共查询到20条相似文献,搜索用时 31 毫秒
1.
Partition coefficients (D) for Nb and Ta between rutile and haplogranite melts in the K2O-Al2O3-SiO2 system have been measured as functions of the K2O/Al2O3 ratio, the concentrations of Nb2O5 and Ta2O5, the temperature, in air and at 1 atmosphere pressure. The Ds increase in value as the K* [K2O/(K2O + Al2O3)] molar ratio continuously decreases from highly peralkaline [K* ∼ 0.9] to highly peraluminous [K* ∼ 0.35] melts. The D values increase more dramatically with a unit decrease in K* in peraluminous melts than in peralkaline melts. This compositional dependence of Ds can be explained by the high activity
of NbAlO4 species in peraluminous melts and the high activity of KONb species (or low activity of NbAlO4 species) in peralkaline melts. A coupled substitution, Al+3 + Nb+5 (or Ta+5) = 2Ti+4, accounts for the Ds of Nb (Ta) being much greater in peraluminous melts than in peralkaline melts because this substitution
allows Nb (Ta) to enter into the rutile structure more easily. The Ds of Ta between rutile and melt are greater than those
of Nb at comparable concentrations because the molecular electronic polarizability of Ta is weaker than that of Nb. The Nb+5 with a large polarizing power forms a stronger covalent bond with oxygen than Ta+5 with a small polarizing power. The formation of the strong bond, Nb-O, distorts the rutile structure more severely than the
weak bond, Ta-O; therefore, it is easier for Ta to partition into rutile than for Nb. These results imply that the utilization
of the Nb/Ta ratio in liquid as a petrogenetic indicator in granitic melts must be done with caution if rutile (or other TiO2-rich phases) is a liquidus phase. The crystallization of rutile will increase the Nb/Ta ratio of the residual liquid because
the Ds of Ta between rutile and melts are greater than those of Nb.
Received: 28 December 1998 / Accepted 27 September 1999 相似文献
2.
Phosphorus solubility mechanisms in haplogranitic aluminosilicate glass and melt: effect of temperature and aluminum content 总被引:1,自引:0,他引:1
Bjorn O. Mysen 《Contributions to Mineralogy and Petrology》1998,133(1-2):38-50
The solubility behavior of phosphorus in glasses and melts in the system Na2O-Al2O3-SiO2-P2O5 has been examined as a function of temperature and Al2O3 content with microRaman spectroscopy. The Al2O3 was added (2, 4, 5, 6, and 8 mol% Al2O3) to melts with 80 mol% SiO2 and ∼2 mol% P2O5. The compositions range from peralkaline, via meta-aluminous to peraluminous. Raman spectra were obtained of both the phosphorus-free
and phosphorous-bearing glasses and melts between 25 and 1218 °C. The Raman spectrum of Al-free, P-bearing glass exhibits
a characteristic strong band near 940 cm−1 assigned to P=O stretching in orthophosphate complexes together with a weaker band near 1000 cm−1 assigned P2O7 complexes. With increasing Al content, the proportion of P2O7 initially increases relative to PO4 and is joined by AlPO4 complexes which exhibit a characteristic P-O stretch mode slightly above 1100 cm−1. The latter complex appears to dominate in meta-aluminosilicate glass and is the only phosphate complex in peraluminous glasses.
When P-bearing peralkaline silicate and aluminosilicate glasses are transformed to supercooled melts, there is a rapid decrease
in PO4/P2O7 so that in the molten state, PO4 units are barely discernible. The P2O7/AlPO4 abundance ratio in peralkaline compositions increases with increasing temperature. This decrease in PO4/P2O7 with increasing temperature results in depolymerization of the silicate melts. Dissolved P2O5 in peraluminous glass and melts forms AlPO4 complexes only. This solution mechanism has no discernible influence on the aluminosilicate melt structure. There is no effect
of temperature on this solution mechanism.
Received: 7 October 1997 / Accepted: 11 May 1998 相似文献
3.
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
4.
Robert L. Linnen Michel Pichavant Franois Holtz 《Geochimica et cosmochimica acta》1996,60(24):4965-4976
The diffusion profile method has been employed to measure tin diffusion coefficients and SnO2 solubility in water-saturated, peralkaline to peraluminous haplogranitic melts at 850°C, 2 kbar, and log ƒO2 conditions ranging from FMQ - 0.57 to FMQ + 3.49. At reduced conditions cassiterite is highly soluble and tin is present dominantly as a Sn2+ species, whereas at oxidized conditions SnO2 is much less soluble, and tin is present dominantly as a Sn4+ species. There is a strong melt composition control on SnO2 solubility; solubilities are at a minimum at the subaluminous composition, increase strongly with alkali content in peralkaline compositions and weakly with Al content in peraluminous compositions. In the case of the latter, this increase can only be distinguished at reduced conditions, e.g., at a log ƒO2 of FMQ - 0.57 cassiterite solubility increases from 2.78 to 4.11 wt% SnO2 for melt with Al/(Na + K)compositions (A.S.I.) of 1.0 and 1.2, respectively. At oxidized conditions SnO2 solubility is 500 ppm for both the A.S.I. 1.0 and 1.2 compositions. By comparison Sn02 solubilities in the most peralkaline composition investigated range from 3.94 wt% to -10 wt% Sn02, for the most oxidized to the most reduced conditions, respectively. Thermodynamic modelling of the data indicates that the Sn4+/ΣSn ratio in the melt is also at a minimum at the subaluminous composition, ranging from 0.4 at log ƒO2 of FMQ + 3.49 to 0.01 at FMQ - 0.57. Over the same log foZ range the Sn4+/ΣSn ratio for the A.S.I. 0.6 composition ranges from 0.98 to 0.4 and for the A.S.I. 1.25 composition, from 0.8 to 0.02.Tin diffusivity is dependent on both fO2 and melt composition. The effective binary diffusion coefficient of tin at reduced conditions is approximately 10−7.5 cm2/sec for the peraluminous compositions and 10−8.2 cm2/sec for the peralkaline compositions. At oxidized conditions these values decrease to approximately 10−8.2 and 10−9.0 cm2/sec, respectively. These are interpreted to reflect relatively fast diffusion where Sn2+ is the dominant valence and tin in this case behaves similar to a network modifier and relatively slow diffusion where Sn4+ is dominant and tin likely has a lower coordination number. Alternatively, the coordination of Sn2+ and Sn4+ is the same, but the bond strengths are different. At fixed fO2 the faster diffusivity in the peraluminous compositions reflects the lower Sn4+/Sn2+ ratio. The fact the Sn4+/Sn2+ ratio in melts varies greatly with ƒO2 at redox conditions near FMQ suggests that the partitioning behaviour of tin possibly changes during the evolution of an igneous suite in general and of a peraluminous granite suite in particular. 相似文献
5.
The structural role and homogeneous redox equilibria of iron in peraluminous,metaluminous and peralkaline silicate melts 总被引:1,自引:3,他引:1
The compositional dependence of the redox ratio (FeO/FeO1.5) has been experimentally determined in K2O-Al2O3-SiO2-Fe2O3-FeO (KASFF) and K2O-CaO-Al2O3-SiO2-Fe2O3-FeO (KCASFF) silicate melts. Compositions were equilibrated at 1,450° C in air, with 78 mol % SiO2. KASFF melts have from 1 to 5 mol % Fe2O3 and include both peraluminous (K2O2O3) and peralkaline (K2O>Al2O3) compositions. KCASFF melts have 1 mol % Fe2O3 encompassing peraluminous, metaluminous (CaO+K2O>Al2O3) and peralkaline compositions. Peralkaline KASFF melts with 1 mol % Fe2O3 have low and constant values for the redox ratio, whereas in peraluminous melts the redox ratio increases with increasing (K2O/Al2O3). Increasing total iron concentration increases the redox ratio in peraluminous melts and slightly decreases the redox ratio in peralkaline melts. Substituting CaO for K2O at fixed total iron (1 mol %) increases the redox ratio in both peraluminous and metaluminous KCASFF melts; however, the redox ratio in peralkaline KCASFF melts is not affected by this exchange. These data indicate that Fe3+ is in four-fold coordination, with K+ or Ca2+ providing local charge balance. The tetrahedral ferric species is most stable in peralkaline melts and least stable in peraluminous melts, due to the competition between Al3+ and Fe3+ for charge balancing cations in the latter melt. Tetrahedral Fe3+ is also less stable when Ca2+ provides local charge balance. The data are consistent with a network modifying role for Fe2+ in the melt.The data are interpreted to reflect the effects of melt composition on the partitioning of K+ and Ca2+ and Fe3+ and Al3+ between various species in the melt. These relationships are discussed in terms of homogeneous equilibria between various iron-bearing and iron-free melt species. The results also reflect the effect of liquid composition on the exchange potentials Fe3+ Al–1 and Ca0.5K–1. The exchange potentials are relatively constant in peralkaline melts, but decrease in metaluminous and peraluminous melts as both (CaO+K2O)/(CaO+K2O+Al2O3) and K2O/CaO decrease. These qualitative observations imply that minerals exhibiting these exchanges will also be similarly affected as liquid composition changes.
Present address: Department of Geological Sciences, Virginia Tech, Blacksburg, VA 24061, USA 相似文献
6.
Water-saturated and water-undersaturated experiments (a
H2
O = 1.0 and 0.5) were performed in the temperature range 780–1040°C at 2 and 5 kbar in order to determine the upper thermal
stability of phlogopite in granitic melts. Starting compositions were: (A) subaluminous mixtures of 20 wt % synthetic phlogopite
and 80 wt % synthetic anhydrous haplogranitic glass; (B) peraluminous mixtures (normative corundum = 4 %) of 20 wt % synthetic
phlogopite and 80 wt % synthetic anhydrous peraluminous haplogranitic glass. The molar quartz: albite: orthoclase ratio of
the glasses of the 2␣kbar runs was 35:39:26 and that of the 5 kbar runs 30:42:28. In the subaluminous system, phlogopite is
stable up to 820°C at a
H2
O = 1.0 and up to 780°C at a
H2
O = 0.5. At higher temperatures, it is replaced by enstatite. In the peraluminous system phlogopite has a remarkably higher
thermal stability (up to 1000°C at 5 kbar and a
H2
O = 1.0) and there is a temperature interval of 80°C at a
H2
O = 1.0, and 90–100°C at a
H2
O = 0.5 between the first appearance of enstatite and the disappearance of phlogopite. In the peraluminous system, phlogopite
is a solid solution (ss) of phlogopite, muscovite, talc and eastonite components. The crystalline product of the phlogopitess breakdown reaction is an aluminous enstatite. The MgO-content of the melt depends on the normative corundum content of the
starting material and the run temperature. It is independent of pressure. In the subaluminous system, the MgO-content ranges
between 0.05 and 0.3 wt % in the temperature interval 780–880°C at both investigated water activities. The MgO-content of
the peraluminous melts at a
H2
O = 1.0 ranges between 0.4 and 1.7 wt % and at a
H2
O = 0.5 between 0.2 and 1.4 wt % in the temperature range 780–980°C.
Received: 28 August 1995 / Accepted: 6 August 1996 相似文献
7.
《Chemical Geology》2006,225(1-2):40-60
Fluorite is the most common fluoride mineral in magmatic silicic systems and its crystallization can moderate or buffer fluorine concentrations in these settings. We have experimentally determined fluorite solubility and speciation mechanisms in haplogranitic melts at 800–950 °C, 100 MPa and aqueous-fluid saturation. The starting haplogranite compositions: peraluminous (alumina saturation index, ASI = 1.2), subaluminous (ASI = 1.0) and peralkaline (ASI = 0.8) were variably doped with CaO or F2O−1 in the form of stoichiometric mineral or glass mixtures. The solubility of fluorite along the fluorite–hydrous haplogranite binaries is low: 1.054 ± 0.085 wt.% CaF2 (peralkaline), 0.822 ± 0.076 wt.% (subaluminous) and 1.92 ± 0.15 wt.% (peraluminous) at 800 °C, 100 MPa and 10 wt.% H2O, and exhibits a minimum at ASI ∼ 1. Fluorite saturation isotherms are strongly hyperbolic in the CaO–F2O−1 space, suggesting that fluorite saturation is controlled by the activity product of CaO and F2O−1, i.e., these components are partially decoupled in the melt structure. The form of fluorite liquidus isotherms implies distinct roles of fluorite crystallization: in Ca-dominant systems, fluorite crystallization is controlled by the fluorine concentration in the melt only and remains nearly independent of calcium contents; in F-rich systems, the crystallization of fluorite is determined by CaO contents and it does not buffer fluorine concentration in the melt. The apparent equilibrium constant, K, for the equilibrium CaO + cF2O−1 = CaF2 (+ associates) is log K= − (2.449 ± 0.085)·Al2O3exc + (4.902 ± 0.066); the reaction-stoichiometry parameter varies as follows: c= − (0.92 ± 0.11)·Al2O3exc + (1.042 ± 0.084) at 800 °C, 100 MPa and fluid saturation where Al2O3exc are molar percent alumina in excess over alkali oxides. The reaction stoichiometry, c, changes at subaluminous composition: in peralkaline melts, competition of other network modifiers for excess fluorine anions leads to the preferential alkali–F short-range order, whereas in peraluminous compositions, excess alumina associates with calcium cations to form calcioaluminate tetrahedra. The temperature dependence of fluorite solubility is described by the binary symmetric Margules parameter, W = 36.0 ± 1.4 kJ (peralkaline), 39.7 ± 0.5 kJ (subaluminous) and 32.8 ± 0.7 kJ (peraluminous). The strong positive deviations from ideal mixing imply the occurrence of CaF2–granite liquid–liquid immiscibility at temperatures above 1258 °C, which is consistent with previous experimental data. These experimental results suggest very low solubilities of fluorite in Ca-rich melts, consistent with the lack of fluorine enrichment in peralkaline rhyolites and calc-alkaline batholiths. On the other hand, high CaO concentrations necessary to crystallize fluorite in F-rich peraluminous melts are not observed in nature and thus magmatic crystallization of fluorite in topaz-bearing silicic suites is suppressed. A procedure for calculating fluorite solubility and the liquidus isotherms for a whole-rock composition and temperature of interest is provided. 相似文献
8.
The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts 总被引:4,自引:0,他引:4
The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H2O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H2O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species. 相似文献
9.
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
10.
The saturation surface of pseudobrookite (Fe2TiO5) was determined for melts in the system SiO2-Al2O3-K2O-FeO-Fe2O3-TiO2 at 1400° C and 1 atm. The variation in concentrations of Fe2O3, TiO2 and Fe2TiO5 in liquids can be used to infer relative changes in activity coefficients of these components with changing K2O/(K2O+Al2O3) of the melts. Saturation concentrations of these components are low and relatively constant in the peraluminous melts and increase with increasing K2O/(K2O+Al2O3) in peralkaline liquids. The activity coefficients of Fe2O3 and TiO2 and Fe2TiO5, therefore, are higher in peraluminous liquids than in peralkaline liquids in this system. In addition, the iron redox ratio was measured as a function of K2O/(K2O+Al2O3) for liquids just below the saturation surface;
was fixed so all variations in redox ratio are entirely due to changes in melt composition. The redox ratio from unsaturated liquids was applied to saturated liquids where redox analysis of the glass is impossible. The homogeneous equilibrium experiments indicate that the activity coefficient of Fe2O3 relative to that of FeO is significantly greater in peraluminous melts than peralkaline melts. Both the heterogeneous and homogeneous equilibria suggest that in peralkaline liquids K+in excess of that required to charge balance tetrahedral Al+3 is used to stabilize both Fe+3 and Ti+4. Calculations show that ferric iron and titanium compete equally effectively for charge-balancing potassium but neither can outcompete aluminum. The observed changes in solution properties of Fe2O3 and TiO2 in the synthetic melts are used to explain variations in Fe-Ti oxide stabilities in natural peraluminous and peralkaline rhyolites and granites. Since the activity coefficients of both ferric iron and titanium are significantly higher in peraluminous liquids than in peralkaline liquids, Fe-Ti oxides should occur earlier in the crystallization sequence in peraluminous rhyolites than in peralkaline rhyolites. In addition, iron will be reduced in peraluminous granites and rhyolites relative to peralkaline ones under comparable P, T, and
. Finally, observed crystallization patterns for minerals containing highly charged cations other than ferric iron and titanium are evaluated in the context of this and other experimental studies. 相似文献
11.
The configurational heat capacity, shear modulus and shear viscosity of a series of Na2O–Fe2O3–Al2O3–SiO2 melts have been determined as a function of composition. A change in composition dependence of each of the physical properties
is observed as Na2O/(Na2O + Al2O3) is decreased, and the peralkaline melts become peraluminous and a new charge-balanced Al-structure appears in the melts.
Of special interest are the frequency dependent (1 mHz–1 Hz) measurements of the shear modulus. These forced oscillation measurements
determine the lifetimes of Si–O bonds and Na–O bonds in the melt. The lifetime of the Al–O bonds could not, however, be resolved
from the mechanical spectrum. Therefore, it appears that the lifetime of Al–O bonds in these melts is similar to that of Si–O
bonds with the Al–O relaxation peak being subsumed by the Si–O relaxation peak. The appearance of a new Al-structure in the
peraluminous melts also cannot be resolved from the mechanical spectra, although a change in elastic shear modulus is determined
as a function of composition. The structural shear-relaxation time of some of these melts is not that which is predicted by
the Maxwell equation, but up to 1.5 orders of magnitude faster. Although the configurational heat capacity, density and shear
modulus of the melts show a change in trend as a function of composition at the boundary between peralkaline and peraluminous,
the deviation in relaxation time from the Maxwell equation occurs in the peralkaline regime. The measured relaxation times
for both the very peralkaline melts and the peraluminous melts are identical with the calculated Maxwell relaxation time.
As the Maxwell equation was created to describe the timescale of flow of a mono-structure material, a deviation from the prediction
would indicate that the structure of the melt is too complex to be described by this simple flow equation. One possibility
is that Al-rich channels form and then disappear with decreasing Si/Al, and that the flow is dominated by the lifetime of
Si–O bonds in the Al-poor peralkaline melts, and by the lifetime of Al–O bonds in the relatively Si-poor peralkaline and peraluminous
melts with a complex flow mechanism occurring in the mid-compositions. This anomalous deviation from the calculated relaxation
time appears to be independent of the change in structure expected to occur at the peralkaline/peraluminous boundary due to
the lack of charge-balancing cations for the Al-tetrahedra. 相似文献
12.
Melt inclusions in pegmatite quartz: complete miscibility between silicate melts and hydrous fluids at low pressure 总被引:10,自引:1,他引:9
Fluorine-, boron- and phosphorus-rich pegmatites of the Variscan Ehrenfriedersdorf complex crystallized over a temperature
range from about 700 to 500 °C at a pressure of about 1 kbar. Pegmatite quartz crystals continuously trapped two different
types of melt inclusions during cooling and growth: a silicate-rich H2O-poor melt and a silicate-poor H2O-rich melt. Both melts were simultaneously trapped on the solvus boundaries of the silicate (+ fluorine + boron + phosphorus) − water
system. The partially crystallized melt inclusions were rehomogenized at 1 kbar between 500 and 712 °C in steps of 50 °C by
conventional rapid-quench hydrothermal experiments. Glasses of completely rehomogenized inclusions were analyzed for H2O by Raman spectroscopy, and for major and some trace elements by EMP (electron microprobe). Both types of melt inclusions
define a solvus boundary in an XH2O–T pseudobinary system. At 500 °C, the silicate-rich melt contains about 2.5 wt% H2O, and the conjugate water-rich melt about 47 wt% H2O. The solvus closes rapidly with increasing temperature. At 650 °C, the water contents are about 10 and 32 wt%, respectively.
Complete miscibility is attained at the critical point: 712 °C and 21.5 wt% H2O. Many pegmatites show high concentrations of F, B, and P, this is particularly true for those pegmatites associated with
highly evolved peraluminous granites. The presence of these elements dramatically reduces the critical pressure for fluid–melt
systems. At shallow intrusion levels, at T ≥ 720 °C, water is infinitely soluble in a F-, B-, and P-rich melt. Simple cooling
induces a separation into two coexisting melts, accompanied with strong element fractionation. On the water-rich side of the
solvus, very volatile-rich melts are produced that have vastly different physical properties as compared to “normal” silicate
melts. The density, viscosity, diffusivity, and mobility of such hyper-aqueous melts under these conditions are more comparable
to an aqueous fluid.
Received: 15 September 1999 / Accepted: 10 December 1999 相似文献
13.
Jürgen Konzett 《Contributions to Mineralogy and Petrology》1997,128(4):385-404
Experiments have been conducted in a peralkaline Ti-KNCMASH system representative of MARID-type bulk compositions to delimit
the stability field of K-richterite in a Ti-rich hydrous mantle assemblage, to assess the compositional variation of amphibole
and coexisting phases as a function of P and T, and to characterise the composition of partial melts derived from the hydrous assemblage. K-richterite is stable in experiments
from 0.5 to 8.0 GPa coexisting with phlogopite, clinopyroxene and a Ti-phase (titanite, rutile or rutile + perovskite). At
8.0 GPa, garnet appears as an additional phase. The upper T stability limit of K-richterite is 1200–1250 °C at 4.0 GPa and 1300–1400 °C at 8.0 GPa. In the presence of phlogopite, K-richterite
shows a systematic increase in K with increasing P to 1.03 pfu (per formula unit) at 8.0 GPa/1100 °C. In the absence of phlogopite, K-richterite attains a maximum of 1.14 K
pfu at 8.0 GPa/1200 °C. Titanium in both amphibole and mica decreases continuously towards high P with a nearly constant partitioning while Ti in clinopyroxene remains more or less constant. In all experiments below 6.0 GPa
ΣSi + Al in K-richterite is less than 8.0 when normalised to 23 oxygens+stoichiometric OH. Rutiles in the Ti-KNCMASH system
are characterised by minor Al and Mg contents that show a systematic variation in concentration with P(T) and the coexisting assemblage. Partial melts produced in the Ti-KNCMASH system are extremely peralkaline [(K2O+Na2O)/Al2O3 = 1.7–3.7], Si-poor (40–45 wt% SiO2), and Ti-rich (5.6–9.2 wt% TiO2) and are very similar to certain Ti-rich lamproite glasses. At 4.0 GPa, the solidus is thought to coincide with the K-richterite-out
reaction, the first melt is saturated in a phlogopite-rutile-lherzolite assemblage. Both phlogopite and rutile disappear ca.
150 °C above the solidus. At 8.0 GPa, the solidus must be located at T≤1400 °C. At this temperature, a melt is in equilibrium with a garnet- rutile-lherzolite assemblage. As opposed to 4.0 GPa, phlogopite
does not buffer the melt composition at 8.0 GPa. The experimental results suggest that partial melting of MARID-type assemblages
at pressures ≥4.0 GPa can generate Si-poor and partly ultrapotassic melts similar in composition to that of olivine lamproites.
Received: 23 December 1996 / Accepted: 20 March 1997 相似文献
14.
The role of phosphorus in rhyolitic liquids as determined from the homogeneous iron redox equilibrium 总被引:1,自引:1,他引:1
The redox ratio of iron is used as an indicator of solution properties of silicate liquids in the system (SiO–Al2O3–K2O–FeO–Fe2O3–P2O5). Glasses containing 80–85 mol% SiO2 with 1 mol% Fe2O3 and compositions covering a range of K2O/Al2O3 were synthesized at 1400°C in air (fixed fO2). Variations in the ratio FeO/FeO1.5 resulting from the addition of P2O5 are used to determine the solution behavior of phosphorus and its interactions with other cations in the silicate melt. In 80 mol% SiO2 peralkaline melts the redox ratio, expressed as FeO/FeO1.5, is unchanged relative to the reference curve with the addition of 3 mol% P2O5. Yet, the iron redox ratio in the 85 mol% SiO2 potassium aluminosilicate melts is decreased relative to phosphorus-free liquids even for small amounts of P2O5 (0.5 mol%). The redox ratio in peraluminous melts is decreased relative to phosphorus- free liquids at P2O5 concentrations of 3 mol%. In peraluminous liquids, complexing of both Fe+3–O–P+5 and Al+3–O–P+5 occur. The activity coefficient of Fe+3 is decreased because more ferric iron can be accommodated than in phosphorus-free liquids. In peralkaline melts, there is no evidence that P+5 is removing K+ from either Al+3 or Fe+3 species. In chargebalanced melts with 3 mol% Fe2O3 and very high P2O5 concentrations, phosphorus removes K+ from K–O–Fe+3 complexes resulting in a redox increase. P2O5 should be accommodated easily in peraluminous rhyolitic liquids and phosphate saturation may be suppressed relative to metaluminous rhyolites. In peralkaline melts, phosphate solubility may increase as a result of phosphorus complexing with alkalis. The complexing stoichiometry may be variable, however, and the relative influence of peralkalinity versus temperature on phosphate solubility in rhyolitic melts deserves greater attention. 相似文献
15.
Zircon (ZrSiO4) and hafnon (HfSiO4) solubilities in water-saturated granitic melts have been determined as a function of melt composition at 800° and 1035°C at 200 MPa. The solubilities of zircon and hafnon in metaluminous or peraluminous melts are orders of magnitude lower than in strongly peralkaline melt. Moreover, the molar ratio of zircon and hafnon solubility is a function of melt composition. Although the solubilities are nearly identical in peralkaline melts, zircon on a molar basis is up to five times more soluble than hafnon in peraluminous melts. Accordingly, calculated partition coefficients of Zr and Hf between zircon and melt are nearly equal for the peralkaline melts, whereas for metaluminous and peraluminous melts DHf/DZr for zircon is 0.5 to 0.2. Consequently, zircon fractionation will strongly decrease Zr/Hf in some granites, whereas it has little effect on the Zr/Hf ratio in alkaline melts or similar depolymerized melt compositions.The ratio of the molar solubilities of zircon and hafnon for a given melt composition, temperature, and pressure is proportional to the Hf/Zr activity coefficient ratio in the melt. The data imply that this ratio is nearly constant and probably close to unity for a wide range of peralkaline and similar depolymerized melts. However, it changes by a factor of two to five over a relatively small interval of melt compositions when a nearly fully polymerized melt structure is approached. For most ferromagnesian minerals in equilibrium with a depolymerized melt, DHf > DZr. Typical values of DHf/DZr range from 1.5 to 2.5 for clinopyroxene, amphibole, and titanite. Because of the change in the Hf/Zr activity ratio in the melt, the relative fractionation of Zr and Hf by these minerals will disappear or even be reversed when the melt composition approaches that of a metaluminous or peraluminous granite. It is thus not surprising that fractional crystallization of such granitic magmas leads to a decrease in Zr/Hf, whereas fractional crystallization of depolymerized melts tends to increase Zr/Hf. There is no need to invoke fluid metasomatism to explain these effects. Results demonstrate that for ions with identical charge and nearly identical radius, crystal chemistry does not alone determine relative compatibilities. Rather, the effect of changing activity coefficients in the melt may be comparable to or even larger than elastic strain effects in the crystal lattice. 相似文献
16.
Equilibrium volumes and expansivities of three liquids in the system anorthite (CaAl2Si2O8)–diopside (CaMgSi2O6) have been derived from dilatometric measurements of the equilibrium length of samples in the glass transition range. The
typical temperature range of 40 K for the measurements is limited at low temperature by the very long times necessary to reach
structural equilibrium and at high temperature by the penetration of the rod used to measure sample dilatation. Despite such
narrow intervals, the expansivities are determined to better than 3% thanks to the high precision with which length changes
are measured. The coefficient of volume thermal expansion (1/V dV/dT) of the fully relaxed liquid just above the glass transition
is found to decrease linearly from diopside composition (139 ± 4 × 10−6 K−1) to anorthite composition (59 ± 2 × 10−6 K−1). These values are greater than those determined for the same liquids at superliquidus temperatures, demonstrating that expansivities
of silicate melts may decrease markedly with increasing temperature. A predictive model based upon partial molar volumes which
vary as a linear function of the logarithm of temperature is proposed.
Received: 25 February 2000 / Accepted: 29 May 2000 相似文献
17.
Phase relations were investigated in the model water-saturated system Si-Al-Na-Li-F-O at high fluorine contents, a temperature
of 800°C, and a pressure of 1 kbar. The obtained aluminosilicate melts are widely variable from quartz- to nepheline-normative
compositions with agpaitic indexes both higher and lower than one. Various fluoride, aluminofluoride, and oxide phases were
observed in the equilibrium assemblage depending on the melt composition: quartz and cryolite associate with the silica richest
aluminosilicate melts, topaz and corundum coexist with peraluminous melts, and villiaumite was observed in highly peralkaline
melts. Extensive immiscibility between aluminosilicate and aluminofluoride melts was observed in the system. Aluminofluoride
melt coexists with quartz- and nepheline-normative aluminosilicate melts with agpaitic indexes (K
a) of 0.7–1.4. The composition of aluminosilicate melt in equilibrium with aluminofluoride melt ranges from 33 to 70 wt % SiO2, from 12 to 24 wt % Al2O3, and from 5 to 16 wt % alkalis. The aluminofluoride melt is variable in composition, its Al/Na ratio ranges from 20/80 to
40/60 depending on the composition of the equilibrium aluminosilicate melt. The experimental aluminosilicate melts equilibrated
with cryolite, topaz, and aluminofluoride melt coincide in major component proportions with the bulk compositions of cryolite-
and topaz-bearing granites and melt inclusions in minerals. 相似文献
18.
Lars Chresten Lund-Hansen Thorbjørn Joest Andersen Morten Holtegaard Nielsen Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451
Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM),
and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with
optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K
d(PAR)), upwelling PAR (K
u(PAR)), particle beam attenuation coefficient (c
p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations
covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation
with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K
d(PAR), particle beam attenuation coefficients (c
p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water
outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic
suspended matter (SPMI) and diffuse attenuation coefficient K
d(PAR) (r
2 = 0.92) and also for particle beam attenuation coefficient (c
p; r
2 = 0.93). The obtained SPMI specific attenuation—K
d*(PAR) = 0.13 m2 g−1 SPMI—and the SPMI specific particle beam attenuation—c
p* = 0.72 m2 g−1—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r
2 = 0.80) correlation with K
u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in
the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results
are discussed and compared to similar studies from both temperate and tropical estuaries. 相似文献
19.
The relationship between the redox ratio Fe+2/(Fe+2+Fe+3) and the K2O/(K2O + Al2O3) ratio (K2O*) were experimentally investigated in silicate melts with 78 mol% SiO2 in the system SiO2-Al2O3-K2O-FeO-Fe2O3, in air at 1,400° C. Quenched glass compositions were analyzed by electron microprobe and wet chemical microtitration techniques. Minimum values of the redox ratio were obtained at K2O*0.5. The redox ratio in peralkaline melts (K2O*>0.5) increases slightly with K2O* whereas this ratio increases dramatically in peraluminous melts (K2O*<0.5) as K2O is replaced by Al2O3. These data indicate that all Fe+3 (and Al+3) occur as tetrahedral species charge balanced with K+ in peralkaline melts. In peraluminous melts, Fe+3 (and Al+3) probably occur as both tetrahedral species using Fe+2 as a charge-balancing cation and as network-modifying cations associated with non-bridging oxygen. 相似文献
20.
An experimental study has been carried out to determine the partition coefficients of tungsten between aqueous fluids and
granitic melts at 800 °C and 1.5 kb with natural granite as the starting material. The effects of the solutions on the partition
coefficients of tungsten show a sequence of P > CO
3
2−
> B > H2O. The effects are limited (generallyK
D
< 0.3) and the tungsten shows a preferential trend toward the melt over the aqueous fluid. The value ofK
D
increases with increasing concentration of phosphorus; theK
D
increases first and then reduces with the concentration of CO
3
2−
when temperature decreases, theK
D
between the solution of CO
3
2−
and the silicate melt increases, and that between the solution of B4O
7
2−
and the silicate melt decreases. The partition coefficients of phosphorus and sodium between fluids and silicate melts have
been calculated from the concentrations of the elements in the melts. TheK
D
value for phosphorus is 0.38 and that for sodium is 0.56. Evidence shows that the elements tend to become richer and richer
in the melts. 相似文献