Plate Tectonics

• Lithosphere 

  • Crust and uppermost mantle 
  • Rigid
• Asthenosphere

  • relatively weak
• Continental drift hypothesis

  • Alfred Wegener
  • German meteorologist and geophysicist
  • The origin of continents and oceans; Pangaea
  • Pangaea = "all land” 
  • Laurasia: North America, Europe and Asia
  • Gondwanaland: South America, Africa, India, Australia, and Antartica 
  • Panthalassa - “all sea” 
• Evidence of the Continental Drift Hypothesis

  • Continental jigsaw puzzle fit
  • Africa and South America fit if Atlantic Ocean is closed
  • Fossil match across continents
  • Fossils of animals and plants that could not have traveled through the oceans: Mesosaurus, Glossopteris, and Lystrosaurus
  • rock type and geologic features
  • Similarities across continents (e.g., Appalachian-Caledonian Mountains)
  • Paleoclimatic evidence
  • Coal seams in Northern Hemisphere with tropical trees
  • Glacial till and striations in Southern Africa, South America, Australia, and India
• Opposition for the CDH

  • no explanation for the mechanism for such movement
  • According to Wegener
  • suggested that it was moving because of tidal waves, continents broke through oceanic crust
• Seafloor Spreading

  • Introduced by Harry Hess in the early 1960s
  • Extensive mapping of the ocean floor during the WW II
  • Submarine volcanoes: mid-oceanic ridges (longest chain of volcanoes), guyots, and seamounts
  • Earth’s crust is moving away from MORs (mid-oceanic ridges)
  • New material is being formed along MORs
• Where do old materials go?

  - Gets melted as it goes further down (trenches)

  - It will be reworked in the mantle
• Additional Evidence for Plate Motion

  • Paleomagnetism and polar wandering 
  • Magnetic Reversals
  • Hot spot volcanism
  • Seismicity and plate boundaries
• Paleomagnetism

  • Old magnetism of the earth
  • ‘Paleo’ = old
  • The compass will point to the North Pole
• Polar wandering 

  • Pertains to the North Pole moving
• Paleomagnetism and polar wandering

  • uses curie point - T at which a minerals magnetic properties change (e.g., magnetite 585C)
  • small magnetite minerals point to the magnetic north during their birth (Paleomagnetism)
• Magnetic Reversals 

  • Magnetic strips on the ocean floor 
  • Magnetic minerals will point to the north or South Pole 
  • These strips move 
• Hot spot volcanism 

  • Localized; long-lasting hot regions below the lithosphere
  • Frame of reference for tracking plate motion 
  • Age of volcanism corresponds to the time elapsed since it was on top for the hotspot/mantle plume 
  • The lithosphere moves (bc of volcanos), while the asthenosphere stays in place 
• Seismicity and plate boundaries

  • Deep earthquakes (>150km): location of subjecting slabs
  • Shallow earthquakes: regions rifting 
• Plate Tectonics Theory

  • UNifying theory of geology
  • lithosphere composed of segments (tectonic plates)
  • PLates in constant motion relate to one another
  • Major Plates
  • North American
  • South American
  • Pacific
  • Eurasian
  • Australian
  • Indian
  • Antarctic
  • Minor PLates
  • Philippine Sea Plate
• Plate boundaries - where most movement occurs
• plate boundaries types

  1. divergent
  2. convergent
  3. transform
• Divergent boundaries or constructive 

  • Where two plates move apart creating new oceanic crust as seafloor 
  • Spreading centers: oceanic ridges and continental rifts 
  • The rift widens, eventually forming a valley 
  • It will forms a sea, as it widens even more 
  • Valley --> sea —> oceans 
  • Will become a separate island 
• Convergent boundaries or disruptive boundaries

  • Where two plates move together forming wither arcs or mountain systems 
  • Continental volcanic arc 
  • Continental plate — oceanic plate = subduction 
  • Oceanic will subduct 
  • Forms subduction zones when oceanic lithosphere is involved
  • Orcogenic belts form in continental vs continental plates
  • Orogenic belts — mountain belts 
  • Why is there no subduction? 
  • Both solid, same density 
  • Oceanic — oceanic 
  • The more dense plate will subduct 
  • Density — depends on the age of the crust 
• Transform boundaries or conservative boundaries

  • Where two plates grind past each other 
  • Connects oceanic ridge systems into a continuous networks 
• Philippine Tectonics

  • Volcanism
  • Pacific ring of fire; 25 active volcanoes
  • Earthquakes
  • Everywhere besides Palawan, why?
  • not located in the fault line, it is in another tectonic plate
  • Convergent Plate Boundary
  • Oceanic vs Oceanic (mature island arc): Philippine mobile belt+ Philippine Fault zone
  • Continental vs oceanic: Palawan micro continental block and suture zones
  • Plates
  • eurasian plate, philippine mobile belt, philippine sea plate
  • trenches
  • west - manila trench, negros ternch, cotobato trench, sulut trench
  • east - east luzon trough, philippine trench
• Philippine tectonic plates moves towards the northwest