CORRELATING PYROXENE CRYSTALS IN LAVAS OF MT. YANA WITH CLASTS IN VOLCANICLASTIC DEBRIS FLOW DEPOSITS OF THE TUSCAN FORMATION: AN ELEMENT OF THE MYANA EXPLORER SELF-GUIDED FIELD TRIP APP

Mt. Yana is an approximately 3 Ma stratovolcano of the ancestral Cascades (1), located 40 km south of the Lassen Volcanic Center. Extensive erosion of the edifice offers easy 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 New research builds on unpublished mapping and data (2) to investigate whether specific lava flows of Mt.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. Image analyses of hand samples (using ImageJ) indicate that the area percent of pyroxene crystals in Tuscan formation clasts (3-12%) are similar to those in Mt. Yana samples (10-13%). Preliminary thin section and 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). To engage the public in learning about ancient Mt. Yana, we have developed the MYana Explorer app, which guides users in an exploration of the interior of the eroded volcano and the research used to reconstruct physical and petrogenetic processes of 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 of glassy magma fragments that were quenched from water/ice interactions. Erosional features in the app include proximal breccias deposited by debris flows. Stops in Chico guide users in observing distal erosional remnants of Mt. Yana at breccia outcrops of the Tuscan Formation. At each stop, MYana Explorer features images with short, informative explanations that guide users in making observations, considering questions about their observations, and options to pursue further information. The MYana Explorer app provides an opportunity for non-geologists to learn about volcanoes in an active field experience and to discover how geologists investigate volcanoes to reconstruct the growth and erosional phases in the “lifespan” of a volcano through geologic time. (1) Clynne & Muffler, 2010; (2) Clynne personal communication