USING PYROXENE CRYSTAL COMPOSITIONS TO CORRELATE MT. YANA PROXIMAL LAVAS WITH DISTAL EROSIONAL BRECCIAS

Mt. Yana is an approximately 3 Ma stratovolcano of the ancestral Cascades (1), located 40 km south of the Lassen Volcanic Center in northern California. Extensive erosion of the edifice offers access to the interior of Mt. Yana to investigate products of the growth and erosion of the volcano. New research builds on unpublished mapping and data (2) to investigate whether specific lava flows of Mt. Yana can be traced to erosional volcaniclastic breccias in the Tuscan Formation, located 70 km downslope, in Chico, CA. Proximal andesite outcrops within the eroded edifice of Mt. Yana host pyroxene phenocrysts that we compared to pyroxene-phyric andesite clasts of the Tuscan Formation. Preliminary image analyses indicates that the area percent of pyroxene crystals in Tuscan formation clasts (3-12%) are similar to those in Mt. Yana samples (10-13%). SEM-EDS analyses indicate that both Mt. Yana and Tuscan Formation samples contain orthopyroxenes (opx) and clinopyroxenes (cpx), and zoned pyroxene crystals (with both opx and cpx). Electron Microprobe Analyses indicates cpx phenocrysts range from Diopside to Augite and opx are Enstatite. Results of this work will be incorporated in the new MYana Explorer app, which guides the public in learning about Mt. Yana. A guided day-hike includes 12 stops that explore volcano growth processes such as volcanic dike emplacement, lava flows, columnar jointing, and hyaloclastite deposits from water/ice interactions. Erosional features presented in the app include proximal breccias deposited by debris flows and stops in Chico guide users to outcrops of the Tuscan Formation, the distal erosional remnants of Mt. Yana (1). The MYana Explorer app provides an opportunity for non-geologists to learn about volcanoes in a field experience and to discover how geologists investigate volcanoes to reconstruct the growth and erosional phases of a volcano through geologic time. (1) Clynne & Muffler, 2010; (2) Clynne personal communication