Sheet Silicates Research Articles

Understanding the deformation mechanism and mechanical characteristics of cementitious mineral analogues from first principles and reactive force field molecular dynamics.

In this paper, first principles and reactive force field molecular dynamics were utilized to study the mechanical properties of tobermorite 9 Å, tobermorite 11 Å and jennite. These are essential minerals in cement chemistry. The mechanical properties calculated by the first-principle method match well with previous experimental results, pointing to the introduction of vdW dispersion-type forces as able to improve the precision. The calculated elastic constants of the three minerals confirm anisotropic mechanical behavior of the layered structures. The crystals jennite and tobermorite 9 demonstrate stronger mechanical behavior in the ab plane than the interlayer direction due to the presence of stable covalent "dreierketten" silicate chains. For tobermorite 11 Å, the Q3 silicate tetrahedrons bridging the neighboring calcium silicate sheets heal the weak interlayer structure and enhance the c-direction stiffness and cohesive strength. Furthermore, analysis of uniaxial tension by reactive force MD elucidated the chemical and mechanical responses of the atomic structures in loading resistance. The stress-strain relation of the layered mineral tensioned along b direction, showing the "strain hardening" region, where stress continues to increase past the yield stage. The strain hardening and ductility enhancement for the minerals is largely due to the ability of the silicate chains to first de-polymerize into short chains or separate tetrahedrons before the broken Q species re-polymerize to form branched networks and ring structures which are able to resist loading. For all three minerals, protons transfer to oxygen and water, resulting in the formation of Si-OH and Ca-OH groups during the strain hardening stage as Si-O-Si or Si-O-Ca bonds start to break and the calcium atoms and silicate morphology is rearranged. Hydrolysis therefore accelerates structural damage and contributes to weakening of mechanical properties in the interlayer direction. Increased tensile stress level in the tobermorite 11 Å can contribute to a greater extent of water damage.

Insights into the interfacial strengthening mechanisms of calcium-silicate-hydrate/polymer nanocomposites.

The mechanical properties of organic/inorganic composites can be highly dependent on the interfacial interactions. In this work, with organic polymers intercalated into the interlayer of inorganic calcium silicate hydrate (C-S-H), the primary binding phase of Portland cement, great ductility improvement is obtained for the nanocomposites. Employing reactive molecular dynamics, the simulation results indicate that strong interfacial interactions between the polymers and the substrate contribute greatly to strengthening the materials, when C-S-H/poly ethylene glycol (PEG), C-S-H/poly acrylic acid (PAA), and C-S-H/poly vinyl alcohol (PVA) were subject to uniaxial tension along different lattice directions. In the x and z direction tensile processes, the Si-OCa bonds of the C-S-H gel, which were elongated and broken to form Si-OH and Ca-OH, play a critical role in loading resistance, while the incorporation of polymers bridged the neighboring silicate sheets, and activated more the hydrolytic reactions at the interfaces to avoid strain localization, thus increasing the tensile strength and postponing the fracture. On the other hand, Si-O-Si bonds of C-S-H mainly take the load when tension was applied along the y direction. During the post-yield stage, rearrangements of silicate tetrahedra occurred to prevent rapid damage. The polymer intercalation further elongates this post-yield period by forming interfacial Si-O-C bonds, which promote rearrangements and improve the connectivity of the defective silicate morphology, significantly improving the ductility. Among the polymers, PEG exhibits the strongest interaction with C-S-H, and thus C-S-H/PEG possesses the highest ductility. We expect that the molecular-scale mechanisms interpreted here will shed new light on the stress-activated chemical interactions at the organic/inorganic interfaces, and help eliminate the brittleness of cement-based materials on a genetic level.

A mélange of subduction temperatures: Evidence from Zr-in-rutile thermometry for strengthening of the subduction interface

The Catalina Schist contains a spectacular, km-scale amphibolite facies mélange zone, thought to be part of a Cretaceous convergent margin plate interface. In this setting, blocks ranging from centimeters up to ≥100 m in diameter are surrounded by finer-grained matrix that is derived from the blocks. Blocks throughout the mélange represent a diversity of protoliths derived from basalts, cherts and other sediments, and hydrated mantle, but all contain assemblages consistent with upper amphibolite-facies conditions, suggesting a relatively restricted range of depths and temperatures over which material within the mélange was metamorphosed. This apparent uniformity of metamorphic grade contrasts with other mélanges, such as the Franciscan Complex, where coexisting rocks with highly variable peak metamorphic grade suggest extensive mixing of materials along the subduction interface. This mixing has been ascribed to flow of material within relatively low viscosity matrix. The Zr content of rutile in samples from across the amphibolite facies mélange of the Catalina Schist was measured to determine peak metamorphic temperatures, identify whether these temperatures were different among blocks, and whether the spatial distribution of temperatures throughout the mélange was systematic or random. Resolvably different Zr contents, between 290 and 720 (±10–40) ppm, are found among the blocks, corresponding to different peak metamorphic temperatures of 650 to 730 (±2–16) °C at an assumed pressure of 1 GPa. These results are broadly consistent with previous thermobarometric estimates. No systematic distribution of temperatures was found, however. Like other mélange zones, material flow within the Catalina Schist mélange was likely chaotic, but appears to have occurred on a more restricted scale compared to some other localities. Progressive metamorphism of mélange matrix is expected to produce rheologically stiffer matrix minerals (such as amphiboles and pyroxenes) at the expense of weaker matrix minerals (sheet silicates), affecting the overall rheological behavior of the mélange, and dictating the scale of flow. The Catalina Schist amphibolite facies mélange matrix appears to provide a snapshot of hotter, stiffer portions of a subduction interface, perhaps more representative of rheological behavior at depths approaching the subarc than is found in some other exhumed mélange zones.

Microstructures in landslides in northwest China – Implications for creeping displacements?

Microstructures, mineralogical composition and texture of selected landslide samples from three landslides in the southern part of the Gansu Province (China) were examined with optical microscopy, transmission electron microscopy (TEM), x-ray diffraction (XRD) and synchrotron x-ray diffraction measurements. Common sheet silicates are chlorite, illite, muscovite, kaolinite, pyrophyllite and dickite. Other minerals are quartz, calcite, dolomite and albite. In one sample, graphite and amorphous carbon were detected by TEM-EDX analyses and TEM high-angle annular dark-field images. The occurrence of graphite and pyrophyllite with very low friction coefficients in the gouge material of the Suoertou and Xieliupo landslides is particularly significant for reducing the frictional strength of the landslides. It is proposed that the landslides underwent comparable deformation processes as fault zones. The low friction coefficients provide strong evidence that slow-moving landsliding is controlled by the presence of weak minerals. In addition, TEM observations document that grain size reduction in clayey slip zone material was produced mainly by mechanical abrasion. For calcite and quartz, grain size reduction was attributed to both pressure solution and cataclasis. Therefore, besides landslide composition, the occurrence of ultrafine-grained slip zone material may also contribute to weakening processes of landslides. TEM images of slip-zone samples show both locally aligned clay particles, as well as kinked and folded sheet silicates, which are widely disseminated in the whole matrix. Small, newly formed clay particles have random orientations. Based on synchrotron x-ray diffraction measurements, the degree of preferred orientation of constituent sheet silicates in local shear zones of the Suoertou and Duang-He-Ba landslide is strong. This work is the first reported observation of well-oriented clay fabrics in landslides.

Defect contributions to the heat capacities and stabilities of some chain, ring, and sheet silicates, with implications for mantle minerals

At temperatures less than ~1500 K, previously published C P data demonstrate that the heat capacities of orthoenstatite, proto-enstatite, diopside, and pseudowollastonite include primarily Debye type vibrational and anharmonic contributions, whereas the alkali chain, sheet, and ring silicates, Na 2 SiO 3 , Li 2 SiO 3 , K 2 SiO 3 , and Na 2 Si 2 O 5 include a third contribution. The third contribution to C P arises from defect formation due to the mobility Na, K, Li, and O 2 − . The contribution becomes apparent at temperatures above 700–800 K for Na and K silicates, and above 900–1000 K for Li metasilicate. With strong thermal agitation, alkali-non-bridging oxygen (NBO) bonds are ruptured with the cations exiting their structural sites to occupy interstitial sites, thereby producing intrinsic Frenkel defects, which contribute to the C P of the alkali silicates. The magnitudes of the C P defect contributions correlate inversely with cation-oxygen bond strengths, as measured by bond dissociation energies. K-O and Na-O bond strengths are weak (239 and 257 kJ/mol) and defect contributions are large for these alkali chain, ring, and sheet silicates. The greater bond strength of Li-O (341 kJ/mol) correlates with a weaker defect contribution to the C P of Li 2 SiO 3 . Mg-O and Ca-O bonds are stronger still (394 and 464 kJ/mol) and no C P defect contributions are observed for the pyroxenes and pseudowollastonite up to ~1500 K. Above ~800 K a polymerization reaction occurs in Na 2 SiO 3 , which produces some Q 3 species and free oxygen (O 2 − or oxide ion). The polymerization reaction annihilates an oxygen structural site so that the O 2 − produced must reside on non-structural sites thus producing intrinsic anionic defects. The same reactions likely occur in Na 2 Si 2 O 5 and K 2 SiO 3 . Raman spectra of Na 2 SiO 3 indicate >10% of Na + and ~1.7% of O 2 − on interstitial sites at 1348 K. Ca- and Mg-bearing mantle minerals subjected to temperature greater than ~1500 K experience the destabilizing effects of disordering (Frenkel defect formation). The minerals may respond either by changing their composition or by changing phase. An abundance of Ca and Na defects in pyroxenes, for example, likely promotes production of new components (e.g., CaAl 2 SiO 6 , NaAlSi 2 O 6 ) in pyroxenes. By their production, Ca and Na defect concentrations are reduced thereby stabilizing the phases. Mg-O bond dissociation and production of intrinsic Mg 2+ and O 2 − point defects within olivine likely destabilize it and promote the phase transition to wadsleyite at the base of the upper mantle.

Intercalation of calcein into layered silicate magadiite and their optical properties.

Calcein–Ca (II), Zn (II) and Al (III) complexes were successfully intercalated into interlayer surfaces of layered silicate magadiite and fluorescence properties of organic metal-chelates in the confined spaces were investigated. Structures, compositions and morphologies of the intercalated magadiites were adequately studied by tests, including X-ray diffraction, energy-dispersive X-ray spectrometer, elemental mapping, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, Fourier-transform infrared spectra, ultraviolet–visible spectroscopy, thermo-gravimetric analysis, differential thermal analysis and scanning electron microscopy. Results confirmed that metal–organic chelate species were immobilized onto the silicate sheets via solid-state interaction. Basal spacings between silicate layers decreased by exchanged metal ions and increased after intercalation of calcein into the interlayer spaces of cation-exchanged magadiites. The encapsulation was obtained by a flexible solid–solid reaction, and the present reaction and products had a potential of application to industrial uses. A speculative mechanism was proposed for reaction by solid-state intercalation. Furthermore, it was found that the complexes in the interlayer space also exhibited special fluorescence properties. The significance of this current work was that it provided a possible route for synthesizing metal–organic complexes that encapsulated in phyllosilicate.

Observation of Intense X-ray Scintillation in a Family of Mixed Anion Silicates, Cs3RESi4O10F2 (RE = Y, Eu-Lu), Obtained via an Enhanced Flux Crystal Growth Technique.

A new family of mixed anion cesium rare earth silicates exhibiting intense scintillation in several ranges of the visible spectrum are reported. Cs3RESi4O10F2 (RE = Y, Eu-Lu) have been synthesized using an enhanced flux growth method for the targeted growth of mixed anion systems. This is the first example of this method being used for the growth of oxyhalides. The compounds crystallize in the triclinic space group P1̅ with the lattice parameters a = 7.0832(2) Å, b = 7.1346(2) Å, c = 16.2121(5) Å, α = 95.8090(10)°, β = 90.0580(10)°, γ = 119.7650(10)° for the Tb analogue. The structure consists of REO6 and REO2F4 polyhedra connected by Si4O10 sheets with a previously unobserved silicate sheet topology that contains the uncommon cyclic Si3O9 trimers. The synthesis, structure, magnetic and optical properties are reported including, notably, intense X-ray scintillation in Cs3TbSi4O10F2.

Microstructures, mineral chemistry and geochronology of white micas along a retrograde evolution: An example from the Aar massif (Central Alps, Switzerland)

This study investigates gneissic tectonites of different mechanical origins, and aims at unravelling the link between microstructures, white mica chemistry and K-Ar data. The highest temperature mylonitic deformation, which is investigated, is dominated by dislocation creep in monomineralic quartz, and viscous granular flow in polymineralic domains. These mylonites show homogenous mineral chemistry, resulting in robust and consistent K-Ar age data. The lowest temperature deformation investigated, is that of a retrograde brittle deformation, producing cohesionless fault gouges. Within the cohesionless fault gouges, frictional granular flow is considered as the main deformation mechanism. The K-bearing phases inside the fault gouges record no chemical resetting during this brittle overprint, but contain mechanically fragmented K-bearing micas and significant amounts of newly produced smectite. This yields K-Ar ages inside of a gouge that are in the range of adjacent mylonite ages, and may not represent the timing of gouge formation. In an effort to understand these uncertainties in K-Ar ages, detailed observations of the microstructural context of K-bearing white mica were made. Microstructural criteria in combination with quantitative element mapping allowed for the discrimination of five important mica-related processes: (1) fracturing/recrystallization of white mica; (2) (re)-precipitation of new fine-grained white mica inside the deforming rock matrix; (3) pseudomorphic replacement of precursor minerals by white mica and chlorite; (4) pseudomorphic replacement of pre-existing white mica without grain size reduction; and (5) remnant grains. The combination of these different processes led to a high variability in mineral chemistry and isotope data for tectonites, which relates directly to variations in the size of the equilibrium volumes. Despite the samples being highly deformed in the presence of fluids, inherited sheet silicates may survive. If inherited sheet silicates are present they contribute to an increase in both the chemical heterogeneity and the apparent K-Ar ages of a sample.

Structure and intercalation behavior of copper II on the layered sodium silicate magadiite material

In this work, the ion-exchange reaction of the sodium silicate Na-magadiite with cupric ions was studied and the mode of interaction of the intercalated Cu2+ ions with silicate sheet was investigated. To do this, Na-magadiite was first synthesized using a hydrothermal method and characterized. It is then used to prepare Cu-exchanged magadiite materials with different copper contents by an ion-exchange reaction. The solids obtained were characterized by chemical and thermogravimetric analyses, powder X-ray diffraction, UV–Visible diffuse reflectance and Fourier transform spectroscopy, scanning electron microscopy and transmission electron microscopy. The results show that magadiite has a high affinity to copper ions and that the experimental exchange rate can be easily predicted. They show also that the intercalated Cu2+ ions are non-hydrated and are in direct interactions with the terminal interlayer ≡Si–O− groups, to which they are also probably strongly linked. Furthermore, the interlayer copper oxide species phase formed are in form of small particles homogeneously dispersed. Finally, the introduction of Cu2+ ions into the interlayer space does not substantially affect the structure of the Cu-exchanged materials but rather tends to stabilize it by increasing the decomposition temperature of the silanol groups .

Muscovite dissolution kinetics as a function of pH at elevated temperature

Mineral reactivity can play an important role in fracture-controlled fluid networks where maintaining or increasing permeability is a goal, such as enhanced geothermal systems. In these systems, dissolution generates new void space, removes cement and physically transports less reactive mineral grains, while secondary precipitation acts to narrow or seal off fluid pathways. Sheet silicate mineral reactivity is likely to affect permeability evolution at the elevated temperatures of geothermal reservoirs because of the high reactive surface area and prevalence of these minerals in hydrothermal zones. To better describe the reactivity of one common sheet silicate, muscovite, we conducted kinetic dissolution experiments using flow-through reactors at temperatures of 100–280°C and a pH range of 2–9. Surface area-normalized muscovite dissolution rates ranged from 0.17–155·10−11molm−2s−1 over this temperature range, but showed little variation with pH above 150°C. Aluminum was released to solution nonstoichiometrically with respect to dissolved silica, most likely resulting from secondary precipitation of an aluminum oxy-hydroxide identified as boehmite (γ-AlO(OH)(s)) by X-ray diffraction in reaction products from experiments conducted at pH≤6. Surface area-normalized muscovite dissolution rates, Ratemus (molm−2s−1), can be described from 25 to 280°C with the following kinetic rate equation: Ratemus=3∙10−3∙e−44R∙T∙aH+0.8+9∙10−6∙e−45R∙T+5∙10−1∙e−61R∙T∙aOH−0.6∙1−e−∆GrRT where the rate and pre-exponential factors are in molm−2s−1; the activation energies, E, are in kJmol−1; aH+ and aOH− represent the activities of H+ and OH−, respectively; R (kJmol−1K−1) is the gas constant; T is the temperature in Kelvins; and ΔGr (kJmol−1) is a measure of how close the aqueous solution is to muscovite equilibrium. The rate equation is constrained by our new data literature rates and has been evaluated against previous formulations with varying dependence on reaction affinity. Although 150°C muscovite rates from Oelkers et al. (2008) show a systematic dependence on reaction affinity, incorporating this dependence did not accurately reproduce the higher-temperature rates. We recommend the rate equation shown above, with an affinity term that slows reaction rates only when solutions are close to equilibrium, for simulating the dissolution of muscovite under geothermal conditions.

In situ preparation and optical properties of metal-8-hydroxyquinoline decoration of layered silicate: Self-assembly in the magadiite interface by solid-solid reaction

We succeeded in the self-assembly of 8-hydroxyquinoline (8Hq)-Li (I), Al (III) and Cu (II) complexes into the interlayer surfaces of layered silicate magadiite (Na2Si14O29·nH2O) and investigated the luminescence of organic metal-chelates in the confined spaces. The measurements, including X-ray diffraction (XRD), Fourier-transform infrared spectra (FT-IR), thermo-gravimetric analysis and differential thermal analysis (TG/DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDS), ultraviolet–visible spectroscopy (UV–Vis) and Photoluminescence spectra (PL), confirmed that the metal-organic chelates species were immobilized onto the silicate sheets via ion-dipole interaction and free diffusion. The encapsulation was obtained by a flexible solid-solid reaction, and the present reaction and products have a potential of application to industrial uses. A speculative mechanism is proposed for reaction by the combination of solid-solid and solid-gas intercalation. Furthermore, it was found that the complexes in the interlayer space showed a special fluorescence property than in the crystal state and the confined space of phyllosilicate shows an influence on properties of complexes. Here, a possibility of synthesizing metal-organic complexes that encapsulated in phyllosilicate is given.

The thermal decomposition of fine-grained micrometeorites, observations from mid-IR spectroscopy

We analysed 44 fine-grained and scoriaceous micrometeorites. A bulk mid-IR spectrum (8–13μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. Corresponding carbonaceous Raman spectra, textural observations from SEM-BSE and bulk geochemical data via EMPA were collected to aid in the interpretation of mid-IR spectra. The 5 spectral groups identified correspond to progressive thermal decomposition. Unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10μm. Thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. Both CI-like and CM-like micrometeorites are shown to pass through the same decomposition stages and produce similar mid-IR spectra. Using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. Since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between CM and CI classes, atmospheric entry should bias the dust flux to favour the survival of CI-like grains, whilst preferentially melting most CM-like dust. However, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of CI:CM dust is heavily skewed in favour of CM material. In addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. These grains may therefore represent regolith micrometeorites derived from the surface of C-type asteroids. Since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0–9.5μm, and since the surfaces of C-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families.

Mineralogical and geochemical analysis of Fe-phases in drill-cores from the Triassic Stuttgart Formation at Ketzin CO2 storage site before CO2 arrival

Reactive iron (Fe) oxides and sheet silicate-bound Fe in reservoir rocks may affect the subsurface storage of CO2 through several processes by changing the capacity to buffer the acidification by CO2 and the permeability of the reservoir rock: (1) the reduction of three-valent Fe in anoxic environments can lead to an increase in pH, (2) under sulphidic conditions, Fe may drive sulphur cycling and lead to the formation of pyrite, and (3) the leaching of Fe from sheet silicates may affect silicate diagenesis. In order to evaluate the importance of Fe-reduction on the CO2 reservoir, we analysed the Fe geochemistry in drill-cores from the Triassic Stuttgart Formation (Schilfsandstein) recovered from the monitoring well at the CO2 test injection site near Ketzin, Germany. The reservoir rock is a porous, poorly to moderately cohesive fluvial sandstone containing up to 2–4 wt% reactive Fe. Based on a sequential extraction, most Fe falls into the dithionite-extractable Fe-fraction and Fe bound to sheet silicates, whereby some Fe in the dithionite-extractable Fe-fraction may have been leached from illite and smectite. Illite and smectite were detected in core samples by X-ray diffraction and confirmed as the main Fe-containing mineral phases by X-ray absorption spectroscopy. Chlorite is also present, but likely does not contribute much to the high amount of Fe in the silicate-bound fraction. The organic carbon content of the reservoir rock is extremely low (<0.3 wt%), thus likely limiting microbial Fe-reduction or sulphate reduction despite relatively high concentrations of reactive Fe-mineral phases in the reservoir rock and sulphate in the reservoir fluid. Both processes could, however, be fuelled by organic matter that is mobilized by the flow of supercritical CO2 or introduced with the drilling fluid. Over long time periods, a potential way of liberating additional reactive Fe could occur through weathering of silicates due to acidification by CO2.

Elastic anisotropy of Tambo gneiss from Promontogno, Switzerland: a comparison of crystal orientation and microstructure-based modeling and experimental measurements

Author(s): Vasin, RN; Kern, H; Lokajicek, T; Svitek, T; Lehmann, E; Mannes, DC; Chaouche, M; Wenk, HR | Abstract: Felsic and mafic gneisses constitute large proportions of the upper and lower continental crust. Gneisses often display high anisotropy of elastic properties associated with preferred orientations of sheet silicates. Here we study the elastic anisotropy of a sample of Tambo gneiss from Promontogno in the Central Alps. We apply optical microscopy, time-of-flight neutron diffraction, neutron and X-ray tomography to quantify mineral composition and microstructures and use them to construct self-consistent models of elastic properties. They are compared to results of ultrasonic measurements on a cube sample in a multi-anvil apparatus and on a spherical sample in an apparatus that can measure velocities in multiple directions. Both methods provide similar results. It is shown that models of microstructure-derived elastic properties provide a good match with ultrasonic experiment results at pressures above 100 MPa. At a pressure of 0.1 MPa the correspondence between the model and the experiment is worse. This may be caused by an oversimplification of the model with respect to microfractures or uncertainties in the experimental determination of S-wave velocities and elastic tensor inversion. The study provides a basis to determine anisotropic elastic properties of rocks either by ultrasonic experiments or quantitative models based on microstructures. This information can then be used for interpretation of seismic data of the crust.

Serpentinization of olivine in troctolites and olivine gabbros from the Hess Deep Rift

To understand the similarity and diversity of serpentinization processes in different rock systems, gabbroic rocks recovered from IODP Site U1415 at the Hess Deep Rift were examined and compared with peridotites from the adjacent ODP Site 895. Textural observations, micro-Raman spectroscopic analyses and electron microprobe analyses indicated that most of the olivine-replacing serpentine in the gabbroic rocks lack the mixing with brucite, which is common in peridotites. At least three stages of serpentinization are observable in the gabbroic rocks; each generation is characterized by different submicroscopic mixtures or solid solutions of sheet silicates: 1) Mg-Fe2+ lizardite+ferri-lizardite+chlorite, 2) Mg-Fe2+ lizardite+ferri-lizardite, and 3) Mg-Fe2+ lizardite+ferri-lizardite+saponite. The first and third generations of serpentine and mixed minerals are relatively Fe-rich, whereas the second generation is Fe-poor and associated with abundant magnetite and pyrrhotite. The major difference between the alteration of gabbroic and peridotitic systems is probably best explained by the iron content and modal abundance of primary olivine and by rock-dominated fluid compositions with a high silica activity due to the alteration of plagioclase in gabbroic rocks. The mineralogical variations between the reported three generations of mixed sheet silicates in gabbroic rocks can be ascribed to variations of silica and/or oxygen activities in the associated fluids under decreasing temperature conditions. The abrupt increase of magnetite crystallization during serpentinization in gabbroic rocks could be caused by oxidation at a relatively high SiO2 activity without the olivine-serpentine-brucite buffering assemblage.

Metal oxide decorated layered silicate magadiite for enhanced properties: insight from ZnO and CuO decoration.

Surface modification of a layered silicate magadiite (mag) was accomplished using cetyltrimethyl ammonium bromide (CTAB), copper oxide (CuO) and zinc oxide (ZnO). All the ions were intercalated using an ion-exchange reaction, and CuO and ZnO are prepared by a precipitation method. A precursor of CTAB modified mag enables good dispersion of the metal oxide on the surface of the lamellas. Characterization techniques (XRD, XRF, TGA, FTIR and XPS spectroscopy) confirmed that CuO and ZnO are homogeneously immobilized onto the silicate sheets of mag. The porosity of the products was explored by BET analysis. SEM and TEM provided the visualization of CuO/ZnO, which were in a good morphology and uniformly distributed on the platelets of the modified mag. Consequently, hybrids with well dispersed metal oxides showed unique properties in photoluminescence and magnetism compared to the metal oxide in the bulk state. The formation mechanism of the synthesis of CuO and ZnO decorated mag was further studied, which can give suggestion for fabricating other metal oxide decorated layered silicates. The significance of this current work is the fact that it provides a new method to prepare well dispersed metal oxides using an easy and flexible precipitation method that can be applied to other layered materials and metal oxides.

Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust

Mid-crustal deformation is classically characterized by the transition from ductile to brittle deformation defining the frictional-to-viscous transition (FVT). Here we investigate an exhumed continental mid-crustal basement section in order to envisage the relationship between ductile and brittle deformation at the FVT. Our detailed study from km- to micro-scale shows that, under greenschist metamorphic conditions, deformation is accommodated by a dense network of highly-localized ductile shear zones. In the investigated case it is not quartz which defines the overall ductile deformation behavior but the viscous granular deformation in shear zones with an ultrafine-grained polymineralic matrix consisting of quartz, feldspar, sheet silicates and epidote. During viscous granular flow mass transfer processes under the presence of fluids promote a chemo-mechanical mixing, resulting in grain size reduction and reaction softening. Coeval with this ductile deformation, fluid-assisted embrittlement occurs, as indicated by biotite-coated fractures, cataclasites and injection of non-cohesive polymineralic gouge material into secondary fractures inside the host rock. The embrittlement during predominant ductile deformation occurs in cycles, i.e. prolonged periods of slow viscous granular flow are interrupted by rapid brittle deformation. We interpret this fluid–assisted cyclic embrittlement evidenced by injection of the fluidized material into off-fault fractures as an alternative equivalent to pseudotachylites and as a microstructural indicator for paleo-seismic activity. With exhumation and associated cooling, localized deformation persists in the ultrafine-grained polymineralic shear zones but progressively transitions to cataclastic flow and finally to pressure-dependent frictional flow; always showing cycles of slow interseismic flow and fast seismic injection events. Overall, in the granitic crust of the Aar-massif, brittle and ductile deformation coexist up to deformation temperatures of minimum 450°C, indicating that the FVT has to be placed in a rather wide range from 8km up to >18–20km in the granitoid crust.

Reliability of very low-grade metamorphic methods to decipher basin evolution: Case study from the Markstein basin (Southern Vosges, NE France)

Low- and very low-grade metamorphic studies investigating the alteration and reaction progress of clay minerals are powerful tools to decipher the thermal evolution of sedimentary and inverted meta-sedimentary basins. Sheet silicates such as illite and chlorite are very common in sedimentary basin sequences. They can be used to determine the grade of diagenesis and low-temperature metamorphism as measured through the XRD: illite Kübler-Index (KI; illite “crystallinity” in older literature) and the chlorite Árkai-Index (ÁI; chlorite “crystallinity” in older literature), respectively. Although the ÁI method is considered to be slightly less sensitive than the KI method, a reliable correlation between both methods is often observed in metamorphic domains with a uniform heat-flow history and minor tectono-structural complexity. Complementary to these methods, the K-white mica b cell dimension provides a robust estimate of pressure facies reached in very low- to low-grade temperature domains.Here, we present a case-study from the Markstein basin located in the Southern Vosges. The lithostratigraphic units in the basin are characterized by deep marine flysch sequences of Upper Devonian to Upper Visean age and volcano-clastic sediments, respectively. The Markstein basin is surrounded by granitoids with intrusion ages between 340 and 326Ma. A previous study showed orogenic deformation characterized by regional folding, and a contact metamorphism found in an outer halo of the granitoids up to 1500m away from the contact (delineated by the occurrence of biotite). Here we present a multi-disciplinary study combining mineral assemblages, illite and chlorite “crystallinity indices”, and K-white mica b cell dimension. Our approach allows to (i) map in (great) detail the areal extent of both regional/burial metamorphic and contact metamorphic domains; (ii) reveal the metamorphic zonation within both domains; and (iii) better constrain regional/burial and contact metamorphic history. The contact metamorphic domain is characterized by the occurrence of biotite and/or actinolite and low K-white mica b cell dimensions, whereas the zone of incipient orogenic metamorphism yields KI and ÁI values of the high-grade diagenesis and anchizone with intermediate K-white b cell dimensions.

Methyl Methacrylate and Alpha-Methyl Styrene: New Strategy for Synthesis of Bloc Copolymers for Use in Potential Biomedical Applications Generated by an Ecologic Catalyst Called Maghnite (Algerian MMT)

A new model for synthesis of the plastics, block copolymers were prepared from methyl methacrylate (MMA) and alpha-methyl styrene (α-MS) by cationic copolymerization in the presence of a new and efficient catalyst of “Maghnite-Na” at 0 °C in bulk. In this paper, the copolymerization of α-MS and MMA was induced in heterogeneous phase catalyzed by Maghnite-Na was investigated under suitable conditions. The “Maghnite-Na” is a montmorillonite sheet silicate clay, with exchanged sodium cations to produce Na-Montmorillonite (Na+-MMT) obtained from Tlemcen, Algeria, was investigated to remove heavy metal ion from wastewater as an efficient catalyst for cationic polymerization of many vinylic and heterocyclic monomers. The synthesized copolymer were characterized by Nuclear Magnetic Resonance (NMR-1H, NMR-13C), FT-IR spectroscopy, Differential Scanning Calorimetry (DSC), and Gel Permeation Chromatography (GPC) to elucidate structural characteristics and thermal properties of the resulting copolymers. The structure compositions of “MMT”, “H+-MMT” and “Na+-MMT” have been developed. The effect of the MMA/α-MS molar ratio on the rate of copolymerization, the amount of catalyst, temperature and time of copolymerization on yield of copolymers was studied. The yield of copolymerization depends on the amount of Na+-MMT used and the reaction time. The kinetic studies indicated that the polymerization rate is first order with respect to monomer concentration. A possible mechanism of this cationic polymerization is discussed based on the results of the 1H-NMR Spectroscopic analysis of these model reactions. A cationic mechanism for the reaction studies showed that monomer was inserted into the growing chains.

Selective Synthesis, Characterization and Kinetics Studies of poly(α-Methyl styrene) induced by Maghnite-Na+ Clay (Algerian MMT)

A new and efficient catalyst of Na-Montmorillonite (Na+-MMT) was employed in this paper for α-methylstyrene (AMS) cationic polymerization. Maghnite clay, obtained from Tlemcen Algeria, was investigated to remove heavy metal ion from wastewater. “Maghnite-Na” is a Montmorillonite sheet silicate clay, exchanged with sodium as an efficient catalyst for cationic polymerization of many vinylic and heterocyclic monomers. The various techniques, including 1H-NMR, 13C-NMR, IR, DSC and Ubbelohde viscometer, were used to elucidate structural characteristics and thermal properties of the resulting polymers. The structure compositions of “MMT”, “H+-MMT” and “Na+-MMT” have been developed. It was found that the cationic polymerization of AMS is initiated by Na+-MMT at 0 °C in bulk and in solution. The influences of reaction temperature, solvent, weight ratio of initiator/monomer and reaction time on the yield of monomer and the molecular weight are investigated. The kinetics indicated that the polymerization rate is first order with respect to the monomer concentration. A possible mechanism of this cationic polymerization is discussed based on the results of the 1H-NMR Spectroscopic analysis of these model reactions. A cationic mechanism for the reaction was proposed. From the mechanism studies, it was showed that monomer was inserted into the growing chains.