Petrology of ultramafic nodules from West Kettle River,near Kelowna,Southern British Columbia

A basanitoid flow of Miocene age, exposed near the West Kettle River, 25 km southeast of Kelowna, British Columbia, contains abundant ultramafic and mafic nodules. The subangular nodules are 1–20 cm across and typically show granular textures. A study of 250 nodules indicates that spinel lherzolite (60%) is the dominant type with subordinate olivine websterite (10%), websterite (7%), clinopyroxenite (4%), wehrlite (4%), pyroxene gabbro (4%), dunite (2%), harzburgite (1%) and granitic rocks (8%). Ultramafic nodules are of two types. Most of the wehrlites and clinopyroxenites belong to the black pyroxene (aluminous clinopyroxene) series, whereas the other clinopyroxene-bearing nodules belong to the green pyroxene (chromian diopside) series. Some spinel lherzolite nodules have distinctive pyroxene- and olivine-rich bands. Microprobe analyses of the constituent minerals of more than thirty nodules from the green pyroxene series indicate that grain to grain variations within individual nodules are small even when banding is present. Olivine, orthopyroxene, clinopyroxene and spinel in spinel lherzolite have average compositions of Fo₉₀, En₉₀, Wo₄₇Fs₅En₄₈, Cr/(Cr+ Al+Fe³)=0.1 and Mg/(Mg+Fe²⁺)=0.8. Equilibration temperatures, which were calculated using the two pyroxene geothermometer of Wells (1977), range between 920–980° C. Based on published phase stability experiments, pressures of equilibration are between 10–18 kbar. In summary, the upper mantle beneath southern British Columbia is dominated by spinel lherzolite but contains some banding on a scale of cm to meters. The temperature in the upper mantle is 950° C at a depth of 30–60 km.On leave from the Geological Institute, University of Tokyo, Japan     

Electrical conductivity,thermopower and <Superscript>57</Superscript>Fe Mössbauer spectroscopy of aegirine (NaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript>)

DC and AC electrical conductivities were measured on samples of two different crystals of the mineral aegirine (NaFeSi₂O₆) parallel () and perpendicular () to the [001] direction of the clinopyroxene structure between 200 and 600 K. Impedance spectroscopy was applied (20 Hz–1 MHz) and the bulk DC conductivity _DC was determined by extrapolating AC data to zero frequency. In both directions, the log _DC – 1/T curves bend slightly. In the high- and low-temperature limits, differential activation energies were derived for measurements [001] of E_A 0.45 and 0.35 eV, respectively, and the numbers [001] are very similar. The value of _DC [001] with _DC(300 K) 2.0 × 10^{–6 –1}cm^–1 is by a factor of 2–10 above that measured [001], depending on temperature, which means anisotropic charge transport. Below 350 K, the AC conductivity () (/2=frequency) is enhanced relative to _DC for both directions with an increasing difference for rising frequencies on lowering the temperature. An approximate power law for () is noted at higher frequencies and low temperatures with () ^s, which is frequently observed on amorphous and disordered semiconductors. Scaling of () data is possible with reference to _DC, which results in a quasi-universal curve for different temperatures. An attempt was made to discuss DC and AC results in the light of theoretical models of hopping charge transport and of a possible Fe²⁺ Fe³⁺ electron hopping mechanism. The thermopower (Seebeck effect) in the temperature range 360 K < T <770 K is negative in both directions. There is a linear – 1/T relationship above 400 K with activation energy E 0.030 eV [001] and 0.070 eV [001]. ⁵⁷Fe Mössbauer spectroscopy was applied to detect Fe²⁺ in addition to the dominating concentration of Fe³⁺.     

Late Hercynian U-vein mineralization in the Alps: fluid inclusion and C,O, H isotopic evidence for mixing between two externally derived fluids

Late Hercynian U-bearing carbonate veins within the metamorphic complex of La Lauzière are characterized by two parageneses. The first is dominated by dolomite or ankerite and the second by calcite and pitchblende. Fluids trapped in the dolomites and ankerites at 350–400° C are saline waters (20 to 15 wt % eq. NaCl) with D –34 to –49. In the calcite they are less saline (17 to 8 wt % eq. NaCl) and trapped at 300–350° C with D –50 to –65. All fluids contain trace N₂, CO₂ and probably CH₄. The carbonates have ¹³C –8 to –14. and derived their carbon from organic matter. Evolution of the physico-chemical conditions from dolomite (ankerite) to calcite deposition was progressive.H and O-isotope studies indicate the involvement of two externally derived fluids during vein development. A D-rich ( –35) low fO₂, saline fluid is interpreted to have come from underlying sediments and entered the hotter overlying metamorphic slab and mixed with more oxidizing and less saline U bearing meteoric waters during regional uplift. This evidence for a sedimentary formation water source for the deep fluid implies that the metamorphic complex overthrusted sedimentary formations during the Late-Hercynian.     

Zwei Seladonite ungewöhnlicher chemiseher Zusammensetzung

Zusammenfassung Die optische, röntgenographische and chemische Untersuchung.zweier Seladonite aus einem Al₂0₃-reichen basaltischen Gestein and einem Porphyr ergab, daß dieses Mineral anscheinend doch häufiger als angenommen eine glaukonitähnliche Zusammensetzung haben and daß sein Chemismus auch von dem Ausgangsgestein abhängen kann. Im Rahmen dieser Untersuchung erhebt sich die Frage, ob es nicht sinnvoll ist, den Begriff Glaukonit auch auf Minerale nicht sedimentärer Herkunft aber der entsprechenden chemischen Zusammensetzung auszudehnen.

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Untill now the term celadonite was used for micaceous minerals which as well occured in igneous rocks as had the chemical composition (K, Na, Ca, H₃O) _<1 (Al, Fe³⁺)₁ (Fe²⁺, Mg)₁ [(OH)₂A_l>0Si_<4O₁₀], while the term glaucontte was restricted to micaceous minerals with the composition (K, Na, Ca, H₃0⁺)_<1 (Al, Fe³⁺, Fe²⁺; Mg)₂[(OH)₂Al_<1Si_>3O₁₀] formed in sedimentary rocks, mainly of marine origin. The few micas with glauconitic composition found in igneous rocks were called celadonites. Based on the analysis of two celadonites of such a kind from one rhyolite and one altered basaltic rock it is discussed, whether the term glaucontte should be extended to micaceous minerals of non-sedimentary origin but glauconitic composition.

     

Corundum,Cr-muscovite rocks at O'Briens,Zimbabwe: the conjunction of hydrothermal desilicification and LIL-element enrichment — geochemical and isotopic evidence

Monomineralic domains of chlorite, corundum and Cr muscovite coexist over a kilometer scale within ultramafic schists of the Harare greenstone belt (2.73 Ga). This exotic lithological association includes the conjunction of some of the most aluminous (Al₂O₃88 wt%) and potassic (K₂O10 wt%) rocks known. The paragenetic sequence developed from chloritecorundumcorundum+ diaspore: Cr muscovite variably overprinted both the corundum and chloritite domains. Terminal stages were marked by sporadic production of andalusite+quartz, and finally margarite.Chlorite (Cr₂O₃=0.31–2.65 wt%), corundum (0.79–2.66 wt%), and diaspore are all Cr-rich varieties. The chromian (Cr₂O₃3.86 wt%) paragonitic muscovite incorporates up to 17% of the paragonite molecule, and significant Mg and Fe substitutions.The suite of rocks are characterized by chondritic Ti/Zr ratios (–x=107), systematically enhanced Cr (up to 14000 ppm) and Ni (up to 1200 ppm) abundances, low levels of the alteration-insensitive incompatible elements Th, Ta, Nb. Chlorite, corundum and Cr muscovite represent progressive stages in the incremental metasomatic alteration of a komatiite precursor. Mass balance calculations, constrained by the isochemical behaviour of Ti, Zr and Hf reveal that the komatiite chloritite transformation involved volumetric contractions of 60% by hydrothermal leaching of Si, Fe, Mn, Ca and Na. Reaction of chloritite to corundum involved further volumetric reductions of 50% due to essentially quantitative loss of Si, Fe, Mn, Mg, K and Ca. Conversion of corundum to muscovite required additions of Si, K, Fe, Mn, Mg, Rb and Ba at 50–200% dilation. K, Rb, Ba, Li and Cs are enriched by up to 2×10³ over background abundances in ultramafic rocks, and the suite is also enriched in B, Se, Te, Bi, As, Sb and Au. REE were extensively leached during chloritite-corundum stages, whereas LREE additions accompany development of muscovite. Ti, Zr, Hf and Al were all concentrated by selective leaching of mobile components, but absolute additions of Al accompanied development of the corundum domains due to Al precipitation in response to depressurization.Corundum ( ¹⁸O=3.5–4.8), muscovite ( ¹⁸O=6.7–7.5) and chlorite (4.5–5.6) are isotopically uniform and formed at 380–520° C from a fluid where ¹⁸O=5.6–6.9. The corundum is ¹⁸O depleted relative to either igneous or anatectic counterparts (O_cor=7.6–8.2), or to gibbsitic laterites ( ¹⁸O=12–17).Previous genetic schemes involving metamorphism of exhalites or bauxite, or Si-undersaturation of magmas, can all be ruled out from the data. The chloritite, corundum, Cr-muscovite association represents sequential alteration products of ultramafic rocks by high temperature, low pH hydrothermal solutions carrying LIL-elements, and in which excursions of pH and/or degree of quartz undersaturation account for the mineralogical transitions. A deep level acid epithermal system, or fluid advection across steep inverted thermal gradients in a thrust regime could account for required hydrothermal conditions.     

Calibration of Al/Si order variations in anorthite

New single crystal diffraction data for natural and heat-treated anorthite crystals (Angel et al. 1990) allow the determination of their states of Al/Si order in terms of a macroscopic order parameter,Q _OD , for the transition. Numerical values ofQ _OD obtained from estimates of site occupancies are shown to vary with the scalar spontaneous strain, _s , as _s Q _OD ² , and with the ratio of the sums of typeb (superlattice) reflections and typea (sublattice) reflections asI _b/I _a Q _OD ² . An empirical calibration for pure anorthite is obtained giving varies between 0.92 and 0.87 in samples equilibrated at T1300° C, but then falls off relatively rapidly with increasing temperature, reaching 0.7 near the melting point ( 1557° C). The observed temperature dependence does not conform to the predictions of the simplest single order parameter models; coupling ofQ _OD withQ of the transition is suspeeted.     

Complexation of Gold(III)-Chloride at the Surface of Hematite

The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H⁺ – FeOH –AuCl ₄ ^- – Cl^-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 pH 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were log _1,1,0,0(int) ^s = 7.10 ± 0.06 andlog _{-1,1,0,0(int)} ^s = - 7.80 ±0.06. The density of proton active surface sites was 2.85nm^-2 and the specific capacitance 2.5 C V^-1 m^-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 pH 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: FeOHAuCl₃(log _0,1,1,-1 ^s = 1.45 ± 0.03),FeOHAuCl₂OH (log _-1,1,1,-2 ^s = -3.89 ± 0.02), FeOHAu(OH)₃ (log _-3,1,1,-4 ^s = -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(FeO)₂Au(OH)H₂O. However, based onstructural arguments this complex was rejected.     

Petrogenesis of voluminous mid-Tertiary ignimbrites of the Sierra Madre Occidental,Chihuahua, Mexico

The mid-Tertiary ignimbrites of the Sierra Madre Occidental of western Mexico constitute the largest continuous rhyolitic province in the world. The rhyolites appear to represent part of a continental magmatic arc that was emplaced when an eastward-dipping subduction zone was located beneath western Mexico.In the Batopilas region of the northern Sierra Madre Occidental the mid-Tertiary Upper Volcanic sequence is composed predominantly of rhyolitic ignimbrites, but volumetrically minor lava flows as mafic as basaltic andesite are also present. The basaltic andesite to rhyolite series is calc-alkalic and contains 1% K₂O at 60% SiO₂. Trace element abundances of a typical ignimbrite with 73% SiO₂ are Sr 225 ppm, Rb 130 ppm, Y 32 ppm, Th 12 ppm, Zr 200 ppm, and Nb 15 ppm. The entire series plots as coherent and continuous trends on variation diagrams involving major and trace elements, and the trends are distinct from those of geographicallyassociated rocks of other suites. We interpret these and other geochemical variations to indicate that the rocks are comagmatic. Mineral chemistry, Sr isotopic data, and REE modelling support this interpretation.Least squares calculations show that the major element variations are consistent with formation of the basaltic andesite to rhyolite series by crystal fractionation of observed phenocryst phases in approximate modal proportions. In addition, calculations modelling the behavior of Sr with the incompatible trace element Th favor a fractional crystallization origin over a crustal anatexis origin for the rock series. The fractionating minerals included plagioclase (> 50%), and lesser amounts of Fe-Ti oxides, pyroxenes, and/or hornblende. The voluminous ignimbrites represent no more than 20% of the original mass of a mantle-derived mafic parental magma.     

Crystal chemistry of natural tellurides II: Redetermination of the crystal structure of krennerite, (Au1−x Ag x ) Te2 withx∼0.2

Summary The crystal structure redetermination of krennerite (a=16.58,b=8.849,c=4.464 Å;Z=8; space group:Pma2-C _2v ^/4 ) with 1063 X-ray data yielded anR-value of 5.8%. Within the structure, there are three crystallographically different noble metal positions. Two of them are statistically occupied by Au and Ag atoms (ratios of 7525 and 5050, respectively) and one position by Au atoms only. The (Au, Ag) atoms are surrounded by six Te atoms with a [2+2+2] coordination. The Au atom has a [4+2] coordination built up by six Te atoms. These three different coordination polyhedra are linked via common Te–Te edges to rugged sheets parallel to (010). These sheets are connected to a framework by four crystallographically different Te atoms—combined to one Te₃ group and two Te₂ dumb bells (with Te–Te<2.9 Å). A fifth Te atom is only surrounded by (Au, Ag) and Au atoms. According to these different structural elements the crystal chemical formula may be written as (Au_2–x Ag _x )Au₂[Te₃][Te₂]₂[Te];x0.8.

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Kristallchemie natürlicher Telluride. II: Neubestimmung der Kristallstruktur des Krennerits, (Au_1–xAg_x) Te₂ mit x0,2

Zusammenfassung Die Kristallstruktur des Minerals Krennerit (a=16,58,b=8,849,c=4.464 Å;Z=8; Raumgruppe:Pma2-C _2v ^/4 ) wurde neu bestimmt. Die Strukturverfeinerung ergab mit 1063 RöntgenintensitätenR=5,8%. In dieser Struktur gibt es drei kristallographisch verschiedene Edelmetallpositionen. Zwei davon sind statistisch mit Au- und Ag-Atomen (Verhältnis 7525 bzw. 5050), eine nur mit Au-Atomen besetzt. Die (Au, Ag)-Atome werden von sechs Te-Atomen in einer [2+2+2]-Koordination umgeben, das Au-Atom besitzt eine [4+2]-Koordination von sechs Te-Atomen. Diese drei verschiedenen Koordinationspolyeder werden über gemeinsame Te–Te-Kanten zu gewellten Schichten parallel (010) verbunden. Durch vier kristallographisch verschiedene Te-Atome-die ihrerseits zu einer Te₃-Gruppe und zwei Te₂-Hanteln (mit jeweils Te–Te<2.9 Å) verbunden sind—werden diese Schichten zu einem Gerüst verknüpft. Ein fünftes Te-Atom wird nur von (Au, Ag)-bzw. Au-Atomen umgeben. Entsprechend diesen verschiedenen Bauelementen kann die kristallchemische Formel wie folgt geschrieben werden. (Au_2–x Ag _x )Au₂[Te₃][Te₂]₂[Te];x0,8.

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With 2 Figures     

Über Strontioginorit,eine neue Ginorit-Varietdt aus dem Zechsteinsalz

Zusammenfassung Strontioginorit (Sr, Ca)₂B₁₄O₂₃ 8 H₂O mit Sr: Ca1,3:0,7 tritt in gut ausgebildeten Kristallen im Alteren Steinsalz von Reyershausen bei Göttingen auf. Es ergaben sich folgende Daten : ₀ = 12,85₀ Å,b ₀ = 14,48 Å,c ₀, = 12,85₅, Å, = 101° 35, RaumgruppeP 2_I/a,Z = 4, Dichte=2,25 gcm^–3,n = 1,512,n _/b = 1,524,n //[101] = 1,577.     

Origin and differentiation of picritic arc magmas,Ambae (Aoba), Vanuatu

Key aspects of magma generation and magma evolution in subduction zones are addressed in a study of Ambae (Aoba) volcano, Vanuatu. Two major lava suites (a low-Ti suite and high-Ti suite) are recognised on the basis of phenocryst mineralogy, geochemistry, and stratigraphy. Phenocryst assemblages in the more primitive low-Ti suite are dominated by magnesian olivine (mg 80 to 93.4) and clinopyroxene (mg 80 to 92), and include accessory Cr-rich spinel (cr 50 to 84). Calcic plagioclase and titanomagnetite are important additional phenocryst phases in the high-Ti suite lavas and the most evolved low-Ti suite lavas. The low-Ti suite lavas span a continuous compositional range, from picritic (up to 20 wt% MgO) to high-alumina basalts (<5 wt% MgO), and are consistent with differentiation involving observed phenocrysts. Melt compositions (aphyric lavas and groundmasses) in the low-Ti suite form a liquid-line of descent which corresponds with the petrographically-determined order of crystallisation: olivine + Cr-spinel, followed by clinopyroxene + olivine + titanomagnetite, and then plagioclase + clinopyroxene + olivine + titanomagnetite. A primary melt for the low-Ti suite has been estimated by correcting the most magnesian melt composition (an aphyric lava with 10.5 wt% MgO) for crystal fractionation, at the oxidising conditions determined from olivine-spinel pairs (fo₂ FMQ + 2.5 log units), until in equilibrium with the most magnesian olivine phenocrysts. The resultant composition has 15 wt% MgO and an mg ^Fe2 value of 81. It requires deep (3 GPa) melting of the peridotitic mantle wedge at a potential temperature consistent with current estimates for the convecting upper mantle (T _p 1300°C). At least three geochemically-distinct source components are necessary to account for geochemical differences between, and geochemical heterogeneity within, the major lava suites. Two components, one LILE-rich and the other LILE- and LREE-rich, may both derive from the subducting ocean crust, possibly as an aqueous fluid and a silicate melt respeetively. A third component is attributed to either differnt degrees of melting, or extents of incompatible-element depletion, of the peridotitic mantle wedge.     

Crystal structure and crystallographic properties of a Schröckingerite from Joachimsthal

Summary The crystal structure of a schröckingerite from Joachimsthal, NaCa₃[UO₂(CO₃)₃](SO₄) F·10H₂O, triclinic, space groupP1,a=9.634(1),b=9.635(1),c=14.391(2) Å, -91.41(1), =92.33(1), =120.26(1)°,V=1151 ų,Z=2, has been determined by X-ray diffraction and refined toR=0.026 for 5451 reflections. The structure contains NaCa₃[UO₂(CO₃)₃] (SO₄) F·6H₂O layers built up from UO₂(CO₃) ₃ ^4– anions, NaO₃(H₂O)₃ octahedra, three kinds of CaO₅F(H₂O)₂ polyhedra, Ca₃F pyramids and Ca-bonded SO₄ tetrahedra. These layers extend atz1/5 andz4/5 parallel to (001). They are linked parallel to c exclusively by hydrogen bonds, both directly as well as via interlayer H₂O molecules. The structure shows a striking trigonal pseudosymmetry within the range 0.04<z<0.96. Atz0 these parts of the structure are dislocated relative to each other by a step of 1 Å parallel to [110]. Morphologic and optical properties of schröckingerite have been investigated in the light of the known crystal structure.

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Kristallstruktur und kristallographische Eigenschaften eines Schröckingerits von Joachimsthal

Zusammenfassung Die Kristallstruktur eines Schröckingerits von Joachimsthal, NaCa₃[UO₂(CO₃)₃](SO₄) F·10H₂O, triklin, RaumgruppeP1,a=9,634(1),b=9,635(1),c=14,391(2) Å, =91,41(1), =92,33(1), =120,26(1)°,V=1151 ų,Z=2, wurde mit Röntgenbeugung bestimmt und für 5451 Reflexe aufR=0.026 verfeinert. Die Kristallstruktur enthält NaCa₃[UO₂(CO₃)₃] (SO₄)I·6H₂O Schichten, die aus UO₂(CO₃) ₃ ^4– . Anionen, NaO₃(H₂O)₃-Oktaedern, drei Arten von CaO₅F(H₂O)₂-Polyedern, Ca₃ F-Pyramiden und an Ca gebundenen SO₄-Tetraedern aufgebaut sind. Diese Schichten erstrecken sich inz1/5 undz4/5 parallel zu (001). Sie sind parallel zuc ausschließlich durch Wasserstoffbrücken verknüpft, und zwar sowohl direkt als auch indirekt durch zwischen den Schichten gelegene Wassermoleküle. Die Struktur zeigt im Bereich 0,04<z<0,96 eine ausgeprägte trigonale Pseudosymmetrie. Derartige Bereiche sind inz0 um etwa 1 Å parallel zu [110] stufenartig gegeneinander versetzt. Morphologische und optische Eigenschaften von Schröckingerit wurden im Licht der bekannten Kristallstruktur untersucht.

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With 6 Figures     

Use of the lattice parameter b 0 of dioctahedral illite/muscovite for the characterization of P/T gradients of incipient metamorphism

The P/T gradient or baric type of low-grade metamorphic terranes can be characterized on the basis of cumulative frequency curves of the lattice parameter b ₀ of dioctahedral micas (Sassi and Scolari 1974), which essentially reflects celadonite content and increases with pressure. The method is here applied to illite/muscovite of sub-greenschist (incipient metamorphism) and low-greenschist facies terranes from the marginal zones of the Swedish Caledonides, Swiss Alps and Venezuelan Andes, where the grade of metamorphism was determined on the basis of illite crystallinity.Complications in the determinations of b ₀ arising from (a) shifts in the spacing of the apparent 060 diffraction peaks of the illites due to the presence of inter-stratified expandable layers, and (b) persistence of more crystalline clastic micas are pointed out.In contrast to the earlier-reported decrease of b ₀ with progressive metamorphism at higher grades, b ₀ tends to increase with grade during incipient metamorphism: it is markedly lower in the diagenetic and low-grade anchimetamorphic grades in the Cambro-Silurian of the Caledonides of Jämtland, western Sweden (zone A), and the Lower Tertiary of the Helvetic zone of the Swiss Alps, than in the higher grade anchizone and epizone of the former terrane.Mean b ₀ values for the intermediate and highest (epizone) grades of the Swedish Caledonides are respectively 9.030 and 9.037 Å compared to the mean value of 9.035 Å for the medium-high pressure, Barrovian-type, terrane of Otago, N.Z. Mean b ₀ of 9.005 Å for the mainly epizonal slates of the Venezuelan Andes lies between those for the low-pressure terranes of Bosost ( 8.992 Å), and the low-medium pressure terrane of northern New Hampshire (9.010 Å). These baric estimates agree well with those for the metamorphic facies series at higher grade produced by the same events.Cumulative b ₀ curves are concluded to be useful for the characterization of P/T gradients of incipient metamorphism, particularly in the higher grade part of the anchizone and the epizone.     

Geochemistry and argon thermochronology of the Variscan Sila Batholith,southern Italy: source rocks and magma evolution

The Sila batholith is the largest granitic massif in the Calabria-Peloritan Arc of southern Italy, consisting of syn to post-tectonic, calc-alkaline and metaluminous tonalite to granodiorite, and post-tectonic, peraluminous and strongly peraluminous, two-mica±cordierite±Al silicate granodiorite to leucomonzogranite. Mineral ⁴⁰Ar/³⁹Ar thermochronologic analyses document Variscan emplacement and cooling of the intrusives (293–289 Ma). SiO₂ content in the granitic rocks ranges from 57 to 77 wt%; cumulate gabbro enclaves have SiO₂ as low as 42%. Variations in absolute abundances and ratios involving Hf, Ta, Th, Rb, and the REE, among others, identify genetically linked groups of granitic rocks in the batholith: (1) syn-tectonic biotite±amphibole-bearing tonalites to granodiorites, (2) post-tectonic two-mica±Al-silicate-bearing granodiorites to leucomonzogranites, and (3) post-tectonic biotite±hornblende tonalites to granodiorites. Chondrite-normalized REE patterns display variable values of Ce/Yb (up to 300) and generally small negative Eu anomalies. Degree of REE fractionation depends on whether the intrusives are syn- or post-tectonic, and on their mineralogy. High and variable values of Rb/Y (0.40–4.5), Th/Sm (0.1–3.6), Th/Ta (0–70), Ba/Nb (1–150), and Ba/Ta (50–2100), as well as low values of Nb/U (2–28) and La/Th (1–10) are consistent with a predominant and heterogeneous crustal contribution to the batholith. Whole rock ¹⁸O ranges from +8.2 to +11.7; the mafic cumulate enclaves have the lowest ¹⁸O values and the two-mica granites have the highest values. ¹⁸O values for biotite±honblende tonalitic and granodioritic rocks (9.1 to 10.8) overlap the values of the mafic enclaves and two-mica granodiorites and leucogranites (10.7 to 11.7). The initial Pb isotopic range of the granitic rocks (²⁰⁶Pb/²⁰⁴Pb 18.17–18.45, ²⁰⁷Pb/²⁰⁴Pb 15.58–15.77, ²⁰⁸Pb/²⁰⁴Pb 38.20–38.76) also indicates the predominance of a crustal source. Although the granitic groups cannot be uniquely distinguished on the basis of their Pb isotope compositions most of the post-tectonic tonalites to granodiorites as well as two-mica granites are somewhat less radiogenic than the syn-tetonic tonalites and granodiorites. Only a few of the mafic enclaves overlap the Pb isotope field of the granitic rocks and are consistent with a cogenetic origin. The Sila batholith was generated by mixing of material derived from at least two sources, mantle-derived and crustal, during the closing stages of plate collision and post-collision. The batholith ultimately owes its origin to the evolution of earlier, more mafic parental magmas, and to complex intractions of the fractionating mafic magmas with the crust. Hybrid rocks produced by mixing evolved primarily by crystal fractionation although a simple fractionation model cannot link all the granitic rocks, or explain the entire spectrum of compositions within each group of granites. Petrographic and geochemical features characterizing the Sila batholith have direct counterparts in all other granitic massifs in the Calabrian-Peloritan Arc. This implies that magmatic events in the Calabrian-Peloritan Arc produced a similar spectrum of granitic compositions and resulted in a distinctive type of granite magmatism consisting of coeval, mixed, strongly peraluminous and metaluminous granitic magmas.     

Formation of Mud-Volcanic Fluids in Taman (Russia) and Kakhetia (Georgia): Evidence from Boron Isotopes

Temperatures of the formation of mud-volcanic waters are determined based on concentrations of some temperature-dependent components (Na–Li, Mg–Li). Estimates obtained for the Taman and Kakhetia regions are similar and range from 45 to 170°, which correspond to depths of 1–4.5 km. The calculated temperatures correlate with the chemical (Li, Rb, Cs, Sr, Ba, B, I, and HCO₃) composition of water and ¹³ (₂) and ¹³ (CH₄) values in spontaneous gases. The isotope values indicate that mechanisms of the formation of ¹³-rich gases, i.e., gases with high ¹³ values (up to +16.0 in ₂ and –23.4 in CH₄) in mud-volcanic systems of Taman and Kakhetia are governed by fluid-generation temperatures rather than the supply of abyssal gases. The ¹¹ value was determined for the first time in mud-volcanic products of the Caucasus region. This value ranges from +22.5 to +39.4 in the volcanic water of Georgia, from –1.2 to +7.4 in the clayey pulp of Georgia, and from –7.6 to +13.2 in the clayey pulp of Taman. It is shown that the ¹¹ value in clay correlates with the fluid-generation temperature and ¹¹ correlates with ¹³ in carbon-bearing gases. These correlations probably testify to the formation of different phases of mud-volcanic emanations in a single geochemical system and suggest the crucial role of temperature in the development of isotope-geochemical features.     

Sr-Nd isotopic constraints on the petrogenesis of the Central Bohemian Pluton,Czech Republic

The Sr-Nd isotopic data for selected granitoids of the Central Bohemian Pluton show a broad negative correlation with the total range of (⁸⁷Sr/⁸⁶Sr)₃₃₀ = 0.7051–0.7129 and _Nd ³³⁰ = +0.2 to –8.9. The older intrusions have more depleted Sr-Nd compositions and calc-alkaline geochemistry (Sázava suite), whereas the younger intrusions shift towards K-rich calc-alkaline (Blatná suite) and shoshonitic rocks (íany and ertovo bemeno suites) with more evolved isotopic signatures. The distribution of the data is interpreted as reflecting a diversity of sources and processes, rather than a single progressive crustal contamination trend. The Sázava suite could have originated by partial melting of metabasites, or of a mantle source with an isotopic composition close to bulk earth, or by hybridization of crustally-derived tonalitic and mantle-derived magmas. Variation within the Blatná suite is modelled by mixing between a moderately enriched [(⁸⁷Sr/⁸⁶Sr)₃₃₀ 0.708, _Nd ³³⁰ –3] mantle component with either an isotopically evolved metasedimentary component, or with more evolved magmas of the suite. The íany suite was most probably produced by partial melting of peraluminous lithologies, possibly of the adjacent Moldanubian unit. The ertovo bemeno suite evolved from strongly enriched mantle-derived magmas [(⁸⁷Sr/⁸⁶Sr)₃₃₀0.7128, _Nd ³³⁰ –7], either through closed-system fractional crystallization or interaction with magma corresponding to leucogranites of the Central Bohemian Pluton.     

Der Strukturtyp von Emmonsit, {Fe2[TeO3]3·H2O}·xH2O (x=0−1)

Zusammenfassung Emmonsit kristallisiert triklin, RaumgruppeP , Gitterkonstanten:a ₀=7,90 Å,b ₀=8,00 Å,c ₀=7,62 Å, =96^o44, =95^o 0, =84^o 28,Z=2. Der Strukturtyp wurde aus 3-dimensionalen photographischen Röntgendaten ermittelt. Die Eisenatome werden je von 6 Sauerstoffen verzerrt oktaedrisch koordiniert. Jedes Telluratom wird von 3 Sauerstoffen in einem Abstand <2,0 Å umgeben. Ein vierter Sauerstoff hat bezüglich dieser drei einen um etwa 25–35% größeren Abstand, so daß jedes Telluratom im weiteren Sinne eine (3+1)-Koordination aufweist.

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The structure type of emmonsite, {Fe₂[TeO₃]₃·H₂O}·xxH₂O (x=0–1)

Summary Emmonsite is triclinic with space groupP , and lattice constantsa ₀=7.90 Å,b ₀=8.00 Å,c ₀=7.62 Å, =96^o 44, =95^o 0, =84⁰ 28,Z=2. The structure type is derived from 3-dimensional photographic X-ray data. The iron atoms are coordinated by six oxygens in the form of a distorted octahedron. Each tellurium atom is coordinated to 3 oxygens at a distance <2.0 Å. Compared with these 3 Te–O distance the distance of a fourth oxygen is only 25 to 35% greater; therefore each tellurium atom has a (3+1)-coordination of oxygens.

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Mit 2 Abbildungen     

Evaluation of biotite-garnet geothermometers: application to the English River subprovince,Ontario

In recent years, there have been numerous calibrations of the biotite-garnet Fe-Mg exchange geothermometer. The Eastern Lac Seul region of the English River subprovince, Ontario, provides an excellent field area in which to compare these calibrations.Trend surface analysis using the temperatures obtained from garnet cores and matrix biotites-showed almost identical trends in the eastern Lac Seul region regardless of the calibration used. The absolute temperatures and the precision of each calibration do, however, show large variation. Geothermometers based solely on lnK_D were found to give more precise results than the calibrations that attempt to incorporate non-Fe-Mg components. The Perchuk and Lavrent'eva (1983) thermometer yields the most precise and accurate results. If a sufficient number of samples are collected over a region, it can be used to estimate metamorphic temperature trends to ±30° C. Metamorphism and migmatization of the English River subprovince occurred during the Kenoran orogeny, 2.68 b.y. ago. Our results show that a thermal anticline has been preserved, with temperatures of 600° C at the north and south contacts with Uchi and Wabigoon Greenstone belts, increasing to 725 °C at the center of the subprovince. A garnet-cordierite in isograd occurs at 650° C and an orthopyroxene in isogradat 700° C.     

Vorratsberechnung von Erdöl- und Erdgas-Lagerstätten

Zusammenfassung Als Grundlage für die Berechnung des Öl- und Gasinhalts werden die geologischen Faktoren (Petrophysik, Porosität, Permeabilität, Haftwasser, Porenverteilung, Nettomächtigkeit, Strukturfläche) sowie die Eigenschaften des Poreninhalts (Phasenbeziehungen) beschrieben. Neben den daraus abzuleitenden statischen Methoden sind aber auch dynamische Methoden des Druck- und Förderverhaltens für die Inhaltsberechnung geeignet (Material-Balance-Prinzip). Die vom Poreninhalt gewinnbaren Öl- und Gasmengen werden mittels dynamischer Verfahren und Modellstudien mittels Computer berechnet. Beispiele an Ölfeldern und Ölfeldbereichen der Bundesrepublik erläutern die Auswirkungen der verschiedenen Lagerstätten-Eigenschaften und deren Energie-Verhalten auf die gewinnbaren Reserven, die bei hochviskosen Ölen bei etwa 15–25%, bei niedrigviskosen Ölen bei etwa 30–75%, bei Erdgasen bei etwa 50–80% Entölungs- bzw. Entgasungsgrad liegen. Von besonderer Bedeutung sind dabei technischer Fortschritt und wirtschaftliche Bedingungen. Am Beispiel der Welt wird gezeigt, daß von den etwa 420 Mrd. t Ölinhalt in allen bekannten Ölfeldern zur Zeit etwa 140 Mrd. t gewinnbar sind, die sich um weitere 110 Mrd. t erhöhen lassen, wenn die wirtschaftlichen Bedingungen in Zukunft den Einsatz neuer technischer Verfahren erlauben.

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The geological factors (petrophysics, porosity, permeability, connate water, pore configuration, net pay, productive area) as well as the properties of the pore filling (phase relations) used for determination of the OIP and the GIP are described. Apart from static methods to be derived from these factors, dynamic methods based on the pressure and production behavior can be used for this purpose (principle of material balance). The oil and gas volumes to be recovered from the pore space are calculated by means of dynamic methods and model studies. Oil fields and oil provinces of the Federal Republic of Germany serve as examples to illustrate the effects of the different reservoir charcteristics and the respective energy behavior on the recoverable reserves. The oil or gas recovery factor is about 15–25% with highly viscous oils, about 25–65% with oils of low viscosity and about 50–80% with natural gases. Technical progress and economic factors are of special importance in this connection. It is shown that in addition to the about 140 billion t of oil presently recoverable from worldwide reserves of all known oil fields of about 420 billion t, recovery of another 140 billion t would be possible in future if new technical methods could be applied under the given economic conditions.

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Résumé Sont décrit comme base du calcul de l'huile et du gaz en place les facteurs géologiques (pétrophysique, porosité, perméabilité, eau interstitielle, répartition des pores, épaisseur nette, surface du gisement) ainsi que les propriétés du contenu des pores (relations de phases). Outre les méthodes statiques en dérivées, se prêtent au calcul du contenu en huile ou en gaz aussi des méthodes dynamiques du comportement de pression/production (balance volumétrique). Les quantités de l'huile ou de gaz récoupérables du contenu des pores sont déterminées par des méthodes dynamiques et par des études modèle à l'aide de computer. Des exemples concernant des champs pétrolifères dans la République Fédérale d'Allemagne expliquent les effets des divers propriétés de gisements et leur comportement énergétique sur les ressources récoupérables dont le facteur de récupération de l'huile/du gaz est d'environ 15 à 25% dans le cas des huiles très visqueuses d'environ 25 à 65% dans le cas des huiles de basse viscosité, et d'environ 50 à 80% dans le cas des gaz naturels. A ce propos, le progrès technologique et les conditions économiques sont d'une importance particulière. L'exemple du monde entier montre que de la quantité de 420 milliards de tonnes de l'huile en place dans tous les champs pétrolifères connus, 140 milliards de tonnes environ sont récupérables à présent. Cette quantité pourrait être augmentée encore par 140 milliards de tonnes si les conditions économiques à l'avenir permettent l'emploi de nouvelles techniques.

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: , , , , .., - , . , , . , , - . , , , ; 15–25%, 25–65 % — 50–80 %, . , 420 , 140 . , 140 .

     

Entwurf einer Mikrogefüge-Einteilung von Marschböden

Zusammenfassung Die üblichen Bodengefügeeinteilungen nach dem Grad der Aggregatbildung waren für die Anwendung an Marschböden unzureichend. Es wird ein Entwurf einer Mikrogefüge-Einteilung besprochen, die auf dem Gehalt an Matrix (Kornanteil < 6. geschätzt) wie auf ihrem Ausrichtungsgrad basiert. Der visuell beurteilte Ausrichtungsgrad der Matrix wird als sehr schwach, schwach, mäßig, stark und sehr stark eingestuft, der geschätzte Matrixgehalt in hoch ( > 40%), mittel (23–40%), gering (5–23%), und sehr gering (0–5%) unterteilt.