Water,iron, redox environment: effects on the wadsleyite–ringwoodite phase transition     

Maria Mrosko  Monika Koch-Müller  Catherine McCammon  Dieter Rhede  Joseph R. Smyth  Richard Wirth 《Contributions to Mineralogy and Petrology》2015,170(1):1-12

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Surface Variability of Alluvial Fans Generated by Disparate Processes,Eastern Death Valley,CA     

Thad Wasklewicz  Monika Mihir  Jennifer Whitworth 《The Professional geographer》2013,65(2):207-223

This study explores the surface variability of alluvial fans from digital elevations model (DEM) derivatives generated from 1-m planimetric resolution airborne laser swath mapping data. Channel and interfluve dimensions of debris flow (DF) fans and fans generated from predominantly fluvial flows and some older debris flows (mixed flow [MF]) are extracted with the aid of a planimetric curvature classification. Significant differences are identified between the fan surface topography of DF and MF fans. MF fans tend to have smaller channel and interfluve widths, have smaller elevation differences between the crest of the interfluve and channel, and are more dissected than DF fans. The morphometric differences between the two fan classes can be explained by differences in the primary processes that develop the surficial features, but also the preponderance for secondary erosional processes acting on the MF fans.  相似文献   

Determination of Fluoride Ions in Iron Ores by UV–VIS Spectrophotometry after Matrix Removal Using Diphonix® Resin     

Agata Jakóbik‐Kolon  Monika Skwira 《Geostandards and Geoanalytical Research》2012,36(1):21-25

A modification of the spectrophotometric method for the determination of fluoride ions in iron‐rich materials is proposed. In this method the iron matrix was successfully removed using Diphonix^® resin. The studied sample was a ferruginous mineral which contained about 38% of iron. The Euronorm certified reference material (ECRM) 676‐1 (Iron Ore Sinter), as a commercially available material having a similar matrix (39.76% w/w Fe) and fluoride level (0.1% w/w), was used to validate the method. After partial digestion in concentrated hydrochloric acid the samples were diluted and passed through Diphonix^® resin. The concentration of fluoride ions was determined by a spectrophotometric method using a Zr:ER complex (λ = 540 nm). The result obtained for the ECRM was in good agreement with the certificate specification and thus proved the method to be applicable for the determination of fluoride ions in iron‐rich materials. Due to the easy digestion step and simple requirements for equipment, this method can be used in most laboratories.  相似文献   

FTIR spectroscopic study of natural andalusite showing electronic Fe–Ti charge-transfer processes: zoning and thermal evolution of OH-vibration bands     

Michail N. Taran  Monika Koch-Müller 《Physics and Chemistry of Minerals》2013,40(1):63-71

We investigated a natural Brazilian Fe–Ti-containing andalusite and its thermal behavior by polarized infrared and optical spectroscopy. Polarized infrared spectra of the Brazilian andalusite and their evolution at thermal annealing in air clearly evidence that there are several types of OH-groups in the structure. Optical spectra and their evolution with temperature indicate that the incorporated iron (about 0.43 wt% calculated as FeO) is in the ferrous and ferric state. Incorporation of ferrous iron in the Al-sites of andalusite is discussed as a possible incorporation mechanism for hydrogen. The weakening and disappearance of the Fe²⁺/Ti⁴⁺ IVCT band in the andalusite spectra under annealing in air is caused by oxidization of Fe²⁺ to Fe³⁺ in Fe²⁺/Ti⁴⁺ IVCT pairs. The process of oxidation is accompanied by a rearrangement of the hydroxyl groups and dehydration of the sample, especially vivid at the final stage of the thermal annealing at 1,200 °C. During thermal annealing, structural hydroxyls of different types apparently transform into each other: the most distinct are the hydroxyls causing the doublet at 3,516 and 3,527 cm^?1 (i.e., H bonded to O1) which seem to transform into the hydroxyls causing the line at 3,461 cm^?1 (i.e., H bonded to O2). The infrared spectra scanned across differently colored zones of the crystal clearly show that some amount of hydroxyls is related to Fe²⁺/Ti⁴⁺ IVCT pairs which are the cause of the red-to-black coloration of the sample in E||c-polarized illumination: it is evident that in a part of the hydroxyl groups, OH-vector changes orientation aligning directly along crystallographic a-axis due to some kind of interaction with Fe²⁺/Ti⁴⁺ IVCT pairs.  相似文献   

An attempt to test Ambartsumian's idea of galaxy origin. I Galaxy cluster shape     

Monika Biernacka  Piotr Flin  H. A. Harutyunyan 《Astrophysics》2008,51(3):313-319

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Evolution of the palaeolake at Ruszkówek (central Poland) during the Eemian Interglacial based on isotope,cladoceran and diatom data     

Joanna Mirosław-Grabowska  Monika Niska  Elwira Sienkiewicz 《Journal of Paleolimnology》2009,42(4):467-481

We present isotope, cladoceran and diatom results from investigations of Eemian sediments of the palaeolake at Ruszkówek, central Poland. Our analyses of the 15-m-thick sediments indicate that sandy silts occur on the bottom, followed by calcareous gyttja, interbedded with lake marl. The upper part of the sequence contains peat and peaty sands. Values of δ¹⁸O change from −9.4‰ to −3.3‰ and δ¹³C values oscillate between −3.2‰ and +7.0‰. Nine isotope zones (Is) were defined and characterized using stable isotope analysis of carbonates. Fifteen species of subfossil Cladocera were found and six faunal zones were distinguished (Cladocera zones). One hundred and twenty-three diatom taxa, representing 31 genera were identified, enabling us to discern six Diatom Assemblage Zones. The isotope, cladoceran, and diatom data correlate well with pollen data that define seven phases of evolution of the palaeolake at Ruszkówek. The palaeolake began during the final phase of the Wartanian (Late Saalian Glaciation). During the early Eemian, the palaeolake reached its maximum depth. During the Early Vistulian glaciation, the palaeolake declined. Changes in the cladoceran and diatom communities indicate initial oligotrophic conditions in the lake, then an increase to mesotrophy, and finally eutrophic conditions.  相似文献   

Spectroscopic studies of synthetic and natural ringwoodite, γ-(Mg,Fe)<Subscript>2</Subscript>SiO<Subscript>4</Subscript>     

Michail N. Taran  Monika Koch-Müller  Richard Wirth  Irmgard Abs-Wurmbach  Dieter Rhede  Ansgar Greshake 《Physics and Chemistry of Minerals》2009,36(4):217-232

Synthetic ringwoodite γ-(Mg_1?x Fe _x )₂SiO₄ of 0.4 ≤ x ≤ 1.0 compositions and variously colored micro-grains of natural ringwoodite in shock metamorphism veins of thin sections of two S6-type chondrites were studied by means of microprobe analysis, TEM and optical absorption spectroscopy. Three synthetic samples were studied in addition with Mössbauer spectroscopy. The Mössbauer spectra consist of two doublets caused by ^VIFe²⁺ and ^VIFe³⁺, with IS and QS parameters close to those established elsewhere (e.g., O’Neill et al. in Am Mineral 78:456–460, 1993). The Fe³⁺/Fe_total ratio evaluated by curve resolution of the spectra, ranges from 0.04 to 0.1. Optical absorption spectra of all synthetic samples studied are qualitatively very similar as they are directly related to the iron content. They differ mostly in the intensity of the observed absorption features. The spectra consist of a very strong high-energy absorption edge and a series of absorption bands of different width and intensity. The three strongest and broadest absorptions of them are attributed to splitting of electronic spin-allowed ⁵ T _2g → ⁵ E _g transitions of ^VIFe²⁺ and intervalence charge-transfer (IVCT) transition between ferrous and ferric ions in adjacent octahedral sites of the ringwoodite structure. The spin-allowed bands at ca. 8,000 and 11,500 cm^?1 weakly depend on temperature, whilst the Fe²⁺/Fe³⁺ IVCT band at ~16,400 cm^?1 displays very strong temperature dependence: i.e., with increasing temperature it decreases and practically disappears at about 497 K, a behavior typical for bands of this type. With increasing pressure the absorption edge shifts to lower energies while the spin-allowed bands shift to higher energy and strongly decreases in intensity. The IVCT band also strongly weakens and vanishes at about 9 GPa. We assigned this effect to pressure-induced reduction of Fe³⁺ in ringwoodite. By analogy with synthetic samples three broad bands in spectra of natural (meteoritic) blue ringwoodite are assigned to electronic spin-allowed transitions of ^VIFe²⁺ (the bands at ~8,600 and ~12,700 cm^?1) and Fe²⁺/Fe³⁺ IVCT transition (~18,100 cm^?1), respectively. Spectra of colorless ringwoodite of the same composition consist of a single broad band at ca. 12,000 cm^?1. It is assumed that such ringwoodite grains are inverse (Fe, Mg)₂SiO₄-spinels and that the single band is caused by the split spin-allowed ⁵ E → ⁵ T ₂ transition of ^IVFe²⁺. Ringwoodite of intermediate color variations between dark-blue and colorless are assumed to be partly inversed ringwoodite. No glassy material between the grain boundaries in the natural colored ringwoodite aggregates was found in our samples and disprove the cause of the coloration to be due to light scattering effect (Lingemann and Stöffler in Lunar Planet Sci 29(1308), 1998).  相似文献   

Geochemistry,mineralogy, and zircon U–Pb–Hf isotopes in peraluminous A-type granite xenoliths in Pliocene–Pleistocene basalts of northern Pannonian Basin (Slovakia)     

Monika?Huraiová  Jean-Louis?Paquette  Patrik?Kone?ny  Abdel-Mouhcine?Gannoun  Vratislav?HuraiEmail authorView author&#;s OrcID profile 《Contributions to Mineralogy and Petrology》2017,172(8):59

Anorogenic granite xenoliths occur in alkali basalts coeval with the Pliocene–Pleistocene continental rifting of the Pannonian Basin. Observed granite varieties include peraluminous, calcic to peralkalic, magnesian to ferroan types. Quartz and feldspars are dominant rock-forming minerals, accompanied by minor early ilmenite and late magnetite–ulvöspinel. Zircon and Nb–U–REE minerals (oxycalciopyrochlore, fergusonite, columbite) are locally abundant accessory phases in calc-alkalic types. Absence of OH-bearing Fe, Mg-silicates and presence of single homogeneous feldspars (plagioclase in calcic types, anorthoclase in calc-alkalic types, ferrian Na-sanidine to anorthoclase in alkalic types) indicate water-deficient, hypersolvus crystallization conditions. Variable volumes of interstitial glass, absence of exsolutions, and lacking deuteric hydrothermal alteration and/or metamorphic/metasomatic overprint are diagnostic of rapid quenching from hypersolidus temperatures. U–Pb zircon ages determined in calcic and calc-alkalic granite xenoliths correspond to a time interval between 5.7 and 5.2 Ma. Positive εHf values (14.2 ± 3.9) in zircons from a 5.2-Ma-old calc-alkalic granite xenolith indicate mantle-derived magmas largely unaffected by the assimilation of crustal material. This is in accordance with abundances of diagnostic trace elements (Rb, Y, Nb, Ta), indicating A₁-type, OIB-like source magmas. Increased accumulations of Nb–U–REE minerals in these granites indicate higher degree of the magmatic differentiation reflected in Rb-enrichment, contrasting with Ba-enrichment in barren xenoliths. Incipient charnockitization, i.e. orthopyroxene and ilmenite crystallization from interstitial silicate melt, was observed in many granite xenoliths. Thermodynamic modeling using pseudosections showed that the orthopyroxene growth may have been triggered by water exsolution from the melt during ascent of xenoliths in basaltic magma. Euhedral-to-skeletal orthopyroxene growth probably reflects contrasting ascent rates of basaltic magma with xenoliths, intermitted by the stagnation in various crustal levels at a <3 kbar pressure. The Tertiary suite of intra-plate, mantle-derived A₁-type granites and syenites is geochemically distinct from pre-Tertiary, post-orogenic A₂-type granites of the Carpatho–Pannonian region, which exhibit geochemical features diagnostic of crustal melting along continental margins.  相似文献   

Lake Tahoe vs. Lake Kinneret phytoplankton: comparison of long-term taxonomic size structure consistency     

Yury Kamenir  Monika Winder  Zvy Dubinsky  Tamar Zohary  Geoff Schladow 《Aquatic Sciences - Research Across Boundaries》2008,70(2):195-203

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Impact of water temperature on nutrient concentrations in the Oder estuary in 1996–1998     

Marianna Pastuszak  Herbert Siegel  Stanisław Sitek  Monika Gerth  Gisela Tschersich  Klaus Nagel  Alfred Grelowski 《Ocean Dynamics》1999,51(4):423-439

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