286 results found
Almeida TP, Muxworthy AR, Kovács A, et al., 2017, Observation of thermally-induced magnetic relaxation in a magnetite grain using off-axis electron holography, Journal of Physics: Conference Series, Vol: 902, Pages: 012001-012001, ISSN: 1742-6588
Almeida TP, Muxworthy AR, Williams W, et al., 2017, Visualising dynamic chemical reactions and magnetic behaviour of nano-scale magnetic materials using electron microscopy (invited), Magnetic Interactions, Edinburgh
Berndt T, Muxworthy AR, 2017, Dating Icelandic glacial floods using a new viscous remanent magnetization protocol, GEOLOGY, Vol: 45, Pages: 339-342, ISSN: 0091-7613
Berndt T, Paterson GA, Cao C, et al., 2017, Experimental test of the heating and cooling rate effect on blocking temperatures, GEOPHYSICAL JOURNAL INTERNATIONAL, Vol: 210, Pages: 255-269, ISSN: 0956-540X
Berndt T, Ramalho RS, Valdez-Grijalva MA, et al., 2017, Paleomagnetic field reconstruction from mixtures of titanomagnetites, Earth and Planetary Science Letters, Vol: 465, Pages: 70-81, ISSN: 0012-821X
Stepwise thermal demagnetization and alternating field (AF) demagnetization are commonly used in paleomagnetic studies to isolate remanent magnetic components of different origins. The magnetically hardest, i.e. highest unblocking temperature/peak field component is often interpreted as the primary magnetization and magnetically softer components as subsequent remagnetizations due to geological events posterior to the formation of the rock, such as reheating or formation of new magnetic minerals. The correct interpretation of the sequence of the geological events such as tectonic rotations from paleomagnetic data often relies on correctly attributing the observed magnetic directions to the remanence carriers and acquisition mechanisms. Using a numerical model to simulate remanence acquisition and stepwise thermal and AF demagnetization experiments, we show that the presence of mixtures of different magnetic minerals, such as magnetite and titanomagnetites of varying titanium-content can have very significant effects on Zijderveld plots. In thermal demagnetization experiments a spurious third component at intermediate temperatures or a continuous curvature may arise from an overlap of the primary remanence with a subsequent thermal or viscous remagnetization carried by small-grained iron-rich magnetite and large-grained titanium-rich titanomagnetite. AF demagnetization plots of magnetic mixtures are even more complex: primary and secondary remanences carried by different minerals may appear as either three or four components in Zijderveld plots. During alternating field demagnetization the highest coercivity component is not necessarily equivalent to the primary remanence and does not necessarily correspond to the highest temperature component in an analogous thermal demagnetization experiment, i.e., the primary remanence direction cannot be recovered. The effects are shown to be due to the different responsiveness of magnetite and titanomagnetites towards viscous or
Berndt T, Ramalho RS, Valdez-Grijalva MA, et al., 2017, Paleomagnetic field reconstruction from mixtures of titanomagnetites, Magnetic Interactions, Edinburgh
Di Chiara A, Muxworthy AR, Trindade RIF, et al., 2017, Paleoproterozoic Geomagnetic Field Strength From the Avanavero Mafic Sills, Amazonian Craton, Brazil, Geochemistry, Geophysics, Geosystems
© 2017. American Geophysical Union. All Rights Reserved. A recent hypothesis has suggested that Earth's inner core nucleated during the Mesoproterozoic, as evidenced by a rapid increase in the paleointensity (ancient geomagnetic field intensity) record; however, paleointensity data during the Paleoproterozoic and Mesoproterozoic period are limited. To address this problem, we have determined paleointensity from samples from three Paleoproterozoic Avanavero mafic sills (Amazonian Craton, Brazil): Cotingo, 1,782 Ma, Puiuà, 1,788 Ma, and Pedra Preta, 1,795 Ma. We adopted a multiprotocol approach for paleointensity estimates combining Thellier-type IZZI and LTD-IZZI methods, and the nonheating Preisach protocol. We obtained an average VDM value of 1.3±0.7 × 10 22 Am 2 (Cotingo) of 2.0±0.4 × 10 22 Am 2 (Puiuà) and 6±4 × 10 22 Am 2 (Pedra Preta); it is argued that the Cotingo estimate is the most robust. Our results are the first data from the upper Paleoproterozoic for South America and are comparable to data available from other regions and similar periods. The new data do not invalidate the hypothesis of that Earth's inner core nucleated during the Mesoproterozoic.
Hofman J, Maher BA, Muxworthy AR, et al., 2017, Biomagnetic Monitoring of Atmospheric Pollution: A Review of Magnetic Signatures from Biological Sensors, ENVIRONMENTAL SCIENCE & TECHNOLOGY, Vol: 51, Pages: 6648-6664, ISSN: 0013-936X
Maidment S, Balikova D, Muxworthy AR, 2017, Magnetostratigraphy of the Morrison Formation, Utah, Terrestrial Depositional Systems Deciphering Complexities Through Multiple Stratigraphic Methods, Editors: Zeigler, Parker, Publisher: Elsevier, ISBN: 9780128032435
Terrestrial Depositional Systems: Deciphering Complexities through Multiple Stratigraphic Methods is the first collection of contributed articles that not only introduces young geoscientists to biostratigraphy, chemostratigraphy, ...
Muxworthy AR, 2017, Considerations for latitudinal time-averaged-field palaeointensity analysis of the last five million years, Frontiers in Earth Science, Vol: 5
© 2017 Muxworthy. Central to palaeomagnetism and geophysics is the assumption that the time-averaged geomagnetic field is approximated by a geocentric-axial-dipole (GAD). In this paper, it is demonstrated through the use of a simple cap model that due to secular variation the time-averaged palaeointensity record will always have a smaller latitudinal dependency than a true GAD field. However, the simple cap model does not fully explain the behavior of the palaeointensity database (averaged over 0–5Ma) especially at high-latitudes. To investigate this dependency I use a Giant Gaussian Processes (GGP) model to estimate the contribution of permanent non-dipole features and determine their statistical significance. It was found that an axial quadrupole term between −5 and −10% of the GAD field combined with octupole term ∼ −15% of the GAD field, best explained palaeointensity latitudinal behavior. In particular, the octupole term with a sign opposite to that of the GAD, is required to describe the palaeointensity behavior at high latitudes, i.e., > 60°.
Muxworthy AR, Bland PA, Davison TM, et al., 2017, Evidence for an impact-induced magnetic fabric in Allende, and exogenous alternatives to the core dynamo theory for Allende magnetization, METEORITICS & PLANETARY SCIENCE, Vol: 52, Pages: 2132-2146, ISSN: 1086-9379
Nagy L, Williams W, Muxworthy AR, et al., 2017, Stability of equidimensional pseudo-single-domain magnetite over billion-year timescales, PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, Vol: 114, Pages: 10356-10360, ISSN: 0027-8424
Paterson GA, Muxworthy AR, Yamamoto Y, et al., 2017, Bulk magnetic domain stability controls paleointensity fidelity, Proceedings of the National Academy of Sciences, ISSN: 0027-8424
Nonideal, nonsingle-domain magnetic grains are ubiquitous in rocks; however, they can have a detrimental impact on the fidelity of paleomagnetic records—in particular the determination of ancient magnetic field strength (paleointensity), a key means of understanding the evolution of the earliest geodynamo and the formation of the solar system. As a consequence, great effort has been expended to link rock magnetic behavior to paleointensity results, but with little quantitative success. Using the most comprehensive rock magnetic and paleointensity data compilations, we quantify a stability trend in hysteresis data that characterizes the bulk domain stability (BDS) of the magnetic carriers in a paleomagnetic specimen. This trend is evident in both geological and archeological materials that are typically used to obtain paleointensity data and is therefore pervasive throughout most paleomagnetic studies. Comparing this trend to paleointensity data from both laboratory and historical experiments reveals a quantitative relationship between BDS and paleointensity behavior. Specimens that have lower BDS values display higher curvature on the paleointensity analysis plot, which leads to more inaccurate results. In-field quantification of BDS therefore reflects low-field bulk remanence stability. Rapid hysteresis measurements can be used to provide a powerful quantitative method for preselecting paleointensity specimens and postanalyzing previous studies, further improving our ability to select high-fidelity recordings of ancient magnetic fields. BDS analyses will enhance our ability to understand the evolution of the geodynamo and can help in understanding many fundamental Earth and planetary science questions that remain shrouded in controversy.
Roberts AP, Almeida TP, Church NS, et al., 2017, Resolving the origin of pseudo-single domain magnetic behavior, Journal of Geophysical Research, ISSN: 0148-0227
Shah J, Muxworthy AR, Almeida TP, et al., 2017, Dusty olivine: our oldest record of rock magnetism? (invited), Magnetic Interactions, Edinburgh
Valdez-Grijalva MA, Muxworthy AR, Williams W, et al., 2017, The FORC function of non-interacting SD to PSD greigite ensembles, Magnetic Interactions, Edinburgh, 2017
Valdez-Grijalva MA, Nagy L, Muxworthy AR, et al., 2017, The magnetic structure and palaeomagnetic recording fidelity of sub-micron greigite (Fe3S4), Earth and Planetary Science Letters, ISSN: 0012-821X
Wilkinson JJ, Vowles K, Muxworthy AR, et al., 2017, Regional remagnetization of Irish Carboniferous carbonates dates Variscan orogenesis, not Zn-Pb mineralization, GEOLOGY, Vol: 45, Pages: 747-750, ISSN: 0091-7613
Abubakar R, Muxworthy AR, Sephton M, et al., 2016, Mapping Petroleum Migration Pathways in Wessex Basin Using Magnetics and Seismic Mapping (poster), Magnetic Interactions 2016
Almeida T, Muxworthy AR, Kasama T, et al., 2016, Effect of maghemization on the magnetic properties of non-stoichiometric pseudo-single-domain magnetite particles (poster), Magnetic Interactions 2016
Almeida TP, Muxworthy AR, Kovacs A, et al., 2016, Direct visualization of the thermomagnetic behavior of pseudo-single-domain magnetite particles, SCIENCE ADVANCES, Vol: 2, ISSN: 2375-2548
Almeida TP, Muxworthy AR, Kovacs A, et al., 2016, Direct observation of the thermal demagnetization of magnetic vortex structures in nonideal magnetite recorders, GEOPHYSICAL RESEARCH LETTERS, Vol: 43, Pages: 8426-8434, ISSN: 0094-8276
Almeida TP, Muxworthy AR, Williams W, et al., 2016, Direct visualization of CRM and TRM of pseudo-single-domain magnetite particles (invited), Magnetic Interaction 2016
Badejo, Muxworthy AR, Fraser A, 2016, Application of magnetic techniques to lateral hydrocarbon migration - Lower Tertiary reservoir systems, UK North Sea (poster), Magnetic Interactions 2016
Berndt T, Muxworthy AR, 2016, Magnetic dating of storm floods, jökulhlaups and tsunamis, EGU 2016
Berndt T, Muxworthy AR, 2016, Viscous Remanent Magnetization Dating of Floods, Beijing Earth and Planetary Interior Symposium
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: 2169-9313
Di Chiara A, Muxworthy AR, Trindade R, 2016, Paleointensity of Proterozoic magmatic rocks from South America (poster), EGU 2016
Dossing A, Muxworthy AR, Supakulopas R, et al., 2016, High northern geomagnetic field behavior and new constraints on the Gilsa event: Paleomagnetic and Ar-40/Ar-39 results of similar to 0.5-3.1 Ma basalts from Jokuldalur, Iceland, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 456, Pages: 98-111, ISSN: 0012-821X
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.