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Notes: A new type of instrument has been designed and built to make Fourier transform nuclear-magnetic-resonance (NMR) spectroscopic measurements at temperatures to at least 1200 °C, with a resolution of about 1 ppm. A sample is rapidly and repeatedly shuttled between the furnace and the radio frequency (rf) coil of the NMR probe (both located within a high field superconducting magnet), spending most of the time in the furnace. During each cycle, a series of rf pulses may be given and a single free-induction decay sampled. The rf coil is located outside of the furnace and is maintained at room temperature despite its close proximity to the sample. Electronic stability and coil "filling factor'' are thus both optimized. The sample temperature drops below that of the furnace when cycling begins, but rapidly approaches a nearly constant value with only small fluctuations. 99% BN has been successfully used as a sample container in experiments on 27Al, 29Si, and 23Na in molten silicates in the system Na2O–Al2O3–SiO2.

Notes: Abstract The salic phases found in leucite-basanites, -trachytes, and -phonolites may be used to portray crystallization in the system NaAlSiO4-KAlSiO4-CaAl2Si2O8-SiO2, the phonolite pentahedron. Only two lavas have been found that contain the assemblage leucite-nepheline-plagioclase-sanidine and liquid, a natural pseudo-invariant assemblage (at 900° C±100) equivalent to the isobaric invariant point of the four component system. The diversity of phases in this group of lavas illustrates the role of halogens in controlling their crystallization paths. Thus the presence of F in the leucite-basanites has stabilized magnesian biotite and suppressed sanidine, as has been found in other basanitic lavas (Brown and Carmichael 1969). The presence of Cl in these same lavas has induced the crystallization of sodalite, which takes the place of nepheline in the groundmass. However in the leucite-trachytes, biotite has suppressed olivine and coexists with sanidine and leucite. The presence of S may produce haüyne at the expense of nepheline, and in general sulphate minerals, which include apatite, have the role in lavas of low silica activity that pyrrhotite plays in liquids of high silica activity. Both pyroxenes and titaniferous magnetites in this suite of lavas are very aluminous. Groundmass crystals of pyroxene may have one-fifth of Si replaced by Al. Other phases which occur occasionally are melanite garnet and a potassium-rich hastingsite, but neither ilmenite nor a sulphide mineral has been found. Phenocryst equilibration temperatures, derived from olivine and Sr-rich plagioclase, are generally in the range from 1,050° C to 1,150° C. The high content of incompatible elements (e.g., K, Ba, Rb, F, Sr, P) in these lavas suggests that they represent a small liquid fraction from a mantle source which possibly contains phlogopite.

Notes: Abstract The interdependence of the Fe(Mg)−1 (e.g., FeO-MgO in silicate melt; CaFeSi2O6-CaMgSi2O6 in pyroxene) and TiAl2(MgSi2)−1 exchange reactions between silicate melts and coexisting Ca-pyroxene has been examined. High-calcium clinopyroxenes were grown in 1 atmosphere melting and crystallization experiments on rock powders spanning the composition range tholeiite to melilitite (1,092〈T〈1,150° C: $$f_{{\text{O}}_{\text{2}} } $$ ∼QFM). Only microprobe analyses of the crystal rims were used in conjunction with those of the quenched glasses. Assuming equilibrium, relationships between apparent distribution coefficients for Fe2+⇄Mg2+ exchange and $$(X_{{\text{Ti}}^{{\text{4 + }}} }^{M1} )^{{\text{CPX}}} $$ suggest that at given values of $$\mu _{{\text{Fe(Mg)}}_{ - {\text{1}}} } $$ extent of Fe(Mg)−1 substitution is strongly coupled with the TiAl2(MgSi2)−1 substitution in pyroxenes near the five-component space CaMg(Si2O6-CaFe(Si)2O6-CaTi(Al)2O6-CaFe‴(Al,Si)2O6-CaAl(Al,Si)2O6. The inferred stabilization of Ti in iron-rich relative to magnesium pyroxene is consistent with the operation of Fe2+⇄Ti4+ intervalence charge transfer interactions (e.g., Rossman 1980) and observations on zoning in natural titanaugites (e.g., Tracy and Robinson 1977). Although the rims of some pyroxenes grown in some melting experiments exhibit prominent zoning in TiAl2(MgSi2)−1, the average values of $$(X_{{\text{Ti}}^{{\text{4 + }}} }^{M1} /X_{{\text{Mg}}^{{\text{2 + }}} }^{M1} )$$ inferred from the compositions of these pyroxenes, together with those of the relatively homogeneous pyroxenes produced in crystallization experiments, exhibit a 1∶1 correlation with values of $$\mu _{{\text{TiAl}}_{\text{2}} ({\text{MgSi}}_{\text{2}} )_{ - 1} } $$ derived from the solution model of Ghiorso et al. (1983) with a standard error of 750 calories. The Ti contents of Ca-rich pyroxenes crystallizing from a wide range of natural silicate liquids can therefore be predicted.

Notes: Abstract The Fe3+/Σ Fe of twenty-nine experimentally formed, iron-bearing silicate glasses has been determined by wet-chemical and Mössbauer spectroscopic methods from 5–10 mg individual splits of 20–40 mg experimental run products. The wet-chemical and Mössbauer analyses were conducted in two separate laboratories (University of California, Berkeley, and the Geophysical Laboratory, respectively). The Fe3+/Σ Fe ranges from less than 0.2 to 0.96, and the total iron oxide content of the samples, from 2.2 to 34.7 wt %, added as Fe2O3. The interlaboratory comparison shows 70% of the Fe3+/ΣFe analyses from the two methods within the quoted uncertainties (±1 σ) of each other and 83% of the analyses within ±2 σ of each other. Replicate analyses in the current data set result in variations within ±1 σ. These uncertainties are similar to those obtained from several hundred Fe3+/Σ Fe analyses of reequilibrated natural rock and simple system compositions carried out with identical analytical methods in the two laboratories. There is no systematic bias in the results from either of the two techniques. The Fe3+/Σ Fe of silicate glasses can be analyzed, therefore, with equal confidence by either the wet-chemical or the Mössbauer spectroscopic method.

Notes: Abstract Results of chemical analyses of glasses produced in 46 melting experiments in air at 1,350° C and 1,450° C on rocks ranging in composition from nephelinite to rhyolite have been combined with other published data to obtain an empirical equation relating in $$(X_{{\text{Fe}}_{\text{2}} {\text{O}}_{\text{3}} }^{{\text{liq}}} /X_{{\text{FeO}}}^{{\text{liq}}} )$$ to T, $$\ln f_{{\text{O}}_{\text{2}} } $$ and bulk composition. The whole set of experimental data range over 1,200–1,450° C and oxygen fugacities of 10−9.00 to 10−0.69 bars, respectively. The standard errors of temperature and $$\log _{10} f_{{\text{O}}_{\text{2}} } $$ predictions from this equation are 52° C and 0.5 units, respectively, for 186 experiments.

Notes: [Auszug] The apparatus developed for high-temperature liquid-state NMR will be described in detail elsewhere. A sample in a 1-cm diameter boron nitride capsule is rapidly shuttled 15 cm between a furnace and a room-temperature radio frequency NMR coil, spending 10 s in the former and -0.5 s in the latter ...

Notes: [Auszug] Deerite was separated from a sample from the type locality, Laytonville, California. The chemical analysis is listed below in Table 1. The formula is appproximately Fe213Fe37Si13O44(OH)11 with minor substitution of titanium and aluminium for ferric iron and manganese for ferrous iron. The inverse ...

Notes: Abstract 29Si magic-angle spinning nuclear magnetic resonance (NMR) spectra are presented for seven crystalline phases of the nepheline group: natural nephelines from a plutonic environment (Bancroft, Ontario) and a volcanic deposit (Mt. Somma, Italy), kalsilite, synthetic pure Na nepheline, carnegieite, and two samples of orthorhombic KAlSiO4. In all phases, nearly all of the Si sites have four Al neighbors, indicating nearly complete Al-Si ordering. Excess Si over the 1:1 stoichiometric Si/Al ratio appears to substitute randomly for Al on an ordered lattice, adding Si sites with 3 and 0 Al neighbors in a 3:1 ratio. Various types of structural disorder, including Al-Si disorder, that are reported from some x-ray diffraction studies are probably long range in nature and are due to the presence of ordered domains. In naturally occurring nepheline, the relative abundance of T sites with three-fold local symmetry is maintained at the ideal stoichiometric value of 1/4, even when the K/(K+Na) ratio is substantially lower. This is in agreement with conclusions reached about the average structure from x-ray data. The distinction between the two sites, at least in terms of the local structure that is reflected in 29Si NMR chemical shifts, is lost in a pure Na nepheline sample.

Notes: Abstract Ferric-ferrous ratios have been measured in 22 experiments on three natural compositions equilibrated at known temperature (950°–1100° C) and oxygen fugacity, and at water-saturated conditions over a pressure range from 0.05 to 0.2 GPa. There does not appear to be any reaction between the melt and the capsule material that affects the redox state of the iron in the melt. An empirical expression for the anhydrous behavior of the redox state of iron in each of these compositions has also been determined at 1 bar as a function of temperature and oxygen fugacity. A direct comparison of the hydrous ferric-ferrous values with the calculated anhydrous values shows that the dissolution of water in a per-alkaline rhyolite, andesite, and an augite minette has no effect on the redox state of the iron in these melts. This result parallels the effect of water on sulfide speciation in basaltic melts, and confirms published results on experimental hydrous basalts.

Notes: Abstract  Pleistocene-Holocene volcanism in the Jalisco block of western Mexico is confined to two conspicuous grabens, where potassic eruptives range from absarokites (48–52% SiO2) and minettes (49–54% SiO2) through basaltic andesites (53–57% SiO2), the most voluminous type, to andesites and their lamprophyric equivalent spessartite (58–62% SiO2); there are no contemporary rhyolitic rocks. This suite has high concentrations of Mg, Cr (〈550 ppm) and Ni (〈450 ppm) accompanied by large concentrations of K, P, Ba (〈4000 ppm) and Sr (〈5000 ppm) and elements such as LREE and Zr (〈600 ppm). No combination of crystal fractionation and/or crustal contamination can reproduce the compositional range of these magmas, which nevertheless are believed to be genetically related because of their proximity in time and space. Hydrous minerals in the lamprophyres and the typical absence of plagioclase phenocrysts in both basaltic andesites and andesites reflect the relatively high concentrations of water in the magmas, which suppressed the crystallisation of feldspar. Experimental verification of the minimal amounts of water required to reproduce the phenocryst assemblages in selected rocks range from 3.5 to 6%. During ascent in a volcanic conduit, andesitic magma may lose water and consequently precipitate plagioclase, or it may ascend more rapidly, retaining more of its initial water, which stabilises phenocrysts of hornblende at the expense of plagioclase. Our estimates of water concentrations, which are consistent with the various low pressure phenocryst assemblages, will be minimal for the magmas in their source regions, and the process of magmatic dewatering on ascent may be typical in well established volcanic conduits. In accord with the compositions of phenocrystic olivine in the basaltic andesites and the minettes, the values of FeO and Fe2O3 of the bulk lavas and scoriae are demonstrably pristine. As a consequence, there are two characteristic features of the Mascota suite: the high range of relative oxygen fugacities (ΔNNO=1–5) and the high Mg# (MgO/MgO+FeO) that ranges from 0.70 to 0.91 (with only one andesite as low as 0.66). From the evidence of phlogopite phenocrysts, a partial melt involving phlogopite would have a higher Mg# than one from olivine (Fo90) and pyroxene alone. As the Mascota series shows a correlation between K2O and Mg#, we conclude that it was generated by partial fusion of the mantle wedge, with a variable contribution of phlogopite and apatite from veins throughout the lherzolitic assemblage. In conformity with an origin by varying increments of partial fusion of a phlogopite-bearing mantle, all incompatible elements vary linearly with Ti (or K) as if phlogopite (+apatite) in the source dominated their contribution to the partial melts. Fluids from dehydration of the subducting slab presumably deposit hydrous and other minerals in veins in the mantle wedge and also increase its redox state. As the Mascota volcanism occurs in grabens closer to the trench than the main andesite arc, it is concluded that the eruption of these small volumes of hydrous magmas require the tectonically favored ascent paths offered by the extensional grabens to reach the surface from their mantle sources.