Crustal magnetization of the Reykjanes Ridge and implications for its along-axis variability and the formation of axial volcanic ridges

We have inverted the sea surface total magnetic field measurements of the R eykjanes Ridge, between 57 degrees N and 63 degrees N, for crustal magnetiz ation intensity assuming a uniformly thick magnetic source layer and direct ion of magnetization corresponding to the geocentric axial dipole field. Th is section of the north Mid-Atlantic Ridge (10 mm/yr half spreading rate) i s unique in that it lies within the influence of the Iceland mantle plume, which causes it to spread obliquely and in the north to resemble morphologi cally a fast-spreading ridge. On a regional scale the axial magnetization a nomalies of the Reykjanes Ridge can be divided into three regimes from sout h to north. These regimes correspond to sections of the ridge with differen t magmatic and tectonic styles which are believed to represent the effects of a pulsing plume beneath Iceland. The axis south of 59 degrees 10'N has t he highest magnetization anomaly with the greatest variability and exhibits the characteristics of a slow-spreading ridge unaffected by a plume. The a xis between 59 degrees 10'N and 60 degrees 50'N has the lowest magnetizatio n anomaly on average and is where we presume the present day plume front is located. The absence of large fault scarps and low magnetization are consi stent with the idea of a midcrustal magma reservoir, where mixing causes th e magma to become less highly fractionated and produces less magnetic lavas . Finally, a moderate increase in the magnetization anomaly and degree of f aulting occurs north of 60 degrees 50'N, signaling a gradual recovery in th e crustal production and underlying structure after the passage of the plum e front. On the local scale, with a few exceptions, the loci of high magnet ization anomalies coincide with the axial volcanic ridges. Notable lateral offsets in axial magnetization and decay in magnitude were found at 57 degr ees 50'N, 58 degrees 05'N, and 59 degrees 12'N. Comparisons with seismic la yer 2A show that variations in the magnetic source layer thickness may acco unt for as much as half of the observed variability in the along-axis magne tization. There are also indications that the relative age of the extrusive s and the degree of faulting and fissuring may be factors affecting the mag netization intensity of volcanic edifices on the seafloor.