MagmaKammern: Surface Loading Changes as Top-Down Controls on Magma Reservoir Formation

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In this project, we will reveal how a volcano's shape (stratovolcano vs. caldera) and growth history influences the depth and construction of magma storage. We will simulate the ascent pathways of magma in the crust by means of numerical and analog models of dike propagation. Previous studies have shown that the loading of a volcanic edifice rotates the principal stresses, thereby steering ascending dikes to focus below the edifices. Surface mass destruction events, such as the formation of a caldera, cause instead a de-focusing of ascending dikes, steering them to erupt offset from the center of the volcano (for example under the rims). In this project we will simulate the incremental growth of a magma chamber below a stratovolcano and below a caldera in different tectonic contexts. We will study how the different shapes of volcanoes and typical loading histories and cycles affect the incremental accumulation of dikes into magma reservoirs. We will link the model results to observations including crustal deformation, seismology, magnetotellurics and petrology. To this aim, we will simulate the ascent of dikes one after the other, considering dike-reservoir and dike-dike interaction, with the background stress due to a surface load and tectonic stress. When the dike is distant, the surface loading and tectonic stress will dominate. Once the dike approaches the storage zone, the stress induced by previously arrested dikes will be proportionally stronger and the dikes will deviate. Dike-dike interaction and the effects of surface loads have been studied separately in the past but never taken together. The question of reservoir formation has been addressed in terms of petrology, geochemistry, thermal development and rock rheology, but never mechanically including stresses controlling the dikes. Crustal deformation studies however show broad patterns that fit well with the idea that surface loads play a strong control on the shape and depth of the magma storage system: calderas are related to sills or top-flatted reservoirs, while stratovolcanoes are linked to vertically developed reservoirs such as ellipsoids. We will go to the root of the process with our simulations. Our new models will be applied to stratovolcanoes and calderas in different tectonic environments to compare the model results with observations. Our project will open a new perspective on magma reservoir research that has never been investigated before: the top-down controls of surface mass changes on the shape and depth of shallow magma storage zones.