Seamount Magnetism From Helbig's Integrals: Application to the Rano Rahi Seamount Field (East Pacific Rise 17°–19°S)

Abstract

Determining accurate magnetization directions is essential for interpreting magnetic anomalies and inferring the subseafloor crustal magnetization of submarine volcanoes. Furthermore, magnetization directions can be used to determine the polarity of the Earth's magnetic field at the time the seamount was formed, which in turn can be correlated with the geomagnetic polarity time scale to provide independent means of dating submarine volcanic edifices. Here I show a new method to determine seamount magnetization directions from observed magnetic anomalies, based on their fundamental properties expressed by Helbig's infinite integrals, and I propose practical strategies to reduce effects associated with limited-size surveys. The method provides more reliable results than conventional methods based on semi-norm minimization, as demonstrated by the example of Ita Mai Tai Seamount on the Magellan Seamount Trail. The systematic application of this method to the Rano Rahi Seamount Field, in proximity of the East Pacific Rise (EPR) 17°–19°S shows a pattern of alternating crustal magnetization polarities, consistent with few available radiometric ages and with the geomagnetic polarity time scale for the last 3.5 Ma. The corresponding correlation provides an independent tool for dating seamounts in this region, yielding an average constructional volume rate in the range ∼0.5 × 10⁻³–1.3 × 10⁻³ km³/yr for each volcano, which implies a significant contribution of the total magma supply rate is produced off-axis.