“…In general, the most common primary ferromagnetic (s.l.) minerals in fault pseudotachylytes are magnetite (Fe 3 O 4 ), and maghemite, (g-Fe 2 O 3 ) [Nakamura and Nagahama, 2001;Fukuchi, 2003;Ferré et al, 2005;Hirono et al, 2006;Zechmeister et al, 2007;Molina Garza et al, 2009]. Post-seismic alteration of these minerals generally leads to formation of more oxidized phases: At Santa Rosa, opaque grains in the pseudotachylyte, identified using optical and electron microscopy, are dominated by euhedral magnetite grains (<5 mm).…”
Section: Ferromagnetic Mineralsmentioning
confidence: 99%
“…Although TRM acquisition is inevitably coseismic due to the quasi instantaneous cooling of the pseudotachylyte melt [Nakamura et al, 2002;Ferré et al, 2005], the timing of CRM acquisition is less well understood. In addition, TRM is generally carried by magnetite, while CRM is typically borne by hematite or goethite, as shown, for example, in a recent study of pseudotachylytes in the Chiapas Massif, southern Mexico [Molina Garza et al, 2009].…”
[1] We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.
“…In general, the most common primary ferromagnetic (s.l.) minerals in fault pseudotachylytes are magnetite (Fe 3 O 4 ), and maghemite, (g-Fe 2 O 3 ) [Nakamura and Nagahama, 2001;Fukuchi, 2003;Ferré et al, 2005;Hirono et al, 2006;Zechmeister et al, 2007;Molina Garza et al, 2009]. Post-seismic alteration of these minerals generally leads to formation of more oxidized phases: At Santa Rosa, opaque grains in the pseudotachylyte, identified using optical and electron microscopy, are dominated by euhedral magnetite grains (<5 mm).…”
Section: Ferromagnetic Mineralsmentioning
confidence: 99%
“…Although TRM acquisition is inevitably coseismic due to the quasi instantaneous cooling of the pseudotachylyte melt [Nakamura et al, 2002;Ferré et al, 2005], the timing of CRM acquisition is less well understood. In addition, TRM is generally carried by magnetite, while CRM is typically borne by hematite or goethite, as shown, for example, in a recent study of pseudotachylytes in the Chiapas Massif, southern Mexico [Molina Garza et al, 2009].…”
[1] We investigate the petrographic, geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from Southern California, the Italian Alps and Kyushyu, Japan. The main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite. These ferrimagnetic grains record a stable, multicomponent magnetization that consists of one or more of the following: coseismic thermal remanent magnetization, coseismic lightning isothermal remanent magnetization and post-seismic chemical remanent magnetization. Fault pseudotachylytes from the three localities display contrasting magnetic properties, which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage.
“…Magnetic susceptibility and rock magnetism have commonly been used to understand the physical characteristics and chemical processes of fault slip zones (Enomoto and Zheng 1998;Nakamura and Nagahama 2001;Ferré et al 2005Ferré et al , 2012. Correlations have been reported between magnetic susceptibility anomalies in borehole log data and the presence of cataclastic zones and faults in the main drill borehole of the German Deep Drilling Project (KTB) (Bosum et al 1997), but the magnetic susceptibility of drill cuttings in the KTB do not support this correlation (Rauen et al 2000).…”
We measured the magnetic susceptibility of the core from the first borehole of the Wenchuan Earthquake (May 12, 2008, Mw7.9) Fault Scientific Drilling Project (WFSD-1) at 1-cm intervals. The correlations between magnetic susceptibility anomalies and fault rock occurrence are shown by a few fault zones in the WFSD-1 core. The values for the mass and ferromagnetic material magnetic susceptibility for the sample at 589.25-m depth are higher than those for the other samples. All the thermomagnetic curves display a rapid increase in slope after 380°C, and a marked peak occurs at about 510°C in the heating curves. The cooling curves are clearly higher than the heating curves. The saturation magnetization (Ms) shows a significant peak at a depth of 589.25 m, as do the mass magnetic susceptibility and the ferrimagnetic magnetic susceptibility. The mechanism principally responsible for the high magnetic susceptibility at a depth of 589.25 m might be the production of new magnetite from iron-bearing silicates (e.g., chlorite) or clays caused by frictional heating during seismic slip. Therefore, we suggest that the presence of high magnetic susceptibility fault gouges in the same country rock can be considered as an indicator of earthquakes or seismic signatures.
“…First, ferrimagnetic minerals in the fault slip zone may acquire a thermal remanent magnetization (TRM) upon cooling (Piper and Poppleton 1988;Ferré et al 2014). Second, earthquake lightning may constitute an additional magnetization process (Enomoto and Zheng 1998;Ferré et al 2005). Third, a fault slip zone may acquire chemical remanent magnetization (CRM) due to neoformation of ferrimagnetic minerals by thermal decomposition during seismic slips (Nakamura et al 2002;Fukuchi 2003;Fukuchi et al 2005;Hirono et al 2006;Chou et al 2012); it can be explained that many kinds of antiferromagnetic or paramagnetic minerals are thermally decomposed into ferrimagnetic minerals.…”
Microscopic billow-like wavy folds have been observed along slip planes of the Nojima active fault, southwest Japan. The folds are similar in form to Kelvin-Helmholtz (KH) instabilities occurring in fluids, which implies that the slip zone underwent "lubrication" such as frictional melting or fluidization of fault gouge materials. If the temperature range for generation of the billow-like wavy folds can be determined, we can constrain the physical properties of fault gouge materials during seismic slip. Here, we report on rock magnetic studies that identify seismic slip zones associated with the folds, and their temperature rises during ancient seismic slips of the Nojima active fault. Using a scanning magneto-impedance magnetic microscope and a scanning superconducting quantum interference device microscope, we observed surface stray magnetic field distributions over the folds, indicating that the folds and slip zones are strongly magnetized. This is due to the production of magnetite through thermal decomposition of antiferromagnetic or paramagnetic minerals in the gouge at temperatures over 350 °C. The presence of micrometer-sized finely comminuted materials in the billow-like wavy folds, along with our rock magnetic results, suggests that frictional heatinginduced fluidization was the driving mechanism of faulting. We found that the existence of the magnetized KH-type billow-like wavy folds supports that the low-viscosity fluid induced by fluidization after frictional heating decreased the frictional strength of the fault slip zone.
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