Titanian chondrodite and clinohumite in marbles from the Ötztal crystalline basement     

Karin Ehlers  Dr. Georg Hoinkes 《Mineralogy and Petrology》1987,36(1):13-25

Summary Marble lenses within the polymetamorphic Ötztal crystalline complex frequently contain pockets of clinohumite and chondrodite and their titanium-rich varieties. Chondrodites contain up to 9.1 wt% TiO₂ and clinohumites about half that amount. The maximum amounts of Ti in both minerals do not exeed values of 0.4 in the formula. XTi and X_F are correlated by a slope of –1, indicating the efficiency of the TiO₂Mg_–1F_–2 substitution at constant OH (Evans andTrommsdorff, 1983). Clinohumites sometimes contain lamellae which have nonstoichiometric cation ratios reflecting a composition between clinohumite and olivine. In many cases Ti-rich clinohumites and chondrodites coexist with Mg-ilmenite. Ti-rich clinohumites and chondrodites often break down to a symplectite of Ti-poor clinohumite (or olivine) and Mg-ilmenite. Parts of the marbles, which are barren of Mg-ilmenite contain F-rich clinohumites. The latter do not show any signs of breakdown features. We conclude therefore that fluorine stabilizes the humite group minerals to a wide range of metamorphic conditions. Ti-rich humite-group minerals are not stable till amphibolite facies conditions, and below F-rich humite-group minerals and olivine are the more stable phases in a H₂O-rich, SiO₂-poor carbonate system.

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Titanreiche Chondrodite und Klinohumite in Marmoren des Ötztalkristallins.

Zusammenfassung In Marmorlinsen des polymetamorphen Ötztalkristaliins kommen häufig titanarme und titanreiche Clinohumite und Chondrodite vor. Die höchsten Titan-Gehalte in Chondrodit betragen 9.1 Gew.-% TiO₂ während Clinohumite nur etwa die Hälfte dieses Wertes enthalten. Dies entspricht einem Maximalgehalt an Titan von 0.4 in den Formeln von Chondrodit und Clinohumit. Eine negative Korrelation zwischen X_Ti, und X_F mit der Steigung von –1 bestätigt die Wirksamkeit der Substitution TiO₂Mg_–1F_–2 bei konstantem OH (Evans undTrommsdorff, 1983). In Clinohumiten konnten nichtstöchiometrische Lamellen nachgewiesen werden, die chemisch zwischen Clinohumit und Olivin zusammengesetzt sind. Ti-reiche Clinohumite und Chondrodite koexistieren immer mit Mg-Ilmenit und wandeln sich häufig an ihren Rändern in einen Symplektit von Ti-ärmerem Clinohumit oder Olivin und Mg-Ilmenit um. In den Mg-Ilmenit freien Bereichen der Marmore kommen stets Ti-arme aber F-reiche Clinohumite vor, die niemals randliche Umwandlungserscheinungen zeigen. Die grobkörnigen (mm-großen) Humitminerale werden der variszischen Metamorphose in Amphibolitfazies zugeschrieben, während die Symplektite als Produkte der eoalpinen grünschieferfaziellen Überprägung angesehen werden. Wir schließen daraus, daß die Humitminerale durch Fluor in einem großen Bereich metamorpher Bedingungen stabilisiert werden, während Ti-reiche Humitminerale bei Bedingungen der Grünschieferfazies instabil werden und F-reiche Humitminerale und Olivin die stabilen Phasen in einem H₂O-reichen, SiO₂-armen Karbonatsystem sind.

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Polymetamorphose und Deckenbau der Strand-Halbinsel/SW-Norwegen     

Prof. Dr. Georg Müller  Dr. Karl W. Strauss 《International Journal of Earth Sciences》1987,76(2):407-418

Zusammenfassung Die Metamorphite der Halbinsel Strand / SW-Norwegen gehören zu einem Deckensystem präkambrischer Gesteine, das während der kaledonischen Orogenese von NNW her auf den Baltischen Schild geschoben worden ist (Sigmond Kildal 1978). Eine hangende Deckeneinheit umfa\t Metagranite, Melagabbroide und Gneise. Ihr granulitfazieller Mineralbestand (Metamorphosealter 1,5 Milliarden Jahre) wurde wahrscheinlich vor 1,18 Milliarden Jahren grünschieferfaziell retrograd überprägt. Die Decke ist nur noch in kleinen Erosionsinseln vorhanden. Eine liegende Dekkeneinheit besteht aus metasedimentären Gesteinen. Sie weist Mineralbestände der höheren Amphibolitfazies auf, die ebenfalls grünschieferfaziell überprägt wurden. Die Al^VI-Gehalte der bei beiden metamorphen Prozessen gebildeten Amphibole deuten bei Anwendung eines Diagramms vonRaase (1974) an, da\ die retrograde Metamorphose hier bei höheren Drücken ablief als die ältere Metamorphose. Ein Gesamtgesteinsalter von 1,16 Milliarden Jahren scheint für diese grünschieferfazielle Metamorphose das gleiche orogene Ereignis anzuzeigen wie für die hangende Einheit. Produkt der schwachen kaledonischen Metamorphose (400 Millionen Jahre) ist Stilpnomelan, der auch im Grundgebirge des Baltischen Schildes auftritt.

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The Strand Peninsula, Stavanger district, Southwestern Norway, has become well known, when V. M.Goldschmidt (1920) published his hypothesis of regional metasomatism. All rocks of the Strand area were assumed to be situated in autochthonous position. The main point ofGoldschmidt's hypothesis was progarde metamorphism of argillaceous sediments and their transformation to albite schists and plagioclase gneisses by metasomatic solutions given off from intruded trondhjemitic magmas.However, in contrast toGoldschmidt's ideas, the granitoid sill of the Ormakam-Moldhesten area, Strand Peninsula, and its wall rocks, which played an important role inGoldschmidt's discussion, are now found to be parts of a polymetamorphous thrust unit.Granulite facies assemblages, mainly consisting of orthopyroxene +clinopyroxene+plagioclase+hastingsite±orthoclase and quartz, have been partially replaced by lowgrade assemblages. Probably, the high-grade metamorphism has an age of about 1.5 Ga (Andresen &Heier 1975) whereas the age of the greenschist facies event may be conform to an orogenic cycle at about 1.15 Ga (Sigmond Kildal 1978).A lower nappe, covering the Strand Peninsula for its most parts, was subject of a petrologic re-examination using the microscope and the microprobe analyser. Its contacts with the hanging nappe as well as those with the underlying gneissic basement are characterized by thrust planes and horizons of phyllonites and cataclasites inside of the nappe and by local brecciation in the uppermost zones of the basement.The rocks of the lower nappe have been formed a long with the upper amphibolite facies as indicated by the following mineral assemblage: andesine + hastingsite and Mg-hornblende + quartz +biotite.Obviously, an inverse order of temperature regimes is recognizable in the allochthonous units. Maximum temperature of the upper nappe reached 800C (Müller &Herbert 1984) whereas T_max of the lower nappe did not exceed 750C.Using a diagram ofRaase (1974) the Al^VI-contents of the primary hastingsitic hornblendes of the lower nappe rocks indicate pressures which range distinctly below 5 kbars, whereas the secondary pargasitic hornblendes were formed at pressures of about 5 kbars. Probably the thrusting happened before the formation of secondary hornblendes took place. The load pressure in the lower nappe (< 5 kbars) was distinctly increased when the upper nappe was thrusted upon the lower one. Consequently the Al^VI-contents of secondary hornblendes indicate increased pressure ( 5 kbars).In the gneisses of the lower nappe late fractures were filled by stilpnomelane, chlorite and quartz. Very probably this depends on thrust movements during the Caledonian orogeny.Verschure et al. (1980) found a similar stilpnomelane formation in adjacent terrains of the basement and proposed a weak Caledonian metamorphism of about 400 my.

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Résumé Les roches métamorphiques de la presqu'Île de Strand (sud-ouest de la Norvège) appartiennent à un empilement de nappes formées de roches pré-cambriennes et charriées vers le SSE sur le bouclier baltique au cours de l'orogenèse calédonienne (Sigmond Kildal 1978).Une nappe supérieure comprend des métagranites, des mélagabbroÏdes et des gneiss. Leurs paragenèses, du facies des granulites (âge du métamorphisme: 1,5 Ga) ont été rétromorphosées dans le facies des schistes verts il y a probablement 1,18 Ga. Cette nappe ne subsiste qu'en petits fragments épargnés par l'érosion.Une nappe inférieure est composée de roches métasédimentaires. Ces roches présentent des paragenèses du faciès supérieur des amphibolites, également rétromorphosées dans le facies des schistes verts. L'application du diagramme de Raase (1974) aux teneurs en Al^VI des amphiboles formées lors des deux processus métamorphiques indique que la rétromorphose s'est déroulée à une pression supérieure à celle du métamorphisme ancien. Un âge de 1,16 Ga sur roche totale semble indiquer que le mÊme processus orogénique a servi de cadre à la rétromorphose en facies des schistes verts dans les deux nappes.Du stilpnomélane, présent tant dans la nappe inférieure que dans le bouclier baltique autochtone, témoigne d'un métamorphisme calédonien (400 Ma) de faible degré.

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Strand ( ) , NNW (Sigmond KILDAL, 1978). , . - 1,5 , 118 , . . . , . Al^VI , , RAASE (1974) , , . 1,6 , , , . (400 ) , .

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Continental ridges in the Arctic Ocean: Lorex constraints     

J.F. Sweeney  J.R. Weber  S.M. Blasco 《Tectonophysics》1982,89(1-3)

Recent multidisciplinary geophysical measurements over the Lomonosov Ridge close to the North Pole support the widely held belief that it was formerly part of Eurasia. The known lithologies, ages, P-wave velocity structure and thickness of the crust along the outer Barents and Kara continental shelves are similar to permitted or measured values of these parameters newly acquired over the Lomonosov Ridge. Seismic, gravity and magnetic data in particular show that the ridge basement is most likely formed of early Mesozoic or older sedimentary or low-grade metasedimentary rocks over a crystalline core that is intermediate to basic in composition. Short-wavelength magnetic anomaly highs along the upper ridge flanks and crest may denote the presence of shallow igneous rocks. Because of the uncertain component of ice-rafted material, seafloor sediments recovered from the ridge by shallow sampling techniques cannot be clearly related to ridge basement lithology without further detailed analysis. The ridge is cut at the surface and at depth by normal faults that appear related to the development of the Makarov Basin. This and other data are consistent with the idea that the Makarov Basin was formed by continental stretching rather than simple seafloor spreading. Hence the flanking Alpha and Lomonosov ridges may originally have been part of the same continental block. It is suggested that in Late Cretaceous time this block was sheared from Eurasia along a trans-Arctic left-lateral offset that may have been associated with the opening of Baffin Bay. The continental block was later separated from Eurasia when the North Altantic rift extended into the Arctic region in the Early Tertiary. The data suggest that the Makarov Basin did not form before the onset of rifting in the Artic.  相似文献   

Polymetamorphic relations in iron ores from the Iron Quadrangle,Brazil: The correlation of oxygen isotope variations with deformation history   总被引：2，自引：0，他引：2  

Joachim Hoefs  Georg Müller  Alfred K. Schuster 《Contributions to Mineralogy and Petrology》1982,79(3):241-251

This study deals with the oxygen isotope composition of hematite-rich ore bodies in the Iron Quadrangle, Brazil. The area studied can be divided into two different regions: a western (W) zone of greenschist facies assemblages and an eastern (E) zone of amphibolite facies with transitions into granulite facies assemblages.The ¹⁸O values of 136 quartz-iron oxide pairs have been determined and temperatures of formation have been calculated. The ¹⁸O values of quartz vary between +6 and 20 except one value near +23, whereas the iron oxides fall between –4 and +10, with nearly 80% of the iron oxide values between –0.5 and 4.0. The regional distribution of the ¹⁸O values is as follows: in the W-region 85% of the quartz are >12, whereas in the E-region only 46% fall in this range, In contrast to quartz the iron oxides do not show any regional differences.The variation of oxygen isotope fractionations between quartz and iron oxides is obviously related to the complex deformation history of the iron ores. Samples with a primary schistosity (S₁) only represent peak metamorphic conditions. In the E-region the (S₁) high temperatures >700° C seem to correspond to orogenic events in the Archaen basement 2,700 m.y. ago. In the W-region S₁-temperatures between 460° and 560° C seem to represent peak metamorphic conditions of the Proterozoic Minas metamorphism 2,000 m.y. ago. Iron ores which have been overprinted by later deformation events are selectively reset to lower isotopic temperatures. The more closely spaced the schistosity planes the larger the extent of a temperature lowering.The genetic processes associated with these hematite-rich ore bodies appear to be sedimentary-metamorphic rather than metasomatic processes. Furthermore, there is no evidence for secondary leaching by weathering solutions.  相似文献   

ΣDDT and PCBs in equatorial Atlantic organisms     

Rolf Roland Weber 《Marine pollution bulletin》1983,14(7):274-275

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<Superscript>57</Superscript>Fe Mössbauer spectroscopy,X-ray single-crystal diffractometry,and electronic structure calculations on natural alexandrite     

Sven-Ulf Weber  Michael Grodzicki  Werner Lottermoser  Günther J. Redhammer  Gerold Tippelt  Johann Ponahlo  Georg Amthauer 《Physics and Chemistry of Minerals》2007,34(7):507-515

Natural alexandrite Al₂BeO₄:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The ⁵⁷Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe³⁺ and Fe²⁺, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe³⁺ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe³⁺ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe³⁺ on M1.  相似文献   

<Superscript>57</Superscript>Fe Mössbauer measurements and electronic structure calculations on natural lawsonites     

S.-U. Weber  M. Grodzicki  C. A. Geiger  W. Lottermoser  G. Tippelt  G. J. Redhammer  M. Bernroider  G. Amthauer 《Physics and Chemistry of Minerals》2007,34(1):1-9

Three natural lawsonites from Syke Rock, Mendocino Co., Reed Ranch, Marin Co., and Blake Gardens, Sonoma Co., all from the Coast Range Region in California, were studied by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe analysis, and X-ray powder diffraction. The samples contain about 0.6, 1.0, and 1.4 wt% of total iron oxide, respectively. ⁵⁷Fe Mössbauer spectra are consistent with the assumption that high-spin Fe³⁺ substitutes for Al in the octahedrally coordinated site. The Mössbauer spectrum of lawsonite from Syke Rock exhibits a second doublet with ⁵⁷Fe hyperfine parameters typical for octahedrally coordinated high-spin Fe²⁺. Electronic structure calculations in the local spin density approximation yield quadrupole splittings for Fe³⁺ in quantitative agreement with experiment indicating, however, that substitution of Al by Fe³⁺ must be accompanied by local distortion around the octahedral site. Model calculations also reproduce the room temperature hyperfine parameters of ferrous high-spin iron assuming the substitution of Ca by Fe²⁺. However, it cannot be excluded that Fe²⁺ may occupy a more asymmetric site within the microstructural cavity occupied by Ca and a H₂O molecule.  相似文献   

The international GLONASS experiment: products, progress and prospects   总被引：2，自引：0，他引：2  

R. Weber  T. A. Springer 《Journal of Geodesy》2001,75(11):559-568

 In October 1998 the IGEX field campaign, the first coordinated international effort to monitor GLONASS satellites on global basis, was started. Currently about 40 institutions worldwide support this effort either by providing GLONASS tracking data or in operating related data and analysis centers. The increasing quality and consistency of the calculated GLONASS orbits (about 25 cm early in 2000), even after the end of the official IGEX field campaign, are shown. Particular attention is drawn to the combination of precise ephemerides in order to generate a robust, reliable and complete IGEX orbits product. Some problems in modeling the effect of solar radiation pressure on GLONASS satellites are demonstrated. Finally, the expected benefits and prospects of the upcoming International GLOnass Service-Pilot Project (IGLOS-PP) of the International GPS Service (IGS) are discussed in more detail. Received: 17 August 2000 / Accepted: 12 April 2001  相似文献   

Growth, ionic and osmotic relations of an Allenrolfea occidentalis population in an inland salt playa of the Great Basin Desert     

Bilquees Gul  Darrell J. Weber  M. Ajmal Khan 《Journal of Arid Environments》2001,48(4):445

Variation in growth, physiology and ionic relations patterns of Allenrolfea occidentalis, a perennial halophyte of dry habitats, was studied under field conditions from May 1996 to November 1997. An A. occidentalis community has a characteristic soil pH of 7·3–8·3. During the two years, the population was exposed to great variations in soil salinity, from 29 to 146 dS m⁻¹, and soil moisture, ranging from drought (9·2%) to wet (19%). The salt concentrations were significantly higher in the surface soil layers than in the subsurface layers. Seasonal changes in dry weight are directly related to soil salinity stress. Allenrolfea occidentalis had greater growth and biomass production under saline conditions. Na⁺and Cl⁻ions were accumulated in plant tissues in much greater amounts than K⁺, Ca²⁺, and Mg²⁺. Soil salinities were significantly reduced at the end of the growing season. Water potentials of the shoots decreased significantly with increasing salinity. The plant (F_v/F_mratio) was more affected by salinity and irradiation levels during the summer period.  相似文献   

Unravelling the pre-Variscan evolution of the Habach terrane (Tauern Window, Austria) by U-Pb SHRIMP zircon data     

Roland Eichhorn  Georg Loth  Allen Kennedy 《Contributions to Mineralogy and Petrology》2001,142(2):147-162

The U-Pb SHRIMP age determinations of zircons from the Habach terrane (Tauern Window, Austria) reveal a complex evolution of this basement unit, which is exposed in the Penninic domain of the Alpine orogen. The oldest components are found in zircons of a metamorphosed granitoid clast, of a migmatitic leucosome, and of a meta-rhyolitic (Variscan) tuff which bear cores of Archean age. The U-Pb ages of discordant zircon cores of the same rocks range between 540 and 520 Ma. It is assumed that the latter zircons were originally also of Archean origin and suffered severe lead loss, whilst being incorporated into Early-Cambrian volcanic arc magmas. The provenance region of the Archean (2.64-2.06 Ga) zircons is assumed to be a terrane of Gondwana affinity: i.e., the West African craton (Hoggar Shield, Reguibat Shield). The Caledonian metamorphism left a pervasive structural imprint in amphibolite facies on rocks of the Habach terrane; it is postdated by discordant zircons of a migmatitic leucosome at <440 Ma (presumably ca. 420 Ma). Alpine and Variscan upper greenschist- to amphibolite-facies conditions caused partial lead loss in zircons of a muscovite gneiss ('white schist') only, where extensive fluid flow and brittle deformation due to its position near a nappe-sole thrust enhanced the grains' susceptibility to isotopic disturbance. The Habach terrane - an active continental margin with ensialic back-arc development - showed subduction-induced magmatic activity approx. between 550 and 507 Ma. Back-arc diorites and arc basalts were intruded by ultramafic sills and subsequently by small patches of mantle-dominated unaltered and (in the vicinity of a major tungsten deposit) altered granitoids. Fore-arc (shales) and back-arc (greywackes, cherts) basin sediments as well as arc and back-arc magmatites were not only nappe-stacked by the Caledonian compressional regime closing the presumably narrow oceanic back-arc basin and squeezing mafic to ultramafic cumulates out of high-level magma chambers (496-482 Ma). It also induced uplift and erosion of deeply rooted crystalline complexes and triggered the development of a successor basin filled with predominantly clastic greywacke-arkosic sediments. The study demonstrates that the basement rocks exposed in the Habach terrane might be the 'missing link' between similar units of the more westerly positioned External domain (i.e., Aar, Aiguilles Rouges, Mont Blanc) and the Austroalpine domain to the east (Oetztal, Silvretta).  相似文献