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Transcript
GEOL 470 Structural Geology OUTLINE Dr. Jeff Amato Geological Sciences 8/26/08 Why structure is important An example of structural analysis Earth Structure Time Scale Why study structural geology? How do we explain the major features of the Earth? Why are there mountains? Matterhorn, Swiss Alps How can solid rock flow like taffy? Morcles Nappe, Swiss Alps Where is the oil? How do faults relate to earthquakes Active mountain. front, Basin and Range Province, Nevada Structural Hazards and Society Structural analysis of a pizza… It all starts with field mapping Brooks Range Foothills, AK A basic tool: the geologic map A structural cross section: Determine deep structure from surface data Summary: Structures include: Folds, faults, joints Foliations, lineations, shear zones Structures are found at every scale Plate, mountain, outcrop, hand sample, thin section Summary: Structural geology is important to society Helps to find resources and determine hazards Summary: Structural analysis is conducted through observation and interpretation: Kinematics: What moved? How much? What direction? Dynamics: What forces and stresses were responsible? Summary: Geologic maps and cross-sections help visualize the big picture Earth Structure How many layers in the earth? Two answers to this… 1) Compositional Classification Each layer has same basic composition. Crust Crust Mantle Crust= low density rock Mantle = high density rock Core= iron 2) Mechanical Classification Each layer will consist of material that behaves the same way under stress Outer Core= liquid Inner Core= solid Mechanical Classification Lithosphere Solid plates, resistant to flow Asthenosphere Solid: flows under stress Outer Core Liquid Inner Core Solid Plates are moving Convection! Oceanic crust vs. Continental crust Why are the oceans deep, and the continents at high elevations? What is density? (r) mass (g) r= volume 3 (cm ) Density of different materials Water: Quartz: Rocks: Iron: Lead: Gold: 1 2.3 8 11 19 g/cm3 g/cm3 2-3.5 g/cm3 g/cm3 g/cm3 g/cm3 Density of different materials Quartz: Gold: 2.3 19 g/cm3 g/cm3 r = 0.9 g/cm3 r = 1.0 g/cm3 Less dense continental crust floats on denser mantle. 0 (km) 10 20 30 40 50 Oceanic crust (3.0 g/cm3) Continental crust is less dense than oceanic crust. Continental crust (2.8 g/cm3) Mantle (3.4 g/cm3) Horizontal distance not to scale Moho discontinuity