文献   

5.
The Yenice–Gönen Fault (YGF) is one of the most important active tectonic structures in the Biga peninsula. On March 18, 1953, a destructive earthquake (Mw = 7.2) occurred on the YGF, which is considered to be a part of the southern branch of the North Anatolian Fault Zone (NAFZ). A 70 km-long dextral surface rupture formed during the Yenice–Gönen Earthquake (YGE).In this study, structural and palaeoseismological features of the YGF have been investigated. The YGF surface ruptures have been mapped and three trenches were excavated at Muratlar, Karaköy and Seyvan sites.According to the palaeoseismic interpretation and the results of 14C AMS dating, Seyvan trench shows that an earthquake of palaeoseismic age ca. 620 AD ruptured a different strand of the 1953 fault, producing rather significant surface rupture displacement, while there are indications that at least two older events occurred during the past millennia. Another set of trenches excavated near Gönen town (Muratlar village) revealed extensive liquefaction not only during the 1953 event, but also during a previous earthquake, dated at 1440 AD. The Karaköy trench shows no indications of recent reactivations.Based on the trenching results, we estimate a recurrence interval of 660 ± 160 years for large morphogenic earthquakes, creating linear surface ruptures. The maximum reported displacement during the 1953 earthquake was 4.2 m. Taking into account the palaeoseismologically determined earthquake recurrence interval and maximum displacement, slip-rate of the YGF has been calculated to be 6.3 mm/a, which is consistent with present-day velocities determined by GPS measurements. According to the geological investigations, cumulative displacement of the YGF is 2.3 km. This palaeoseismological study contributes to model the behaviour of large seismogenic faults in the Biga Peninsula.  相似文献   

6.
Heat flow and lithospheric thermal regime in the Northeast German Basin   总被引：3，自引：0，他引：3  
New values of surface heat flow are reported for 13 deep borehole locations in the Northeast German Basin (NEGB) ranging from 68 to 91 mW m− 2 with a mean of 77 ± 3 mW m− 2. The values are derived from continuous temperature logs, measured thermal conductivity, and log-derived radiogenic heat production. The heat-flow values are supposed free of effects from surface palaeoclimatic temperature variations, from regional as well as local fluid flow and from thermal refraction in the vicinity of salt structures and thus represent unperturbed crustal heat flow. Two-D numerical lithospheric thermal models are developed for a 500 km section along the DEKORP-BASIN 9601 deep seismic line across the basin with a north-eastward extension across the Tornquist Zone. A detailed conceptual model of crustal structure and composition, thermal conductivity, and heat production distribution is developed. Different boundary conditions for the thickness of thermal lithosphere were used to fit surface heat flow. The best fit is achieved with a thickness of thermal lithosphere of about 75 km beneath the NEGB. This estimate is corroborated by seismological studies and somewhat less than typical for stabilized Phanerozoic lithosphere. Modelled Moho temperatures in the basin are about 800 °C; heat flow from the mantle is about 35 to 40 mW m− 2. In the southernmost part of the section, beneath the Harz Mountains, higher Moho temperatures up to 900 to 1000 °C are shown. While the relatively high level of surface heat flow in the NEGB obviously is of longer wave length and related to lithosphere thickness, changes in crustal structure and composition are responsible for short-wave-length anomalies.  相似文献   

7.
The Ibituruna quartz-syenite was emplaced as a sill in the Ribeira-Araçuaí Neoproterozoic belt (Southeastern Brazil) during the last stages of the Gondwana supercontinent amalgamation. We have measured the Anisotropy of Magnetic Susceptibility (AMS) in samples from the Ibituruna sill to unravel its magnetic fabric that is regarded as a proxy for its magmatic fabric. A large magnetic anisotropy, dominantly due to magnetite, and a consistent magnetic fabric have been determined over the entire Ibituruna massif. The magmatic foliation and lineation are strikingly parallel to the solid-state mylonitic foliation and lineation measured in the country-rock. Altogether, these observations suggest that the Ibituruna sill was emplaced during the high temperature (~ 750 °C) regional deformation and was deformed before full solidification coherently with its country-rock. Unexpectedly, geochronological data suggest a rather different conclusion. LA-ICP-MS and SHRIMP ages of zircons from the Ibituruna quartz-syenite are in the range 530–535 Ma and LA-ICP-MS ages of zircons and monazites from synkinematic leucocratic veins in the country-rocks suggest a crystallization at ~ 570–580 Ma, i.e., an HT deformation > 35My older than the emplacement of the Ibituruna quartz-syenite. Conclusions from the structural and the geochronological studies are therefore conflicting. A possible explanation arises from 40Ar–39Ar thermochronology. We have dated amphiboles from the quartz-syenite, and amphiboles and biotites from the country-rock. Together with the ages of monazites and zircons in the country-rock, 40Ar–39Ar mineral ages suggest a very low cooling rate: < 3 °C/My between 570 and ~ 500 Ma and ~ 5 °C/My between 500 and 460 Ma. Assuming a protracted regional deformation consistent over tens of My, under such stable thermal conditions the fabric and microstructure of deformed rocks may remain almost unchanged even if they underwent and recorded strain pulses separated by long periods of time. This may be a characteristic of slow cooling “hot orogens” that rocks deformed at significantly different periods during the orogeny, but under roughly unchanged temperature conditions, may display almost indiscernible microstructure and fabric.  相似文献   

8.
Several goethites were obtained through the hydrolysis at 60 °C of Fe(III) solutions containing variable amounts of Mn(II) ions. The obtained samples were thermally treated at temperatures ranging from 180 to 310 °C until the complete phase transformation to hematite was achieved. The effect of Mn in the dehydroxylation process was investigated using X-ray diffraction (XRD) and the Rietveld refinement of XRD data together with scanning electron microscopy (SEM), differential thermogravimetric analysis (DTA) and Fourier transform infrared spectroscopy (FTIR). In all cases, the formed hematites retained the acicular shape of the precursor goethite. The dehydroxylation temperature increased with the increase of the Mn content in the parent goethite. The cell parameters of both phases decreased with the thermal treatment, however the decrease in the goethite b-parameter was more pronounced. This fact could be attributed to the distortion in the goethite structure by the presence of manganese. The band shifts in the FT-IR spectra of the goethites with different Mn substitution were analysed. The intensities of the hydroxyl vibrations were indicative of the degree of dehydroxylation.The chemical reactivity of all the samples, before and after the thermal treatment, was also studied. The kinetic experiments were carried out at 40 °C in 4 mol dm− 3 HCl. The acid dissolution of all Mn-goethites showed a congruent behavior indicative of a homogeneous distribution of Mn in the goethite crystals, this trend was not observed in the formed hematites presenting a high Mn content. The dissolution rate in goethites increased with the increase of Mn content, the opposite effect was observed in the corresponding hematites. The activation energy in both phases was also obtained and indicated that the Mn substitution produces an opposite effect on goethite- and hematite-phases. Different kinetic laws were applied in order to explain the dissolution behavior, but the modified first-order Kabai equation described the dissolution data best.  相似文献   

9.
The objective of the study was to characterize changes of reflectance, reflectance anisotropy and reflectance indicating surface (RIS) shape of vitrinite, sporinite and semifusinite subjected to thermal treatment under inert conditions. Examination was performed on vitrinite, liptinite and inertinite concentrates prepared from channel samples of steam coal (Rr = 0.70%) and coking coal (Rr = 1.25%), collected from seam 405 of the Upper Silesian Coal Basin. The concentrates were heated at temperatures of 400–1200 °C for 1 h time in an argon atmosphere.All components examined in this study: vitrinite, sporinite and semifusinite as well as matrix of vitrinite and liptinite cokes, despite of rank of their parent coal, show, in general, the most important changes of reflectance value and optical anisotropy when heated at 500 °C, 800 °C (with the exception of bireflectance value of sporinite) and 1200 °C.After heating the steam coal at 1200 °C, the vitrinite and the semifusinite reveal similar reflectances, whereas the latter a slightly stronger anisotropy. Sporinite and matrix of liptinite coke have lower reflectances but anisotropy (Rbi and Ram values) similar to those observed for vitrinite and semifusinite. However, at 1000 °C sporinite and matrix of liptinite coke have the highest reflectivity of the studied components. The RIS at 1200 °C is the same for all components.The optical properties of the three macerals in the coking coal become similar after heating at 1000 °C. Coke obtained at 1200 °C did not contain distinguishable vitrinite grains. At 1200 °C semifusinite and vitrinite coke matrix have highest Rr values among the examined components. Maximum reflectance (Rmax) reach similar values for vitrinite and sporinite, slightly lower for semifusinite. Matrix of liptinite coke and matrix of vitrinite coke have considerably stronger anisotropy (Rbi and Ram values) than other components. RIS at 1200 °C is also similar for all components.  相似文献   

10.
The integration of new and published geochronologic data with structural, magmatic/anatectic and pressure–temperature (P–T) process information allow the recognition of high-grade polymetamorphic granulites and associated high-grade shear zones in the Central Zone (CZ) of the Limpopo high-grade terrain in South Africa. Together, these two important features reflect a major high-grade D3/M3 event at ~ 2.02 Ga that overprinted the > 2.63 Ga high-grade Neoarchaean D2/M2 event, characterized by SW-plunging sheath folds. These major D2/M2 folds developed before ~ 2.63 Ga based on U–Pb zircon age data for precursors to leucocratic anatectic gneisses that cut the high-grade gneissic fabric. The D3/M3 shear event is accurately dated by U–Pb monazite (2017.1 ± 2.8 Ma) and PbSL garnet (2023 ± 11 Ma) age data obtained from syntectonic anatectic material, and from sheared metapelitic gneisses that were completely reworked during the high-grade shear event. The shear event was preceded by isobaric heating (P = ~ 6 kbar and T = ~ 670–780 °C), which resulted in the widespread formation of polymetamorphic granulites. Many efforts to date high-grade gneisses from the CZ using PbSL garnet dating resulted in a large spread of ages (~ 2.0–2.6 Ga) that reflect the polymetamorphic nature of these complexly deformed high-grade rocks.  相似文献   

11.
We have studied the paleomagnetism of the middle Cretaceous Iritono granite of the Abukuma massif in northeast Japan together with 40Ar–39Ar dating. Paleomagnetic samples were collected from ten sites of the Iritono granite (102 Ma 40Ar–39Ar age) and two sites of its associated gabbroic dikes. The samples were carefully subjected to alternating field and thermal demagnetizations and to rock magnetic analyses. Most of natural remanent magnetizations show mixtures of two components: (1) H component, high coercivity (Bc > 50–90 mT) or high blocking temperature (Tb > 350–560 °C) component and (2) L component, relatively low Bc or low Tb component. H component was obtained from all the 12 sites to give a mean direction of shallow inclination and northwesterly declination (I = 29.9°, D = 311.0°, α95 = 2.7°, N = 12). This direction is different from the geocentric axial dipole field at the present latitude (I = 56.5°) and the typical direction of the Cenozoic remagnetization in northeast Japan. Since rock magnetic properties indicate that the H component of the Iritono granite is carried mainly by magnetite inclusions in plagioclase, this component probably retains a primary one. Thus the shallow inclination indicates that the Abukuma massif was located at a low latitude (16.1 ± 1.6°N) about 100 Ma and then drifted northward by about 20° in latitude. The northwesterly deflection is attributed mostly to the counterclockwise rotation of northeast Japan due to Miocene opening of the Japan Sea. According to this model, the low-pressure and high-temperature (low-P/high-T) metamorphism of the Abukuma massif, which has been well known as a typical location, would have not occurred in the present location. On the other hand, the L component is carried mainly by pyrrhotite and its mean direction shows a moderate inclination and a northwesterly declination (I = 42.8°, D = 311.5°, α95 = 3.3°, N = 9). Since this direction is intermediate between the H component and early Cenozoic remagnetization in northeast Japan, some thermal event would have occurred at lower temperature than pyrrhotite Curie point ( 320 °C) during the middle Cretaceous to early Cenozoic time to have resulted in partial remagnetization.  相似文献   

12.
Phengite samples (2M 1 and 3T politypes) and a synthetic end-member muscovite specimen were studied by in situ high-temperature synchrotron radiation X-ray diffraction. The measured volume thermal expansion of 2M 1 phengite (<α V> ≈ 36.6 × 10−6 K−1) was systematically greater than <α V> of the 3T polytype (≈33.3 × 10−6 K−1). A positive linear correlation between the average thermal expansion on (001) plane and the mean tetrahedral rotation angle at ambient condition is proposed on the ground of new measurements and literature data. Dehydroxylation processes were observed in 2M 1, starting at 1,000 K in 3T at 800 and 945 K in synthetic muscovite. Rietveld refinements allowed a determination of structural variations upon heating of phengite samples and their dehydroxylate phases. The phengite structure expands by regularizing the tetrahedral sheet and by reducing the bond length differences between the outer and inner coordination shell of the interlayer site. The dehydroxylate phase derived from 2M 1 is characterized by fivefold polyhedra in the low temperature form as a consequence of two OH groups reacting to form H2O + O (residual). The dehydroxylate exhibits an increase of the cation–cation distances along the M–Or–M bonds with respect to low-temperature phengite structures. For the 3T phase, we were unable to achieve completion of dehydroxylation. The refined structural model of the dehydroxylate phase shows two hydroxyl sites, but at a short distance from one another. This result suggests that the dehydroxylation reaction did not proceed to completion. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

13.
The metamorphic evolution of a key sector of the western Mediterranean internal Alpine orogenic belt (southern Calabrian Peloritani Orogen) is identified and described by means of P–T pseudosections calculated for selected metapelite specimens, showing evidence of multi-stage metamorphism.Attention focused on the two lowermost basement nappes of the Aspromonte Massif (southern Calabria), which were differently affected by poly-orogenic multi-stage evolution. After a complete Variscan orogenic cycle, the upper unit (Aspromonte Peloritani Unit) was involved in a late-Alpine shearing event. In contrast, the several underlying metapelite slices, here grouped together as Lower Metapelite Group, show exclusive evidence of a complete Alpine orogenic cycle.In order to obtain reliable P–T constraints, an integrated approach was employed, based on: a) garnet isopleth thermobarometry; and b) theoretical predictions of the P–T stability fields of representative equilibrium assemblages. This approach, which takes into account the role of the local equilibrium volumes in controlling textural developments, yielded reliable information about P–T conditions from early to peak metamorphic stages, as well as estimates of the retrograde trajectory in the pseudosection P–T space.According to inferred detailed P–T paths, the evolution of the Aspromonte Peloritani Unit is characterised by a multi-stage Variscan cycle, subdivided into an early crustal thickening stage with P–T conditions ranging from 0.56 ± 0.05 GPa at 570 ± 10 °C to 0.63–0.93 GPa at 650–710 °C (peak conditions) and evolving to a later crustal thinning episode in lower P–T conditions (0.25 GPa at 540 °C), as documented by the retrograde trajectory.Conversely, the prograde evolution of the rocks of the Lower Metapelite Group shows evidence of a HP-LT early Alpine multi-stage cycle, with P–T evolving from 0.75–0.90 GPa at 510–530 °C towards peak conditions, with pressure increasing northwards from 1.12 ± 0.02 GPa to 1.24 ± 0.02 GPa, and temperatures of 540–570 °C.A late-Alpine mylonitic overprint affected the rocks of both the Aspromonte Peloritani Unit and the Lower Metapelite Group. This overprint was characterised by an initial retrograde decompression trajectory (0.75 ± 0.05 GPa at 570–600 °C), followed by a joint cooling history, ranging from 0.38 ± 0.14 at temperature from 450 to 520 °C.These inferred results were then used: a) to interpret the Lower Metapelite Group as a single crystalline basement unit exclusively affected by a complete Alpine orogenic cycle, according to the very similar features of P–T paths, comparable petrography and analogous structural characteristics; b) as a tool for more reliable correlations between the Aspromonte Massif, the other Calabrian terranes and the north African Orogenic Complexes. They may therefore consider a contribution to the geodynamic modelling of the western Mediterranean.  相似文献   

14.
Ilmenite separated from beach sands of Bangladesh was oxidized for 1 h at 950 °C and then reduced in charcoal for 4 h at 1050 °C. This was followed by leaching in 5% to 15% hydrochloric acid solution in temperature range of 30 to 75 °C for periods of up to 2 h. The results were compared with those obtained by leaching of ilmenite reduced without oxidizing. Oxidation prior to reduction of the ilmenite was found to increase both the extent and the rate of leaching. The residual iron contents after leaching were also found to be lower than that obtained for non-oxidized samples. The kinetic data of leaching of ilmenite reduced after oxidation was found to follow first order reaction model, i.e., G(α) = − ln(1 − α) up to an α value of 0.5 (i.e. up to 50% reduction) and then changed to spherical model, i.e., G(α) = [1 − (1 − α)]3. On the other hand, leaching of ilmenite reduced without oxidizing was found to follow the Ginstling-Brounshtein reaction, i.e., G(α) = 1 − (2/3)α − (1 − α)2/3 throughout the leaching process. Oxidation of ilmenite prior to reduction was also found to have decreased the activation energy of leaching from 43 kJ/mol, found for samples leached after reduction without oxidizing, to 30 kJ/mol.  相似文献   

15.
Glide systems of hematite single crystals in deformation experiments   总被引：1，自引：0，他引：1  
The critical resolved shear stresses (CRSSs) of hematite crystals were determined in compression tests for r-twinning, c-twinning and {a}<m>-slip in the temperature range 25 °C to 400 °C, at 400 MPa confining pressure, and a strain rate of 10− 5 s− 1 by Hennig-Michaeli, Ch., Siemes, H., 1982. Experimental deformation of hematile crstals betwen 25 °C and 400 °C at 400 MPa confining pressure. In: Schreyer, W. (Ed.) High Pressure Research in Geoscience, Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, p. 133–150. In the present contribution newly performed experiments on hematite single crystals at temperatures up to 800 °C at strain rates of 10− 5 s− 1 and 300 MPa confining pressure extends the knowledge about the CRSS of twin and slip modes. Optical observations, neutron diffraction goniometry, SEM forescatter electron images and electron backscatter diffraction are applied in order to identify the glide modes. Both twinning systems and {a}<m>-slip were confirmed by these methods. Besides the known glide systems the existence of the (c)<a>-slip system could be stated. Mechanical data establish that the CRSS of r-twinning decreases from 140 MPa at 25 °C to  5 MPa at 800 °C and for {a}<m>-slip from > 560 MPa at 25 °C to  40 MPa at 700 °C. At room temperature the CRSS for c-twinning is around 90 MPa and at 600 °C  60 MPa. The data indicate that the CRSSs above 200 °C seem to be between the values for r-twinning and {a}<m>-slip. For (c)<a>-slip only the CRSS at 600 °C could be evaluated to  60 MPa. Exact values are difficult to determine because other glide systems are always simultaneously activated.  相似文献   

16.
The Cobre–Babilonia vein system formed during a single major hydrothermal stage and is part of the Taxco district in Guerrero, southern Mexico. Homogenization and ice melting temperatures range from 160 to 290 °C and from − 11.6 to − 0.5 °C, respectively. We determined an approximate thermal gradient of 17 to 20 °C per 100 m using fluid inclusions. A thermal peak marked by the 290 °C isotherm is interpreted as a major feeder channel to the veins. The highest content of Zn + Pb in ore coincides with the 220 and 240 °C isotherms. Salinities of mineralizing fluids range from 0.8 to 15.6 wt.% NaCl equiv, and are distributed in two populations that can be related with barren or ore-bearing vein sections, with 0.8 to 6 wt.% NaCl equiv and 7 to 15.6 wt.% NaCl equiv, respectively. δ13C and δ18O water values from calcite from the Cobre–Babilonia vein system and the Esperanza Vieja and Guadalupe mantos range − 5.4‰ to − 10.4‰ and 9.9‰ to 13.4‰, respectively. δ34S values range from 0‰ to 3.2‰ and − 0.7‰ to − 4.3‰ in sphalerite, − 4‰ to 0.9‰ in pyrite, and − 1.4‰ to − 5.5‰ in galena. Both fluid inclusion and stable isotope data are compatible with magmatic and meteoric sources for mineralizing fluids. Also, sulfur isotope compositions suggest both magmatic and sedimentary sources for sulfur.  相似文献   

17.
Experimental studies concerning the dissolved air flotation (DAF) of fine (dp < 100 μm) quartz particles, using two different flotation cells (setups), are presented. Pure and well characterised quartz samples were treated with a commercial amine as collector prior to flotation and bubbles were characterised by the LTM-BSizer technique. Bubble size distribution showed 71% (by volume) and 94% (by number) of the bubbles having sizes (db) lower than 100 μm (i.e. microbubbles). The Sauter and arithmetic mean diameters were 79 μm and 56 μm, respectively, for the bubbles generated at 300 kPa (gauge) saturation pressure (after 30 minute saturation time). Quartz particle size distribution (obtained by laser diffraction) showed a volume-moment diameter of 13 μm. The Rosin–Rammler–Bennett, Gates–Gaudin–Schumann and log-normal distribution functions were well fitted (R2 > 0.96) to the bubble size distribution and quartz particle size distribution data. Values of total quartz recovery ranging from 6% to 53% (by mass) were obtained for the DAF experiments under different collector concentrations (up to 2 mg g− 1), with an optimal collector concentration found at 1 mg g− 1. These results are significant considering that 27% (by volume) of the quartz particles are ultrafine (dp < 5 μm), demonstrating the widely-known efficiency of DAF to remove small particles when applied in the field of water and wastewater treatment. The true flotation behaviour, as a function of particle diameter (dp), exhibits a local minimum when particles are approximately 3–5 μm in size. The results contribute to the discussion in the literature about the existence of such a minimum, which is generally interpreted as a change in the mechanism of particle collection from convection (collision) to diffusion at lower particle sizes.  相似文献   

18.
Aggregates composed of olivine and magnesiowüstite have been deformed to large strains at high pressure and temperature to investigate stress and strain partitioning, phase segregation and possible localization of deformation in a polyphase material. Samples with 20 vol.% of natural olivine and 80 vol.% of (Mg0.7Fe0.3)O were synthesized and deformed in a gas-medium torsion apparatus at temperatures of 1127 °C and 1250 °C, a confining pressure of 300 MPa and constant angular displacement rates equivalent to constant shear strain rates of 1–3.3 × 10− 4 s− 1. The samples deformed homogeneously to total shear strains of up to γ  15. During constant strain rate measurements the flow stress remained approximately stable at 1250 °C while it progressively decreased after the initial yield stress at the lower temperature. Mechanical data, microstructures and textures indicate that both phases were deforming in the dislocation creep regime. The weaker component, magnesiowüstite, controlled the rheological behavior of the bulk material and accommodated most of the strain. Deformation and dynamic recrystallization lead to grain refinement and to textures that were not previously observed in pure magnesiowüstite and may have developed due to the presence of the second phase. At 1127 °C, olivine grains behaved as semi-rigid inclusions rotating in a viscous matrix. At 1250 °C, some olivine grains remained largely undeformed while deformation and recrystallization of other grains oriented for a-slip on (010) resulted in a weak foliation and a texture typical for pure dry olivine aggregates. Both a-slip and c-slip on (010) were activated in olivine even though the nominal stresses were up to 2 orders of magnitude lower than those needed to activate these slip systems in pure olivine at the same conditions.  相似文献   

19.
The thermal dehydroxylation of a goethite-carbonate solid solution was studied with combined Fourier-transform infrared (FTIR)-Temperature programmed desorption (TPD) experiments. The TPD data revealed dehydroxylation peaks involving the intrinsic dehydroxylation of goethite at 560 K and a low temperature peak at 485 K which was shown to be associated to the release of non-stoichiometric water from the goethite bulk and surface. The FTIR and the TPD data of goethite in the absence of adsorbed carbonate species revealed the presence of adventitious carbonate mostly sequestered in the goethite bulk. The release of carbonate was however not only related to the dehydration of goethite but also from the crystallization of hematite at temperatures exceeding 600 K. The relative abundance of surface hydroxyls was shown to change systematically upon goethite dehydroxylation with a preferential stripping of singly-coordinated OH sites followed by a dramatic change in the dominance of the different surface hydroxyls upon the formation of hematite.  相似文献   

20.
Burial depth, cumulative displacement, and peak temperature of frictional heat of a fault system are estimated by thermal analysis in the fold–thrust belt of the Western Foothills complex, western Taiwan based on the vitrinite reflectance technique. The regional thermal structure across the complex reveals that the rocks were exposed to maximum temperatures ranging from 100 °C to 180 °C, which corresponds to a burial depth of 3.7–6.7 km. A large thermal difference of 90 °C were observed at the Shuilikeng fault which make the eastern boundary of the fold–thrust belt where it is in contact with metamorphic rock of Hsuehshan Range. The large thermal difference corresponds to cumulative displacements on the Shuilikeng fault estimated to be in the range of 5.2–6.9 km. However, thermal differences in across the Shuangtung and Chelungpu faults cannot be determined apparently due to small vertical offsets. The large displacement observed across the Shuilikeng fault is absent at the other faults which are interpreted to be younger faults within the piggyback thrust system. Localized high temperatures adjacent to fault zones were observed in core samples penetrating the Chelungpu fault. Three major fracture zones were observed at core lengths of 225 m, 330 m, and 405 m and the two lower zones which comprise dark gray narrow shear zones. A value of vitrinite reflectance of 1.8%, higher than the background value of 0.8%, is limited at a narrow shear zone of 1 cm thickness at the fracture zone at 330 m. The estimated peak temperature in the range of 550–680 °C in the shear zone is far higher than the background temperature of 130 °C, and it is interpreted as due to frictional heating during seismic faulting.  相似文献   

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