EESC Tectonic plates

Principles of the Theory of Tectonic Plates- (Guaranteed to be on the exam)

  1. The lithosphere is broken into numerous plates

  2. These plates move on top of the underlying asthenosphere

  3. sea

  4. The plates interact at plate boundaries, generating geologic activity

  5. the geologic activity is concentrated at plate boundaries

Types of Plate Boundaries

  1. Divergent boundary- two plates move away from each other

  2. Convergent boundary- two plates collide

  3. Transform boundary-two plates slide past each other

Continental Margins

Defined as the region where land meets the ocean

  • two types of margines

  • Active continental margins: Associated with active tectonic boundary

  • Passive Margins: NOT Associated with active tectonic boundary

Passive-margin continental crust thins out seaward

  1. transitions into oceanic crust

  2. develops a wide continental shelf

Convergent plate boundaries

Subduction Zones

  • Convergent plate boundaries where an oceanic convergent plate dives back into the mantle (Subduction")

  • Oceanic crust is destroyed and recycled back into the earth

  • Two Types: Continental vs oceanic lithosphere, oceanic vs oceanic

  • Continental vs oceanic: Oceanic subducts every time because of proper density. Continental is too buoyant.

  • Oceanic vs. Oceanic: Whoever is even a little slightly denser will subduct. Older will subduct under younger plates.

  • Subducting plate: Plate that subducts

  • Overriding Plate: Plate that does not subduct

  • Feature of Subduction Zones:

  • Trenches- Point where Oceanic crust bends and subducts (deepest part of the ocean and arc shaped)

  • Volcanic Mountain chains or Arcs

  • Continental Volcanic Arcs—Chain of volcanoes forming on the continental crust

  • Island Arcs—chain of volcanic islands forming on the oceanic crust

Continental Collision Zones

  • When two continental plates collide

  • nothing subducts, continental crust thickens and creates mountains

  • Ex. The himalayas

Divergent Plate Boundaries

  • Oceanic lithospheric plates move away from each other

  • Sea floor spreading occurs between plates

  • Sea floor spreading is responsible for the generation of newe oceanic crust and new oceanic lithosphere

  • generates new oceanic lithosphere

  • Commonly referred to as “Mid ocean Ridges” (MOR)

Mid-Ocean Ridges

  • MOR — Associated with and represent divergent boundaries

  • ridges are underwater mountain ranges

  • not a gap but a series of vertical cracks in rock

  • mid ocean ridges represent the plate boundary where two plates move away from each other

Seafloor Spreading Process

  • something that occurs at divergent plate boundaries

  • process by which new oceanic crust is created at MOR, creating and widening ocean basins

  • Asthenosphere rises at MOR, partially melts, rises at where the lithosphere is thinnest (Which is at MOR’s)

  • Normally a solid, as asthenosphere rises the pressure decreases which allows it to melt.

  • resulting magma rises as a mush of crystals and magma

  • magma erupts along fractures at the mid ocean ridge

  • lava cools, adding material to each plate

  • new oceanic crust is created, then spreads away from the boundary

Evolution of Ocean Basins

  • Continued sea floor spreading cause ocean basins to widen

  • lithosphere ages and cools with distance from the MOR

  • Aging oceanic lithosphere “sits” lower on the asthenosphere= deep abyss

  • Younger lithosphere at MOR “sits” higher on the asthenosphere= mountain range

Continental rifting

  • when continental lithosphere stretches This causes:

  • The lithosphere to thin, but elongate

  • this results in a widening rift basin

  • causes fault and earthquakes

  • The underlying asthenosphere to rise = Magma forms

  • this generates volcanoes with the basin

  • Not technically a plate boundary b/c its still one plate

  • Once the continental plate splits into two separate plates, continental rifting is complete

Transform Plate Boundaries

Lithospheric Plates slide past each other

Nothing is created or destroyed

Characterized by: Earthquakes, lack of volcanism

Two types: Oceanic and continental

Oceanic Transform Boundaries

  • Most abundant type of transform boundary

  • Segments MOR

Oceanic Transform faults

  • Active zone of faulting is in between MOR segments

  • Earthquakes occur here

  • Beyond the MOR segments, there is no fault motion

  • An inactive fracture zone forms

Continental Transform boundaries

  • Continental transforms—cut through continental crust