Mass Cycling through Crustal Magma Chambers and the Influence of Thermo-Mechanical State on Magma Compositions through Time
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Magma chambers are a fundamental component of crustal magma transport modulating erupted volumes, compositions, and timing of eruptions. However, we understand little about how eruption episodicity relates to magma chamber evolution. A sizable amount of research has been done on the thermo-mechanical and chemical evolution of a chamber, but little has been done in combining the two. The many influences on composition make inference of crustal processes from erupted compositions dicult, but there are patterns of eruptive evolution in well- characterized systems that suggest something systematic is occurring. We have developed a coupled thermo-mechanical-chemical model in order to characterize melt evolution through cycles of chamber filling, rupture, and drainage in a thermally evolving, viscoelastic crust. We consider a deeply seated oblate spheroidal chamber, calculating pressure, temperature, volume, elemental concentration, partitioning between crystals and melt, and crustal temperature through time. We characterize the time dependence of chamber failure, thermal longevity, and melt elemental concentrations on mechanical parameters and influx rates, exploring the dependence on depth, primary and crustal compositions. These results should be important for constraining physical controls on eruption episodicity and predictions of instability at magmatic centers.