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Serpentinites of the Zermatt-Saas ophiolite complex and their texture evolution (2004)

Li, X.-P. ; Rahn, M. ; Bucher, K.

Oxford, UK : Blackwell Science Inc

Journal of metamorphic geology 22 (2004), S. 0

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ISSN: 1525-1314

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: The Zermatt-Saas serpentinite complex is an integral member of the Penninic ophiolites of the Central Alps and represents the mantle part of the oceanic lithosphere of the Tethys. Metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean-floor hydration, subduction-related high-pressure overprint, meso-Alpine greenschist facies metamorphism, and late-stage hydrothermal alteration. The early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures. The primary serpentine minerals were completely replaced by antigorite. The stable assemblage in subduction-related mylonitic serpentinites is antigorite–olivine–magnetite ± diopside. The mid-Tertiary greenschist facies overprint is characterized by minor antigorite recrystallization. Textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high-pressure metamorphism of up to 2.5 GPa and 650 °C. The Zermatt-Saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1525-1314.2004.00503.x

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Very low-grade metamorphism of the Taveyanne greywacke, Glarus Alps, Switzerland (1994)

RAHN, M. ; MULLIS, J. ; ERDELBROCK, K. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of metamorphic geology 12 (1994), S. 0

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ISSN: 1525-1314

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic Eocene-Oligocene Taveyanne greywacke of the Glarus Alps, Eastern Switzerland. Presented data indicate an increase of metamorphic grade from zeolite facies to prehnite-pumpellyite and pumpellyite-actinolite facies. Low-grade outcrops contain laumontite, minor corrensite and pumpellyite (assemblage type 1), whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite (type 2), prehnite—pumpellyite-(Al)—white mica (type 3), a single outcrop shows pumpellyite-actinolite facies (type 4). From the zeolite to prehnite-pumpellyite/pumpellyite-actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain ≤1 mm) in type 1, to a few millimetres in type 2, and to a whole thin section in type 3. Metamorphic P-T conditions were determined by a combination of chlorite thermometry, fluid inclusion and vitrinite reflectance data. Peak temperatures range from 170-190d̀ C for zeolite facies to 270-310d̀ C for prehnite-pumpellyite and pumpellyite-actinolite facies. For the higher temperature range, pressures of 2-3 kbar are derived indicating a geothermal gradient of 24-32d̀ C km-1. The well-constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed. The best correspondence to the temperatures determined here is for the Cathelineau calibration. In addition, in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1525-1314.1994.tb00047.x

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3

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Photorefractive polymer composite trapping properties and a link with chromophore structure (1998)

West, K. S. ; West, D. P. ; Rahn, M. D. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 84 (1998), S. 5893-5899

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The photorefractive properties and the phase stability of polymer composites are dependent on the detail of the alkyl chain substituent attached to the electro-optic dye within the composite. Photorefractive composites based on poly (N-vinylcarbazole) (PVK), sensitized with trinitrofluorenone (TNF) and mixed with a concentration of 47.5 wt. % of electro-optic dye have been tested for photorefractive performance. Two alternative azo dyes of identical molecular weight have been used to produce alternative composites; both dyes were modified to suppress spatial isomerism and incorporated an eight carbon alkyl chain at the electropositive end of the chromophore: either a straight octyl chain or a branched ethylhexyl chain was substituted. The reorientational enhancement of photorefractive performance is similar in the composites resulting from these dyes. The dye with a straight octyl chain led to a composite with improved holographic performance. The dye with a branched ethylhexyl chain led to a composite exhibiting lower diffraction efficiency, but with superior phase stability. A tentative explanation is offered for these differences based on the shape of the alkyl substituent and its effect on a trapping mechanism involving the dye molecules and the sensitisor anions in PVK:TNF-based photorefractive composites. © 1998 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.368905

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Titanian clinohumite formation in the Zermatt-Saas ophiolites, Central Alps (1998)

Rahn, M. K. ; Rahn, K.

Springer

Mineralogy and petrology 64 (1998), S. 1-13

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ISSN: 1438-1168

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Description / Table of Contents: Zusammenfassung Das in den Serpentiniten der Zermatt Region (Zentralschweiz) weit verbreitet vorkommende Mineral Titan-Clinohumit (Ti-Chu) ist ein stabiler Bestandteil der grünschieferfaziellen Paragenese Antigorit (Atg)-Forsterit (Fo)-Diopsid (Di)-Magnetit (Mag). Das rotbraune Fluor-freie Mineral findet sich hauptsächlich in der Form kleiner Körner in pseudomorphen Aggregaten nach primärem Clinopyroxen. Von diesem sind gelegentlich noch reliktische, stark korrodierte Körner erhalten. Die Zersetzung des primären Clinopyroxen (Cpx) führt zur Bildung von Ti-Chu welche durch die folgende schematische Reaktion beschrieben werden kann: $$Cpx + H_2 O + O_2 \Rightarrow Ti - Chu + Atg + Di + Mag$$ Obige Reaktion transferiert CaTiAl2O6 Komponente aus dem primären Pyroxen in den Ti-Clinohumit, wobei Al in den Antigorit eingebaut wird. Die Eisen-Pyroxen Komponente wird zu Magnetit oxidiert, während fast stöchiometrisch reiner Diopsid als grünschieferfazielle Neubildung in den Serpentiniten rekristallisiert. Die Bildungsreaktion ist eine typische retrograde Hydratationsreaktion und bildet neben dem Hydrat Ti-Chu auch das wasserreiche Mineral Antigorit. Der Charakter der Reaktion und die beobachteten Gefüge deuten darauf hin, dass Ti-Chu sehr wahrscheinlich bei der Serpentinisierung des Mantelteils der ozeanischen Lithosphäre durch eine ozeanische Metamorphose gebildet wurde. Die Ultramafitite wurden später als Serpentinite frühalpin subduziert und gemeinsam mit den basischen Teilen der Ophiolithe hochdruckmetamorph umgewandelt. Die Mineralvergesellschaftung Ti-Chu + Atg + Fo + Di + Mag blieb nach ihrer Bildung stabil und durchlief den gesamten alpinen Druck-Temperatur Pfad ohne weitere Veränderung.

Notes: Summary Titanian clinohumite (Ti-Chu) represents a stable constituent of the greenschist facies assemblage antigorite (Atg)-forsterite (Fo)-diopside (Di)-magnetite (Mag) in serpentinites of the Zermatt area, Central Switzerland. The red-brown fluorine-free mineral occurs as small grains within pseudomorphs after primary clinopyroxene, small corroded relics of which are still present. The clinopyroxene (Cpx) replacement by Ti-Chu can be described by a schematic reaction $$Cpx + H_2 O + O_2 \Rightarrow Ti - Chu + Atg + Di + Mag$$ The reaction transfers the CaTiAl2O6 component from primary Cpx to Ti-Chu, Al is transferred into antigorite. The Fe-pyroxene component is oxidized to magnetite, and pure, nearly stoichiometric diopside recrystallized as a new greenschist facies pyroxene in the serpentinite. Ti-Chu probably formed during oceanic metamorphism, based on the nature of the Ti-Chu forming reaction and the observed textures, (i.e. hydration of the oceanic lithosphere before subduction-related high-pressure metamorphism). According to recent experimental data, the stability field of Ti-Chu extends to higher temperatures than found for antigorite above a pressure of 2.3 GPa. Consequently, the phase remains stable at P-T conditions suggested for the early-Alpine subduction-related metamorphism of the area. Ti-Chu is proposed to have formed during oceanic metamorphism, and remained stable during subsequent early-Alpine subduction and later meso-Alpine greenschist facies overprint. A younger generation of coarse Ti-Chu formed under greenschist facies conditions and is found in late hydrothermal veins together with pure diopside and magnetite.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01226561

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5

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Meiotic behavior of the X1X2Y1Y2 quadrivalent of the primateAlouatta caraya (1996)

Rahn, M. I. ; Mudry, M. ; Merani, M. S. ; [et al.]

Springer

Chromosome research 4 (1996), S. 350-356

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ISSN: 1573-6849

Keywords: Alouatta caraya ; multiple sex chromosomes ; quadrivalent analysis ; synaptonemal complex

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract A multiple sex chromosome system was found in three unrelated individuals of the primateAlouatta caraya. This mechanism is originated by a translocation between the Y chromosome and one of the autosomes (A7). Mitotic karyotypes show two small, acrocentric chromosomes (AY and YA), which are the translocation products. In metaphase I of male meiosis, there is a very long chain quadrivalent in which the order of the element is: X−YA−A7−AY. Segregation in the quadrivalent is alternate and gives balanced products. Synaptonemal complex karyotypes at pachytene show the structure of the quadrivalent made by the four axes. There is a slight difference in the relative length of AY and YA and the kinetochore of A7 aligns with that of AY. The synaptic pattern and changes in the quadrivalent during pachytene are described. Thin sections of the quadrivalent body show that the chromatin packing in the sex chromosome region is different from that of the autosomal region. This X1X2Y1Y2/X1X1XX2 sex chromosome system may be extended among other members of the genusAlouatta.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02257270

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Asymmetry and resolution of the synaptonemal complex in the XY pair ofChinchilla laniger (1985)

Solari, A. J. ; Rahn, M. I.

Springer

Genetica 67 (1985), S. 63-71

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ISSN: 1573-6857

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract The meiotic behavior of the XY pair of the chinchilla (C. laniger), has been studied with C-banding and with the microspreading procedure for synaptonemal complex (SC) karyotyping. The large X chromosome of the chinchilla has a paracentromeric and two subterminal (stl and st2) C+ bands, while the minute Y chromosome has a C+ long arm. At metaphase-I the X chromosome is associated end-to-end with the short arm of the Y chromosome. The appearance of the X axis in microspread spermatocytes is delayed up to early pachytene. The X axis, as well as the Y axis appear as thick, separated threads. The thick X and Y axes are then co-aligned without forming a SC. The Y axis becomes thinner and then an asymmetrical SC is formed between the axes. This SC becomes symmetrical by a later thinning of the corresponding part of the X axis. During mid-pachytene an additional SC is formed at the other end of the XY pair in many cells. During late pachytene the SCs become resolved and finally the four termini are separated from each other although they tend to be located in the same region of the nucleus. These observations suggest that the SCs in the XY pair of the chinchilla are formed between non-homologous regions. The presence of non-homologous synapsis suggests that the XY pair ofC. laniger is joined by an achiasmatic mechanism, different from the chiasmatic joining usually found in eutherian mammals. The presence of subterminal C+ bands in the X chromosome may be a hindrance for the formation of a SC during early pachytene. It is concluded that the XY pair of the chinchilla shows an intermediate behavior when compared to that of the sand rat on one side, and that of most mammals having a euchromatic X chromosome, on the other side.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF02424462

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What perturbs isotherms? An assessment using fission-track thermochronology and thermal modelling along the Gotthard transect, Central Alps (2009)

Glotzbach, C. ; Spiegel, C. ; Reinecker, J. ; [et al.]

In: Geological Society Special Publication 324: 111-124.

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Publication Date: 2009-10-06

Description: Interpretation of low-temperature thermochronological data usually relies on assumptions on the shape of isotherms. Recently, a number of thermal modelling approaches investigate and predict the theoretical influence of topography on isotherms. The application and proof of these predictions is not well confirmed by measured data. Here we present apatite fission-track (AFT) data from samples collected along the Gotthard road tunnel and its corresponding surface line to test these predictions. AFT ages broadly cluster around 6 Ma along the tunnel. No correlation of tunnel ages with superimposed topography is seen, which means that topography-induced perturbation of isotherms under given boundary conditions (topographic wavelength 12 km; relief 1.5 km; exhumation rate 0.45 km Ma-1) can be neglected for the interpretation of AFT ages. Thus, in areas characterized by similar topographies and exhumation rates, apparent exhumation rates deduced from the age-elevation relationship (AER) of AFT data need no correction for topography-induced perturbation of isotherms. Three-dimensional (3D) numerical thermal modelling was carried out incorporating thermally relevant parameters and mechanisms, such as topography, geology, thermal conductivities and heat production. Modelling reveals a strong influence on the shape of isotherms caused by spatially variable thermal parameters, especially heat production rates. Therefore, not only topography has to be considered for interpreting low-temperature thermochronological data, but also other parameters like heat production rates. Supplementary material: 1. Electron microprobe analyses, 2. Topography and model extend, 3. Model parameters are all available online at http://www.geolsoc.org.uk/SUP18380.

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