Intrusive features

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Batholiths

  • Largest intrusive features
  • commonly created in the process of orogeny due to high silica so gets **** when the crust thickens and pushes it down
  • typically made from Granite - high silica, large crystals, coarse grained igneous rock
  • often dome shaped
  • can reach 100km across
  • usually discordant
  • several plutons make a batholith
  • need large amounts of Magma
  • country rocks are altered into metamorphic aureole

Example - Donegal Ireland

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Sills

Horizontal along the bedding planes of sedimentary rock

  • vertical cooling cracks
  • dolerite rocks
  • contact metamorphism
  • vary in thickness from 1-20km across

Example - Whin Sill Northermberland

  • Dolerite 300 years ago
  • 70m  maximum thickness
  • crustal extenson occured between layers of country rock
  • Right across Northumberland from Bamburgh
  • rock is highly resistant so surrounding sedimentary rock has a eroded away to reveal striking landforms

 - sea cliffs at Bamburgh castle, waterfalls at high tees,  bold escarpement such as those on hadrians wall where it was built

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Dykes

Disocordant vertical new walls of intrusive igenous rock

magma forced up along cracks to force the intrustion into other cracks which opens new cracks due to high pressure within the rocks - this can produce many dykes - called a dyke swarm

they cut through layers instead of sills that go inbetween

contact metamorphism with other country rocks

basalctic or dolerite

can form rock walls when eroded

E.g Kildonan dyke swarm, Isle of Arran

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Volcanic plugs

much closer to the surface than other intrusive features

if a volcano has very viscous silica rich lava it can clog up the vent of a volcano which creates a plug of magma which solidifies and blocks the vent

its a clyinldracl pillar of resistant rock

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