Homogeneous geochemical signal of Jan Mayen intraplate volcanism and its radial dispersion along adjacent ultra-slow spreading ridges.

Abstract:

The volcanically active Jan Mayen Island is found on the northern tip of the Jan Mayen microcontinent, a continental fragment rifted from the Greenland coast 25 My ago following the ridge jump from Aegir to Kolbeinsey Ridge. The recurrent debate about the origin of Jan Mayen is partly due to the complex geological setting of the island. It is located directly south of the Jan Mayen Fracture Zone (JMFZ) and between the ultraslow Mohns and Kolbeinsey spreading ridges. Over the years, this intraplate volcanic suite has been diversely interpreted as an isolated hotspot, as Icelandic plume material dispersed in the northern Atlantic, as the result of melting of a sub-continental lithospheric mantle, or as a result from the coincidence of a continental fragment in the prolongation of a spreading center. However, recent U-series data (Elkins et al., 2011; 2014; in prep.) as well as geophysical high-resolution S-velocity model (Rickers et al., 2013) both indicate a high-temperature anomaly in this area, supporting the hotspot hypothesis.

We present new major, trace elements, Sr, Nd, Pb and Hf isotope data for samples collected near Jan Mayen and along Kolbeinsey and Mohns Ridges, together with a new bathymetry map. One of the most striking results from Jan Mayen area is the relative homogeneity in the geochemical signature around the island compared to other hotspots. These limited geochemical variations are surprising considering that these lavas are erupted on top of a fragment of continental crust in a ridge-hotspot-fracture zone context. Along Kolbeinsey and Mohns Ridges, we observed a radial dispersion and mixing of Jan Mayen signature within the local depleted upper mantle. The difference in the geochemical gradients on both sides of the JMFZ could be linked to the difference in ridge morphology between Kolbeinsey (orthogonal, symmetric spreading, shallow and high magma supply) and Mohns Ridges (oblique, asymmetric spreading, deeper and weaker magma supply).