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Diagram showing the major different types of shear zones. Displacement, shear strain, and depth distribution are also indicated. Strength profile and change in rock type with depth in idealised fault/shear zone Margin of a dextral sense ductile shear zone (about 20 m thick), showing transition from schists outside the zone to mylonites inside, Cap de Creus,
A shear zone is a tabular to sheetlike, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to the zone. Typically this is a type of fault, but it may be difficult to place a distinct fault plane into the shear zone. Shear zones may form zones of much more intense foliation, deformation, and folding.
Diagram showing a quartz-rich layer in a dextral shear zone developing an oblique foliation.The geometrical relationships of the fabric elements are indicated.. Oblique foliation is mainly encountered in shear zones, where it forms as a result of the shearing deformations within the affected zone.
In sheared zones, however, planar fabric within a rock may not be directly perpendicular to the principal stress direction due to rotation, mass transport, and shortening. Foliation may be formed by realignment of micas and clays via physical rotation of the minerals within the rock.
Orogenic gold deposits show a spatial relationship to structural discontinuities, including faults, fractures, dilatation zones and shear zones. [2] The ore- hosting structures are subsidiary faults or shear zones (mostly D3–D4 in a D1 to D4 structural sequence), [ clarification needed ] } which are always related to a major regional-scale ...
The microstructures of ductile shear zones are S-planes, C-planes and C' planes. S-planes or schistosity planes are parallel with the shear direction and are generally defined by micas or platy minerals. Define the flattened long-axis of the strain ellipse. C-planes or cissalement planes form oblique to the shear plane. The angle between the C ...
Fault and shear zone contacts can be represented by either discrete breaks and discontinuities, or ductile deformation without a physical break in stratigraphy. [9] Fault surface contacts show discrete breaks and have an attitude and position which describes the contact between two formations. [ 3 ]
The pebbles thus record important information on the orientation of the shear zone (subvertical) and the direction of movement of the shear zone, and the overall change in pebble shape from originally sub-spherical to presently elongate cigar-shaped, allows one to quantify the strain experienced by the rock mass in the geologic past.