Decompression of Krafla magma: From immobile magma mush to explosive foaming?

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IDDP-1 demonstrated that non-eruptively degassed rhyolite melt is present at about 2 km depth under Krafla Caldera, raising many questions, as: Is there true magma in IDDP-1, or only a melt ooze that entered the borehole from hypersolidus felsite? If the intrusion formed during the last eruption, why did it not erupt? Ultimately this finding and the questions arising from it triggered KMDP. The objectives of this proposal are intimately linked to several core objectives of the KMDP and also manifested in the scientific program suggested in the successful KMDP-project. The two central, synergetically interlinked objectives of this proposal are: (1) to constrain the response of rhyolitic magma in general, and Krafla magma in special to slow decompression (in shallow depths). This encompasses the questions if, when and how bubbles will nucleate and grow, the formation of permeable networks, and possibly magma fragmentation. (2) To constrain the mobility of rhyolitic magma towards surrounding host rocks in compressional and tensional (decompression) regimes. The proposed approach is based on unique laboratory experiments, exploring possible scenarios as the rhyolitic magma responses to slow decompression under P-T conditions relevant to KMDP. Several types/compositions of silicate melts ('magma') will be studied, beginning with hydrated standard glass, synthetic silicate melts with the major components of the rhyolite from IDDP-1 and natural and hydrated obsidian from the last rhyolitic eruption of Krafla, finally Krafla natural rhyolitic magma from KMPD-well (in case obtained). The magma response to slow decompression will be mapped in the range of 800-920°C & 16-55 MPa, from 'nothing' to minor nucleation to explosive foaming and fragmentation, enabling us to constrain the eruptability of Krafla magma. The mobility of Krafla magma will be explored by two approaches: In the first, a permeable felsite (brittle, non-fragmenting) will be tightly placed above the rhyolitic magma then both will be slowly decompressed forcing the magma to interact with the felsite in response to decompression. The second approach makes use of the high-T, high-load uniaxial press. A cylindrical magma sample inside a larger, metal-jacketed cylindrical felsite sample will be subjected at temperatures relevant to KMDP to loading and unloading/decompression events. The interactions will be explored using tomography and (micro-)textural techniques. Together these approaches will allow constraining interaction between silicate melt and felsite and the mobility of the melts, respectively. The research proposed here is expected to provide answers critical for understanding how magmas are generated, evolve and interact in the shallow crust as well as how they will react upon disturbance as for instance drilling.