Name __________________________ Geochemistry, Fall 2005 Supplemental questions U-Pb dating and data analysis using Isoplot By now you have had the chance to look at, think about, and work with U and Pb isotope chemistry data collected from zircons from the Indian Himalaya on a Sensitive High Resolution Ion MicroProbe. The program Isoplot uses this isotope data and plugs the data into several age and error estimate equations to calculate U-Pb ages for these Himalayan zircons. You have plotted concordia diagrams, histograms and probability density curves to look at the age distribution from these analyses, and calculated weighted mean ages from groups of similar-age data. Now I’d like you to describe your reasoning behind your plots and assess the data and your interpretation of the isotope data. Please explain what the concordia plots tell you: What is a concordia line? What constitutes a concordant analysis and why is a concordant analysis superior to a discordant analysis? Why is it appropriate to ignore very discordant data? A sketch or labeled printout may help your explanation.Name __________________________ Geochemistry, Fall 2005 Assess the data you were given by age group. Please describe your data briefly and/or evaluate the weighted mean ages you calculated: Proterozoic data (600 Ma and older): Paleozoic data (c. 400-500 Ma ages): Paleocene-Eocene data (40-60 Ma): Some people are lumpers, others are splitters: Why did you choose your final weighted mean ages? Why did you include or exclude certain samples in the weighted mean age? Why did you decide to lump all samples together or break the data up into multiple age
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