Integrating Research and Education > Crystallography > Cpx Geobarometer > Directions > Part 1: Reading Assignment and Questions

Part 1: Reading Assigment and Questions

Reading assignment

Skim the following papers....
  • Nimis, P. (1995) A clinopyroxene geobarometer for basaltic systems based on crystal-structure modeling. Contributions to Mineralogy and Petrology, 121, 115-125.
  • Nimis, P., and Ulmer, P. (1998) Clinopyroxene geobarometry of magmatic rocks. Part 1. An expanded structural geobarometer for anhydrous and hydrous basic and ultrabasic systems. Contributions to Mineralogy and Petrology, 133, 122-135.
  • Nimis, P. (1999) Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems. Contributions to Mineralogy and Petrology, 135, 62-74. (Just read the abstract, introduction, and concluding remarks for this one)

Questions to answer

Answer the following questions, based on what you learned from the three assigned papers. The paper containing the answer is given to help you find the answer more efficiently.
  1. How is the clinopyroxene geobarometer different from other geobarometers used in petrology? (Nimis, 1999)
  2. What is the crystal-chemical basis of the cpx geobarometer?–which two crystallographic parameters are pressure-sensitive in cpx? (Nimis, 1995; Nimis and Ulmer, 1998)
  3. How was the cpx geobarometer calibrated for anhydrous, basaltic melts? (Nimis, 1995)
  4. Does the cpx geobarometer determine the depth of partial melting, the depth of cpx crystallization, or the depth of magma emplacement? (Nimis, 1995)
  5. Using the most recent calibration of the cpx geobarometer (Nimis and Ulmer, 1998), determine the depth of cpx crystallization (in anhydrous basalt) of a cpx crystal with Vcell=431Å3 and VM1=11.7Å3.
  6. Is the cpx geobarometer valid for high Al2O3 rocks containing garnet? Why or why not? (Nimis, 1995)
  7. Could the cpx geobarometer be applied to determine the pressures of eclogite formation? Why or why not?
  8. What whole-rock compositions are appropriate for the cpx geobarometer? (use all three papers)
  9. What is the advantage of Nimis' "crystal structure modelling" approach over determining the crystal structure by single-crystal x-ray techniques? (Nimis, 1995)