Seamount volcanism at the Reykjanes Ridge: Relationship to the Iceland hot spot

Abstract

The axial zone of the Reykjanes Ridge is covered with small (0.5–3 km in diameter) volcanoes that pile together to form larger axial volcanic ridges. This style of volcanism is similar to that at the Mid‐Atlantic Ridge (MAR) and may be common to slow spreading ridges despite proximity of the Reykjanes Ridge to the Iceland hot spot. In this study we quantitatively investigate the population of seamounts in three study areas at the Reykjanes Ridge. Areas A and B are centered at 62°N and 60°N, respectively. Area C is centered at 58°N and is located south of the transition in ridge morphology from an axial high to an axial graben. Using multibeam bathymetry data, 541 seamounts (summit height H > 50 m) were identified in the three areas, and their size and shape statistics were compiled. Additionally, 105 seamounts in areas B and C were recognized in deep‐towed side scan images, and their surface morphologies (hummocky or smooth) were recorded. On the basis of estimated population parameters, we find that seamounts at the Reykjanes Ridge are more abundant (310±20 per 103 km2), on average, than at the MAR between 24° and 30°N (200±10 per 103 km2). Significant along‐axis variations exist at the Reykjanes Ridge, however, which are not simply related to distance from the hot spot: area B has nearly twice the abundance of seamounts as either area A or area C. Variation in the characteristic height of the seamount population is also observed between the Reykjanes Ridge (68±2 m) and the MAR (58±2 m), but no significant variation is found between our three study areas. A dramatic change in seamount surface morphology occurs between areas B and C (there are no side scan data from area A). Area C has 78% hummocky seamounts (similar to the proportion observed at the MAR), while area B has 83% smooth seamounts. On the basis of these results, we present a conceptual model for building the shallow crust at the slow spreading Reykjanes Ridge that takes into account the possible influence of the Iceland hot spot on the crustal melt delivery system and its influence on variables that control seamount abundances, sizes, shapes, and surface morphologies. In this model we suggest that the increased seamount production and proliferation of smooth seamounts in area B may be associated with a pulse of hot spot material, in the form of asthenosphere of higher temperature, that has recently affected area B.