Florian Heidelbach - Academia.edu (original) (raw)

Papers by Florian Heidelbach

Biopolymers, 1999

... Thomas A. Waigh 1 ,; Athene M. Donald 2,* ,; Florian Heidelbach 3 ,; Christian Riekel 3 ,; Mi... more ... Thomas A. Waigh 1 ,; Athene M. Donald 2,* ,; Florian Heidelbach 3 ,; Christian Riekel 3 ,; Michael J. Gidley 4. ... Waigh, TA, Donald, AM, Heidelbach, F., Riekel, C. and Gidley, MJ (1999), Analysis of the native structure of starch granules with small angle x-ray microfocus scattering. ...

Zenodo (CERN European Organization for Nuclear Research), Aug 18, 2023

European Journal of Mineralogy, Jun 12, 2013

Two twisted quartz crystals (gwindels) from the Alps were studied by transmission electron micros... more Two twisted quartz crystals (gwindels) from the Alps were studied by transmission electron microscopy and large-angle convergent-beam electron diffraction (LACBED) to elucidate the twist mechanism. We found that torsion results from a distribution of straight screw geometrically necessary b ¼ 1 3 2110 dislocations with a dislocation density of the order of 10 10 m À2. This dislocation microstructure induces an Eshelby twist which can account for the observed twist of a few degrees per centimetre. This microstructure suggests that twisted gwindel quartz forms by the spiral growth mechanism which enables crystal growth under small driving forces.

Journal of Geophysical Research, May 3, 2011

Significant variations in flow behavior are known to exist both vertically and laterally in Earth... more Significant variations in flow behavior are known to exist both vertically and laterally in Earth's upper mantle. The sources of such variation may be thermal, compositional, or reflect differences in the chemical activity of components, such as oxygen, silica, and water. We report on the effects of oxygen fugacity on dislocation creep of dunite, with a view to understanding potential strength heterogeneity in the mantle. Although room pressure experiments on single crystals of olivine have shown a clear dependence of creep rate on oxygen fugacity, no prior deformation study of polycrystalline olivine-rich rocks has demonstrated such a dependency under high-pressure conditions. In this study we performed a series of dry creep experiments on a natural dunite under carefully controlled thermochemical conditions, including oxygen fugacity. The samples, cored from coarsegrained Åheim dunite with a grain size of ∼0.9 mm, were deformed under triaxial compression at oxygen fugacities fixed by either the iron/wüstite or the nickel/nickel oxide solid state buffers, temperatures between 1150°and 1277°C, and differential stresses up to 300 MPa. The results of a global fit to all experimental data indicate a power law dependence of creep rate on oxygen fugacity, with an oxygen fugacity exponent of m = 0.20 ± 0.01, n = 3.6 ± 0.1, A = 10 2.6±0.3 s −1 MPa −3.6 Pa −0.2 , and an activation energy for creep of 449 ± 7 kJ/mol. This activation energy is significantly less than the commonly used value of 535 kJ/mol because the earlier experiments made no corrections for the effects of oxygen fugacity. When applied to planetary interiors, an increase in oxygen fugacity by a factor of ∼10 3.5 , from the iron/wüstite to the fayalite-magnetite-quartz buffers, will result in a factor of ∼5 decrease in viscosity.

AGU Fall Meeting Abstracts, Dec 1, 2006

ABSTRACT

AGU Fall Meeting Abstracts, Dec 1, 2006

ABSTRACT Slip plane orientations of some deep-focus earthquakes suggest that earthquakes can be t... more ABSTRACT Slip plane orientations of some deep-focus earthquakes suggest that earthquakes can be triggered by reactivation of pre-existing faults in the transition zone. In order to test this theory, we have studied the effect of the olivine-wadsleyite transition on the remobilization of pre-existing olivine faults by performing axisymmetric deformation experiments in a multi-anvil apparatus. Experiments were performed on 3 mm long, 1.5 mm wide cores of San Carlos olivine polycrystals at temperatures of 1173-1273 K and pressures of 6-14 GPa. Microseismicity (AE) related to brittle events in the sample was monitored using 8 1-5 MHz bandwidth PZT transducers that are attached to the back truncations of the tungsten carbide anvils. Cold axisymmetric compression of olivine to 6 GPa pressure results in a conical fault system that crosscuts the sample. AE hypocenters locate near faults and indicate high P-low T frictional sliding. The fault zones consist of fine-grained olivine gouge with a fractal dimension of 2.6±0.1 between 0.1-10 mum grain sizes. The gouge has a random CPO after isothermal compression from 6 to 7 GPa at 1173 K in 1 hour. AE signals from the fault zones during hot compression were indistinguishable from those observed during cold compression and near consistent with stick-slip behavior. Subsequent isothermal compression into the wadsleyite stability field shows no AE-activity. A pre-existing olivine fault zone deformed at 14 GPa and 1173-1273 K was replaced in 20 minutes by wadsleyite with a narrow grain size range (~0.8-1.0 mum). Fault zone wadsleyite has a clear CPO with a- and b-axes oriented in the direction of and perpendicular to the shear direction respectively. This suggests that wadsleyite accommodated renewed fault displacement by dislocation creep. Wadsleyite outside the fault zones does not have a CPO. Thus, under these conditions, fault zone wadsleyite appears weaker than the "wall rock" olivine, suggesting a mechanical weakening during the transition. Such a shear localization process on old faults might contribute to seismogenic slip within the Earth, where run-away processes are possible.

AGU Fall Meeting Abstracts, Dec 1, 2010

Abstract Diffusion is an extremely important process which exerts influence over the rheological ... more Abstract Diffusion is an extremely important process which exerts influence over the rheological behaviour of the Earth's interior. A good understanding of the rates of diffusion in the minerals composing the Earth's mantle is essential to quantitatively understand the viscosity of the lower mantle which, in turn, controls a host of dynamic phenomena from the thermal and chemical coupling with the core to the formation of plumes. Ammann et al., 2010a suggest, based on first principles calculations, that the anisotropy in the diffusivity ...

AGU Fall Meeting Abstracts, Dec 1, 2010

Materials Science Forum, Sep 1, 2005

Materials Science Forum, May 1, 1994

$Research paper thumbnail of Fluid-assisted fracturing, cataclasis, and resulting plastic flow in mylonites from the Moresby Seamount detachment, Woodlark Basin$

Journal of Structural Geology, Nov 1, 2013

The Moresby Seamount detachment (MSD) in the Woodlark Basin (offshore Papua New Guinea) is a larg... more The Moresby Seamount detachment (MSD) in the Woodlark Basin (offshore Papua New Guinea) is a large active low-angle detachment excellently exposed at the seafloor, and cutting through mafic metamorphic rocks. Hydrothermal infiltration of quartz followed by that of calcite occurred during cataclastic deformation. Subsequent deformation of these a priori softer minerals leads to mylonite formation in the MSD. This study aims at a better understanding of the deformation mechanism switch from cataclastic to plastic flow. Deformation fabrics of the fault rocks were analyzed by light-optical microscopy. Rheologically critical phases were mapped to determine distributions and area proportions, and EBSD was used to measure crystallographic preferred orientation (CPO). Strong calcite CPOs indicate dominant dislocation creep. Quartz CPOs, however, are weak and more difficult to interpret, suggesting at least some strain accommodation by diffusion creep mechanisms. When quartz aggregates are intermixed with the polymineralic mylonite matrix diffusion creep grain boundary sliding may be dominant. The syntectonic conversion from mafic cataclasites to more siliceous and carbonaceous mylonites induced by hydrothermal processes is a critical weakening mechanism enabling the MSD to at least intermittently plastic flow at low shear stresses. This is probably a crucial process for the operation of low-angle detachments in hydrated and dominantly mafic crust.

Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, Sep 1, 1996

The texture and microstructure of annealed, rolled and recrystallized copper (99.99%) were invest... more The texture and microstructure of annealed, rolled and recrystallized copper (99.99%) were investigated using conventional X-ray diffraction and single-crystal electron backscattering diffraction (EBSP) in a scanning electron microscope. From the EBSP data, misorientation distribution functions for next neighbor orientation relationships were derived, which show that the undeformed (annealed) starting material and the recrystallized sample have primary and secondary twin correlations, whereas in the deformed sample no preferred misorientations are observed. The microtexture of a single grain with twin lamellae in the deformed sample was analyzed in detail using automated analysis of electron backscattering diffraction patterns. The twin relationship is transformed continuously into a high angle grain boundary during deformation. Orientation gradients within one grain increase steadily up to 20°.

Journal of Synchrotron Radiation, Mar 1, 1997

$Research paper thumbnail of Microdiffraction Experiments on Single Polymeric Fibers by Synchrotron Radiation$

Macromolecules, Feb 1, 1997

It is shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fiber... more It is shown that wide-angle X-ray scattering patterns can be obtained from single polymeric fibers with a 2 µm synchrotron radiation beam in a few seconds per pattern. Preferred orientation was observed for an ultrahigh molecular weight polyethylene fiber where orthorhombic plus monoclinic phases were found to coexist in the outer parts of the fiber. For a poly(p-phenyleneterephthalamide) fiber (Kevlar 49) the radial sheet model was verified, but an important texture appears to be present.

Geological Magazine, Jul 20, 2023

We present kinematic, radiometric, geochemical and PT data, which help to constrain the tectonome... more We present kinematic, radiometric, geochemical and PT data, which help to constrain the tectonometamorphic evolution of the Tripolitza Unit (TPU). The age of both the metamorphic peak (P = 0.4 ±0.2 GPa, T = ca. 310 °C) and top-to-the WNW mylonitic thrusting, attributed to the emplacement of the hanging Pindos nappe, has been constrained at 19 ±2.5 Ma using Rb-Sr on synkinematic white mica of a basal mylonite of NW Crete. This early tectonic event is also documented by the oldest generation of veins, which cut through less metamorphic (T = 240 ±15 °C) late Bartonian/Priabonian Nummulite limestone exposed as olistolith in TPU flysch of central Crete. Calcite of these veins yielded a similar U-Pb age at 20 ±6 Ma. U-Pb dating of matrix calcite, on the other hand, reflect the time of sedimentation (38.4 ±5.7 Ma and 37.6 ±1.2 Ma), which is in line with the faunal content of the black limestone. Geochemical data and U-Pb calcite ages of fibres of the Nummulite test (32.3 ±3.1 Ma and 34.6 ±0.9 Ma) suggest unexpected pseudomorphic fibre replacement during late Priabonian/early Rupelian diagenesis. Additional calcite veins, which developed at ca. 10–11 and 7 – 9 Ma (U-Pb on calcite), are attributed to top-to-the S thrusting and subsequent extension, respectively. The resulting anticlockwise rotation of the shortening direction within the TPU from WNW-ESE at ca. 20 Ma to N-S at ca. 10 Ma has significant implications for the geodynamic evolution of the External Hellenides.

$Research paper thumbnail of X-Ray Microdiffraction From a Twist Grain Boundary Phase$

APS, Mar 1, 1997

The ESRF Microfocus Undulator Beamline was used to study the commensurability of the TGBc liquid ... more The ESRF Microfocus Undulator Beamline was used to study the commensurability of the TGBc liquid crystal phase. The TGBc phase is comprised of arrays of screw-edge dislocations which rotate blocks of smectic-C layers through a constant rotation angle. The phase has a distinctive n-fold diffraction pattern which can be explained by a commensurate lock-in of the block rotation angle to a rational fraction of 2pi, namely 2pi/n. The issue is whether the lock-in is intrinsic or a dominate contribution to the diffraction from isolated regions of the sample. To probe local structure, 13 KeV X-rays were focused using an ellipsoidal mirror through a 30mum diameter collimator with a resulting flux of 10^12 ph/sec. The diffraction pattern was collected on a lens coupled, scintillating screen, CCD area detector. By limiting the exposure time to 0.2sec (to avoid sample damage), clear diffraction patterns could be obtained and the 30mum beam was rastered across a 4 x 3mm area of the sample. The diffraction pattern was everywhere uniform demonstrating that lock-in was intrinsic to the sample rather than occuring in isolated regions.