Search or filter publications

Filter by type:

Filter by publication type

Filter by year:

to

Results

  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Morgan JV, Gulick SPS, Bralower T, Chenot E, Christeson G, Claeys P, Cockell C, Collins GS, Coolen MJL, Ferrière L, Gebhardt C, Goto K, Jones H, Kring DA, Le Ber E, Lofi J, Long X, Lowery C, Mellett C, Ocampo-Torres R, Osinski GR, Perez-Cruz L, Pickersgill A, Poelchau M, Rae A, Rasmussen C, Rebolledo-Vieyra M, Riller U, Sato H, Schmitt DR, Smit J, Tikoo S, Tomioka N, Urrutia-Fucugauchi J, Whalen M, Wittmann A, Yamaguchi KE, Zylberman Wet al., 2016,

    The formation of peak rings in large impact craters

    , Science, Vol: 354, Pages: 878-882, ISSN: 0036-8075

    Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust.

  • Journal article
    Johnson BC, Blair DM, Collins GS, 2016,

    Formation of the Orientale lunar multiring basin

    , Science, Vol: 354, Pages: 441-444, ISSN: 0036-8075

    Multiring basins, large impact craters characterized by multiple concentric topographic rings, dominate the stratigraphy, tectonics, and crustal structure of the Moon. Using a hydrocode, we simulated the formation of the Orientale multiring basin, producing a subsurface structure consistent with high-resolution gravity data from the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft. The simulated impact produced a transient crater, ~390 kilometers in diameter, that was not maintained because of subsequent gravitational collapse. Our simulations indicate that the flow of warm weak material at depth was crucial to the formation of the basin’s outer rings, which are large normal faults that formed at different times during the collapse stage. The key parameters controlling ring location and spacing are impactor diameter and lunar thermal gradients.

  • Journal article
    Kring DA, Kramer GY, Collins GS, Potter RWK, Chandnani Met al., 2016,

    Peak-Ring Structure and Kinematics from a Multi-disciplinary Study of the Schrödinger Impact Basin

    , Nature Communications, Vol: 7, ISSN: 2041-1723

    The Schrödinger basin on the lunar farside is ~320 km in diameter and the best-preservedpeak-ring basin of its size in the Earth–Moon system. Spectral and photogeologic analyses ofdata from the Moon Mineralogy Mapper instrument on the Chandrayaan-1 spacecraft and theLunar Reconnaissance Orbiter Camera (LROC) on the LRO spacecraft indicate the peak ring iscomposed of anorthositic, noritic, and troctolitic lithologies that were juxtaposed by severalcross-cutting faults during peak ring formation. Hydrocode simulations indicate the lithologieswere uplifted from depths up to 30 km, representing the crust of the lunar farside. Combining2geological and remote-sensing observations with numerical modeling, here we show a DisplacedStructural Uplift model is best for peak rings, including that in the K-T Chicxulub impact crateron Earth. These results may help guide sample selection in lunar sample return missions that arebeing studied for the multi-agency International Space Exploration Coordination Group.Determining which lunar landing site may yield information about the lunar interior is veryimportant with impact basins usually the best sites. Kring et al. provide a geological map of theSchrödinger basin on the moon via a multidisciplinary approach of remote sensing and numericalmodeling.

  • Conference paper
    Penny C, Muxworthy AR, Fabian K, 2016,

    The Curie temperature of magnetite nanoparticles (poster)

    , EMRS Fall 2016
  • Conference paper
    Shah J, Bates H, Muxworthy AR, Russell SS, Genge MJet al., 2016,

    A micro-CT conglomerate test (poster)

    , 15th Castle Meeting
  • Conference paper
    Penny C, Muxworthy AR, Fabian K, 2016,

    The Curie temperature of magnetite nanoparticles (poster)

    , 15th Castle Meeting
  • Conference paper
    Shah J, Muxworthy AR, Almeida TP, Kovacs A, Russell SS, Genge M, Williams W, Dunin-Borkowski REet al., 2016,

    Determining the magnetic recording fidelity of chondrule dusty olivine

    , 15th Castle Meeting
  • Journal article
    Almeida TP, Muxworthy AR, Kovacs A, Williams W, Nagy L, Conbhuí PC, Frandsen C, Supakulopus R, Dunin-Borkowski REet al., 2016,

    Direct observation of the thermal demagnetization of magnetic vortex structures in non-ideal magnetite recorders

    , Geophysical Research Letters, Vol: 43, Pages: 8426-8434, ISSN: 1944-8007

    The thermal demagnetization of pseudo-single-domain (PSD) magnetite (Fe3O4) particles, which govern the magnetic signal in many igneous rocks, is examined using off-axis electron holography. Visualization of a vortex structure held by an individual Fe3O4 particle (~ 250 nm in diameter) during in situ heating is achieved through the construction and examination of magnetic-induction maps. Step-wise demagnetization of the remanence-induced Fe3O4 particle upon heating to above the Curie temperature, performed in a similar fashion to bulk thermal demagnetization measurements, revealed its vortex state remains stable under heating close to its unblocking temperature, and is recovered upon cooling with the same or reversed vorticity. Hence, the PSD Fe3O4 particle exhibits thermomagnetic behavior comparable to a single-domain carrier, and thus vortex-states are considered reliable magnetic recorders for paleomagnetic investigations.

  • Conference paper
    Shah J, Muxworthy AR, Almeida T, Kovacs A, Russell SS, Genge M, Dunin-Borkowski Ret al., 2016,

    Hot Holography: Magnetic recording fidelity of dusty olivine (poster)

    , 13th UK Planetary Forum Early Career Scientists’ Meeting
  • Journal article
    Berndt T, Muxworthy AR, Fabian K, 2016,

    Does size matter? Statistical limits of paleomagnetic field reconstruction from small rock specimens

    , Journal of Geophysical Research: Solid Earth, Vol: 121, Pages: 15-26, ISSN: 2169-9356

    As samples of ever decreasing sizes are being studied paleomagnetically, care has to be taken that the underlying assumptions of statistical thermodynamics (Maxwell-Boltzmann statistics) are being met. Here we determine how many grains and how large a magnetic moment a sample needs to have to be able to accurately record an ambient field. It is found that for samples with a thermoremanent magnetic moment larger than 10−11Am2 the assumption of a sufficiently large number of grains is usually given. Standard 25 mm diameter paleomagnetic samples usually contain enough magnetic grains such that statistical errors are negligible, but “single silicate crystal” works on, for example, zircon, plagioclase, and olivine crystals are approaching the limits of what is physically possible, leading to statistic errors in both the angular deviation and paleointensity that are comparable to other sources of error. The reliability of nanopaleomagnetic imaging techniques capable of resolving individual grains (used, for example, to study the cloudy zone in meteorites), however, is questionable due to the limited area of the material covered.

  • Conference paper
    Shah J, Muxworthy AR, Almeida TP, Kovacs A, Russell SS, Genge M, Dunin-Borkowski Ret al., 2016,

    In-situ heating holography of chondrule dusty olivine

    , Magnetic Interactions
  • Conference paper
    Shah J, Muxworthy AR, Almeida T, Kovacs A, Russell SS, Genge M, Dunin-Borkowski REet al., 2015,

    Electron Holography of Chondrule Dusty Olivine (poster)

    , Meteorites and Solar System formation workshop
  • Journal article
    Almeida TP, Muxworthy AR, Kovács A, Williams W, Dunin-Borkowski REet al., 2015,

    Visualisation of high temperature magnetisation states in magnetite grains using off-axis electron holography

    , Journal of Physics: Conference Series, ISSN: 1742-6588
  • Journal article
    Abubakar R, Muxworthy AR, Southern P, Watson JS, Fraser AJ, Almeida TP, Sephton MA, Abubakar R, Muxworthy AR, Sephton MA, Fraser Aet al., 2015,

    Formation of magnetic minerals in hydrocarbon-generation conditions

    , Marine and Petroleum Geology, ISSN: 1873-4073

    In this paper, we report the pyrolysis and formation of magnetic minerals in three source rock samples from the Wessex Basin in Dorset, southern England. The experimental conditions in the laboratory recreated the catagenesis environment of oil source rocks. Magnetic analysis of both the heated and the unheated samples at room temperature and at very low temperatures (5 K), coupled with transmission electron-microscopy imaging and X-ray analysis, revealed the formation of nanometre-sized (<10 nm), magnetic particles that varied across the rock samples analysed, but more importantly across the pyrolysis temperature range. Magnetic measurements demonstrated the formation of these magnetic minerals peaked at 250 °C for all rock samples and then decreased at 300 °C before rising again at 320 °C. The newly formed magnetic minerals are suggested to be primarily pyrrhotite, though magnetite and greigite are also thought to be present. The sizes of the magnetic minerals formed suggest a propensity to migrate together with oil potentially explaining the magnetic anomalies observed above and within oil fields.

  • Journal article
    Potter RWK, Kring DA, Collins GS, 2015,

    Scaling of basin-sized impacts and the influence of target temperature

    , Geological Society of America Special Papers, Vol: 518, Pages: 99-113, ISSN: 0072-1077

    We produce a set of scaling laws for basin-sized impacts using data from a suiteof lunar basin numerical models. The results demonstrate the importance of preimpacttarget temperature and thermal gradient, which are shown to greatly infl uencethe modifi cation phase of the impact cratering process. Impacts into targets withcontrasting thermal properties also produce very different crustal and topographicprofi les for impacts of the same energy. Thermal conditions do not, however, signifi -cantly infl uence the excavation stage of the cratering process; results demonstrate,as a consequence of gravity-dominated growth, that transient crater radii are generallywithin 5% of each other over a wide range of thermal gradients. Excavationdepth-to-diameter ratios for the basin models (~0.12) agree well with experimental,geological, and geophysical estimates, suggesting basins follow proportional scaling.This is further demonstrated by an agreement between the basin models andPi- scaling laws based upon fi rst principles and experimental data. The results of thiswork should also be applicable to basin-scale impacts on other silicate bodies, includingthe Hadean Earth.

  • Journal article
    Almeida TP, Muxworthy AR, Kasama T, Williams W, Damsgaard C, Frandsen C, Pennycook TJ, Dunin-Borkowski REet al., 2015,

    Effect of maghemization on the magnetic properties of nonstoichiometric pseudo-single-domain magnetite particles

    , Geochemistry Geophysics Geosystems, Vol: 16, Pages: 2969-2979, ISSN: 1525-2027

    The effect of maghemization on the magnetic properties of magnetite (Fe3O4) grains in the pseudo-single-domain (PSD) size range is investigated as a function of annealing temperature. X-ray diffraction and transmission electron microscopy confirms the precursor grains as Fe3O4 ranging from ~ 150 nm to ~ 250 nm in diameter, whilst Mössbauer spectrometry suggests the grains are initially near-stoichiometric. The Fe3O4 grains are heated to increasing reaction temperatures of 120 – 220 ºC to investigate their oxidation to maghemite (γ-Fe2O3). High-angle annular dark field imaging and localized electron energy loss spectroscopy reveals slightly oxidized Fe3O4 grains, heated to 140 ºC, exhibit higher oxygen content at the surface. Off-axis electron holography allows for construction of magnetic induction maps of individual Fe3O4 and γ-Fe2O3 grains, revealing their PSD (vortex) nature, which is supported by magnetic hysteresis measurements, including first order reversal curve analysis. The coercivity of the grains is shown to increase with reaction temperature up to 180 ºC, but subsequently decreases after heating above 200 ºC; this magnetic behavior is attributed to the growth of a γ-Fe2O3 shell with magnetic properties distinct from the Fe3O4 core. It is suggested there is exchange coupling between these separate components that results in a vortex state with reduced vorticity. Once fully oxidized to γ-Fe2O3, the domain states revert back to vortices with slightly reduced coercivity. It is argued that due to a core/shell coupling mechanism during maghemization, the directional magnetic information will still be correct, however, the intensity information will not be retained.

  • Conference paper
    Shah J, Muxworthy AR, Russell SS, Genge MJet al., 2015,

    USING MICRO-CT TO MAP METEORITIC MAGNETISM.

    , 78th Annual Meeting of the Meteoritical-Society, Publisher: WILEY-BLACKWELL, ISSN: 1086-9379
  • Conference paper
    Shah J, Muxworthy AR, Almeida TP, Kovacs A, Russell SS, Genge MJ, Dunin-Borkowski REet al., 2015,

    VISUALIZING THE MAGNETIC BEHAVIOR OF CHONDRULE DUSTY OLIVINE USING ELECTRON HOLOGRAPHY.

    , 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,

    MAGNETIC FABRICS IN ALLENDE: IMPLICATIONS FOR MAGNETIC REMANENCE ACQUISITION.

    , 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.

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: http://wlsprd.imperial.ac.uk:80/respub/WEB-INF/jsp/search-t4-html.jsp Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=416&limit=20&page=2&respub-action=search.html Current Millis: 1642749793227 Current Time: Fri Jan 21 07:23:13 GMT 2022