279 results found
Shah J, Muxworthy AR, Almeida T, et al., Electron Holography of Chondrule Dusty Olivine (poster), Meteorites and Solar System formation workshop
Almeida TP, Muxworthy AR, Kovacs 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, ISSN: 1742-6588
A synthetic basalt comprising magnetic Fe3O4 grains (~ 50 nm to ~ 500 nm in diameter) is investigated using a range of complementary nano-characterisation techniques. Off-axis electron holography combined with in situ heating allowed for the visualisation of the thermally-induced magnetic relaxation of an Fe3O4 grain (~ 300 nm) from an irregular domain state into a vortex state at 550˚C, just below its Curie temperature, with the magnetic intensity of the vortex increasing on cooling.
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
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, ISSN: 1525-2027
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, 1782 Ma, Puiuà 1788, and Pedra Preta, 1795 Ma. We adopted a multi-protocol approach for paleointensity estimates combining Thellier-type IZZI and LTD-IZZI methods, and the non-heating Preisach protocol. We obtained an average VDM value of 1.3 ± 0.7 × 1022Am2 (Cotingo) of 2.0 ± 0.4 × 1022Am2 (Puiuà) and 6 ± 4 × 1022Am2 (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, ISSN: 2296-6463
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., Proc Natl Acad Sci U S A, Vol: 114, Pages: 10356-10360
Interpretations of paleomagnetic observations assume that naturally occurring magnetic particles can retain their primary magnetic recording over billions of years. The ability to retain a magnetic recording is inferred from laboratory measurements, where heating causes demagnetization on the order of seconds. The theoretical basis for this inference comes from previous models that assume only the existence of small, uniformly magnetized particles, whereas the carriers of paleomagnetic signals in rocks are usually larger, nonuniformly magnetized particles, for which there is no empirically complete, thermally activated model. This study has developed a thermally activated numerical micromagnetic model that can quantitatively determine the energy barriers between stable states in nonuniform magnetic particles on geological timescales. We examine in detail the thermal stability characteristics of equidimensional cuboctahedral magnetite and find that, contrary to previously published theories, such nonuniformly magnetized particles provide greater magnetic stability than their uniformly magnetized counterparts. Hence, nonuniformly magnetized grains, which are commonly the main remanence carrier in meteorites and rocks, can record and retain high-fidelity magnetic recordings over billions of years.
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
Mac Niocaill C, Muxworthy AR, Vowles K, et al., 2016, Palaeomagnetic dates of Irish Zn-Pb deposits record regional remagnetization related to Variscan fluid flow, Magnetic Interactions 2016
Maidment S, Muxworthy AR, 2016, A chronostratigraphic framework for the Morrison Formation and the latitudinal biodiversity gradient in Morrison dinosaurs (poster), 76th Annual Meeting Society of Vertebrate Paleontology
Maidment S, Muxworthy AR, 2016, A chronostratigraphic framework for the Morrison formation, western USA: A sequence stratigraphic and magnetostratigraphic approach (poster), Magnetic Interactions 2016
Muxworthy AR, 2016, How Well Does Preisach Theory Predict Pseudo-Single-Domain Behavior? (poster), Magnetic Interactions 2016
Muxworthy AR, 2016, Recovering ancient magnetic field intensities from rocks and meteorites using FORC Measurements (invited), 2nd FORC Workshop
Muxworthy AR, Almeida TP, Williams W, et al., 2016, Imaging magnetic stability of PSD magnetite, 15th Castle Meeting
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