共查询到20条相似文献,搜索用时 46 毫秒
1.
Diffusion rates for sulfur in rhyolite melt have been measured at temperatures of 800–1100° C, water contents of 0–7.3 wt%,
and oxygen fugacities from the quartz-fayalite-magnetite buffer to air. Experiments involved dissolution of anhydrite or pyrrhotite
into rhyolite melt over time scales of hours to days. Electron microprobe analysis was used to measure sulfur concentration
profiles in the quenched glasses. Regression of the diffusion data in dry rhyolite melt gives Dsulfur=0.05·exp{−221±80RT}, which is one to two orders of magnitude slower than diffusion of other common magmatic volatiles such as H2O, CO2 and Cl-. Diffusion of sulfur in melt with 7 wt% dissolved water is 1.5 to 2 orders of magnitude faster than diffusion in the anhydrous
melt, depending on temperature. Sulfur is known to dissolve in silicate melts as at least two different species, S2− and S6+, the proportions of which vary with oxygen fugacity; despite this, oxygen fugacity does not appear to affect sulfur diffusivity
except under extremely oxidizing conditions. This result suggests that diffusion of sulfur is controlled by one species over
a large range in oxygen fugacity. The most likely candidate for the diffusing species is the sulfide ion, S2−. Re-equilibration between S2− and S6+ in oxidized melts must generally be slow compared to S2− diffusion in order to explain the observed results. In a silicic melt undergoing degassing, sulfur will tend to be fractionated
from other volatile species which diffuse more rapidly. This is consistent with analyses of tephra from the 1991 eruption
of Mount Pinatubo, Philippines, and from other high-silica volcanic eruptions.
Received: 26 April 1995 / Accepted: 1 November 1995 相似文献
2.
To interpret the degassing of F-bearing felsic magmas, the solubilities of H2O, NaCl, and KCl in topaz rhyolite liquids have been investigated experimentally at 2000, 500, and ≈1 bar and 700° to 975 °C.
Chloride solubility in these liquids increases with decreasing H2O activity, increasing pressure, increasing F content of the liquid from 0.2 to 1.2 wt% F, and increasing the molar ratio
of ((Al + Na + Ca + Mg)/Si). Small quantities of Cl− exert a strong influence on the exsolution of magmatic volatile phases (MVPs) from F-bearing topaz rhyolite melts at shallow
crustal pressures. Water- and chloride-bearing volatile phases, such as vapor, brine, or fluid, exsolve from F-enriched silicate
liquids containing as little as 1 wt% H2O and 0.2 to 0.6 wt% Cl at 2000 bar compared with 5 to 6 wt% H2O required for volatile phase exsolution in chloride-free liquids. The maximum solubility of Cl− in H2O-poor silicate liquids at 500 and 2000 bar is not related to the maximum solubility of H2O in chloride-poor liquids by simple linear and negative relationships; there are strong positive deviations from ideality
in the activities of each volatile in both the silicate liquid and the MVP(s). Plots of H2O versus Cl− in rhyolite liquids, for experiments conducted at 500 bar and 910°–930 °C, show a distinct 90° break-in-slope pattern that
is indicative of coexisting vapor and brine under closed-system conditions. The presence of two MVPs buffers the H2O and Cl− concentrations of the silicate liquids. Comparison of these experimentally-determined volatile solubilities with the pre-eruptive
H2O and Cl− concentrations of five North American topaz and tin rhyolite melts, determined from melt inclusion compositions, provides
evidence for the exsolution of MVPs from felsic magmas. One of these, the Cerro el Lobo magma, appears to have exsolved alkali
chloride-bearing vapor plus brine or a single supercritical fluid phase prior to entrapment of the melt inclusions and prior
to eruption.
Received: 6 November 1995 / Accepted: 29 January 1998 相似文献
3.
Electrical conductivity of hydrous basaltic melts: implications for partial melting in the upper mantle 总被引:1,自引:0,他引:1
Huaiwei Ni Hans Keppler Harald Behrens 《Contributions to Mineralogy and Petrology》2011,162(3):637-650
The Earth’s uppermost asthenosphere is generally associated with low seismic wave velocity and high electrical conductivity.
The electrical conductivity anomalies observed from magnetotelluric studies have been attributed to the hydration of mantle
minerals, traces of carbonatite melt, or silicate melts. We report the electrical conductivity of both H2O-bearing (0–6 wt% H2O) and CO2-bearing (0.5 wt% CO2) basaltic melts at 2 GPa and 1,473–1,923 K measured using impedance spectroscopy in a piston-cylinder apparatus. CO2 hardly affects conductivity at such a concentration level. The effect of water on the conductivity of basaltic melt is markedly
larger than inferred from previous measurements on silicate melts of different composition. The conductivity of basaltic melts
with more than 6 wt% of water approaches the values for carbonatites. Our data are reproduced within a factor of 1.1 by the
equation log σ = 2.172 − (860.82 − 204.46 w
0.5)/(T − 1146.8), where σ is the electrical conductivity in S/m, T is the temperature in K, and w is the H2O content in wt%. We show that in a mantle with 125 ppm water and for a bulk water partition coefficient of 0.006 between
minerals and melt, 2 vol% of melt will account for the observed electrical conductivity in the seismic low-velocity zone.
However, for plausible higher water contents, stronger water partitioning into the melt or melt segregation in tube-like structures,
even less than 1 vol% of hydrous melt, may be sufficient to produce the observed conductivity. We also show that ~1 vol% of
hydrous melts are likely to be stable in the low-velocity zone, if the uncertainties in mantle water contents, in water partition
coefficients, and in the effect of water on the melting point of peridotite are properly considered. 相似文献
4.
《Chemical Geology》2007,236(1-2):1-12
The nucleation of H2O bubbles in magmas has been proposed as a trigger for volcanic eruptions. To determine how bubbles nucleate heterogeneously in silicate melts, experiments were carried out in which high-silica rhyolitic melts were hydrated at 800 °C and either 50 or 125 MPa, and then decompressed by 20–91 MPa at temperatures that ranged between 550 and 700 °C, and held at the lower pressures for 10–720 s before being quenched. Bubbles nucleated in number densities (NB) that vary between 3 × 107 and 2 × 108 cm− 3. Blocky shaped magnetite or the ends of needle-shaped hematite acted as sites for nucleation, but only if a minimum super-saturation was exceeded, which increases with increasing melt viscosity. Bubbles did not nucleate along the lengths of hematite needles nor on plagioclase. Both the beginning and ending times of the nucleation event increases with increasing melt viscosity. Using nucleation theory predictions, neither the slower nucleation rates nor the changing activation of nucleation sites can be adequately explained by the differences in temperature, water diffusivity, or viscosity. Instead, the variations in nucleation kinetics are best explained by changes in surface tension between melt and vapor, resulting from the increasing polymerization of the melt at lower temperatures and water contents. Because only ∼ 108 bubbles cm− 3 nucleate on magnetite in the rhyolite melt used, almost regardless of experimental conditions, results from this study may not be directly comparable to vesicle numbers in volcanic pumice of different compositions. 相似文献
5.
Wei Tian Ian H. Campbell Charlotte M. Allen Ping Guan Wenqing Pan Mimi Chen Hongjiao Yu Wenping Zhu 《Contributions to Mineralogy and Petrology》2010,160(3):407-425
We report major and trace element composition, Sr–Nd isotopic and seismological data for a picrite–basalt–rhyolite suite from
the northern Tarim uplift (NTU), northwest China. The samples were recovered from 13 boreholes at depths between 5,166 and
6,333 m. The picritic samples have high MgO (14.5–16.8 wt%, volatiles included) enriched in incompatible element and have
high 87Sr/86Sr and low 143Nd/144Nd isotopic ratios (εNd (t) = −5.3; Sri = 0.707), resembling the Karoo high-Ti picrites. All the basaltic samples are enriched in TiO2 (2.1–3.2 wt%, volatiles free), have high FeOt abundances (11.27–15.75 wt%, volatiles free), are enriched in incompatible
elements and have high Sr and low Nd isotopic ratios (Sri = 0.7049–0.7065; εNd (t) = −4.1 to −0.4). High Nb/La ratios (0.91–1.34) of basalts attest that they are mantle-derived magma with negligible crustal
contamination. The rhyolite samples can be subdivided into two coeval groups with overlapping U–Pb zircon ages between 291 ± 4
and 272 ± 2 Ma. Group 1 rhyolites are enriched in Nb and Ta, have similar Nb/La, Nb/U, and Sr–Nd isotopic compositions to
the associated basalts, implying that they are formed by fractional crystallization of the basalts. Group 2 rhyolites are
depleted in Nb and Ta, have low Nb/La ratios, and have very high Sr and low Nd isotopic ratios, implying that crustal materials
have been extensively, if not exclusively, involved in their source. The picrite–basalt–rhyolite suite from the NTU, together
with Permian volcanic rocks from elsewhere Tarim basin, constitute a Large Igneous Province (LIP) that is characterized by
large areal extent, rapid eruption, OIB-type chemical composition, and eruption of high temperature picritic magma. The Early
Permian magmatism, which covered an area >300,000 km2, is therefore named the Tarim Flood Basalt. 相似文献
6.
The heat capacity at constant pressure, C
p, of chlorapatite [Ca5(PO4)3Cl – ClAp], and fluorapatite [Ca5(PO4)3F – FAp], as well as of 12 compositions along the chlorapatite–fluorapatite join have been measured using relaxation calorimetry
[heat capacity option of the physical properties measurement system (PPMS)] and differential scanning calorimetry (DSC) in
the temperature range 5–764 K. The chlor-fluorapatites were synthesized at 1,375–1,220°C from Ca3(PO4)2 using the CaF2–CaCl2 flux method. Most of the chlor-fluorapatite compositions could be measured directly as single crystals using the PPMS such
that they were attached to the sample platform of the calorimeter by a crystal face. However, the crystals were too small
for the crystal face to be polished. In such cases, where the sample coupling was not optimal, an empirical procedure was
developed to smoothly connect the PPMS to the DSC heat capacities around ambient T. The heat capacity of the end-members above 298 K can be represented by the polynomials: C
pClAp = 613.21 − 2,313.90T
−0.5 − 1.87964 × 107
T
−2 + 2.79925 × 109
T
−3 and C
pFAp = 681.24 − 4,621.73 × T
−0.5 − 6.38134 × 106
T
−2 + 7.38088 × 108
T
−3 (units, J mol−1 K−1). Their standard third-law entropy, derived from the low-temperature heat capacity measurements, is S° = 400.6 ± 1.6 J mol−1 K−1 for chlorapatite and S° = 383.2 ± 1.5 J mol−1 K−1 for fluorapatite. Positive excess heat capacities of mixing, ΔC
pex, occur in the chlorapatite–fluorapatite solid solution around 80 K (and to a lesser degree at 200 K) and are asymmetrically
distributed over the join reaching a maximum of 1.3 ± 0.3 J mol−1 K−1 for F-rich compositions. They are significant at these conditions exceeding the 2σ-uncertainty of the data. The excess entropy of mixing, ΔS
ex, at 298 K reaches positive values of 3–4 J mol−1 K−1 in the F-rich portion of the binary, is, however, not significantly different from zero across the join within its 2σ-uncertainty. 相似文献
7.
This study is aimed at determining the diffusion coefficient of net-work modifiers (mainly Na, K, and Ca) in a two-phase melt-NaCl
system, in which the melts are granitic and the system is NaCl-rich in composition. The diffusion coefficients of Na, K, and
Ca were measured at the temperatures of 750 – 1400°C, pressures of 0.001 × 108 – 2 × 108 Pa, and initial H2O contents of 0 wt% –6.9 wt% in the granitic melts. The diffusion coefficients of Fe and Mg were difficult to resolve. In
all experiments a NaCl melt was present as well. In the absence of H2O, the diffusion of net-work modifiers follows an Arrhanious equation at 1 × 105 Pa: lgDca=−3. 88−5140/T, lgDk =−3. 79−4040/T, and lgDNa, =−4.99−3350/T, where D is in cm2 /s andT is in K. The diffusion coefficients of Ca, Na, K, and Fe increase non-linearly with increasing H2O content in the melt. The presence of about 2 wt% H2O m the melt will lead to a dramatical increase in diffusivity, but higher H2O content has only a minor effect. This change is probably the result of a change in the melt structure when H2O is present. The diffusion coefficients measured in this study are significantly different from those in previous works.
This may be understood in terms of the “transient two-liquid equilibrium” theory. Element interdiffusion depends not only
on its concentration, but also on its activity co-efficient gradient, which is reflected by the distribution coefficient,
of the two contacting melts. 相似文献
8.
The viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040° C have
been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques.
The micropenetration viscometry has been performed in the viscosity range of 109 Pa s to 1012 Pa s. The samples ranged in water content from 0.4 to 3.5 wt%. For samples with up to 2.5 wt% H2O, the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment
to be constant over the duration of the measurements. Above this water content a measurable loss of water occurs during the
viscometry.
The viscosity data illustrate an extremely nonlinear decrease in viscosity with added water. The viscosity drops drastically
with the addition of 0.5 wt% of water and then shallows out at water contents of 2 wt%. An additional viscosity datum point
obtained from the analysis of fluid inclusions in a water-saturated HPG8 confirms a near invariance of the viscosity with
the addition of water between 2 and 6 wt%. These measurements may be compared directly with the data of Hess et al. (1995,
in press) for the effects of excess alkali and alkaline earth oxides on the viscosity of HPG8 (also obtained at 1 bar). The
viscosity of the melts, compared on an equivalent molar basis, increases in the order H2O<(Li2O<Na2O< K2O<Rb2O,Cs2O<BaO<SrO<CaO<MgO< BeO). The extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation
scheme of Shaw (1972) for the range of water contents investigated here. The speciation of water in the quenched glasses can
be used to quantify the dependence of the viscosity on hydroxyl content. Considering only the hydroxyl groups as active fluidizers
in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes
larger. Consequences for degassing calcalkaline rhyolite are discussed.
Received: 17 August 1995/Accepted: 8 January 1996 相似文献
9.
Alexander Bartels Francesco Vetere Francois Holtz Harald Behrens Robert L. Linnen 《Contributions to Mineralogy and Petrology》2011,162(1):51-60
Viscosity experiments were conducted with two flux-rich pegmatitic melts PEG0 and PEG2. The Li2O, F, B2O3 and P2O5 contents of these melts were 1.04, 4.06, 2.30 and 1.68 and 1.68, 5.46, 2.75 and 2.46 wt%, respectively. The water contents
varied from dry to 9.04 wt% H2O. The viscosity was determined in internally heated gas pressure vessels using the falling sphere method in the temperature
range 873–1,373 K at 200 and 320 MPa pressure. At 1,073 K, the viscosity of water-rich (~9 wt% H2O) melts is in the range of 3–60 Pa s, depending on the melt composition. Extrapolations to lower temperature assuming an
Arrhenian behavior indicate that highly fluxed pegmatite melts may reach viscosities of ~30 Pa s at 773 K. However, this value
is a minimum estimation considering the strongly non-Arrhenian behavior of hydrous silicate melts. The experimentally determined
melt viscosities are lower than the prediction of current models taking compositional parameters into account. Thus, these
models need to be improved to predict accurately the viscosity of flux-rich water bearing melts. The data also indicate that
Li influences significantly the melt viscosity. Decreasing the molar Al/(Na + K + Li) ratio results in a strong viscosity
decrease, and highly fluxed melts with low Al/(Na + K + Li) ratios (~0.8) have a rheological behavior which is very close
to that of supercritical fluids. 相似文献
10.
N. Cluzel D. Laporte A. Provost I. Kannewischer 《Contributions to Mineralogy and Petrology》2008,156(6):745-763
We performed decompression experiments to simulate the ascent of a phenocryst-bearing rhyolitic magma in a volcanic conduit.
The starting materials were bubble-free rhyolites water-saturated at 200 MPa–800°C under oxidizing conditions: they contained
6.0 wt% dissolved H2O and a dense population of hematite crystals (8.7 ± 2 × 105 mm−3). Pressure was decreased from the saturation value to a final value ranging from 99 to 20 MPa, at constant temperature (800°C);
the rate of decompression was either 1,000 or 27.8 kPa/s. In all experiments, we observed a single event of heterogeneous
bubble nucleation beginning at a pressure P
N equal to 63 ± 3 MPa in the 1,000 kPa/s series, and to 69 ± 1 MPa in the 27.8 kPa/s series. Below P
N, the degree of water supersaturation in the liquid rapidly decreased to a few 0.1 wt%, the nucleation rate dropped, and the
bubble number density (BND) stabilized to a value strongly sensitive to decompression rate: 80 mm−3 at 27.8 kPa/s vs. 5,900 mm−3 at 1,000 kPa/s. This behaviour is like the behavior formerly described in the case of homogeneous bubble nucleation in the
rhyolite-H2O system and in numerical simulations of vesiculation in ascending magmas. Similar degrees of water supersaturation were measured
at 27.8 and 1,000 kPa/s, implying that a faster decompression rate does not result in a larger departure from equilibrium.
Our experimental results imply that BNDs in acid to intermediate magmas ascending in volcanic conduits will depend on both
the decompression rate and the number density of phenocrysts, especially the number density of magnetite microphenocrysts (1–100 mm−3), which is the only mineral species able to reduce significantly the degree of water supersaturation required for bubble
nucleation. Very low BNDs (≈1 mm−3) are predicted in the case of effusive eruptions ( ≈ 0.1 kPa/s). High BNDs (up to 107 mm−3) and bimodal bubble size distributions are expected in the case of explosive eruptions: (1) a relatively small number density
of bubbles (1–100 mm−3) will first nucleate in the lower part of the conduit ( ≈ 10 kPa/s), either at high pressure on magnetite or at lower pressure on quartz and feldspar (or by homogeneous nucleation
in the liquid) and (2) then, extreme decompression rates near the fragmentation level ( ≈ 103 kPa/s) will trigger a major nucleation event leading to the multitude of small bubbles, typically a few micrometers to a
few tens of micrometers in diameter, which characterizes most silicic pumices. 相似文献
11.
Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study 总被引:2,自引:2,他引:0
Marcus Freise Francois Holtz Marcus Nowak James S. Scoates Holger Strauss 《Contributions to Mineralogy and Petrology》2009,158(4):505-527
Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the
effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen
Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet
Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence
of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments
were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log
fO2 ~ ΔQFM + 4) and reducing conditions (log fO2 ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the
fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual
melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages
with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The
pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C,
with a water content below 2 wt% H2O and a log fO2 ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich
residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O. 相似文献
12.
Solubility of manganotantalite, zircon and hafnon in highly fluxed peralkaline to peraluminous pegmatitic melts 总被引:2,自引:0,他引:2
Marieke Van Lichtervelde Francois Holtz John M. Hanchar 《Contributions to Mineralogy and Petrology》2010,160(1):17-32
The behavior of tantalum and zirconium in pegmatitic systems has been investigated through the determination of Ta and Zr
solubilities at manganotantalite and zircon saturation from dissolution and crystallization experiments in hydrous, Li-, F-,
P- and B-bearing pegmatitic melts. The pegmatitic melts are synthetic and enriched in flux elements: 0.7–1.3 wt% Li2O, 2–5.5 wt% F, 2.8–4 wt% P2O5 and 0–2.8 wt% B2O3, and their aluminum saturation index ranges from peralkaline to peraluminous (ASILi = Al/[Na + K + Li] = 0.8 to 1.3) with various K/Na ratios. Dissolution and crystallization experiments were conducted at
temperatures varying between 700 and 1,150°C, at 200 MPa and nearly water-saturated conditions. For dissolution experiments,
pure synthetic, end member manganotantalite and zircon were used in order to avoid problems with slow solid-state kinetics,
but additional experiments using natural manganotantalite and zircon of relatively pure composition (i.e., close to end member
composition) displayed similar solubility results. Zircon and manganotantalite solubilities considerably increase from peraluminous
to peralkaline compositions, and are more sensitive to changes in temperature or ASI of the melt than to flux content. A model
relating the enthalpy of dissolution of manganotantalite to the ASILi of the melt is proposed: ∆H
diss (kJ/mol) = 304 × ASILi − 176 in the peralkaline field, and ∆H
diss (kJ/mol) = −111 × ASILi + 245 in the peraluminous field. The solubility data reveal a small but detectable competitivity between Zr and Ta in the
melt, i.e., lower amounts of Zr are incorporated in a Ta-bearing melt compared to a Ta-free melt under the same conditions.
A similar behavior is observed for Hf and Ta. The competitivity between Zr (or Hf) and Ta increases from peraluminous to peralkaline
compositions, and suggests that Ta is preferentially bonded to non-bridging oxygens (NBOs) with Al as first-neighbors, whereas
Zr is preferentially bonded to NBOs formed by excess alkalies. As a consequence Zr/Ta ratios, when buffered by zircon and
manganotantalite simultaneously, are higher in peralkaline melts than in peraluminous melts. 相似文献
13.
G. Diego Gatta Marco Merlini Hanns-Peter Liermann André Rothkirch Mauro Gemmi Alessandro Pavese 《Physics and Chemistry of Minerals》2012,39(5):385-397
The thermoelastic behavior of a natural clintonite-1M [with composition: Ca1.01(Mg2.29Al0.59Fe0.12)Σ3.00(Si1.20Al2.80)Σ4.00O10(OH)2] has been investigated up to 10 GPa (at room temperature) and up to 960°C (at room pressure) by means of in situ synchrotron
single-crystal and powder diffraction, respectively. No evidence of phase transition has been observed within the pressure
and temperature range investigated. P–V data fitted with an isothermal third-order Birch–Murnaghan equation of state (BM-EoS) give V
0 = 457.1(2) ?3, K
T0 = 76(3)GPa, and K′ = 10.6(15). The evolution of the “Eulerian finite strain” versus “normalized stress” shows a linear positive trend. The
linear regression yields Fe(0) = 76(3) GPa as intercept value, and the slope of the regression line leads to a K′ value of 10.6(8). The evolution of the lattice parameters with pressure is significantly anisotropic [β(a) = 1/3K
T0(a) = 0.0023(1) GPa−1; β(b) = 1/3K
T0(b) = 0.0018(1) GPa−1; β(c) = 1/K
T0(c) = 0.0072(3) GPa−1]. The β-angle increases in response to the applied P, with: βP = β0 + 0.033(4)P (P in GPa). The structure refinements of clintonite up to 10.1 GPa show that, under hydrostatic pressure, the structure rearranges
by compressing mainly isotropically the inter-layer Ca-polyhedron. The bulk modulus of the Ca-polyhedron, described using
a second-order BM-EoS, is K
T0(Ca-polyhedron) = 41(2) GPa. The compression of the bond distances between calcium and the basal oxygens of the tetrahedral
sheet leads, in turn, to an increase in the ditrigonal distortion of the tetrahedral ring, with ∂α/∂P ≈ 0.1°/GPa within the P-range investigated. The Mg-rich octahedra appear to compress in response to the applied pressure, whereas the tetrahedron
appears to behave as a rigid unit. The evolution of axial and volume thermal expansion coefficient α with temperature was
described by the polynomial α(T) = α0 + α1
T
−1/2. The refined parameters for clintonite are as follows: α0 = 2.78(4) 10−5°C−1 and α1 = −4.4(6) 10−5°C1/2 for the unit-cell volume; α0(a) = 1.01(2) 10−5°C−1 and α1(a) = −1.8(3) 10−5°C1/2 for the a-axis; α0(b) = 1.07(1) 10−5°C−1 and α1(b) = −2.3(2) 10−5°C1/2 for the b-axis; and α0(c) = 0.64(2) 10−5°C−1 and α1(c) = −7.3(30) 10−6°C1/2for the c-axis. The β-angle appears to be almost constant within the given T-range. No structure collapsing in response to the T-induced dehydroxylation was found up to 960°C. The HP- and HT-data of this study show that in clintonite, the most and the less expandable directions do not correspond to the most and
the less compressible directions, respectively. A comparison between the thermoelastic parameters of clintonite and those
of true micas was carried out. 相似文献
14.
Effects of nitrogen fertilization on soil respiration in temperate grassland in Inner Mongolia,China 总被引:5,自引:0,他引:5
Qin Peng Yunshe Dong Yuchun Qi Shengsheng Xiao Yating He Tao Ma 《Environmental Earth Sciences》2011,62(6):1163-1171
Nitrogen addition to soil can play a vital role in influencing the losses of soil carbon by respiration in N-deficient terrestrial
ecosystems. The aim of this study was to clarify the effects of different levels of nitrogen fertilization (HN, 200 kg N ha−1 year−1; MN, 100 kg N ha−1 year−1; LN, 50 kg N ha−1 year−1) on soil respiration compared with non-fertilization (CK, 0 kg N ha−1 year−1), from July 2007 to September 2008, in temperate grassland in Inner Mongolia, China. Results showed that N fertilization
did not change the seasonal patterns of soil respiration, which were mainly controlled by soil heat-water conditions. However,
N fertilization could change the relationships between soil respiration and soil temperature, and water regimes. Soil respiration
dependence on soil moisture was increased by N fertilization, and the soil temperature sensitivity was similar in the treatments
of HN, LN, and CK treatments (Q
10 varied within 1.70–1.74) but was slightly reduced in MN treatment (Q
10 = 1.63). N fertilization increased soil CO2 emission in the order MN > HN > LN compared with the CK treatment. The positive effects reached a significant level for HN
and MN (P < 0.05) and reached a marginally significant level for LN (P = 0.059 < 0.1) based on the cumulative soil respiration during the 2007 growing season after fertilization (July–September
2007). Furthermore, the differences between the three fertilization treatments and CK reached the very significant level of
0.01 on the basis of the data during the first entire year after fertilization (July 2007–June 2008). The annual total soil
respiration was 53, 57, and 24% higher than in the CK plots (465 g m−2 year−1). However, the positive effects did not reach the significant level for any treatment in the 2008 growing season after the
second year fertilization (July–September 2008, P > 0.05). The pairwise differences between the three N-level treatments were not significant in either year (P > 0.05). 相似文献
15.
A new Rb−Sr age of 779±10 Ma has been obtained for a suite of andesite-daciterhyolite from the Malani Igneous Province of
southwestern Rajasthan, dated earlier at 745±10 Ma by Crawford and Compston (1970). The associated basalts may be slightly
younger than the felsic volcanics and have a mantle source. The felsic volcanics on the other hand were most probably derived
by fractional crystallization of a crustal magma (Srivastavaet al 1989a, b).40Ar−39Ar systematics of three samples viz., a basalt, a dacite and a rhyolite show disturbed age spectra indicating a thermal event
around 500–550 Ma ago. This secondary thermal event is quite wide-spread and possibly related to the Pan-African thermo-tectonic
episode observed in the Himalayas and south India. 相似文献
16.
The accepted standard state entropy of titanite (sphene) has been questioned in several recent studies, which suggested a
revision from the literature value 129.3 ± 0.8 J/mol K to values in the range of 110–120 J/mol K. The heat capacity of titanite
was therefore re-measured with a PPMS in the range 5 to 300 K and the standard entropy of titanite was calculated as 127.2
± 0.2 J/mol K, much closer to the original data than the suggested revisions. Volume parameters for a modified Murgnahan equation
of state: V
P,T
= V
298° × [1 + a°(T − 298) − 20a°(T − 298)] × [1 – 4P/(K
298 × (1 – 1.5 × 10−4 [T − 298]) + 4P)]1/4 were fit to recent unit cell determinations at elevated pressures and temperatures, yielding the constants V
298° = 5.568 J/bar, a° = 3.1 × 10−5 K−1, and K = 1,100 kbar. The standard Gibbs free energy of formation of titanite, −2456.2 kJ/mol (∆H°f = −2598.4 kJ/mol) was calculated from the new entropy and volume data combined with data from experimental reversals on the
reaction, titanite + kyanite = anorthite + rutile. This value is 4–11 kJ/mol less negative than that obtained from experimental
determinations of the enthalpy of formation, and it is slightly more negative than values given in internally consistent databases.
The displacement of most calculated phase equilibria involving titanite is not large except for reactions with small ∆S. Re-calculated baric estimates for several metamorphic suites yield pressure differences on the order of 2 kbar in eclogites
and 10 kbar for ultra-high pressure titanite-bearing assemblages. 相似文献
17.
Konstantin D. Litasov Anton Shatskiy Eiji Ohtani Tomoo Katsura 《Physics and Chemistry of Minerals》2011,38(1):75-84
The H2O content of wadsleyite were measured in a wide pressure (13–20 GPa) and temperature range (1,200–1,900°C) using FTIR method.
We confirmed significant decrease of the H2O content of wadsleyite with increasing temperature and reported first systematic data for temperature interval of 1,400–1,900°C.
Wadsleyite contains 0.37–0.55 wt% H2O at 1,600°C, which may be close to its water storage capacity along average mantle geotherm in the transition zone. Accordingly,
water storage capacity of the average mantle in the transition zone may be estimated as 0.2–0.3 wt% H2O. The H2O contents of wadsleyite at 1,800–1,900°C are 0.22–0.39 wt%, indicating that it can store significant amount of water even
under the hot mantle environments. Temperature dependence of the H2O content of wadsleyite can be described by exponential equation
C\textH2 \textO = 6 3 7.0 7 \texte - 0.00 4 8T , C_{{{\text{H}}_{2} {\text{O}}}} = 6 3 7.0 7 {\text{e}}^{ - 0.00 4 8T} , where T is in °C. This equation is valid for temperature range 1,200–2,100°C with the coefficient of determination R
2 = 0.954. Temperature dependence of H2O partition coefficient between wadsleyite and forsterite (D
wd/fo) is complex. According to our data apparent Dwd/fo decreases with increasing temperature from D
wd/fo = 4–5 at 1,200°C, reaches a minimum of D
wd/fo = 2.0 at 1,400–1,500°C, and then again increases to D
wd/fo = 4–6 at 1,700–1,900°C. 相似文献
18.
Summary The Kassiteres-Sappes district represents a multi-centered, porphyry-epithermal system developed during the Oligocene to Miocene
at a composite calc-alkaline to high-K calc-alkaline volcanic edifice. Precious and base metal mineralization postdates the
emplacement of dacite and rhyolite porphyries and is partly superimposed on earlier microdiorite-related porphyry-style mineralization
exposed at the Koryfes Hill prospect. A second mineralized porphyry-type system genetically related to a dacite porphyry body
developed near the St Demetrios deposit. Tellurides occur mainly at the St Barbara prospect and the St Demetrios deposit.
Based on petrographic, electron microprobe, and scanning electron microscope analyses, hessite, petzite, sylvanite, altaite,
stützite and native tellurium occur in the St Barbara prospect. These tellurium-bearing minerals are hosted in intermediate-sulfidation
type veins and accompanied by pyrite, chalcopyrite, tetrahedrite-group minerals, galena and native gold/electrum. The St Demetrios
mineralization includes hessite, altaite, stützite, and tetradymite in close spatial relation to a high-sulfidation assemblage
composed of enargite, chalcopyrite, goldfieldite, and native gold. Tellurides were deposited at logfTe2 values of −8.5 to −7.1 and logfS2 values of −10.7 to −7.9 (275 °C). The ore systems are characterized by Au, Ag, Te, Bi, and Mo, which suggests a magmatic
contribution to the mineralizing fluids. Ore-forming components were likely derived from both the dacite and rhyolite porphyries. 相似文献
19.
Arne P. Willner Axel Gerdes Hans-Joachim Massonne Alexander Schmidt Masafumi Sudo Stuart N. Thomson Graciela Vujovich 《Contributions to Mineralogy and Petrology》2011,162(2):303-327
The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is
composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde
garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470°C and 1.4 GPa, 530°C, when the penetrative s2-foliation was formed. The average age of garnet crystallization of 390 ± 2 Ma (2σ) was determined from three four-point Lu–Hf
mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are
followed by a decompression path with slight heating at 0.5 GPa, 560°C. Fluid release during decompression caused equilibration
of mineral compositions at the rims and also aided Ar diffusion. An 40Ar/39Ar plateau age of white mica at 353 ± 1 Ma (1σ) indicates the time of cooling below 350–400°C. These temperatures were attained
at pressures of 0.2–0.3 GPa, indicative of an average exhumation rate of ≥1 mm/a for the period 390–353 Ma. Late hydrous influx
at 0.1–0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica.
At 284–295 Ma, the entire basement cooled below 280°C (fission track ages of zircon) after abundant post-collisional granitoid
intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm
of 10–12°C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent–continent
collisional setting. 相似文献
20.
Measurements taken between July 2006 to May 2007 at the Maqu station in the Upper Yellow River area were used to study the
surface radiation budget and soil water and heat content in this area. These data revealed distinct seasonal variations in
downward shortwave radiation, downward longwave radiation, upward longwave radiation and net radiation, with larger values
in the summer than in winter because of solar altitudinal angle. The upward shortwave radiation factor is not obvious because
of albedo (or snow). Surface albedo in the summer was lower than in the winter and was directly associated with soil moisture
and solar altitudinal angle. The annual averaged albedo was 0.26. Soil heat flux, soil temperature and soil water content
changed substantially with time and depth. The soil temperature gradient was positive from August to February and was related
to the surface net radiation and the heat condition of the soil itself. There was a negative correlation between soil temperature
gradient and net radiation, and the correlation coefficient achieved a significance level of 0.01. Because of frozen state
of the soil, the maximum soil thermal conductivity value was 1.21 W m−1°C−1 in January 2007. In May 2007, soil thermal conductivity was 0.23 W m−1°C−1, which is the lowest value measured in the study, likely due to the fact that the soil was drier then than in other months.
The soil thermal conductivity values for the four seasons were 0.27, 0.38, 0.55 and 0.83 W m−1°C−1, respectively. 相似文献