POWTEX Neutron Diffractometer at FRM II - new perspectives for in-situ rock deformation analysis

EGU2012-13521 In Geoscience quantitative texture analysis here defined as the quantitative analysis of the crystallographic preferred orientation (CPO), is a common tool for the investigation of fabric development in mono- and polyphase rocks, their deformation histories and kinematics. Bulk texture measurements also allow the quantitative characterisation of the anisotropic physical properties of rock materials. A routine tool to measure bulk sample volumes is neutron texture diffraction, as neutrons have large penetration capabilities of several cm in geological sample materials. The new POWTEX (POWder and TEXture) Diffractometer at the neutron research reactor FRM II in Garching, Germany is designed as a high-intensity diffractometer by groups from the RWTH Aachen, Forschungszentrum Jülich and the University of Göttingen. Complementary to existing neutron diffractometers (SKAT at Dubna, Russia; GEM at ISIS, UK; HIPPO at Los Alamos, USA; D20 at ILL, France; and the local STRESS-SPEC and SPODI at FRM II) the layout of POWTEX is focused on fast time-resolved experiments and the measurement of larger sample series as necessary for the study of large scale geological structures. POWTEX is a dedicated beam line for geoscientific research. Effective texture measurements without sample tilting and rotation are possible firstly by utilizing a range of neutron wavelengths simultaneously (Time-of-Flight technique) and secondly by the high detector coverage (9.8 sr) and a high flux (�~1x10 7 n/cm2s) at the sample. Furthermore the instrument and the angular detector resolution is designed also for strong recrystallisation textures as well as for weak textures of polyphase rocks. These instrument characteristics allow in-situ time-resolved texture measurements during deformation experiments on rocksalt, ice and other materials as large sample environments will be implemented at POWTEX. The in-situ deformation apparatus is operated by a uniaxial spindle drive with a maximum axial load of 250 kN, which will be redesigned to minimize shadowing effects inside the cylindrical detector. The HT deformatione experiments will be carried out in uniaxial compression or extension and an upgrade to triaxial deformation conditions is envisaged. The load frame can alternatively be used for ice deformation by inserting a cryostat cell for temperatures down to 77 K with a triaxial apparatus allowing also simple shear experiments on ice. Strain rates range between 10-8 and 10-3 s-1 reaching to at least 50% axial strain. The deformation apparatus is designed for continuous long-term deformation experiments and can be exchanged between in-situ and ex-situ placements during continuous operation inside and outside the neutron detector

Correlation of magnetic fabric and crystallographic preferred orientations of naturally deformed carbonate — mica rocks from the Alpi Apuane in Italy and the Damara Orogen in Namibia

The anisotropy of magnetic susceptibility (AMS) is a time-efficient method to describe crystallographic preferred orientations of rocks and has been applied in a wide field of sedimentary, metamorphic and magmatic geology. The method, however, suffers from limitations which mainly result from the interference of diamagnetic, paramagnetic and ferromagnetic fabrics (de Wall 2005) — the term ferromagnetism is used in a wider sense here, including e.g. ferrimagnetism. The AMS is an integral parameter which describes a crystallographic preferred orientation as an ellipsoid. The quantitative correlation of the AMS with the crystallographic preferred orientations should help to allow a closer view at the applicability and the limitations of the AMS analysis (see also Schmidt et al. 2006 a, b)... The results of this study are based on a large variety of fabric types of carbonate-mica marbles and mylonites, i.e. varying mica content, grain sizes, grain shapes, types and intensities of the crystallographic preferred orientation. The presented first correlations of the AMS and CPO for the single mineral phases in general demonstrate a good matching. Regarding the comparison of texture types and the AMS, limitations are possible. While single c-axis maxima and girdle-like c-axis distributions can be also distinguished by the AMS, it is obvious that distinguishing between these types and the double c-axis type is not possible at the present stage.conferenc

Measurement of calcite crystallographic-preferred orientations by magnetic anisotropy and comparison to diffraction methods

The anisotropy of magnetic susceptibility (AMS) of rocks reflects the preferred orientations of minerals. Therefore AMS is a quick and easy way to characterize rock fabrics (Hrouda 1982,Borradaile 1988); the obtained result is also called the magnetic fabric of the rock. The method has been often used to measure the orientation of ferromagnetic minerals, mainly magnetite, but in recent studies it has been increasingly used to measure textures of paramagnetic minerals as phyllosilicates (Lüneburg et al. 1999, Cifelli et al. 2004). A further application is the measurement of diamagnetic textures, especially calcite textures. Calcite is suitable for the AMS method, because it has a high magnetic anisotropy with the minimum susceptibility along the crystallographic c-axis. Therefore a preferred orientation of the c-axes, which can be induced by deformation, generates a magnetic fabric...conferenc

Fracturing and vein formation in the middle crust - a record of co-seismic loading and post-seismic stress relaxation

Metamorphic rocks approaching the crustal scale brittle-ductile transition (BDT) during exhumation are expected to become increasingly affected by short term stress fluctuations related to seismic activity in the overlying seismogenic layer (schizosphere), while still residing in a long-term viscous environment (plastosphere). The structural and microstructural record of quartz veins in low grade – high pressure metamorphic rocks from southern Evia, Greece, yields insight into the processes and conditions just beneath the long-term BDT at temperatures of about 300 to 350°C, with switches between brittle failure and viscous flow as a function of imposed stress or strain rate...conferenc

Gefügecharakterisierung von Calcitmyloniten und Marmoren bezüglich senkrecht zueinander stehender Faltenteilstrukturen, Alpi Apuane, Italien

Im nördlichen Teil des Appenin in Italien ist der metamorphe Komplex der Alpi Apuane in Form eines tektonischen Fensters sehr gut aufgeschlosssen. Die metamorphen Gesteine der Alpi Apuane — Metakarbonate, Kiesel- und Karbonatschiefer sowie Phyllite — sind aufgrund der Kollision der korsischsardischen Mikroplatte mit der italienischen Halbinsel im mm bis km- Maßstab verfaltet worden. Im zentralen Teil der Alpi Apuane biegt das generelle N–S Streichen der Faltenstrukturen in eine E–W Richtung um. Faltenstrukturen mit senkrecht zueinander stehenden Faltenachsen sind charakteristisches Strukturmerkmal u.a. ‘Metamorpher Kernkomplexe’ und Schlüssel zum Verständnis von Deformationsgeschichte und mechanismen. Die Entwicklung dieser Strukturen wird kontrovers diskutiert...conferenc

RF Analyses of Integrated Ku-band Antenna

In the ACASIAS project an integrated antenna for Ku-band satellite communication has been developed. The design of this integrated antenna has to meet structural, electromagnetic and thermal requirements. This paper addresses the electromagnetic performance of the antenna both by design and by measurement. For the design of the antenna, the electromagnetic interaction of the antenna with the conducting Carbon Fibre Reinforced Plastic (CFRP) ribs of the orthogrid and the interaction with the Glass Fibre Reinforced Plastic (GFRP) skin of the panel have been analysed. In addition, the influence of potential lightning diverters on the antenna performance has been analysed. The radiation pattern of a single antenna tile and the radiation pattern of an antenna tile integrated in the orthogrid fuselage panel were measured. The results of the antenna measurements are compared with the results of the simulations carried out for the design of the antenna

Quantitative Neutron and X-ray texture analysis of Quartz mylonites - a comparative study

We investigated five mylonitic quartz veins from the Adamello pluton (southern Alps, Italy) which accumulated different amounts of shear deformation in the range between 4.5 to over 15. All quartz mylonites consist of a fine grained (35-40 m grainsize) dynamically recrystallized aggregate and show a strong crystallographic preferred orientation (CPO or texture), dominated by a strong Y-maximum of c-axis, whose intensity is expected to strengthen with increasing strain. The CPO has been measured by different texture diffraction methods at the Neutron Material Science Diffractometer STRESS-SPEC at the research reactor FRM II in Garching near Munich and with an x-ray diffractometer optimized for geological sample material located at the University of G\uf6ttingen. The high penetration capabilities of neutrons allowed the texture determination of the complete cubic quartz sample volume of about 4 cm3. In contrast, 90% of the x-ray CuK radiation detected from the sample in reflection geometry has penetration depths of up to 45 m in quartz (Wenk 1998). Applying a beam diameter of about 7 mm by means of a glass fibre polycapillary results in a measured sample volume of 1.73 mm3. Combining the measurements of three orthogonal sample directions, the measured sample volume sums up to 5.19 mm3. Due to the defocussing effect in X-ray diffraction, a correction function derived from randomly oriented powder samples has to be applied and only incomplete pole figures (tilt angle 75\ub0) could be obtained. To obtain complete pole figures, we (1) combined the measurements of three orthogonal sample sections and (2) applied the WIMValgorithm (e.g.Wenk et al 1998) as an orientation distribution function (ODF) to recalculate complete pole figures. For a quantitative comparison with the X-ray data, the WIMV-algorithm was also applied on the neutron diffraction data to also obtain a quantitative texture analysis. The experimental and recalculated pole figures of the three orthogonal sample directions measured by X-ray are very similar between the individual directions. This proves a high texture homogeneity and a reliable defocussing correction. Consequently the added experimental pole figures from the three sample directions show a very good agreement as well. The comparison between the X-ray and neutron pole figures shows in general a good accordance. Minor differences are related to grain statistics, small sample heterogeneities and minor effects from the defocusing correction. From the geological view these are negligible. Furthermore, this study shows that the STRESS-SPEC neutron diffractometer, although optimized for material science applications is well suitable for the measurement of geological samples, when critical grain-size/volume ratios are not exceeded. References: Wenk, H.-R. (1998): Pole figure measurements with diffraction techniques. In: Texture and Anisotropy (edited by Kocks, U. F., Tom\ue9, C. N., Wenk, H.-R.), Cambridge University Press 1998, pp. 126-177 Wenk, H. R., S. Matthies, J. Donovan, and D. Chateigner (1998): BEARTEX: A Windows-based program system for quantitative texture analysis, J. Appl. Crystallogr., 31(2), 262\u2013269, doi: 10.1107/ S002188989700811X

Development of crystallographic preferred orientation in natural quartz veins during post-magmatic cooling and deformation of granitoid plutons: comparison between Adamello (Avio intrusion; Southern Alps, Italy) and Sierra Nevada (Lake Edison intrusion; California).

We investigated the microstructure and crystallographic preferred orientation (CPO) of quartz within veins from two different granitoid intrusions (Avio intrusion, (AV) in the Adamello-Italy, and Lake Edison intrusion (LE) in the Sierra Nevada-California). The veins localized post-magmatic crystal-plastic deformation during cooling to the host rock temperature at a depth of about 10 km. They developed during high temperature conditions as tabular fillings of joints and were later deformed by simple shear parallel of the vein wall mainly at T 500C. Synkinematic localized granitoid mylonites at the boundary of the quartz veins show recrystallization of biotite and plagioclase, and formation and recrystallization of myrmekites. The AV samples has been described recently by Pennacchioni et al. (2010). In the study presented here, we introduce a comparison with new data from the LE quartz veins. The collected samples include a complete range from weakly (WDV) to moderately (MDV: with a well-developed foliation, but non-pervasive fine recrystallization) and, lastly, strongly deformed veins (SDV: well-foliated, completely recrystallized to fine aggregates) showing homogeneous (AV) and heterogeneous (LE) strain. The weakly deformed samples consist of large millimetric grains showing coarse (100s microns subgrain size) polygonizations, incipient fine recrystallizations (a few 10s microns grainsize) along discrete conjugate bands and locally strongly interlocked grains. The CPO was determined by X-ray texture goniometry and computer-integrated polarization microscopy (CIP). In the AV, the CPO of WDV is characterized by a dominant peripheral maximum of c-axes showing a small (< 10) synthetic angle with the shear plane - sometimes as a part of a girdle including Y-maxima. In the LE, the CPO of WDV shows different types including a single maximum or girdles oriented from a low synthetic to almost an orthogonal angle in respect to the foliation. The CPO evolution of AV and LE veins are similar in view of that both show the development of a new strong c-axis CPO in the MDV and SDV consisting of a partial YZ girdle centered on the Y axis or an almost single-crystal Y-maximum. These CPOs in MDV and SDV are consistent with dominant prism slip. The CPO evolution of the veins is discussed in terms of two end-member models: (i) the WDV and the MDV-SDV developed at different times and were deformed at different temperatures, or (ii) the WDV represent pristine veins from which MDV-SDV developed with a major change of deformation mechanism during increasing strain. References Pennacchioni, G., Menegon, L., Leiss, B., Nestola, F., Bromiley, G., 2010. Development of crystallographic preferred orientation and microstructure during plastic deformation of natural coarse-grained quartz veins. Journal of Geophysical Research 115, B12405, 23 pp., doi:10.1029/2010JB007674