Discriminant Analysis Applied to Establish Major-Element Field Boundaries for Tectonic Varieties of Basic Rocks

Abstract

The statistical method of linear discriminant analysis has been applied to distinguish Pliocene to Recent basic rocks on the basis of their major-element composition. Studied basic rock suites are from four tectonic settings: island arc, continental rift, ocean island, and mid-ocean ridge. Field boundaries were derived by computing probability functions replacing the past practice of fitting lines by "eye." Highly successful discrimination diagrams have been obtained. A testing set shows that the rate of correct classification ranges from 76% to 96%, and from 80% to 92% when three and four tectonic groups are considered at a time, respectively. The high potential of this approach to identify different tectonic settings for basic rocks is only reduced by the complex tectonic history shown by a few of the compiled samples, by crustal contamination effects in some basic rock samples, and the similarities of mantle sources tapped in different tectonic settings.