Jimmy Stigh

The influence of foliation on the fragility of granitic rocks, image analysis and quantitative microscopy

Fabric-dependent anisotropy is important in understanding the mechanical behaviour of foliated rocks because the foliation creates mechanically weak discontinuities. Using optical microscopy, a foliation index (FIX) was calculated for a group of granitic rocks in southern Sweden that displays a range of textures from foliated to nonfoliated. Image analysis from scanning electron microscope with backscattered detector (SEM/BSE) images was used in order to measure the rock texture of these samples. The analyses were compared with the Los Angeles (LA) test, which measures resistance of rock aggregate to fragmentation. The results demonstrate that the measured grain size, shape and spatial arrangement are important parameters controlling the fragility of the rock. Both the texture and foliation must be taken into account to obtain a significant relationship with the mechanical analyses. We suggest that this alternative method could be a helpful tool for predicting a rocks suitability as an aggregate as it gives a better understanding of the material properties compared to mechanical testing.

The nature and origin of an anorthosite associated ilmenite-rich leuconorite, Hakefjorden Complex, south-west Sweden

Abstract Ilmenite-rich leuconorite (IRL) occurs in the Neoproterozoic Hakefjorden Complex (HFC; a norite–anorthosite intrusion) in south-western Sweden. The medium to fine-grained IRL comprises a disc-shaped, subhorizontal unit within the complex with gradual transitions into the host norite. It is characterised by a well-developed subhorizontal magmatic foliation, displayed by the preferred orientation of tabular plagioclase crystals, and it consists of subequal amounts of labradorite and ilmenite with minor interstitial orthopyroxene. The IRL contains a variety of inclusions comprising decimeter- to meter-size anorthosite and norite blocks from the hosting HFC, and millimeter- to decimeter-size magmatic segregations, formed within the IRL-unit, such as Fe–Ti oxide-, fine-grained anorthosite- and fine-scale igneous layered plagioclase–orthopyroxene inclusions. The latter are disc- to sheet-shaped, usually concordant to the foliation and interpreted to represent igneous layers disrupted during deformation in the magmatic state. The deformation also caused the magmatic foliation during simple shear conditions (no lineation is observed), which wraps around all inclusion types. Fractional crystallization starting with deep crustal anorthosite and ultramafic differentiation produced a late stage liquid unusually enriched in Fe and Ti. Such a liquid with plagioclase in suspension is put forward as parental for the IRL. Fe–Ti oxide subsolidus re-equilibration during slow cooling modified the oxide compositions and textural relations indicate that annealing and textural coarsening played an important role in the formation of the densely packed Fe–Ti oxide inclusions.

Constraints for a structural subdivision of the Southwest Scandinavian Domain in Sweden

Abstract Differences in structural overprinting of rocks east and west of a Sveconorwegian shear zone, the Mylonite Zone, Varmland County, SW Sweden, reveal that this part of the Southwest Scandinavian Domain should be subdivided into different structural domains. We here distinguish the Southwest Scandinavian Domain of eastern Varmland to be affected by Sveconorwegian ductile deformation mainly, where the most prominent structural elements are a foliation and mineral lineations, one of which is associated with open, roughly upright, N–S trending folds. Rocks of western Varmland have a pre-Sveconorwegian deformation history characterized by stromatic veining and isoclinal folding. Subsequent Sveconorwegian thrusting overprints these structures in localised shear zones. One of these is the Mylonite Zone, which roughly marks the eastern border of Gothian folding in this area.

Physical properties and durability of fresh and impregnated Limestone and Sandstone from central Sweden used for thin stone flooring and cladding

Publisher Summary Rocks differ in physical and chemical properties depending on their geochemistry, grain size, grain shape, and porosity. Physical properties crucial for thin stone flooring and cladding have been investigated on fresh and impregnated Jamtland limestone and Dala sandstone. The tests performed were three-point load bending strength, uniaxial compressive strength, abrasion resistance, water absorption (including density), effective porosity, and air permeability. The physical properties were correlated to a chemical weathering test simulating natural stone material corrosion because of acid rain. The fresh sandstone showed higher bending strength, compressive strength, abrasion resistance, water absorption and porosity, and lower permeability than the fresh limestone. The impregnated limestone showed much higher bending strength than the fresh limestone. Thus, it can be concluded that the impregnated limestone showed improved bending strength and chemical properties compared to the fresh limestone, but impaired water absorption, porosity, and permeability. Fresh and impregnated sandstone did not show any distinct differences in physical and chemical properties. For thin stone flooring and cladding the fresh Dala Sandstone is more suitable than the fresh Jamtland limestone because it is less vulnerable to mechanical stress and less sensitive to acid rain.

Polybaric evolution of the Hakefjorden Complex, southwestern Sweden, deduced from partial dissolution in andesine megacrysts

Abstract Disequilibrium textures in andesine megacrysts, showing re‐sorbed morphologies, of the post‐kinematic Sveconorwegian Hakefjorden Complex provide important information about the emplacement mechanism. These textures consist of fine cellular plagioclase inter‐growths occurring as 0.4–2.5 mm mantles around the megacrysts and as entirely cellular grains. Outside the cellular mantle the megacrysts are covered by a normally zoned rim. The cellular mantles consist of two phases, one relatively Na‐rich (An45) and one relatively Ca‐rich (An59). Compositionally, the Na‐rich phase is similar to the non‐cellular megacryst core (An46) and the Ca‐rich phase is similar to the inner part of the normally zoned rim (An60). This rim grades from An60) to An30 which is about the same as the matrix plagioclases of the surrounding norite. The cellular network of plagioclase intergrowths is interpreted as a result of partial dissolution caused by decompression during the emplacement. The emplacement mechanism can be sum...

Origin and emplacement of two compositional layered ultramafic bodies in the Caledonides of Västerbotten, Sweden

Abstract The distribution of the main elements in two often more or less serpentinized, olivinitic—peridotitic bodies in the Bjorkvattnet—Virisen—Fattjarn area of the Swedish Caledonides of Vasterbotten County was found to vary in the outcrops according to a compositional layering. This can be illustrated by calculating the normative mineral components of the rock, i.e. olivine and pyroxene. Olivinite/harzburgite interlayering and chromium-rich spinel banding have allowed of field identification of the compositional layering. It is obvious that all the analyses from the two investigated bodies can be plotted within the field of Alpine-type, ultramafic rocks. The ultramafic material is thought to be derived from a non-hydrous, refractory depleted upper mantle. At an early, probably pre-orogenic stage, a change from a peridotitic—dunitic state into a serpentinitic mineralogy occurred. Olivines and pyroxenes were converted into serpentine minerals. The serpentinites protruded, during Ordovician subduction, i...

Bending strength properties of untreated and impregnated igneous, sedimentary and metamorphic dimension stones of different thickness

Abstract A production method has been developed that makes it possible to produce dimension stone tiles only 4 mm thick without high amounts of waste material. The tiles are impregnated with a mixture of potassium-based water-glass, water, colloidal silica, and Berol 048 (non-ionic surfactant), using a repeated cycling between vacuum and atmospheric pressure. Mineralogy, fabric, and porosity affect the mechanical properties of rock used as dimension stone in the building industry. Tests for bending strength have been performed on tiles of eight different untreated and impregnated samples of igneous, sedimentary, and metamorphic rocks. Samples of three different thicknesses (4, 7 and 10 mm) were used in the tests. The untreated rock samples that had a fine-grained texture, low crack density, high mafic mineral content or a distinct ductile metamorphic texture showed the highest bending strength values, whereas those that had high amounts of carbonate minerals, and high crack or void density exhibited the lowest values. The stone types that gained the most from impregnation, in general, were those with high crack or void density.