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  • Conference paper
    Shah J, Muxworthy AR, Almeida TP, Kovacs A, Russell SS, Genge MJ, Dunin-Borkowski REet al., 2015,


    , 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379
  • Conference paper
    Muxworthy AR, Bland PA, Collins G, Moore Jet al., 2015,


    , 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379
  • Journal article
    Muxworthy AR, Williams W, 2015,

    Critical single-domain grain sizes in elongated iron particles: implications for meteoritic and lunar magnetism

    , Geophysical Journal International, Vol: 202, Pages: 578-583, ISSN: 1365-246X

    Kamacite particles (Fe–Ni, Ni < 5 per cent), are very common in extra-terrestrial materials, such as meteorites. It is normally assumed that for kamacite particles to be reliable recorders of magnetic fields, they need to be magnetically uniform (single domain, SD) and thermally stable. Larger particles subdivide into non-uniform multidomain (MD) magnetic structures that produce weaker magnetic signals, while small SD particles become magnetically unstable due to thermal fluctuations and exhibit superparamagnetic behaviour. In this paper we determine the first micromagnetic calculation of the stable SD range domain-state phase diagram for metallic iron; previous calculations were analytical. There is a significant increase in the critical size for the SD/MD threshold size, for example, for cube-shaped iron particles, the critical SD/MD threshold has now been estimated to be 25 nm, compared to 17 nm for previous estimates. The larger critical SD/MD threshold size for iron, agrees better with previously published nanometric observations of domain state for FeNi particles, then early analytical models.

  • Conference paper
    Muxworthy AR, Heslop D, 2015,

    Recovering Ancient Magnetic Field Intensities From Rocks Using FORC Measurements (poster)

    , HMM2015
  • Conference paper
    Shah J, Muxworthy AR, Genge M, 2015,

    A micro-CT approach to the paleomagnetic conglomerate test

    , Magnetic Interactions 2015
  • Journal article
    Jacobs CT, Goldin TJ, Collins GS, Piggott MD, Kramer SC, Melosh HJ, Wilson CRG, Allison PAet al., 2015,

    An improved quantitative measure of the tendency for volcanic ash plumes to form in water: implications for the deposition of marine ash beds

    , JOURNAL OF VOLCANOLOGY AND GEOTHERMAL RESEARCH, Vol: 290, Pages: 114-124, ISSN: 0377-0273
  • Journal article
    Miljkovic K, Wieczorek MA, Collins GS, Solomon SC, Smith DE, Zuber MTet al., 2015,

    Excavation of the lunar mantle by basin-forming impact events on the Moon

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 409, Pages: 243-251, ISSN: 0012-821X
  • Journal article
    Bland PA, Collins GS, Davison TM, Abreu NM, Ciesla FJ, Muxworthy AR, Moore Jet al., 2014,

    Pressure-temperature evolution of primordial solar system solids during impact-induced compaction

    , Nature Communications, Vol: 5, Pages: 1-13, ISSN: 2041-1723

    Prior to becoming chondritic meteorites, primordial solids were a poorly consolidated mix of mm-scale igneous inclusions (chondrules) and high-porosity sub-μm dust (matrix). We used high-resolution numerical simulations to track the effect of impact-induced compaction on these materials. Here we show that impact velocities as low as 1.5 km s−1 were capable of heating the matrix to >1,000 K, with pressure–temperature varying by >10 GPa and >1,000 K over ~100 μm. Chondrules were unaffected, acting as heat-sinks: matrix temperature excursions were brief. As impact-induced compaction was a primary and ubiquitous process, our new understanding of its effects requires that key aspects of the chondrite record be re-evaluated: palaeomagnetism, petrography and variability in shock level across meteorite groups. Our data suggest a lithification mechanism for meteorites, and provide a ‘speed limit’ constraint on major compressive impacts that is inconsistent with recent models of solar system orbital architecture that require an early, rapid phase of main-belt collisional evolution.

  • Journal article
    Collins GS, 2014,

    Numerical simulations of impact crater formation with dilatancy

    , Journal of Geophysical Research: Planets, Vol: 119, Pages: 2600-2619, ISSN: 2169-9097

    Impact‐induced fracturing creates porosity that is responsible for many aspects of the geophysical signature of an impact crater. This paper describes a simple model of dilatancy—the creation of porosity in a shearing geological material—and its implementation in the iSALE shock physics code. The model is used to investigate impact‐induced dilatancy during simple and complex crater formation on Earth. Simulations of simple crater formation produce porosity distributions consistent with observations. Dilatancy model parameters appropriate for low‐quality rock masses give the best agreement with observation; more strongly dilatant behavior would require substantial postimpact porosity reduction. The tendency for rock to dilate less when shearing under high pressure is an important property of the model. Pressure suppresses impact‐induced dilatancy: in the shock wave, at depth beneath the crater floor, and in the convergent subcrater flow that forms the central uplift. Consequently, subsurface porosity distribution is a strong function of crater size, which is reflected in the inferred gravity anomaly. The Bouguer gravity anomaly for simulated craters smaller than 25 km is a broad low with a magnitude proportional to the crater radius; larger craters exhibit a central gravity high within a suppressed gravity low. Lower crustal pressures on the Moon relative to Earth imply that impact‐induced dilatancy is more effective on the Moon than Earth for the same size impact in an initially nonporous target. This difference may be mitigated by the presence of porosity in the lunar crust.

  • Conference paper
    Døssing A, Muxworthy AR, Mac Niocaill C, Riishuus Met al., 2014,

    High-Latitude Geomagnetic Secular Variation and Paleointensity during 6-0.5 Ma: Paleomagnetic Results from Eastern Iceland

    , AGU Fall
  • Conference paper
    Dodd S, Mac Niocaill C, Muxworthy AR, 2014,

    The Etendeka large igneous province, Namibia. A 4 Ma duration from detailed magnetostratigraphy (poster)

    , AGU Fall
  • Conference paper
    Abubakar R, Muxworthy AR, Fraser A, Sephton MA, Watson JS, Southern P, Paterson GA, Heslop Det al., 2014,

    Mapping Petroleum Migration Pathways Using Magnetics (poster)

    , AGU Fall
  • Journal article
    Court RW, Sephton MA, 2014,

    New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment

    , Geochimica et Cosmochimica Acta, Vol: 145, Pages: 175-205, ISSN: 0016-7037
  • Journal article
    Miljković K, Collins GS, Bland PA, 2014,

    Reply to comment on: “Supportive comment on: “Morphology and population of binary asteroid impact craters”, by K. Miljković, G.S. Collins, S. Mannick and P.A. Bland – An updated assessment”

    , Earth and Planetary Science Letters, Vol: 405, Pages: 285-286, ISSN: 0012-821X

    In Miljković et al. (2013) we resolved the apparent contradiction that while 15% of the Near Earth Asteroid (impactor) population are binaries, only 2–4% of craters formed on Earth and Mars (target planet) are doublet craters. Using 3D hydrocode simulations to explore the physics of binary impacts, we showed that only 2% of binary asteroid impacts produced well-separated doublets, while the rest covered morphologies ranging from overlapping to elliptical or even circular. We then generated a complete classification dataset to aid in the identification of the (sometimes subtle) morphological characteristics consistent with a binary asteroid impact. We thank Schmieder et al. (2013) for providing additional detailed geochronological constraints which indicate that our lower bound of 2% doublet craters on Earth may in fact be ≤1.5%.

  • Conference paper
    Almeida TP, Kasama T, Muxworthy AR, Williams W, Hansen TW, Dunin-Borkowski REet al., 2014,

    Visualisation of chemical remanent magnetisation in pseudo-single domain Fe3O4 particles examined by environmental TEM and off-axis electron holography

    , International Microscopy Congress
  • Conference paper
    Muxworthy AR, Williams W, Almeida TP, 2014,

    Understanding the effect of chemical alteration on palaeomagnetic signals (invited)

    , The Castle Meeting
  • Journal article
    Court RW, Sims MR, Cullen DC, Sephton MAet al., 2014,

    Searching for Life on Mars: Degradation of Surfactant Solutions Used in Organic Extraction Experiments

    , Astrobiology, Vol: 14, Pages: 733-752, ISSN: 1531-1074
  • Journal article
    Montgomery W, Lerch P, Sephton MA, 2014,

    In-situ vibrational optical rotatory dispersion of molecular organic crystals at high pressures

    , Analytica Chimica Acta, Vol: 842, Pages: 51-56, ISSN: 0003-2670
  • Journal article
    Luong D, Court RW, Sims MR, Cullen DC, Sephton MAet al., 2014,

    Extracting organic matter on Mars: A comparison of methods involving subcritical water, surfactant solutions and organic solvents

    , Planetary and Space Science, Vol: 99, Pages: 19-27, ISSN: 0032-0633
  • Conference paper
    Shah J, Muxworthy AR, Russell S, Genge Met al., 2014,

    Magnetic remanence of l/ll4 Bjurböle: timing, intensity, and implications (poster)

    , 77th Annual Meteoritical Society Meeting

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