Inclusions trapped in olivine of lunar mare and Hawaiian lava lake basalts have yielded data on the following: (1) composition of the melt at the time of olivine crystallization, except for subsequent crystallization of olivine on the walls (from probe analyses on natural or laboratory homogenized glasses); (2) amount and nature of immiscible sulfide melt, and the stage at which it separated (from simple microscopy) (3) equilibrium temperatures and sequence of melting, the nature of the phases other than olivine crystallized within the inclusions during cooling, and a crude measure of the solidus temperature of the trapped fluids (from phase-disappearance heating experiments on crystallized inclusions); (4) relative cooling rates of different flows and some constraints on absolute cooling rates (from simple microscopy and annealing experiments); (5) possible distinctions between phenocrysts and exotic xenocrysts (from the composition of inclusions); (6) presence of a vapor phase at the time of growth of the olivine and some data on its composition (from crushing-stage studies); and (7) minimum pressures at the time of olivine growth (from gas inclusions). Limitations are imposed by the suitability of the available inclusions, by the implicit assumptions, particularly as to the representativeness of the sample, and by the experimental techniques. Not all types of data can be obtained on any given sample, and several important questions and conflicts remain unanswered. In spite of these shortcomings, some of these data are believed to be valid, and some cannot be obtained otherwise.
Aqueous and non-aqueous inclusions in 84 samples of various minerals from a wide range of geologic environments were studied with the freezing stage in order to gain an insight into the range of concentrations and compositions of fluid inclusions. Inclusions in most Mississippi Valley-type ore minerals contain highly concentrated saline solutions, showing freezing temperatures between --23.4 degrees and --10.5 degrees C; minerals from ore deposits of more typically hydrothermal affiliations mainly show temperatures of --9.4 degrees to nearly 0 degrees C; and inclusions in quartz crystals from sedimentary, metamorphic, and igneous rock environments show a wide range of freezing temperatures. Inclusions in pegmatite minerals in particular vary over a wide range, from the most concentrated solutions found in any inclusion (> 40% salts) to fairly dilute solutions ( 2 . Other geologic environments sampled include Colombian emerald, pegmatitic topaz and fluorite, the Triassic traprock zeolite assemblage, and sedimentary halite beds.Not all the phenomena exhibited by inclusions at low temperature are completely understood at present but several crystalline hydrate phases, such as NaCl.2H 2 O and CO 2 .5 3/4H 2 O (structural formula 8CO 2 .46H 2 O), are shown to be stable in inclusions of appropriate composition even at temperatures above 0 degrees C, and probably exist in the inclusions in natural rocks in polar regions. More significantly, the formation and recognition of such phases aid in establishing the gross composition of individual inclusions far too small for chemical analysis.The data obtained are useful in a variety of ways, such as: discriminating among gas, liquid, and supercritical fluid, and among liquid water, liquid oil, and liquid CO 2 in inclusions; improving precision of the pressure corrections applied to inclusion filling temperature determinations; proving the general lack of leakage into or out of inclusions; estimating the minimum pressure at the time of deposition of certain samples; verifying the lack of extraneous solid crystallization nuclei in the inclusions and hence their formation from exceedingly quiet, clean solutions; determining the total equivalent NaCl concentrations and some information concerning the composition of the fluids from which ores have formed; and determining changes in the composition of the fluids bathing a single crystal during its growth, and at certain times throughout its history.
New experiments were performed on small quartz crystals and cleavage fragments of sphalerite and calcite, none requiring sawing, grinding or polishing. Quartz samples were run at external water pressures of 2000 and 4000 bars, and temperatures from 100 degrees to 400 degrees C for up to 17 days. Internal pressures exceeded external by 2000-3000 bars in some runs. 'From this work and a review of the literature [authors] conclude that most inclusions have not suffered major leakage. Some previous experiments indicating leakage may be explained by microfractures introduced during sample preparation.' Leakage, by diffusion, of substances like hydrogen is not precluded.
Laser-excited Raman spectroscopy has been successfully applied to the identification and partial analysis of solid, liquid, and gaseous phases in fluid inclusions. The procedure is no panacea for problems of analysis of fluid inclusions, but some unique features make it very useful. In particular, the measurement is performed in situ; it is nondestructive; and it can produce qualitative and quantitative data, some of which cannot be obtained otherwise, for samples as small as 10 -9 gram.
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