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Journal articleTurney J, Muxworthy AR, Sims M, et al., 2024,
Quantifying the characteristics of magnetic oil-water contacts in mature hydrocarbon reservoirs and their capacity for understanding hydrocarbon remigration
, Geophysical Journal International, Vol: 237, Pages: 570-587, ISSN: 0956-540XIncreasing magnetization within mature hydrocarbon reservoirs provides a new technique in identifying oil–water contacts (OWCs) in cored wells with the potential to assess yield thereby reducing the need for further exploration. Authigenic precipitation of magnetic minerals at OWCs may also help locate palaeocontacts (PCs), where structural changes to the petroleum system have caused hydrocarbon remigration. This study determines the magnetic characteristics of magnetic enhancements at OWCs and possibly PCs in silliclastic and carbonate reservoirs at the Wytch Farm oil field, Wessex Basin, UK. Increases in saturation magnetization and susceptibility are observed at the OWC in 11 of the 12 analysed cored reservoirs owing to the increased presence of magnetite and vivianite. Geochemical analysis and shallow reservoirs suggest biogenic and inorganic mineral precipitation is extensive at the OWC depending on iron, sulphur and phosphorus availability. Similar magnetic characteristics have been observed in magnetic enhancements above the OWC in numerous wells which may represent OWCs before a basin-wide easterly tilt caused hydrocarbon remigration in the Cenozoic. Multiple magnetic enhancements above the OWC in westerly onshore wells, suggest this remigration may have occurred as numerous phases.
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Journal articleLin F, Qi L, Zhang N, et al., 2024,
An ongoing lithospheric dripping process beneath northeast China and its impact on intraplate volcanism
, Geology, ISSN: 0091-7613<jats:p>Unique intraplate volcano eruptions and westward volcano migration since the Oligocene have been observed in northeast China, where an overriding continental zone is tectonically controlled by the subduction of the northwestern Pacific plate and the opening of Japan Sea. Interestingly, these intraplate magmatic events occur around a subsiding basin (the Songliao Basin), but no volcanic activity has been observed within the Songliao Basin. The geodynamic mechanism responsible for these volcanoes remains unclear. To address the geodynamic process beneath northeast China, we conducted numerical models constrained by data from regional reconstruction and seismic and volcanic studies. The vertical velocity field of mantle convection and lithospheric partial melting structures derived from our models show that mantle upwelling and melting centers migrate from east to west in northeast China with the westward propagation of the sub-horizontal slab in the transition zone, leading to the observed volcano migration. Also, with the subduction retreat of the northwestern region of the Pacific plate and the opening of the Japan Sea, significant lithospheric thickness differences developed between the Changbaishan-Mudanjiang region and the Songliao Basin, leading to lithospheric unstable dripping. This dripping structure prevents the partial melting of the lithosphere but facilitates the subsidence of the Songliao Basin. Moreover, the lithospheric dripping model successfully predicts upper mantle structures consistent with the proposed tomography model, the observed Moho depth, and surface topography variations. Thus, lithospheric dripping induced by lithospheric thickness differences and the retreating subduction of the Pacific slab provides a robust mechanism for the unique geodynamic processes in northeast China.</jats:p>
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Journal articleDøssing A, Kolster ME, Silva ELS, et al., 2024,
Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland
, Scientific Reports, ISSN: 2045-2322 -
Journal articleNorth T, Muxworthy A, Williams W, et al., 2024,
The effect of stress on paleomagnetic signals: a micromagnetic study of magnetite's single-vortex response
, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276In this study we use micromagnetic modeling to show that the magnetizations of magnetically single-vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single-domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single-vortex and equant single-domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single-vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity.
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Journal articleNagy L, Tauxe L, Williams W, et al., 2023,
Chasing tails: Insights from micromagnetic modeling for thermomagnetic recording in non-uniform magnetic structures
, Geophysical Research Letters, Vol: 49, ISSN: 0094-8276Paleointensities are key to understanding the formation and evolution of Earth and are determined from rocks which record magnetic fields upon cooling; however, experimental protocols for estimating paleointensities frequently fail. The primary reason is that laboratory protocols assume that rocks are dominated by uniformly magnetized, single-domain grains, instead of much more common non-uniformly magnetized grains. Our model for larger grains shows a multiplicity of stable domain states; with preferred states changing as a function of temperature. We show that domain state distribution depends on the thermal history of the sample—in nature and the laboratory. From numerical thermomagnetic modeling, we show that particles with non-uniform domain states will theoretically fail standard experimental paleointensity protocols, preventing us from determining reliable ancient geomagnetic field intensities. We propose that recognizing this type of behavior, and the resulting bias, will yield more reliable paleointensity records, and a better understanding of the Earth.
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Journal articleTurney J, Weiss D, Muxworthy AR, et al., 2023,
Greigite formation in aqueous solutions: critical constraints into the role of iron and sulphur ratios, pH and Eh, and temperature using reaction pathway modelling
, Chemical Geology, Vol: 635, Pages: 1-16, ISSN: 0009-2541Greigite forms as an intermediate phase along the pyrite reaction pathway. Despite being considered metastable, it is observed in numerous shallow natural systems, suggesting it could be a unique proxy for diagenetic and environmental conditions. We use thermodynamic reaction pathway modelling in PHREEQC software, to understand the role of iron and sulphur ratios, pH and Eh, and temperature on the formation and retention of greigite in aqueous solutions. With newly available experimental thermodynamic properties, this work identifies the chemical boundary conditions for greigite formation in aqueous solutions. Greigite precipitation is likely favourable in anoxic and alkaline aqueous solutions at or below 25 °C. Our numerical experiments show that greigite is closer to saturation in iron-rich solutions with minor sulphur input. Greigite precipitation in strongly alkaline solutions suggest polysulfides and ferric iron-bearing minerals may be favourable reactants for its formation. Greigite precipitates at iron and sulphur concentrations that are over two orders of magnitude greater than iron sulphide-hosted natural porewaters. This disparity between model and field observations suggest microenvironments within bulk solutions may be important for greigite formation and retention. These constraints suggest greigite is more likely to form alongside pyrite in shallow, non-steady state aqueous solutions.
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Journal articleNoble JPP, Bending SJ, Muxworthy AR, et al., 2023,
Simplified Model for Minor and Major Loop Magnetic Hysteresis and its Application for Inference of Temperature in Induction Heated Particle Beds
, Journal of Physics D: Applied Physics, ISSN: 0022-3727 -
Journal articleDi Chiara A, Muxworthy AR, Trindade RIF, et al., 2023,
Mesoproterozoic geomagnetic field strength from Nova Guarita mafic dykes (Amazon Craton)
, Studia Geophysica et Geodaetica: a journal of geophysics, geodesy, meteorology and climatology, ISSN: 0039-3169 -
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
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