Trachyandesite

A volcanic rock defined modally by Q/(Q+A+P) < 20% or F/(F+A+P) < 10%, P/(A+P) between 65 and 90%, and M < 35
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Geochemical and petrographic data for intrusions peripheral to the Big Timber Stock, Crazy Mountains, Montana

The Paleocene Fort Union Formation hosts a compositionally diverse array of Eocene plugs, dikes, and sills arrayed around the Eocene Big Timber stock in the Crazy Mountains of south-central Montana. The geochemistry and petrography of the sills have no

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