Discussion
A chondrite normalised REE pattern of quartzo-feldspathic gneiss shows a sharp positive anomaly of Eu, which indicate presence of :
Answer: A
A sharp positive Eu anomaly indicates plagioclase in the sample.
Under reducing magmatic conditions europium occurs partly as Eu2+, which is about the same size as Ca2+ and substitutes for it in plagioclase feldspar. Plagioclase therefore takes in much more Eu than the neighbouring rare earths, so a rock rich in plagioclase (or formed from plagioclase accumulation) shows a positive Eu anomaly on a chondrite-normalised plot.
Quartz and sillimanite take in almost no rare earth elements, and clinopyroxene does not single out europium in this way.
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