The ductile/brittle transition of polycrystalline aggregates in terms of their single crystal cubic properties

The Kröner solution is used to determine the shear modulus of any polycrystalline aggregate composed of cubic crystals. This solution from the self-consistent method takes the form of a cubic equation specified by the three elastic properties of the crystal. The ductile/brittle transition for homogeneous and isotropic materials in uniaxial tension is specified by terms of the shear modulus and the bulk modulus of the aggregate. These two basic results are then combined to specify the ductile/brittle transition of the polycrystalline aggregate in terms of its cubic crystal symmetry elastic properties. The various forms that the combined results take are developed and interpreted. Examples and detailed results are given for carbon-diamond, copper, tungsten, iron, silicon, lithium and platinum element type polycrystal materials. The tungsten and iron cases very closely bracket the ductile/brittle transition for all of the solids forming elements of the Periodic Table, one from the brittle side and the other from the ductile side.

ECOMAN: a new open source software for Exploring the Consequences of Mechanical Anisotropy in the maNtle

<p>Coupling large-scale geodynamic and seismological modelling appears to be a promising methodology for better understanding the Earth’s recent dynamics and present-day structure. So far, the two types of modelling have been mainly conducted separately, and a code capable of linking these two investigation methodologies is still lacking.</p><p>In this contribution we introduce ECOMAN, a new open source software that allows modelling the strain-induced mantle fabrics and related elastic anisotropy, and for performing different seismological synthetics, such as SKS splitting measurements and P- and S-wave isotropic and anisotropic inversions (Faccenda et al., in preparation).  </p><p>As an input, the software requires the velocity, pressure, temperature (and additionally the fraction of deformation accommodated by dislocation creep) fields (averaged each 100 kyr for typical mantle strain rates) outputted by the large-scale mantle flow models.</p><p>The strain-induced mantle fabrics are then modelled with D-Rex (Kaminski et al., 2004, GJI), an open source code that has been parallelized and modified to account for fast computation, combined diffusion-dislocation creep (Faccenda and Capitanio, 2012a, GRL; 2013, Gcubed), LPO of transition zone and lower mantle polycrystalline aggregates, P-T dependence of single crystal elastic tensors (Faccenda, 2014, PEPI), advection and non-steady-state deformation of crystal aggregates in 2D/3D cartesian/spherical grids with basic/staggered velocity nodes (Hu et al., 2017, EPSL). The new version of D-Rex can solve for the LPO evolution of 100.000s polycrystalline aggregates of the whole mantle in a few hours, outputting the full elastic tensor of poly-crystalline aggregates as a function of each single crystal orientation, volume fraction and P-T scaled elastic moduli.</p><p>Extrinsic elastic anisotropy due to grain- or rock-scale fabrics or fluid-filled cracks can also be estimated with the Differential Effective Medium (DEM) (Ferreira et al., Nat. Geo; Sturgeon et al., Gcubed, 2019). Similarly, extrinsic viscous anisotropy can be modelled yielding viscous tensors to be used in large-scale mantle flow simulations (de Montserrat et al., in preparation).  </p><p>The crystal aggregates can then be interpolated in a tomographic grid for (i) visual inspection of the mantle elastic properties  (such as Vp and Vs isotropic anomalies; radial, azimuthal, Vp and Vs anisotropies; reflected/refracted energy at discontinuities for different incidence angles as imaged by receiver function studies; ), (ii) generating input files for large-scale synthetic waveform modelling (e.g., SPECFEM3D format; FSTRACK format to calculate SKS splitting (Becker et al., 2006, GJI)), or to perform teleseismic P- and S-wave isotropic and anisotropic inversions with the method developed recently by (VanderBeek and Faccenda, 2021, in review).</p>

High-Pressure Crystallization of iPP Nucleated with 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol

1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the α- form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the γ- polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2–1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (Tc) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic γ- form. As a consequence, Tc and the γ- form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of Tc and the decrease of grain size under high pressure of 200–300 MPa required higher content of DMDBS than the nucleation of the α-form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity.

Mg-Phengite in Carbonate Rock Syngenetically Formed from Hydrothermal Fluid: Micro-Textural Evidence and Mineral Chemistry

Phengite series is a dioctahedral solid solution between two end-members of muscovite [K1[Al2]VI[Al1,Si3]IVO10(OH)2] and celadonite [K1[(Fe3+,Al)1,(Mg,Fe2+)1]VI[Si4]IVO10(OH)2], which have a hetero-valent substitution of AlVIAlIV ↔ (Mg, Fe)VISiIV. In this study, we report a hydrothermal-originated authigenic Mg-phengite-series mineral, which occurred as polycrystalline aggregates (Type 1), pore-fillings (Type 2) and well-crystallized lath form (Type 3) from the Haengmae Formation, a dolomite–pebble-bearing fine sand-sized dolostone, in South Korea. Based on micro-textural observation, three types of Mg-phengite are associated with crystalline dolomite, and are followed by calcite precipitation as pore-filling, indicating that these should be formed by the influx of a Mg-rich hydrothermal fluid after the deposition of some clastic sediments and before calcite-filling. The structural formula based on O10(OH)2 shows that the number of Mg atoms per formula unit (apfu) of Mg-phengite ranges from 0.00 to 0.70 with no Fe, which is relatively high, compared with the previously reported metamorphic phengites. In REEs mineral chemistry, the Mg-phengites are characterized by the enrichment of REEs and by the particular enrichment of LREEs in the polycrystalline aggregates of Mg-phengite. It strongly suggests that the Mg-phengite should be formed by the infiltration of the highly evolved Mg- and REEs-enriched hydrothermal fluid into the clastic sedimentary rock (Haengmae Formation) as a strata-bound form, syngenetically or during early diagenesis.

MAVEPROS: a new open source software to predict mantle elastic properties and build realistic tomographic models

<p>Coupling large-scale geodynamic and seismological modelling appears a promising methodology for the understanding of the Earth’s recent dynamics and present-day structure. So far, the two types of modelling have been mainly conducted separately, and a code capable of linking these two methodologies of investigation is still lacking.</p><p>In this contribution I present MAVEPROS, a new open source software that allows both for the modelling of strain-induced mantle fabrics and seismic anisotropy, and for the generation of realistic synthetic tomographic models.</p><p>As an input, the software requires the velocity, pressure, temperature (and additionally the fraction of deformation accommodated by dislocation creep) fields (averaged each 100 kyr for typical mantle strain rates) outputted by the large-scale mantle flow models.</p><p>The strain-induced mantle fabrics are then modelled with D-Rex (Kaminski et al., 2004, GJI), an open source code that has been parallelized and modified to account for fast computation, combined diffusion-dislocation creep (Faccenda and Capitanio, 2012a, GRL; 2013, Gcubed), LPO of transition zone and lower mantle polycrystalline aggregates, P-T dependence of single crystal elastic tensors (Faccenda, 2014, PEPI), advection and non-steady-state deformation of crystal aggregates in 2D/3D cartesian/spherical grids with basic/staggered velocity nodes (Hu et al., 2017, EPSL), homogeneous sampling of the mantle by implementation of the Deformable PIC method (Samuel, 2018, GJI), apparent anisotropy in layered or crack-bearing rocks estimated with the Differential Effective Medium (DEM) (Sturgeon et al., Gcubed, 2019). The new version of D-Rex can solve for the LPO evolution of 100.000s polycrystalline aggregates of the whole mantle in a few hours, outputting the full elastic tensor of poly-crystalline aggregates as a function of each single crystal orientation, volume fraction and P-T scaled elastic moduli.</p><p>The crystal aggregates can then be interpolated in a tomographic grid for either visual inspection of the mantle elastic properties  (such as Vp and Vs isotropic anomalies; radial, azimuthal, Vp and Vs anisotropies; reflected/refracted energy at discontinuities for different incidence angles as imaged by receiver function studies; ), or to generate input files for large-scale synthetic waveform modelling (e.g., SPECFEM3D format; FSTRACK format to calculate SKS splitting (Becker et al., 2006, GJI)).</p>