Geology3.05 KB
Geological Processes and Rock Transformation
Fundamental Geological Concepts
- Anatexis: High-temperature process where rocks melt completely to become magma.
- Metamorphism: A set of changes occurring in rocks while remaining in a solid state due to increased temperature and pressure.
- Orogeny: Historical periods of mountain building (e.g., Alpine, Hercynian, Caledonian) involving igneous, metamorphic, and tectonic phenomena.
- Orogen: Relief formed by the folding of the Earth's crust due to tectonic plate collisions.
Stress and Deformation Mechanics
- Stress: Force applied per unit of surface area.
- Compression: Force acting perpendicular to the surface, pushing or compressing materials.
- Tension: Force acting perpendicular to the surface, pulling or separating materials.
- Shear: Force acting parallel to the surface.
- Elastic Deformation: Temporary and reversible; the rock recovers its original shape and volume once the stress is removed.
- Plastic Deformation: Permanent alteration; the rock remains deformed after the stress is removed.
- Brittle Deformation: Alteration occurring when the applied stress exceeds the rock's strength, causing fracture.
Fold Structures and Terminology
- Fold: Structure formed by lateral or shear compression forces, appearing as waves.
- Hinge: The zone of maximum curvature where strata change their dip or direction.
- Flanks: The lateral sides of a fold that dip in opposite directions.
- Axial Plane: The surface connecting the hinges of different strata.
- Fold Axis: The intersection between the axial plane and the hinge.
Classification of Folds
- Anticline: Fold where the oldest materials are found in the core.
- Syncline: Fold where the most modern materials are found in the core.
- Symmetric Fold: The angles of the two flanks are equal; the hinge and crest coincide.
- Inclined Fold: The axial plane is slightly tilted.
- Knee Fold: One flank is thinned due to intense folding.
- Recumbent Fold: The axial plane is horizontal.
- Overturned Fold: The hinge is below the horizontal, and the axial plane is nearly vertical.
- Isopachous Fold: Strata maintain uniform thickness throughout the fold.
- Anisopachous Fold: Strata exhibit varying thickness throughout the fold.
- Overthrust: Intense folding that evolves into sliding along a fault plane.
- Nappe: A type of folding where stress exceeds the limit of plasticity, causing the rock to break and slide.
