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geol 314 t3
| Question | Answer |
|---|---|
| Deeper | high temps/pressures, Cataclastic: microscopic brittle deformation, mesoscopic flow |
| 10/15km | . Brittle-plastic transition, Varies depending on composition. Mylonite: ductilly deformed, fine grained, foliated, fault-zone rock. |
| Faults are response to | shear stress; so they only occur when differential stress does not equal zero. |
| Anderson’s Theory of Faulting(Cuolomb fractures) | Form at 30° to σ₁, with strike perpendicular to σ₃. Can rotate and doesn’t hold true for pre-existing fractures. Stress field may change with depth. |
| Normal Fault | σ₁ is vertical, σ₂ &σ₃ are horizontal. Dip of fault plane should be about 60°. |
| Reverse Fault | σ₃ is vertical, σ₁ & σ₂ are horizontal. Dip of fault planes should be 30°. |
| Strike slip fault | σ₂ is vertical, σ₁&σ₃ are horizontal. Fault planes should be vertical. |
| Fault system | tectonic classification of a group of related faults. |
| Fault arrays | geometric classification of a group of related faults. |
| Antithetic fault | Faults in the opposite direction of major fault |
| Synthetic fault | Fault is the same direction of major fault. |
| Normal fault system | Usually form relay or parallel arrays. Can be listric, planar or have fault bends. Forms in rift zones, passive margins, and mid ocean ridges. |
| Half-graben | rotation of a block long a normal fault, block is bounded by fault on only one side. |
| Horst and Grabens | Down thrown blocks are grabens. Up thrown blocks are horst. |
| Reverse fault systems | Arrays of thrust faults, Form in response to regional shortening, Occur in conjunction with folding. |
| Fold-thrust belts | A tectonic province in which thrusting occurs in conjunction with formation of folds. |
| Strike Slip fault | Occur at transform boundaries, Occur within plates, as components of convergent orogens and mid ocean ridges. Often splay at surface, creating flower structure. |
| Cataclastic flow | acts like a bean bag. At macroscopic scale ductile deformation. At microscopic scale there is brittle deformation. |
| Point defects | Vacancies, & impurities( Substitutions, interstitials) Vacancies- unoccupied sites in the crystal lattice. |
| Substitutions | An atom in lattice is replaced by another atom. |
| Interstitials | atom is incorporated within the crystal at a non-lattice site. |
| Line defects | Linear array of lattice imperfections. |
| Edge dislocation | Extra half-plane of atoms in the lattice. |
| Burgers circuit | Circuit around a dislocation fault to close by one or more atomic distances off. |
| Crystal plasticity | Dislocation can migrate through crystal lattice.( Glide, Cross-slip& Climb, Twinning) |
| Glide | Dislocation are not free to move in any direction on crystal lattice. At low temps, restricted to movement along glide planes. |
| Cross-slip & Climb | Edge location confined to a single glide plane. Can climb to a parallel glide plane if there are vacacnes to accept the lowest atoms of the extra half-plane. Facilitated by raising temps. |
| Twinning | Deformation mechanism that rotates the crystal lattice over a discreet angle such that the twin boundary becomes a crystallographic mirror plane. Such a planar defect is produced by the motion of partial dislocations. |
| Diffusional Mass Transfer | Occurs when an atom or point defect migrates(Pressure solution, Grain-boundary diffusion, Volume diffusion). |
| Volume diffusion | vacancies through the entire body |
| Grain-boundary diffusion | Concentrated along a narrow region at grain boundaries. |
| Pressure Solution | Low temperature, Chemically active fluid in/on grain boundaries. Fluid dissolved Hinge area |
| Hinge Line | The ling of greatest curvature in a folded surface. |
| Limb | The less curved portion of a fold. |
| Inflection point | Point where the sense of curvature changes. |
| Cylindrical fold | Fold in which a straight hinge line parallels the fold axis. The folded surface wraps partway around a cylinder. |
| Non-cylindrical fold | Has a curved hinge line. |
| Crest | Highest point of a curve. |
| Trough | Lowest point of a curve |
| Axial Surface | The surface containing the hinge lines from consecutive folded surfaces. |
| Fold profile plane | Surface perpendicular to hinge line…used as a reference plane from which to describe the fold shape. (Cross section). |
| Inter-limb angle | angle btwn two fold limbs. |
| Wavelength | The distance between two hinges of the same orientation. |
| Arclength | The distance between two hinges of the same orientation measured over the folded surface. |
| Harmonic Folds | Folded stack have approximately the samse wavelength and amplitude. |
| Disharmonic Folds | Layers have different wavelengths and/or amplitudes. |
| Detachment horizon | When a series of folded layers is completely decoupled from unfolded layers above and below. ( Bunched rug on floor. Rug folds, floor doesn’t.) |
| Fold Classification | Fold shape in three dimensions. Fold facing, separating upward-facing folds and downward facing folds. Fold orientation. Fold shape in the profile plane. |
| Plunge of Hinge Line | 0-10 Horizontal; 10-30 shallow; 30-60 Intermediate; 60-80 Steep; 80-90 Vertical. |
| Dip of Axial Surface | 0-10 Recumbent; 10-70 inclined; 70-90 Upright. |
| Interlimb agle | 0-10 Isoclinal; 10-60 Tight; 60-120 Open; 120-180 Gentle. |
| Dip-isogon analysis | connect point on the upper and lower boundary of a folded layer where the layers have the same dip relative to a reference frame. |
| Class 1 (Convergent dip isogons) | When the dip isogons intersect in a point in the core of the fold. |
| Class 1b(Parallel Fold) | Convergent dip isogons; Layers maintain a constant true thickness, but thickness parallel to the axial surface varies. Parallelism breaks down in core of fold because of space limitations. |
| Enveloping Surface | A line that is tangential t the hinge zones of a series of small folds in a layer. |
| Symmetric Fold | Enveloping surface and the axial surface are approximately perpendicular. |
| Asymmetrical | Axial surface that is not perpendicular. |
| Monoclines | Fold structure with only one titled limb, usually result from a vertical fault in the subsurface near the tilted portion of the structure. |
| Kink folds | small folds(less than a meter) that are characterized by straight limbs and sharp hinges |
| Chevron Folds | larger scale version of kink folds |
| Box fold | Broad, flat hinge area with steeply dipping limbs |
| Ptygmatic Fold | irregular and isolated structures that typically occur as tightly folded veins or thin layers of strongly contrasting lithology. |
| Culmination | high point along hinge line |
| Depression | low point along hinge line |
| Doubly plunging anticline | structures with hinge lines that laterally change curvature. |
| En echelon folds | Gradually opening fold is replaced by a neighboring, gradually tightening fold of opposite form. |
| Sheath fold | Extreme hinge line curvature. Typically see eye shaped cross section of nose of the fold. |
| Superimposition(Fold overprinting) | Folds of a later generation are superimposed on fold of an earlier generation. A superposed fold must be younger than the structure it folds. Fold interference patterns |
| Type 0 Fold | Upright F1 fold and Upright F2 fold. Hinge lines and axial surfaces of both generation are the same |
| Type 1 Fold | Upright F1 fold and Upright F2 fold. Hinge lines and axial surfaces of two generations are perpendicular. (Dome and basin Structure) |
| Type 2 Fold | Recumbent F1, Upright F2 fold. Hinge lines and axial surfaces of two generations are perpendicular. (Mushroom structure). Type 3 Fold |
| Active folding | layering of material has mechanical significance. Presence of layers with different competencies affects the strain pattern.( Bending, Buckling). |
| Bending | Applied force is at an oblique angle to the layering. |
| Buckling | Force is parallel to the mechanical anisotropy. |
| Flexural slip folds | Fold that form from slip btwn layers. Strain only accumulates on edges that are at some angles Circles become ellipses. The bed thickness does not change. Class 1 B fold. In three dimensions the strain state of the fold is plane strain. |
| Flexural flow folding | slip that occurs on individual grains within a layer, without presence of visible slip surfaces. |
| Neutral-surface fold | Has a layer in the center of the fold that has no strain accumulated in it. While all of the others circles are being ellipsed. |
| Shear folding | Class 2 Type fold |
| Tectonic fabrics | forms as a result of tectonic deformation. Orientations provide clues to strain state. |
| Primary fabrics | form during the formation of the rock. |
| Random Fabric | fabric elements with no preferred orientation. |
| Preferred fabric | fabric elements are aligned in some way, and/or are repeated at regular spacing. Typical or deformed rocks. |
| Foliation | fabric elements is planar or tabular |
| Lineation | fabric element is a linear feature. |
| Continuous fabric | is present at all scales. |
| Spaced fabric | obvious spacing between fabric elements. |
| Tectonites | rock with a penetrative tectonic fabric. |
| L-tectonite | When linear fabric elements dominate. |
| S- tectonite | When dominantly planar fabrics are present. |
| LS-tectonites | When both linear and planar fabrics are present. |
| Fractures | not considered to be foliations. |
| Cleavage | Secondary fabric element |
| Disjunctive cleavage | is a foliation that forms mostly in sedimentary rocks that have been subjected to a tectonic differential stress under sub-greenshcist facies metamorphic conditions. |
| Cleavage domains | An array of subparallel fabric elements in which the original rock fabric and composition have been markedly changed by the process of pressure solution. |
| Microlithon | The interval in which original rock fabric and composition are more or less preserved that separates domains from one another. |
| High clay content | closely spaced domains |
| Sutured domain | In cross section, such domains resemble the tooth like or jagged sutures on a skull. |
| Domain Spacing | 10cm to 1 m weak cleavage;1cm- 10cm moderate cleavage; less than 1 cm strong cleavage. |
| Pencil cleavage | clay grains generally oriented parallel to bedding during sedimentation/compaction. If strata undergoes layer-parallel compression, secondary cleavage can form perpendicular to bedding. Found in weakly deformed shale. |
| Slaty cleavage | Strong dimensionally preferred orientation of phyllosilicates in a very clay-rich rock and resulting rock is slate. Phyllitic Cleavage |
| Phyllite | rock composed of strongly aligned white mica or chlorite. Has distinctive silky luster. |
| Schistosity | continued metamorphism causes mica and other minerals to react and grow more coarse. With an anisotropic stress field, mica has strongly preferred orientation. Specific mineral form depending on pressure, temp, parent composition, introduced fluids. |
| Porphyroblast | Garnet grows in the schist. Garnet- kyanite schist. |
| Crenulation cleavage | pre-existing foliation that is shortened in a direction at a low angle to the foliation. “Crinkles” |
| Transposition | Process by with a preexisting foliation is transposed into a new orientation. |
| Gneissic Layering | Felsic and mafic minerals begin to separate, forms alternating light/dark bands. |
| Paragneiss | formed from a sedimentary parent rock. |
| Migmatization | Partial melting. Felsic mineral melt first; Mafic minerals are metamorphic, felscic minerals are igneous. |
| Lineation | Any fabric element that can be represented by a line. |
| Fold hinge lineation | Folds that are closely spaced, the fold hinges effectively define a rock rabric that is measured by this… |
| Mullions | cuplike corrugations that form at the contact between units of different competencies in a deformed multilayered sequence. |
| Boudins | perpendicular to σ₃ tablet-shaped lenses of a relatively rigid lithology, embedded in a weaker matrix, that have collectively undergone layer-parallel stretching. (Chocolate tablet boudinage). |
| Intersection lineation | linear fabric formed by the intersection of two planar fabric elements. |
| Bedding cleavage intersection | An intersection lineation used in the field, that manifested by the traces of cleavage domains on a bedding plane( or vice versa). |
| Groove lineation’s | Form by plowing of surface irregularities. |
| Fiber lineation’s | Formed when vein mineral fibers precipitate along a sliding surface. |
| Mineral lineation | Farbric element defining this lineation is the size of a mineral grain or a cluster of mineral grains. Occur in foliation plane of metamorphic rocks, on shear surface, or in plane of mylonitic foliation. |
| Ductile shear zone | a tabular band of definable width in which there is considerable higher strain than in the surrounding rock. Higher strain than in surrounding rock. Non-coaxial. Boundaries are parallel. |
| Frictional regime | Friction dominate the deformation at upper levels of the discontinuity in this crustal segment. First few km. Cataclastic flow. |
| Plastic Regime | Below 10-15km. Crystal-plasticity. Diffusion. Temperature increases about 300°. |
| Brittle-plastic transition | Zone between a dominantly friction and dominantly plastic regime. |
| Mylonites | Cohesive, foliated fault rock, formed dominantly by crystal-plastic processes. |
| Ultramylonite | Mylonite in which the proportion of matrix is 90-100% |
| Protomylonite | Proportion of matrix is < 50% |
| Clastomylonite | Mylonite that contains relatively large grains or aggregates that remain after mylonization reduced the grain size of most of the host rock. |
| Blastomylonite | Mylonite that contains relatively large grains that grew during mylonitization. |
| Sense of displacement | describes the relative motion of opposite sides of the zone(left/right lateral) |
| Grain tail complexes | Grains have tails of material with a composistion and/or grain . σ-type- does not cross the reference plane when tracing the tail away. Δ-type – trail crosses the reference plane when tracing the tail. |
| Syntheic fractures | fractures oriented at low angle to mylonitc foliation. Parallel to the mylonitic foliation. |
| Antithetic fractures | Fractures at angles greater than 45° to the foliation show an opposite sense of movement. |
| C-S | Used to determine the degree of non-coaxiality or the kinematic viscosity number. |
| C-C’ | the strain significance is incompletely understood, but their formation reflects a component of extension along the main anisotropy of the mylonite. Synthetic structure. |
| Snowball garnets | Formation of ductile shear zones involves an internal rotation. Mineral granets shows this behavior, in which “trapped” ,matrix grains eventually produce a spiraling trail. |
| Homogenous strain in shear zones | Circle become ellipses. Ellipses have same axial ratio and orientation. |
| Heterogeneous strain in shear zones | Ellipses have different axial ratios and orientations. |
Created by:
hermis1986
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