Structure and evolution of Axial Volcanic Ridges: Constraining the architecture, chronology and evolution of ocean ridge magmatism.

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Mid-ocean ridges (MORs) are the loci of the most voluminous volcanism on our planet, the products of which have generated 60% of the Earth's surface crust. Unlike its sub-aerial counterpart, MOR volcanism is hidden from view beneath several kilometres of water, leaving the processes largely unknown. For many MORs, this volcanism forms axial volcanic ridges (AVRs), a few kilometres wide and tens of kilometres long, which appear episodic or cyclic in their evolution. Although the processes that generate AVRs, their episodicity, effusion rates and links to melt extraction from the Earth's mantle are the focus of much speculation, little is actually known in sufficient detail to unravel their evolution. This is largely because we have not had the tools capable of studying volcanic architecture, sampling volcanic stratigraphy or determining age relationships between erupted units at the fine scale required. In recent years a new generation of submersible instruments has been developed that now allow us to image to sub-metre resolutions and to collect samples to similar precision, and hence to address AVR genesis directly. Recent developments in dating techniques, coupled with improvements in the precision of geochemical analyses, are now providing the means to test many of the models describing MOR volcanism. Here, we propose a detailed study using the high-resolution tools now available to unravel the complex processes of MOR volcanism. We will use measurements of the variation of the Earth's magnetic field strength, variations in sediment accumulation, and radiomentric dating (including newly-developed uranium series dating) of young basalts, to estimate precise ages. The complexity of the study requires collaboration across different laboratories and between different continents. By pooling our resources in this international programme. our study will yield new insights into the time scales, eruption rates, lava volumes and interaction between the volcanoes and their underlying mantle source. These insights are essential if we are to understand this key component of the Earth System - and hence its relationship to Earth evolution as a whole.