2. Wochenbericht MSM17/1

MSM 17/1, PLEIADES Zweiter Wochenbericht 29.11.-05.12.201

1. Wochenbericht MSM17/1

MSM 17/1, PLEIADES Erster Wochenbericht 22.11.-28.11.201

3. Wochenbericht MSM17/1

MSM 17/1, PLEIADES Dritter Wochenbericht 6.12.- 12.12.201

High resolution bathymetric survey on the NW slope of Walvis Ridge, offshore Namibia

Expedition 17/1 of the German research vessel R/V MARIA S. MERIAN, carried out geophysical surveys and experiments between November and December 2010 in the area around Walvis Ridge, Southeast Atlantic Ocean. Among the data collected, a high-resolution bathymetric dataset aquired on the northwestern slope of the ridge offers some important preliminary insights into the tectonic evolution of the ridge and the adjoining lower continental slopes and ocean basin. The NE-SW trending Walvis Ridge has a trapezoid shape and is likely built up by thick sequences of plateau basalts, with top of basement rocks inclined to the south. Sediments are almost absent on the NW side of the ridge, preserving a fascinating mountainscape formed early in the tectonic history, most probably on-land. This interpretation is supported by clear denudational features, like steep cliffs up to 150 m high, and deeply incised valleys, defining paleo-drainages. Isolated, flat-topped guyots seaward of the ocean-continent boundary attest to a later history of wave abrasion and progressive subsidence of Walvis Ridge

6. Wochenbericht MSM17/1

MSM 17/1, PLEIADES Sechster und letzter Wochenbericht 27.12.- 29.12.201

Neutron time-of-flight texture measurements in Dubna: Status and developments

The multidetector texture diffractometer SKAT (from Russian: Spektrometer Kolitshestvennovo Analiza Tekstury) at the pulsed reactor IBR-2 in Dubna, Russia, started operation in March 1997 and is open for users from all countries. Application of time-of-flight (TOF) diffraction to texture measurements offers the opportunity to record complete diffraction patterns, i.e., to measure several pole figures simultaneously. To allow high spectral resolution for measurements on polyphase geological samples with many diffraction patterns, the instrument was placed at the end of an over 100m long flight path. In this paper, we will summarize advantages and disadvantages of the SKAT, as well as intended improvements.conferenc

4. Wochenbericht MSM17/1

MSM 17/1, PLEIADES Vierter Wochenbericht 13.12.- 19.12.201

Crystal plasticity and superplasticity in quartzite; A natural example

Plastically deformed quartzites from the Betic Movement Zone (Betic Cordilleras, Spain) exhibit microstructures indicative of crystal plasticity on a mineral grain scale. Quartzites with dynamically recrystallized grain sizes larger than 10 μm have strong crystallographic preferred orientations, narrow grain boundaries, little creep damage, and an inverse proportionality of dislocation density and grain size. Mylonites with grain sizes smaller than 10 μm have low crystallographic preferred orientations, wide grain boundaries (up to 1000 Å), abundant creep damage, and decreasing dislocation density with diminishing grain size. This is thought to reflect a clear-cut shift in deformational regimes from dislocation creep to superplastic flow at 10 μm grain size. Superplasticity can be acquired by quartzites which suffer dynamic recrystallization to grain sizes smaller than 10 μm during an initial dislocation creep stage. Dislocation motion is the major accomodating mechanism for strain incompatibilities that arise during grain-boundary sliding in the mylonites.It seems reasonable to estimate flow stresses from unbound dislocation densities and dynamically recrystallized grain sizes in the tectonite specimens. In the mylonites, dynamically recrystallized grain size probably reflects the stress magnitude before the shift in deformational mechanisms, and an estimate for late stage stresses is provided by unbound dislocation densities. In both deformational regimes the flow strength appears to depend on the extent of dynamic recrystallization

3. Wochenbericht SO244/1

SO-244 Leg 1, GeoSea 09.11. – 15.11.201

Geotechnical characterization of trench- and slope sediments off Southern Chile: preliminary results

To understand seismogenesis in shallow parts of subduction zones, it is vital to know about strength and frictional parameters of subducted sediment. For this purpose, PETROTEC, as part of the TIPTEQ-Project, gathers geotechnical data for sediments deposited on the incoming Nazca Plate, the trench and the slope off the southern Chilean coast during the last 5 Ma, and whose equivalents are now being underthrusted into the seismogenic zone beneath South America. Material comes from gravity cores collected during R/V SONNE Cruises SO181 (Flüh E. & Grevemeyer I (Editors) 2005), SO102 (Hebbeln D, Wefer G, et al. 1995) and SO156 (Hebbeln D, et al. 2001), as well as from ODP Leg 141 (Behrmann JH, et al. 1992) drill cores. Sediment strength and frictional properties are determined by triaxial testing, ring shear testing and direct shear testing...conferenc