In my study of magmatic rocks, I want to know the magmatic evolutional process.All the samples were collected from the same tectonic unit with the same age. Whether the magma have experience partial melting or fractional crystallization is a key question. I have tried the La/Sm-La diagram and Harker diagram. But I don't know how to interpreted the diagrams. I have upload the diagrams as attachment Can some kind researchers help me or tell me other methods to solve the problem? What is the relation between ultramafic-mafic magmatic rocks and intermediate-acid magmatic rocks in the research? Thanks a lot！
Dear Ms. Wang Ruirui,
In this diagram right above corner means lesser partial melting, and left lower part of diagram shows more percentage of partial melting. The line between these two corners show the trend of partial melting.
Another case is moving from left to right horizontally. In this case the crystal fractionation increases.
So in your diagram, the granites and intermediate magmatic rocks tend to have lesser percentage of partial melting rather than ultramafic-mafic rocks in areas A and B.
In each group of samples you can see a trend from left to right, showing crystal fractionation of magma.
by clicking on attached link you can find more information.
http://www.tulane.edu/~sanelson/eens212/magmadiff.htm
Dear Ms Wang,
The following textbooks : The Interpretation of Igneous Rocks by K.G Cox, J.D.Bell & R.J.Pankhurst, Igneous Petrogenesis by M.J.Wilson and Basic Analytical Petrology by Paul Ragland, will help and would prove useful to your present project.
Regards,
M.Jayabalan.
Hi Wang,
what is your question? You write "Whether the magma have experience partial melting or fractional crystallization is a key question. ".
A magma cannot experience partial melting, of course.
Before playing with incompatible elements you have, first of all, to check the petrography of your rocks and then the major element composition. Trace elements come after. Unfortunately this is a common approach of too many geochemists. They simply ignore or underevaluate the message from major elements and directly to to a specific incompatible element ratio or a given isotopic ratio.
Let you start from the roots, al also the very old (but still valid, at least for the basic concepts) book of Kox, Bell and Pankhurst do.
The content of incompatible elements, like REE, in the melt decreases with increasing degree of melting and increases with increasing degree of fractional crystallization. This is true only if you are dealing with "normal" compositions (e.g., basaltic to mildly evolved melts). If you deal with more exotic compositions (e.g., lamproites, kamafugites, carbonatites, kimberlites, or very evolved melts such as agpaitic phonolites and so on) the concept itself of incompatible element may change and the abundance vector in Harker-type diagrams can be inverted.
Cheers,
michele
Unless I misunderstood your question, I think you are mixing two separate questions (processes) into one.
The partial melting (I think) you refer to applies to the process of producing a magma by melting a mantle rock. Whereas crystal fractionation applies to a crystallizing magma. Both processes can therefore occur in succession. Say an initial basalt is formed by partial melting of mantle rocks and this basalt magma can than evolve to say a granite through the process of crystal fractionation.
The La/Sm vs La diagram may help you examine the partial melting, whereas the major element Harker-diagrams can tell you something about crystal fractionation. The link provided in Masoud's answer will help you understand both.
Best,
Roel
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