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1.
Natural springs have been reliable sources of domestic water and have allowed for the development of recreational facilities and resorts in the Central Appalachians. The structural history of this area is complex and it is unknown whether these natural springs receive significant recharge from modern precipitation or whether they discharge old water recharged over geological times scales. The main objective of this study was to use stable isotopes of water ( $\delta^{18} {\text{O}}_{{{\text{H}}_{2} {\text{O}}}}$ and $\delta^{2} {\text{H}}_{{{\text{H}}_{2} {\text{O}}}}$ ), dissolved inorganic carbon ( $\delta^{13} {\text{C}}_{\text{DIC}}$ ) and dissolved sulfate ( $\delta^{34} {\text{S}}_{{{\text{SO}}_{4} }}$ and $\delta^{18} {\text{O}}_{{{\text{SO}}_{4} }}$ ) to delineate sources of water, carbon and sulfur in several natural springs of the region. Our preliminary isotope data indicate that all springs are being recharged by modern precipitation. The oxygen isotope composition indicates that waters in thermal springs did not encounter the high temperatures required for O isotope exchange between the water and silicate/carbonate minerals, and/or the residence time of water in the aquifers was short due to high flow rates. The carbon isotopic composition of dissolved inorganic carbon and sulfur/oxygen isotopic composition of dissolved sulfate provide evidence of low-temperature water–rock interactions and various biogeochemical transformations these waters have undergone along their flow path.  相似文献   

2.
A detailed hydrogeochemical study of groundwater in the Cecina coastal plain (Livorno province, Italy) and its inner sectors was undertaken in 2008, as chemical analyses carried out on groundwater since 2006 have revealed Cr(VI) concentrations of up to 49 μg/L (well above the permissible limit of 5 μg/L). Ophiolite outcrops are present throughout the study area, and their fragments likely represent a significant portion of the existing multilayered aquifer skeleton. Waters delivered by the serpentinite outcrops have a typically Mg–HCO3 composition, whereas those of the coastal plain are prevailingly of the Ca/Mg–HCO3 type with significant Mg contents. Significant NO3 contamination characterises the studied coastal plain, and an interesting negative correlation exists between Cr(VI) and both NO3 and SO4 deriving from the widespread use of (NH4)2SO4 as a farm fertilizer. Chromium speciation calculations carried out using the EQ3NR code reveal that the prevailing Cr(VI) species in solution is CrO4 2?; however, CaCrO4° and MgCrO4° neutral complexes represent significant percentages (up to 42 %). These findings suggest that the mobility and consequently the bioavailability of Cr(VI) can be significantly enhanced by these neutral complexes, which are not considered to be affected by adsorption/desorption processes. The Cr(VI) source, investigated by means of the Mg/SiO2 molar ratio, seems to be represented mainly by Mg-bearing minerals of the chlorite group. Petrographic observations confirm the occurrence of this mineral group. The interaction between rainwater and the local serpentinite rock was simulated at different $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ conditions by reaction path modelling using the EQ3/6 software package. $P_{{{\text{O}}_{ 2} }}$ was varied in accordance with the assumption that redox conditions are determined in part by NO3. Results are in good agreement with experimental data on spring waters and subordinately with data on some coastal plain groundwater, which plot in a rather wide $P_{{{\text{CO}}_{ 2} }}$ and $P_{{{\text{O}}_{ 2} }}$ field. Although the dissolved Cr content is mostly of natural origin, fertilization may affect its fate.  相似文献   

3.
This study presents accurate and precise iron isotopic data for 16 co-magmatic rocks and 6 pyroxene–magnetite pairs from the classic, tholeiitic Red Hill sill in southern Tasmania. The intrusion exhibits a vertical continuum of compositions created by in situ fractional crystallisation of a single injection of magma in a closed igneous system and, as such, constitutes a natural laboratory amenable to determining the causes of Fe isotope fractionation in magmatic rocks. Early fractionation of pyroxenes and plagioclase, under conditions closed to oxygen exchange, gives rise to an iron enrichment trend and an increase in $ f_{{{\text{O}}_{2} }} $ of the melt relative to the Fayalite–Magnetite–Quartz (FMQ) buffer. Enrichment in Fe3+/ΣFemelt is mirrored by δ57Fe, where VIFe2+-bearing pyroxenes partition 57Fe-depleted iron, defining an equilibrium pyroxene-melt fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{px}} - {\text{melt}}}} \le - 0.25\,\permille \times 10^{6} /T^{2} $ . Upon magnetite saturation, the $ f_{{{\text{O}}_{2} }} $ and δ57Fe of the melt fall, commensurate with the sequestration of the oxidised, 57Fe-enriched iron into magnetite, quantified as $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{melt}}}} = + 0.20\,\permille \times 10^{6} /T^{2} $ . Pyroxene–magnetite pairs reveal an equilibrium fractionation factor of $ \Updelta^{57} {\text{Fe}}_{{{\text{mtn}} - {\text{px}}}} \approx + 0.30\,\permille $ at 900–1,000?°C. Iron isotopes in differentiated magmas suggest that they may act as an indicator of their oxidation state and tectonic setting.  相似文献   

4.
In order to evaluate the effect of trace and minor elements (e.g., P, Y, and the REEs) on the high-temperature solubility of Ti in zircon (zrc), we conducted 31 experiments on a series of synthetic and natural granitic compositions [enriched in TiO2 and ZrO2; Al/(Na + K) molar ~1.2] at a pressure of 10 kbar and temperatures of ~1,400 to 1,200 °C. Thirty of the experiments produced zircon-saturated glasses, of which 22 are also saturated in rutile (rt). In seven experiments, quenched glasses coexist with quartz (qtz). SiO2 contents of the quenched liquids range from 68.5 to 82.3 wt% (volatile free), and water concentrations are 0.4–7.0 wt%. TiO2 contents of the rutile-saturated quenched melts are positively correlated with run temperature. Glass ZrO2 concentrations (0.2–1.2 wt%; volatile free) also show a broad positive correlation with run temperature and, at a given T, are strongly correlated with the parameter (Na + K + 2Ca)/(Si·Al) (all in cation fractions). Mole fraction of ZrO2 in rutile $ \left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) $ in the quartz-saturated runs coupled with other 10-kbar qtz-saturated experimental data from the literature (total temperature range of ~1,400 to 675 °C) yields the following temperature-dependent expression: $ {\text{ln}}\left( {\mathop X\nolimits_{{{\text{ZrO}}_{ 2} }}^{\text{rt}} } \right) + {\text{ln}}\left( {a_{{{\text{SiO}}_{2} }} } \right) = 2.638(149) - 9969(190)/T({\text{K}}) $ , where silica activity $ a_{{{\text{SiO}}_{2} }} $ in either the coexisting silica polymorph or a silica-undersaturated melt is referenced to α-quartz at the P and T of each experiment and the best-fit coefficients and their uncertainties (values in parentheses) reflect uncertainties in T and $ \mathop X\nolimits_{{{\text{ZrO}}_{2} }}^{\text{rt}} $ . NanoSIMS measurements of Ti in zircon overgrowths in the experiments yield values of ~100 to 800 ppm; Ti concentrations in zircon are positively correlated with temperature. Coupled with values for $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ for each experiment, zircon Ti concentrations (ppm) can be related to temperature over the range of ~1,400 to 1,200 °C by the expression: $ \ln \left( {\text{Ti ppm}} \right)^{\text{zrc}} + \ln \left( {a_{{{\text{SiO}}_{2} }} } \right) - \ln \left( {a_{{{\text{TiO}}_{2} }} } \right) = 13.84\left( {71} \right) - 12590\left( {1124} \right)/T\left( {\text{K}} \right) $ . After accounting for differences in $ a_{{{\text{SiO}}_{2} }} $ and $ a_{{{\text{TiO}}_{2} }} $ , Ti contents of zircon from experiments run with bulk compositions based on the natural granite overlap with the concentrations measured on zircon from experiments using the synthetic bulk compositions. Coupled with data from the literature, this suggests that at T ≥ 1,100 °C, natural levels of minor and trace elements in “granitic” melts do not appear to influence the solubility of Ti in zircon. Whether this is true at magmatic temperatures of crustal hydrous silica-rich liquids (e.g., 800–700 °C) remains to be demonstrated. Finally, measured $ D_{\text{Ti}}^{{{\text{zrc}}/{\text{melt}}}} $ values (calculated on a weight basis) from the experiments presented here are 0.007–0.01, relatively independent of temperature, and broadly consistent with values determined from natural zircon and silica-rich glass pairs.  相似文献   

5.
We present new equilibrium mixed-volatile (H2O–CO2) solubility data for a phonotephrite from Erebus volcano, Antarctica. H2O–CO2-saturated experiments were conducted at 400–700 MPa, 1,190 °C, and ~NNO + 1 in non-end-loaded piston cylinders. Equilibrium H2O–CO2 fluid compositions were determined using low-temperature vacuum manometry, and the volatile and major element compositions of the glassy run products were determined by Fourier transform infrared spectroscopy and electron microprobe. Results show that the phonotephrite used in this study will dissolve ~0.8 wt% CO2 at 700 MPa and a fluid composition of $ X_{{{\text{H}}_{ 2} {\text{O}}}} $ ~0.4, in agreement with previous experimental studies on mafic alkaline rocks. Furthermore, the dissolution of CO2 at moderate to high $ X_{{{\text{H}}_{ 2} {\text{O}}}}^{\text{fluid}} $ in our experiments exceeds that predicted using lower-pressure experiments on similar melts from the literature, suggesting a departure from Henrian behavior of volatiles in the melt at pressures above 400 MPa. With these data, we place new constraints on the modeling of Erebus melt inclusion and gas emission data and thus the interpretation of its magma plumbing system and the contributions of primitive magmas to passive and explosive degassing from the Erebus phonolite lava lake.  相似文献   

6.
Property and behaviour of sand–pile interface are crucial to shaft resistance of piles. Dilation or contraction of the interface soil induces change in normal stress, which in turn influences the shear stress mobilised at the interface. Although previous studies have demonstrated this mechanism by laboratory tests and numerical simulations, the interface responses are not analysed systematically in terms of soil state (i.e. density and stress level). The objective of this study is to understand and quantify any increase in normal stress of different pile–soil interfaces when they are subjected to loading and stress relief. Distinct element modelling was carried out. Input parameters and modelling procedure were verified by experimental data from laboratory element tests. Parametric simulations of shearbox tests were conducted under the constant normal stiffness, constant normal load and constant volume boundary conditions. Key parameters including initial normal stress ( $ \sigma_{{{\text{n}}0}}^{\prime } $ ), initial void ratio (e 0), normal stiffness constraining the interface and loading–unloading stress history were investigated. It is shown that mobilised stress ratio ( $ \tau /\sigma_{\text{n}}^{\prime } $ ) and normal stress increment ( $ \Updelta \sigma_{\text{n}}^{\prime } $ ) on a given interface are governed by $ \sigma_{{{\text{n}}0}}^{\prime } $ and e 0. An increase in $ \sigma_{{{\text{n}}0}}^{\prime } $ from 100 to 400 kPa leads to a 30 % reduction in $ \Updelta \sigma_{\text{n}}^{\prime } $ . An increase in e 0 from 0.18 to 0.30 reduces $ \Updelta \sigma_{\text{n}}^{\prime } $ by more than 90 %, and therefore, shaft resistance is much lower for piles in loose sands. A unique relationship between $ \Updelta \sigma_{\text{n}}^{\prime } $ and normal stiffness is established for different soil states. It can be applied to assess the shaft resistance of piles in soils with different densities and subjected to loading and stress relief. Fairly good agreement is obtained between the calculated shaft resistance based on the proposed relationship and the measured results in centrifuge model tests.  相似文献   

7.
Single crystals of two novel calcium oxotellurate(IV) nitrates were grown under hydrothermal conditions and were structurally characterized by X-ray diffraction. Ca $_5$ Te $_4\text {O}_{12}$ (NO $_3$ ) $_2$ (H $_2$ O) $_2$ [ $Cc$ , $Z=4$ , $a=25.258(3)$ Å, $b=5.7289(7)$ Å, $c=17.0066(19)$ Å, $\beta =124.377(2)^{\circ}$ , $R[F^2 > 2\sigma (F^2)]=0.043$ , 4083 $F^2$ data, 281 parameters] can be described as a non-classic order/disorder (OD) structure, which fulfills the basic principle of OD theory, viz. local equivalence of polytypes, but does not strictly follow the vicinity condition (VC) of OD theory. The structure is made up from an alternating stacking of non-polar layers composed of isolated [TeO $_3$ ] units and Ca $^{2+}$ ions and polar layers containing NO $_3^-$ ions and water molecules. The electron lone-pairs of the [TeO $_3$ ] units protrude into the free space of the anion/water layers. The crystal under investigation was a non-classic OD-twin of domains of a maximum degree of order (MDO). At the twin plane a fragment of the second MDO polytype is located. The main building blocks of Ca $_6$ Te $_5\text {O}_{15}$ (NO $_3$ ) $_2$ [ $P2_1/c$ , $Z=4$ , $a=15.494(2)$ Å, $b=5.6145(7)$ Å, $c=39.338(4)$ Å, $\beta =142.480(5)^{\circ}$ , $R[F^2 > 2\sigma (F^2)]=0.043$ , 3026 $F^2$ data, 307 parameters] are isolated [TeO $_3$ ] units and Ca $^{2+}$ ions which are connected to a three-dimensional framework perforated by channels in which the N atoms of the nitrate anions are located and the electron lone-pairs of the [TeO $_3$ ] units protrude. The structure can topologically be derived from the structure of Ca $_5$ Te $_4\text {O}_{12}$ (NO $_3$ ) $_2$ (H $_2$ O) $_2$ by removing the water molecules and connecting the CaTeO $_3$ layers with additional [TeO $_3$ ] units and Ca $^{2+}$ ions.  相似文献   

8.
Oxygen fugacity ( $ f_{{{\text{O}}_{ 2} }} $ f O 2 ) is a fundamental but little known intensive variable in mantle processes. It influences the P/T position of a mantle solidus and the composition of mantle-derived melts and fluids and constrains mantle-core equilibria and a number of geophysical properties of the mantle. An important source of information on oxidation states is the ferric–ferrous iron ratio in mantle spinels. Since the magnetite component is low in mantle spinels, normal analytical errors translate into considerable $ f_{{{\text{O}}_{ 2} }} $ f O 2 uncertainties. In this study, we analyzed the Fe3+–Fetot ratio of chromites present as inclusions in diamond and other mantle-related occurrences by point-source Mössbauer spectroscopy using single-crystal absorbers as well as conventional Mössbauer spectroscopy using powder absorbers. The studied spinels have been previously analyzed by single-crystal X-ray diffraction and electron microprobe. The ferric–ferrous ratios found are normally similar to the different techniques apart from some samples where a large number of grains have been used for the analyses (powder absorbers). The general agreement between the different techniques allows us to conclude that the studied chromites are stoichiometric. However, conventional Mössbauer spectroscopy on powder absorbers should be conducted with great care, since the method requires a relatively large amount of sample material. Spinel frequently occurs as small grains, and the large number of crystals required may possess different degrees of oxidation/alteration and, consequently, different ferric–ferrous ratio leading to possible errors in the interpretation of the results.  相似文献   

9.
Spectral ratios of teleseismic P waves for 15 deep (>200 km) earthquakes recorded at 146 High-Sensitivity Seismographic Network stations in the Kanto district and its surrounding area, eastern Japan, were inverted for attenuation parameter $ t_P^{ * } $ . The dataset consisted of good-quality vertical-component seismograms, whose P phases were handpicked. The P wave spectral ratios with high signal-to-noise ratios were calculated up to 1 Hz for all the station pairs, linear regressed, and then inverted for $ t_P^{ * } $ using the technique of least squares . The result showed that the active volcanic areas were clearly characterized by high $ t_P^{ * } $ . In contrast, $ t_P^{ * } $ varied in the nonvolcanic areas. The present result on the $ t_P^{ * } $ distribution was roughly consistent with the shallow part (<30 km) of an attenuation structure, which has been previously obtained based on 3-D tomography by using records of high-frequency (around 5 Hz) P waves from local earthquakes. This suggested that the present method of $ t_P^{ * } $ estimation is valid. The advantage and possible application to other areas were also discussed.  相似文献   

10.
Macroscopic behavior of expansive soil is governed by surface forces rather than gravitational forces. These physicochemical surface forces can be investigated through two electromagnetic properties in response to an applied electromagnetic field as real (relative) permittivity, κ′, and effective (electrical) conductivity, σ. This paper presents the results of dielectric measurements on four natural expansive soils using 1–100 MHz electromagnetic waves in two different test setups. The equipment setup, calibration process and measurement limitations are evaluated, and the dielectric spectra, in terms of the dispersion of real permittivity/effective conductivity with frequency, are presented. A procedure is presented to quantify the thickness of a fully developed diffuse double layer (DDL). The influence of salt concentration on DDL, as well as the dielectric responses, is assessed. Two parameters of special physical meaning are defined in the article: ${\upkappa} _{{{\text{inf}}}}^{\prime }$ , representative of the dielectric response by sample mineralogy, microstructure and saturation ratio, and σdc, combining the roles assumed by both surface conduction and pore fluid conduction. Evaluation is attempted on their magnitudes at the optimum compaction state and evolutions at different one-dimensional deforming stages. Extensive analysis is performed on the roles of ${\upkappa} _{{{\text{inf}}}}^{\prime }$ and σdc on the hydration status and structural anisotropy of an oedometer sample.  相似文献   

11.
Precious metals accompany all types of epithermal deposits. In general, the largest of these deposits occur in intrusive or extrusive rocks of alkaline or calc-alkaline affinity. The Apigania Bay vein system and Au–Ag mineralization is hosted in Mesozoic marbles and schists, and is composed primarily of five nearly parallel, high-angle quartz veins that extend for at least 200 m. Gold–silver mineralization, in association with more than thirty ore and vein minerals, is developed in three stages and occurs at the contact of marbles and schists. Zones of epidote–chlorite–calcite and sericite–albite alteration are associated with precious metal-bearing milky and clear quartz veins. Fluid inclusion studies suggest that hydrothermal mineralization was deposited under hydrostatic pressures of ~100 bars, at temperature of 120–235°C, from low to moderate, calcium-bearing, saline fluids of 0.2 to 6.8 equiv. wt.% NaCl. Calculated isotope compositions (δ18O?=??4.7‰ to 1.7‰ and δD?=??120‰ to ?80‰) for waters in equilibrium with milky and clear quartz are consistent with mixing with dilute, low temperature meteoric ore fluids. Calculated δ 13CCO2 (0.6‰ to 1.1‰) and δ 34SH2S (?7.3 to ?0.3‰) compositions of the ore fluids indicate exchange, in an open system, with a metasedimentary source. Gold and silver deposition was associated with degassing of hydrogen due to intense uplift of the mineralizing area. The physicochemical conditions of mineralization stages I to III range between 200°C and 150°C, $f_{{\text{S}}_2 } = 10^{ - 18.1} $ to 10?16.8, $f_{{\text{O}}_2 } = 10^{ - 44.0} $ to 10?41.5, pH?=?6.9 to7.6, $f_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 3.4} $ to 10?2.6 and $a_{{\text{H}}_{\text{2}} {\text{S}}} = 10^{ - 2.7} $ to 10?2.6. Apigania Bay could be possibly considered the latest evolutional phase of Tinos hydrothermal system.  相似文献   

12.
Sr- and Ca-rich waylandite, $ {\left( {{\hbox{B}}{{\hbox{i}}_{0.{54}}}{\hbox{S}}{{\hbox{r}}_{0.{31}}}{\hbox{C}}{{\hbox{a}}_{0.{25}}}{{\hbox{K}}_{0.0{1}}}{\hbox{B}}{{\hbox{a}}_{0.0{1}}}} \right)_{\Sigma 1.12}}{{\hbox{H}}_{0.{18}}}{\left( {{\hbox{A}}{{\hbox{l}}_{{2}.{96}}}{\hbox{C}}{{\hbox{u}}_{0.0{2}}}} \right)_{\Sigma 2.98}}{\left[ {{{\left( {{{\hbox{P}}_{0.{97}}}{{\hbox{S}}_{0.0{3}}}{\hbox{S}}{{\hbox{i}}_{0.0{1}}}} \right)}_{\Sigma 1.00}}{{\hbox{O}}_4}} \right]_2}{\left( {\hbox{OH}} \right)_6} $ , from Wheal Remfry, Cornwall, United Kingdom has been investigated by single-crystal X-ray diffraction and electron microprobe analyses. Waylandite crystallises in space group R $ \overline 3 $ ? m, with the cell parameters: a?=?7.0059(7) Å, c?=?16.3431(12) Å and V?=?694.69(11) Å3. The crystal structure has been refined to R 1?=?3.76%. Waylandite has an alunite-type structure comprised of a rhombohedral stacking of (001) composite layers of corner-shared AlO6 octahedra and PO4 tetrahedra, with (Bi,Sr,Ca) atoms occupying icosahedrally coordinated sites between the layers.  相似文献   

13.
Magnesiowüstite, (Mg0.08Fe0.88)O, and wüstite, Fe0.94O, were compressed to ~36?GPa at ambient temperature in the diamond anvil cell (DAC) at the Advanced Light Source. X-ray diffraction patterns were taken in situ in radial geometry in order to study the evolution of crystallographic preferred orientation through the cubic-to-rhombohedral phase transition. Under uniaxial stress in the DAC, {100}c planes aligned perpendicular to the compression direction. The {100}c in cubic became { $\left\{ {10\bar 14} \right\}$ }r in rhombohedral and remained aligned perpendicular to the compression direction. However, the {101}c and {111}c planes in the cubic phase split into { ${10{\bar{1}}4}$ }r and { ${11{\bar{2}}0}$ }r, and (0001)r and { ${10{\bar{1}}1}$ }r, respectively, in the rhombohedral phase. The { ${11{\bar{2}}0}$ }r planes preferentially aligned perpendicular to the compression direction while { ${10{\bar{1}}4}$ }r oriented at a low angle to the compression direction. Similarly, { ${10{\bar{1}}1}$ }r showed a slight preference to align more closely perpendicular to the compression direction than (0001)r. This variant selection may occur because the 〈 ${10{\bar{1}}4}$ 〉r and [0001]r directions are the softer of the two sets of directions. The rhombohedral texture distortion may also be due to subsequent deformation. Indeed, polycrystal plasticity simulations indicate that for preferred { ${10{\bar{1}}4}$ }〈 ${1{\bar{2}}10}$ 〉r and { ${11{\bar{2}}0}$ }〈 ${{\bar{1}}101}$ 〉r slip and slightly less active { ${10{\bar{1}}1}$ }〈 ${{\bar{1}}2{\bar{1}}0}$ 〉r slip, the observed texture pattern can be obtained.  相似文献   

14.
Groundwater-level data from an aquifer test utilizing four pumped wells conducted in the South Pasco wellfield in Pasco County, Florida, USA, were analyzed to determine the anisotropic transmissivity tensor, storativity, and leakance in the vicinity of the wellfield. A weighted least-squares procedure was used to analyze drawdowns measured at eight observation wells, and it was determined that the major axis of transmissivity extends approximately from north to south and the minor axis extends approximately from west to east with an angle of anisotropy equal to N4.54°W. The transmissivity along the major axis ${\left( {T_{{\xi \xi }} } \right)}$ is 14,019 m2 day–1, and the transmissivity along the minor axis ${\left( {T_{{\eta \eta }} } \right)}$ is 4,303 m2 day–1. The equivalent transmissivity $T_{e} = {\left( {T_{{\xi \xi }} T_{{\eta \eta }} } \right)}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-0em} 2}} = 7,767{{\text{m}}^{2} } \mathord{\left/ {\vphantom {{{\text{m}}^{2} } {{\text{day}}^{{ - {\text{1}}}} }}} \right. \kern-0em} {{\text{day}}^{{ - {\text{1}}}} }$ , and the ratio of anisotropy is 3.26. The storativity of the aquifer is 7.52?×?10?4, and the leakance of the overlying confining unit is 1.37?×?10?4 day?1. The anisotropic properties determined for the South Pasco wellfield in this investigation confirm the results of previous aquifer tests conducted in the wellfield and help to quantify the NW–SE to NE–SW trends for regional fracture patterns and inferred solution-enhanced flow zones in west-central Florida.  相似文献   

15.
The effectiveness of transmitting underground water in rock fractures is strongly influenced by the widths of the fractures and their interconnections. However, the geometries needed for water flow in fractured rock are also heavily controlled by the confining pressure conditions. This paper is intended to study the seepage properties of fractured rocks under different confining pressures. In order to do this, we designed and manufactured a water flow apparatus that can be connected to the electro-hydraulic servo-controlled test system MTS815.02, which provides loading and exhibits external pressures in the test. Using this apparatus, we tested fractured mudstone, limestone and sandstone specimens and obtained the relationship between seepage properties and variations in confining pressure. The calculation of the seepage properties based on the collection of water flow and confining pressure differences is specifically influenced by non-Darcy flow. The results show that: (1) The seepage properties of fractured rocks are related to confining pressure, i.e. with the increase of confining pressure, the permeability $ k $ decreases and the absolute value of non-Darcy flow coefficient $ \beta $ increases. (2) The sandstone coefficients $ k $ and $ \beta $ range from $ 1.03 \times 10^{ - 18} $ to $ 1.53 \times 10^{ - 17} $  m2 and $ - 1.13 \times 10^{17} $ to $ - 2.35 \times 10^{18} $  m?1, respectively, and exhibit a greater change compared to coefficients of mudstone and limestone. (3) From the regression analysis of experimental data, it is concluded that the polynomial function is a better fit than the power and logarithmic functions. The results obtained can provide an important reference for understanding the stability of rock surrounding roadways toward prevention of underground water gushing-out, and for developing underground resources (e.g. coal).  相似文献   

16.
Mineralization of groundwater in volcanic aquifers is partly acquired through silicates weathering. This alteration depends on the dissolution of atmospheric, biogenic, or mantellic gaseous CO2 whose contributions may depend on substratum geology, surface features, and lava flow hydrological functionings. Investigations of $ {\text{P}}_{{{\text{CO}}_{ 2} {\text{eq}}}} $ and δ13CTDIC (total dissolved inorganic carbon) on various spatiotemporal scales in the unsaturated and saturated zones of volcanic flows of the Argnat basin (French Massif Central) have been carried out to identify the carbon sources in the system. Mantellic sources are related to faults promoting CO2 uplift from the mantle to the saturated zone. The contribution of this source is counterbalanced by infiltration of water through the unsaturated zone, accompanied by dissolution of soil CO2 or even atmospheric CO2 during cold periods. Monitoring and modeling of δ13CTDIC in the unsaturated zone shows that both $ {\text{P}}_{{{\text{CO}}_{ 2} {\text{eq}}}} $ and δ13CTDIC are controlled by air temperature which influences soil respiration and soil-atmosphere CO2 exchanges. The internal geometry of volcanic lava flows controls water patterns from the unsaturated zone to saturated zone and thus may explain δ13C heterogeneity in the saturated zone at the basin scale.  相似文献   

17.
In a regional metamorphic terrain where six isograds have been mapped based on mineral reactions that are observed in metacarbonate rocks, the P-T conditions and fugacities of CO2 and H2O during metamorphism were quantified by calculations involving actual mineral compositions and experimental data. Pressure during metamorphism was near 3,500 bars. Metamorphic temperatures ranged from 380° C (biotite-chlorite isograd) to 520° C (diopside isograd). \(f_{{\text{CO}}_{\text{2}} }\) and \(f_{{\text{CO}}_{\text{2}} }\) / \(f_{{\text{H}}_{\text{2}} {\text{O}}}\) in general is higher in metacarbonate rocks below the zoisite isograd than in those above the zoisite isograd. Calculated \(f_{{\text{CO}}_{\text{2}} }\) and \(f_{{\text{H}}_{\text{2}} {\text{O}}}\) are consistent with carbonate rocks above the zoisite isograd having equilibrated during metamorphism with a bulk supercritical fluid in which \(P_{{\text{CO}}_{\text{2}} }\) + \(P_{{\text{H}}_{\text{2}} {\text{O}}}\) = P total. Calculations indicate that below the zoisite isograd, however, \(P_{{\text{CO}}_{\text{2}} }\) + \(P_{{\text{H}}_{\text{2}} {\text{O}}}\) was less than Ptotal, and that this condition is not due to the presence of significant amounts of species other than CO2 and H2O in the system C-O-H-S. Calculated \(P_{{\text{CO}}_{\text{2}} }\) /( \(P_{{\text{CO}}_{\text{2}} }\) + \(P_{{\text{H}}_{\text{2}} {\text{O}}}\) ) is low (0.06–0.32) above the zoisite isograd. The differences in conditions above and below the zoisite isograd may indicate that the formation of zoisite records the introduction of a bulk supercritical H2O-rich fluid into the metacarbonates. The results of the study indicate that \(f_{{\text{CO}}_{\text{2}} }\) and \(f_{{\text{H}}_{\text{2}} {\text{O}}}\) are constant on a thin section scale, but that gradients in \(f_{{\text{CO}}_{\text{2}} }\) and \(f_{{\text{H}}_{\text{2}} {\text{O}}}\) existed during metamorphism on both outcrop and regional scales.  相似文献   

18.
A new experimental model has been designed to simulate the influence of a natural fracture network on the propagation geometry of hydraulic fractures in naturally fractured formations using a tri-axial fracturing system. In this model, a parallel and symmetrical pre-fracture network was created by placing cement plates in a cubic mold and filling the mold with additional cement to create the final testing block. The surface of the plates will thus be weakly cemented and form pre-fractures. The dimension and direction of the pre-fractures can be controlled using the plates. The experiments showed that the horizontal differential stress $\Updelta \sigma$ and the angle $\Updelta \theta$ between the maximum horizontal principal in situ stress and the pre-fracture are the dominating factors for the initiation and propagation of hydraulic fractures. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma \ge 2{\text{ MPa}}$ or $\Updelta \theta = 60^\circ$ and $\Updelta \sigma \ge 4{\text{ MPa}}$ , the direction of the initiation and propagation of the hydraulic fractures are consistent with or deviate from the normal direction of the pre-fracture. When the hydraulic fractures approach the pre-fractures, the direction of the hydraulic fracture propagation will be consistent with the normal direction of the pre-fracture. Otherwise, the hydraulic fracture will deflect and perpendicularly cross the parallel and symmetric pre-fracture network. For $\Updelta \theta = 90^\circ$ and $\Updelta \sigma < 2{\text{ MPa}},\,\Updelta \theta = 60^\circ$ , and $\Updelta \sigma < 4{\text{ MPa}}$ or $\Updelta \theta = 45^\circ$ and $\Updelta \sigma = 4 - 8{\text{ MPa}}$ , before the hydraulic fracture and the pre-fractures intersect, the direction of the hydraulic fracture propagation remains unchanged, and the pre-fractures open or dilate when the hydraulic fracture propagates to the intersection point, forming a complicated hydraulic fracture network with the propagation region of the overall hydraulic fracture network taking the shape of an ellipse. In this condition, the complexity level of the hydraulic fracture is controlled by the net pressure, the compressive normal stress acting on the pre-fractures, the shearing strength and the cohesion strength of the planes of weakness. The conclusions of this research are inconsistent with the formulation of the approach angle that has been widely accepted by previous studies. The principle of hydraulic fracture propagation is that it follows the least resistance, the most preferential propagation, and the shortest propagation path.  相似文献   

19.
Orthorhombic post-perovskite CaPtO3 is isostructural with post-perovskite MgSiO3, a deep-Earth phase stable only above 100 GPa. Energy-dispersive X-ray diffraction data (to 9.4 GPa and 1,024 K) for CaPtO3 have been combined with published isothermal and isobaric measurements to determine its P–V–T equation of state (EoS). A third-order Birch–Murnaghan EoS was used, with the volumetric thermal expansion coefficient (at atmospheric pressure) represented by α(T) = α0 + α1(T). The fitted parameters had values: isothermal incompressibility, $ K_{{T_{0} }} $  = 168.4(3) GPa; $ K_{{T_{0} }}^{\prime } $  = 4.48(3) (both at 298 K); $ \partial K_{{T_{0} }} /\partial T $  = ?0.032(3) GPa K?1; α0 = 2.32(2) × 10?5 K?1; α1 = 5.7(4) × 10?9 K?2. The volumetric isothermal Anderson–Grüneisen parameter, δ T , is 7.6(7) at 298 K. $ \partial K_{{T_{0} }} /\partial T $ for CaPtO3 is similar to that recently reported for CaIrO3, differing significantly from values found at high pressure for MgSiO3 post-perovskite (?0.0085(11) to ?0.024 GPa K?1). We also report axial P–V–T EoS of similar form, the first for any post-perovskite. Fitted to the cubes of the axes, these gave $ \partial K_{{aT_{0} }} /\partial T $  = ?0.038(4) GPa K?1; $ \partial K_{{bT_{0} }} /\partial T $  = ?0.021(2) GPa K?1; $ \partial K_{{cT_{0} }} /\partial T $  = ?0.026(5) GPa K?1, with δ T  = 8.9(9), 7.4(7) and 4.6(9) for a, b and c, respectively. Although $ K_{{T_{0} }} $ is lowest for the b-axis, its incompressibility is the least temperature dependent.  相似文献   

20.
The diffusion of water in natural obsidian and model dacitic melts (Ab90Di8Wo2, mol %) has been studied at water vapor pressure up to 170 MPa, temperatures of 1200°C, H2O contents in melts up to ～6 wt % using a high gas pressure apparatus equipped with a unique internal device. The experiments were carried out by a new low-gradient technique with application of diffusion hydration of a melt from fluid phase. The water solubility in the melts and its concentration along $C_{H_2 O} $ diffusion profiles were determined using IR microspectrometry by application of the modified Bouguer-Beer-Lambert equation. A structural-chemical model was proposed to calculate and predict the concentration dependence of molar absorption coefficients of the hydroxyl groups (OH?) and water molecules (H2O) in acid polymerized glasses (quenched melts) in the obsidian-dacite series. The water diffusion coefficients $D_{H_2 O} $ were obtained by the mathematical analysis of concentration profiles and the analytical solution of the second Fick diffusion law using the Boltzman-Matano method. It was shown experimentally that $D_{H_2 O} $ exponentially increases with a growth of water concentration in the obsidian and dacitic melts within the entire range of diffusion profiles. Based on the established quantitative correlation between $D_{H_2 O} $ and viscosity of such melts, a new method was developed to predict and calculate the concentration, temperature, and pressure dependences of $D_{H_2 O} $ in acid magmatic melts (obsidian, rhyolite, albite, granite, dacite) at crustal T, P parameters and water concentrations up to 6 wt %.  相似文献   

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