CIEN 203_L3 Plate Tectonics

Plate Tectonics

Learning Objectives

• Apply the scientific method to the hypothesis of continental drift.

• Cite additional evidence for plate tectonics.

• Discuss interactions of different plates and their relation to volcanoes and earthquakes.

• Name tectonic features specific to the Philippines.

Review: Layers of the Earth

• Earth's Structural Layers

  • Lithosphere: Rigid layer including the crust and uppermost mantle.

  • Asthenosphere: Plastic layer beneath the lithosphere.

  • Mesosphere: Rigid part of the mantle extending to about 2885 km.

  • Outer Core: Liquid layer composed mainly of iron and nickel (~5155 km)

  • Inner Core: Solid part of the Earth (~6371 km)

Topic Outline

I. Continental Drift HypothesisII. Seafloor SpreadingIII. Additional Evidence for Plate MotionIV. Plate Tectonics TheoryV. Types of Plate BoundariesVI. Mechanisms of Plate MotionsVII. Tectonic Features of the Philippines

I. Continental Drift Hypothesis

• Alfred Wegener: German meteorologist and geophysicist; proposed the concept of Pangaea (~200 million years ago).

  • Pangaea: Supercontinent meaning "all land."

    • Laurasia: North America, Europe, Asia.

    • Gondwanaland: South America, Africa, India, Australia, Antarctica.

  • Panthalassa: The ocean that surrounded Pangaea. “all sea”

Evidence Supporting Continental Drift

• Continental Jigsaw Puzzle Fit:

  • Africa and South America align if the Atlantic Ocean were closed.

• Fossil Matches Across Continents:

  • Mesosaurus, Glossopteris, and Lystrosaurus fossils found across separated continents indicating they could not have crossed oceans.

• Rock Type and Geologic Features:

  • Similar geological formations (e.g., Appalachian-Caledonian Mountains).

• Paleoclimate Evidence:

  • Presence of coal seams from tropical trees in northern regions, and glacial deposits in warm regions like southern Africa and South America.

Opposition to the Hypothesis

• Questions remained regarding the mechanism for continental movement (e.g., theory of tides, oceanic crust displacement).

II. Seafloor Spreading

• Introduced by Harry Hess in the early 1960s, following extensive ocean floor mapping during WWII.

• Features:

  • Submarine volcanoes, mid-oceanic ridges, guyots, seamounts.

• Earth's crust moves away from mid-ocean ridges, forming new material as it does.

III. Additional Evidence for Plate Motion

• Paleomagnetism and Polar Wandering:

  • Magnetite minerals show the direction of magnetic north upon their formation; changes in magnetic orientation were tracked, confirming plate movements.

• Magnetic Reversals:

  • Magnetic strips on the ocean floor, indicating past magnetic field direction.

• Hot Spot Volcanism:

  • Fixed points below the lithosphere that lead to localized volcanic activity; can indicate plate movement based on age of associated volcanoes.

• Seismicity and Plate Boundaries:

  • Distribution of earthquakes varying by depth indicates subduction zones and rifting regions.

IV. Plate Tectonics Theory

• A unifying framework in geology, asserting that the lithosphere consists of tectonic plates that are in constant motion relative to one another.

• Major Tectonic Plates:

  • North American, South American, Pacific, Eurasian, Australian, Indian, Antarctic.

V. Plate Boundaries

Divergent Boundaries (Constructive)

• Plates moving apart, creating new oceanic crust through seafloor spreading centers (e.g., mid-ocean ridges).

Convergent Boundaries (Destructive)

• Plates moving together forming arcs and mountain ranges; can create subduction zones depending on the type of lithosphere involved:

  • Oceanic vs. Oceanic

  • Oceanic vs. Continental

Transform Boundaries (Conservative)

• Plates sliding past one another, creating faults and connecting ridge systems into a uniform structure.

VI. Mechanisms for Plate Motion

• Driven by mantle convection, temperature and density gradients, including ridge push, slab pull, and mantle drag.

VII. Philippine Tectonics

• Volcanism:

  • Located in the Pacific Ring of Fire; approximately 25 active volcanoes.

• Earthquakes:

  • Occur throughout the country, particularly with exceptions in Palawan; major causes linked to plate interactions.

• Tectonic Plates involved:

  • Eurasian Plate, Philippine Mobile Belt, and Philippine Sea Plate.

• Trenches:

  • Major trenches present include Manila Trench, Negros Trench, Cotobato Trench, Sulu Trench, and East Luzon Trough, reflecting significant tectonic activity.