Hydrated obsidian chips were held at temperatures ranging from 450 to 600°C to determine the equilibrium speciation of water in the melt. The equilibrium speciation data are used to formulate a regular solution model to determine the speciation of water in rhyolitic melts at any temperature and water content. The solubility of water in rhyolitic melts at 850°C as a function of pressure as determined by extraction manometry on quenched glasses.
The solubility of water in a rhyolitic melt at 850°C as a function of pressure, as determined by infrared spectroscopy on quenched glass. The fractionation of hydrogen isotopes between saturated rhyolitic melts and water vapor as a function of the total amount of water dissolved in the solution. In addition, I present a series of experimental results describing the solubility of water in rhyolitic melts.
The Solubility of Water in Granitic Mel!
Knowledge of the solubility of water in silicate magmas under geological conditions is extremely useful. The variable and scattered results presented in the studies described above necessitate a re-examination of water solubility in silicate melts. 800°C and corresponds to the release of the hydroxyl component in dissolved water in the glass.
II came within I% (less than three Ilmol) of the total amount of water loaded in the experiment, showing the quality of the technique. The results of the water content analyzes from infrared spectroscopic measurements are shown in fig. Conversely, knowledge of the water content in the system can lead to the determination of the water content of a magma.
Nevertheless, both studies indicate a decrease in the partial molar volume of the total melt with dissolution of water. My results suggest that the dissolution of water has no effect on the total volume of the melt (the partial molar volume of water is close to zero).
The Speciation of Water in Granitic Melt
The effect of temperature on the equilibrium of the two species in the melt has been discussed, but not fully investigated. The concentration of the individual species is plotted against the total water content of the glass in Fig. The similarity of the speciation of water in these samples suggests that they have undergone similar thermal histories (see, e.g., Stolper, 1989).
The speciation of water in the glasses in Tables 2.1 and 2.2 is illustrated in Figure 2.3; the natural logarithm of the Ks parameter is plotted as a function of the total water content of the glass. Knowledge of Keq provides insight into the nature of the equilibrium of the aquatic species. An understanding of the temperature dependence of Keq will provide insight into the energies associated with the reaction of water with silicate melt.
For example, the quenching rate of the experiment is a complicated function of several factors as discussed above. Knowledge of the true temperature dependence of the speciation with total water content will enable the identification of the actual fictitious temperature in the re-equilibrated melt; i.e. the respective intersections of the true isotherms with the fictitious temperature curve in Fig. I now describe the results of a set of experiments which, in conjunction with the low water content data, provide the complete calculation of the temperature dependence of the speciation of water in glasses and melts with variable water content.
The water content of the melt at the intersection of the true isotherm with the quenching stop isotherm determines the fictitious temperature for that melt. Knowing the fictitious temperature coupled with the quench rate fixes a point on the melting curve t. The intersection of the true isotherm with the residence isotherm associated with the slowest quenching rate provides a second point on the t-curve.
Due to the inhomogeneity of the samples (up to 13% total water; see Table 2.5) used in this. The disparity in water speciation results in samples with identical water content and similar estimated quench rates (from the cold seal and cylinder-piston apparatus) highlights the problem of estimating the actual quench rate occurring at the onset of behavior of glass. . The extinguishing speed of the fast extinguishing apparatus (~ I second) is also shown as a horizontal line.
The Fractionation of Hydrogen Isotopes in Granitic Melt
What is the ratio of the isotopic composition of water in a magma at the Earth's surface to the water at its source area. Their technique, following Shepherd (\ 938), also enabled precise measurement of the water content of the two characteristic vitreous regions. I present the results of the first experimental determination of the fractionation factors governing the isotopic equilibrium of hydrogen isotopes in a silicate melt water vapor system.
Thus, separate isotope analyzes of the vapor phase and the dissolved melt phase determine the distribution of isotopes between vapor and melt for each experiment. The analyzes of the isotopic composition of samples passed through the extraction line involve several errors. The isotopic composition of the vapor: The procedure for extracting the vapor from the charges is detailed in Chapter 1.
The isotopic composition of the glass: The water representative of the dissolved component in the melt was extracted from quenched glass chips on the extraction line illustrated in figure. The isotopic composition of the samples is subtracted from the isotopic composition of the vapor to determine the bulk. fractionation in the melt vapor system. 3.4, in which hypothetical fractionation factors are assigned to describe the equilibrium of the vapor with the two melts.
The isotopic composition of the bulk melt is shown as a gray sphere in the one-dimensional diagram in Fig. On the other hand, the binding environments are associated with. the formation of the hydroxyl groups are significantly different from both the vapor and dissolved molecular species. The results of the experiments described above represent the first comprehensive determination of the fractionation factors that control the equilibrium of hydrogen isotopes between the dissolved species in a silicate melt.
The mass fractionation of hydrogen isotopes in the melt-vapor system is dependent on the water content of the melt; at low total water content, fractionation between melt and vapor is controlled by the fractionation factor between vapor and hydroxyl groups (uvapor.OH. Error bars are assigned by propagating 2%0 uncertainties in the isotopic analyzes of the vapor, the melt, and the blank measurements. Compositions in the upper three-phase region of the system KAISi30g-H20 at pressures up to 6 kilobars.
A Modified Rapid-Qilench Cold-Seal PreSStrre Vessel
The Influence of Blllk Composition on the Speciation of Water
Startio& matc:ria1 01 jadeitic c:ompxitioa wu pc-eparc:d by piodin& BUJ11\& jadeite (sampk provided by Prokaor W. de powda was lbc:u dried and saved as dcxnDcd abow: for the KAS composition. AD apcrimc: DtI .eft: a11lnUd willi pare: waitt ftpDI'.u.:d ooly the manometric: mc::uu.remc:DtI ror c:ah1:ntioD with a W :cau.sc: molar absorption c:odTicieots depends. same: molar absorption c::odIicierIts pro~. skilfully makes the Dot over this lance of silicate composition. Di.O"ere:nce ill the relative proportions of the two transient spc:c:ies must rda.tcd to diO"e:r=oes OJ c:oolin, rates bc:c:ause the two Ids of JI .a .ae:p. off from melting cquilib~tcd at the same ta:Dpera- ture and ov.:r it: same pressure int.e:rYal. For all compositions studied. The OH content increases rapidly at low total 9IIater contents and then slows down or even begins to decrease at high 9IIater contents. Ihe va1jd;l)' of Ihe porticulaI dcscriptioa of rda.tioosb.ip bctwcc:o water activity and oompoaboa can be tested by detmninina: if water activity is ill • tcrits of melts equilibrated with water vapor O't' a" • ranr. . i p Kanaafuu: acrecmcnt 01 keenya isa gaarii 6t jildii func:tioa jildii I1ICU1lmI> TlIcIc fiu proYick: a basis for cstimatinJ dcMities 01 by droul Jlu:Ies. with kDOWD total water CODtc:nts. kompositioa add with the prerequisites from trIaicb. the Jiu.ws were qumc:seng.
