Plate Tectonics

• Before plate tectonics:

  • no coherent theory to explain Earth’s structure and processes

  • Neptunism – all rocks come from deposition from a primordial ocean

  • Plutonism – all rocks are formed by igneous processes (crystallization from magma)
• Highest point on the earth's surface ( 8,848 m)- Mt. Everest

  Deepest part of the ocean ( 11,033 m)- Mariana Trench
• Continental Drift Theory

  • proposed by Alfred Wegener
  • continents were once a single large mass together (Pangaea) surrounded by a large ocean (Panthalassa)
• Continental Drift Theory

  • Pangaea then broke off into two large mass the northern Laurasia and the southern Gondwanaland with the Tethys Sea separating the two. Continuous drifting lead the land mass into continents we have at present.
• Continental Drift Theory: Evidences

  1. Fit of the continents
  2. Fossil Evidences
  3. Similar Lithologies (rock types) across continents
  4. Paleoclimate
• Evidences of Continental Drift Theory

  Fit of the continents

  -coastlines and continental shelves fit perfectly especially the continents of South America and Africa
• Evidences of Continental Drift Theory

  
  

  Fossil Evidence

  • Glossopteris (a fern fossil) found in 5 continent (Gondwanaland continents); immobile and grows in certain temperature and environment
  • Cynognathus (land therapsids) and Mesosaurus (freshwater alligator-like reptile) were found in Africa and South America. Both are land-dominant animals that are
  • Lystrosaurus (land-dwelling herbivore) found in Africa, India, and Antarctica. Its build would have the swimming capability to traverse oceans.
• Evidences of Continental Drift Theory

  
  

  Similar lithologies (rock types) across continents

  • Rock and geologic structures found in one continent close match rocks found in distant continents
  • Appalachian Mountains (N. America) and Caledonian Mountains (Europe)
  • Cape Fold Belt (Africa) and igneous formation (S. America)
• Evidences of Continental Drift Theory

  Paleoclimate

  • Glacial deposits found in warm climate continents (South America, India, South Africa, Australia, Antarctica)
  • Tropical plants and coal deposit found in frozen regions (Canada, Arctic, Europe and Asia)
• Why was continental drift theory rejected?

  Wegener was not able to explain credible mechanism for the continental drift.

  • he used the Sun and moon's gravitational forces to explain the gradual movement of the continents (not strong enough)
• Seafloor Spreading

  • Oceanographers were equipped with new marine tools and funding for oceanographic exploration
  • Discovery of OCEANIC RIDGE SYSTEM
  • Oceanic crust near these ridge systems were found to be younger
• Seafloor Spreading

  • New crust are being created in this ridge system, via convection in the mantle, pushing old crust away
  • No oceanic crust is older than 200 mya (oldest continental crust is 4.5 bya)
  • Harry Hess theorized how continents drift via seafloor spreading
• Paleomagnetism (remnant magnetism)

  • magnetic field is created by the geodynamo
  • magnetic north is determined by angle of the earth's axis (located 11.5 degrees away from true north)
  • volcanic rocks usually contains magnetite (iron-bearing mineral)
  • Curie Temperature -temperature where magnetic minerals change magnetic behavior
• Paleomagnetism- record of magnetic field throughout time

  • It was discovered that rocks with increasing age point to pole locations increasingly far from present magnetic pole positions.
  • • Earth has more than one magnetic pole at various times
  • • The continents moved relative to each other over time
• Paleomagnetism

  Apparent Polar Wandering

  • A moving continent will retain a record of changing paleomagnetic directions through time that reflect the changing orientations and distances to the pole (which is held fixed).
  • The resulting path of observed pole positions is called an “apparent polar wander path” or APWP
• Paleomagnetism

  Magnetic Reversals as evidence to seafloor spreading

  • Geomagnetic Reversal - shifting of the pole’s polarity over time (the north magnetic pole becomes the south magnetic pole and vice versa)
  • happens every 300, 000 years (last reversal happened 770, 000 years ago)
  • new crust created in oceanic ridges records this reversal in polarities throughout geologic time
• What is the unifying Theory of Geology as it tries to explain how geologic processes and features on Earth are closely related?

  Plate Tectonics
• Plate Tectonics

  • brought together in 1968 based on evidences presented from continental drift theory, seafloor spreading, and paleomagnetic evidences
• Identify the seven major plates.

  A) North America

  B) Eurasia

  C) Pacific

  D) South America

  E) Africa

  F) Antarctic

  G) Australia

  
• Identify the 8 minor plates

  A) Juan de Fuca

  B) Cocos

  C) Caribbean

  D) Arabian

  E) Indian

  F) Scotia

  G) Philippine sea

  H) Nazca

  
• Tectonic Plate

  • are slabs of rock, or PLATES, that the continents and oceans rests on
  • also called lithospheric plate because it consists of the crust and the uppermost mantle
  • these plates can move few centimeters a year (1 cm/yr to 17 cm/yr)
• Plate Boundaries:

  • Convergent boundary -plates collide with each other
  • Divergent boundary -plates separate from each other
  • Transform boundary -plates slide from each other
• Convergent Boundary

  • aka Destructive Plate Boundary
  • Ocean-Continent Convergent boundary: Andes Mountains (Nazca Plate – South American Plate) "AnSA"
  • Ocean-Ocean Convergent Boundary: Philippine Island Arc (Philippine Sea Plate – Eurasian Plate) "psE"
  • Continent-Continent Convergent Boundary: Himalayan Mountain Ranges (Indian Plate – Eurasian Plate) "iE"
• Divergent Boundary

  • Constructive Plate Boundary: new crust is created in the mid-oceanic ridge and pushes older crust away
  • Continental Rift : African Rift Valley "CRARV"
  • Mid-Ocean Ridge : Mid-Atlantic Ridge "MORMAR"
• Transform Plate Boundary

  • AKA Conservative Plate Boundary
  • San Andreas Fault (Pacific Plate – North American Plate) "SAPNA"
• Plate Tectonics

  • Earthquakes were used to map the plate boundaries

  • Distribution of volcanoes have also strong connection with plate boundaries (Pacific Ring of Fire)
• Additional evidences on Plate
• Additional evidences on Plate Tectonics

  Hotspot Volcanism

  • formation of Hawai'i
  • created from mantle plume, stationary and semi-permanent source of magma
  • created chains of volcanic islands due to plate movement
• Additional evidences on Plate Tectonics

  Global Positioning System (GPS) data

  • plate motions are tracked by satelites, radars, and laser, from different areas
  • different rates of movement from each plate
  • Pacific Plate - fastest 10 cm/yr
  • Antarctic Plate - slowest 1 cm/ yr
• John Tuzo Wilson

  1. advanced the Plate Tectonics Theory
  2. Concept of stationary hotspot (Hawai’i)
  3. Proposed transform boundary as the third type of plate boundary
  4. Proposed the Wilson Cycle
• How does the plates move

  • the asthenosphere is partially molten and has plastic properties allowing the lithosphere to move over it
  • it is driven by heat escaping from the mantle
  • constant movement of heat in the mantle leads to circular convection currents
  • convection occurs due to uneven heating and different densities of materials within the liquid
• Theories on how the plates move:

  1. ridge-push/ slab-pull
  2. one layer convection
  3. two-layer convection
• Philippine Tectonics

  Philippines can be divided into two distinct terranes

  1. Philippine Mobile Belt
  2. Palawan Microcontinental Block
• Palawan (Micro)continental Block (PCB)

  • originally from mainland Asia that drifted away due to opening of the South China Sea (33 mya)
  • includes Palawan, Panay Island and Mindoro (parts of Zamboanga, and Romblon)
  • contains the oldest rocks in the Philippines
• Identify the Philippine geological features

  A) Sundaland Plate

  B) South China Sea

  C) PCB

  D) PMB

  E) Sulu Sea

  F) Sulu-Negros Trench

  G) Celebes Sea

  H) Cotabato Trench

  I) Philippine Trench

  J) Philippine sea plate

  K) Manila Trench

  L) East Luzon Trough

  
• Philippine Mobile Belt (PMB)

  • formed by the collision of at least three plates (Sunda Plate, Philippine Sea Plate, Indo-Australian Plate, and Eurasian Plate)
  • Most of the islands formed at various points (Northern islands formed 50 mya)
• Subduction Zones – The Philippines is surrounded by subduction zones resulting in actively-deforming PMB

  • Manila Trench - SCS oceanic trench subducts into the Manila Trench creating the West Luzon Arc
  • Negros Trench – subduction of the Sulu Sea Basin (Kanlaon)
  • Sulu Trench - subduction of the Sulu Sea Basin at different orientation (Sulu-Zamboanga Arc)
  • Cotabato Trench- formation of Cotabato Arc (Matutom and Parker)
• Subduction Zones (Eastern part)

  • East Luzon Trough - ancient subduction zone with no associated volcanic arc
  • Philippine Trench - longest trench that is 250 km long and propagates to the south. It is relatively young (5 Ma). Responsible for the Bicol-Leyte volcanic Arc (Mayon, Bulusan, Iriga)
• Philippine Fault

  • longest fault in the Philippines that traverses the entire length of the archipelago.
  • it is relatively young (not greater than 5 Ma).
  • It is generally a left lateral fault that functions in a shear partitioning environment whereby it accommodates a component of the oblique convergence between the PSP and Philippine archipelago
• Philippine Seas

  1. West Philippine Sea
  2. Philippine Sea
  3. Sulu Sea
  4. Celebes Sea