Rheology of PDMS-corundum sand mixtures from the Tectonic Modelling Lab of the University of Bern (CH)

This dataset provides rheometric data of silicone (Polydimethylsiloxane, PDMS SGM36)-corundum sand mixtures used for analogue modelling in Zwaan et al. (2016, 2017), Zwaan and Schreurs (2017) and in the Tectonic Modelling Lab of the Institute of Geological Sciences at the University of Bern (CH). The PDMS is produced by Dow Corning and its characteristics have been described by e.g. Rudolf et al. (2016a,b). The corundum sand (Normalkorund Braun 95.5% F120 by Carlo Bernasconi AG: https://www.carloag.ch/shop/catalog/product/view/id/643), has a grainsize of 0.088-0.125 mm and a specific density of 3.96 g cm^-3. Further rheological characteristics are described by Panien et al. (2006). The density of the tested materials ranges between 1 (pure PDMS) and 1.6 g cm^-3 (increasing corundum sand content in mixture). The material samples have been analysed in the Helmholtz Laboratory for Tectonic Modelling (HelTec) at GFZ German Research Centre for Geosciences in Potsdam using an Anton Paar Physica MCR 301 rheometer in a plate-plate configuration at room temperature. Rotational (controlled shear rate) tests with shear rates varying from 10^-4 to 10^-1 s^-1 were performed. According to our rheometric analysis, the material is quasi Newtonian at strain rates below 10^-3*s^-1 and weakly shear rate thinning above. Viscosity and stress exponent increase systematically with density from ~4*10^4 to ~1*10^5 Pa*s and from 1.06 to 1.10, respectively. A first application of the materials tested can be found in Zwaan et al. (2016). Detailed information about the data, methodology and a list of files and formats is given in the "data description" and "list of files" that are included in the zip folder and also available via the DOI landing page

Komplexität von Deformationsmustern in der Entwicklung von Akkretionskeilen

This thesis addresses the complexity in the patterns of deformation in accretionary wedges based on analogue modelling. A combined approach of 1) statistically assessing results from sand wedges 2) mechanically analyzing fault behavior in the structural evolution of sand wedge and 3) comparing varying wedge geometry and dynamics to theory, are used in an effort to unravel the complexity that develops as the wedge evolves. This thesis comprises of three manuscripts addressing these three approaches respectively. The experimental database is derived from analysis of 27 analogue sand wedge models where the friction of the basal décollement is varied. The kinematics of the analogue sand wedge is monitored using Particle Image Velocimetry (PIV) that provides detailed information on the displacements in the wedge. The statistical approach (Chi square test, ANOVA test) consists of quantifying the degree of both intrinsic variations in the results of the model and extrinsic variation caused by the varying basal friction. In particular the statistical study shows that intrinsic variability of fault and wedge observables is related to the mechanics and material properties of the wedge. In addition, results show that analogue experiments are reproducible. The next study presented in this thesis reflects on the faults of the wedge. Fault activity, in particular fault formation, reactivation and underthrusting are described. The observations are explained mechanically in relation to the fault geometry and the changing frictional properties along the fault plane. It is also demonstrated that fault activity governs the shape, activity and eventual zonation of the wedge. Additionally, a comparison between two theories 1) Critical taper theory and the 2) Minimum work theory is performed to recognize which theory best represents the deformation in accretionary wedges. The critical taper theory focuses on the geometry of the wedge and the minimum work theory focuses on the energy in the wedge. It is evident that both theories are applicable, however at different stages of an accretionary cycle. Overall, the minimum work theory determines the path of deformation needed to reach that geometry determined by the critical taper theory. Research to explore the role of ductile behavior in the wedge is also initiated. Preliminary stages of the research include the characterization of a new elasto-plastic viscous material called Carbopol that behaves in a viscous manner after a certain yield strength is overcome i.e. Herschel Bulkley fluid. A rheological study tests the effect of concentration of three different types of commercial Carbopol products. Besides this research, the monitoring of forces in analogue models is also attempted with a new setup. The combination of high resolution force recordings and visual PIV data provides an insightful view into the dynamics of the model.In der vorliegenden Arbeit wird die Komplexität von Deformationsmustern in der Entwicklung von Akkretionskeilen durch folgende Ansätze aufgezeigt: (1) Die statistische Auswertung von Ergebnissen von Analog-Sandkeilen, (2) Erklärungen des mechanischen Verhaltens von Störungen, der wichtigsten Strukturelemente solcher Keile, und (3) der Vergleich von Keilgeometrie und Keildynamik mit der zugrundeliegenden Theorie. Der Experimentaufbau umfasst eine systematische Studie von 27 Analogmodellen von Sandkeilen, in denen die Reibung der basalen Abscherung variiert wird. Die zeitliche Entwicklung dieser Analogsandkeile wird mithilfe der Particle Image Velocimetry (PIV) aufgezeichnet, die detaillierte Information hinsichtlich von Versätzen innerhalb eines Keils ermöglicht. Die statistischen Ansätze (Chi-Quadrat-Test, ANOVA-Test) beinhalten die Quantifizierung der intrinsischen Variation der Modellierungsergebnisse sowie der extrinsischen Variation, die durch die Variation der basalen Reibung verursacht wird. Die statistische Auswertung zeigt insbesondere, dass die intrinsische Variabilität von beobachtbaren Größen der Störungen und Keile von der Mechanik und den Materialeigenschaften der Keile abhängen. Des Weiteren belegen die Ergebnisse, dass Analogexperimente reproduzierbar sind. Die folgende Studie in der Arbeit richtet sich auf die Störungen, insbesondere die Bildung, Reaktivierung und Unterschiebung, innerhalb von Keilen. Beobachtungen werden hinsichtlich der Mechanik von Störungsgeometrie und veränderter Reibungseigenschaften einer Störungsebene erklärt. Es wird ebenfalls gezeigt, dass Form, Aktivität und mögliche Zonierungen von Keilen durch die Störungsaktivität bestimmt werden. Des Weiteren zeigt der Vergleich zweier Theorien, der Theorie der kritischen Keile und der Theorie der minimalen Arbeit, welche der beiden Theorien die Deformation in Akkretionskeilen am besten beschreibt. Die Theorie der kritischen Keile stützt sich auf die Keilgeometrie während die Theorie der minimalen Arbeit die Kräftebilanz in einem Keil betrachtet. Beide Theorien sind von Bedeutung, jedoch in verschiedenen Stadien der Keilentwicklung. Generell wird durch die Theorie der minimalen Arbeit der Deformationspfad beschrieben, der zur Erlangung einer bestimmten Keilgeometrie führt. Die Arbeit zeigt auch Wege auf, die die Rolle der initialen duktilen Deformation betreffen. Vorläufige Stadien dieser Forschung beinhalten die Charakterisierung von neuen elasto-plastischen, viskosen Materialien, wie Carbopohl, das nach Erreichen der Versagensgrenze spröde deformiert. Dahingehend überprüft eine rheologische Studie den Einfluss die Konzentration von drei kommerziell erhältlichen Carbopol-Produkten. Darüberhinaus wird durch einen neuen Experimentaufbau die Aufzeichnung von Kräften in Analogexperimenten untersucht. Die Kombination von hochauflösender Aufzeichnung von Kräften und visueller PIV-Daten ermöglicht neue Betrachtungen der Dynamik von Modellen

Rheology of PDMS-corundum sand mixtures from the Tectonic Modelling Lab of the University of Bern (CH)

This dataset provides rheometric data of silicone (Polydimethylsiloxane, PDMS SGM36)-corundum sand mixtures used for analogue modelling in Zwaan et al. (2016, 2017), Zwaan and Schreurs (2017) and in the Tectonic Modelling Lab of the Institute of Geological Sciences at the University of Bern (CH). The PDMS is produced by Dow Corning and its characteristics have been described by e.g. Rudolf et al. (2016a,b). The corundum sand (Normalkorund Braun 95.5% F120 by Carlo Bernasconi AG: https://www.carloag.ch/shop/catalog/product/view/id/643), has a grainsize of 0.088-0.125 mm and a specific density of 3.96 g cm^-3. Further rheological characteristics are described by Panien et al. (2006). The density of the tested materials ranges between 1 (pure PDMS) and 1.6 g cm^-3 (increasing corundum sand content in mixture). The material samples have been analysed in the Helmholtz Laboratory for Tectonic Modelling (HelTec) at GFZ German Research Centre for Geosciences in Potsdam using an Anton Paar Physica MCR 301 rheometer in a plate-plate configuration at room temperature. Rotational (controlled shear rate) tests with shear rates varying from 10^-4 to 10^-1 s^-1 were performed. According to our rheometric analysis, the material is quasi Newtonian at strain rates below 10^-3*s^-1 and weakly shear rate thinning above. Viscosity and stress exponent increase systematically with density from ~4*10^4 to ~1*10^5 Pa*s and from 1.06 to 1.10, respectively. A first application of the materials tested can be found in Zwaan et al. (2016). Detailed information about the data, methodology and a list of files and formats is given in the "data description" and "list of files" that are included in the zip folder and also available via the DOI landing page