Plate tectonics shape Earth's surface through powerful forces. These forces create diverse landscapes, from towering mountains to deep ocean trenches. Understanding tectonic settings helps explain how our planet's crust deforms and changes over time.

Structural geology reveals the hidden stories within rocks. By studying folds, faults, and other features, geologists can piece together Earth's past. This knowledge helps us interpret the complex history of our planet's ever-changing surface.

Tectonic Settings and Crustal Deformation

Tectonic settings for crustal deformation

• Convergent plate boundaries involve the collision of two plates
  • Subduction zones occur where an oceanic plate descends beneath another plate
    • Oceanic-continental convergence leads to the formation of volcanic arcs and accretionary wedges (Andes Mountains)
    • Oceanic-oceanic convergence results in the formation of island arcs and deep-sea trenches (Mariana Trench)
  • Continental-continental collision occurs when two continental plates collide, leading to the formation of high mountain ranges (Himalayas)
• Divergent plate boundaries involve the separation of two plates
  • Mid-ocean ridges are underwater mountain ranges where seafloor spreading occurs, forming new oceanic crust (Mid-Atlantic Ridge)
  • Continental rifting occurs when a continent is stretched and thinned, leading to the formation of rift valleys (East African Rift)
• Transform plate boundaries involve plates sliding past each other horizontally
  • Strike-slip faults accommodate the lateral displacement of crust (San Andreas Fault, North Anatolian Fault)

Structural geology in geologic features

• Mountain ranges are formed by compressional forces at convergent plate boundaries
  • Folding and faulting of rock layers occur due to compression
  • Uplift and erosion shape the mountain range over time
• Basins are formed by extensional forces at divergent plate boundaries or within plates
  • Subsidence occurs as the crust stretches and thins
  • Sediment accumulation fills the basin over time
  • Examples include foreland basins adjacent to mountain ranges and rift basins in extensional settings
• Other geologic features influenced by structural geology include:
  • Plateaus, which are uplifted regions of flat-lying sedimentary rocks (Colorado Plateau, Tibetan Plateau)
  • Domes, which are circular or elliptical uplifts of rock layers (Black Hills, Adirondack Mountains)

Stress Fields and Structural Features

Regional stress and structural development

• Stress fields influence the development of structural features
  • Compressional stress leads to the shortening of crust and the formation of thrust faults and folds
  • Extensional stress leads to the stretching of crust and the formation of normal faults and grabens
  • Shear stress leads to the lateral movement of crust and the formation of strike-slip faults
• Structural features develop in response to stress fields
  • Folds are formed by compressional stress
    1. Anticlines are upward-arching folds
    2. Synclines are downward-arching folds
  • Faults are formed by different types of stress
    1. Normal faults form under extensional stress, with the hanging wall moving down relative to the footwall
    2. Reverse faults form under compressional stress, with the hanging wall moving up relative to the footwall
    3. Strike-slip faults form under shear stress, with lateral movement of fault blocks
  • Joints are fractures in rock with no displacement, often forming in response to regional stress fields

Interpreting geologic history through structure

• Field observations are crucial for interpreting geologic history
  • Orientation of rock layers provides information about past deformation events
  • Identification of folds, faults, and other structures helps reconstruct the tectonic history
• Cross-sections are used to visualize the subsurface geology
  • Interpretation of deformation events and their timing can be inferred from cross-sections
• Stereographic projections are used to represent 3D orientation data on a 2D surface
  • Analysis of fold and fault geometries can be performed using stereographic projections
• Tectonic reconstruction involves integrating structural data with other geologic information
  • Interpretation of past plate movements and deformation events is possible through tectonic reconstruction
  • Reconstruction of paleogeography and tectonic settings helps understand the geologic history of an area (reconstruction of the supercontinent Pangaea)