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Structure Exam 1
| Term | Definition |
|---|---|
| deformation | structures, such as faults or folds. processes, for instance, fracturing. themeasurable changes that have occurred in a particular volume of rock. location, orientation, shape, size/volume. |
| displacement vectors | have magnitude and direction. undeformed volume of rock are A, B, C, and D. The connecting links (AA0, BB0, CC0, and DD0) are displacement vectors. |
| displacement field | whole family of displacement vectors. The displacement field is in fact the deformation. |
| deformation paths | establishing the displacement field sets the stage for interpreting the motions themselves - deformation paths |
| kinematic analysis | interpreting the motions themselves,including the deformation paths for each block and the V field for the movement. motion of objects leading to the deformed state, doesn't include causal forces of motion.slip on faults,strain,deformational histories |
| dynamic analysis | interprets deformation in terms of force, stress, tracion and mechanics responsible for the formation of structures, as well as evaluating the strength of the materials during deformation. physics of deformation. |
| loading | Generally speaking, deformation of rock bodies results from the loading by gravitational, tectonic, thermal, and/or impact forces, which generate stresses that may exceed rock strength. |
| gravitational loading | the weight of thousands of meters of sediments within a depositional basin produces stresses that generally result in the thinning and compaction of the sediments as they are buried deeper and deeper. |
| tectonic loading | seen today in the slow, steady, northsouth head-on convergence of continental lithosphere of the Indian-Australian plate against the continental lithosphere of the Eurasian plate ( |
| thermal loading. | Deformation that accompanies the cooling of certain basalt flows yields spectacular examples of thermal loading. The cooling causes uniform shrinkage and contraction expressed in columnar jointing of hexagonal character |
| Impact loading | incredibly high stresses. Meteor Crater, located in northern Arizona, where asteroid impact (loading) created a bull’s-eye of deformational destruction. |
| shatter cones | Other telltale signs of impact loading are shatter cones, which are linearly etched fractures with distinctive conical shapes. Debris associated with shatter cones can include glass formed as a result of impact-induced shock melting. |
| structural geology | “study of the architecture of the Earth’s crust, insofar as it has resulted from deformation” |
| exfoliation jointing | ?Figure 1.18? |
| Moho | marks the base of the crust and the top of the mantle, lies within lithospheric plates. The Moho is thought to mark a lithological transition to underlying ultramafic rocks. It is a compositional boundary. |
| Oceanic crust | thin, ranging from about 4 to 9 km in thickness. It is composed predominantly of rocks of basaltic composition that are relatively high in density |
| Continental crust | thick, ranging from approximately 25 to 70 km, and composed of rocks of granitic composition having relatively low density |
| transpressive deformation | An oblique convergence of plates |
| transtensive deformation | An oblique divergence |
| Primary structures | structure that formed at same time as rock. ie) in sediment before the sediment become sedimentary rock, lava or magma before it becomes volcanic or intrusive igneous rock. cross bedding or ripple marks in sandstone |
| Secondary structures | most bear a direct relationship to tectonics and regional deformation. joints, faults, folds, metamorphic fabrics, and shear zones, foliations/lineations |
| Joints | smooth, planar fractures that cut through rock bodies and rock layers, and along which there has been almost imperceptible movement. formperpendicular to the direction inwhich the rock body or layer is being stretched. |
| veins | Movement of fluid along fractures is commonly recorded in the presence of veins (Figure 1.28), composed of minerals that precipitated from solution under favorable conditions of temperature and pressure. |
| shear fractures | Some joints prove to be shear fractures, which form by an ever-so-slight sliding or shearing movement parallel (not perpendicular!) to the plane of the fracture. |
| Faults | discrete fracture surfaces, or discrete narrow-to-broad zones, along which rocks have been offset by slip or shearing movements parallel to the fault surface(s) or fault zone(s). |
| Folds | beds and layers are transformed into curved, bent, and crumpled shapes |
| Descriptive analysis | structures and measuring their locations, geometries, and orientations, materials, primary Structures • geologic mapping and cross sections • statistical analysis of structures • description of bore-holes • Ideally no interpretation |
| Geometric analysis | basis for describing deformation. This kind of geometric analysis produces the field of displacement vectors for material points in the deformed volume of rock, and thus establishes the deformation |
| transformations | The displacement field can be described in terms of transformations (equations) that can take the array of material points in the undeformed volume and arrange them into their new array in the deformed body. translation, rotation, distortion, dilation. |
| translation | (change in position), |
| rotation | (change in orientation),spinning |
| distortion | (change in shape |
| dilation | (change in size) ie:due to a heating-up or a cooling-off down |
| strain | evaluating that part of the deformation that is all about distortion (changes in shape) and dilation (change in size) |
| deformation | name given to the displacement field |
| deformation rate | ? |
| Down-Structure Method of Viewing Folds | Normal profile views of plunging folds can be seen at a glance by viewing the geologic map patterns in the direction of plunge, at an angle of inclination of view corresponding to the amount of plunge. |
| Balanced Cross-Sections | developed for folded and thrusted regions, but they can be applied to extended regions as well |
| flexural slip | The individual layers buckle and fold (the “flexural” part), and as they do they slide past each other by layer-parallel slippage. 1. low cohesive strength along bedding planes, 2. layers are strong and stiff. |
| minor structures | Folding results in the formation of a delightful and curious array of smallscale structures. small folds and faults; slickenlines and crystal fiber lineations; a variety of cleavages and penetrative lineations |
| closure of the fold | Where a sealed reservoir is folded into a dome or anticline, the closure of the fold prevents further upward migration of the oil and gas |
| Saddle reef deposits | lodes of quartz and precious metals that occupy the cores of folds, in openings where bedding and/or foliation has been separated by fold-forming movements |
| Strata-bound ore deposits | commonly associated with folded, metamorphic rocks |
| anticline | fold that is convex in the direction of the youngest beds in the folded sequence. Anticlines = old rocks in core |
| synformal anticline | "“upside-down” anticline" fold that is convex in the direction of the youngest beds in the folded sequence |
| antiformal synclines | fold that "“upside-down” syncline" is convex in the direction of the oldest beds in the folded sequence |
| syncline | fold that is convex in the direction of the oldest beds in the folded sequence. Synclines = young rocks in core |
| front limb | overturned limb |
| back limb | more gently dipping right-side-up limb |
| asymmetric folds | dip of the front limb is steeper than that of the back limb, or differently lengthed limbs.occur within shear zones or fault zones.may reveal the direction of differential shear or (fault)slip.median trace & the axial trace intersect at oblique angle. |
| antiform | a fold that is convex upward |
| synform | fold that is concave upward |
| recumbent | means that the fold lies on its side |
| isoclinal | means that the limbs of the fold are equally inclined |
| anticlinorium | regional anticline. mountain-range-scale anticlinal fold belt with numerous second order folds |
| synclinorium | regional syncline. mountain-range-scale synclinal fold belt with numerous second order folds |
| monocline | They are broad step-like folds that cause otherwise horizontal or very shallowly dipping strata to bend abruptly to steeper inclinations within very narrow zones |
| hinge point | The hinge of a sharp, angular folded surface is sometimes a single point. Hinge Point = point of maximum curvature |
| the hinge zone | distinguished by the maximum curvature achieved along the folded surface |
| inflection points | Curved limb segments of opposing convexity join at locations known as inflection points. inflection point = point on fold limb where curvature changes |
| axial surface | passes through successive hinge lines in a stacking of folded surfaces. curviplanar surface passes through all of the points of maximum curvature in all of the folded layers. |
| axial plane | The axial surface of a fold may be planar |
| axial trace | normal profile view, passes through successive hinge points in the stacking of folded surfaces. line formed by intersection of the axial surface with the earth’s surface or with the plane of a cross section |
| crestal surface | passes through points of highest elevation for each bed within the folded sequence. |
| plunge | dip of the axial surface. ie) plunge of the hinge line. |
| fleuty diagram | used for describing folds on the basis of the geometric interrelationship of axial surface and hinge line. describes orientation of fold using words. |
| reclined fold | one whose hinge line plunges directly down the dip of the fold’s axial surface |
| fold axis | geometric (thus imaginary) linear structural element that does not possess a fixed location. It is the closest approximation to a straight line that when moved parallel to itself generates the form of the fold. |
| cylindrical folds | folds that possess axes |
| Noncylindrical folds | do not possess fold axes |
| center-line axis | runs right down the center of cone and passes through the vertex, which lies in the direction of the tip of the cone |
| beta β diagram | The orientation of the axis of the fold (β) is the line of intersection of the fold limbs.trend and plunge of a fold axis deduced stereographically in the manner described. |
| pi (π) diagram | calculate orientation of a fold through the construction of a pi (π) diagram. This requires plotting the limbs of the folded surface as poles, not as great circles. the poles to each limb are fitted to a common great circle, known as a π circle |
| bisecting surface | the bisecting surface of a fold is a close approximation to the axial surface. For a given folded surface, the bisecting surface passes through the hinge line and splits the angle (the interlimb angle) between the limbs |
| polar tangent plot | another device for determining the trend and plunge of a fold on the basis of bedding orientations. different template than stereonets. |
| SCAT | Statistical Curvature Analysis Technique. methodology for identifying faults in the subsurface, and for evaluating the shapes and orientations of folds associated with faulting. DO WE NEED TO KNOW? |
| chevron fold | planar limbs that meet at a discrete hinge point or at a very restricted subangular hinge zone "heart rate monitor" |
| cuspate fold | exhibits curved limbs that are opposite in sense of curvature to those of most ordinary folds. "mountains with curved limbs" |
| Box folds/conjugate folds | are composed of three planar limbs connected by hinge points or narrow, restricted subangular hinge zones "puzzle piece" |
| Teardrop folds | continuously curved folded surfaces shaped, of course, like teardrops. They are involuted and curve back on themselves. |
| Circular folds | perfectly curved S shapes on its side |
| Elliptical | like circular folds but with assymetrical limbs |
| interlimb angle | Fold tightness is described in terms of interlimb angle (Ramsay, 1967), the internal angle between the limbs of the folded surface |
| Gentle folds | marked by interlimb angles ranging from 170 to 180. |
| Open fold | 90 |
| Tight fold | 10 |
| Isoclinal fold | parallel |
| rootless folds | Many folds encountered in the field are not linked structurally to other folds: they are rootless, cut off on either side by faults and/or shear zones. |
| Symmetrical folds | a median trace and an axial trace that are mutually perpendicular; thus fold height and fold width are measured along mutually perpendicular lines |
| concentric folds/parallel folds | Individual folded layers that are marked by uniform thickness. profile forms commonly are circular or elliptical. Surfaces that separate individual folded layers in an ideal concentric fold are perfectly parallel. |
| decollement zone | folded layers become detached from their underlying foundation. layer-parallel slippage and rock flowage. |
| similar folds | Individual folded layers that display thickening in the hinge and thinning on the limbs, and nearly the same geometry from one layer to the next one |
| Class 1 folds | curvature of the inner arc that is greater than that of the outer arc. |
| Class 2 folds | ideal similar folds, distinguished by identical curvatures of the inner and outer arcs. |
| Class 3 folds | curvature of the outer arc that is greater than that of the inner arc |
| Class 1A folds | a layer thickness in the hinge that is less than layer thickness on the limbs. thickened limbs |
| Class 1B folds | ideal concentric folds, distinguished by uniform layer thickness across the whole fold profile. Concentric Fold |
| Class 1C | intermediate between ideal concentric folds (class 1B) and ideal similar folds (class 2). They show a modest thickening in the hinge, and a modest thinning on the limbs. thickened hinge |
| dip isogons | connecting points of equal inclination on the outer and inner bounding surfaces of the folded layer are constructed graphically. |
| buckling | It can be shown both theoretically and experimentally that an instability develops when layers of different mechanical properties are subjected to layer-parallel stresses |
| buckling equations? | ? |
| layer-parallel strain | stretch (S). equation? |
| finite element modeling | techniques in addressing folding by buckling? |
| competency contrast | between a stiff layer sandwiched between soft layers) on fold form |
| ptygmatic fold | Large wavelength, rounded forms are produced |
| cuspatelobate folds | where competency contrast is low, the amplification rate of buckling is very small. As a result, the folds that are created are of shortwavelength |
| Flexural folding | mechanism of folding. takes place when the mechanical influence of layering in a rock is very strong. The layers actively participate in the folding by bending and flexing |
| Flexural-slip folding | buckling by layer-parallel slip along contacts between layers.layers slip like pages in a paperback book is flexed.The bending of actual layers is the flexural part of the mechanism.the differential movement of each layeris the slip part of the mechanism |
| Flexural-flow folding | the bending by layer-parallel flow or shear within mechanically soft units sandwiched between stiff units. like the flow of ice cream when squeezed between the stiff, competent cookie layers on top and bottom of an ice-cream sandwich |
| layer-parallel stretching/shortening | When an individual layer is actively buckled, rock on the outer arc of the hinge undergoes layer-parallel stretching, and rock on the inner arc of the hinge experiences layer-parallel shortening |
| Boudins/Boudinage | form in sequences of alternating soft and stiff layers that have been subjected to flattening and extension. Stiffer layers tend to break or neck, and the softer layers tend to flow and fill in, wherever required. sausages. ductile contrast b/w layers |
| drag folds (or parasitic folds | asymmetric minor folds formed in this way are valuable for at least three reasons.S and Z folds indicates the direction of the anticlinal axis |
| kink folds | sharp hinges, straight limbs, and an asymmetry expressed by a short limb connecting two longer limbs. Superficially, kink folds resemble buckle folds or flexural-slip folds, but they are really a distinct class. |
| dextral | Z-shaped kink folds |
| sinistral | S-shaped kink folds |
| kink bands | narrow zones where foliation is kinked |
| Passive folds | display profile forms that are class 1C, 2, or 3, typified by some degree of apparent layer thickening in the hinge and thinning on the limbs. the mechanical influence of layering in a sequence of rocks is very weak |
| free folding | properties of folds depend entirely on the physical/mechanical properties of the layers that are shortened. origins considered exclusively on the basis of buckling, flexural-slip, ductility contrast, and degree of cohesion along layer boundaries. |
| forced folding | form of the folds are “forced upon” the layers by virtue of the orientation and form of faults with which the folding is associated, and by which the folds are driven |
| joint sets | families of parallel, evenly spaced joints that can be identified through mapping and analysis of the orientations, spacing, and physical properties of the joints within a given system. |
| systematic joints | planar, parallel, traceable for some distance, and regularly, evenly spaced at distances of centimeters, meters, tens of meters, or even hundreds of meters |
| joint system. | Two or more sets constitute a joint system. |
| nonsystematic joints | Some joints are so irregular in form, spacing, and orientation that they cannot be readily grouped into distinctive, through-going sets. |
| joint surfaces | commonly ornamented by markings that record details of joint propagation and perturbations of the local state of stress |
| shear fractures | microfaults. They form not by tensional opening perpendicular to a fracture face, but through shear traction parallel to the fracture surface. |
| slickenlines | products of shearing movement parallel to the fracture surface. T |
| opening (mode I) | <- -> pulling apart motion |
| sliding (mode II) | like shearing .sliding parallel to fracture |
| scissoring (mode III) | like scissors. rotational motion |
| tip line | name given to the leading edge of a fracture front, separating the fracture surface from yet unfractured host rock |
| fracture tip | the discrete point where the tip line intersects some 2D surface, most commonly the surface of the jointed outcrop |
| Far-field stresses | driven and sustained over long periods of time by large-scale processes (e.g., plate-tectonic loading) that create a regularity of stress orientation over a significant length scale. |
| local stresses | perturbations and/or concentrations of the far-field stresses, and they may rise to magnitudes where the strength of the rock is exceeded, thus producing joints |
| fracture toughness | resistance to fracturing. |
| stress intensity | Fracturing (in this case, jointing) is sure to occur when the stress intensity exceeds fracture toughness |
| subcritical; | stress intensity is less than fracture toughness. |
| Plumes | record the direction of propagation |
| Ribs/undulations | are marked by a slight shift in joint orientation where the velocity of joint propagation slowed down or was arrested. Each rib records the position of the front of the propagating joint at some point in time. |
| fringes | project outward from the main joint face by some small amount. Fringes of joints are the outermost margins of a given joint surface. They are terminations of the main joint face, where the energy required for propagating the joint dissipates. Serated |
| origin | point of initiation of a joint surface |
| Fracture Spacing Ratio | FSR is bed thickness divided by median joint spacing for these data from a single bed. |
| Rose diagrams | showing orientations of (A) systematic joints versus (B) cross-joints... Studying Joints |
| stress reduction shadow | is said to exist in the region of the layer immediately adjacent to the newly formed joint |
| undersaturated jointing | ? |
| saturated jointing | ? |
| tensile strength tests | the basic procedure is to hold one principal stress constant, and then progressively increase or decrease the other to create an everincreasing differential stress. |
| Griffith law of failure | ? |
| lithostatic pressure | the pressure derived from the weight of the entire column of overlying rock). |
| fault zone | composed of countless subparallel and interconnecting closely spaced slip surfaces. consist of numerous closely spaced fault surfaces, commonly separating masses of broken rock |
| shear zones | At deep crustal levels, where rocks tend to deform plastically under conditions of elevated temperature and confining pressure, shear displacement is achieved |
| fissures | large fractures that have accommodated conspicuous dilational opening. Fissures form at the surface of the Earth where active tectonic processes, notably earthquakes and volcanism, create local stretching and pull-apart. |
| Fault scarps | offsets or steps in the land surface that coincide with locations of faults |
| fault-line scarps | located along or near the trace of a fault and are marked by a topographic relief that simply reflects the differential resistance to erosion of the rocks brought into contact by faulting. |
| Slickensides | the smooth or shiny fault surfaces themselves |
| slickenlines. | straight, fine-scale, delicate skin-deep lines that occupy the fault surface itself and record the direction of slip. striations produced by frictional abrasion along the fault surface during differential displacement of the wall rocks |
| fault grooves and fault mullions | reflections of undulations that mark the fault surface itself, produced by the grinding and tooling of the two fault blocks moving past one another, earthquake by earthquake. |
| slip-fiber lineations | produced by the preferred directional growth of minerals during the faulting and in the direction of movement |
| Slickolites | They form along fault surfaces where fault movement in combination with stylolitic pressure solution results in removal of material through dissolution creep. |
| Chatter marks | These small, asymmetrical, step-like features are typically oriented perpendicular to striations. |
| breccias. | brittle fault rocks |
| Comminution | word that we use to describe rocks being broken and ground down into finer and finer size during faulting. |
| Megabreccias & microbreccias | clasts larger than 0.5 m. clasts that are smaller than 1 mm but greater than about 0.1 mm..angular clasts of wall rock lithologies in a matrix of finer grained, crushed wall rock |
| Gouge | Gouge is a light-colored very fine-grained clayey fault rock that is commonly found along fault surfaces and within fault zones (Figure 6.28). Grain size generally is less than 0.1 mm. powdery or muddy clayey fault rock with no cohesion |
| Cataclasite | grain-size similar to gouge, may be dark colored, strongly indurated (has cohesion), consists of very fine crushed fragments. Ultracataclastite is almost glassy in texture (extremely fine-grained). |
| pseudotachylite | rarely exposed but telling component of certain major fault zones, particularly those that have faulted the deep reaches of the Earth’s crust |
| Tachylite | basaltic volcanic glass, |
| Drag folds | a distortion of bedding (or other rock layering) resulting from shearing of rock bodies past one another.can be used to determine the direction and sense of slip during faulting. |
| sigmoidal drag folds | if each end of a fault-bounded layer is curled by drag |
| rollover anticline | Originally horizontal bedding in the hanging wall of a normal-slip fault can become folded in such a way that it actually dips toward the fault surface |
| Listric faults | curved faults that flatten, or decrease in dip, with depth |
| en echelon tension fractures, | mode I features created in noncoaxial shear, form at right angles to the direction of maximum instantaneous stretching |
| allochthonous/allochthon | far out of place |
| autochthonous/autochthon | retain their original location because they have not been thrusted |
| decollement/basal shearing plane | the detachment of the upper cover from its substratum |
| thin-skinned overthrusting | ? |
| hydraulic pumping | Again and again the fluid pressure builds to levels sufficient for thrusting to occur, establishing a cyclic process |
| Cutoff lines | mark the intersection of the thrust with the stratigraphic horizon that is cut. |
| lateral ramps | places where a thrust flat abruptly cuts up-section laterally along the strike of the thrust sheet. |
| imbricate fans | Imbricate fans are marked by a set of curved triangular thrust slices that converge into a more shallowly dipping sole thrust |
| duplexes | visualize a set of thrust faults in which the flats and ramps all tie together, thus completely isolating individual faultbound block. Such fault-bounded blocks are called horses. |
| active roof duplex | In true duplexes, the thrust faults that laterally confine each horse are parallel to the very frontal ramp of the duplex |
| passive roof duplexes | duplex underthrusts strata in the foreland |
| blind thrust | discrete entities, slashing up from depth towards the Earth’s surface and commonly transferring their fault split into folds |
| younger-onolder | crustal stretching due to extension |
| older-on-younger | crustal shortening due to compression |
| horsts; | Relatively uplifted blocks bounded by the normal-slip faults |
| graben | down-dropped blocks between horsts |
| antithetic fault | ? |
| synthetic fault | ? |
| growth fault | When the surface becomes cut and displaced, the fault operates as a growth fault, which means that as the normal faulting takes place so too does sedimentation within the fault-controlled basin that progressively develops. Down- |
| fault segments | You see “start-and-stop” traces of discrete fault surfaces in maps of systems of normal faulting. Individual discrete fault traces |
| Riedel shears (R0-shears) | synthetic strike-slip faults. they form at an acute angle of about 15 to the main line of faulting |
| Riedel shears (R 0 -shears) | antithetic strike-slip faults are conjugate , and they form at a high angle of about 75 to the main line of faulting |
| bends or jogs | Fault curvature |
| Releasing bends/restraining bends | tend to create open space/sites of crowding |
| stepovers. | At stepovers, one strike-slip fault segment ends, and another one, of essentially the same trend, begins |
| rhombochasm, | a very deep depression bounded by master strike-slip faults that are stepped. |
| pop-ups | topographic and structural highs from which sediments are shed. |
| velocity vectors | determining velocities of motion for each displacement vector, thus establishing velocity vectors for individual material points in a volume of material |
| field of velocity vectors | for the whole array of material points |
| displacement, | distance between initial and final position of the material point |
| rake | ? |
| axis of rotation | trend and plunge |
| sense of rotation | clockwise vs counterclockwise |
| magnitude of rotation | measured in degrees |
| listric normal faulting | Listric normal faults curve with depth in such a way that the fault surface is concave upwards |
| homogeneous deformation | lines that were straight before deformation remain straight;lines that were parallel before deformation remain parallel. strain must be systematic and uniform across the body that has been deformed.transforms perfect spheres into perfect ellipsoids. |
| aspect ratio | As the block is progressively shortened in one direction and lengthened in another, without changing area, the circle is transformed to ellipses of greater and greater |
| L length, S stretch, e extension | e=(lf-lo)/lo :: S=lf/lo=1+e |
| angular shear | Greek letter psi (ψ). The full description requires a sign (positive equals counterclockwise; negative equals clockwise) and a magnitude expressed in degrees. |
| shear strain, symbolized by the Greek letter gamma (γ), | γ=tan ψ |
| Strain Ellipses | The finite strain ellipse and its principal axes.The long axis, S1 (greatest stretch), is the direction ofmaximumfinite stretch. The short axis (least stretch), S3, is the direction of minimum finite stretch |
| quadratic elongation λ | λ=S squared |
| Plane strain | strain is essentially two-dimensional, that is, there is neither stretching nor shortening in the direction perpendicular to the plane that contains the directions of maximum and minimum finite stretch (S1 and S3). |
| Coaxial deformation | Cube is converted to progressively flatter shapes by vertical shortening and horizontal extension. |
| Simple shear | a special case of noncoaxial strain. top and bottom surfaces neither stretch nor shorten. they maintain their original lengths, which is the original length of the edge of the cube. In this special case there is no change in area (volume in 3D). |
| finite strain | Without information about how the strain accrued, we can describe only the total finite strain as we see it. |
| incremental or instantaneous strain ellipse | used to portray how a circle is affected by the smallest increments of deformation. The instantaneous strain ellipse will be nearly circular because it attempts to portray infinitesimally small amounts of strain. |
| rheology | strength and behavior) of the materials at the time they were deforming |
| Force | push or a pull that changes, or tends to change, the state of rest or state of motion of a body. Force can cause a body in a state of rest to accelerate, and can cause a moving body to accelerate or decelerate or change direction. |
| Challenges to the Structural Geologist | Poor Exposure •See only end results (snapshot) •Problems with scales of observations •Complexity •time |
| Structural Analysis | •Descriptive Analysis •Kinematic Analysis •Dynamic Analysis |
| Unconformity | A gap in the rock record, where this gap represents a period of time when no layers were deposited, or represents an ancient erosional surface along which previously deposited layers were removed -disconformity -nonconformity -angular unconformity |
| nonconformity | igneous + sedimentary ie) grand canyon |
| angular unconformity | An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. |
| roof pendant | ? |
| diapirs | ? |
| Primary Igneous Structures | • Pumice foliation • Flow Banding • Pillows • Columnar Joints |
| Pumice foliation | welded tuff |
| columnar joints | Columns form perpendicular to cooling surface |
| Primary Sedimentary Structures | cross bedding, graded beds, mudcracks, |
| hinge line | line formed by connecting all possible hinge points along a folded surface |
| To specify the orientation of a fold, measure | 1. Strike and dip of axial plane 2. Bearing and plunge of hinge line |
| Water Gaps | ? |
| Dip-Slip | slip parallel to dip of fault |
| sinistral | left lateral (or “left-handed) strike slip |
| dextral | right lateral (or “right-handed) strike slip |
| Slickenlines with an offset bed will give | displacement vector (get orientation from slickenlines, and magnitude and sense form the offset bed) Thursday, October |
| Reverse Drag | ? |
| Tension Gashes (Extensional Veins) within a Fault Zone | Interpretation of Slip Using Strain Ellipse |
| s = tα | Slip Between Layers s = amount of slip α = dip of limb (in radians!) t = layer thickness |
| Disharmonic Folds | ? |
| Transposition | ? |
| Sheath Folds | ? |
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