Magma Mixing Due to Disruption of a Compositional Interface

摘要

The chemical compositions of glassy pumices are used to investigate the relationship between two ash-flow sheets that were erupted from the same volcanic center. The first ash-flow sheet, the large volume (>1200 km sup 3 ) Topopah Spring Member, represents an eruption from a magma body that contained a sharp compositional interface between a high-silica rhyolite and a lower-silica quartz latite. The second ash-flow sheet is the smaller volume (<40 km sup 3 ) Pah Canyon Member. It represents an eruption of a relatively homogenous magma that is intermediate in composition to the compositions of the Topopah Spring Member. Mixing of the quartz latite and rhyolite magmas to produce the Pah Canyon Member is evaluated using variation diagrams of the major and trace elements, ratio-ratio plots, and least-squares multiple linear regression. The latter includes two independent tests, one using the major elements, and the other using selected trace elements. Fractional crystallization of the quartz latite to produce the Pah Canyon Member is evaluated using multiple linear regression with both the major elements and selected trace elements. (ERA citation 11:052287)