Igneous processes

Question 1

Platinum group elements

Answer 1

platinum, palladium, indium, osmium, rhodium, ruthenium

Question 2

Chalcophile

Answer 2

Elements combine more readily with sulphur than with oxygen

Question 3

Siderophile

Answer 3

Elements dissolve in iron, either as solid solutions or in the liquid state. They form bonds with carbon or sulphur but not with oxygen

Question 4

Magma mixing

Answer 4

Magmas of different compositions tend to be immiscible. If combined in a magma chamber factors such as density and thermal contrasts keep them separate. Normally takes a vigorous stirring mechanism e.g. convection within the chamber, to produce magma that has an intermediate composition between that of the parent magmas.

Question 5

Contamination

Answer 5

Stoping breaks of pieces of country rock which is incorporated into the magma as xenoliths. If the xenoliths melt and become assimilated they can contaminate the magma and change its bulk composition

Question 6

Magma differentiation

Answer 6

It consists of a number of processes that cause a parent magma to evolve into magmas of different compositions. This leads to different igneous rocks being produced from a single parent.

Question 7

Fractional crystallisation

Answer 7

Olivine and pyroxene form at high temps, they use Fe +Mg from the magma in their crystal lattices. Plagioclase crystals in Ca then form. Magma becomes depleted in Fe, Ca +Mg. Remaining liquid becomes enriched in silica, potassium, sodium + water. Composition of magma changes overtime.

Question 8

Gravity settling

Answer 8

Denser minerals e.g. olivine + pyroxene sink to form layer at base of intrusion or magma chamber. Layer of dense, early formed minerals is called cumulate layer. Crystal which remain in magma will react overtime following Bowen’s reaction series. GS removes crystals from remaining liquid so they can no longer react with remaining magma changing composition of magma.

Question 9

Filter pressing

Answer 9

There is a point where the crystal and liquid exist as a slushy mass. Due to weight of overlying crystals liquid gets squeezed out, forming a separate layer above. This liquid is depleted in elements which are incorporated into early formed crystals and enriched in elements which form felsic minerals.