Obtaining a reliable characteristic remanent magnetization (ChRM) from volcanic rock samples is an important challenge in paleomagnetism. Volcanic rocks acquire a thermoremanent magnetization when they cool in the Earth's magnetic field that is proportional to the direction and strength of the magnetic field at the time of cooling. TRMs of natural rocks are often regarded to be the most reliable data source for geomagnetic field models because of their ability to store information on the paleomagnetic field for thousands to millions of years (e.g., Panovska et al., 2019;Pavón-Carrasco et al., 2021). Full vector ChRMs consist of both directional and intensity information on the past geomagnetic field, but they can generally only be obtained for 10%-20% of volcanic samples carrying TRMs (e.g., Nagy et al., 2017;Tauxe & Yamazaki, 2015). One of the reasons for the low success rates is that only single domain (SD) or pseudo-single domain (PSD) iron oxide grains, typically with diameters <1 μm, are reliable recorders of the Earth's magnetic field. Larger multidomain (MD) grains are

Geological materials and archeological artifacts containing magnetic particles record the direction and intensity of the past geomagnetic field as they cool. These thermoremanent magnetizations are our primary source of information on the behavior of the Earth's magnetic field. Obtaining reliable paleointensities and paleodirections from samples with a large variation in grain sizes is a challenge due to differences in magnetic behavior between grains that differ in size, shape, and chemistry (e.g., Dunlop & Özdemir, 1997;Tauxe & Yamazaki, 2015). In paleomagnetic measurement techniques that rely on bulk measurements, the contributions of individual grains are measured collectively, that is, the signals of many millions of grains result in a single magnetic moment for the entire sample. This possibly obscures information from grains that record the paleofield well by the signal of nonperfect recorders in the sample. Especially, the presence of large (>>1 μm), multidomain (MD) grains often prevents a reliable interpretation of a magnetic signal from a bulk sample. Samples consisting of predominantly single-domain (SD) grains or slightly larger (<1 μm) pseudo-single domain (PSD) grains with complex domain structures such as vortices or "flower states" generally produce more reliable paleomagnetic data (e.g., Nagy et al., 2017Nagy et al., , 2019.Over the past decades, a number of studies have focused on high-end magnetometry techniques to assess the magnetic state of magnetic recorders and micromagnetic processes in them on a (sub) micrometer scale (e.g.,

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&lt;p&gt;Micromagnetic tomography (MMT) is a new promising paleomagnetic technique that obtains magnetic moments for individual iron-oxides. These magnetic moments are inferred from surface magnetometry data obtained with quantum diamond microscopy (QDM), and iron-oxide positions determined with micro X-Ray computed tomography (MicroCT). Different to classical techniques, MMT does not depend on bulk measurements of samples. This makes it possible to only select the most reliable magnetic recorders. To make this improvement possible, MMT first has to deal with the presence of undetected magnetic carriers in basaltic rock samples used in previous MMT studies. Although particles smaller than 1 &amp;#181;m are good recorders of the magnetic field and may be visible in surface magnetometry, they are not detected by MicroCT. This violates one of the foundations of MMT and may disturb magnetic moments of other detected grains. However, it is currently unknown how many of these small disturbing particles are present in Hawaiian basaltic samples. We know that the smallest disturbing grains have a diameter of around 40 nm, since particles smaller than this threshold become superparamagnetic and cannot store magnetic signals. For this reason we want to obtain a grain-size distribution for iron-oxides from 20 nm to 10 &amp;#181;m to cover the complete range of grains that are capable of storing Earth&amp;#8217;s magnetic field. This requires a combination of FIBSEM slice-and-view and MicroCT techniques; FIBSEM detects single and pseudo-single domain grains with sizes between 20 nm and 1 &amp;#181;m and MicroCT detects multi-domain grains with sizes larger than 1 &amp;#181;m. Subsequently, FIBSEM and MicroCT data are combined to obtain the full spectrum of grain sizes. Unfortunately, grains are not uniformly distributed in the samples, so a scaling by volume would not produce a realistic spectrum. Therefore, based on observations that iron-oxides grains cluster on the interfaces of other minerals, we calculated how many times FIBSEM mineral interfaces from FIBSEM data fit the mineral interfaces from MicroCT data. Then, this factor is used to scale the FIBSEM iron-oxides to MicroCT iron-oxides and to obtain a complete distribution of all grain sizes. Interestingly, this distribution shows a clear peak in grain size at 70-80 nm. Furthermore, the smallest grain fraction is fitted a lognormal trend, but the fraction larger than 0.18 &amp;#181;m are fitted an exponential decay trend. With these trendlines in place we have finally acquired a realistic set of boundary conditions for the distribution of iron-oxide particles in basaltic rocks. This enables us to populate models with a realistic distribution of particles, which ultimately may shed light on the disturbing presence of small iron-oxides in MMT results. If we know the effect of these disturbances, we will understand which grains MMT can solve with highest certainty, ultimately leading to paleomagnetic interpretations on grain scale.&lt;/p&gt;

Obtaining a reliable characteristic remanent magnetization (ChRM) from volcanic rock samples is an important challenge in paleomagnetism. Volcanic rocks acquire a thermoremanent magnetization when they cool in the Earth's magnetic field that is proportional to the direction and strength of the magnetic field at the time of cooling. TRMs of natural rocks are often regarded to be the most reliable data source for geomagnetic field models because of their ability to store information on the paleomagnetic field for thousands to millions of years (e.g., Panovska et al., 2019;Pavón-Carrasco et al., 2021). Full vector ChRMs consist of both directional and intensity information on the past geomagnetic field, but they can generally only be obtained for 10%-20% of volcanic samples carrying TRMs (e.g., Nagy et al., 2017;Tauxe & Yamazaki, 2015). One of the reasons for the low success rates is that only single domain (SD) or pseudo-single domain (PSD) iron oxide grains, typically with diameters <1 μm, are reliable recorders of the Earth's magnetic field. Larger multidomain (MD) grains are

Obtaining a reliable characteristic remanent magnetization (ChRM) from volcanic rock samples is an important challenge in paleomagnetism. Volcanic rocks acquire a thermoremanent magnetization when they cool in the Earth's magnetic field that is proportional to the direction and strength of the magnetic field at the time of cooling. TRMs of natural rocks are often regarded to be the most reliable data source for geomagnetic field models because of their ability to store information on the paleomagnetic field for thousands to millions of years (e.g., Panovska et al., 2019;Pavón-Carrasco et al., 2021). Full vector ChRMs consist of both directional and intensity information on the past geomagnetic field, but they can generally only be obtained for 10%-20% of volcanic samples carrying TRMs (e.g., Nagy et al., 2017;Tauxe & Yamazaki, 2015). One of the reasons for the low success rates is that only single domain (SD) or pseudo-single domain (PSD) iron oxide grains, typically with diameters <1 μm, are reliable recorders of the Earth's magnetic field. Larger multidomain (MD) grains are

&lt;p&gt;The recently developed Micromagnetic Tomography (MMT) technique allows precise recovery of magnetic moments of individual magnetic grains in a sample. By combining high resolution scanning magnetometry and micro X-ray computed tomography (MicroCT) MMT has the potential to become an important asset in rock-magnetic and paleointensity studies. However, uncertainties in magnetic moment solutions obtained through MMT are yet enigmatic, making a geologic application of MMT results uncertain. Therefore, we have made a first attempt in addressing those mathematical uncertainties surrounding MMT, by studying the effect of five parameters that directly influence the uncertainty of magnetic moment solutions: grain concentration of the sample, thickness of the sample, size of the sample's surface, noise level in the magnetic scan, and sampling interval of the magnetic scan. The effect of MicroCT errors are not included in this study, since those errors are better solved by improving the experimental routine than by mathematical corrections. We assess how well the magnetic moments are resolved as function of the aforementioned five parameters by setting up series of numerical models in which we assign dipole magnetizations to randomly placed grains. We perturb per model the surface magnetic field with different instrumental noise levels and sample these fields with a varying interval. The MMT inversion provides the magnetic moment per grain, and additionally produces the covariance matrix and standard deviations, which are used to define a statistical uncertainty ratio and signal strength ratio for each solution. We show that the magnetic moments of a majority of grains under realistic conditions are solved with very small uncertainties. However, increasing the grain density and sample thickness carry major challenges for the MMT inversions. Fortunately, we can use the newly defined signal strength ratio to extract grains with the most accurate solutions, even from these challenging models. Thereby we have developed an quantitative routine to individually select the most reliable grains from MMT results. This will ultimately enable determining paleodirections and paleointensities from large subsets of grains in a sample using MMT.&lt;/p&gt;

&lt;p&gt;The magnetic information stored in volcanic rocks is a valuable archive of the history of the behavior of the Earth&amp;#8217;s magnetic field. Micromagnetic Tomography (MMT) allows to determine magnetic moments of individual iron-oxide grains in rocks. Theoretically this enables us to separate contributions from non-ideal recorders and ideal recorders, overcoming the difficulties arising from bulk measurements. Here we present results from two sister specimens from the 1907-flow from Hawaii&amp;#8217;s Kilauea volcano to which MMT was applied. One specimen was imaged both by the Quantum Diamond Microscope in Harvard and by the MicroCT scanner Nanoscope&amp;#8211;S in Delft, producing magnetic moments of 1,646 individual grains. The sister sample underwent stepwise AF-demagnetization: a step toward classic paleomagnetic analysis, from which we present (preliminary) results. In MMT, individual grains are allocated a magnetization through a least-squares inversion. For the first sample, we produced more than one magnetization for each grain, because each grain was present in multiple unique inversion &amp;#8216;tiles&amp;#8217; (smaller sub-areas &amp;#160;due to computational constraints). This enabled a statistical analysis of the (robustness of) results, presented here. For the second sample (preliminary) demagnetization results per grain are presented. We also present results of an investigation into a parameter for selecting grains that can be reliably resolved from the statistical analysis. For both samples only relatively large iron-oxide grains (diameter &gt; 1.5 -&amp;#160; 2 &amp;#181;m) were resolved, as the resolution of the MicroCT was limited. However, any analysis of magnetism at grain level is a step in understanding how magnetizations are stored in individual grains, and is of importance for those specimens that only contain large iron-oxides.&lt;/p&gt;