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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.
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.
It is common practice to assume that the deformation is plane strain simple shear deformation. This type of strain field assumes that deformation occurs in a tabular zone where displacement is parallel to the shear zone boundary. Furthermore, during deformation the incremental strain axis maintains a 45-degree angle to the shear zone boundary.
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 ...
For economic geology such as petroleum and mineral development, as well as research, modeling of structural geology is becoming increasingly important. 2D and 3D models of structural systems such as anticlines, synclines, fold and thrust belts, and other features can help better understand the evolution of a structure through time.
The presence of these shear zones suggest that strain is partitioned within the Coast Orogen which resulted in horizontal translation of terranes for several hundred kilometers parallel to the orogen. [12] Block diagram illustrating the difference between homogeneous and partitioned strain within transpressive and transtensive tectonic regimes.
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 ]