Time: 50 mins Intramural

1) The equation C_x = C_o/(K - X(K-1)) is the standard form describing variations in element concentration, C_x, with the proportion of residual liquid, X, during single mineral fractionation processes.

What are "C_o" and "K" and under what circumstances does this equation reduce to:

a) C_{x =} C_o/X; (3)

b) C_{x =} C_o; (3)

c) C_{x =} 0. (3)

d) what trace elements are compatible with: (3)

K-feldspar;

garnet;

clinopyroxene.

e) If a basaltic liquid contains 300 ppm Ni, and olivine in equilibrium with the liquid contains 3600 ppm Ni, (and if the relative concentration of Ni in olivine and liquid does not change with crystallization, and if all the olivine stays in equilibrium with the basalt liquid) what fraction of the liquid would need to crystallize in order to reduce the Ni concentration of the liquid to 100 ppm. (5)

2) Draw the fractionation relationship you would expect to find in an X-Y plot of:

a) Y versus Nb. (3)

b) Cr versus Ti (3)

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3) In a plot of Ca/Zr versus Mg/Zr, what fractionation |

trend would likely be produced by the crystallization of: |

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a) olivine (3) |

b) clinopyroxene (3) |

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4) How would you use Zr, Ti , and Sr to discriminate between MORB and arc rocks. (3)

4) What do the following acronyms refer to? Name one characteristic geochemical feature of each: (4)

MORB

LKT

WPB

CA

5) What are the four major kinds of chondrite normalized spidergram pattern? Under what circumstances might the pattern change for the same sample? (5)

6) a) What controls the oxygen isotopic composition of the polar ice caps? (3)

c) How would you expect carbon isotopes to fractionate during a period of mass biogenic extinction? (3)

d) How does the carbon composition of sea water respond to periods of glacial cooling of the Earth? (3)

e) How does iron influence the sulphur isotopic composition of seawater?(3)

8) a) Why is element compatibility a factor in understanding the behaviour of the

Rb-Sr, Re-Os, and Sm-Nd isotopic systems? (5)

b) Illustrate how the concepts of a 'Bulk Earth' and a 'Depleted Mantle' are exemplified through measurements of isotopic Sr ratios? (5)

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