Creation of new lithosphere and destruction of old

• Spreading centers and subduction zones
• Arc-trench systems of the world
• Locations of the highest and deepest parts of the earth

Plate Margins- Divergent, Convergent and Transform

• Divergent Margins (Spreading Center)
  • Oceanic: Mid-Atlantic Ridge etc
    Vocanism, Shallow Earthquakes
  • Continental: East African Rift Valley, etc
    Volcanism, earthquakes and lakes
• Convergent Margins (Subduction)
  Formation of trenches on the Ocean floor
  • Ocean - Ocean collision
    Island- arcs on the ocean floor- Japan
  • Ocean - Continent collision
    Trench at continental edge
    Vocanic arcs on the continental edge-Andes
  • Continent - Continent collision
    No trench or subduction
    Uplift, magmatism, faulting and earthquakes
    Formation of great Mtn. Chains on land-The Himalayas
• Transform Margins - San Andreas Fault
  Earthquakes
  No volcanism

Initiation of the Plate Tectonic cycle

Intra-Plate volcanism

• Hot-Spots (Mantle Plumes)
  Fixed with respect to plate motions
  Examples:
  • Hawaiian volcanic chain
  • Iceland
  • Yellowstone
  Origin of mantle plumes

Plate boundaries most active sites of deformation

• Earthquakes- contrasts between ridges and subduction zones
• shallow and deep focus earth quake mechanisms
• Volcanic activity - the Ring of Fire
• Three Zones of volcanism - two at plate margins and one intraplate

Mountain Building

• Volcanic arcs in continental regions
• Island arcs in the ocean basins
• Accretion of exotic blocks

Driving mechanisms- the cause of Plate Tectonics

• Convective motions-pushing lithospheric plates apart
• Cold dense lithosphere sinking and pull of slab
• gravity sliding
• Push by rising plumes

Reconstruction of position of continents through time

• Pangea at ~200 million years ago
• Breakup and motions at 180 million years ago
  • Laurasia and Gondwana land
  • Ridge system between N. Amer and Africa
  • Birth of the Atlantic
  • Northward motion of Africa and India
  • Ridge system between Antarctica and northen part of Gondwana land
  • Antarctica and Australia together in one piece
• Motions about 135 million years ago
  • Splitting of Africa and South America
  • Birth of the South Atlantic
• Motions 65 million years ago
  • Full fledged Atlantic ocean
  • Break up of Madagascar from Africa
  • Rift system south of Africa and break up of Australia from Antarctica
• Current configuration

The fate of downgoing lithospheric slabs

• Evidence from deep focus earth quakes
• Mixing of slabs in the lower mantle
• Slabs all the way to the core mantle boundary

Plate Tectonics - a giant recycling system and a new paradigm

Is it real: Evidence from direct measurements
Satellite Laser Ranging (SLR) techniques