STRUCTURAL GEOLOGY (GROUP 7)

structural geology

One important area of geology that focuses on the study of rock deformation is structural geology. It focuses on comprehending the Earth's interior structure and the processes such as faulting, fracturing, folding, and tectonic forces that have shaped it over time. In disciplines like civil engineering, resource exploration, and seismic investigations, this information is essential.

geological map

A ____________ is a visual representation that displays the distribution, type, and structure of rocks at the Earth’s surface. It is an essential tool for geologists helping them interpret the geological history of an area and identify structural features

components of geological map

• rock units

• structural features

• strike and dip symbols

• legend and scale

rock units

represented by colors

structural features

includes faults, folds, and joints

strike and dip symbols

indicate the orientation of rock layersl

legend and scale

provide information on symbols and measurements

fractures

Fractures are discontinuities in rock that occur when stress exceeds the rock's strength. These breaks can range in scale from microscopic cracks to large fault zones that extend for hundreds of kilometer

types of fractcures

• faults

• fissure

• joints

formation of fractures

A fracture forms in response to stress. More specifically the rock breaks and forms a fracture when the applied stress reaches a certain limit, namely the rock strength. The stress associated with the fracture formation maybe extension, shear, or both.

folds

bends or curves in rock layers that form when rocks are compressed(squeezed). They are usually seen in areas where the Earth’s crust has been pushed together.

7 types of folds

• anticline

• syncline

• monocline

• chevron

• recumbent

• isoclinal

• dome and basin

anticline fold

is a type of fold created in a rock when it is subjected to compressional stress that causes the rocks to bend or curve downward. The oldest layers are found in the fold’s core or center.

syncline fold

is the opposite of an anticline fold. A syncline fold is created in a rock when it is subjected to compressional stress that causes the rock to bend or curve upward. The youngest layer is found in the fold’s core

monocline fold

is step-like fold in rock strata consisting of a zone of steeper dip within an otherwise horizontal or gently dipping sequence.

chevron fold

are a structural feature characterized by repeated well behaved folded beds with straight limbs and sharp hinges. Chevron folds are typically found in mountain belts, where they can be used to infer the direction of compressive stress. They can also be found in sedimentary basins, where they can be used to map out the distribution of different rock types

recumbent fold

is a fold in which the axial plane is essentially horizontal, meaning that the two limbs of the fold are parallel to the ground. Recumbent folds are often isoclinal, meaning that the limbs of the fold are also parallel to each other

isoclinal fold

is a type of fold in which the limbs are parallel or nearly parallel to each other. This is in contrast to other types of folds, such as symmetrical folds, in which the limbs are at an angle to each other

dome and basin

is a type of geological structure that consists of a central dome-shaped uplift surrounded by a basin shaped depression. Dome and basin folds can be found in all types of tectonic settings, but they are particularly common in areas of compressional deformation, such as mountain belts.

joint

• Brittle-fracture surface in rocks.

• Little or no displacement along the surface.

• Found in nearly all surface rocks

formation of joints

• caused by stress exceeding rock strength

• results from cooling, uplift, erosion, or tectonic forces

• can be influenced by sediment compaction or igneous activity

types of joints

• systematic joints - regular, planar, predictable

• non-systematic joints - irregular and scattered

• types by origin - tectonic, cooling exfoliation

• special type - columnar joints in igneous rocks

joint

Joints are classified based on their appearance and origin. Systematic joints are regular and evenly spaced, while nonsystematic joints are irregular. They can also form due to different processes, such as tectonic joints from crustal stress, cooling joints in igneous rocks as they contract, and exfoliation joints from pressure release, often forming curved surfaces