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Zorluk: OrtaEarth's Interior and Plate Tectonics

When an oceanic plate collides with a continental plate at a convergent boundary, the oceanic plate is forced downward into the mantle. Why does the oceanic plate sink beneath the continental plate during this collision?

  1. A
    Continental crust is thinner and denser than oceanic crust, allowing it to displace the underlying oceanic slab.
  2. Oceanic crust is denser and composed primarily of basaltic rock, causing it to sink beneath the less dense granitic continental crust.Cevap
  3. C
    Continental crust is older and cooler, creating downward thermal convection that pulls the oceanic plate into the mantle.
  4. D
    Oceanic crust contains a higher concentration of quartz and silica, which softens at lower temperatures to permit subduction.

Cevap

Oceanic crust is denser and composed primarily of basaltic rock, causing it to sink beneath the less dense granitic continental crust.
The correct answer identifies that subduction occurs because oceanic crust is denser than continental crust. Oceanic lithosphere is primarily mafic (basaltic) with a density of approximately 3.0 g/cm33.0\text{ g/cm}^3, whereas continental lithosphere is primarily felsic (granitic) with a lower density of approximately 2.7 g/cm32.7\text{ g/cm}^3. When compression occurs at a convergent boundary, the heavier oceanic lithosphere sinks into the semi-fluid asthenosphere beneath the more buoyant continental plate.

Adım Adım Çözüm

1
Compare the composition and density of oceanic crust with continental crust.
Oceanic crust consists predominantly of basalt with a density of roughly 3.0 g/cm33.0\text{ g/cm}^3, whereas continental crust consists predominantly of granite with a density of roughly 2.7 g/cm32.7\text{ g/cm}^3.
Relative density governs the buoyancy and physical behavior of tectonic plates upon collision.
2
Apply the principles of isostasy and plate convergence to determine which plate subducts.
Because the basaltic oceanic plate is denser and heavier, gravitational slab pull forces it beneath the more buoyant granitic continental plate and down into the asthenosphere.
At a convergent boundary, the denser plate always subducts beneath the less dense plate.

Anahtar Kavram

Density-driven subduction at convergent plate boundaries
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Earth's Interior and Plate Tectonics

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