Three-dimensional polynomial trend analysis applied to igneous petrogenesis

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Three-dimensional polynomial trend-surface analysis has been applied to wholerock measurements of specific gravity, SiO2, Fe 2O3 + MgO, and Na2O + KzO from each of the four principal intrusive units of the Audubon-Albion stock, Colorado. Except in the earliest unit (orthoclase gabbro), the three-dimensional variability of these parameters indicates a simple pattern of crystallization dominated by gravitative settling with little or no convective motion. Petrography and petrochemistry of the orthoclase gabbro indicate that it originated mainly as a crystal cumulate, whereas trend-surface analysis suggests that it was rotated and rafted into its present position during a later period of intrusion. Hence, statistical treatment of subtle petrologic variations offers insight into otherwise obscure petrogenetic processes and, in favorable situations, produces information that can be used to interpret subsequent structural history.

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Memoir of the Geological Society of America