What are some processes that could affect the composition of magma other than fractional crystallization? Please describe the processes:0008
I believe you're asking about Magma Differentiation between a collection of igneous rock formations in a closed area, specifically other than fractional crystallization?
So for those that are unclear what we are talking about, this is about the differing processes that affect mineral composition of igneous rock formations.
There are several different mineral compositions or types of rock in the earth's core. Magma melts these minerals or rocks and once expelled through the mantle and crust they settle as igneous rock formations that are studied by geologists. (I am sure there are better more expansive explanations but this is how I understand it). By studying rock formations in a closed area or in close proximity geologists can study the composition of said rocks that give them clues as to the original composition of the different rocks that were melted by the magma.
Some of these processes are as follows. Crystal fractionation.
Singular melting events from distinct sources.
2 or more magmas mixing together.
Contamination or assimilation of magmas by the earth's crust or crustal rocks.
Differing degrees of partial melting of rocks from the same core source.
Liquid Immiscibility.
So the short but too long explanation of these I'd this.
Crystal fractionation is when rocks containing different elements such as potassium, rubidium, magnesium, etc.... are melted together some of the elements have a higher melting point, differing densities can form crystals that are ejected from or dropped out of the magma thus changing the composition of the resultant igneous rocks. For instance some rocks on the bottom of the formation may contain high concentrations of an element with a lower melting point, while other rocks may have very little of that element. This would be indicative of crystal fractionation.
Contamination or assimilation is somewhat self explanatory. As the magma is pushed through the crust, some of the crystal rock will melt into the magma, thus changing the composition.
Singular melting events from distinct source rocks is again pretty much how it sounds. The composition of the magma would be somewhat consistent and fluid, however this type event has been historically hard to prove.
There are also varying degrees of melt from magma which would produce a completely different composition. Elements that have higher melting points would not be as dense in the first formations yet prevalent in the "melt 2" phase.
Magmas mixing together would cause one melt, the hotter of the two to absorb many of the denser elements but would maintain a similar yet distinct composition by density between the two magmas. The differences would be evident in the viscosity, density, and temperature.
Liquid Immiscibility is when two magmas meet but are unable to mix due to differences in the equilibrium of substances contained within each magma. For a liquid to be a liquid then all liquid and solid elements contained within the liquid must be in equilibrium, meaning the reaction of elements has reached a balance. When two liquids are in equilibrium they do not always mix, such as oil and water.
I know this is not a very good explanation and crystal fractionation has a lot to do with water content that I didn't even attempt but this is the best I can do as far as explaining what I know about it.
Hope this helps,
FDC