Anisotropy of Magnetic Susceptibility

As iron-bearing minerals-ferrimagnetic minerals in particular-are sensitive to stress, temperature, and presence of fluids in fault zones, their magnetic properties provide valuable insights into physical and chemical processes affecting fault rocks. Here, we review the advances made in magnetic studies of fault rocks in the past three decades. We provide a synthesis of the mechanisms that account for the magnetic changes in fault rocks and insights gained from magnetic research. We also integrate nonmagnetic approaches in the evaluation of the magnetic properties of fault rocks. Magnetic analysis unveils microscopic processes operating in the fault zones such as frictional heating, energy dissipation, and fluid percolation that are otherwise difficult to constrain. This makes magnetic properties suited as a "strain indicator," a "geothermometer," and a "fluid tracer" in fault zones. However, a full understanding of faulting-induced magnetic changes has not been accomplished yet. Future research should focus on detailed magnetic property analysis of fault zones including magnetic microscanning and magnetic fabric analysis. To calibrate the observations on natural fault zones, laboratory experiments should be carried out that enable to extract the exact physicochemical conditions that led to a certain magnetic signature. Potential avenues could include (1) magnetic investigations on natural and synthetic fault rocks after friction experiments, (2) laboratory simulation of fault fluid percolation, (3) paleomagnetic analysis of postkinematic remanence components associated with faulting processes, and (4) synergy of interdisciplinary approaches in mineral-magnetic studies. This would help to place our understanding of the microphysics of faulting on a much stronger footing. Plain Language Summary The Earth's surface is riddled with faults that largely contribute to landscape evolution and human activities. Some of these faults produce earthquakes of different magnitudes including some with catastrophic consequences. Understanding faulting mechanisms benefits society when predictions about rupture are made. Fault zones preserve an excellent record of chemical and physical processes involved in failure. Among other analytical methods, magnetic studies prove to be an emergent and untapped source of information on these processes. These methods, focused on prefaulting, synfaulting, and postfaulting mineral changes, have resulted in significant advances in our understanding of the conditions of faulting. In this review, we present an extensive account of the state of knowledge and highlight current challenges and future avenues of fault magnetism research.

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“…The shape parameter ( T ) is also shown. Figures 7a and 7b are reprinted from Cho et al (2015), and Figure 7c is modified from Dubey (2014).…”

Section: Rock and Mineral Magnetism Of Fault Rocksmentioning

confidence: 99%

Faulting Processes Unveiled by Magnetic Properties of Fault Rocks

Yang

Chou

Ferré

et al. 2020

Reviews of Geophysics

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“…Diamagnetic materials have a small, negative susceptibility, whereas in paramagnetic materials, magnetic susceptibility is small and positive. Ferromagnetic materials have large and positive susceptibilities, and small amounts (>0.1% of the total mass) will dominate the bulk response of a sample (Dubey ). At high applied field strengths, ferromagnetic materials display hysteretic behavior, where magnetization will tend to saturate and persist after the applied field is removed.…”

Section: Theory and Literature Reviewmentioning

confidence: 99%

Enhanced nondestructive characterization of ordinary chondrites using complex magnetic susceptibility measurements

Oliver

Ralchenko

Samson

et al. 2017

Meteorit & Planetary Scien

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Ordinary chondrites have previously been nondestructively characterized using bulk magnetic susceptibility, broadly reflecting their Fe-Ni alloy content. We seek to expand the information that can be recovered from magnetic susceptibility by using the University of Toronto Electromagnetic Induction Spectrometer (UTEMIS) to measure the complex magnetic susceptibility tensor of 20 ordinary chondrites samples in addition to 16 Gao-Guenie (H5) chondrites at 35 frequencies from 90 Hz to 64 kHz, at variable low applied field strengths <10 A m À1 . Following removal of the field-dependent component of susceptibility, frequency dependence, in-and out-of-phase components, and bulk magnetic susceptibility were interpreted. Most meteorites showed no frequency-dependent in-phase responses, but had a frequency-dependent out-of-phase response attributed to eddy currents induced in conductive minerals. Greater in-and out-of-phase frequency dependence correlated with lower fayalite content in olivine and was, in turn, inversely proportional to Fe-Ni alloy content. The uncertainty in the UTEMIS measurements ranges from approximately 0.05% for low-frequency in-phase measurements to a maximum of 3% for low-frequency out-of-phase measurements. This uncertainty level was far lower than the intra-meteorite variability for the Gao-Guenie suite suggesting inhomogeneity at scales of approximately 10 g.

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