Variations In Rheology Research Articles

Investigation of the Viscoelastic Behavior Variation of Glass Mat Thermoplastics (GMT) in Compression Molding.

Compression molding is a lightweight technology that allows to preserve fiber length and retain better mechanical properties compared to injection molding. In compression molding development, a suitable material such as glass fiber mat thermoplastics (GMT) is often used. However, because of the complicated micro-structure of the fibers and the fiber–resin matrix interactions, it is still quite challenging to understand the mechanism of compression molding and it is very difficult to obtain a uniformly compressed GMT product. In this study, we propose a method to measure the rheological properties of GMT through a compression system. Specifically, we utilized a compression molding system to record the relation between the loading force and the displacement. This quantitative information was used to estimate the power-law index and viscoelastic parameters and predict viscosity. Moreover, the estimated viscoelastic parameters of GMT were implemented into Moldex3D to evaluate the flow behavior under compression. The results showed that the trend of the loading force variation was consistent in numerical simulation and experiments. However, at the final stage of compression molding, the experimental loading force was much higher than that estimated by simulation. To find out the mechanism causing this deviation, a series of studies were performed. Through TGA measurement, we found that the fiber content of the center portion of the compressed part increased from 63% to 85% during compression. This was expected, as a result of the fiber–polymer matrix separation effect. This fiber–polymer matrix separation effect influenced the power-law index and rheological parameters of GMT, making them fluctuate. Specifically, the power-law index changed from 1.0 to 0.62. These internal changes of the rheological properties further induced a much higher loading force in the real experimental GMT system. We further verified the rheological properties variation using pure polyamide (PA) and found that since there is no fiber–polymer matrix interactions the power-law index and curve-fitting rheological parameters were almost constant. The mechanism causing the deviation was therefore validated.

Computer vision for real-time extrusion quality monitoring and control in robotic construction

Abstract In this paper, a vision-based real-time extrusion quality monitoring system is developed for robotic construction. Initially, the details related to the extrusion system, data acquisition and processing unit, and the proposed algorithm are discussed. The reliability and responsiveness of the developed system is then evaluated on six determined levels of material variation. To demonstrate its application, the vision algorithm is used to develop an innovative closed-loop extrusion system. This system is able to automatically adjust the extrusion rate based on the vision system feedback. Such self-regulating extrusion system would be able to continuously print layers of acceptable dimensions using any printable mixture, without the need for prior calibration and despite some mixture rheology variations. All in all, the high precision and responsiveness of the developed system demonstrates the great potential for computer vision as a real-time quality monitoring and control tool for robotic construction.

Modifications of basic-oxygen-furnace slag microstructure and their effect on the rheology and the strength of alkali-activated binders

Microstructure tailoring of metallurgical slags allows the production of alternative construction binders with customized properties. In this study, the variations of rheology and strength of alkali-activated basic-oxygen-furnace (BOF) slags are quantified. Two modifications of BOF slag were created adding amounts of alumina and silica at high temperature (>1250 °C). The additions, defined by thermodynamic modeling, lowered the liquidus temperature facilitating the generation of amorphous when the slag was fast cooled. The first modification (SAT1) incorporated 5 wt% silica and 11 wt% alumina, while the second (SAT2) included around 13 wt% alumina. Both modifications generated a hybrid microstructure composed of cementitious and non-cementitious crystalline phases and an amorphous fraction. During alkali activation using NaOH solutions of 0.25 M, rheological measurements on fresh paste using SAT2 registered plastic viscosity values 2.3 times higher than those of SAT1. The compressive strength after 28 days for the binder developed from SAT2 slag was 10–30% stronger than the one from SAT1. These binders showed similar crystalline reaction products but compositional differences in the amorphous gel correlated to the initial slag modification. The detected differences in the binder properties are significant enough to justify BOF-slag engineering as a way to deliver customized precursors for alkali activation.

Effect of glass fiber distributions on the mechanical and fracture behaviors of injection-molded glass fiber-filled polypropylene with 2-Hole Tension specimens

In this study, various fracture characteristics of plastic parts were experimentally investigated using newly designed specimens with 2 holes to observe the deformation and fracture behaviors of injection-molded plastic parts fabricated by short glass fiber (GF)-reinforced polypropylene (PP). This 2-hole tension (2HT) specimen affects the flow pattern of resin and the orientation of GF during the injection molding process, and various stress concentrations and distributions can be generated under a simple tensile load. The effects of rheological and mechanical variations of the resin on the deformation and fracture behavior of the test specimens were successfully investigated using the 2-hole tension specimens. In addition, it was confirmed that the non-uniform distribution of GF observed in the hole arrays region through the computed tomography (CT) scan is related to the crack propagation pathway, which ultimately affects the fracture behavior of the specimen.

Architecture and Tectono-magmatic evolution of the Campos Rifted Margin: Control of OCT structure by basement inheritance

Abstract The formation of rifted margins involves the deformation of pre-existing lithosphere whose rheological and mechanical behavior during extension is complex since it is the product of numerous earlier tectonic events. In this work we investigate the Campos Rifted Margin (CRM) architecture, with the aim of exploring the role of basement inheritance and early magmatism on margin evolution. We present a new compilation of high resolution aeromagnetic data, integrated with seismic interpretation and crustal thickness from 3D gravity inversion, to resolve margin architecture, ocean-continent transition (OCT) structure and the oceanward extent of continental basement. We examine the lateral variation of crustal rheology, necking geometry and rift segmentation, revealing striking spatial heterogeneities that separate three distinct sectors along the Campos margin. The basement of the Campos Rifted Margin consists of Precambrian/Eo-Paleozoic Ribeira Belt (RB) and the easternmost Cabo Frio Tectonic Domain (CFTD) whose Neoproterozoic-Cambrian nappes and thrusts are well preserved offshore and give a rheologically layered crust. This pre-rift basement configuration, along with the Mesozoic magmatism, has resulted in different crustal responses to extension which vary from north to south. It influenced the temporal and spatial distribution of deformation, and as a consequence, the necking geometry, subsidence and sedimentary evolution of the margin. We show that the Campos basin evolution was controlled by crustal inheritance corresponding to that observed in onshore basement terranes. The more massive basement of the northern Campos basin can be correlated with the post-collisional Cambro-Ordovician magmatic province of the Aracuai belt that partially obliterated the earlier orogenic structures. The lack of a structured crust localized the strain generating the observed narrow necking zone. In addition, its more mafic composition resulted in a competent crust which also influenced the rifting processes. In contrast the basement of the central and southern Campos margin, represented by the Cabo Frio Tectonic Domain, is structurally and petrologically distinct from the Aracuai Belt and has layered orogenic crust which responded differently to rifting stresses forming the observed wide necking zone. We propose that the Campos Rifted Margin evolved from a pre-rift complex inherited rheology which dominated the first stages of rifting. However once the crust was highly extended, the deformation was nearly synchronous regionally, leading to giant salt basin formation and breakup.

S‐Wave Receiver Function Analysis of the Pampean Flat‐Slab Region: Evidence for a Torn Slab

AbstractFlat‐slab subduction is an atypical form of subduction where the downgoing plate assumes a low‐angle or subhorizontal geometry as it descends beneath the overriding plate. These systems have profound impacts on upper‐plate deformation and volcanism, yet there are outstanding questions regarding the causes, initiation, and termination of flat‐slab subduction. The Pampean flat‐slab region, located in the South American Cordillera, is an ideal locale to study the evolution of these systems due to its well‐constrained geologic history and the continuity of subduction along the western margin of the continent. In this work, we utilize S wave receiver functions (SRFs) to measure the thicknesses and geometry of the subducting Nazca plate lithosphere and the overriding South American plate within the region. Results from this study show overthickened Nazca Plate crust (~15–20 km thick) in the flat‐slab region. Prior to the slab steepening, SRFs indicate a velocity increase rather than a decrease at the top of slab crust, which is consistent with a transition from basalt to eclogite within the crust as it dehydrates. Margin parallel cross sections are consistent with differing transitions between flat‐subduction and more‐typical subduction occurring to the north and south. In the north, the transition appears to be gradual, consistent with slab bending. To the south, SRFs indicate an abrupt change, consistent with slab tearing. These differences are consistent with significant variations in slab rheology along the margin, which may reflect differing thermal regimes. This work has global implications for the three‐dimensional effects of flat‐slab subduction.

Glacial isostatic adjustment along the Pacific coast of central North America

We infer the GIA signal and its uncertainty along the central Pacific coast of North America using 680 sea-level index points and over 20,000 model runs sampling >700 (1-D) Earth viscosity models and 29 ice sheet reconstructions. Due to the large spatial extent and different tectonic settings of the study area, we divided it into three sub-regions (northern, central and southern) for which model parameters were inferred separately. Also, given that this region is tectonically active, the influence of this process (as well as sediment isostatic adjustment) was accounted for where possible by removing it from the data using published estimates. Our results indicate that it is not possible to produce an acceptable to for all of the RSL data with a single set of model parameters, suggesting significant lateral variability in viscous structure. Specifically, low viscosities (1019–1020 Pas) are inferred in the upper mantle within the northern region (southwestern British Columbia and northwest Washington) compared to those inferred (2–5 × 1020 Pas) for the central and southern regions (extending from southern Washington to southern California). High quality model fits were obtained for all data except those from the northern region where no single parameter set was able to capture both the rapid and large RSL fall during the late glacial and the monotonic rise during the mid-to-late Holocene at all localities. This suggests the need for an Earth model that incorporates departures from a linear Maxwell rheology (as applied here) and/or lateral variations in viscosity structure. Using our optimal model parameter sets, we show that GIA is a significant contributor to both contemporary vertical land motion and relative sea level change in our study region and so should be considered when interpreting observations of these signals and for making future relative sea level projections. Model output of present-day vertical land motion at 483 GPS stations and sea-level change at 56 tide gauge stations is provided (with estimated uncertainty) so that these data can be used to study non-GIA processes more accurately.

Rheological properties of lignosulfonate intercalated layered double hydroxides modified bitumen before and after ultraviolet aging

Rheological property of bitumen is closely related to the service life of bituminous pavement, which is mainly affected by temperature, vehicle load and ultraviolet (UV) ray. In this paper, lignosulfonate intercalated layered double hydroxides modified bitumen (LLMB) were researched by Fourier transform infrared (FTIR) spectrometer characterization, aging index and storage stability test. Meanwhile, rheological properties of LLMB before and after UV aging were investigated by temperature susceptibility, dynamic viscoelastic properties and rheological model analyses. The results showed that the introduction of lignosulfonate intercalated layered double hydroxide (LS-LDHs) could strengthen the anti-UV aging ability of bitumen more effectively and had better high temperature storage stability than layered double hydroxides (LDHs). From rheological performance measurement, LS-LDHs could weaken the temperature susceptibility of bitumen observably. Compared with pristine bitumen (PB), the values including loss tangent (tanδ), complex modulus (G∗) and rutting factor (G∗/sinδ) of LLMB got higher. According to rheological model analyses, the addition of LS-LDHs affected the models of bitumen hardly, but restrained instantaneous elastic, delayed elastic and viscous deformation. Therefore, LS-LDHs could enhance rigidity, high temperature performance and resistance to deformation of bitumen significantly. After UV aging, the rheological parameters variations and deformation arguments amplitudes of LLMB were lowest among PB, layered double hydroxides modified bitumen (LMB) and LLMB, which demonstrated that LS-LDHs improved the UV aging resistance of bitumen prominently.

A Natural Glycyrrhizic Acid‐Tailored Light‐Responsive Gelator

The construction of stimuli-responsive materials by using naturally occurring molecules as building blocks has received increasing attention owing to their bioavailability, biocompatibility, and biodegradability. Herein, a symmetrical azobenzene-functionalized natural glycyrrhizic acid (trans-GAG) was synthesized and could form stable supramolecular gels in DMSO/H2 O and MeOH/H2 O. Owing to trans-cis isomerization, this gel exhibited typical light-responsive behavior that led to a reversible gel-sol transition accompanied by a variation in morphology and rheology. Additionally, this trans-GAG gel displayed a distinct injectable self-healing property and outstanding biocompatibility. This work provides a simple yet rational strategy to fabricate stimuli-responsive materials from naturally occurring, eco-friendly molecules.

Porous gravity currents: Axisymmetric propagation in horizontally graded medium and a review of similarity solutions

Abstract We present an investigation on the combined effect of fluid rheology and permeability variations on the propagation of porous gravity currents in axisymmetric geometry. The fluid is taken to be of power-law type with behaviour index n and the permeability to depend from the distance from the source as a power-law function of exponent β. The model represents the injection of a current of non-Newtonian fluid along a vertical bore hole in porous media with space-dependent properties. The injection is either instantaneous ( α = 0 ) or continuous (α > 0). A self-similar solution describing the rate of propagation and the profile of the current is derived under the assumption of small aspect ratio between the current average thickness and length. The limitations on model parameters imposed by the model assumptions are discussed in depth, considering currents of increasing/decreasing velocity, thickness, and aspect ratio, and the sensitivity of the radius, thickness, and aspect ratio to model parameters. Several critical values of α and β discriminating between opposite tendencies are thus determined. Experimental validation is performed using shear-thinning suspensions and Newtonian mixtures in different regimes. A box filled with ballotini of different diameter is used to reproduce the current, with observations from the side and bottom. Most experimental results for the radius and profile of the current agree well with the self-similar solution except at the beginning of the process, due to the limitations of the 2-D assumption and to boundary effects near the injection zone. The results for this specific case corroborate a general model for currents with constant or time-varying volume of power-law fluids propagating in porous domains of plane or radial geometry, with uniform or varying permeability, and the possible effect of channelization. All results obtained in the present and previous papers for the key parameters governing the dynamics of power-law gravity currents are summarized and compared to infer the combinations of parameters leading to the fastest/lowest rate of propagation, and of variation of thickness and aspect ratio.

3D modeling of crustal shortening influenced by along-strike lithological changes: Implications for continental collision in the Western and Central Alps

The European Alps show major along-strike variations in the partitioning of crustal shortening between the upper and the lower plates, either explained by lateral variation in temperature and rheology, or by along-strike changes in crustal-scale lithology. Here, we present the first 3D thermomechanical geodynamic model to test the potential impact of along-strike lithological (and associated rheological) changes and lateral temperature variations on crustal shortening during continental collision in the Western and Central Alps. Numerical modeling results suggest a minor impact of lateral thermal variations and lithological changes in the lower plate for the Alpine orogeny. In contrast, lateral lithological changes in the upper plate structure, defined by the presence of the buried Ivrea Body in the Western Alps, should play a major role in determining the present-day architecture of the Alpine belt. Our models suggest that the Ivrea Body acts as a strong, rigid buttress constraining crustal shortening to the lower plate, promoting the formation of the Jura fold-and-thrust belt, and supporting the higher surface elevation observed in the Western Alps. On the other hand, in the Central Alps where the Ivrea Body is absent, much broader distribution of crustal shortening results in lower surface elevation. Numerical modeling results also suggest that crustal shortening in the Central Alps is focused within the upper plate during the final stages of continental collision, favored by the indentation of thickened upper crust of the lower plate, and by detachment of the Adriatic upper crust from the underlying lithosphere.

О КОЛЕБАНИЯХ ПЬЕЗОКЕРАМИЧЕСКОГО ЦИЛИНДРА С ОКРУЖНОЙ ПОЛЯРИЗАЦИЕЙ

The paper deals with of the problem of radial vibrations of a piezoceramic cylinder with circumferential polarization taking into account rheology. The piezoelectric characteristics of the cylinder are functions of the radial coordinate. The cylinder is considered as a piecewise homogeneous electroelastic body consisting of individual prisms. Assuming that the sectioned cylinder is infinitely long and there are no axial deformations in it, boundary value problems on the plane deformation of infinitely long prisms are constructed. In the special case, when all prisms of the sectioned cylinder are in identical conditions of electric loading and external mechanical loads are absent, the boundary problem for the cylinder reduces to the boundary problem for a separate prism. Rheological properties were modeled within the framework of the correspondence principle by replacing the material characteristics with complex moduli-functions of the vibration frequency. A comparison of the concept of complex modules with the widespread linear frequency approximation of the corresponding functions is performed. The solution of the problem was based on the method of shooting. The results of computational experiments on the determination of the amplitude-frequency characteristics for some laws of material inhomogeneity are presented. A series of computational experiments for various inhomogeneity laws and for a different set of initial data is performed, which made it possible to analyze the dependence of the resonant frequencies on the laws of variation of physical characteristics and rheology. A method for reconstructing of the inhomogeneity laws from information on the values of dimensionless functions-radial displacement and radial stress in a certain set of points inside the region using spline approximations is performed. The results of computational experiments have shown sufficient effectiveness of the proposed method.

Enceladus’s crust as a non-uniform thin shell: I tidal deformations

The geologic activity at Enceladus’s south pole remains unexplained, though tidal deformations are probably the ultimate cause. Recent gravity and libration data indicate that Enceladus’s icy crust floats on a global ocean, is rather thin, and has a strongly non-uniform thickness. Tidal effects are enhanced by crustal thinning at the south pole, so that realistic models of tidal tectonics and dissipation should take into account the lateral variations of shell structure. I construct here the theory of non-uniform viscoelastic thin shells, allowing for depth-dependent rheology and large lateral variations of shell thickness and rheology. Coupling to tides yields two 2D linear partial differential equations of the fourth order on the sphere which take into account self-gravity, density stratification below the shell, and core viscoelasticity. If the shell is laterally uniform, the solution agrees with analytical formulas for tidal Love numbers; errors on displacements and stresses are less than 5% and 15%, respectively, if the thickness is less than 10% of the radius. If the shell is non-uniform, the tidal thin shell equations are solved as a system of coupled linear equations in a spherical harmonic basis. Compared to finite element models, thin shell predictions are similar for the deformations due to Enceladus’s pressurized ocean, but differ for the tides of Ganymede. If Enceladus’s shell is conductive with isostatic thickness variations, surface stresses are approximately inversely proportional to the local shell thickness. The radial tide is only moderately enhanced at the south pole. The combination of crustal thinning and convection below the poles can amplify south polar stresses by a factor of 10, but it cannot explain the apparent time lag between the maximum plume brightness and the opening of tiger stripes. In a second paper, I will study the impact of a non-uniform crust on tidal dissipation.

Neotectonic Deformation in Central Eurasia: A Geodynamic Model Approach

AbstractCentral Eurasia hosts wide orogenic belts of collision between India and Arabia with Eurasia, with diffuse or localized deformation occurring up to hundreds of kilometers from the primary plate boundaries. Although numerous studies have investigated the neotectonic deformation in central Eurasia, most of them have focused on limited segments of the orogenic systems. Here we explore the neotectonic deformation of all of central Eurasia, including both collision zones and the links between them. We use a thin‐spherical sheet approach in which lithosphere strength is calculated from lithosphere structure and its thermal regime. We investigate the contributions of variations in lithospheric structure, rheology, boundary conditions, and fault friction coefficients on the predicted velocity and stress fields. Results (deformation pattern, surface velocities, tectonic stresses, and slip rates on faults) are constrained by independent observations of tectonic regime, GPS, and stress data. Our model predictions reproduce the counterclockwise rotation of Arabia and Iran, the westward escape of Anatolia, and the eastward extrusion of the northern Tibetan Plateau. To simulate the observed extensional faults in the Tibetan Plateau, a weaker lithosphere is required, provided by a change in the rheological parameters. The southward movement of the SE Tibetan Plateau can be explained by the combined effects of the Sumatra trench retreat, a thinner lithospheric mantle, and strik‐slip faults in the region. This study offers a comprehensive model for regions with little or no data coverage, like the Arabia‐India intercollision zone, where the surface velocity is northward showing no deflection related to Arabia and India indentations.

Deepwater HP/HT Drilling-Fluid Development and Applications in the South China Sea

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 182429, “Deepwater HP/HT Drilling-Fluid Development and Field Applications in the Western South China Sea,” by Hexing Liu, Zhong Li, Yi Huang, Manzong Fang, and Zhiqin Liu, China National Offshore Oil Corporation, prepared for the 2016 SPE Asia Pacific Oil and Gas Conference and Exhibition, Perth, Australia, 25–27 October. The paper has not been peer reviewed. Thirty percent of the deepwater wells in the western South China Sea have high-pressure and high-temperature (HP/HT) characteristics. After incorporating analyses of engineering and geological environments for deepwater HP/HT wells in the Lingshui Block, the authors suggest in the complete paper that the solution for drilling problems in deepwater HP/HT wells should start with drilling fluid. Researchers have developed a novel water-based-drilling-fluid system compatible with deepwater HP/HT wells in the Lingshui Block on the basis of a conventional drilling fluid and further optimization. Introduction Most of the reservoirs in the South China Sea are not only deeply buried with a low seabed temperature but also have HP/HT characteristics in the lower part of the well interval. The low temperature of the seawater environment causes an increase of drilling-fluid viscosity in the riser and deteriorates the rheology, leading to a buildup of equivalent circulating density (ECD) that might induce lost circulation. HP/HT reservoir conditions will also result in a narrow drilling-fluid window. The drilling fluid has to be HT-resistant and must prevent overflow and wellbore instability, as well as increase the safe drilling-fluid window. The Lingshui deepwater gas field in the western South China Sea is a typical HP/HT reservoir. Its greatest operational water depth is 1688 m, and its highest well temperature is 167°C. The estimated reservoir temperature of the Lingshui Block is 176°C, with the maximum pressure coefficient reaching 2.01. Challenges Encountered in Use of Drilling Fluids in the Western South China Sea The major challenges encountered in the use of drilling fluids in deepwater HP/HT wells in the Lingshui Block can be placed into two general categories as follows: The deep water and HP cause further narrowing of the drilling window. The coexistence of HP and HT makes the drilling-fluid performance difficult to maintain. The existence of a water interval of a few hundred meters or even a few kilometers in deepwater blocks usually forms a 2 to 4°C low-temperature interval from the seabed up to 500 m below sea level. The low-temperature environment gives rise to rheology variations of drilling fluid in the riser, which may cause a gelling effect with increasing viscosity and density, producing a higher friction in the wellbore flow and increasing the risk of formation leakage at the casing shoe. Conventional deepwater wells usually only focus on low-temperature resistance without considering the effect of HT. However, HT will cause degradation and cross-linking of certain drilling-fluid additives, weakening the antipollution characteristics and the water solubility of the additive.

Influence of Low‐Molecular‐Weight Glutenin Subunit Haplotypes on Dough Rheology in Elite Common Wheat Varieties

The low‐molecular‐weight glutenin subunits (LMW‐GSs) are a class of wheat seed storage proteins encoded by a multigene family located at the Glu‐3 loci that influences wheat end‐use quality. Owing to ambiguities in the LMW‐GS allele nomenclature and to the complexity of the Glu‐3 loci organization, a clear relationship between LMW‐GS alleles and wheat end‐use quality has not been adequately determined. In the present study, four sets of elite common wheat varieties were analyzed for their LMW‐GS genic profile, along with their dough rheology and end‐product baking properties. Among these varieties, variation at the Glu‐A3 locus had a major impact on the analyzed dough rheology parameters, followed by the Glu‐B3 and Glu‐D3 loci. Also, the genes located at the linkage groups Glu‐A3‐3, Glu‐B3‐3, and Glu‐D3‐5 were more highly associated with dough strength, mixing, and extensibility properties. Results obtained in this study clearly indicate that there are specific LMW‐GS haplotypes that are more highly associated than others to variation in dough rheology.

Analysis of rheological behaviour of self-compacting concrete made with recycled aggregates

This research focuses on studying the fresh state behaviour of self-compacting recycled concrete (SCRC) using rheology as a fundamental tool. For said purpose, a reference self-compacting concrete (SCC) was designed and it was modified to obtain other two SCCs with different water to cement ratios. Lastly, the natural coarse aggregate of each SCC was replaced with recycled aggregate using three different replacement percentages, 20%, 50% and 100% (by volume). At 15min from the contact time of water with cement (reference time), two different tests were carried out with a rheometer: a stress growth test and a flow curve test.The results show that the specificity of SCRC design lies in the quantity of extra water necessary to compensate the recycled aggregate absorption during the mixing protocol and in the intrinsic characteristics of this particular aggregate. Mainly the rough texture when both natural and recycled coarse aggregates are crushed-shaped and the fines content in the recycled aggregate and generated during mixing by the wear of old adhered mortar change the baseline mortar.All these singularities lead to different “rheological variations – (w/c)ef” curves in a SCRC compared to a SCC. The SCRC curves present higher slope than the SCC ones, so they predict higher rheological variations, especially when the w/c ratio is low.

Effects of lateral variations of crustal rheology on the occurrence of post-orogenic normal faults: The Alto Tiberina Fault (Northern Apennines, Central Italy)

The Northern Apennines (NA) are characterized by formerly compressive structures partly overprinted by subsequent extensional structures. The area of extensional tectonics migrated eastward since the Miocene. The youngest and easternmost major expression of extension is the Alto Tiberina Fault (ATF). We estimate 2D rheological profiles across the NA, and conclude that lateral rheological crustal variations have played an important role in the formation of the ATF and similar previously active faults to the west. Lithospheric delamination and mantle degassing resulted in an easterly-migrating extension-compression boundary, coinciding at present with the ATF, where (i) the thickness of the upper crust brittle layer reaches a maximum; (ii) the critical stress difference required to initiate faulting at the base of the brittle layer is at a minimum; and (iii) the total strengths of both the brittle layer and the whole lithosphere are at a minimum.Although the location of the fault is correlated with lithospheric rheological properties, the rheology by itself does not account for the low dip (~20°) of the ATF. Two hypotheses are considered: (a) the low dip of the ATF is related to a rotation of the stress tensor at the time of initiation of the fault, caused by a basal shear stress (~100MPa) possibly related to corner flow associated with delamination; or (b) the low dip is associated to low values of the friction coefficient (≤0.5) coupled with high pore pressures related to mantle degassing.Our results establishing the correlation between crustal rheology and the location of the ATF are relatively robust, as we have examined various possible compositions and rheological parameters. They also provide possible general indications on the mechanisms of localized extension in post-orogenic extensional setting. The hypotheses to account for the low dip of the ATF, on the other hand, are intended simply to suggest possible solutions worthy of further study.

The interior structure of Ceres as revealed by surface topography

Ceres, the largest body in the asteroid belt (940 km diameter), provides a unique opportunity to study the interior structure of a volatile-rich dwarf planet. Variations in a planetary body's subsurface rheology and density affect the rate of topographic relaxation. Preferential attenuation of long wavelength topography (≥150 km) on Ceres suggests that the viscosity of its crust decreases with increasing depth. We present finite element (FE) geodynamical simulations of Ceres to identify the internal structures and compositions that best reproduce its topography as observed by the NASA Dawn mission. We infer that Ceres has a mechanically strong crust with maximum effective viscosity ∼1025 Pa s. Combined with density constraints, this rheology suggests a crustal composition of carbonates or phyllosilicates, water ice, and at least 30 volume percent (vol.%) low-density, high-strength phases most consistent with salt and/or clathrate hydrates. The inference of these crustal materials supports the past existence of a global ocean, consistent with the observed surface composition. Meanwhile, we infer that the uppermost ≥60 km of the silicate-rich mantle is mechanically weak with viscosity <1021 Pa s, suggesting the presence of liquid pore fluids in this region and a low temperature history that avoided igneous differentiation due to late accretion or efficient heat loss through hydrothermal processes.

Pre-existing normal faults have limited control on the rift geometry of the northern North Sea

Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation of a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian–Triassic and Late Jurassic–Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere-scale numerical models. Our study indicates that additional regional studies of natural rifts are required to test and refine the predictions of physical and numerical models, more specifically, our study suggests models not explicitly recognising or including thermal or rheological effects might over emphasise the role of discrete pre-existing rift structures such as normal faults.