Magma differentiation

Magma differentiation

The formation of secondary magmas from a single parent magma

Which minerals melt first?

Minerals with higher silica content

Slow cooling magma

Gabbro

Fast cooling magma

Basalt

What happens to the composition of the melt over time?

Becomes more silicic as minerals with higher silica melt off first

Fractional crystallisation - stage 1

As olivine, augite and Ca rich Plagioclase form at high temperatures, the magma becomes depleted in iron, magnesium and calcium

What is the remaining liquid rich in? (fractional crystallisation stage 2)

Silica, potassium, sodium and hot watery fluids

Gravity settling

Early formed crystal sink to the base of the chamber to form a cumulate layer

Filter Pressing

The weight of the crystals presses on the liquid and forces it upwards

Magmatic segregation

Magmas of different compositions are immiscible

How to mix 2 immiscible magmas?

Need a strong stirring mechanism to create intermediate magma, eg. convection currents

Enclaves and Xenoliths

Incomplete magma mixing. Bits of igneous rock different to the surrounding rock