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1.
Dense sand-bentonite buffer ( γd = 1.67Mg/m3) has been proposed in Canada as one of several barriers for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: (1) isothermal consolidated undrained triaxial (CIU¯) tests; and (2) isothermal drained constant-p′ (CID) triaxial tests. Specimens were consolidated at effective stresses up to 9.0 MPa and temperatures up to 100°C. The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressqf, and higher pore water pressure changesΔuf. The net result is curved peak strength envelops in plots ofqf versuspf′ that are higher at elevated temperatures, even though the strengths,qf of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes. The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great. 相似文献
2.
Prior, D.B. and Graham, J., 1974. Landslides in the Magho district of Fermanagh Northern ireland. Eng. Geog., 8: 341–359. Rotational slumps, shallow debris slides and active shallow rotational slides are identified on slopes developed on rocks of Carboniferous Age. The rotational slides occur on shales which weather to produce a clay-rich soil. Direct shear tests give drained values ofφ′r = 8.2° andc′r = 5.0kN/m2. Conventional stability analyses suggest that the residual cohesion parameter is significant. Stability calculations are facilitated by the use of a dimensionless stability coefficient. 相似文献
3.
Experimental studies of synthetic and natural basalt systems suggest that conditions of magma genesis and fractionation depend fundamentally on mantle temperatures and lithospheric stress fields. In general, compressional settings are more conducive to polybaric fractionation than extensional settings and in this regard, the Anatolian magmatic province offers a natural laboratory for comparing near-coeval basalt eruptions as a function of regional tectonics — compressional (collision-related) régimes dominating in eastern Anatolia and extensional tectonics characterizing a western province related to Aegean Sea opening. Projection of Plio-Quaternary basalt normative compositions from the Western Anatolia Extensional Province (WAEP), the Central Anatolian ‘Ova’ Province (CAOP), and Eastern Anatolia Compressional Province (EACP) are projected onto Ol–Ne–Cpx and Pl–Cpx–Ol planes in the simplified basalt system (Ne–Cpx–Ol–Qz), each showing distinctive liquid lines of descent. WAEP basalts are mostly constrained by low-pressure (< 0.5 GPa) cotectics while CAOP and EACP compositions conform to moderate and/or high-pressure (0.8–3.0 GPa) cotectics. Overall, a quasi-linear shift from moderate and/or high-pressure to low-pressure equilibria matches the westward transgression from compressional east Anatolia to the extensional west Anatolian–Aegean region. Comparison of their respective primary (mantle-equilibrated) magmas–simulated by normalizing their compositions to MgO = 15 wt.% (Mg-15)–with parameterized anhydrous and H 2O-undersaturated experimental melts suggests they segregated from spinel- to garnet-lherzolite mantle facies at pressures between c. 2 and 3 GPa (c. 70–100 km depth) under H 2O-undersaturated conditions. Interpolated potential temperatures ( Tp) and lithospheric stretching factors ( β) range as follows: (1) eastern Anatolian basalts associated with the Arabian foreland show Tp varying between 1250 and 1400 °C (except for the Karacalidag alkali basalts, south of the Bitlis–Zagros fracture zone, for which Tp ranges up to 1450 °C), for β values of 1.2–1.8. Tp values for central Anatolia (e.g. Sivas) range between 1300 and 1375 °C (except for Karapinar, Egrikuyu and Hasandag, which show < 1150 °C), and β values of 1.3–1.4. For western Anatolian basalts, Tp range mostly between 1250 and 1330 °C, except for a single value for Canakkale of 1400 °C and Kula sample showing Tp < 1200 °C, and β values of 1.3–2.0. Variation of these conditions is as great or greater than that between provinces, although there are clearly significant constraints on the inferred polybaric to low-pressure isobaric fractionation régimes. Covariation of total FeO, TiO 2, La/Yb, Ce/Sm, Zr/Y and Zr/Nb reflects small but significant differences in bulk composition and ambient melt fraction while the covariance of Ce/Sm and Sm/Yb is consistent with the segregation of primitive melts at the spinel- to garnet-lherzolite transition. 相似文献
4.
The seismic characteristic of Hindukush–Pamir–Himalaya (HPH) and its vicinity is very peculiar and has experienced many widely distributed large earthquakes. Recent work on the time-dependent seismicity in the Hindukush–Pamir–Himalayas is mainly based on the so-called “regional time-predictable model”, which is expressed by the relation log T= cMp+ a, where T is the inter-event time between two successive main shocks of a region and Mp is the magnitude of the preceded main shock. Parameter a is a function of the magnitude of the minimum earthquake considered and of the tectonic loading and c is positive (0.3) constant. In 90% of the cases with sufficient data, parameter c was found to be positive, which strongly supports the validity of the model. In the present study, a different approach, which assumes no prior regionalization of the area, is attempted to check the validity of the model. Nine seismic sources were defined within the considered region and the inter-event time of strong shallow main shock were determined and used for each source in an attempt at long-term prediction, which show the clustering and occurrence of at least three earthquakes of magnitude 5.5≤ Ms≤7.5 giving two repeat times, satisfying the necessary and sufficient conditions of time-predictable model (TP model). Further, using the global applicability of the regional time- and magnitude-predictable model, the following relations have been obtained: log Tt=0.19 Mmin+0.52 Mp+0.29 log m0−10.63 and Mf=1.31 Mmin−0.60 Mp−0.72 log m0+21.01, where Tt is the inter-event time, measured in years; Mmin the surface wave magnitude of the smallest main shock considered; Mp the magnitude of preceding main shock; Mf the magnitude of the following main shock; and m0 the moment rate in each source per year. These relations may be used for seismic hazard assessment in the region. Based on these relations and taking into account the time of occurrence and the magnitude of the last main shock in each seismogenic source, time-dependent conditional probabilities for the occurrence of the next large (Ms≥5.5) shallow main shocks during the next 20 years as well as the magnitudes of the expected main shocks are determined. 相似文献
5.
The dissolution and precipitation rates of boehmite, AlOOH, at 100.3 °C and limited precipitation kinetics of gibbsite, Al(OH) 3, at 50.0 °C were measured in neutral to basic solutions at 0.1 molal ionic strength (NaCl + NaOH + NaAl(OH) 4) near-equilibrium using a pH-jump technique with a hydrogen-electrode concentration cell. This approach allowed relatively rapid reactions to be studied from under- and over-saturation by continuous in situ pH monitoring after addition of basic or acidic titrant, respectively, to a pre-equilibrated, well-stirred suspension of the solid powder. The magnitude of each perturbation was kept small to maintain near-equilibrium conditions. For the case of boehmite, multiple pH-jumps at different starting pHs from over- and under-saturated solutions gave the same observed, first order rate constant consistent with the simple or elementary reaction: . This relaxation technique allowed us to apply a steady-state approximation to the change in aluminum concentration within the overall principle of detailed balancing and gave a resulting mean rate constant, (2.2 ± 0.3) × 10−5 kg m−2 s−1, corresponding to a 1σ uncertainty of 15%, in good agreement with those obtained from the traditional approach of considering the rate of reaction as a function of saturation index. Using the more traditional treatment, all dissolution and precipitation data for boehmite at 100.3 °C were found to follow closely the simple rate expression: Rnet,boehmite=10-5.485{mOH-}{1-exp(ΔGr/RT)}, with Rnet in units of mol m−2 s−1. This is consistent with Transition State Theory for a reversible elementary reaction that is first order in OH− concentration involving a single critical activated complex. The relationship applies over the experimental ΔGr range of 0.4–5.5 kJ mol−1 for precipitation and −0.1 to −1.9 kJ mol−1 for dissolution, and the pHm ≡ −log(mH+) range of 6–9.6. The gibbsite precipitation data at 50 °C could also be treated adequately with the same model:Rnet,gibbsite=10-5.86{mOH-}{1-exp(ΔGr/RT)}, over a more limited experimental range of ΔGr (0.7–3.7 kJ mol−1) and pHm (8.2–9.7). 相似文献
6.
With the help of two-dimensional numerical models this paper investigates three aspects of heterogeneous deformation around rigid objects: (1) the nature of particle paths; (2) the development of strain shadow zones; and (3) the drag patterns of passive markers. In simple shear, spherical objects develop typically a concentric vortex motion, showing particle paths with an eye (double-bulge)-shaped separatrix. The separatrix has no finite dimension along the central line, parallel to the shear direction. Under a combination of pure shear and simple shear, the particle paths assume a pattern with a bow-tie shaped separatrix. With increase in the ratio of pure shear to simple shear ( Sr), the separatrix around the object shrinks in size. The axial ratio of the object ( R) is another important factor that controls the geometry of particle paths. When R<1.5, the loci of a particle close to the object form an elliptical shell with the long axis lying along the central line. With increase in axial ratio R, the loci form a doublet elliptical shell structure. Objects with R>3 do not show closed particle paths, but give rise to elliptical or circular spiral particle paths. The development of strain shadow zones against equant rigid bodies depends strongly on the strain ratio Sr. When Sr=0 (simple shear), they develop opposite to the extensional faces of the object, forming a typical σ-type tail. The structure has a tendency to die out with an increase in the pure shear component of the bulk deformation (Sr). The initial angle of the long axis of the object with the shear direction (φ) and the axial ratio of the object (R) determine the development of strain shadow zones near inequant rigid objects. Objects with large R and φ between 60 and 120° form pronounced zones of low finite strain, giving rise to strain shadow structures. A geometrical classification of diverse drag patterns of passive markers around rigid objects is presented along with their conditions of formation. 相似文献
8.
Mesozoic alkaline intrusive complexes are widespread in the southern portion of the North China Craton and can provide some important constraints on the evolution of the Mesozoic lithosphere beneath the region. Three selected intrusive complexes (Tongshi, Hongshan, and Longbaoshan) are generally high in alkalis (K 2O+Na 2O=913 wt.%) and Al 2O 3 (1421.6 wt.%) and low in CaO and TiO 2 (<0.6 wt.%), with high and variable SiO 2 contents. Rocks from these complexes are all enriched in LREE and LILE (Cs, Rb, Ba, U, Th), depleted in Nb and Ti, have a highly positive Pb anomaly, and are characterized by lack of a clear Eu anomaly despite trace element abundances and isotopic ratios that vary greatly between complexes. The Tongshi complex has high Cs (2.68.5 ppm) and REE abundances (∑REE=112.6297 ppm, (La/Yb) N=13.130.9) and MORB-like Sr–Nd–Pb isotopic ratios (( 87Sr/ 86Sr) i<0.704; εNd>0; ( 206Pb/ 204Pb) i>18). The Hongshan complex has low REE concentrations (∑REE=28.2118.7 ppm, (La/Yb) N=4.614.7) and is moderately enriched as demonstrated by their Sr–Nd isotopic ratios (( 87Sr/ 86Sr) i>0.706; εNd<−7). The Longbaoshan complex is extremely REE enriched (∑REE=211.3392.6 ppm, (La/Yb) N=32.460.9) and has an EM2-like Sr–Nd isotopic character (( 87Sr/ 86Sr) i>0.7078; εNd<−11). We suggest that the Tongshi complex originated from the asthenosphere and the Hongshan complex and the Longbaoshan complex were derived from the partial melting of previously subduction-modified lithospheric mantle, in response to post-collisional lithospheric extension and asthenospheric upwelling. The occurrence of these alkaline intrusive complexes demonstrates that the lithosphere beneath the region must have been considerably thinned at the time of intrusion of these complexes. This study also shed light on the temporal evolution of the Mesozoic lithosphere and the timing of the lithospheric thinning. 相似文献
9.
We present the results of a thrust fault reactivation study that has been carried out using analogue (sandbox) and numerical modelling techniques. The basement of the Pannonian basin is built up of Cretaceous nappe piles. Reactivation of these compressional structures and connected weakness zones is one of the prime agents governing Miocene formation and Quaternary deformation of the basin system. However, reactivation on thrust fault planes (average dip of ca. 30°) in normal or transtensional stress regimes is a problematic process in terms of rock mechanics. The aim of the investigation was to analyse how the different stress regimes (extension or strike-slip), and the geometrical as well as the mechanical parameters (dip and strike of the faults, frictional coefficients) effect the reactivation potential of pre-existing faults. Results of analogue modelling predict that thrust fault reactivation under pure extension is possible for fault dip angle larger than 45° with normal friction value (sand on sand) of the fault plane. By making the fault plane weaker, reactivation is possible down to 35° dip angle. These values are confirmed by the results of numerical modelling. Reactivation in transtensional manner can occur in a broad range of fault dip angle (from 35° to 20°) and strike angle (from 30° to 5° with respect to the direction of compression) when keeping the maximum horizontal stress magnitude approximately three times bigger than the vertical or the minimum horizontal stress values. Our research focussed on two selected study areas in the Pannonian basin system: the Danube basin and the Derecske trough in its western and eastern part, respectively. Their Miocene tectonic evolution and their fault reactivation pattern show considerable differences. The dominance of pure extension in the Danube basin vs. strike-slip faulting (transtension) in the Derecske trough is interpreted as a consequence of their different geodynamic position in the evolving Pannonian basin system. In addition, orientation of the pre-existing thrust fault systems with respect to the Early to Middle Miocene paleostress fields had a major influence on reactivation kinematics. As part of the collapsing east Alpine orogen, the area of the Danube basin was characterised by elevated topography and increased crustal thickness during the onset of rifting in the Pannonian basin. Consequently, an excess of gravitational potential energy resulted in extension (σv > σH) during Early Miocene basin formation. By the time topography and related crustal thickness variation relaxed (Middle Miocene), the stress field had rotated and the minimum horizontal stress axes (σh) became perpendicular to the main strike of the thrusts. The high topography and the rotation of σh could induce nearly pure extension (dip-slip faulting) along the pre-existing low-angle thrusts. On the contrary, the Derecske trough was situated near the Carpathian subduction belt, with lower crustal thickness and no pronounced topography. This resulted in much lower σv value than in the Danube basin. Moreover, the proximity of the retreating subduction slab provided low values of σh and the oblique orientation of the paleostress fields with respect to the master faults of the trough. This led to the dominance of strike-slip faulting in combination with extension and basin subsidence (transtension). 相似文献
10.
We analyze the interannual monthly variability of oxygen isotope ratios in data from IAEA stations along the Atlantic coast of South America between 23° and 34° S to evaluate the influence of parameters such as temperature, rainfall amount and moisture source contribution on meteoric water recharging two karst systems in subtropical Brazil. In addition, a 2 year monitoring program performed on soil and cave drip and rimstone pool waters from sampling sites with contrasting discharge values and located at 100 and 300 m below the surface in the Santana Cave System (24°31′ S; 48°43′ W), is used to test the influence of hydrologic and geologic features on the temporal variations of seepage water δ18O. Interannual monthly variations in δ18O of rainfall reflect primarily regional changes in moisture source contribution related to seasonal shifts in atmospheric circulation from a more monsoonal regime in summer (negative values of δ18O) to a more extratropical regime in winter (positive values of δ18O). Variations in groundwater δ18O indicate that the climatic signal of recent rainfall events is rapidly transmitted through the relatively deep karst aquifer to the cave drip waters, regardless of location of collection in the cave. In addition, the data also suggest that water replenishment in the system is triggered by the increase in hydraulic head during periods when recharge exceeds the storage capacity of the soil and epikarst reservoirs. Significant perturbations in the groundwater composition, characterized by more positive values of δ18O, are probably connected to an increased Atlantic moisture contribution associated with extratropical precipitation. This implies that the δ18O of speleothems from caves in this region may be a suitable proxy for studying tropical–extratropical interactions over South America, a feature that is intrinsically related to the global atmospheric circulation. 相似文献
11.
The abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplied with reduced carbon. A flow-through, fixed-bed laboratory reactor vessel, the Catalytic Reactor Vessel (CRV) system, has been developed to investigate mineral–surface promoted organic synthesis at temperatures up to 400°C and pressures up to 30 MPa, conditions relevant to seafloor hydrothermal systems. Here we present evidence that metastable methanol can be directly synthesized from a gas-rich CO 2–H 2–H 2O mixture in the presence of a mineral substrate. Experiments have been performed without a substrate, with quartz, and with a mixture of quartz and magnetite. Temperatures and pressures in the experiments ranged from 200°C to 350°C and from 15 to 18 MPa, respectively. Maximum conversion of 5.8×10 −4% CO 2 to CH 3OH per hour was measured using a mixture of magnetite and quartz in the reactor. After passivation of the stainless steel reactor vessel, experiments demonstrate that methanol is formed at temperatures up to 350°C in the presence of magnetite, and that the formation rate decreases over time. The experiments also show a loss of surface reactivity at 310°C and a regeneration of surface reactivity with increased temperature up to 350°C. Concentrations of CO 2 and H 2 used in the experiments simulate periodic, localized and dynamic conditions occurring within the seafloor during and immediately following magmatic diking events. High concentrations of CO 2 and H 2 may be generated by dike injection accompanied by exsolution of CO 2 and reaction of dissolved H 2O with FeO in the magma to form H 2. The experiments described here examine how the ephemeral formation of an H 2–CO 2-rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions. These experiments show that the presence of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such H 2O, CO 2 and H 2 under geologically realistic conditions. 相似文献
12.
In order to identify and characterise fluids associated with metamorphic rocks from the Chaves region (North Portugal), fluid inclusions were studied in quartz veinlets, concordant with the main foliation, in graphitic-rich and nongraphitic-rich lithologies from areas with distinct metamorphic grade. The study indicates multiple fluid circulation events with a variety of compositions, broadly within the C–H–O–N–salt system. Primary fluid inclusions in quartz contain low salinity aqueous–carbonic, H 2O–CH 4–N 2–NaCl fluids that were trapped near the peak of regional metamorphism, which occurred during or immediately after D2. The calculated P– T conditions for the western area of Chaves (CW) is P=300–350 MPa and T500 °C, and for the eastern area (CE), P=200–250 MPa and T=400–450 °C. A first generation of secondary fluid inclusions is restricted to discrete cracks at the grain boundaries of quartz and consists of low salinity aqueous–carbonic, H 2O–CO 2–CH 4–N 2–NaCl fluids. P– T conditions from the fluid inclusions indicate that they were trapped during a thermal event, probably related with the emplacement of the two-mica granites. A second generation of secondary inclusions occurs in intergranular fractures and is characterised by two types of aqueous inclusions. One type is a low salinity, H2O–NaCl fluid and the second consists of a high salinity, H2O–NaCl–CaCl2 fluid. These fluid inclusions are not related to the metamorphic process and have been trapped after D3 at relatively low P (hydrostatic)–T conditions (P<100 MPa and T<300 °C). Both the early H2O–CH4–N2–NaCl fluids in quartz from the graphitic-rich lithologies and the later H2O–CO2–CH4–N2–NaCl carbonic fluid in quartz from graphitic-rich and nongraphitic-rich lithologies seem to have a common origin and evolution. They have low salinity, probably resulting from connate waters that were diluted by the water released from mineral dehydration during metamorphism. Their main component is water, but the early H2O–CH4–N2–NaCl fluids are enriched in CH4 due to interaction with the C-rich host rocks. From the early H2O–CH4–N2–NaCl to the later aqueous–carbonic H2O–CO2–CH4–N2–NaCl fluids, there is an enrichment in CO2 that is more significant for the fluids associated with nongraphitic-rich lithologies. The aqueous–carbonic fluids, enriched in H2O and CH4, are primarily associated with graphitic-rich lithologies. However, the aqueous–carbonic CO2-rich fluids were found in both graphitic and nongraphitic-rich units from both the CW and CE studied areas, which are of medium and low metamorphic grade, respectively. 相似文献
13.
Dynamic compaction tests of bentonite-based materials (BBMs) with 100, 70 and 50% bentonite contents have been performed using five powdery bentonites with different physicochemical properties to establish the simplified evaluation method for dynamic compaction properties of BBMs. For a given bentonite content and a total compaction energy condition, the maximum dry density, ρdmax, and the optimum water content, wopt, which are well-known indexes of compaction properties, for BBMs were determined according to the type of bentonite used for BBMs. For evaluation of those values of BBMs derived in this study, the plastic limit of BBM, wpbbm, was defined as the plastic limit that was measured using the sample pulverized to a maximum grain size of less than 425 μm in the case of BBM with sand having a maximum grain size of more than 425 μm and was measured using the powdery bentonite itself in the case of BBM without sand. This study proposed equations for evaluating ρdmax and wopt of BBMs with more than 50% bentonite content under the total compaction energy conditions of 551–2755 kN-m/m 3 using wpbbm. Finally, we related the equations derived in this study to the equation for evaluating hydraulic properties of compacted BBMs proposed in previous work and proposed the preparation method of BBMs with more than 50% bentonite content for constructing BBM buffer by in-situ compaction method. 相似文献
14.
The process of shape-transformation of quartz inclusions from polyhedral to spherical grains in albite single crystals during metamorphism is mainly controlled by the grain boundary diffusion of oxygen along the quartz/albite interface to reduce the interfacial free energy. The rate of the process, which is represented by the growth rate of the curvature of the edge surface of the grain, depends significantly on temperature and on the grain size of the quartz inclusion. The relations between temperature, T, the time, tr, and the critical radius, Rc, which is equal to the radius of maximum spherical grains, are given by log Rc = −0.11 Eb/ RT + 0.25log tr + C, in which Eb is the activation energy of the grain boundary diffusion of oxygen along the quartz/albite interface and C is a material constant. The mean critical radius of spherical quartz inclusions in albite is 5 μm for the upper chlorite zone and garnet zone, 10 μm for the lower biotite zone, and 20 μm for the upper biotite zone in the Sambagawa metamorphic terrain. The mean values of the critical radii of spherical quartz inclusions in oligoclase of the Ryoke metamorphic rocks is about 5 μm for the chlorite zone and about 10–20 μm for the sillimanite zone. Assuming temperatures of about 350°C for the upper chlorite and garnet zones, 400°C for the lower biotite zone, 550°C for the upper biotite zone, and 700°C for the sillimanite zone, the activation energy for the grain boundary diffusion of oxygen along the quartz/plagioclase interfase is estimated to be about 30 kcal/mol. 相似文献
15.
Strontium chemical diffusion has been measured in albite and sanidine under dry, 1 atm, and QFM buffered conditions. Strontium oxide-aluminosilicate powdered sources were used to introduce the diffusant and Rutherford Backscattering Spectroscopy (RBS) used to measure diffusion profiles. For the 1 atm experiments, the following Arrhenius relations were obtained: Sanidine (Or61), temperature range 725–1075°C, diffusion normal to (001): D=8.4 exp(−450±13 kJ mol−1/RT) m2s−1. Albite (Or1), temperature range 675–1025°C, diffusion normal to (001): D=2.9 × exp(−224±11 kJ mol−1/RT) m2s−1. The alkali feldspars in this and earlier work display a broad range of activation energies for Sr diffusion, which may be a consequence of the thermodynamic non-ideality of the alkali feldspar system and/or the mixed alkali effect. 相似文献
16.
Grossular–wollastonite–scapolite calc–silicate granulites from Maligawila in the Buttala klippe, which form part of the overthrusted rocks of the Highland Complex of Sri Lanka, preserve a number of spectacular coronas and replacement textures that could be effectively used to infer their P–T–fluid history. These textures include coronas of garnet, garnet–quartz, and garnet–quartz–calcite at the grain boundaries of wollastonite, scapolite, and calcite as well as calcite–plagioclase and calcite–quartz symplectites or finer grains after scapolite and wollastonite respectively. Other textures include a double rind of coronal scapolite and coronal garnet between matrix garnet and calcite. The reactions that produced these coronas and replacement textures, except those involving clinopyroxene, are modelled in the CaO–Al 2O 3–SiO 2–CO 2 system using the reduced activities. Calculated examples of T– XCO2 and P– XCO2 projections indicate that the peak metamorphic temperature of about 900–875 °C at a pressure of 9 kbar and the peak metamorphic fluid composition is constrained to be low in XCO2 (0.1< XCO2<0.30). Interpretation of the textural features on the basis of the partial grids revealed that the calc–silicate granulites underwent high-temperature isobaric cooling, from about 900–875 °C to a temperature below 675 °C, following the peak metamorphism. The late-stage cooling was accompanied by an influx of hydrous fluids. The calc–silicate granulites provide evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex, earlier considered by some workers to be confined exclusively to the meta-igneous rocks. The coronal scapolite may have formed under open-system metasomatism. 相似文献
17.
About half the diamonds studied from the Cenozoic placer deposits along the Namibian coast belong to the peridotitic suite. The peridotitic mantle source is heterogeneous ranging from lherzolitic to strongly Ca depleted (down to 0.24 wt.% CaO in garnet) and shows large variations in Cr/Al ratio, illustrated by very low to very high Cr 2O 3 contents in garnet (2.6–17.3 wt.%). The Cr-rich end of this range includes exceptionally high Cr 2O 3 contents in Mg-chromite (70.7 wt.%) and clinopyroxene (3.6 wt.%). Garnet-olivine thermometry appears to indicate two groups, one that equilibrated at temperatures between 1200 and 1220°C and a second between 960 and 1100°C. Combined estimates of pressure and temperature based on garnet-orthopyroxene pairs indicate a large variance in geothermal gradients, corresponding to 38–42 mW/m 2 surface heat flow. The trace-element composition of peridotitic garnet inclusions (determined by SIMS) also indicates large diversity. Two principal groups, corresponding to different styles of metasomatic source enrichment, are recognized. The first group ranges from extremely LREEN-depleted patterns, through trough-shaped REEN to sinusoidal patterns with the position of the first peak gradually moving from the LREEN to the MREEN. This series of REE patterns is interpreted to reflect a range of metasomatic agents with decreasing LREE/HREE. Only in the case of the two garnets with REEN peaking at Sm–Eu is this process connected with enrichment in Zr, without significant introduction of Y and Ti. The metasomatism responsible is interpreted as reflecting percolation of CHO-fluids through harzburgite under sub-solidus conditions. A second group of garnets shows an increase from LREEN–MREEN and almost flat (lherzolitic garnet) to moderately declining MREEN–HREEN at super-chondritic levels. This second style of metasomatism is caused by an agent carrying HFSE and showing only moderate enrichment in LREE over HREE, which points towards silicate melts. 相似文献
18.
The paper gives an overview of the phase relations in carbonic fluid inclusions with pure, binary and ternary mixtures of the system CO 2–CH 4–N 2, compositions, which are frequently found in geological materials. Phase transitions involving liquid, gas and solid phases in the temperature range between −192°C and 31°C are discussed and presented in phase diagrams ( PT, TX and VX projections). These diagrams can be applied for the interpretation of microthermometry data in order to determine fluid composition and molar volume (or density). 相似文献
19.
Rhenium and osmium in organic-rich sedimentary rocks are dominantly hydrogenous, but any nonhydrogenous component will influence the accuracy and precision of the Re–Os date obtained. To minimize the influence of any nonhydrogenous Re and Os, we evaluate analysis of isolated organic matter from the whole rock, together with whole rock analysis using a CrO 3–H 2SO 4 digestion medium instead of inverse aqua regia, for a black shale unit of the Exshaw Formation, Canada. This unit previously returned a whole rock Re–Os date of 358±10 Ma (Model 3) [Geochim. Cosmochim. Acta (2002)] using inverse aqua regia dissolution. Organic matter isolated from the whole rock matrix using the HF–BF 3 technique [Org. Geochem. 20 (1993) 249] yields scattered data and a Re–Os date of 449±220 Ma (Model 3, MSWD=616). The organic matter analyses show similar 187Os/ 188Os values, but significantly lower 187Re/ 188Os values in comparison to the whole rock analyses. We show that the Re–Os systematics of organic matter are altered during chemical isolation, and as such we suggest that the HF–BF 3 method should not be used for Re–Os analysis of organic matter. Whole rock Re–Os analysis using a CrO 3–H 2SO 4 digestion medium yields significantly better regression analysis compared with the inverse aqua regia method, and the Re–Os data identify two distinct initial 187Os/ 188Os values for the sample set. Separate regressions of these data yield precise dates [366.1±9.6, MSWD=2.2 and 363.4±5.6 Ma, MSWD=1.6 (Model 3)], which are indistinguishable from the age constraints for this formation (363.4±0.4 Ma, U–Pb monazite). Comparison of the Re–Os dates obtained from aqua regia and CrO 3–H 2SO 4 methods suggests that the former may contain nonhydrogenous Re and Os, whereas the CrO 3–H 2SO 4 method dominantly liberates hydrogenous Re–Os from organic matter, allowing for better stratigraphic age determinations and evaluation of the Os isotope composition of seawater. 相似文献
20.
Several shales and oils ranging in age from 3 million to 2·7 billion years have been investigated for their hydrocarbon content using gas chromatography and mass spectrometry as primary analytical tools. From the Soudan Shale from Minnesota (2·7 × 10 9yr) the C 18, C 19, C 20 and C 21 isoprenoid-alkanes were obtained. The Antrim shale from Michigan (about 265 × 10 6 yr) yielded the C 16, C 18, C 19, C 20 and C 21 isoprenoids, as well as a C 16 iso-alkane and the C 18 and C 19 cyclohexyl n-alkanes. The San Joaquin Oil (30 × 10 6 yr) and the Abbott Rock Oil (3 × 10 6 yr) contained the C 16, C 18, C 19, C 20 and the C 18, C 19, C 20 and C 21 isoprenoids respectively. In addition, a series of iso-alkanes (C 16−C 18), anteiso-alkanes (C 16−C 18) and n-alkylcyclohexanes (C 16−C 19) as well as a C 21 isoprenoid were obtained from the Nonesuch Seep Oil (1 × 10 9 yr). This analysis provides a comprehensive picture of the types of biogenic hydrocarbons found in oils and shales of widely differing ages, and in particular, the finding of isoprenoid alkanes in the Soudan Shale furnishes evidence for life processes at that period of geological time. 相似文献
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