Rates and processes of tephra alteration in Surtsey volcano: a combined observational and experimental approach

点击翻译按钮获取中文摘要

ICDP supports the SUSTAIN drilling project aimed at investigating the formation and hydrothermal alteration of Surtsey volcano in the Vestmanaeyjar archipelago, Iceland. Rapid and intense reactions between tephra and circulating fluids were critical in the formation and evolution of Surtsey. These processes of glass-water interaction are also important in crust-ocean geochemical budgets and they support specifically adapted intracrustal microbial life. This proposal requests funds to conduct comprehensive and systematic investigations of the role of temperature and permeability in the processes and rates of tephra alteration. Also budgeted are a fraction of the operational costs, without which SUSTAIN cannot be launched. The work proposed makes use of x-ray computer microtomography (µ-CT) to image and quantify the distribution and connectedness of pore space in tephra and to relate these parameters to the nature and extent of tephra alteration reactions. Microscopic and microanalytical work will be used to identify the secondary phase assemblages and mineral compositions. These examinations of SUSTAIN drill core samples will be complemented by laboratory- and field-based experimental approaches, making use of hydrothermal flow-through cells and borehole incubation studies, respectively. In both lines of study, cylindrical bodies of tephra (19 mm in diameter) will be subjected to natural or artificial solutions for durations between 15 and 24 months and under controlled conditions of up to 1 MPa and 150°C. The reaction progress will be gauged in the laboratory using concomitant µ-CT measurements and chemical compositions of outflow solutions. After termination of the experiments, µ-CT measurements and subsequent microscopy and microanalytical work will assess the spatial distribution of permeability and the extent and nature of secondary mineral formation. The relative rates of palagonitization and formation of secondary phases such as zeolites and tobermorite will be evaluated and related to permeability evolution. These results will yield new insights into the general mechanisms governing tephra alteration and their consequences for hydrothermal mass transfers and geomechanically relevant textural development of tephra bodies in young seamounts and oceanic islands. The proposed work will be closely coordinated with related efforts by collaborating scientists within SUSTAIN to maximize the novelty and strength of the tephra alteration model and its implications for (bio)geochemical processes and rock mechanical properties.