10.3 Plate Tectonics By: Brendan, Sid, and Andy

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Volcanoes  There are 800 volcanoes worldwide that are un-identified  The main group of volcanoes are around the “Ring of Fire” near the pacific boundary  Another group is Intraplate Volcanism-based off of how hot the mantle below it is

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Intraplate Volcanism  Intraplate Volcanism is when volcano processes happen in planes and not on the edge of boundaries.  The most widely know one is/is in Hawaii  They’re mantle plumes in the lower mantle that rise due to convection. They come up from a massed area, called a plume head, and go through a long neck like vent called a plume tail

Mantle PLumes  Mantle plumes appear to form deep within Earth at the core-mantle boundary.  Once the plume nears the top of the mantle, decompression melting forms basaltic magma.  Hot spots are the result of this which are small volcanic regions a few hundred kilometers across

Intraplate

Hawaii  Hawaii lies above the mantle plume. The plume and all the volcanoes are currently active  The seven islands are becoming normal like volcanoes  The main phase of volcanoes ended on Oahu 3 million years ago  On Kauai it ended 5 million years ago  The magma that hardens forms the islands that are there today.

Convergent Plate Boundaries  The basic connection between plate tectonics and volcanism is that plate motions provide the mechanisms by which mantle rocks melt to generate magma.  Here, slabs of oceanic crust are pushed down into the mantle. As a slab sinks deeper into the mantle, the increase in temperature and pressure drives water from the oceanic crust.

O-C  When an Ocean boundary is converging with a Continental boundary the ocean will go under and have volcanoes forming what looks like a arc. The difference from these arcs and ocean arcs would be the magma that is formed  The magma would have more silica content making it’s viscosity lower

O-C

O-O  When the two oceanic boundaries converge they will form volcanoes at the ocean floor that will eventually rise up to form normal volcano arcs on the surface of the water.

O-O

CP Boundaries cont. BoundariesExplanation Ocean-Ocean Volcanism at a convergent plate where one oceanic slab descends beneath another results in the formation of a chain of volcanoes on the ocean floor. These volcanic structures grow large enough to rise above the surface and are called volcanic island arcs. Ocean-Continent Volcanism associated with convergent plate boundaries may also develop where slabs of oceanic lithosphere are subducted under continental lithosphere to produce a continental volcanic arc.

Divergent  There is much more magma in divergent boundaries due to the fact that the pressure is so much less than the others and the immense amounts of magma will just flow to the area.

Divergent Plate Boundaries  Most magma is produced along the oceanic ridges during seafloor spreading. Below the ridge axis where the plates are being pulled apart, the solid yet mobile mantle rises upward to fill in the rift where the plates have separated.  The rock undergoes decompression melting, producing large amounts of magma. This newly formed basaltic magma is less dense than the mantle rock from which it was formed, so it buoyantly rises.

Pulls Apart

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