Chlorite PPL properties. Many thanks to the donor for this interesting material. Entire thin section scan. A thin section of mylonite which was collected from the metamorphic region of Lom, Central Norway. The rock has been strongly affected by retrograde metamor- phism as shown by Na-zoisitization. The ductile minerals, quartz and mica, form undulous sheets between layers of feldspar (such sheets being called ‘quartz ribbons’ because of their appearance in thin section). Field of … In places has later been silicified (compare unit Jsi).. The students are pointing to one metamorphic feature with their pencils. Sem Micrographs Of An Etched Thin Section Showing Smectite Kerogen Download Scientific Diagram . Image 33023 is a 900 by 405 pixel JPEG Uploaded: Apr11 12. Twin Gliding and other mechanisms based on plane defects. The transition is gradual and known as the brittle-plastic transition. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock. The section is then polished on both sides using a fine diamond paste until it has a thickness in the range of 2-12 μm. Note how the planar, and circular markers change orientation and thickness across the zone. It turns out that crystal defects - departures from the ideal lattice structure - are critically important in allowing crystals to deform. In most cases, the strengths indicate that it's impossible, with geologically reasonable stresses, to simultaneously break all the bonds in a crystal, so as to (for example) shear the crystal. Many of the illustrations in this section are from a… XPL image, 2x (Field of view = 7mm). From Jean-Pierre Burg. The section is overlain by Precambrian Sturt tillite. VDPM 09.17. Proc Iodp 309 312 Site 1256 Mylonite with rotated clasts in plane polarized light. Instructors: OER Design with Guided Inquiry Learning Approach, Students: Learn with a Guided Inquiry Approach, Module 2: Using the Petrographic Microscope, 2.3 Light and Optics Part 1: Electromagnetic Spectrum, Properties of Light, 2.3 Light and Optics Part 2: Refractive Index, Polarized Light, Birefringence, 2.5 Common Issues Using a Petrographic Microscope, 2.6 Properties Under Plane Polarized Light, 2.7 Properties Under Cross Polarized Light. Mylonite: a mylonite is a foliated and usually lineated rock that shows evidence for strong ductile deformation and normally contains rounded porphyroclasts and lithic fragments of similar composition to minerals in the matrix. BIOTITE PERCUSSION FIGURES IN NATURALLY DEFORMED MYLONITES 375 The biotites from the mylonite horizons Prographie examination of the mylonite from Anhui in thin section has shown that it consists mainly of plagioclase, quartz and biotite. Kyanite - Al 2 SiO 5 Kyanite was named in 1789 by Abraham Gottlieb Werner from the Greek word "kyanos", meaning "blue". It is hard to know what the protolith was, but based upon the porphyroclasts it was likely an ultramafic or mafic rock. The brown minerals (in ppl) are likely some type of … Image 33023 is a 900 by 405 pixel JPEG Uploaded: Apr11 12. This mylonite is located in the same outcrop as mylonite 1 (mylonite 2 is farther south than mylonite 1). The quartz grains in this view range in color from white to gray to black, and they form a tight interlocking network. Plane polarized light. 1. Hopefully you can see porphyroclasts (augens) and mylonite texture in the thin section images below. Hopefully you can see porphyroclasts (augens) and mylonite texture in the thin section images below. In thin section, S surfaces are defined by quartz ribbons- containing 150-250 prn-sized grains, aligned biotite grains (aspect ratios 50 X loo0 pm in sections perpendicular to (001) plants) and minor recrystallized muscovite. Fig.5: Mylonite from Cap de Creus, Spain, showing marked contrast between quartz, which has flowed plastically and recrystallized to fine-grained aggregates with "ribbon microstructure", and orthose, which shows evidence of much less plastic deformation and extensive fracturing and fragmentation. Originally uploaded in Cutting Edge:Courses:Petrology. Over time, this collection should become more orderly and comprehensive, but don't hold your breath. Fig.3: Diagrams showing asymmetrical porphyroclasts and other microstructures indicating sense of shear in mylonites. Click on the image to make it larger. Fig.2: Ideal shear zone. The dark layered rock in the upper part of the photograph is mylonite formed from Moine Schists. The foliation is defined by thin (< 2 mm) ribbons of quartz, and by slightly flattened feldspar porphyroclasts up to 1 cm in size. The Moine Thrust itself lies between these dark rocks and the white Durness limestone in the centre of the photograph. At the microscopic scale the banding is not perfectly flat, as it wraps around more resistant crystals. Fig.4: Geometric softening due to grain shape and lattice rotation into shear plane. The foliation is defined by thin (< 2 mm) ribbons of quartz, and by slightly Mylonites form deep in the crust where temperature and pressure are high enough for the rocks to deform plastically (ductile deformation). The first set of samples are from the level 3 module 'Understanding the Continents'. In thin sections of mylonite, feldspars are seen to be fractured and fragmented, quartz has recrystallised to aggregates of much smaller grains (commonly with irregular grain boundaries) and biotite has been largely retrograded to chlorite. Movie of grain boundary migration. Gneiss-Mylonite Section Micro-XRF image of a thin section of an antitaxial calcite vein in a gneiss-mylonite section, acquired on an XGT-5000 X-ray fluorescence microscope. The Layered Series. Click on the image to make it larger. Thin section of mylonite xpl. Click on the image to make it larger. A thin sliver of rock is cut from the sample with a diamond saw and ground optically flat. S-C fabric is visible in the thin section. Fine-grained rocks, particularly those containing minerals of high birefringence, such as calcite, are sometimes prepared as ultra-thin sections.An ordinary 30 μm thin section is prepared as described above but the slice of rock is attached to the glass slide using a soluble cement such as Canada balsam (soluble in ethanol) to allow both sides to be worked on. There is another structure above and to the left of the blue pencil. Ultra-thin sections. A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed in thin section or even by the naked eye. Thin section Moine mylonite, Moine Thrust Zone, Knockan Crag The cleavage of the mylonite is due to the aligned flakes of mica (here they have a yellowish colour). Fig.1: Simplfied model of the connection between faults, which normally form in the upper crust, and classic ductile shear zones. Porphyroclasts are mostly qtz, rusty brown layers are clays produced by shearing. The first set of samples are from the level 3 module 'Understanding the Continents'. Thin Section Microscope Slide of a Mylonite from northern Sardinia. The indentations show positions of former … Many thanks to the donor for this interesting material. def. The depth depends on the temperature gradient and the mineralogy of the crust. In this type of work it’s important to collect oriented rock samples. Field of … Are the amphiboles prophyroclasts or porphyroblasts? Migmatite, Auvergne, France [ Back : Home] Migmatite is a partly molten rock consisting of a solidified liquid (clear color) + a refractory residue (dark color). It’s possible to learn what goes on in mylonite formation by looking at microscopic thin sections from shear zones. 1st = plane polarized light; 2nd = cross-polarized light. 1st = plane polarized light; 2nd = cross-polarized light. 1st = plane polarized light; 2nd = cross-polarized light. Moine mylonite, Moine Thrust Zone Knockan Crag Outcrop. The footwall mylonite is strongly foliated (suggestive of flattening, rather than constriction) and lineated (WSW-trending). 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