THE GEOLOGIC MAP OF WRANGELL-SAINT ELIAS NATIONAL PARK AND PRESERVE, SOUTHEAST CENTRAL ALASKA, USGS SCIENTIFIC INVESTIGATIONS MAP SIM-2877 BY RICHTER AND OTHERS, 2005 — A USEFUL TOOL FOR UNDERSTANDING MESOZOIC AND CENOZOIC CRUSTAL EVOLUTION OF ALASKA

Hot off the press, this compilation map includes 50 years of scientific exploration within a 13 million acre region of eastern Alaska bordering Canada's Yukon Territory. A dynamic assemblage of 7 tectonostratigraphic terranes has deformed the crust throughout the Mesozoic and Cenozoic. This map will be a useful tool en route for unraveling Alaska's tectonic mysteries.

Northward terrane migration has resulted in collisional mountain building of the Eastern Alaska Range, the Mentasta, the Nutzotin, the Chugach, and the Saint Elias Mountains since the Jurassic (200 Ma.), demonstrating southern continental margin doubling, subduction, underthrusting, rapid uplift, basin building, and the creation of the massive Wrangell Mountains volcanic field. Activity continues as witnessed by Mt. Wrangell's consistent steam plumes and the intense 7.9 magnitude earthquake that ripped along the Denali and Totschunda faults in 2003.

Separated by major thrust and strike-slip fault systems, the individual terranes are: the Windy, the Wrangellia Composite, the Southern Margin Composite, and the Yakutat. The Windy's Paleozoic rocks accreted in Triassic and Early Jurassic time (225-180 Ma). The Wrangellia Composite terrane (Peninsular, Wrangellia, and Alexander(?) terranes), followed during the Early Cretaceous (110-85 Ma). Wrangellia merged with Alexander(?) at some stage in the Paleozoic prior to docking. Wrangellia's Pennsylvanian-Permian volcanic arc is overlain by a sequence of thick Triassic flood basalts and limestones, and Jurassic sedimentary rocks. The Southern Margin Composite terrane (Chugach and Prince William terranes) anchored with the Chugach marine flysch in the latest Cretaceous (about 67 Ma) followed by the Prince William Tertiary deep-sea fan and volcanic rocks during the Eocene (about 50 Ma). The active Oligocene-age (26 Ma) Yakutat block, responsible for the Wrangell volcanic province, is caught in a tangle of subduction and accretionary processes that are the source of frequent earthquakes throughout the entire region.