batholiths recognise and describe. these are large igneous bodies that are >100 km 2 in size....
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![Page 1: Batholiths Recognise and describe. These are large igneous bodies that are >100 km 2 in size. They are usually plutonic. Formation: Accumulation of large](https://reader036.vdocuments.net/reader036/viewer/2022072016/56649eeb5503460f94bfd073/html5/thumbnails/1.jpg)
Batholiths
Recognise and describe.These are large igneous bodies that are >100 km2 in size.They are usually plutonic.Formation:Accumulation of large amounts of magma by:Permitted (cauldron subsidence/stoping) orForceful (doming).
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Bosses and Stocks
These are smaller intrusions.
The dictionary definition of a boss is a knob like intrusion.
I couldn’t find a picture
A stock is like a batholith but < 100 km2 .
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Dykes
You know these.
They are small scale intrusions (no more than a few 100 m wide).
They form close to the surface: Hypabyssal.
Dykes are discordant: cut across the beds.
They often force their way along lines of weakness such as faults.
In cross section or a map they will cross cut beds.
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Ring Dykes
These are associated with cauldron subsidence.This is a kind of permitted intrusion.The force of the intrusion causes the rocks above to form a cylindrical fracture.The centre of the cylinder sinks into the magma chamber and magma shoots up the cylindrical fracture to form a ring dyke.On a map they will look circular and cross cutting.
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Cone Sheets
These form inverted cones of dykes.
They are focussed on the magma chamber and then widen upwards.
Successive cone sheets form as the centre of the eruptions moves.
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Sills
You also know these.They are also small scale intrusions (no more than a few 100 m wide).They also form close to the surface: Hypabyssal.Sills are concordant: run parallel to the beds.They often force their way along lines of weakness such as bedding planes.In cross section and map views they run parallel to the beds.
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Transgressive Sills
You also know these.They are also small scale intrusions (no more than a few 100 m wide).They also form close to the surface: Hypabyssal.Transgressive sills are concordant for most of the time but occasionally cut up through the beds before becoming concordant again.
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Transgressive sills 2
They often force their way along lines of weakness such as bedding planes, but will follow a weakness across beds if they find it (often a fault).In cross section and map views they run parallel to the beds for most of the time but will cut across beds briefly.
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Laccoliths
These occur where there is small scale intrusion that has a flat base and a domed top.
These are often fed by “Feeder Dykes”.
The magma forces it’s way along the beds like a sill but will also dome upwards forcing the overlying beds into a dome.