Crystal cargoes along the Reykjanes Ridge: insights into magmatic processes at a slow-spreading, plume-influenced mid-ocean ridge

The Reykjanes Ridge (RER) is a 1000 km-long slow-spreading segment of the Mid-Atlantic Ridge that extends southwest from the Reykjanes Peninsula, Iceland. The Icelandic mantle plume exerts a chemical and thermal influence on the ridge that varies spatially, expressed in systematic changes in glass geochemistry, magma flux, crustal thickness and magma storage depths along the ridge [1, 2]. The RER is arguably one of the best-studied segments of mid-ocean ridge globally. However, very little is known about the nature of magmatic processes along the RER. Specifically, we do not know whether there are systematic changes in the assembly, storage and transport of magmas along the ridge with varying proximity to the mantle plume.

We present the first systematic investigation of magmatic processes along the RER with a geochemical and petrological study of mid-ocean ridge basalts (MORB) dredged from a ~900 km transect along the ridge. The crystal cargoes of these samples preserve records of recharge, mixing and ascent, as well as the pressure-temperature conditions of magma storage. We combine EPMA analyses with textural observations from BSE and EDS mapping to reconstruct the complex magmatic histories of individual crystals and of crystal populations. Zoning and resorption textures in individual crystals reveal how magmatic conditions changed during crystal storage and growth. We observe different types of crystal textures and different crystal populations that recur along the ridge, and we determine the spatial distribution of these variations.

Our goal is to identify signatures of mush disaggregation and mixing between magma and crystal populations, and to assess whether the relative importance of these processes changes along the RER with proximity to the Iceland mantle plume. This work represents a new contribution to the relatively limited data on crystal cargoes in global MORBs, and will allow us to place constraints on how crystallisation and magma storage at mid-ocean ridges may vary according to magma flux, crustal thickness and mantle chemistry on a global scale.

 

References
[1] Murton, B. J., Taylor, R. & Thirlwall, M., 2002. Plume-Ridge Interaction: A Geochemical Perspective from the Reykjanes Ridge. Journal of Petrology, 43.

[2] Baxter, R.J.M. & Maclennan, J., 2024. Influence of magma flux on magma storage depths along the Reykjanes Ridge. Earth and Planetary Science Letters, 631.