Preece, S.J., 1997, Geochemical variation in the <5 Ma Wrangell Volcanic Field, Alaska, with an emphasis on the Skookum Creek Volcanic Complex: Oxford, Ohio, Miami University, Ph.D. dissertation, 547 p., illust.
The Wrangell Volcanic Field (WVF), Alaska, consists of volcanoes that were active starting at ~26 Ma and continuing until present day. Volcanoes in the western <5 Ma WVF define a double volcanic chain with a topographically subdued area between the chains, referred to as front-side volcanoes, interior, and back-side volcanoes. Geochemical trends coincide with the geographic division. Trend I is the dominant composition in the interior. Zones of crustal weakness in the interior allow the Trend 1 magmas to reach the surface with less crustal interaction. All basalts belong to Trend 1. Trend 2a is the dominant composition in the front-side and back-side volcanoes. Crustal thinning from the front side to the back side causes slight chemical differences in Trend 2a. Trend 2b is restricted to the ends of the WVF at Mounts Drum and Churchill. Trend 2b contains an adakite endmember likely derived from partial melting of young underplated basalt. Trend 2b magmatic systems are the source of Type II tephra beds found in Alaska and the Yukon. The Skookum Creek Volcanic Complex (SCVC) is an extinct volcano in the WVF, dominated by Trend 2a with minor quantities of Trend 1 eruptive products. The volcano was active between 3.25 and 2.25 Ma and contains three main eruptive phases: Initiation, Teresa, and Old Faithful. A fourth vent, the Pecos Vent, represents unique compositions within the SCVC. The SCVC evolved through time from Initiation Phase bimodal volcanism to predominantly intermediate volcanism in the Teresa and Old Faithful phases and the Pecos Vent. The Teresa and Old Faithful phases constructed large edifices with a basaltic andesite to andesite main cone and, later, flank eruptions of andesite to rhyolite. A wide variety of high-Ni-potential parental compositions are present that are not simply related to the intermediate compositions. Important processes in the petrogenesis in the SCVC vary with time and include crystal fractionation, magma mixing, and crustal contamination.
Theses and Dissertations
