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1.
Elastic wave velocities for dense (99.8% of theoretical density) isotropic polycrystalline specimens of synthetic pyrope (Mg3Al2Si3O12) were measured to 1,000 K at 300 MPa by the phase comparison method of ultrasonic interferometry in an internally heated gas-medium apparatus. The temperature derivatives of the elastic moduli [(∂Ks/∂T) P = −19.3(4); (∂G/∂T) P = −10.4(2) MPa K−1] measured in this study are consistent with previous acoustic measurements on both synthetic polycrystalline pyrope in a DIA-type cubic anvil apparatus (Gwanmesia et al. in Phys Earth Planet Inter 155:179–190, 2006) and on a natural single crystal by the rectangular parallelepiped resonance (RPR; Suzuki and Anderson in J Phys Earth 31:125–138, 1983) method but |(∂Ks/∂T) P | is significantly larger than from a Brillouin spectroscopy study of single-crystal pyrope (Sinogeikin and Bass in Phys Earth Planet Inter 203:549–555, 2002). Alternative approaches to the retrieval of mixed derivatives of the elastic moduli from joint analysis of data from this study and from the solid-medium data of Gwanmesia et al. in Phys Earth Planet Inter 155:179–190 (2006) yield ∂2 G/∂P∂T = [0.07(12), 0.20(14)] × 10−3 K−1 and ∂2 K S /∂P∂T = [−0.20(24), 0.22(26)] × 10−3 K−1, both of order 10−4 K−1 and not significantly different from zero. More robust inference of the mixed derivatives will require solid-medium acoustic measurements of precision significantly better than 1%.  相似文献   

2.
The low-temperature heat capacity (C P) of stishovite (SiO2) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol−1 K−1, which is considerably smaller (by 2.86 J mol−1 K−1) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007).  相似文献   

3.
Laboratory tracer experiments were conducted to investigate longitudinal dispersivity (α x ) as well as the transversal (α y ) and vertical (α z ) dispersivities in homogeneous 3–5 mm sandy aquifer. The experiments were carried out in a channel 12-m long, 1.35-m wide and 0.60-m high which was built in the Hydraulics Laboratory of Civil Engineering Department in Dokuz Eylul University. NaCl was used as a tracer and conductivity values were measured at 220 measurement points. Mass Transport 3 Dimensional (Zheng and Wang in SERDP-99-1, US Army Engineer Research and Development Center, Vicksburg, MS, 1999; MT3DMS code) which is a three-dimensional solute transport simulation model incorporating finite differences solution option was used to solve the three-dimensional advective–dispersive transport equation. The estimated dispersivity values were modified until an acceptable compatibility between the observed and calculated concentrations at measurement points was reached. The best match was obtained for α x  = 12 cm, α y /α x  = 0.2 and α z /α x  = 0.05. These values are compatible with those encountered in the literature.  相似文献   

4.
In this study, an alternate approach to establish the e-log p relationships for clayey soils within a vertical pressure range of 10–1,000 kPa is discussed. Skempton’s compression index equation correlating the liquid limit, w L, and the compression index, C c, and the reported equation correlating the void ratio at liquid limit, e L, and the void ratio at a vertical pressure of 100 kPa, e 100, by Burland (1990), were used to establish the e-log p relationships for several reconstituted normally consolidated clayey soils. Consolidation test results of 13 clayey soils covering a sufficiently wide range of liquid limit were selected from the literature. Also, consolidation tests were carried out on two highly expansive soils in this study. A comparison of the experimental consolidation test results with the calculated e-log p relationships in the current study indicated that in general, the agreements between the calculated relationships and the experimental results are good. The agreements were found to be slightly better for soils with liquid limits less than about 70%. A comparison of the calculated e-log p relationships in the current study with that determined following methods suggested by Nagaraj and Srinivasa Murthy (1983) and Burland (1990) showed that all the three methods yielded very similar results for soils with liquid limit less than 70%. For soils with liquid limits greater than 70%, the difference between the e-log p relationships calculated in this study and that following Burland (1990)’s method was insignificant, whereas Nagaraj and Srinivasa Murthy (1983)’s method slightly over-predicted the void ratios at larger vertical stresses.  相似文献   

5.
The standard thermodynamic properties at 25°C, 1 bar (ΔG fo, ΔH fo, S o, C Po, V o, ω) and the coefficients of the revised Helgeson–Kirkham–Flowers equations of state were evaluated for several aqueous complexes formed by dissolved metals and either arsenate or arsenite ions. The guidelines of Shock and Helgeson (Geochim Cosmochim Acta 52:2009–2036, 1988) and Sverjensky et al. (Geochim Cosmochim Acta 61:1359–1412, 1997) were followed and corroborated with alternative approaches, whenever possible. The SUPCRT92 computer code was used to generate the log K of the destruction reactions of these metal–arsenate and metal–arsenite aqueous complexes at pressures and temperatures required by the EQ3/6 software package, version 7.2b. Apart from the AlAsO4o and FeAsO4o complexes, our log K at 25°C, 1 bar are in fair agreement with those of Whiting (MS Thesis, Colorado School of Mines, Golden, CO, 1992). Moreover, the equilibrium constants evaluated in this study are in good to fair agreement with those determined experimentally for the Ca–dihydroarsenate and Ca–hydroarsenate complexes at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) and for Fe(III)–hydroarsenate complex at 25°C (Raposo et al., J Sol Chem 35:79–94, 2006), whereas the disagreement with the log K measured for the Ca–arsenate complex at 40°C (Mironov et al., Russ J Inorg Chem 40:1690, 1995) might be due to uncertainties in this measured value. The implications of aqueous complexing between dissolved metals and arsenate/arsenite ions were investigated for seawater, high-temperature geothermal liquids and acid mine drainage and aqueous solutions deriving from mixing of acid mine waters and surface waters. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.  相似文献   

6.
Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) 18O/16O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233–262, 1997; Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010), these authors find variations in δ18Ool (~4.6–6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231–241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) speculate that δ18Ool values for La Palma olivine grains measured by LF (Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δ18Ool values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δ18Ool is weakly correlated (R 2 = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514–524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member δ18O values for HIMU-peridotite (δ18O = 5.3 ± 0.3 ‰) and depleted pyroxenite (δ18O = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226–234, 2011), there are significant differences in the predicted δ18O values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565–6589, 2010) proposed a mantle source for La Palma lavas with low-δ18O (<5 ‰), rather than higher-δ18O (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349–363, 2011). Here we question the approach of using weakly correlated variations in δ18Ool and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques.  相似文献   

7.
A 1-D velocity model for the Marche region (Central Italy) was computed by inverting P- and S-wave arrival times of local earthquakes. A total of 160 seismic events with a minimum of ten observations, a travel time residual ≤0.8 s and an azimuthal gap lower than 180° have been selected. This “minimum 1-D velocity model” is complemented by station corrections, which can be used to take into account possible near-surface velocity heterogeneities beneath each station. Using this new P-wave velocity model and the program HYPOELLIPSE (Lahr 1999), the selected local events were relocated. Earthquake locations in this study are of higher quality with respect to the original ones. The obtained minimum 1-D velocity model can be used to improve the routine earthquake locations and represents a further step towards more detailed seismotectonic studies of the area.  相似文献   

8.
We have experimentally determined the tracer diffusion coefficients (D*) of 44Ca and 26Mg in a natural diopside (~Di96) as function of crystallographic direction and temperature in the range of 950–1,150 °C at 1 bar and f(O2) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a–c and b–c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(26Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion “compensation relation”, converging to logD ~ −19.3 m2/s and T ~ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming that D* varies roughly linearly as a function of angle with respect to the c axis in the a–c plane, at least within a limited domain of ~20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(⊥(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient. We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca–Mg), on composition in the diopside–clinoenstatite mixture, using the available data on mixing property in this binary system. Our D*(Ca) values parallel to the c axis are about 1–1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca–Mg) values calculated from our data at 1,100–1,200 °C is ~0.6–0.7 log unit greater than the experimental quasibinary D((Ca–Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ~0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (~4 and ~6 cm3/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations.  相似文献   

9.
This paper presents a computer tool that automatically predicts mining subsidence using the generalized n-k-g influence function detailed in (González Nicieza et al. Int J Rock Mech Min Sci 42(3):372–387, 2005). This function depends on two physical concepts: the first is gravity, which characterizes the forces acting on the ground, and the second, the convergence of the roof and floor of the mine workings due to the stress state of the ground. The developed tool also allows other influence functions to be used to predict subsidence, namely the spatial influence function (Ramírez Oyanguren et al. 2000) and the normal-type classical (Knothe, Arch Gór Hut 1, 1952) and modified (González Nicieza et al. Bull Eng Geol Environ 66(3):319–329, 2007) time functions. Moreover, the inputting and periodic updating of data from subsidence monitoring surveys is controlled by one of the tool’s modules using a method that minimizes errors resulting from time discontinuities in landmarks measurements. In addition, when actual landmarks measurements exist, the developed tool allows calibration of the subsidence parameters, minimizing the errors between actual measurements and those obtained by prediction. The tool includes a viewer, developed using OpenGL, which enables the results of the calculations carried out to be viewed, allowing the point of view to be varied. It also includes the option of viewing and saving the results of the calculations carried out over the original topographic plane defined in the AutoCAD DXF data file format. The efficacy of the tool is demonstrated via its application to a real case of mining work carried out in a village in the Principality of Asturias, Spain.  相似文献   

10.
The return periods and occurrence probabilities related to medium and large earthquakes (M w 4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007. The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude M w 6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal heterogeneity and seismotectonics complexity in northeast India and adjoining regions.  相似文献   

11.
In coastal lowland plains, increased water demand on a limited water resource has resulted in declining groundwater levels, land subsidence and saltwater encroachment. In southwestern Kyushu, Japan, a sinking of the land surface due to over pumping of groundwater has long been recognized as a problem in the Shiroishi lowland plain. In this paper, an integrated model was established for the Shiroishi site using the modular finite difference groundwater flow model, MODFLOW, by McDonald and Harbaugh (1988) and the modular three-dimensional finite difference groundwater solute transport model, MT3D, by Zheng (1990) to simulate groundwater flow hydraulics, land subsidence, and solute transport in the alluvial lowland plain. Firstly, problems associated with these groundwater resources were discussed and then the established model was applied. The simulated results show that subsidence rapidly occurs throughout the area with the central prone in the center part of the plain. Moreover, seawater intrusion would be expected along the coast if the current rates of groundwater exploitation continue. Sensitivity analysis indicates that certain hydrogeologic parameters such as an inelastic storage coefficient of soil layers significantly contribute effects to both the rate and magnitude of consolidation. Monitoring the present salinization process is useful in determining possible threats to fresh groundwater supplies in the near future. In addition, the integrated numerical model is capable of simulating the regional trend of potentiometric levels, land subsidence and salt concentration. The study also suggests that during years of reduced surface-water availability, reduction of demand, increase in irrigation efficiency and the utilization of water exported from nearby basins are thought to be necessary for future development of the region to alleviate the effects due to pumping.  相似文献   

12.
Modern chemical sediments display a distinctive rare earth element + yttrium (REE + Y) pattern involving depleted LREE, positive La/La*SN, Eu/Eu*SN, and YSN anomalies (SN = shale normalised) that is related to precipitation from circumneutral to high pH waters with solution complexation of the REEs dominated by carbonate ions. This is often interpreted as reflecting precipitation from surface waters (usually marine). The oldest broadly accepted chemical sediments are c. 3,700 Ma amphibolite facies banded iron-formation (BIF) units in the Isua supracrustal belt, Greenland. Isua BIFs, including the BIF international reference material IF-G are generally considered to be seawater precipitates, and display these REE + Y patterns (Bolhar et al. in Earth Planet Sci Lett 222:43–60, 2004). Greenland Eoarchaean BIF metamorphosed up to granulite facies from several localities in the vicinity of Akilia (island), display REE + Y patterns identical to Isua BIF, consistent with an origin by chemical sedimentation from seawater and a paucity of clastic input. Furthermore, the much-debated magnetite-bearing siliceous unit of “earliest life” rocks (sample G91/26) from Akilia has the same REE + Y pattern. This suggests that sample G91/26 is also a chemical sediment, contrary to previous assertions (Bolhar et al. in Earth Planet Sci Lett 222:43–60, 2004), and including suggestions that the Akilia unit containing G91/26 consists entirely of silica-penetrated, metasomatised, mafic rock (Fedo and Whitehouse 2002a). Integration of our trace element data with those of Bolhar et al. (Earth Planet Sci Lett 222:43–60, 2004) demonstrates that Eoarchaean siliceous rocks in Greenland, with ages from 3.6 to 3.85 Ga, have diverse trace element signatures. There are now geographically-dispersed, widespread examples with Isua BIF-like REE + Y signatures, that are interpreted as chemically unaltered, albeit metamorphosed, chemical sediments. Other samples retain remnants of LREE depletion but are beginning to lose the distinct La, Eu and Y positive anomalies and are interpreted as metasomatised chemical sediments. Finally there are some siliceous samples with completely different trace element patterns that are interpreted as rocks of non-sedimentary origin, and include metasomatised mafic rocks. The positive La/La*SN, Eu/Eu*SN and YSN anomalies found in Isua BIFs and other Eoarchaean Greenland samples, such as G91/26 from Akilia, suggests that the processes of carbonate ion complexation controlling the REE − Y patterns were already established in the hydrosphere at the start of the sedimentary record 3,600–3,850 Ma ago. This is in accord with the presence of Eoarchaean siderite-bearing marbles of sedimentary origin, and suggests that CO2 may have been a significant greenhouse gas at that time.  相似文献   

13.
Arching is a well known phenomenon, which effects stress developments which were investigated and compared using analytical and numerical solutions. Marston’s (1930) solution was extended to a generalised 3-dimensional rectangular stope and later modified for square and circular stopes for comparison with FLAC results. Aubertin et al. (2003) & Li et al. (2003) models were improved significantly by placing the backfill within narrow stopes as lifts or layers in numerical modelling where the normal stress variation with depth were found to be more realistic. The FLAC results were compared with analytical solutions which were developed by previous researchers and modified by the authors to evaluate the arching effects in backfilled placed in narrow and circular stopes. It appeared from the investigation herein that δ = 0.67 ϕ and K = K o condition gives a very close match with the numerical model solutions obtained from FLAC. Many laboratory tests were conducted to find out friction angles for four Australian mines, which were between 30 and 49 degrees.  相似文献   

14.
Zr diffusion in titanite   总被引：2，自引：0，他引：2  
Chemical diffusion of Zr under anhydrous, pO2-buffered conditions has been measured in natural titanite. The source of diffusant was either zircon powder or a ZrO2–Al2O3–titanite mixture. Experiments were run in sealed silica glass capsules with solid buffers (to buffer at NNO or QFM). Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. The following Arrhenius parameters were obtained for Zr diffusion parallel to c over the temperature range 753–1,100°C under NNO-buffered conditions: D Zr = 5.33 × 10−7 exp(−325 ± 30 kJ mol−1/RT) m2 s−1 Diffusivities are similar for experiments buffered at QFM. These data suggest that titanite should be moderately retentive of Zr chemical signatures, with diffusivities slower than those for O and Pb in titanite, but faster than those for Sr and the REE. When applied in evaluation of the relative robustness of the recently developed Zr-in-titanite geothermometer (Hayden and Watson, Abstract, 16th V.M. Goldschmidt Conference 2006), these findings suggest that Zr concentrations in titanite will be less likely to be affected by later thermal disturbance than the geothermometer based on Zr concentrations in rutile (Zack et al. in Contrib Mineral Petrol 148:471–488, 2004; Watson et al. in Contrib Mineral. Petrol, 2006), but much less resistant to diffusional alteration subsequent to crystallization than the Ti-in-Zircon geothermometer (Watson and Harrison in Science 308:841–844, 2005).  相似文献   

15.
The comment by Day et al. (Contrib Mineral Petrol, 2012) (1) discusses the validity of the previously obtained oxygen isotope data for El Hierro and La Palma (Canary Island) olivines, (2) questions the approach by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) of using weakly correlated variations of δ18Oolivine values with X px (proportion of pyroxenite-derived melt in the parental magma), and (3) provides reasons why oxygen isotope data by secondary ion mass spectrometry (SIMS) “offer sensitive means for detecting melt-crust interactions.” We respond these comments and report a new set of oxygen isotope measurements performed by SIMS and single-grain laser fluorination methods. These measurements confirm our previous data and conclusions and demonstrate the ability of the SIMS technique to analyze O isotopes in terrestrial samples with 2-sigma uncertainty better than ±0.25 ‰.  相似文献   

16.
A well-characterized suite of vesuvianite samples from the volcanic ejecta (skarn or syenites) from Latium (Italy) was studied by single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy and secondary-ion mass-spectrometry (SIMS). OH-stretching FTIR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3,700–3,300 cm–1) and a very broad composite absorption below 3,300 cm–1. Measurements with E//c or Ec show that all bands are strongly polarized with maximum absorption for E//c. They are in agreement with previous band assignments (Groat et al. Can Mineral 33:609, 1995) to the two O(11)–H(1) and O(10)–H(2) groups in the structure. Pleochroic measurements with changing direction of the E vector of the incident radiation show that the orientation of the O(11)–H(1) dipole is OHc~35°, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at ~10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H2O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolini et al. in Am Mineral 87:1477, 2002) the SiO2 and FeO content of the matrix were assumed as the major factors to be considered at a first approximation in the selection of the standards for H. The lack of vesuvianite standards for quantitative SIMS analysis of H2O has been here overcome by selecting low-silica elbaite crystals (Ottolini et al. in Am Mineral 87:1477, 2002). The resulting integrated molar absorption FTIR coefficient for vesuvianite is i=100.000±2.000 l mol–1 cm–2. SIMS data for Li, B, F, Sr, Y, Be, Ba REE, U and Th are also provided in the paper.  相似文献   

17.
Analytical expressions for the variation in D La and D Yb with increasing liquid SiO2 for olivine, plagioclase, augite, hornblende, orthopyroxene, magnetite and ilmenite (Brophy in Contrib Mineral Petrol 2008, online first) have been combined with numerical models of hydrous partial melting, of mid-ocean ridge (MOR) cumulate gabbro melting, and fractional crystallization of slightly hydrous mid-ocean ridge basalt (MORB) magma to assess a melting versus fractionation origin for oceanic plagiogranite. For felsic magmas (>63 wt.% SiO2) the modeling predicts the following. MOR cumulate gabbro melting should yield constant or decreasing La and constant Yb abundances with increasing liquid SiO2. The overall abundances should be similar to those in associated mafic magmas. MORB fractional crystallization should yield steadily increasing La and Yb abundances with increasing SiO2 with overall abundances significantly higher than those in associated mafic magmas. Application to natural occurrences of oceanic plagiogranite indicate that both MOR cumulate gabbro melting and MORB fractionation are responsible. Application of the model results to Icelandic rhyolites strongly support a fractional crystallization rather than a crustal melting origin.  相似文献   

18.
A refined thermodynamic model of H2O and CO2 bearing cordierite based on recent data on volatile incorporation into cordierite (Thompson et al. in Contrib Mineral Petrol 142:107–118, 2001; Harley and Carrington in J Petrol 42:1595–1620, 2001) reflects non-ideality of channel H2O and CO2 mixing. The dependence of cordierite H2O and CO2 contents on P, T and equilibrium fluid composition has been calculated for the range 600–800°C and 200–800 MPa. It has been used for establishing thermodynamic conditions of cordierite formation and the following retrograde P–T paths of cordierite rocks from many localities. Estimates of the H2O and CO2 activities have shown that cordierites in granites, pegmatites and high-pressure granulites were formed in fluid-saturated conditions and wide range of H2O/CO2 relations. Very low cordierite H2O contents in many migmatites may be caused not only by fluid-undersaturated conditions at rock formation and H2O leakage on retrograde P–T paths but also by the presence of additional volatile components like CH4 and N2. The pressure dependence of cordierite-bearing mineral equilibria on fluid H2O/CO2 relations has been evaluated.  相似文献   

19.
Aquifer systems in tropical hard rock catchments generally comprise a sequence of three layers — an upper layer of weathered material (regolith), an intermediate zone of semi-weathered material and a basal zone of fresh, but often fractured, rocks. There is evidence that all three are hydraulically connected and for the purpose of this paper the three zones are referred to as ‘regolith-fractures aquifer’ (RFA). Field evidence is presented which shows that the bulk of the drawdown in boreholes in RFA systems is generally incurred during the early period of pumping — usually within 200 minutes of pump start-up. Well losses are an important part of this early drawdown and a judicious management of the pumping scheme during the early period could result in a reduction in the drawdown. One way of managing the pumping scheme is through phased pumping, whereby a desired total discharge (Q) is imposed in incremental steps (Q1, Q2, …, Q) during the early period of pumping (generally the first 200 to 300 minutes). This paper presents field data which shows reductions in drawdons arising from phased pumping during the early period.  相似文献   

20.
Experiments were performed in the system O–S–Fe–Ni designed to extend our understanding of the chemistry of sulfide liquids. Results indicate that adding nickel to Fe-rich sulfide liquids in equilibrium with silicate liquids extends their stability field to much higher oxygen fugacities and lower sulfur fugacities. Increasing Ni/Fe at a given temperature and sulfur and oxygen fugacity is accompanied by a significant decrease in the oxygen content of the sulfide liquid. Results of these experiments are combined with data from the literature to calibrate an associated regular solution model for O–S–Fe–Ni liquids. This model represents a complete refit of the associated regular solution model of Kress (Contrib Mineral Petrol 139:316–325, 2000). The resulting model is combined with the olivine solution model of Hirschmann (Am Mineral 76:1232–1248, 1991) to explore the effect of variations in oxygen and sulfur fugacities on the distribution of Fe and Ni between olivine and sulfide liquid. Predicted olivine–sulfide distribution trends parallel those observed by Gaetani and Grove (Geochim Cosmochim Acta 61:1829–1846, 1997), Gaetani and Grove (Earth Planet Sci Lett 169:147–163, 1999), Brenan and Caciagli (Geochim Cosmochim Acta 64:307–320, 2000) and Brenan (Geochim Cosmochim Acta 67:2663–2681, 2003), but are systematically offset toward lower predicted Ni in the sulfide. Nevertheless our results are consistent with the assertion that low K D os values in magmatic ore deposits such as the J-M Reef reflect high iron contents in the sulfides combined with relatively high oxygen fugacities.
Victor KressEmail:
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