Extension Thinning Research Articles

Geochemistry, provenance, and metamorphic evolution of Gabal Samra Neoproterozoic metapelites, Sinai, Egypt

Metapelites are exposed at Wadi Ba’ba, east of Abu Zenima city; represent the northwestern extension of the Fieran-Solaf Metamorphic Complex, Sinai Peninsula, Egypt. The metapelites are characterized by qtz + pl (An 24–28) + bt + grt ± crd ± sil mineral assemblage, indicating upper amphibolite facies with peak metamorphic conditions of 700 °C and pressures of 7 kbar, as determined by conventional geothermobarometeric methods. This resulted in incipient migmatization, forms patches of leucosomes and melanosomes. Geochemical investigation indicates that the precursor sediments of the metapelites had been deposited as immature Fe-rich shales from source materials of dominantly intermediate composition. Source area exhibited weak to moderate chemical weathering in a tectonically active continental marginal basin within a continental-arc system. A strong shallow-dipping foliation, characterizing the metapelites, was folded around an open antiform with sub-horizontal south plunging hinge. Phase equilibria calculations in the KFMASH system indicate that the peak metamorphic conditions formed at 730–750 °C and 6.8–7.9 kbar. This was followed by a retrogression formed at 770–785 °C and 3.9–4.5 kbar. Hence, this implies an isothermal decompression and rapid exhumation of the metapelites from depth (25–29 km) in the lower crustal level at peak conditions, continuous to include shallow to middle crustal level (14–17 km), at overprint retrograde conditions. Subsequent isobaric cooling took place at 720–750 °C and 3.6–4.5 kbar. The resulting isothermal decompression followed by isobaric cooling clockwise P–T path of the metapelites is more likely, in which the high-temperatures attained maximum conditions during isothermal decompression were enhanced by heat flux, due to the presence of an active magmatic arc that formed on top of subducting young lithosphere. This is supported by a moderate geothermal gradient of 27–43 °C/km and dating compatibility of the Sinai granitoids and the metamorphic complexes. The P–T path segment records the tectonothermal histories of crustal thickening as a result of the East and West Gondwana collision at the metamorphic peak. This was subsequent by extensional and crustal thinning with syn-metamorphic magmatic intrusions, during P–T path retrogression, which resulted in the final assembly of the Arabian–Nubian Shield during Neoproterozoic.

The rheology of polymer solution elastic strands in extensional flow

We apply micro-oscillatory cross-slot extensional flow to a semi-dilute poly(ethylene oxide) solution. Micro-particle image velocimetry (μPIV) is used to probe the real local flow field. Extreme flow perturbation is observed, where birefringent strands of extended polymer originate from the stagnation point. This coincides with a large increase in the extensional viscosity. The combination of stagnation point flow and μPIV enables us to investigate directly the stress and strain rates in the strand and so determine the true extensional viscosity of the localised strand alone. The Trouton ratio in the strand is found to be ~4000, amongst the highest values of Trouton ratio ever reported. Consideration of the flow in the exit channels surrounding the highly elastic strand suggests a maximum limit for the pressure drop across the device and the apparent extensional viscosity. This has implications for the understanding of high Deborah number extensional thinning reported in other stagnation point flow situations.

Effect of aspect ratio and fluid elasticity on chain orientation in isothermal film casting process

The characteristics of extensional flow and the chain orientations of the isothermal film casting process utilizing a two-dimensional (2-D) viscoelastic model with finite element methods (FEM) were studied. Steady state and transient solutions were obtained for a relatively large aspect ratio regime by employing successive iterative schemes. In this work, higher aspect ratios of the equipment caused highly oriented molecular structures because the aspect ratio increases as the flow changes from planar to uniaxial extensional flow. Fluid viscoelasticity always alleviated the neckin phenomenon and led to the planar extension regime even if dichotomous behavior was observed for draw resonance in extensional thickening and thinning fluids. Consequently, the change in the characteristic of extensional deformation from uniaxial deformation to the planar extension deteriorated the molecular orientation.

Lithospheric-scale extension during Grampian orogenesis in Scotland

Abstract This contribution presents a new model for the Grampian-age tectonothermal development of the Buchan Block and Barrovian-type regions to its west, in the Grampian Terrane, Scotland. The model has drawn on evidence gathered from field mapping, microstructural analysis, metamorphic petrology and mafic magma geochemistry to propose that emplacement of the Grampian gabbros and regional metamorphic heating associated with production of Barrovian- and Buchan-type units occurred during syn-orogenic (Grampian-age), lithospheric-scale extension. Extension followed lithospheric thickening associated with the initiation of Grampian orogenesis and was followed by renewed lithospheric thickening and termination of the extensional heating. Mantle melting to produce the Grampian gabbros of the Grampian Terrane was achieved by extensional thinning of the lithosphere and decompression melting of the asthenosphere at depths of less than 70 km. Advection of heat from the mantle with emplacement of the Grampian gabbros augmented elevated heat budgets associated with attenuation of isotherms during extension. Deposition of the uppermost Dalradian (the Whitehills and Boyndie Bay Groups and the Macduff Slates) occurred during Grampian-age lithospheric extension. A gently-dipping, mid-crustal detachment focused metamorphic heat sources and accommodated significant lithospheric-scale strain, allowing independent thermal evolution of units in its hanging wall (the Buchan Block) and footwall (Barrovian-type units).

Analysis of entrance pressure drop techniques for extensional viscosity determination

In this work, a novel (patent pending) orifice die design for precise extensional viscosity data determination from entrance pressure drop measurements has been developed and tested both theoretically (through Finite Element Analysis) and experimentally. It has been demonstrated that the proposed novel orifice die allows much more precise extensional viscosity measurements for polymer melts in comparison with conventional orifice dies. Moreover, it has been found that, for extensional strain hardening and extensional strain thinning polymer melts, the corrected Cogswell model and Binding/Gibson model should be preferred, respectively. Otherwise, the extensional viscosity determination can be rather erroneous.

On the transient coating of a straight tube with a viscoelastic material

We examine the pressure-driven coating of a straight, long tube with a finite amount of viscoelastic liquid. This combines the formation and elongation of an open bubble pushing the liquid downstream with the motion of the advancing liquid front and the deposition of a film along the tube wall. The mixed finite element method is combined with the discontinuous Galerkin method for computing the polymeric contribution to the stress tensor, while a quasi-elliptic grid generation scheme is used for tessellating the highly deforming domain. Global remeshing is adopted to overcome local distortion and coarsening of the mesh which arises from the attachment of advancing front nodes on the wall. The accuracy of the solution is achieved by selectively refining the mesh along areas where sharp boundary layers in stress arise and in particular at the bubble front. An extensive parametric analysis is performed using the affine, single-mode Phan-Tien and Tanner constitutive model. The thickness of the remaining film increases as the solvent contribution to viscosity decreases, because of the sharply increased normal viscoelastic stresses along the bubble front. The effect of decreasing the extensional parameter ɛ PTT is similar because this decreases the shear and extensional thinning in the liquid. The transient nature of the process delays the development of the viscoelastic stresses as the Deborah number increases. The streamlines relative to the liquid tip follow the usual ‘fountain flow’ pattern as long as the bubble and the liquid front do not interact. The non-affine, multi-mode PTT model with constants obtained from the literature for a PIB solution in C14 predicts a slightly thinner deposited film and a flatter bubble front because of its stronger shear thinning. Moreover, it predicts a higher dimensionless bubble velocity because of the very small viscosity ratio of the solvent and a V-shape in the radial distribution of the first normal stress difference and the birefringence just behind the contact line in qualitative agreement with experiments and theory for planar fountain flow.

Thermal effects of linked lithospheric and upper crustal–scale processes: Insights from numerical modeling of the Cenozoic Central Catalan Coastal Ranges (NE Spain)

Processes influencing the thermal state of the continental crust, such as heat upwelling related to rifting and isotherm reorganization due to mass redistribution by erosion, deposition, and (fault‐)tectonic transport, operate at different scales, and their effects overlap. In this paper, we use lithospheric‐ as well as crustal‐scale numerical modeling tools in order to quantify the contributions of these various factors to the geothermal field, establishing their relative relevance. We apply the models to address the thermal evolution of the Catalan Coastal Ranges (NE Spain) during the Cenozoic, a period that is characterized by a change in tectonic style, from Pyrenean compression to extension related to the western Mediterranean rifting. Results of the lithospheric‐scale thermal model for extensional basins show an increase in the geothermal surface gradient of about 11°C/km in the Catalan Coastal Ranges during the Neogene, related to extensional thinning of the lithosphere in the Valencia Trough (western Mediterranean). Predictions of the upper crustal–scale thermal model, incorporating fault motions and surface mass redistribution (erosion and sedimentation), point to little changes in the isotherms due to fault block movements in the Paleogene and Neogene. In contrast, erosion appears to have a significant effect on the thermal history of basement rocks sited in the shallowest crust. Comparison of the integrated lithospheric‐ and upper crustal–scale modeling results with apatite fission track and apatite (U‐Th)/He thermochronology data reveals larger amounts of Neogene to present cooling than predicted by the models. On the basis of this unresolvable mismatch, we suggest that, similar to present, forced fluid convection along fault planes played an important role in the evolution of the geothermal field during the Neogene stage of rifting.

Biaxial Extensional Viscosity of Sheeted Noodle Dough

ABSTRACTThe flows encountered during the sheeting process contain a more extensional component and more stretching than simple shear. Evaluating the properties of the extensional rheological flow of wheat flour dough is essential to better understand the sheeting process and the final quality of the product. Our results show that the curves of biaxial extensional viscosity versus extensional strain rate for dough from different wheat cultivars including Dark Northern Spring (DNS), Hard Red Winter (HRW), and Western White Wheat (WW) with protein contents of 7.81–18.09% and water contents of 32–40% could be discriminated. During a lubricated compression test, the sheeted dough displayed a region of extensional thickening followed by a region of mild extensional thinning, giving rise to an s‐shaped extensional stress‐strain rate curve. The higher degree of extensional thinning was exhibited for the sheeted dough prepared from the flour of DNS and HRW wheat mixture with an extensional thinning index of n = 0.65–0.74; while the lower degree of extensional thinning was displayed for the DNS wheat with an extensional thinning index of n = 0.89–0.96. The data of biaxial extensional viscosity (ηBmax) versus water content and protein content could be described by power relationships. The results suggest that biaxial extensional viscosity can be a useful modeling and process design parameter that objectively represents the rheological properties during dough sheeting.

How dilute are dilute solutions in extensional flows?

We investigate the concentration dependence of the characteristic relaxation time of dilute polymer solutions in transient uniaxial elongational flow. A series of monodisperse polystyrene solutions of five different molecular weights (1.8×106⩽M⩽8.3×106g∕mol) with concentrations spanning five orders of magnitude were dissolved in two solvents of differing solvent quality (diethylphthalate and oligomeric styrene). Optical measurements with a capillary breakup extensional rheometer of the rate of filament thinning and the time to breakup in each fluid are used to determine the characteristic relaxation time. A criterion for a lower sensitivity limit is introduced, in the form of a minimum concentration cmin necessary for experimental resolution of the effects of polymeric viscoelasticity. This criterion is validated by experiment and comparison to numerical calculations with a multimode bead-spring dumbbell model. These calculations also rationalize previous paradoxical observations of extensional thinning in fluid threads of ultradilute polymer solutions in which stress relaxation apparently occurred faster than predicted by the Zimm theory. Above this minimum sensitivity limit we show that the effective relaxation time of moderately dilute solutions (0.01⩽c∕c*⩽1) in transient extensional flow rises substantially above the fitted value of the relaxation time extracted from small amplitude oscillatory shear flow and above the Zimm relaxation time computed from kinetic theory and intrinsic viscosity measurements. This effective relaxation time exhibits a power-law scaling with the reduced concentration (c∕c*) and the magnitude of the exponent varies with the thermodynamic quality of the solvent. The scaling of this “self-concentration” effect appears to be roughly consistent to that predicted when the dynamics of the partially elongated and overlapping polymer chains are described within the framework of blob theories for semi-dilute solutions.

Lithosphere types in North China: Evidence from geology and geophysics

On the basis of the characteristics of geology and geophysics in North China, three types of lithosphere, namely, the cratonic, the orogenic and the rift lithospheres can be classified. In terms of petrological method (based on the information from Precambrian rock assemblages, igneous activities, deep-seated enclaves, etc.) and the relationship between seismic velocity and rock compositions, the crust-mantle petrological and chemical structure models can be set up. Researching results indicate that the geology and geophysics of North China platform bears the similar characteristics in comparison with those of the global typical cratons. The Eerduosi(Ordos) block located in the west of the North China Platform is a remnant of cratonic lithosphere after the North China platform had undergone “activation” in Mesozoic and “reconstruction” in Cenozoic times. The continental crust consists mainly of TTG rock assemblage while the subcontinental lithosphere mantle mainly consists of strongly depleted harzburgite. The craton was finally formed in late Archaean and early Proterozoic, and has been kept in stability up to present; its crustal-mantle petrological structures of lithosphere can be set up as a reference for the study of North China craton and even Sino-Korean craton. In the Mesozoic period, the middle and east areas of North China platform were activated in the Yanshanian orogenic process, the continental crust was reformed by material and heat-transfer of convective mantle and the original crustal TTG component was reconstructed to be granitic crust, and the subcontinental lithosphere mantle was replaced by the Yanshanian harzburgite-lherzolite. The Yanshan-Taihang Mountains were the remnants of orogenic lithosphere after the rifting in eastern North China in Cenozoic. The present thickness of continental crust and lithosphere in the Yanshan-Taihang Mountains is not equal to their thickness during the Yanshanian orogenic movement because they had undergone the crustal extensional thinning in Cenozoic, however, the material and structure of lithosphere mantle-crust were formed during the Yanshanian orogenic movement. In the Cenozoic Period, the rift-type lithosphere, as represented by the North China plain, was formed by the continental rifting occurring in the eastern part of North China. The continental granitic crust, which had been “acidified” at the Yanshanian period, was basified again by the eruption of basalt magma along the continental rifting, and the subcontinental lithosphere mantle formed in Yanshanian was destroyed and replaced by the Himalayan mantle which consists mainly of lherzolite. Both the crust and the lithospheric mantle in the rift have undergone extensional thinning and thermal erosion at lithospheric-scale, the material and structure of the present mantle-crust lithosphere, attained from geophysical exploration, was formed in Cenozoic. The formation and evolution of lithosphere in North China indicate that the material and heat transferred by convective mantle into the continental crust was the key for different types of lithosphere forming, and the crust-mantle petrologic structure was the records of lithosphere evolution, and it was the integrated results of the deep processes of the China continental dynamic system and the Pacific Plate subduction located in the eastern margin of the North China platform in Mesozoic-Cenozoic time.

Simultaneous stress and birefringence measurements during uniaxial elongation of polystyrene melts with narrow molecular weight distribution

Tensile stress and flow-induced birefringence have been measured during uniaxial elongation at a constant strain rate of two polystyrene melts with narrow molecular weight distribution. For both melts, the stress- optical rule (SOR) is found to be fulfilled upto a critical stress of 2.7 MPa, independent of strain rate and temperature. Estimation of the Rouse times of the melts, from both the zero-shear viscosity and the dynamic-shear moduli at high frequency, shows that the violation of the SOR occurs when the strain rate multiplied by the Rouse time of the melt exceeds by approximately 3. The presented results indicate that in contrast to current predictions of molecular theories, the regime of extensional thinning observed by Bach et al. (2003) extends well beyond the onset of failure of the SOR, and therefore the onset of chain stretch in the non-Gaussian regime.

Rheological properties of poly(trimethylene terephthalate) in capillary flow

AbstractThe shear viscosity, extensional viscosity, and die swell of the PTT melt were investigated using a capillary rheometer. The results showed that the PTT melt was a typical pseudoplastic fluid exhibiting shear thinning and extensional thinning phenomena in capillary flow. There existed no melt fracture phenomenon in the PTT melt through a capillary die even though the shear rate was 20,000 s−1. Increasing the shear rate would decrease the flow activation energy and decline the sensitivity of the shear viscosity to the melt temperature. The molecular weight had a significant influence on the flow curve. The flow behavior of the PTT melt approached that of Newtonian fluid even though the weight‐molecular weight was below 43,000 s−1 at 260°C. The extensional viscosity decreased with the increase of the extensional stress, which became more obvious with increasing the molecular weight. The sensitiveness of the extensional viscosity to the melt temperature decreased promptly along with increasing the extensional strain rate. The die swell ratio and end effect would increase along with increasing the shear rate and with decreasing the temperature, which represented that the increase of the shear rate and the decrease of temperature would increase the extruding elasticity of the PTT melt in the capillary die. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 705–709, 2005

Mantle‐like Sr–Nd isotope composition of Fe–K subalkaline granites: the Peneda–Gerês Variscan massif (NW Iberian Peninsula)

AbstractThe Peneda–Gerês massif is one of the most representative NW Iberian late‐ to post‐orogenic Variscan granitic plutons. It resulted essentially from the subsynchronous emplacement, at 290–296 Ma, of two granitic magmas of Fe–K subalkaline affinity, with primitive isotopic composition: Sri = 0.703–0.707 and εNdi=−1.5 to −2.4. An origin by mantle input followed by mantle–crust interactions is proposed, implying the contribution of a less enriched mantle component than that involved in the genesis of synorogenic hybrid granitoids of Mg–K subalkaline affinity. A less voluminous aluminopotassic and isotopically more evolved magma (Sri=0.708–0.709 and εNdi=−3.5 to −3.9) with little or no mantle input was also generated, suggesting the involvement of lower crust materials. Therefore, this study suggests an input of juvenile magmas in late Variscan times, the mantle‐like isotope signature of Fe–K granitic magmatism being clearly related to a geodynamic setting of extensional processes, large‐scale uplift and thinning.

Geodynamic modelling of crustal deformation of the North China block: a preliminary study

The North China block (NCB) has experienced at least two stages of crustal deformation throughout the Mesozoic as revealed by the compressional structural styles before the late Jurassic and the extensional tectonics in the late Mesozoic. The E–W structural trends of the late Triassic Qinling-Dabie and Yinshan-Yanshan orogenic belts, which respectively represent the southern and northern boundaries of the North China block, clearly indicate N–S shortening of the NCB, whereas the widely distributed NNE-trending extensional basins call for E–W-directional crustal stretching during the late Mesozoic. On the basis of the Mesozoic tectonic evolution in the NCB, we employ a mountain-basin evolution system to model these geodynamic processes. The N–S shortening (late Triassic to early late Jurassic) may result from subduction and collision between the North China and South China blocks, along with the collision between the North China–Mongolian and Siberian plates. Horizontal extensional thinning of a previously thickened, unstable lithosphere may have led to the formation of extensional basins as a consequence of so-called strike-slip collapse, which was possibly triggered by the easterly roll-back of the descending subducted slab of the ancient Pacific plate.

Numerical simulation of film casting using an updated lagrangian finite element algorithm

AbstractThis paper presents a new numerical algorithm for 2D nonisothermal time‐stepping simulations of a nonlinear viscoelastic cast film process. A significant contribution of the algorithm is that an updated Lagrangian description of motion is employed, as opposed to the more conventional Eulerian description generally used for continuous polymer processing simulations. Furthermore, use is made of a Perzynatype constitutive equation, which is different from what is usually employed for molten polymers. The constitutive equation accommodates viscoelasticity, extensional thinning/thickening, and strain‐hardening. This new numerical algorithm can find the steady‐state film properties, and it can predict the onset of instability by observing draw resonance. The critical draw ratio is determined from the response problem, which means that the mathematical complications of the more common linear stability analysis are avoided. In terms of the stability of the film, it was observed that stability is decreased by extensional thinning, strain‐hardening, and higher relaxation times, and stability is increased by higher heat transfer coefficients and higher ratios of air‐gap length to die width.

Exhumation of high- and ultrahigh-pressure metamorphic rocks by slab extraction

Research Article| October 01, 2003 Exhumation of high- and ultrahigh-pressure metamorphic rocks by slab extraction Nikolaus Froitzheim; Nikolaus Froitzheim 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Search for other works by this author on: GSW Google Scholar Jan Pleuger; Jan Pleuger 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Search for other works by this author on: GSW Google Scholar Sybille Roller; Sybille Roller 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Search for other works by this author on: GSW Google Scholar Thorsten Nagel Thorsten Nagel 2Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Nikolaus Froitzheim 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Jan Pleuger 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Sybille Roller 1Geologisches Institut, Universität Bonn, Nußallee 8, D-53115 Bonn, Germany Thorsten Nagel 2Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, New York 10964, USA Publisher: Geological Society of America Received: 17 Apr 2003 Revision Received: 08 Jul 2003 Accepted: 09 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2003) 31 (10): 925–928. https://doi.org/10.1130/G19748.1 Article history Received: 17 Apr 2003 Revision Received: 08 Jul 2003 Accepted: 09 Jul 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Nikolaus Froitzheim, Jan Pleuger, Sybille Roller, Thorsten Nagel; Exhumation of high- and ultrahigh-pressure metamorphic rocks by slab extraction. Geology 2003;; 31 (10): 925–928. doi: https://doi.org/10.1130/G19748.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Exhumation of high- and ultrahigh-pressure metamorphic rocks in collisional orogens may be explained by upward extrusion of these rocks, erosion of their overburden, or extensional thinning of the overburden. Some high-pressure terranes, such as the Adula nappe in the Central Alps, fit none of these scenarios. We propose an additional way in which part of the overburden may be removed: it may sink off into the deeper mantle (slab extraction). Structural and metamorphic relationships in and around the Adula nappe indicate that the emplacement of this Alpine high- to ultrahigh-pressure nappe (to 3.2 GPa) in a pile of lower-pressure nappes resulted from the interaction of two subduction zones that accommodated the closure of two ocean basins, ultimately leading to the extraction of the intervening slab. In terms of mechanics, the cause of the exhumation is, in this case, not the buoyancy of the high-pressure rocks, but the negative buoyancy of the extracted slab. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Numerical modelling of PT-paths related to rapid exhumation of high-pressure rocks from the crustal root in the Variscan Erzgebirge Dome (Saxony/Germany)

The Bohemian Massif in the Central European Variscides contains many crustal slices with (ultra-)high-pressure rocks related to continent-continent collision. After closure of pre-existing oceans during the Devonian, excess crustal thickness was maintained for about 50 Ma until at around 340 Ma large volumes of high-pressure rocks from the crustal root were exhumed within a few million years. We relate this event to delamination and complete detachment of the lithospheric mantle, causing a crustal-scale isostatic instability. In the Erzgebirge dome, a model region in the northern part of the massif, an array of interrelated PTtd-paths with “decompression/cooling” and “decompression/heating” trajectories in juxtaposed tectonometamorphic units has been established. Numerical 2D-experiments using a rheologically, thermally and dynamically consistent convection technique show three stages of the crustal evolution related to delamination and detachment of mantle lithosphere under the crustal root: (1) During delamination a rapid overthickening of the crust can occur with the crust penetrating down to >160 km depth. (2) After detachment extensional crustal thinning controlling exhumation occurs with escape of rocks from the crustal root towards the margins of the orogen through tectonically weak zones. Horizontal displacement exceeds vertical by a factor of ∼3. (3) Forced circulation in the weak zones follows and upward flow of lower crustal rocks is compensated by subduction of upper crustal rocks in the footwall of these zones. One-dimensional modelling was used in order to further understand basic processes and to simulate the rock record in detail. According to 2D and 1D modelling, strongly decelerating exhumation rates with decreasing overburden and a late increase in the geothermal gradient due to upward heat transfer are necessary corollaries of this scenario, in keeping with observations from the Erzgebirge dome. Exhumation PT-paths do not conform to one single uniform exhumation trajectory; rather, assemblages of interrelated PTtd-paths are characteristic.

Using filament stretching rheometry to predict strand formation and "processability" in adhesives and other non-Newtonian fluids

The spinning of polymeric fibers, the processing of numerous foodstuffs and the peel and tack characteristics of adhesives are all associated with the formation, stability and, ultimately, the longevity of thin fluid `strands'. This tendency to form strands is usually described in terms of the tackiness of the fluid or by heuristic concepts such as `stringiness' (Lakrout et al. J Adhesion 1999). The dynamics of such processes are complicated due to spatially and temporally non-homogeneous growth of extensional stresses, the action of capillary forces and the evaporation of volatile solvents. We describe the development and application of a simple instrument referred to as a microfilament rheometer (MFR) that can be used to readily differentiate between the dynamical response of different pressure-sensitive adhesive fluid formulations. The device relies on a quantitative observation of the rate of extensional thinning or `necking' of a thin viscous or viscoelastic fluid filament in which the solvent is free to evaporate across the free surface. This high-resolution measurement of the radial profile provides a direct indication of the ultimate time to break up of the fluid filament. This critical time is a sensitive function of the rheological properties of the fluid and the mass transfer characteristics of the solvent, and can be conveniently reported in terms of a new dimensionless quantity we refer to as a processability parameter P. We demonstrate the usefulness of this technique by presenting our results in the form of a case study in which we measure the visco-elasto-capillary thinning of slender liquid filaments for a number of different commercial polymer/solvent formulations and relate this to the reported processing performance of the materials. We also compare the MFR observations with the prediction of a simple 1D theory derived from the governing equations that model the capillary thinning of an adhesive filament.

NE Atlantic continental rifting and volcanic margin formation

Abstract Deep seismic data from the Hatton-Rockall region, the mid-Norway margin and the SW Barents Sea provide images of the crustal structure that make it possible to estimate the relative amounts of crustal thinning for the Late Jurassic-Cretaceous and Maastrichtian-Paleocene NE Atlantic rift episodes. In addition, plate reconstructions illustrate the relative movements between Eurasia and Greenland back to Mid-Jurassic time. The NE Atlantic rift system developed as a result of a series of rift episodes from the Caledonian orogeny to early Tertiary time. The Late Palaeozoic rifting is poorly constrained, particularly with respect to timing. However, rifted basin geometries, inferred to be of this age, are observed at depth in seismic data on the flanks of the younger rift structures. Intra-continental rifting in Late Jurassic-Cretaceous times caused c. 50–70 km of crustal extension and subsequent Cretaceous basin subsidence from the Rockall Trough-North Sea areas in the south, to the SW Barents Sea in the north. In late Early to early Late Cretaceous times, new rifting occurred in the Rockall Trough and Labrador Sea associated with the northward propagation of North Atlantic sea-floor spreading. When sea-floor spreading was approached in the Labrador Sea the Rockall rift apparently became extinct. The final NE Atlantic rift episode was initiated near the Campanian-Maastrichtian boundary, lasted until continental separation near the Paleocene-Eocene transition, and caused c. 140 km extension. The late syn-rift and the earliest sea-floor spreading periods were affected by widespread igneous activity across a c. 300 km wide zone along the rifted plate boundary. The deep seismic data provide lower-crustal structural geometries that represent boundary conditions for a better mapping and understanding of the extensional thinning of the crust. The crustal geometries question extension estimates previously made from basin subsidence analysis, and aid in the definition of bodies of magmatic underplating beneath the outer volcanic margins.

A New Cell Opening Mechanism in Flexible Polyurethane Foam

Literature on the polyurethane foam cell opening mechanism is reviewed and discussed. A new cell opening mechanism is proposed. Cell opening is observed to be triggered by urea precipitation which changes the rheology of the polyurethane dramatically. The foam matrix shows extensional thinning behavior after urea phase separation. The extensional thinning behavior will lead to localized cell window thinning. The cell window thickness distribution will lead to different film rupture times for individual cell windows and will result in cell windows in different states. Some windows are totally missing and others leave torn-off films. Windows with only pin holes or totally closed were also observed. The cell opening event is shown to be a continuous process rather than a sudden event.