Zeolites play a crucial part in acid-base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure-function relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam-electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90 degrees mismatch in structure and pore alignment but also from small angle differences of 0.5 degrees-2 degrees for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm.
New microstructural data on experimentally deformed “wet” and “dry” natural olivine rocks (Anita Bay and Åheim dunite), together with the other reliable experimental data, indicate that the experimental stress‐recrystallized grain size relationship in olivine‐rocks is largely independent of water content and temperature, and is only slightly dependent on the flow properties of the material. The experimental data cover a stress range of 30–300 MPa, water contents from <30 ppm to 300 ppm, and temperatures in the range 1100–1650°C. Local melt contents of up to 10 volume% cannot be demonstrated to have a significant effect on the stress—grain size relationship.
We report here for the first time the occurrence of relics of majoritic garnet within orogenic garnet peridotites from Otrøy, Western Gneiss Region, Norway. The microstructural evidence consists of two‐pyroxene exsolution from garnet. Majoritic garnets are only stable at depths greater than 150 km. Estimates of the initial composition of the majoritic garnets imply pressures of 6–6.5 GPa indicating that the Otrøy peridotites were derived from depths > 185 km.
Mineral‐chemical data indicate that the present mineral compositions equilibrated at mantle conditions around 805 ± 40 °C and 3.2 ± 0.2 GPa.
Estimates of the initial pressure temperature (PT) conditions and PTtime (t) path are consistent with a multistage, multiorogenic exhumation history with upwelling of hot asthenosphere up to ≈ 100 km in the Pre‐Cambrian followed by subsequent crustal emplacement and exhumation during the Caledonian orogeny.
The buoyancy and strength of sub-continental lithospheric mantle is thought to protect the oldest continental crust (cratons) from destruction by plate tectonic processes. The exact origin of the lithosphere below cratons is controversial, but seems clearly to be a residue remaining after the extraction of large amounts of melt. Models to explain highly melt-depleted but garnet-bearing rock compositions require multi-stage processes with garnet and clinopyroxene possibly of secondary origin. Here we report on orogenic peridotites (fragments of cratonic mantle incorporated into the crust during continent-continent plate collision) from Otrøy, western Norway. We show that the peridotites underwent extensive melting during upwelling from depths of 350 kilometres or more, forming a garnet-bearing cratonic root in a single melting event. These peridotites appear to be the residue after Archaean aluminium depleted komatiite magmatism.
[1] Properties of partially molten rocks depend strongly on the grain-scale melt distribution. Experimental samples show a variety of microstructures, such as melt lenses, layers, and multigrain melt pools, which are not readily explained using the theory for melt distribution based on isotropic interface energies. These microstructures affect the melt distribution and the porosity-permeability relation. It is still unclear how the melt distribution changes with increasing melt fraction. In this study, electrical conductivity measurements and microstructural investigation with scanning electron microscopy and electron backscatter diffraction are combined to analyze the melt distribution in synthetic, partially molten, iron-free olivine rocks with 0.01-0.1 melt fraction. The electrical conductivity data are compared with the predictions of geometric models for melt distribution. Both the conductivity data and the microstructural data indicate that there is a gradual change in the melt distribution with melt fraction (X m ) between 0.01 and 0.1. At a melt fraction of 0.01, the melt is situated in a network of triple junction tubes, and almost all grain boundaries are free from melt layers. At 0.1, the melt is situated in a network of grain boundary melt layers, as well as occupying the triple junctions. Between melt fractions 0.01 and 0.1, the number of grain boundary melt layers increases gradually. The electrical conductivity of the partially molten samples is best described by Archie's law (s sample /s melt = CX m n ) with parameters C = 1.47 and n = 1.30.Citation: ten Grotenhuis, S. M., M. R. Drury, C.
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