Answer to Question #258382 in General Chemistry for stacie

Question

A granite has zircon and hornblende. A mass spectrometer measured values of:

207Pb/235U = 0.66579

206Pb/238U = 0.08421

40Ar/40K = 0.19739

235U decays to 207Pb with a decay constant () of 9.72 x 10-10/yr

238U decays to 206Pb with a of 1.54 x 10-10 /yr

40K decays to 40Ar with a of 5.543 x 10-10/yr.

The closure temperature of a mineral is the temperature at which daughter product is stops diffusing out of the mineral and is instead retained. The closure temperature of U-Pb in zircon is 900 °C while for K-Ar in hornblende it is 550 °C

Part B. What is the U-Pb age of the zircon? Clearly write the equation you are using to calculate the value. State your answer in units of Ma.

Part C. What is the K-Ar age of the hornblende? Clearly write the equation you are using to calculate the value. State your answer in units of Ma.

Part D. What are two possible explanations for the difference in these two ages? 

Answer 1

The answer to your question is provided in the image: