Petrographic and geochemical variation along the Reykjanes Ridge, 57°N–59°N

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Abstract
High-density sampling of the neo-volcanic zone along the Reykjanes Ridge has been used to test the relationship between bathymetric features and geochemistry. The axial region has short wavelength features which correspond to elongate, en-echelon volcanic ridges. These ridges sit atop intermediate wavelength features, termed swells and troughs. A broad correspondence is found between the sections containing more fractionated samples and the intermediate wavelength swells. Conversely, the troughs are dominated by more primitive lavas. This suggests that swells represent areas of greater melt flux, resulting in thicker crust and hence generally more fractionation. Progressively higher concentrations of incompatible elements are found northwards along the ridge, with increases occurring as a series of steps that do not correlate with short or intermediate wavelength bathymetric features. The northward increase in ratios such as Nb/Zr suggests that sections of the ridge are fed by similar aggregate melt fractions, and that melt fractions become slightly smaller northwards. Changes or consistency in ratio, particularly Rb/Nb, cannot be explained by progressively greater northward incorporation of a component from the Icelandic plume mantle.