MagmaCourse: Fluid pathways below the Eger Rift constrained by numerical and analog simulations.

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The aim of this proposal is to obtain a conceptual model of deep fluid pathways consistent with observations, especially seismic and magnetotelluric (MT) observations that are sensitive to fluids, mineralization and presence of magma (Q1 and Q2). We plan for the first time to combine mechanical models (numerical simulations and complementary laboratory analog models) with constrained MT inversions and geochemical models in a loop process where the output of one model is used as input for the next step.The Vogtland/West Bohemia seismic swarms are a prominent example of crustal seismicity where fluids are playing a primary role, and relate to one of the few intra-plate seismically active regions of Europe. Many debates and unanswered questions revolve around these seismic swarms, here we list a selection: Q1) The role played by the intra-continental tectonics of the area. The area is a Paleozoic suture that was reactivated by Cenozoic post-orogenic extension, creating the 300km long and 50km wide Eger Graben and the Cheb-Domazlice Graben. Abundant, spatially distributed alkaline volcanism is associated with this area. What controls the spatial distribution of the volcanism and its geochemistry? How are seismicity and volcanism linked?Q2) Deep fluid pathways. Isotope ratios reveal that the high CO2 flux, reaching the surface in the form of CO2 rich mofettes and hydrothermal activity, originates directly from the upper mantle. What are the pathways followed by the magma and by the other fluids, and what factors are controlling them? What are the composition and the physicochemical properties of the fluids while they are migrating?Q3) Channeling of the fluids into pre-existing faults and the triggering factors for the seismicity. In the last 30 years multiple swarms have occurred in the area. What is the mechanics of the pressurized fluids entering into the pre-existing fault zone? What are the mechanisms supporting fluid movement? What is the composition of the crustal fluids reaching the seismogenic volume? What are their physical properties, and how do they evolve with time? How is the fluid-rock coupling converting fluid pressurization into rock stressing?These interconnected questions represent key questions for the ICDP Eger Rift project. We will develop new numerical and analog mechanical and geochemical models, and use them to constrain the model space of existing 2D inversion models, that are now non-unique. We will use available deep crustal seismic data and MT data acquired along 2 perpendicular profiles (autumn 2015) and on a dense grid (spring 2016) in the area of earthquake swarms and mofettes. A close cooperation with the MT group aimed at directly countercheck individual assumptions is novel and pioneering. The generation of the seismicity in the seismogenic zone will be addressed in a follow-up proposal.