mar-22-2002-test-geochemistry

Geochemistry Midterm
Peach Bottom Slate / Rare Earth Elements

Eric Thern
March 28, 2002

This document shows up on my website sooo much better... latex really wrecked this in document form!
http://www.thern.org/projects/geology/geochemistry/takehome-exam/mar-22-2002-test-geochemistry/

Peach Bottom Slate

First determine the mean and standard deviation of the major oxides given.
Evaluate the quality of the Peach Bottom data. Note that two of the samples are duplicates. Examine the totals. Is the data of good quality, why or why not?
Plot the mean of the major oxides. Use a logarithmic scale so silica does not dominate the chart. Now plot as an additional series the major element concentration of PAAS, which represents the upper continental crust.
Now add plus and minus error bars using the standard deviation as the error. Which elements show statistically different values between PAAS and PB?
Note the differences between the two series. If we assume the Peach Bottom slate originally was similar to composition to the upper continental crust, what chemical changes have occurred during metamorphism? Which minerals appear to have been effected?
(Bonus) Can you think of an alternative explanation for the chemical differences?
Normalize the REEs of each of the seven substrate units to chondritic values and plot on a logarithmic scale. Also normalize the PAAS values that are representative of upper continental crust and plot on the same graph.
Examine the spidergram. What can you say about the pattern of REEs from the lichens grown on different substrates with radically different chemistry? How do they compare with PAAS? What inference can be drawn regarding the composition of REEs on the lichens?
Describe REE patterns of the lichen samples and PAAS. What are its key features (enrichments, anomalies, etc.) and what do they say about the continental crust?
Why is lichen chemistry depleted in the REEs compared to PAAS?
Compare the patterns to chondritic values. Where would chondritic values plot on this graph and what general pattern would it have?
(Bonus x2) Determine the between REE Lichen samples and REE PAAS.
Raw data for Peach Bottom slate / PAAS REEs graphs:
Raw data for Rare Earth Elements in Lichen / PAAS graphs:
GNUPlot setup file:
About this document ...

Eric Thern
2002-03-28