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Journal articleMuxworthy AR, Turney J, Qi L, et al., 2023,
Interpreting high-temperature magnetic susceptibility data of natural systems
, Frontiers in Earth Science, Vol: 11, ISSN: 2296-6463High-temperature susceptibility (HT-χ) data are routinely measured in Earth, planetary, and environmental sciences to rapidly identify the magnetic mineralogy of natural systems. The interpretation of such data can be complicated. Whilst some minerals are relatively unaltered by heating and are easy to identify through their Curie or Néel temperature, other common magnetic phases, e.g., iron sulphides, are very unstable to heating. This makes HT-χ interpretation challenging, especially in multi-mineralogical samples. Here, we report a review of the HT-χ data measured primarily at Imperial College London of common magnetic minerals found in natural samples. We show examples of “near pure” natural samples, in addition to examples of interpretation of multi-phase HT-χ data. We hope that this paper will act be the first reference paper for HT-χ data interpretation.
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Journal articleSteele SC, Fu R, Volk MWR, et al., 2023,
Paleomagnetic evidence for a long-lived, potentially reversing martian dynamo at ~3.9 Ga
, Science Advances, Vol: 9, Pages: 1-13, ISSN: 2375-2548The 4.1-billion-year-old meteorite Allan Hills 84001 (ALH 84001) may preserve a magnetic record of the extinct martian dynamo. However, previous paleomagnetic studies have reported heterogeneous, nonunidirectional magnetization in the meteorite at submillimeter scales, calling into question whether it records a dynamo field. We use the quantum diamond microscope to analyze igneous Fe-sulfides in ALH 84001 that may carry remanence as old as 4.1 billion years (Ga). We find that individual, 100-μm-scale ferromagnetic mineral assemblages are strongly magnetized in two nearly antipodal directions. This suggests that the meteorite recorded strong fields following impact heating at 4.1 to 3.95 Ga, after which at least one further impact heterogeneously remagnetized the meteorite in a nearly antipodal local field. These observations are most simply explained by a reversing martian dynamo that was active until 3.9 Ga, thereby implying a late cessation for the martian dynamo and potentially documenting reversing behavior in a nonterrestrial planetary dynamo.
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Journal articlePerkins JR, Fraser AJ, Muxworthy AR, et al., 2023,
Basin and petroleum systems modelling to characterise multi-source hydrocarbon generation: A case study on the inner Moray Firth, UK North Sea
, Marine and Petroleum Geology, Vol: 151, Pages: 106180-106180, ISSN: 0264-8172 -
Journal articleBaker EB, Muxworthy A, 2023,
Using Preisach theory to evaluate chemical remanent magnetization and its behavior during Thellier-Thellier-Coe paleointensity experiments
, Journal of Geophysical Research: Solid Earth, ISSN: 2169-9356 -
Journal articleHu J, Zhang Y, Jia D, et al., 2023,
Combining paleomagnetic and Re-Os isotope data to date hydrocarbon generation and accumulation processes
, Journal of Geophysical Research: Solid Earth, ISSN: 2169-9356 -
Journal articleNorth TL, Collins G, Davison T, et al., 2023,
The heterogeneous response of Martian meteorite Allan Hills 84001 to planar shock
, Icarus, Vol: 390, ISSN: 0019-1035Impact-generated shock waves can change the physical properties of meteorites and their constituent minerals. Accounting for these effects is key to recovering information about the early solar system from meteorite observations. ALH 84001 is a rare ancient sample from the Martian crust, providing a unique window into the thermal and metamorphic evolution of Mars. A well-studied meteorite, past geochemical and petrologic investigations have attempted to deduce its thermal and impact history with some contradictory results. By simulating the passage of a planar shock wave through a synthetic analog for samples of ALH 84001 using the iSALE-2D shock physics code we have determined the meteorite’s likely thermodynamic and physical response during an impact. Our simulations show that heterogeneous shear heating, induced by the planar shock wave, can produce strong thermal gradients on the sub-millimeter ‘mesoscale’ throughout the meteorite, even in relatively weak shock waves (5 GPa). We are able to place new constraints on deformation events experienced by the meteorite during its time on the parent body, including the maximum pressure ALH 84001 has experienced since it acquired its remanent magnetization and its subsequent ejection from Mars.
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Journal articleElmore RD, Muxworthy A, Heij G, et al., 2022,
Remagnetization and Diagenesis
, Frontiers in Earth Science, ISSN: 2296-6463 -
Journal articleMoreno R, Williams W, Muxworthy A, et al., 2022,
The meaning of maxima and minima in first order reversal curves: determining the interaction between species in a sample
, Journal of Magnetism and Magnetic Materials, Vol: 564, ISSN: 0304-8853First-order reversal curves (FORCs) are a characterization technique for magnetic materials used in a wide range of research fields. Since their first application in the Earth Sciences two decades ago, their importance in science has been continuously growing and new experimental techniques have been subsequently designed based on the original idea of FORCs. Nonetheless, very recent experimental works on very well designed and simple magnetic structures demonstrate that even for the most simple cases the interpretation of FORC data lacks understanding. In this work, we address this problem analytically, explaining the meaning of maxima, minima and noisy tails and set a strategy to extract the interaction field between magnetic structures. The origin of this interaction field is often the magnetostatic energy, however, we propose that this strategy could be applied for estimating exchange interactions too.
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Journal articleMuxworthy A, Lam C, Green D, et al., 2022,
Magnetic characterisation of London’s airborne nanoparticulate matter
, Atmospheric Environment, Vol: 287, Pages: 1-8, ISSN: 1352-2310Iron-bearing particulate matter produced by vehicle emissions is known to be toxic. To better quantify potential health risks, we have conducted the first magnetic study of a time-series of London's inhalable particulate matter (<10 μm, PM10), captured by three monitoring stations in central London (Marylebone Road, Earl's Court Road and Oxford Street) through 2010 and 2012. We conducted room-temperature analysis on all the samples, and a limited number of samples were analysed at both high and low temperatures. The high-temperature measurements identified magnetite as the dominant magnetic phase. The low-temperature measurements revealed high numbers of nanoparticles, which, assuming magnetite, are in the grain-size range 1–4 nm. It is estimated that as much as ∼40% of the total magnetic signal at 10 K is from particles <4 nm, that are magnetically ‘invisible’ at room-temperature and are being routinely under-estimated in room temperature-based magnetic studies. From the low-temperature measurements, the total concentration of magnetite was estimated at ∼7.5%, significantly higher than previously reported. The room-temperature magnetic data were compared with other pollution data, e.g., NOX and PM10, and meteorological data. Mass-dependent terms like the saturation magnetisation were found to display a strong correlation with NOX and PM10, indicating a common source for these pollutants, i.e., vehicle emissions. Magnetic coercivity measurements, which are independent of abundance, and provide information on grain-size, were consistent across all three sampling localities, again suggesting a major dominant source. Relatively small variations in coercivity were correlated with meteorological events, e.g., temperature and precipitation, suggesting preferential removal of larger airborne grains, i.e., >50 nm.
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Journal articleAbdulkarim M, Muxworthy AR, Fraser A, 2022,
High temperature susceptibility measurements: A potential tool for the identification of oil water transition zone (OWTZ) in petroleum reservoirs
, Frontiers in Earth Science, Vol: 10, ISSN: 2296-6463Determining the position and thickness of the oil water transition zone (OWTZ) in hydrocarbon reservoirs is important to reserveestimation and production planning. This paper describes a magnetic method of identifying this zone. High temperaturesusceptibility (HT‐χ) measurements on core samples from Paleogene reservoirs of the UK Central North Sea revealed distinctsignatures around the oil water interface. Rapid increases in susceptibilities at temperatures < 250 °C were observed forsamples around the oil water interface unlike the main oil leg where alteration involving increase in susceptibility occurred atsignificantly slower rates and higher temperatures. The HT‐χ data together with Mössbauer measurements revealed that thevariation in alteration characteristics is due to the increasing concentration of hexagonal pyrrhotite and/or lepidocrocite aroundthe oil water interface. Hexagonal pyrrhotite was identified in reservoirs existing at temperatures of < 80 °C, whilelepidocrocite dominated the signature around the contact of deeper reservoirs. These observations suggest that the precipitationof hexagonal pyrrhotite is related to OWTZ centred biogenic activities i.e., biodegradation. The dominance of lepidocrocite indeeper diagenetic settings has been related to hydrolysis of hydrocarbon at the oil water interface, together with cessation ofbiogenic activities.
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Conference paperNorth TL, Muxworthy AR, Collins GS, et al., 2022,
THERMOREMANENT MAGNETISATION RECORDED DURING IMPACT-INDUCED COMPACTION EXPERIMENTS ON SYNTHETIC CHONDRITIC METEORITES
, LSPC, Publisher: WILEY, ISSN: 1086-9379 -
Journal articleAbdulkarim MA, Muxworthy A, Fraser A, et al., 2022,
Effect of hydrocarbon presence and properties on the magnetic signature of the reservoir sediments of the Catcher Area Development (CAD) region, UK North Sea
, Frontiers in Earth Science, Vol: 10, Pages: 1-20, ISSN: 2296-6463This paper presents a detailed study investigating the effect of hydrocarbon presence on magnetic mineral diagenesis in sediments from the Catcher Area Development (CAD) region, UK North Sea, between 1,000 and 1,500 m (True Vertical Depth Sub-Sea). Magnetic analysis of core samples from hydrocarbon fields of the region and nearby dry-well sandstones (background) was carried out to determine if their signatures can serve as a proxy for understanding petroleum reservoir systems. From the background samples, nanometric and micron-sized magnetite, hematite and titano-iron oxides, were identified. Hydrocarbon presence in the reservoir sediments was found to diminish the iron-oxide signature and favour the precipitation of hexagonal pyrrhotite, siderite and potentially vivianite, lepidocrocite, greigite and paramagnetic iron sulphides. Hexagonal pyrrhotite was found at the oil-water transition zones. This relationship is possibly related to biodegradation at this interface. Siderite was found in increased abundance at shallower depths within the reservoir, which we attribute to hydrocarbon vertical migration and biodegradation. The interbedded shales also experienced significant magnetic mineral diagenesis that depended on its proximity to the hydrocarbon plume. These findings suggest that mineral magnetism can be applied to the identification of oil-water transition zones, reserve estimation, production planning and the determination of hydrocarbon migration pathways. It also suggests that mineral magnetic methods can be used to estimate the timing of hydrocarbon migration.
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Journal articleRoberts AP, Heslop D, Zhao X, et al., 2022,
Unlocking information about fine magnetic particle assemblages from first-order reversal curve diagrams: Recent advances
, EARTH-SCIENCE REVIEWS, Vol: 227, ISSN: 0012-8252 -
Journal articleAbdulkarim M, Muxworthy A, Fraser A, et al., 2022,
Siderite occurrence in petroleum systems and its potential as a hydrocarbon-migration proxy: a case study of the Catcher Area Development and the Bittern area, UK North Sea
, Journal of Petroleum Science and Engineering, ISSN: 0920-4105 -
Journal articleRoberts AP, Zhao X, Hu P, et al., 2021,
Magnetic domain state and anisotropy in hematite (alpha-Fe2O3) from first-order reversal curve diagrams
, Journal of Geophysical Research. Solid Earth, ISSN: 2169-9356
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