Accretionary Wedge #43: Fun with Chemographic Projections

This month’s Accretionary Wedge calls for posts on our favorite geological illustrations. Some of my personal favorites are drawn by Dr. Kurt Hollocher from Union College. His collection of hand-drawn thin sections is enough to make any petrologist drool.

One of Dr. Hollocher’s most whimsical illustrations involves the AFM chemographic projection. Chemographic projections are often used in metamorphic petrology to plot complex compositions on two-dimensional triangular diagrams. A popular chemographic projection for metapelites is the AFM diagram, which represents Al2O3, FeO, and MgO at its corners. In his series of AFM diagrams, Dr. Hollocher has a little fun with the retrograde garnet-out reaction.

Retrograde chloritoid-in reaction. Courtesy of Dr. Kurt Hollocher.

Poor garnet. Courtesy of Dr. Kurt Hollocher.

Garnet is doomed! Courtesy of Dr. Kurt Hollocher.

Goodbye garnet. Courtesy of Dr. Kurt Hollocher.

The progressive garnet-out reaction. Courtesy of Dr. Kurt Hollocher.

Almost gone. Courtesy Dr. Kurt Hollocher.

Hello chlorite pesudomorph after garnet! Courtesy of Dr. Kurt Hollocher.

Special thanks to Dr. Kurt Hollocher for the fantastic illustrations and the permission to use them in our Accretionary Wedge Post.

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