Unravelling the magnetic signal of individual grains in a Hawaiian lava
using Micromagnetic Tomography
Abstract
Micromagnetic Tomography (MMT) is a new technique that allows to
determine magnetic moments of individual grains in volcanic rocks.
Current MMT studies either showed that it is possible to obtain magnetic
moments of relatively small numbers of grains in ideal sample material,
or provided important theoretical advances in MMT inversion theory
and/or its statistical framework. Here we present a large-scale
application of MMT on a sample from the 1907-flow from Hawaii’s Kilauea
volcano producing magnetic moments of 1,646 individual grains. To assess
the robustness of the MMT results, we produced 261,305 individual
magnetic moments in total: an increase of three orders of magnitude
compared to earlier studies and a major step towards the number of
grains that is necessary for paleomagnetic applications of MMT.
Furthermore, we show that the recently proposed signal strength ratio is
a powerful tool to scrutinize and select MMT results. Despite this
progress, still only relatively large iron-oxide grains with diameters
>1.5-2 µm can be reliably resolved, impeding a reliable
paleomagnetic interpretation. To determine the magnetic moments of
smaller (< 1 µm) grains that may exhibit PSD behavior and are
therefore better paleomagnetic recorders, the resolution of the MicroCT
and magnetic scans necessary for MMT must be improved. Therefore, it is
necessary to reduce the sample size in future MMT studies. Nevertheless,
our study is an important step towards making MMT a useful paleomagnetic
and rock-magnetic technique.