Intrusive Activity

Chapter 18.2

• Molten Magma is less dense than surrounding rocks.

• This forces magma to move upward intrude into, the overlying crust.

Intrusive ActivityA. Magma can force the overlying rock apart and enter the

newly formed fissures.

B. Magma can also cause blocks of rock to break off and sink into the magma, where the rocks may eventually melt.

C. Magma can melt the rock into which it intrudes.

Plutons• Plutons are

intrusive igneous rock bodies that can be exposed at Earth’s surface as a result of uplift and erosion and are classified based on their size, shape, and relationship to surrounding rocks.

Plutons

Batholiths

– Batholiths, the largest plutons, are irregularly shaped masses of coarse-grained igneous rocks covering at least 100 km2 and take millions of years to form.

BatholithsThe Sierra Nevada and San Gabriel

mountains are large Batholiths

Stocks

– Stocks are irregularly shaped plutons that are similar to batholiths but smaller in size.

Laccoliths– A laccolith is a mushroom-shaped pluton with a round top and flat bottom

resulting from a Magma intrusion into parallel rock layers close to Earth’s surface.

Laccoliths

– A sill is a pluton, ranging from only a few centimeters to hundreds of meters in thickness, that forms when magma intrudes parallel to layers of rock.

Sills

Sills

• Glacier Park in PreCambrian rocks

– A dike is a pluton, ranging from a few centimeters to several meters wide and up to tens of kilometers long, that cuts across preexisting rocks.

Dikes

Dikes

Dikes• Sierra Nevada

Dike Near Shiprock NM

Dike Near Shiprock NM

Dike Near Shiprock NM