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0100 0702000 do the following 1 construct isotope

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Unformatted text preview: ing present day estimates for the Sr isotopic attributes of different earth reservoirs: 87Rb/86Sr 87Sr/86Sr Continental Crust 0.15 0.707 Uniform Reservoir 0.0827 0.7045 Depleted Mantle 0.0100 0.702000 Do the following: 1) Construct isotope evolution diagrams for: a) 87Sr/86Sro – t in 100 Ma increments from 0 to 3500 Ma. 2) Looking at these plots what do you notice about the 87Sr/87Sr values of the crust and mantle relative to the uniform reservoir over time? 3) What do you think happened in the earth at ~2.5 Ga? 4) What should the isotopic signature of modern MORBs be? 5) What about granitic rocks presently forming in volcanoes in the Cascades of western North America, what type of 87Sr/86Sr signatures would you expect them to have? Part 3. Rb Sr Isotope Geochemistry of Ancient Rocks I You will find in the table data for Mesoproterozoic (1300 Ma) anorthositic and granitoid rocks from Labrador (Emslie et al., 1994): 87Rb/86Sr 87Sr/86Sr Sample Name Rock Type EC91 ­91 anorthosite 0.0282 0.703955 EC91 ­35 anorthosite 0.0400 0.704789 EC91 ­88 anorthosite 0.0803 0.704925 NA4522 anorthosite 0.0117 0.706104 RM69 ­385A anorthosite 0.0100 0.705342 NC8937 anorthosite 0.0475 0.705547 EC90 ­198 ferrodiorite 0.0640 0.710183 EC90 ­114 ferrodiorite 0.0199 0.706338 EC90 ­216 ferrodiorite 0.0595 0.706751 EC89 ­345 granite 1.7341...
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