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Batholiths Recognise and describe.

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Presentation on theme: "Batholiths Recognise and describe."— Presentation transcript:

1 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) or Forceful (doming).

2 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 .

3 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.

4 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.

5 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.

6 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.

7 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.

8 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.

9 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.


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