268-1 Computational Modeling of Polybaric Open System Magma Evolution in Translithospheric Magma Storage and Transport Zones

Session: Old and the New, Long and the Short: Perspectives on Integration of Timescales of Magmatic Processes: Special Session Related to MGPV Awards to Madison Myers and Anita Grunder (Posters)

Poster Booth No.: 199

Presenting Author:

Wendy Bohrson

Authors:

Bohrson, Wendy A.¹, Spera, Frank J.², Brown, Guy A.³, Strasser, Valerie⁴, Distefano Musser, Monike⁵, Estes, Bailey J.⁶, Antoshechkina, Paula⁷

(1) Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA, (2) Department of Earth Science, UCSB, Santa Barbara, CA, USA, (3) Deborah and Guy Brown, LLC, Montecito, CA, USA, (4) Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA, (5) Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA, (6) Geology and Geological Engineering, Colorado School of Mines, Golden, CO, USA, (7) Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA,

Abstract:

As magmas evolve in translithospheric storage and transport zones, they experience changes that affect their physiochemical characteristics. Over a century of research has produced a wealth of field, analytical, and dynamical data that elucidate complex open-system processes controlling magma genesis and transport. A fruitful approach couples such data with computational models that quantify how, when, and where magmas evolve. Comparison between models and data from rocks, glasses, melt inclusions, and minerals, as well as estimates of magma temperature, density, and viscosity, facilitates robust petrogenetic interpretations that are critically evaluated through assessment of data and model uncertainties.

 

The Magma Chamber Simulator (MCS) models the open-system, polybaric evolution of magma storage regions and the connecting conduits by incorporating different types of crystallization (fractional, equilibrium, or concurrent (which allows some crystals to be removed and others to remain in equilibrium with melt), stoping, assimilation of crustal melts, mixing of magmas, and entrainment of cumulates/mush. Thermodynamic paths, including Gibbs minimization and isenthalpic/isentropic constraints, are implemented self-consistently, allowing for open-system behavior. This array of MCS models provides insights into how petrological processes influence melt/mineral chemistry and affords estimates of magma temperature, viscosity, and density, as well as the pressure(s) of magma storage. Models also enable testing of the chronological sequence of processes. Recently enhanced capabilities of MCS allow tracking of magma changes during transport between storage zones and during eruption. These new modeling capabilities illuminate (e.g.) the pressure and degree to which magmas vesiculate and the impact decompression has on crystal populations (e.g., crystal rims, microlites).  An effective modeling approach employs sensitivity testing that involves refining a broad range of input variables (e.g., pressure, parent magma composition, initial volatile content, redox) through iterative modeling.

 

Case studies of the 1915 Lassen Peak eruption (magma mixing) and historical eruptions of Mount Etna (magma mixing + crustal assimilation + entrainment) demonstrate the efficacy of using MCS to quantify open-system behavior. Crystal size distribution and plagioclase microlite compositions in 1915 Lassen rocks illustrate how MCS decompression models elucidate the pressures at which magma formed a mafic foam and trace the origin of microlites in mixed products. MCS is an essential tool because it allows rigorous testing of hypotheses based on field, petrochemical, geochronological, and dynamical data, which leads to fresh quantitative insight into translithospheric magma systems.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7827

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