Geoscience Seminar on the Geologic History of Alaska

Posted on 1/31/2011 10:06:41 PM

Dr. Ron Cole, Allegheny College, will be speaking at the weekly Geoscience Seminar over the lunch hour on February 4, 2011. The title of his talk is “Colliding Terranes and Volcanic Eruptions: Geologic Events that Shaped Denali National Park and Mineral Resources in South-Central Alaska."

All seminars are in Walsh Hall, Room 104, from 12:15 to 1:15 p.m.


South-central Alaska, including Denali National Park, was shaped by a dynamic tectonic history that included terrane collision and unique episodes of volcanism during early Cenozoic time. Field observations show that volcanic systems ranged from complex composite volcanoes to small lava plateaus fed by fissures. One composite volcano complex formed the Paleocene Cantwell volcanic rocks that are preserved within Denali National Park. Cantwell volcanic activity included pyroclastic eruptions, the outpouring of lavas, and catastrophic debris avalanches analogous to those that formed during the 1980 eruption of Mount St. Helens. The Cantwell volcanics filled a basin that formed by north-south shortening during Late Cretaceous terrane accretion. The Cantwell volcanics were subsequently deformed along the Denali fault system, a major strike-slip fault in southern Alaska that remains active today. Field relationships, radiometric ages, and geochemical data show that the Cantwell volcanics correlate across the Denali fault with granitic plutons that form the high peaks of the Alaska Range (including Mount Denali, the tallest peak in North America).

More regionally, radiometric ages and geochemical data for Cenozoic volcanic and plutonic rocks across south-central Alaska show that these igneous rocks did not form as part of a “typical” continental margin arc system. Instead they were formed during mantle emplacement and high heat flow following spreading ridge subduction and/or slab break off upon terrane accretion. While economic mineral deposits of southern Alaska are associated with Late Cretaceous and Cenozoic igneous rocks, there is a lack of basic understanding of the origin and geologic context of the host magmatic systems. This ongoing research will provide a geologic framework for magmatism that can be applied to better understand the plate kinematics that shaped southern Alaska and better predict the origin and distribution of mineral deposits.