Structural Geology

Symmetrical and Asymmetrical folds

.is a fold that is concave upward. An anticlinorium is a large anticline on which minor folds are superimposed, and a synclinorium is a large syncline on which minor folds are superimposed. A symmetrical fold is one in which the axial plane is vertical. An asymmetrical fold is one in which the axial plane is inclined

Normal Fault

A fault in which the hanging wall has moved downward relative to the footwall.

Reverse fault

A fault in which the hanging wall has moved upward relative to the footwall.

Fault scarp

A fault scarp is a small step on the ground surface where one side of a fault has moved vertically with respect to another.[1] It is the topographic expression of faulting attributed to the displacement of the land surface by movement along faults. They are exhibited either by differential movement and subsequent erosion along an old inactive geologic fault (a sort of old rupture), or by a movement on a recent active faul

Inclined Folds

A fold in which the angle of dip of the axial plane is between 10° and 80°, and the highest and lowest points on the fold surfaces do not necessarily coincide with the hinge points.

Fold

A geological fold occurs when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur singly as isolated folds and in extensive fold trains of different sizes, on a variety of scales.

Monocline

A monocline (or, rarely, a monoform) is a step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently-dipping sequence.

Thrust fault

A reverse fault in which the fault plane is inclined at an angle equal to or less than 45°

Homocline

A simple rock structure in which all layers tilt in the same direction, especially with a near uniform dip angle

Geologic Structure

Feature, such as a fold, fracture, joint, or fault, that disrupts the continuity of rock units.

Block Diagram and Geologic Cross Section

Geology . a perspective representation of the geology of an area showing surface contours and generally including two vertical cross sections.

Fault and Joint

In geology the term joint refers to a fracture in rock where the displacement associated with the opening of the fracture is greater than the displacement due to lateral movement in the plane of the fracture (up, down or sideways) of one side relative to the other. Typically, there is little to no lateral movement across joints. This makes joints different from a fault which is defined as a fracture in rock in which one side slides laterally past the other with a displacement that is greater than the separation between the blocks on either side of the fracture. Joints normally have a regular spacing related to either the mechanical properties of the individual rock or the thickness of the layer involved. Joints generally occur as sets, with each set consisting of joints sub-parallel to each other.

Axial Plane

The axial plane of a fold is the plane or surface that divides the fold as symmetrically as possible

Contact

The boundary of different rocks, represented by a line drawn on a geologic map or cross-section separating the different rocks or geologic formations

Limb (of a fold)

The flanks of a fold are known as the limbs.

Hinge Line (fold axis)

The line separating the region in which a beach has been thrust upward from that in which it is horizontal. A line in the plane of a hinge fault separating the part of a fault along which thrust or reverse movement occurred from that having normal movement

Attitude

The orientation of a rock layer, a surface/plane line

Fault Plane and Fault trace (Fault trace also called fault line)

The plane along which the break or shear of a fault occurs. a line on a rock surface or the ground that traces a geological fault.

Plunging fold and trend of a plunging hinge line

The trend and plunge of a linear hinge line gives you information about the orientation of the fold

Domes and Basins

a dome is a deformational feature consisting of symmetrically-dipping anticlines; their general outline on a geologic map is circular or oval. The strata in a dome are upwarped in the center; if the top of a dome is eroded off, the result will be a series of concentric strata that grow progressively older from the outside-in, with the oldest rocks exposed at the center. Many geologic domes are too large to be appreciated from the surface, and are apparent only in maps a. A broad tract of land in which the rock strata are tilted toward a common center. b. A large, bowl-shaped depression in the surface of the land or ocean floor

Strike-slip fault

a fault in which rock strata are displaced mainly in a horizontal direction, parallel to the line of the fault.

Oblique-slip fault

a fault on which the movement is along both the strike and the dip of the fault

Dip-slip fault

a fault on which the movement is in the direction of the dip of the fault

transform fault

a strike-slip fault occurring at the boundary between two plates of the earth's crust.

Syncline Folds

a syncline is a fold with younger layers closer to the center of the structure. A synclinorium (plural synclinoriums or synclinoria) is a large syncline with superimposed smaller folds.[1] Synclines are typically a downward fold, termed a synformal syncline (i.e. a trough); but synclines that point upwards, or perched, can be found when strata have been overturned and folded (an antiformal syncline).

Anticline Folds

an anticline is a fold that is convex up and has its oldest beds at its core. The term is not to be confused with antiform, which is a purely descriptive term for any fold that is convex up. Therefore if age relationships between various strata are unknown, the term antiform should be used.

Structural Geology

branch of geology that deals with the form, arrangement, and internal structure of rocks —called also geotectonic geology

Horst and graben

horst and graben refer to regions that lie between normal faults and are either higher or lower than the area beyond the faults. A horst represents a block pushed upward by the faulting, and a graben is a block that has dropped due to the faulting. Horst and Graben are formed when normal fault of opposite dip occur in pair with parallel strike lines . Horst and Graben are always formed together .Graben are usually represented by low-lying areas such as rifts and river valleys whereas horsts represent the ridges standing between/on either side of these valleys.

Geologic Map

is a special-purpose map made to show geological features. Rock units or geologic strata are shown by color or symbols to indicate where they are exposed at the surface. Bedding planes and structural features such as faults, folds, foliations, and lineations are shown with strike and dip or trend and plunge symbols which give these features' three-dimensional orientations.

Formation

is the fundamental unit of lithostratigraphy. A formation consists of a certain number of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined on the thickness of the rock strata they consist of and the thickness of different formations can therefore vary widely.

Overturned fold and Recumbent fold

overfold (overturned fold) A fold in which the axial plane is inclined so that the fold limbs dip in the same direction, although not necessarily by the same amount. One limb is thus 'overturned'. A fold whose hinge line and axial plane are horizontal or subhorizontal. M. J. Fleuty (1964) suggests that the term recumbent fold be restricted to a fold whose axial plane does not dip more than 10°.

Strike and Dip

refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike (or strike angle) can be given as either a quadrant compass bearing of the strike line (N25°E for example) or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given (where the example of N25°E would simply be 025), or the azimuth number followed by the degree sign (example of N25°E would be 025°). The dip gives the steepest angle of descent of a tilted bed or feature relative to a horizontal plane, and is given by the number (0°-90°) as well as a letter (N,S,E,W) with rough direction in which the bed is dipping

Pluton,batholith,stock,dike,sill,lacolith

see lab manual (igneous section)

Hanging Wall

the block of rock that lies above an inclined fault or an ore body

Footwall

the block of rock that lies on the underside of an inclined fault or of a mineral deposit.