Part 3: Use the Clinopyroxene Geobarometer

Download the CpxBar program

Download the CpxBar geobarometry program for Windows/Excel from the research page of Paolo Nimis at the University of Padua in Italy. Before doing anything else, read the short "Read me!" sheet in this file.

Download the clinopyroxene data

The file Cpx Data (Excel 19kB Jan3 05) contains compositions of the same clinopyroxenes that you downloaded crystal structures for in Part 2. After reading the "Read me!" sheet in the CpxBar spreadsheet, input the clinopyroxene compositional data into the CpxBar spreadsheet. Be sure the compositions meet the various checks in columns R-W.

Answer the following questions

Volcanic crater of Mt. Noorat in Victoria, Australia. Details
  1. Based on the compositions of these rocks (as determined by their rock names), which calibration of the clinopyroxene structural geobarometer (BA, BH, TH, or MA) is the most appropriate for these samples from Australia?
  2. The "BA" calibration is the only one that doesn't require a temperature estimate. For simplicity, use this calibration to determine the relative crystallization depths for the magmas at the four localities (i.e., list the localities in order of increasing average cpx-crystallization depth).
  3. How does increasing temperature affect pressure estimates as determined by the BH, TH, and MA calibrations (all of which are T-dependent)? Experiment by typing in a few T's ranging from 1200-1300 °C to find out. Does this relationship make sense? Explain.
  4. Do these estimated pressures make sense? Assuming a lithologic column with an average density corresponding to ~3 km/kbar, would these pressure estimates correspond to upper crust, lower crust, upper mantle, or lower mantle? Does this make sense petrologically?

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