Geological Structures and Earth's Dynamic Processes

Topographic Maps: Representation of Earth's Surface

A topographic map represents relief through symbols. These maps are created by cartographers and topographers. They provide a three-dimensional scale representation of the Earth's surface relief, or any portion of it, on a two-dimensional plane.

Geological Events: Understanding Earth's Processes

A geological event refers to an elemental geological unit or occurrence. It is a geological phenomenon that occurs or has occurred, not necessarily determined by specific time-space and energy parameters, but rather as a consequence of a particular environmental change (e.g., an outcrop).

The Wilson Cycle: Oceanic Crust Evolution

The Wilson Cycle describes the evolution of oceanic crust. If a single oceanic crust exists, it can fragment (possibly due to ascending thermal plumes), leading to the breaking of the lithosphere and the creation of a mid-ocean ridge (Rift-Valley stage, e.g., the Atlantic Ocean). When one side of the fragmented crust subducts, the oceanic crust will also subduct (including ridges that can be subducting) in subduction zones. Finally, an oceanic crust that continuously collides with another plate may lead to a Himalayan-type orogeny.

Rock Deformation: Classification and Structures

Elastic and Brittle Deformation

• Elastic Deformation: This type of deformation is only perceived by seismic waves (P and S waves) and tides, manifesting as holistic efforts within the rock.
• Brittle Deformation: This deformation leaves indelible marks on rocks, such as fractures.

Types of Joints (Diaclases)

Joints are breaks in rocks where no significant movement is appreciated on either side.

• Syngenetic Joints (Sinclases): Joints that originate at the same time the rock forms.
• Tectonic Joints (Tectoclas): Joints caused by tectonic movements and stresses (e.g., compression affecting granite associated with folds).
• Sheeting Joints: Joints formed by the erosive decomposition of a rock. For these to appear, there must have been prior erosion, and the rock massif must not be decompressed.
• Shrinkage Cracks: Typically, these are clay shrinkage cracks, which result from the contraction of clays (which swell when wet and shrink upon drying).
• Columnar Joints (Lava Flow Joints): Distinct joints found in basaltic lava flows.

Faults: Understanding Earth's Fractures

A fault is a break in the rock with displacement, where two parts slide past each other.

Elements of a Fault

• Hanging Wall: The block of rock located above the fault plane.
• Footwall: The block of rock located below the fault plane.
• Upthrown Block: The block that topographically rises due to the fault's effect.
• Downthrown Block: The block that is depressed (sinks) relative to the fault center.
• Fault Slip (Throw): The distance between two points that were originally together before the fracture occurred.
• Fault Mirrors or Striae: Highly polished rock surfaces with striations, produced when movement occurs along the fault plane.
• Fault Scarp: A topographic feature on the Earth's surface created by a fault.

Fault Classification by Movement and Stress

• Normal/Direct Fault: Characterized by downward movement, typically associated with extensional stresses.
• Reverse Fault: Characterized by upward movement, typically associated with compressional stresses.
• Strike-Slip Fault: Characterized by horizontal movement along the fault plane.

Fault Systems and Landforms

Fault systems are groupings of faults with a common characteristic, such as a stepped arrangement or similar orientation. These systems can produce distinct landforms:

• If depressions are formed, they are known as a graben or tectonic trench.
• If elevated ground is formed, it is known as a horst or tectonic block.

Folds and Related Structures in Geology

A fold is a continuous plastic deformation manifested as bends in the constituent elements of the rock.

Key Elements of Folds

• Hinge: The zone of maximum curvature or bending within a fold.
• Flank (Limb): The sides of a fold, where the strata are less curved.
• Axial Plane: An imaginary plane that connects the hinge lines of all folded surfaces within a fold.
• Fold Axis: A line that, when moved, generates the entire folded surface.

Associated Structures

• Schistosity: Planar fabrics in metamorphic rocks that form parallel to the axial plane of folds.
• Thrust Sheets (Nappes): Large-scale faults that can involve translations of more than 100 km.
• Diapir or Domes: Deformations resulting from the upward movement of viscous materials.

Tectonic Styles: Regional Deformation Patterns

Tectonic styles are characteristic deformation patterns affecting a large region, often defined by the dominant geological structures present.

• Alpine Style: A deformation style affecting the crustal level, typical of the Alps, where deformation corresponds to a thrust belt.
• Jurassic Style: Characterized by a predominance of concentric folds (e.g., the Iberian Range).
• Saxon Style: Dominated by diapirs and folds (e.g., the Catalan Ranges).
• Teutonic Style: Where faults predominate (e.g., present-day Galicia).