1,500 Ma ago, a Volcano-clastic sediment mixture was made up of volcanic sediments and clastic sediments with a ratio of 1:2. The respective isotope ratios of both sediments are as follows:
Volcanic sediments: 87Sr/86Sr = 0.703, Sr = 300 ppm, Rb = 10 ppm.
Clastic sediments: 87Sr/86Sr = 0.720, Sr = 100 ppm, Rb = 100 ppm.
This rock then solidified and deposited throughout 500Ma. At this point the rock gets heated through orogeny and experiences partial melting to become a magma which then solidified into a granite (final form).
The Rb/Sr ratio of this magma (granite) is 3 times the Volcano-clastic sediment mixture’s Rb/Sr ratio. The granite then ages for a 1000 Ma until present.
Calculate the average 87Sr/86Sr ratio of the Volcano-clastic sediment mixture.
Calculate the initial 87Sr/86Sr ratio of the Granite.
Calculate the present 87Sr/86Sr ratio of the Granite.
Draw a (t) vs -(87Sr/86Sr) isochron.
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