Geochronology of Plutonic Rocks and Their Tectonic Terranes in Glacier Bay National Park and Preserve, Southeast Alaska

摘要

We have identified six major belts and two nonbelt occurrences of plutonic rocks in Glacier Bay National Park and Preserve and characterized them on the basis of geologic mapping, igneous petrology, geochemistry, and isotopic dating. The six plutonic belts and two other occurrences are, from oldest to youngest: (1) Jurassic (201.6145.5 Ma) diorite and gabbro of the Lituya belt; (2) Late Jurassic (161.0145.5 Ma) leucotonalite in Johns Hopkins Inlet; (3) Early Cretaceous (145.599.6 Ma) granodiorite and tonalite of the Muir-Chichagof belt; (4) Paleocene tonalite in Johns Hopkins Inlet (65.555.8 Ma); (5) Eocene granodiorite of the Sanak-Baranof belt; (6) Eocene and Oligocene (55.823.0 Ma) granodiorite, quartz diorite, and granite of the Muir-Fairweather felsic-intermediate belt; (7) Eocene and Oligocene (55.823.0 Ma) layered gabbros of the Crillon-La Perouse mafic belt; and (8) Oligocene (33.923.0 Ma) quartz monzonite and quartz syenite of the Tkope belt. The rocks are further classified into 17 different combination age-compositional units; some younger belts are superimposed on older ones. Almost all these plutonic rocks are related to Cretaceous and Tertiary subduction events.