Trace Element Geochemistry Questions and Answers

Q: A chondrite normalised REE pattern of quartzo-feldspathic gneiss shows a sharp positive anomaly of Eu, which indicate presence of :

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.

Q: Which one of the following lunar materials shows positive europium anomaly ?

The lunar material with a positive europium anomaly is anorthosite.Under the reducing conditions of the Moon most europium is divalent, Eu2+, which substitutes readily for calcium in plagioclase while the other rare earths, all trivalent, do not. The lunar highland anorthosites, which floated as plagioclase on the early magma ocean, are therefore enriched in Eu relative to its neighbours.The complementary melts left behind are depleted in Eu. KREEP, the residual liquid rich in potassium, rare earths and phosphorus, and the mare basalts, including the Apollo 11 high-K basalts and quartz tholeiites, all show negative europium anomalies.

A chondrite normalised REE pattern of quartzo-feldspathic gneiss shows a sharp positive anomaly of Eu, which indicate presence of :

A.Plagioclase in the sample
B.Quartz in the sample
C.Clinopyroxene in the sample
D.Sillimanite in the sample

Exam Year(s)

MH SET - 2020, SET Exam - 2020,

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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Which one of the following lunar materials shows positive europium anomaly ?

A.KREEP
B.Anorthosite
C.Apollo 11 Hi-K Basalt
D.Apollo 11 Quartz Tholeiite

Exam Year(s)

MH SET - 2021, SET Exam - 2021,

Answer: B

The lunar material with a positive europium anomaly is anorthosite.

Under the reducing conditions of the Moon most europium is divalent, Eu²⁺, which substitutes readily for calcium in plagioclase while the other rare earths, all trivalent, do not. The lunar highland anorthosites, which floated as plagioclase on the early magma ocean, are therefore enriched in Eu relative to its neighbours.

The complementary melts left behind are depleted in Eu. KREEP, the residual liquid rich in potassium, rare earths and phosphorus, and the mare basalts, including the Apollo 11 high-K basalts and quartz tholeiites, all show negative europium anomalies.

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