IGPP is pleased to invite you to join its Winter 2022 Seminar Series presentation featuring Georgia Tech'ss Darcy Cordell. Dr Cordell's talk, "Estimating The Melt Fraction of Magma Reservoirs Using MELTS and Magnetotellurics" will be available via Zoom on Tuesday, January 18, 2022, starting at 12:00pm. Zoom: https://ucsd.zoom.us/j/95825941234?pwd=ZzFZUys5bGdLQWlVMWhMSUpKYTQyQT09. Password: melt.
Date: Tuesday, January 18, 2022
Time: 12:00 pm, Pacific Time
Note: This meeting will be recorded. Please make sure that you are comfortable with this before registering.
Other Authors: Samer Naif, Juliana Troch, Christian Huber
Abstract: Estimating the melt fraction and volatile content of regions of partial melt beneath silicic volcanoes has important implications for volcanic hazards since higher melt fraction, volatile-rich magmas are more buoyant and have a lower viscosity, and thus are more susceptible to mobilization and possibly eruption. Magnetotelluric (MT) data can be used to model subsurface bulk resistivity structures through inversion algorithms. Using empirical relationships, the bulk resistivity can be converted to estimates of melt fraction, temperature, and water content to infer magma reservoir properties and volcanic hazard. The standard conversion approach treats melt fraction, temperature, and water content as independent variables, but they are thermodynamically correlated.
In this study, we use the thermodynamic MELTS model to constrain the possible combinations of melt fraction, temperature, and water content such that MT interpretations are petrologically consistent. This is contrasted with the standard approach to highlight the benefits of the new approach. In addition, probabilistic 1-D Bayesian inversion that incorporates these constraints can be used to find a distribution of models and interpretations which fit the MT data and provide a better understanding of the uncertainty in MT-derived estimates of melt fraction. We apply this method to two different magmatic systems: the Laguna del Maule Volcanic Field (LdMVF), central Chile, and the Altiplano-Puna Magma Body (APMB), southern Bolivia. In both cases, the derived bulk resistivity values align with the petrologically-coupled estimates of temperature and water content. In the case of LdMVF, this results in reasonable melt fraction estimates between 10% and 20%. However, the bulk resistivity of the APMB results significantly higher melt fractions which requires further study.