PETROGRAPHIC AND GEOCHEMICAL VARIATION ALONG THE REYKJANES-RIDGE, 57-DEGREES-N-59-DEGREES-N

High-density sampling of the neo-volcanic zone along the Reykjanes Rid ge has been used to test the relationship between bathymetric features and geochemistry. The axial region has short wavelength features whic h correspond to elongate, en-echelon volcanic ridges. These ridges sit atop intermediate wavelength features, termed swells and troughs. A b road correspondence is found between the sections containing more frac tionated samples and the intermediate wavelength swells. Conversely, t he troughs are dominated by more primitive lavas. This suggests that s wells represent areas of greater melt dux, resulting in thicker crust and hence generally more fractionation. Progressively higher concentra tions of incompatible elements are found northwards along the ridge, w ith increases occurring as a series of steps that do not correlate wit h 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 b ecome slightly smaller northwards. Changes or consistency in ratio, pa rticularly Rb/Nb, cannot be explained by progressively greater northwa rd incorporation of a component from the Icelandic plume mantle.