Preliminary rock magnetic and anisotropy of magnetic susceptibility results from the Reykjanes Ridge basalts, Atlantic Ocean (IODP Expeditions 384 and 395C)

Abstract

The Reykjanes Ridge is located in the North Atlantic Ocean, southwest of Iceland. Here, the oceanic crust is characterized by a series of V-shaped ridges (VSRs) and V-shaped troughs (VSTs), the formation of which has been linked to three alternative hypotheses: i) thermal pulsing, ii) propagating rifts, and iii) buoyant mantle upwelling. During International Ocean Discovery Program Expeditions 384 and 395C, a transect of five sites were drilled eastwards of the modern Mid-Atlantic Ridge (between 20-30°W) at a latitude of ~60°N, to investigate VSTs/VSRs formation. In this preliminary study, we analyze basalt samples from four sites, two from VSRs and two from VSTs, using rock magnetic and anisotropy of magnetic susceptibility (AMS) techniques, to investigate the differences between VSRs and VSTs. We analyzed the samples at the CIMaN-ALP (Peveragno) and INGV (Rome) Laboratories of paleomagnetism through bulk susceptibility, AMS, stepwise demagnetization of natural remanent magnetization through alternating field and temperature, hysteresis loops and FORC diagrams, and susceptibility vs temperature curves. Rock magnetism was used to determine the rock magnetic properties of each sample and investigate its correlation with the degree of alteration observed in the basalts. The AMS was measured to determine the magnetic fabric as a proxy of the magmatic fabric, where, for instance, lava flow-like fabric would be typical of an unaltered basalt. Preliminary results suggest that basalts from VSTs are generally characterized by higher susceptibility values, while the AMS shows a mixed behavior (well defined or dispersed) independently from the structural position. Further rock magnetic data, integrated with petrological, structural and geochemical data will be correlated to the pervasiveness of alteration in each site, the age of basalts and their distance from the Mid-Atlantic Ridge to test the three hypotheses.