Structural Geology Flashcards by Engr. Joed Bautista

The branch of
geology that deals with the form, arrangement,
and internal structure of the rocks, and esp. with
the description, representation, and analysis of
structures, chiefly on a moderate to small scale.

structural geology

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defined as a geometric feature in a
rock whose form, shape and distribution can be described.
These features are separated into primary, secondary,
tectonic and non-tectonic structures

geological structure

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structures that are acquired during the
genesis of a rock.

primary structures

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locally driven or small scale features
not immediately due to tectonic interaction

non-tectonic structures

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structures that are acquired after the genesis of the rock

secondary structures

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according to which slow incremental changes, such as erosion, brought about all the Earth’s geological features. also known as gradualism

uniformitarianism

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theorizes that the Earth has largely been shaped by
sudden, short-lived, violent events, possibly worldwide in scope.

catastrophism

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states that layers of sediment are
originally deposited horizontally under the action of gravity

principle of original horizontality

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it states that in undeformed stratigraphic sequences, the oldest strata will lie at the bottom of the sequence, while newer material stacks upon the surface to form new deposits over time

law of superposition

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states that the geologic feature which cuts another is the
younger of the two features

principle of cross-cutting relationships

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states that layers of sediment initially extend laterally in all directions; in other words, they are laterally continuous. As a result, rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.

principle of lateral continuity

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grading of particles from coarse to
fine from bottom to top in bands, several feet thick which are repeated with great regularity through a formation

graded bedding

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– is an arrangement of laminar transverse
to the bedding plane in straight sloping lines or concave forms

cross bedding

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is found in widespread and thinner
sandstones and is indicative of shallow-water
conditions of deposition

current bedding

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type of analysis that Interprets deformational movements that formed the structures

kinematic analysis

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type of analysis that recognize, describe structures by measuring their locations, geometries and orientations
* Break a structure into structural elements - physical & geometric

descriptive analysis

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type of analysis that Interprets forces and stresses from interpreted deformational
movements of structures

dynamic analysis

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types of kinematic analysis

distortion, dilation, rotation, translation

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means slope or inclination

dip

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The angle of inclination of a
bedding plane with horizontal
plane

amount of dip

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direction along which the
inclination of the bedding plane
occurs

dip direction

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measures the direction angle

clinometer

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measure the dip direction

compass

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defined as the direction of a
line formed by the intersection of
a bedding plane and a horizontal
plan

strike

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strike is always at _________ with the true dip direction

right angle

When the dip layer is measured in a direction that is essentially at right angle (90 deg) to the strike of that particular layer.

true dip

types of angle of dip

Horizontal - 0 deg Inclined - 0-90 deg Vertical - 90 deg

When the dip of layer is measured in any other direction which is not at right angle (90 deg) to its strike direction

apparent dip

When sedimentary rocks are deposited in an originally sloping basin they are also inclined in the same fashion. Thus, if original slope of the basin of deposition is anything between 5-10 degrees the sedimentary formations accumulating over there in the period of time, will also have the same direction, such dips are called Depositional Gradient

Primary Dip

in inclination induced in the strata after its deposition due to the Tectonic Force. Secondary dip may range in value up to vertical (90). Most folded mountain ranges of the world strata exhibit this kind of dip

secondary dip

are inclinations of the rocks exposed in a limited area of observation. They may be primary or secondary or may not show any appreciable variation laterally or with depth

local dip

an averaged general inclination of a series of formation exposed over a wide area . These rocks may show varying local dips, both in respect of degree and directions of inclination.

regional dip

Force applied over an area

stress

observable deformation in the rock

strain

the result of rapidly applied high stress which "break the rock"

brittle deformation

contact between two rock units

unconformity

the result of slowly applied, constant, low stress which "bend the rock"

ductile deformation

Preferred orientation of planar rock bodies and/or minerals

foliation

Zones of deformed rock that have accommodated movement

shear zone

Preferred orientation of linear minerals and rocks

lineation

are usually erosional contacts that are parallel to the bedding planes of the upper and lower rock units

disconformity

the contact that separates a younger sedimentary rock unit from an igneous intrusive rock or metamorphic rock unit

nonconformity

the contact that separates a younger, gently dipping rock unit from older underlying rocks that are tilted or deformed layered rock.

angular unconformity

Once the elastic limit (strength) of a rock is surpassed, it either flows or fractures.

brittle deformation

fractures along which no appreciable displacement has occurred

joints

often accomplished by gradual slippage along planes of weakness within the atomic structure of mineral grains

ductile deformation

joint that share a similar orientation in the same area. Or it is a family of parallel evenly spaced joints

joint set

two or more intersecting joint sets in the same area

joint system

which the block have separated for the small distance to right angle to the fracture surface

open joints

there is no such separation. Joints may be capable of allowing fluid (gas and water ) to pass through the rock

closed joints

small in their extension confined to only one part of layer. It is called as discontinuous joints.

small joints

existence of asperities between discontinuity suggest stability of shearing

roughness

distance between discontinuity surface

separation

in the case of UG excavation, discontinuity is considered continuous if _________ than the dimension of the excavation

its length is greater

In tunnels, GW in liters per minute per _______ of the excavation should be determined

10 meters

fractures at the scale of centimeters or less

shear fractures

A fracture or break in a rock along which a movement occurs

fault

Shear Fractures at the scale of a millimetre or less which may be visible only under a microscope.

micro faults

fragmented rock produced by the grinding action of a fault at low pressure (low depth) activity

cataclasite

recrystallized rock generated by deep (high pressure) fault motion

mylonite

types of faults according to attitude of the fault surface

high angle fault - fault dip > 45 deg low angle fault - fault dip < 45 deg

fault zone rocks that contain mylonites that deform in a ductile manner

ductile shear zones

3 criteria for recognizing faults

Features intrinsic to faults themselves Effects on geologic or stratigraphic units Effects on physiographic features

are linear features characterized by sharp increases in the topographic slope; they suggest the presence of faults

scarps

- are continuously linear breaks in slope that result directly from displacement of topography by a fault

fault scarp

a smoothly polished surface caused by frictional movement between rocks along the two sides of a fault. This surface is normally striated in the direction of movement.

slickensides

relative displacement parallel to the dip of the fault plane (up-down movement)

dip-slip fault

are linear topographic features characterized by an anomalous decrease in slope. They form where a fault displaces an originally smooth slope so that a strip of shallower slope results, or where erosion of the less resistant rocks in a fault zone produces a shallower slope than is supported by the surrounding, more resistant rocks

fault benches

relative displacement parallel to the strike of the fault plane (left and right movement)

strike-slip fault

movement along the direction of the strike and slip (combination movement)

oblique-slip fault

type of fold in the form of an arch rock dip away from the axis and the oldest rocked exposed at the centr

anticline

type of fold that is uniform direction of strike but variable angle of dip

monocline

a reverse fault that has a dip of <45 deg

thrust fault

type of fold in the form of a through. rocks dip towards the axis and the youngest rocks exposed at the center

syncline

non curved parts of a fold

limbs/sides/flanks

curved portion of fold

hinge zone

limbs dip in the opposite direction at the same angle (symmetrical)

vertical

limbs dip in the opposite direction at different angle (asymmetrical)

inclined