How do Mylonites form?
Mylonite is a metamorphic rock formed by ductile deformation during intense shearing encountered during folding and faulting, a process termed cataclastic or dynamic metamorphism. Colour – variable, grey to black, but can form in a variety of colours dependent on parent rock composition.
What is a slip lineation?
Slip lineation or slickenside on a fault or shear. surface—Showing bearing and direction of. plunge of offset.
How are the various lineations defined and how do they develop?
Minerals can grow in a preferred direction on fractures. These lineations form when there is an extensional component during deformation and are defined by the fibrous growth on that deformational surface. Groove and fibrous lineations can be found together along a fault depending on the fault movement throughout time.
Where is lineation formed?
Lineation may be formed during deformation by the parallel alignment of minerals, fossils, or pebbles; by parallel crenulation cleavages; or by striations and grooves resulting from the movement of a rock over a plane, e.g. a fault surface (see SLICKENSIDE), or flexural slip during folding.
How are Boudins formed?
Boudinage is a geological term for structures formed by extension, where a rigid tabular body such as hornfels, is stretched and deformed amidst less competent surroundings. The competent bed begins to break up, forming sausage-shaped boudins.
How do Lineations form?
Stretching lineations are formed by shearing of rocks during asymmetric deformation of a rock mass. This is parallel to the direction in which a shearing force, as found in a shear zone, stretches the rock. Shortening occurs at the same time as elongation but in a perpendicular sense to the stretched rod.
Where are metamorphic rocks formed?
the Earth’s crust
Metamorphic rocks are formed within the Earth’s crust. Changing temperature and pressure conditions may result in changes to the mineral assemblage of the protolith. Metamorphic rocks are eventually exposed at the surface by uplift and erosion of the overlying rock.
How do rocks produce Boudinage?
Boudinage is a geological term for structures formed by extension, where a rigid tabular body such as hornfels, is stretched and deformed amidst less competent surroundings. The competent bed begins to break up, forming sausage-shaped boudins. They can also form rectangular structures.
Why do sometimes pinch and swell structures develop instead of boudins?
Upon extension, the stronger layers lengthen via heterogeneous thinning leading to the development of pinch and swell structures (i.e. thinning of the strong layer is periodic). Amplification of thinning in the pinched regions eventually led to the segmentation of the stronger layers into boudins separated by necks.
What is the difference between serpentine and serpentinite?
Firstly, “serpentine” refers to a group of minerals, not a rock. Serpentinite is a metamorphosed version of rocks that make up oceanic crust after they are incorporated into subduction zones (plate boundaries where oceanic plates are thrust under continental plates).