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Modeling the Distribution of Iron-oxides in Basalt by combining FIB-SEM and MicroCT Measurements
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  • Frenk Out,
  • Rosa A de Boer,
  • John Walmsley,
  • Lennart Vincent de Groot
Frenk Out
Utrecht University

Corresponding Author:f.out@uu.nl

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Rosa A de Boer
Utrecht University
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John Walmsley
University of Cambridge
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Lennart Vincent de Groot
Utrecht University
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Micromagnetic tomography (MMT) aims to go beyond paleomagnetic measurements on bulk samples by obtaining magnetic moments for individual iron-oxide grains present in a sample. To obtain accurate MMT results all magnetic sources and all their magnetic signals should be known. Small particles (<<1 µm) are often not detected by MicroCT analyses, but do have a magnetic signal, and therefore hamper obtaining reliable MMT results. Currently it is unknown how many of these small ‘ghost grains’ are present in basaltic samples. Here we aim to obtain a realistic grain-size distribution for iron-oxides in a typical Hawaiian basalt. We characterize the entire grain-size range of interest to paleomagnetism, from the superparamagnetic threshold of ∼40 nm to multidomain grains with sizes up to 10 μm. This requires a combination of FIB-SEM slice-and-view and MicroCT techniques: FIB-SEM characterizes the grains between 20 nm and 1 μm and MicroCT detects iron-oxides >750 nm. The FIB-SEM and MicroCT data are combined through normalizing the grain-size distribution using the surface area of non-magnetic minerals that are characterised in both datasets. Then, a lognormal-like grain-size distribution is acquired for the entire grain-size range. Our dataset enables future studies to populate (MMT) models with a realistic distribution of even the smallest iron-oxide grains, which ultimately may shed light on the confounding influence of such ghost grains on MMT results.
06 Sep 2023Submitted to ESS Open Archive
11 Sep 2023Published in ESS Open Archive