Recognizing crust and mantle reservoirs

Figun 7.6 Approximate ranges of 5 0 and Sr/ Sr in common igneous and sedimentary rocks (adapted from Magaritz e/(i/., 1978). 

Radiogenic isotopes, on the other hand, show differences between crust and mantle reservoirs which are a function of long-lived differences in parent/daughter element ratios and indicate the isolation of the reservoirs from one another for long periods of Earth history. This gives rise to crustal reservoirs which generally are enriched in Sr/ Sr and in radiogenic lead isotopes but depleted in Nd/ Nd relative to the mantle. 

However, crustal contamination is rarely a simple mixing process and frequendy it involves three components — a melt, a precipitating cumulate phase and a 

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