Where do ductile shear zones form?
Accordingly, ductile shear zones are frequent in metamorphic rocks. They range in width from infinitesimal to several kilometres. Shear strain intensity is nil or low in the wall rock, progressively increases across the gradients and is strongest at the contiguity plane between both gradients.
What is slaty cleavage in geology?
Since the nature of cleavage is dependent on scale, slaty cleavage is defined as having 0.01 mm or less of space occurring between layers. Slaty cleavage often occurs after diagenesis and is the first cleavage feature to form after deformation begins.
What type of rock is mylonite?
The mylonite is a fine-grained, partially recrystallized metamorphic rock produced by dynamic recrystallization with pronounced foliation as a result of intense shearing during large-scale movements along faults and thrusts.
What is the difference between fault zone and shear zone?
A shear zone is a zone in which shearing has occurred so that the rock mass is crushed and brecciated. A shear zone is the outcome of a fault where the displacement is not confined to a single fracture, but is distributed through a fault zone.
What causes shear zone?
In geology, a shear zone is a thin zone within the Earth’s crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear zone takes the form of a fracture called a fault.
How do you identify phenocryst?
A phenocryst is an early forming, relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of an igneous rock. Such rocks that have a distinct difference in the size of the crystals are called porphyries, and the adjective porphyritic is used to describe them.
What is slaty foliation?
Slaty foliation refers to sheet-like layering within a metamorphic rock. This is characterized by millimeter-thick folia/layers in the rock, that are typically formed by the compaction of fine-sedimentary rocks such as mudstone and shale.
What is Phyllitic cleavage?
Rock cleavage in which flakes are produced that are barely visible to the unaided eye. It is coarser than slaty cleavage and finer than schistose cleavage. Ref: Leet, 1.
What is Crystalloblastic texture?
Crystalloblastic textures are crystalline textures produced by metamorphic recrystallization. Examples of crystalloblastic textures include. Granoblastic: a nonschistose rock with equidimensional crystals. Nematoblastic: development during recrystallization of slender parallel prismatic crystals.
What is Porphyroclastic texture?
the uneven granular texture of a rock caused by the presence of large crystals, or porphyroblasts, in a fine-grained groundmass. Unlike phenocrysts, porphyroblasts form during recrystallization in the course of metasomatism of solid rock.
What is mylonite made from?
The mylonites can be formed by converting many kinds of rocks, particularly those predominantly composed of quartz, feldspar, calcite, dolomite, sericite, and chlorite. The likely parent rocks are sandstone, granite, granodiorite, diorite, limestone, marble, and dolostone (Fig. 7.7).
What is mylonite made of?
Mylonite rock comprises biotite-quartz-feldspar and displays strong fluxion banding (flow layers) with numerous white porphyroblasts and porphyroclasts of feldspar that shows a strong component of flattening into the fabric implying blastesis during the mylonitization.