Magma reservoir evolution at a slow-spreading mid-ocean ridge

Mid-ocean ridges form the largest magmatic system on Earth. Oceanic crust is formed when the upper mantle wells up and partially melts in response to plate separation. The melts thus formed rise upwards, forming the magma reservoirs of the lower oceanic crust, and erupt to form mid-ocean ridge basalts.

The nature of magma reservoirs at mid-ocean ridges remains poorly constrained. Traditional models hold that they are bodies of pure melt in which magma evolution is controlled by fractional crystallisation. This model is increasingly challenged, and a new paradigm in which magma reservoirs are comprised of crystal mush - a mixture of melt and crystals - has now emerged. Melt transport and evolution in mush reservoirs may be controlled by porous flow, which has fundamental implications for the eruption dynamics and geochemical signatures of mid-ocean ridge basalts.

This project will reconstruct the architecture and evolution of magma reservoirs at the Mid-Atlantic Ridge. It will capitalise on core that will be recovered from Hole U1309D (30 degrees N) by scientific ocean drilling. Previous drilling at this location has shown that this section contains an excellent record of fossilised magma reservoirs beneath a slow-spreading mid-ocean ridge.

This project will integrate core observations with state-of-the-art element mapping and measurements of mineral major- and trace elements to address three challenges:

1) The size of magma reservoirs;
2) The melt composition and evolution within these reservoirs;
3) The thermal histories of the reservoirs.

Together, these different components will enable a test of the different end member models for reservoir architecture and melt transport. The outcome is a rigorous assessment of the nature and evolution of magma reservoirs beneath the Mid-Atlantic Ridge, with implications for magma evolution of oceanic basalts, which may serve as a template for mafic igneous systems generally.