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Chemical complexity and source of the White River Ash, Alaska and Yukon

October 1, 2014

The White River Ash, a prominent stratigraphic marker bed in Alaska (USA) and Yukon (Canada), consists of multiple compositional units belonging to two geochemical groups. The compositional units are characterized using multiple criteria, with combined glass and ilmenite compositions being the best discriminators. Two compositional units compose the northern group (WRA-Na and WRA-Nb), and two units are present in the eastern group (WRA-Ea and the younger, WRA-Eb). In the proximal area, the ca. 1900 yr B.P. (Lerbekmo et al., 1975) WRA-Na displays reverse zoning in the glass phase and systematic changes in ilmenite composition and estimated oxygen fugacity from the base to the top of the unit. The eruption probably tapped different magma batches or bodies within the magma reservoir with limited mixing or mingling between them. The 1147 cal yr B.P. (calibrated years, approximately equivalent to calendric years) (Clague et al., 1995) WRA-Ea eruption is only weakly zoned, but pumices with different glass compositions are present, along with gray and white intermingled glass in individual pumice clasts, indicating the presence of multiple magmatic bodies or layers. All White River Ash products are high-silica adakites and are sourced from the Mount Churchill magmatic system.

Publication Year 2014
Title Chemical complexity and source of the White River Ash, Alaska and Yukon
DOI 10.1130/GES00953.1
Authors S.J. Preece, Robert G. McGimsey, J.A. Westgate, N.J.G. Pearce, W.K. Hartmann, W.T. Perkins
Publication Type Article
Publication Subtype Journal Article
Series Title Geosphere
Index ID 70171512
Record Source USGS Publications Warehouse
USGS Organization Volcano Hazards Program; Volcano Science Center