Geol 11

• Neptunism proposed that all rocks come from deposition from a primordial ocean
• Before Plate Tectonics, there was no coherent theory to explain the Earth’s structure and processes
• The highest point on the Earth’s surface is Mount Everest, 8,848m (29,030 ft.) high
• Continental Drift Theory states that Pangea broke off into two large masses, Laurasia and Gondwanaland, with the Tethys Sea separating them
• Seafloor Spreading

  1. Discovery of Oceanic Ridge System

  2. New crust creation via convection in the mantle pushing old crust away

  3. No oceanic crust is older than 200 mya
• Continental Drift Theory was proposed by Alfred Wegener in a series of papers from 1910-1928
• Continental Drift Theory was rejected due to the inability to explain a credible mechanism for the continental drift
• Rocks with increasing age point to pole locations
• Theories before Plate Tectonics

  • Neptunism
  • Plutonism
• Plutonism proposed that all rocks are formed by igneous processes (crystallization from magma)
• Continental Drift Theory suggests that continents were once a single large mass (Pangea) surrounded by a large ocean (Panthalassa)
• The deepest part of the ocean, the Marianas Trench, is 11,033m (36,199 ft.) deep
• Evidences supporting Continental Drift Theory

  1. Fit of the continents

  2. Fossil evidence

  3. Similar lithologies across continents

  4. Paleoclimate
• Paleomagnetism


  Record of magnetic field throughout time
• Harry Hess theorized how continents drift via seafloor spreading
• Volcanic rocks usually contain magnetite (iron-bearing mineral)
• Paleomagnetism


  Record of the magnetic field throughout time
• Earth has more than one magnetic pole at various times
• Plate Tectonics was brought together in 1968 based on evidences presented from continental drift theory, seafloor spreading, and paleomagnetic evidences
• Earth’s lithosphere is made up of moderately rigid plates consisting of continental, oceanic, or a combination of both
• Plate boundaries can move a few centimeters a year
• 8 minor plates

  • Philippine Sea Plate, Nazca Plate, Cocos Plate, Caribbean Plate, Arabian Plate, Scotia Plate, Indian Plate, Juan de Fuca Plate
• Apparent Polar Wandering


  1. A moving continent retains a record of changing paleomagnetic directions through time that reflect the changing orientations and distances to the pole

  2. The resulting path of observed pole positions is called an “apparent polar wander path” or APWP
• Divergent Boundary

  1. Constructive Plate Boundary: new crust is created in the mid-oceanic ridge and pushes older crust away

  2. Continental Rift

  3. Mid-Ocean Ridge
• Hotspot Volcanism: Formation of Hawaii from a mantle plume, creating chains of volcanic islands due to plate movement
• Earthquakes were used to map the plate boundaries
• Curie Temperature


  Temperature where magnetic minerals change magnetic behavior
• Rocks with increasing age point to pole locations increasingly far from present magnetic pole positions
• The continents moved relative to each other over time
• Plate Tectonics is a unifying theory of geology as it explains how geologic processes and features on Earth are closely related
• North is determined by the angle of the earth’s axis (located 11.5 degrees away from true north)
• Magnetic Reversals as Evidence to Seafloor Spreading

  1. Geomagnetic Reversal - shifting of the pole’s polarity over time

  2. Happens every 300,000 years (last reversal happened 770,000 years ago)

  3. New crust created in oceanic ridges records this reversal in polarities throughout geologic time
• 7 major plates

  • Eurasian, Australian, Pacific, North American, South American, African
• Convergent Boundary

  1. Destructive Plate Boundary

  2. Ocean-Continent Convergent Boundary

  3. Ocean-Ocean Convergent Boundary

  4. Continent-Continent Convergent Boundary
• Tectonic Plate


  Slabs of rock that the continents and oceans rest on, consisting of the crust and the uppermost mantle
• Distribution of volcanoes has a strong connection with plate boundaries (Pacific Ring of Fire)
• Global Positioning System (GPS) data tracks plate motions by satellites, radars, and lasers from different areas
• Transform Plate Boundary

  Conservative Plate boundary
• Philippine Mobile Belt formed by the collision of at least three plates (Sunda Plate, Philippine Plate, Indo-Australian Plate, and Eurasian Plate)
• Formation of Hawaii

  1. Created from mantle plume, stationary and semi-permanent source of magma

  2. Created chains of volcanic islands due to plate movement