Redistribution of HFSE elements during rutile replacement by titanite   总被引：2，自引：0，他引：2  

Friedrich Lucassen  Peter Dulski  Rainer Abart  Gerhard Franz  Dieter Rhede  Rolf L. Romer 《Contributions to Mineralogy and Petrology》2010,160(2):279-295

Titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon. We investigated an amphibolite sample from the Tromsø eclogite facies terrain in Northern Norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite. Patchy compositional zoning of Al, Ti, and F in titanite relates to the presence of a fluid with variable Ti/Al and/or F during its growth. Laser ablation ICP–MS and electron microprobe data for high field strength elements (HFSE: Nb, Zr, Ta, and Hf) of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal (~8 mm) and a systematic decrease towards uniform HFSE contents in the large core. HFSE contents of smaller rutile grains (~0.5 mm) and rutile inclusions (<100 μm) in the titanite overgrowth are similar or higher than in the rims of large rutile crystals. Element profiles from the rim inward demonstrate that HFSE enrichment in rutile is controlled by diffusion. HFSE ratios in diffusion-altered rutile show systematic variations compared with the uniform core composition of the large rutile. Modelling of Zr and Nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid-dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems. Variations of HFSE contents in the newly formed titanite show no systematic spatial distribution. HFSE ratios in titanite and the rims of rutile are different, indicating different solid/fluid distribution coefficients in these minerals. Element fractionation by diffusion into the relict rutile and during fluid-mediated growth of new titanite could substantially change the HFSE budget of these minerals and could affect their use for geochemical tracing and other applications, such as Zr-based geothermobarometry.  相似文献   

Complete recycling of a magmatic arc: evidence from chemical and isotopic composition of Quaternary trench sediments in Chile (36°–40°S)     

Friedrich Lucassen  Michael Wiedicke  Gerhard Franz 《International Journal of Earth Sciences》2010,99(3):687-701

Marine Quaternary trench and slope sediments were sampled along the margin of the Southern Andes, Chile between 36° and 40°S. Major and trace element contents indicate only minor influence of weathering and transport fractionation. The whole rock composition of the sediments is similar to the average rock of the Cretaceous to Holocene magmatic arc of this section of the southern volcanic zone. Sr, Nd, and Pb isotope composition of the sediments also resembles closely the average composition of the magmatic arc. The contribution of compositionally distinct Palaeozoic crust, which makes up most of the volume of the forearc, is ~0–20% crustal Sr, Nd, and Pb according to the isotope record of the trench and slope sediments. Input of sediments from the continent into the subduction system was dominated by detritus from the magmatic arc at least for the last 20 My on the basis of the Oligocene to Holocene exhumation history of the margin.  相似文献   

XMM–Newton observations of bright ROSAT selected active galactic nuclei with low intrinsic absorption     

L. C. Gallo  I. Lehmann  W. Pietsch  Th. Boller  W. Brinkmann  P. Friedrich  D. Grupe 《Monthly notices of the Royal Astronomical Society》2006,365(2):688-698

We present a sample of 21 ROSAT bright active galactic nuclei (AGNs), representing a range of spectral classes, and selected for follow-up snapshot observations with XMM–Newton . The typical exposure was between 5 and 10 ks. The objects were primarily selected on the bases of X-ray brightness and not on hardness ratio; thus the sample cannot be strictly defined as a 'soft'sample. One of the main outcomes from the XMM–Newton observations was that all of the AGN, including 11 type 1.8–2 objects, required low levels of intrinsic absorption  ( N _H≲ 10²¹ cm⁻²)  . The low absorption in type 2 systems is a challenge to account for in the standard orientation-based unification model, and we discuss possible physical and geometrical models which could elucidate the problem. Moreover, there does not appear to be any relation between the strength and shape of the soft excess, and the spectral classification of the AGN in this sample. We further identify a number of AGN which deserve deeper observations or further analysis: for example, the low-ionization nuclear emission regions (LINERs) NGC 5005 and NGC 7331, where optically thin thermal and extended emission is detected, and the narrow-line Seyfert 1 II Zw 177, which shows a broad emission feature at ∼ 5.8 keV.  相似文献   

Memorial for Hans Voshage     

Friedrich Begemann  Heinrich Wnke 《Meteoritics & planetary science》1989,24(4):354-354

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Shock-implanted noble gases II: Additional experimental studies and recognition in naturally shocked terrestrial materials     

Donald Bogard  Friedrich Hrz  Pratt Johnson 《Meteoritics & planetary science》1989,24(2):113-123

Abstract— Several experimentally and naturally shocked silicate samples were analyzed for noble gas contents to further characterize the phenomenon by which ambient gases can be strongly implanted into silicates by shock and to evaluate the possible importance of this process in capturing planetary atmospheres in naturally shocked samples. Gas implantation efficiency is apparently mineral independent, as mono-mineralic powders of oligoclase, labradorite, and diopside and a powdered basalt shocked to 20 GPa show similar efficiencies. The retentivity of shock-implanted gas during stepwise heating in the laboratory is defined in terms of two parameters: activation energy for diffusion as determined from Arrhenius plots, and the extraction temperature at which 50% of the gas is released, both of which correlate with shock pressure. These gas diffusion parameters are essentially identical for radiogenic ⁴⁰Ar and shock-implanted ⁴⁰Ar in oligoclase and labradorite shocked to 20 GPa, suggesting that the two ⁴⁰Ar components occupy analogous lattice sites. Our experiments indicate that gas implantation occurs through an increasing production of microcracks/defects in the lattice with increasing shock pressure. The ease of diffusive loss of implanted gas is controlled by the degree of annealing of these microcracks/defects. Identification of a shock-implanted component requires relatively large concentrations of implanted gas which is strongly retained (i.e., moderate activation energy) in order to separate implanted gas from surface adsorbed gases. Literature data on shocked terrestrial samples indicate only weak evidence for shock-implanted gases, with an upper limit for ⁴⁰Ar of ～ 10^?6 cm³STP/g. New analyses of shocked samples from the Wabar Crater indicate the presence of shock-implanted Ar, having concentrations (～ 10^?4 cm³STP/g) and activation energies for diffusive loss which are essentially that expected from experimental studies. Lack of sufficient target porosity or the presence of ground water may explain the sparse evidence for shock-implanted gas at other terrestrial craters. Although Wabar Crater may represent an unusually favorable environment on Earth for shock-implanting gases, surfaces of other planetary bodies, such as Mars, may frequently provide such environments. Analyses of returned samples from old Martian terraines may document temporal changes in earlier atmospheric composition.  相似文献   

Neutral gas composition measurements between 80 and 120 km     

D. Offermann  V. Friedrich  P. Ross  U. Von Zahn 《Planetary and Space Science》1981,29(7):747-764

Atmospheric composition in the turbopause regime was determined by four rocket-borne mass spectrometers, which employed shock-freezing cryo-ion sources. Number densities of N₂, O₂, O, Ar and CO₂ are presented for these experiments. The results are compared with those of other rocket experiments taken from the literature. Ar/N₂ ratios are analyzed with respect to atmospheric turbulence. Magnitude and variability of atomic oxygen layer maximum density and layer content are discussed. Variations of O densities and simultaneous Ar/N₂ ratio changes are compared. Six CO₂ measurements are discussed in terms of CO₂/N₂ ratios.  相似文献   

1973 supplement to exploration geochemistry bibliography     

H.E. Hawkes  F.C. Canney  P.R. Donovan  G.H. Friedrich  C.F. Gleeson  M.B. Mehrtens  P. Lowenstein 《Journal of Geochemical Exploration》1974,3(1):89-128

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Surface features on glass spherules from the Luna 16 sample     

Jack B. Hartung  Friedrich Hörz  David S. McKay  Frank L. Baiamonte 《Earth, Moon, and Planets》1972,5(3-4):436-446

Two ellipsoidal spherules approximately 0.5 mm in diameter were studied in detail using a scanning electron microscope. A variety of surface features were observed: vesicles, mounds, dimples, streaks, ridges, grooves, accretion phenomena, and high-speed impact craters. The diameters of 27 glass-lined pits formed by impact on one spherule range from less than 1m to approximately 50m. Intermediate-sized glass-lined pits surrounded by concentric fractures demonstrate the transition between larger craters that have both a pit and a spall zone and generally smaller craters that have only a pit. Assuming all craters showing evidence of impact-related melting or flow are the result of primary impacts, the differential mass spectrum of impacting meteoroids in the range 10^–11 to 10^–10 g is in good agreement with a spectrum based on satellite-borne particle-detecting experiments.  相似文献   

Elektronenstrahl-Mikroanalyse des Meteoriten von Steinbach     

Gerhard Dörfler  Friedrich Hecht  Erwin Plöckinger 《Mineralogy and Petrology》1965,10(1-4):413-429

Zusammenfassung Eine uns vom Naturhistorischen Museum in Wien freundlicherweise zur Verfügung gestellte Probe des Meteoriten von Steinbach wurde mit einem Elektronenstrahl-Mikroanalysator vom Typ CAMECA qualitativ und quantitativ auf die chemische Zusammensetzung der einzelnen Phasen untersucht.Besonders eingehend wurde dabei die Metallphase analysiert, da diese sich durch die Anwesenheit einer gut ausgebildeten Widmanstättenschen Struktur in Gegenwart von Tridymit als Druckindikator auszeichnet.Die nichtmetallischen Phasen wurden ebenfalls quantitativ bestimmt und ergeben leicht abweichende Ergebnisse von den Analysen vonN. Story-Maskelyne, O. Winkler undF. Heide. Interessant sind vor allem der relativ hohe Mangangehalt in Bronzit und Chromit sowie der Chromgehalt des Troilits.Die Anwendung der neuen Berechnungen über die Abkühlungsgeschichte der Meteoritenmutterkörper vonWood auf unsere quantitativen Analysen ergab eine Abkühlungsgeschwindigkeit von 10°/Million Jahre, was einem Mutterkörper von ca. 50–90 km Durchmesser und einem Zentraldruck von 200 b entspricht.

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Summary A sample of the meteorite of Steinbach, made available by the Naturhistorisches Museum at Vienna, has been analyzed qualitatively and quantitatively by a CAMECA electron-beam microanalyzer.Detailed examination has been made on the structure of the metal phase, as the presence of a well-grown Widmanstätten-structure in contact with trydimite as a pressure-indicator is a direct proof for the formation of the Widmanstätten-structure without pressure.The nonmetallic phases have been analyzed quantitatively and the results are slightly different from those ofStory-Maskelyne, Winkler andHeide. Very interesting is the relatively high content of manganese in bronzite and chromite, also the chromium content of troilite.The application of the new computations ofWood, dealing with the cooling history of meteorite-parentbodies to our quantitative analyses indicate a cooling rate of 10° C/Million years, according to a parentbody of appr. 50–90 km diameter and a central pressure of appr. 200 b.

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Herrn Professor Dr.F. Machatschki zum 70. Geburtstag gewidmet.  相似文献   

Laboratory studies for beam plasma discharge experiments with rockets     

S.B. Lyakhov  A.D. Maiorov  G.G. Managadze  O.A. Povalyaev  A.I. Chmil  L.Yu. Kochmarev  E.G. Shustin  M.F. Friedrich  W.K. Riedler  A.N. Laliashvili  A. Kiraga  Z. Kłoss  Z. Kravchic  N.A. Leonov 《Planetary and Space Science》1982,30(4):347-357

Laboratory results of beam plasma discharge (BPD) (dimensions several metres) in a homogeneous atmosphere and a jet of neutral gas are presented. The beam was obtained by an electron gun of the same type as used in rocket experiments.The BPD parameters glow intensity, electromagnetic field and its spectrum, electron density as well as the flux of scattered electrons were measured. In addition, photographs of the BPD were taken. The threshold of BPD ignition was determined as a function of gas pressure and beam parameters. The initial stage of BPD formation as well as various types of oscillatory processes in the discharge were studied. A possible process of BPD initiation is presented.  相似文献