Lecture 4 PPT

Zones of Volcanism

  • Major tectonic plates involved in volcanism:

    • Juan De Fuca Plate
    • Cocos Plate
    • Pacific Plate
    • East Pacific Rise
    • Eurasian Plate
    • North American Plate
    • Nazca Plate
    • South American Plate
    • Antarctic Plate
    • African Plate
    • Indian-Australian Plate

  • Types of plate boundaries explored:

    • Divergent boundaries (e.g., Mid-Atlantic Ridge)
    • Convergent boundaries (subduction zones)
    • Transform boundaries

Where do Volcanoes Form?

  • Primary formation correlation: MAGMA = VOLCANOES!!!

How is Magma Generated?

  • Key points:
    • Magma is most commonly generated at plate boundaries or hot spots (Primary Focus of this lecture).
    • Melting occurs at the upper mantle where temperatures allow for partial melting of the mantle's solid material.
    • Notably, the mantle itself is completely solid and not hot enough to melt entirely; hence:
    • Partial melting: A small fraction of the solid melts while retaining parts of the original solid material.
    • The process is slow and gradual.
    • The composition of magma resulting from partial melting differs from that of the solid that was melted.
  • Diagram explanation:
    • The lithosphere and asthenosphere extend primarily for the first 660 km; this is where magma generation predominantly occurs in the upper mantle.

Volcanism at Divergent Plate Boundaries

  • Formation Process: Ceases when tectonic plates diverge (pull apart), facilitating upwelling and melting within the mantle.
  • Magma Movement: It rises through the crust and erupts onto the surface.
  • Volcanic formations: Often appear as a linear chain parallel to the rift valley or ridge.
  • Generalizations:
    • Oceanic Divergent Example: Mid-Atlantic Ridge or Iceland
    • Lava Composition: Mafic lavas
    • Dominant Rock: Basalt
    • Eruption Style: Effusive (peaceful)
    • Melting Mechanism: Decompression melting
    • Origin of Magma: Upper mantle
    • Continental Divergent Example: East African Rift
      • Lava Composition: Felsic lavas
      • Rocks: Rhyolite, pumice, obsidian, tuffs
      • Eruption Style: Explosive (violent)
      • Melting Mechanism: Decompression melting
      • Origin of Magma: Upper mantle

O-O and O-C Convergent Zone of Volcanism

  • Pacific Ring of Fire Overview:

    • Major tectonic plates involved:

    • Eurasian Plate

    • Pacific Plate and Juan De Fuca Plate

    • North American Plate

    • Caribbean Plate

    • Major volcanoes and volcanic regions include:

    • Aleutian Islands

    • Rainier

    • St. Helens

    • Kilauea

    • Merapi, Taal (Philippines)

    • Mayon, Krakatoa, etc.

  • Formation Process:

    • When oceanic crust subducts beneath continental crust, the mantle melts to generate magma.
    • Resulting magma rises and erupts through the continental crust, creating a chain of arc-shaped volcanoes that parallel the trench.
    • Characteristics of Generalizations on Convergent Plate Boundary Volcanism:
    • Lava Composition: Intermediate and Felsic lavas
    • Rock Types: Andesite, rhyolite, pumice, tuffs
    • Eruption Style: Explosive
    • Melting Mechanism: Flux melting
    • Origin of Magma: Upper mantle

Does Volcanism Only Occur at Plate Boundaries?

  • Notable examples of volcanism outside plate boundaries:
    • Craters of the Moon, Idaho
    • Mauna Loa, Hawaii
    • Inyo Craters, Long Valley Caldera
    • Columbia River Gorge
    • Yellowstone National Park

Intraplate Volcanism

  • Overview of hotspots and intraplate volcanism.

    • Mechanism of hot spot volcanism involves a rising mantle plume beneath tectonic plates.

    • Formation Process: As tectonic plates move over the hotspot, magma formed from the plume rises through the crust and erupts at the surface.

    • Intraplate Volcanism Characteristics:

    • Oceanic Crust Example: Hawaii

      • Lava Composition: Mafic lavas
      • Rock Types: Basalt
      • Eruption Style: Effusive eruptions
      • Melting Mechanism: Decompression melting
      • Origin of Magma: Mantle plume

    • Continental Crust Example: Yellowstone

      • Lava Composition: Felsic lavas
      • Rock Types: Rhyolite, pumice, obsidian, tuffs
      • Eruption Style: Extremely explosive (supervolcano)
      • Melting Mechanism: Decompression melting

  • Diagram Explanation: Illustrative representation of hot spots and their relation to plate movements and formations of volcanic islands.

Hot Spot Examples

  • Specific instances of hot spot volcanism in oceanic regions:

    • Midway Islands, Kauai, Molokai, Maui, Oahu, Hawaii
    • Each island varies in age specific to tectonic plate motion, with the youngest at Hawaii moving towards older locations like Midway (e.g., ages range from present to millions of years).

  • Specific examples by region:

    • Columbia River Basalts, Yellowstone NP (detailed volcanic ages are mentioned).

  • All distinctions rest on the interplay of crustal composition (oceanic vs continental) and magmatic behaviors depending on the position of tectonic plates above mantle plumes, leading to varied eruption styles.