Age and Regional Relationships of Granitoid Rocks of the Adirondack Highlands

Approximately 55% of the Adirondack highlands is underlain by granitic to tonalitic rocks that can be subdivided into five groups based on age, composition, and field occurrence: (1) early calcalkaline tonalites (ca. 1300 Ma) and associated granitic rocks (ca. 1250 Ma) of the southern and eastern highlands, (2) older anorogenic plutonic rocks (1145-1160 Ma) that occur throughout the highlands, (3) younger anorogenic plutonic rocks (ca. 1130 Ma) that envelop anorthosite massifs in the central highlands, (4) younger granitic rocks (1095-1105 Ma) of the northwest highlands, and (5) late leucogranitic rocks (1060-1080 Ma) that occur throughout the northern highlands. The data presented here are in good agreement with zircon ages from the Green Mountains of Vermont as well as from southern Ontario and Quebec and suggest similar geologic histories for these regions. These results document a protracted and complicated evolution for this portion of the Grenville Province.