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• Who was the proponent of the Principle Of Original Horizontality

  1. Nicolaus Steno
• He is the scientist that coined the phrase "The Present is the Key to the Past"

  James Hutton
• Major contributor to the Geosyncline Theory of Mountain Building

  
  

  James Hall (1811-1898)
• Proponent for the Continental Drift Theory

  Alfred Wegner (1880-1930)
• Proponent for the theory of Sea Floor Spreading

  Harry H. Hess (1906-1969)
• are geometric features in rock bodies whose shape, form, and distribution can be described.

  whom also undergo orces that continue to shape the planet: Weathering, Erosion, Geological Forces (tectonics, earthquakes, volcanoes)

  Geologic Structures
• Classifications of geologic structures by geometry

  • Planar (or subplanar) surface
  • Curviplanar surface
  • Linear feature (joint, vein, fault, fold, shear zone, foliation, lineation)
• Classification of geologic structures by geologic significance

  • Primary: formed as a consequence of the formation process of the rock itself
  • Local gravity-driven: formed due to slip down an inclined surface; slumping at any scale driven by local excess gravitational potential
  • Local density-inversion driven: formed due to local lateral variations in rock density, causing a local buoyancy force
  • Fluid-pressure driven: formed by injection of unconsolidated material due to sudden release of pressure
  • Tectonic: formed due to lithospheric plate interactions, due to regional interaction between the asthenosphere and the lithosphere, due to crustal-scale or lithosphere-scale gravitational potential energy and the tendency of crust to achieve isostatic compensation
• Classification of geologic structures by timing of formation

  • Syn-formational: formed at the same time as the material that will ultimately form the rock
  • Penecontemporaneous: formed before full lithification, but after initial deposition
  • Post-formational: formed after the rock has fully formed, as a consequence of phenomena not related to the immediate environment of rock formation
• Classification of geologic structures by process of formation - deformation mechanism

  • Fracturing: related to development or coalescence of cracks in rock
  • Frictional sliding: related to the slip of one body of rock past another, or of grains past one another, both of which are resisted by friction
  • Plasticity: resulting from deformation by the internal flow of crystals without loss of cohesion, or by non-frictional sliding of crystals past one another
  • Diffusion: resulting from material transport either solid-state or assisted by a fluid (dissolution)
• Classification of geologic structures by mesoscopic cohesiveness during deformation

  • Brittle: formed by loss of cohesion across a mesoscopic discrete surface
  • Ductile: formed without loss of cohesion across a mesoscopic discrete surface
  • Brittle/ductile: involving both brittle and ductile aspects
• types of Deformation

  • Brittle: formed by loss of cohesion across a mesoscopic discrete surface
  • Ductile: formed without loss of cohesion across a mesoscopic discrete surface
  • Brittle/ductile: involving both brittle and ductile aspects
• what Deformation scaleis used to differentiate brittle and ductile deformation?

  Mesoscopic scale is critical in the distinction between brittle and ductile deformation, as ductile deformation can involve microscopic-scale fracturing and frictional sliding
• Strain significance

  1. Contractional: resulting in shortening of a region

  2. Extensional: resulting in extension of a region

  3. Strike-slip: resulting from movement without either shortening or extension
• it is the study of the forces that deform the earth's rocks and the description and mapping of deformed rock bodies and structures

  Structural Geology
• Structural geologists analyze Earth's forces by studying deformation, fracturing, and folding of the Earth's crust
• Structural geology is the study of rocks deformed by stress and strain, trying to understand stress and strain forces to decipher their pre-deformed state
• Deformation occurs when rocks are subjected to stresses greater than their own internal strength, caused by stress and strain
• Strain


  Resultant of the stress applied; end product
• Types of stress

  • Tensional stress (or extensional stress), which stretches rock
  • Compressional stress, which squeezes rock
  • Shear stress, which results in slippage and translation
• Tension


  Action of equal forces acting away from each other
• Compression


  Action of oppositely directed forces acting towards each other at the same time
• Shear


  Action of coinciding and oppositely directed forces acting parallel to each other across a surface
• Tectonic stresses are a result of internal energy that deforms the Mantle and Crust, bending rocks (ductile strain) and breaking rocks (brittle strain), leading to movements along faults and earthquakes
• Geologic responses to stress include ductile deformation occurring deeper and with higher temperatures, and brittle deformation occurring shallower and with cooler temperatures
• Types of stress rocks undergo

  • Extension or tension (pulling apart)
  • Compression (pushing together)
  • Shearing or twisting (one portion in one direction, the other portion in another direction)
• Ductile Deformation products

  • Anticline - upwarping of rocks to produce an "A-like" structure
  • Syncline - downwarping of rocks to produce "spoon-like" structure
  • Dome - three-dimensional anticline resembling an inverted soup bowl
  • Basin - three-dimensional syncline resembling an upright soup bowl
• Brittle Deformation products

  • Joints - rocks fracture, producing a fracture with no offset
  • Faults - rocks fracture, producing a fracture with offset
• Elastic response to stress involves returning to the original state, while Viscous response involves matter's resistance to flow under applied force
• Joints


  Rocks fracture, they can simply crack producing a fracture with no offset
• Faults


  Rocks fracture, they can also crack producing a fracture with offset
• Responses to stress


  • Elastic
  • Viscous
  • Visco-elastic
• Elastic stress


  Matter returns to its original state
• Viscous


  Matter's resistance to flow, applied force causes atomic bonds to break and atomic vacancies to migrate, flow causes permanent (non-recoverable) deformation
• Visco-elastic


  Material has both elastic and viscous properties at the same time
• Brittle Failure


  When elastic stresses exceed the material 'failure' strength, an elasto-dynamic instability nucleates, propagates, and stops, permanent non-recoverable displacement occurs
• Elastic Deformation


  Temporary change in shape or size that is recovered when the deforming force is removed
• Ductile (Plastic) Deformation


  Permanent change in shape or size, undergoes smooth and continuous plastic deformation under stress, does NOT recover original shape
• Brittle Deformation (Rupture)


  Applied force is increased, the rock undergoes little change until it suddenly breaks along zones of weakness
• Rheology


  The study of the relationship between stress and strain in deforming materials