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Enthalpies of solution have been measured on a series of muscovite—paragonitemicas in 20.1% HF at 50C under isoperibolic conditions. Themolar enthalpy of formation of paragonite at 298 K, for whichno calorimetrically measured value is currently available, hasbeen determined to be –5937.5 (3) kJ. An inversion ofall calorimetric, volumetric and phase equilibrium data hasbeen performed, giving a range of mixing models compatible withmost experimental data. The following expressions of the mixingproperties of 2M1 micas for enthalpy (Hex) and volume (Vex)at pressures up to 10 kbar, forcing excess entropy (Sex) tobe zero and using a subregular mixing model are favoured: Hex(kJ) = [10.6+4.45(1–2Xms)]Xms(1–Xms) Vex(J/bar) = 0.452Xms(1–Xms). However, mixing models of higher order with asymmetric negativeSex are also possible. KEY WORDS: muscovite; paragonite; solvus; calorimetry; solid solution
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Experimental Crystallization of Leucogranite Magmas 总被引：25，自引：8，他引：17
Both crystallization and melting experiments have been carriedout on two natural, biotite-muscovite (DK) and tourmaline-muscovite(GB) High Himalayan leucogranites (HHL) at 4 kbar, logfO2 =FMQ–05, aH2O = 1–0•03, and at five temperaturesbetween 803 and 663C H2O contents of the quenched glasses wereanalysed by ion microprobe. Plagioclase and biotite are theliquidus phases for reduced melt H2O contents and H2O-rich conditions,respectively. H2O saturation limits range from 8 to 10 wt%.DK has a wider crystallization interval than GB (150 vs 80Cfor conditions close to H2O saturation), and a slightly higherH2O-saturated solidus (645 compared with 630C for GB). Tourmalinenever crystallized spontaneously from the melt. Tourmaline seedsalways reacted out to biotite in the biotite-muscovite sample,whereas they remained stable in the tourmaline-muscovite sample.Biotite is replaced by hercynite as the main ferromagnesianphase at high temperature and reduced aH2O. Muscovite crystallizationis restricted to near-solidus conditions. The compositions ofplagioclase, alkali feldspar, biotite and muscovite are givenas a function of bulk composition, temperature and aH2O. Glasscompositions are richer in normative quartz than the 4 kbarH2O-saturated Qz–Ab–Or eutectic, and become moreperaluminous and less mafic with increasing fractionation. Biotitecrystallization in peraluminous liquids is favoured by elevatedFe, Mg and Ti contents. Muscovite crystallization is not promotedunder H2O-saturated conditions. Tourmaline stability is stronglydependent on aH2O. For GB, tourmaline is present at elevatedtemperatures for intermediate values of aH2O (803 C, 0–7),but not above 650C for H2O-saturated conditions. Comparisonof the natural crystallization sequence with experiments suggestsinitial water contents between 5 and 75 wt % for the DK magma,and > 7 wt% for the GB magma. Plagioclase core compositionsgive minimum temperatures of 700C for GB and 750C for DK,consistent with an emplacement of these HHL as almost entirelyliquid bodies. The restricted occurrence of biotite in the GBgranite suggests that it reacted out during the magmatic evolution,owing to a marked change in fO2 toward more oxidizing conditions.Tourmaline leucogranites can be generated from biotite leucogranitesby fractional crystallization under conditions of increasingdegree of oxidation. KEY WORDS: leucogranite; melting experiments; crystlization experiments; Himalayas; phase relations
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In the albite-orthoclase-nepheline-kalsilite-water system theassemblage analcite-melt (±nepheline albite and orthoclase)can only exist in the pressure range 5 to 13 Kbars and at temperaturesbetween 640 and 600 °C. Primary igneous analcite will havea similar restricted PT range which probably means that interstitialanalcite found in many high-level dike rocks is secondary. 相似文献
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