Explain 4 looking at the isotopic signatures of the

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Unformatted text preview: 0.740156 C90 ­195 granite 3.0298 0.762570 EC90 ­108 granite 0.0110 0.712483 1) Provide a table with the four headers from the above table and calculate initial 87Sr/86Sr ratios and add these to the table. 2) Which group of rocks above have had the least crustal contamination? Explain. 3) Which group of rocks has experienced the greatest crustal contamination? Explain. 4) Looking at the isotopic signatures of the ferrodiorites are these more compatible with fractionation from anorthositic or granitic parental magmas? Explain. Part 4. Rb Sr Isotope Geochemistry of Ancient Rocks II You will find in the table below Rb ­Sr data for various sulphides from the Neves Corvo VMS deposit in Spain. 87Rb/86Sr 87Sr/86Sr Sample Rock Type NC ­1 cassiterite ore 0.216 0.711374 NC ­2 cassiterite ore 0.527 0.712172 NC ­4cass NC ­5 NC ­7 NC ­9 NC ­10 NC ­11pyr pure cassiterite Cu(Sn) stockwork ore mineralized volcanic rock Cu ­rich stockwork ore Cu ­rich stockwork ore pyritic stockwork 0.120 0.706 0.711054 0.713133 5.135 1.093 0.781 0.701 0.735563 0.716175 0.715107 0.713656 Assuming that all of these sulphides samples are cogenetic: 1) Plot a whole ­rock isochron and calculate the age of the sulphides. Is it Devonian or Early Mississippian (assume the Devonian ­Mississippian boundary is 360 Ma)? Calculate the initial ratio of the samples as well. 2) Using the calculated isochron age, find all the initial 87Sr/86Sr ratios for these samples and add it to your table. 3) Assuming that all of th...
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This document was uploaded on 03/06/2014 for the course ES 4211 at Memorial University.

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