Variation in bridgmanite grain size accounts for the mid-mantle viscosity jump

A viscosity jump of one to two orders of magnitude in the lower mantle of Earth at 800–1,200-km depth is inferred from geoid inversions and slab-subducting speeds. This jump is known as the mid-mantle viscosity jump1,2. The mid-mantle viscosity jump is a key component of lower-mantle dynamics and evolution because it decelerates slab subduction3, accelerates plume ascent4 and inhibits chemical mixing5. However, because phase transitions of the main lower-mantle minerals do not occur at this depth, the origin of the viscosity jump remains unknown. Here we show that bridgmanite-enriched rocks in the deep lower mantle have a grain size that is more than one order of magnitude larger and a viscosity that is at least one order of magnitude higher than those of the overlying pyrolitic rocks. This contrast is sufficient to explain the mid-mantle viscosity jump1,2. The rapid growth in bridgmanite-enriched rocks at the early stage of the history of Earth and the resulting high viscosity account for their preservation against mantle convection5–7. The high Mg:Si ratio of the upper mantle relative to chondrites8, the anomalous 142Nd:144Nd, 182W:184W and 3He:4He isotopic ratios in hot-spot magmas9,10, the plume deflection4 and slab stagnation in the mid-mantle3 as well as the sparse observations of seismic anisotropy11,12 can be explained by the long-term preservation of bridgmanite-enriched rocks in the deep lower mantle as promoted by their fast grain growth

Quantitative characterization of plastic deformation of single diamond crystals: A high pressure high temperature (HPHT) experimental deformation study combined with electron backscatter diffraction (EBSD)

We report the results of a high-pressure high-temperature (HPHT) experimental investigation into the deformation of diamonds using the D-DIA apparatus. Electron backscatter diffraction (EBSD) data confirm that well-defined 300–700 nm wide {111} slip lamellae are in fact deformation micro-twins with a 60° rotation around a axis. Such twins formed at high confining pressures even without any apparatus-induced differential stress; mechanical anisotropy within the cell assembly was sufficient for their formation with very little subsequent lattice bending ( slip system dominates as expected for the face-centred cubic (FCC) structure of diamond. Slip occurs on multiple {111} planes resulting in rotation around axes. Deformation microstructure characteristics depend on the orientation of the principal stress axes and finite strain but are independent of confining pressure and nitrogen content. All of the uniaxially deformed samples took on a brown colour, irrespective of their initial nitrogen characteristics. This is in contrast to the two quasi-hydrostatic experiments, which retained their original colour (colourless for nitrogen free diamond, yellow for single substitutional nitrogen, Type Ib diamond) despite the formation of {111} twin lamellae. Comparison of our experimental data with those from two natural brown diamonds from Finsch mine (South Africa) shows the same activation of the dominant slip system. However, no deformation twin lamellae are present in the natural samples. This difference may be due to the lower strain rates experienced by the natural samples investigated. Our study shows the applicability and potential of this type of analysis to the investigation of plastic deformation of diamonds under mantle conditions

The effect of dynamic recrystallisation on the rheology and microstructures of partially molten rocks

This work was founded by the joint project “Rheology of the continental crust in collision”, funded by the Procope scheme of PHC Egide in France and by the DAAD PPP scheme in Germany. M-GL acknowledges the support of the Juan de la Cierva programme of the Government of Spain’s Ministry for Science, Innovation and Universities. EGR acknowledges the support of the Beatriu de Pinós programme of the Government of Catalonia's Secretariat for Universities and Research of the Department of Economy and Knowledge (2016 BP 00208). This work benefited from discussions with Pi L. Jolivet and E. Burov within the ERC project RHEOLITH. We thank Elisabetta Mariani and Marcin Dabrowski for their helpful comments, together with the editorial guidance of Dave Healy and Bill Dunne.Peer reviewedPostprin

Disequilibrium melt distribution during static recrystallization

Melt migration and segregation, and the rheology of partially molten rocks in the upper mantle and lower crust, strongly depend on the grain-scale distribution of the melt. Current theory for monomineralic aggregates predicts a perfectly regular melt framework, but high-temperature experiments with rock-forming minerals + melt show considerable deviations from this predicted geometry. Disequilibrium features, such as fully wetted grain boundaries and large melt patches, have been described; these were mainly attributed to surface-energy anisotropy of the minerals. We present static analogue experiments with norcamphor + ethanol that allow continuous in situ observation of the evolving liquid distribution. The experiments show that all previously reported disequilibrium features can form during fluid-enhanced static recrystallization when small grains are consumed. There is no need to invoke surface-energy anisotropy, although this might enhance the effect. All disequilibrium features are transitory and evolve back toward equilibrium geometry. However, because the system undergoes continuous static recrystallization, disequilibrium features are always present in a partially molten polycrystalline aggregate and therefore control its properties

Einflüsse von Bauteiltoleranzen und Bauteilfehlern bei der akustischen Resonanzanalyse

Bei der akustischen Resonanzanalyse werden Fehlstellen integral durch die Verschiebung der Eigenresonanzen eines Bauteils nachgewiesen, wobei die Bauteiltoleranzen, die ebenfalls zu Resonanzverschiebungen führen, eine wichtige Rolle spielen. An einem einfachen Bauteil- Aluminium- Stab- wurde eine Abschätzung der Einflüsse von Bauteiltoleranzen auf theoretischer Basis möglich und durch Experimente verifiziert. Dargestellt werden: a) Analytische Gleichungen zur Berechnung der Eigenresonanzen der Dehn- und Biegeschwingungen eines Stabes mit kreiszylinderischem Querschnitt. b) Vergleich der analytischen Lösungen mit FEM- Rechnungen c) Vergleiche der Theorie mit den Ergebnissen praktischer Messungen. d) Die Genauigkeit des Verfahrens durch Messungen an Bauteilen mit variierenden Abmessungen. e) Erste Messungen an definierten, künstlich eingebrachten Fehlern

Deformation of melt-bearing systems—insight from in situ grain-scale analogue experiments

The deformation behaviour of partially molten rocks was investigated using in situ analogue experiments with norcamphor+ethanol, as well as partially molten KNO3+LiNO3. Three general deformation regimes could be distinguished during bulk pure shear deformation. In regime I, above ca. 8-10 vol.% liquid (melt) fraction ([phi]bulk), deformation is by compaction, distributed granular flow, and grain boundary sliding (GBS). At [phi]bulk<8-10 vol.% (regime II), GBS localizes in conjugate shear zones. Liquid segregation is inefficient or even reversed as the dilatant shear zones draw in melt to locally exceed the 8-10 vol.% threshold. At even lower [phi]bulk (regime III), grains form a coherent framework that deforms by grain boundary migration accommodated dislocation creep, associated with efficient segregation of remaining liquid. The transition liquid fraction between regimes I and II ([phi]LT) depends mainly on the grain geometry and is therefore comparable in both analogue systems. The transition liquid fraction between regimes II and III ([phi]GBS-L) varies between 4-7 vol.% for norcamphor-ethanol and ca. 1 vol.% for KNO3+LiNO3 and depends on system specific parameters. Regime II behaviour in our experiments can explain the frequently observed small melt-bearing shear zones in partially molten rocks and in HT experiments

Praktische Beispiele der US-Prüfung an hochbelastbaren Stahl- und Wasserbau-Konstruktionen mit Hilfe elektronisch scannender Ultraschall Phased Array Techniken

Im Stahl- und Wasserbau werden Bleche mittels Schweißnähten gefügt bzw. mit angeschweißten Stehbolzen versteift. Diese hochbelasteten Fügebereiche sind dabei einer zfP zu unterziehen, wobei typischerweise eine manuelle Ultraschallprüfung eingesetzt wird. Die komplexen Geometrien der Fügebereiche machen automatische Prüfungen schwierig. Handprüfungen mit A- Bildauswertungen, aber auch automatisierte, mechanisch scannende Prüfungen sind zum einen sehr aufwendig, zum anderen ist die erhaltene Echofolge oft sehr schwierig zu interpretieren. Durch den Einsatz einer Phased Array- Technik mit virtueller Prüfkopfverschiebung- eine Gruppe von n Einzelschwingern (n = 16) aus einer Gesamtanzahl von N Einzelschwingern (N =128) wird elektronisch verschoben- können derartige Prüfaufgaben gelöst werden, dabei werden neben den primären A- Bildern auch B- und C- Bilder aufgenommen und dargestellt. Anhand einiger Beispiele: § Prüfung von Schweißnähten für Messerhalter von Feldhäckslern. § Prüfung von Schweißnähten an Absperrschotten für Talsperren. § Prüfung der Schweißnähte an Versteifungsbolzen in Stahlbrückenträgern. wird der Erfolg dieser Technik demonstriert