Date of Graduation
Summer 2026
Degree
Master of Science in Geography and Geology
Department
School of Earth, Environment & Sustainability
Committee Chair
Gary Michelfelder
Abstract
The conditions under which large silicic magma systems in the Andean Central Volcanic Zone (CVZ) store, evolve, and produce eruptible magma are still under debate, even though these systems constitute some of the planet's most voluminous and hazardous magmatic environments. This thesis uses an integrated plagioclase-based geochemical and diffusion chronometry approach to study the thermal state, pre-eruptive timescale, and magma storage conditions beneath three large silicic lava domes (Chao Dacite, Chillahuita, and Tocorpuri). The duration of high-temperature (≥750 °C) magma mobility before eruption is constrain using Sr and Mg diffusion profiles, while melt evolution, reservoir stratification, and crystal–melt coupling are reconstructed using plagioclase major-element compositions, trace-element systematics, and intra-crystalline zoning. Strong correlations between plagioclase anorthite content and trace element geochemistry shows that plagioclase reliably captures melt evolution across all domes. Dome-specific storage environments (e.g., thermally buffered, melt-rich reservoir beneath Chao, an intermediate, periodically reactivated mush beneath Chillahuita, and shallow, reactive crystal-rich mush beneath Tocorpuri) are shown by systematic variations in major- and trace-element behavior. Diffusion chronometry produces consistently short Sr timelines (~1 to < 500 years), suggesting that eruptible magma volumes were only produced during brief pre-eruptive heating events, despite the significant chemical variability and complex development histories recorded in plagioclase. The preservation of sharp trace-element zoning further implies long-term storage at near-solidus conditions, with diffusion-permissive thermal episodes being transient and eruption-linked. The results collectively show that the CVZ silicic lava domes were sourced from a vertically extensive, transcrustal crystal-mush system (probably the Altiplano-Puna Magma Body) where long-lived cold storage is punctuated by short-lived thermal rejuvenation that triggers eruption. This integrated mineral-scale record offers new insights into the timescales, dynamics, and structure of large silicic magma reservoirs, with significant implications for understanding volcanism and assessing hazards in continental arc environments.
Keywords
silicic magma reservoirs; lava domes; diffusion chronometry; crystal mush; plagioclase phenocryst; zoning; Central Volcanic Zone; magma recharge; rejuvenation
Subject Categories
Geology | Volcanology
Copyright
© Bezali Kwame Danso
Recommended Citation
Danso, Bezali Kwame, "Magma Residence and Storage Conditions at Large Silicic Domes Using Strontium and Magnesium Diffusion, Andean Central Volcanic Zone, Chile" (2026). Graduate Theses/Dissertations. 4187.
https://bearworks.missouristate.edu/theses/4187
