DEFINITION OF TONALITIC SUITE The tonalitic suite outcrops in the extremesouthern Adirondacks where they are highly deformed. Thesetonalitic rocks are one of the oldest suites in the Adirondacksand have been dated at circa 1.3 billion years. The tonaliticgneiss is thought to be igneous in origin based on the presenceof xenoliths from the surrounding rock and the subophitic textures.Strong calc-alkaline trends suggest that these rocks arearc-related; however, this geochemical signature does not differentiatebetween an island-arc and an Andean arc-type setting.This suite may be correlative with tonalitic rocks in theGreen Mountains of Vermont based on age relations and petrographicfeatures. They are also similar in composition withthe somewhat younger Elzevirian batholith (1.27–1.23 billionyears old) in the central metasedimentary belt. Consequently,the tonalitic suite in the Adirondacks is thought to have beenemplaced in the early intraoceanic history of the Elzevirian arc,prior to collision at circa 1,200 million years ago.
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