Hotspots and Mantle Plumes
The problem of intraplate volcanism
Some volcanoes are isolated in the middle of plates and do not seem to be
at all related to plate boundaries. these volcanoes
Anatomy of a mantle plume.
- Mantle plumes form somewhere deep in the mantle, perhaps as deep
as the core-mantle boundary
- They start as a buildup of heat. The heated material rises
because of its bouyancy
- The material stops rising and begins to accumulate somewhere in the
asthenosphere because of similar bouyancy.
- basaltic magma is derived from the spreading plume through the process
of partial melting.
- Eventually the magma makes its way to the surface.
Volcanic Activity Associated with a Mantle Plume
Under Oceanic Crust
- Plume spreads at the asthenosphere - lithosphere boundary
- Plume produces basaltic magma by partial melting
- Basaltic magma rises by bouyancy to ocean floor.
- Volcano formed by basaltic eruptions
- Plate moves but plume stays in the same place
- New volcano formed by same process.
- Chain of volcanos formed getting progressively older away from the
current plume.
Under Continental Crust
- Plume spreads at the asthenosphere - lithosphere boundary
- Plume produces basaltic magma by partial melting
- Basaltic magma rises by bouyancy to the base of continental crust
- Basalt forms pools at base of continental crust
- Continental crust melts to form granitic magma
- Large magma chambers accumulate below surface
- eruptions release large amounts of lava forming rhyolite flows and
pyroclastics
- emptied magma chambers may form large calderas
- basaltic magma pool eventually seeps upward through fractures forming
dikes and filling up calderas
- leaves a trail of progressively older rhyolite flows covered by basalt
flows with active rhyolite flow above mantle plume.
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