Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization

© 2016 Elsevier B.V..Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain (SD) monoclinic pyrrhotite (Fe7S8). The samples were in the form of a powder and a powder dispersed in epoxy. "Non-ideal" refers to a powder fraction of predominantly SD size with a minor contribution of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence carrier in several types of meteorites (carbonaceous chondrites, SNC. . .), which justifies the usage of synthetic compositions as analogous to natural samples. Data were collected from 5 to 633 K and include low-field magnetic susceptibility (χ0), thermomagnetic curves, major hysteresis loops, back-field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pressure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data (such as zero-field-cooled and field-cooled remanence datasets together with room temperature SIRM cooling-warming cycles) as well as XRD and Mössbauer spectra. The characteristic Besnus transition is observed at ∼33 K. FORC diagrams indicate interacting SD grains. The application of hydrostatic pressure up to 2 GPa using nonmagnetic high-pressure cells resulted in the demagnetization of the sample by 32-38%. Repeated cycling from 1.8 GPa to atmospheric pressure and back resulted in a total remanence decrease of 44% (after 3 cycles). Pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for

The effects of 10 to >160 GPa shock on the magnetic properties of basalt and diabase

© 2016. American Geophysical Union. All Rights Reserved.Hypervelocity impacts within the solar system affect both the magnetic remanence and bulk magnetic properties of planetary materials. Spherical shock experiments are a novel way to simulate shock events that enable materials to reach high shock pressures with a variable pressure profile across a single sample (ranging between ∼10 and >160 GPa). Here we present spherical shock experiments on basaltic lava flow and diabase dike samples from the Osler Volcanic Group whose ferromagnetic mineralogy is dominated by pseudo-single-domain (titano)magnetite. Our experiments reveal shock-induced changes in rock magnetic properties including a significant increase in remanent coercivity. Electron and magnetic force microscopy support the interpretation that this coercivity increase is the result of grain fracturing and associated domain wall pinning in multidomain grains. We introduce a method to discriminate between mechanical and thermal effects of shock on magnetic properties. Our approach involves conducting vacuum-heating experiments on untreated specimens and comparing the hysteresis properties of heated and shocked specimens. First-order reversal curve (FORC) experiments on untreated, heated, and shocked specimens demonstrate that shock and heating effects are fundamentally different for these samples: shock has a magnetic hardening effect that does not alter the intrinsic shape of FORC distributions, while heating alters the magnetic mineralogy as evident from significant changes in the shape of FORC contours. These experiments contextualize paleomagnetic and rock magnetic data of naturally shocked materials from terrestrial and extraterrestrial impact craters

MAGNETIC CHARACTERIZATION OF NON-IDEAL SINGLE-DOMAIN MONOCLINIC PYRRHOTITE AND ITS DEMAGNETIZATION UNDER HYDROSTATIC PRESSURE UP TO 2 GPA WITH IMPLICATIONS FOR IMPACT DEMAGNETIZATION.

79th Annual Meeting of the Meteoritical-Society, Berlin, GERMANY, AUG 07-12, 2016International audienc

MAGNETIC PROPERTIES AND PETROGRAPHY OF URENGOITES AND SOUTH-URAL GLASS.

80th Annual Meeting of the Meteoritical-Society, Santa Fe, NM, JUL 23-28, 2017International audienc

Obsidian and mafic volcanic glasses from the Philippines and Vietnam found in the Paris Museum Australasian tektite collection

International audienceDuring the systematic magnetic susceptibility survey of the Paris Museum Australasian tektite collection, we identified three previously overlooked occurrences of volcanic glass that resembles tektites, based on anomalous magnetic properties, high water content, the presence of microcrystals, and anomalous chemical composition. These occurrences are from the Phu Yen province in south-central Vietnam (two rhyolitic glass fragments) and from the Philippines: one from northern Luzon Island (a basaltic rounded etched glass), one from Santa Mesa near Manilla (a dozen small rounded rhyolitic gravels). The two occurrences in the Philippines are quite similar to previously described volcanic glasses from the nearby Pagudpod and Nagcarlan localities, respectively. The rhyolitic glass specimens from the Phu Yen province are the first documentation of a geological occurrence of obsidian in Vietnam. This work is a warning note that glass samples with anomalous properties found among tektite collections may correspond to volcanic pseudotektites instead of real tektites with anomalous composition. The basaltic glass sample from the Philippines locally shows microcrystalline quench textures previously unknown in natural samples. These findings may also be of interest for archeologists involved in glass artifacts sourcing

Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization

© 2016 Elsevier B.V..Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain (SD) monoclinic pyrrhotite (Fe7S8). The samples were in the form of a powder and a powder dispersed in epoxy. "Non-ideal" refers to a powder fraction of predominantly SD size with a minor contribution of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence carrier in several types of meteorites (carbonaceous chondrites, SNC. . .), which justifies the usage of synthetic compositions as analogous to natural samples. Data were collected from 5 to 633 K and include low-field magnetic susceptibility (χ0), thermomagnetic curves, major hysteresis loops, back-field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pressure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data (such as zero-field-cooled and field-cooled remanence datasets together with room temperature SIRM cooling-warming cycles) as well as XRD and Mössbauer spectra. The characteristic Besnus transition is observed at ∼33 K. FORC diagrams indicate interacting SD grains. The application of hydrostatic pressure up to 2 GPa using nonmagnetic high-pressure cells resulted in the demagnetization of the sample by 32-38%. Repeated cycling from 1.8 GPa to atmospheric pressure and back resulted in a total remanence decrease of 44% (after 3 cycles). Pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for

Obsidian and mafic volcanic glasses from the Philippines and Vietnam found in the Paris Museum Australasian tektite collection

International audienceDuring the systematic magnetic susceptibility survey of the Paris Museum Australasian tektite collection, we identified three previously overlooked occurrences of volcanic glass that resembles tektites, based on anomalous magnetic properties, high water content, the presence of microcrystals, and anomalous chemical composition. These occurrences are from the Phu Yen province in south-central Vietnam (two rhyolitic glass fragments) and from the Philippines: one from northern Luzon Island (a basaltic rounded etched glass), one from Santa Mesa near Manilla (a dozen small rounded rhyolitic gravels). The two occurrences in the Philippines are quite similar to previously described volcanic glasses from the nearby Pagudpod and Nagcarlan localities, respectively. The rhyolitic glass specimens from the Phu Yen province are the first documentation of a geological occurrence of obsidian in Vietnam. This work is a warning note that glass samples with anomalous properties found among tektite collections may correspond to volcanic pseudotektites instead of real tektites with anomalous composition. The basaltic glass sample from the Philippines locally shows microcrystalline quench textures previously unknown in natural samples. These findings may also be of interest for archeologists involved in glass artifacts sourcing

Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization

© 2016 Elsevier B.V..Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain (SD) monoclinic pyrrhotite (Fe7S8). The samples were in the form of a powder and a powder dispersed in epoxy. "Non-ideal" refers to a powder fraction of predominantly SD size with a minor contribution of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence carrier in several types of meteorites (carbonaceous chondrites, SNC. . .), which justifies the usage of synthetic compositions as analogous to natural samples. Data were collected from 5 to 633 K and include low-field magnetic susceptibility (χ0), thermomagnetic curves, major hysteresis loops, back-field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pressure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data (such as zero-field-cooled and field-cooled remanence datasets together with room temperature SIRM cooling-warming cycles) as well as XRD and Mössbauer spectra. The characteristic Besnus transition is observed at ∼33 K. FORC diagrams indicate interacting SD grains. The application of hydrostatic pressure up to 2 GPa using nonmagnetic high-pressure cells resulted in the demagnetization of the sample by 32-38%. Repeated cycling from 1.8 GPa to atmospheric pressure and back resulted in a total remanence decrease of 44% (after 3 cycles). Pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for

Magnetic characterization of non-ideal single-domain monoclinic pyrrhotite and its demagnetization under hydrostatic pressure up to 2 GPa with implications for impact demagnetization

© 2016 Elsevier B.V..Here we present a comprehensive magnetic characterization of synthesized non-ideal single-domain (SD) monoclinic pyrrhotite (Fe7S8). The samples were in the form of a powder and a powder dispersed in epoxy. "Non-ideal" refers to a powder fraction of predominantly SD size with a minor contribution of small pseudo-single-domain grains; such non-ideal SD pyrrhotite was found to be a remanence carrier in several types of meteorites (carbonaceous chondrites, SNC. . .), which justifies the usage of synthetic compositions as analogous to natural samples. Data were collected from 5 to 633 K and include low-field magnetic susceptibility (χ0), thermomagnetic curves, major hysteresis loops, back-field remanence demagnetization curves, first-order reversal curves (FORCs), alternating field and pressure demagnetization of saturation isothermal remanent magnetization (SIRM), low temperature data (such as zero-field-cooled and field-cooled remanence datasets together with room temperature SIRM cooling-warming cycles) as well as XRD and Mössbauer spectra. The characteristic Besnus transition is observed at ∼33 K. FORC diagrams indicate interacting SD grains. The application of hydrostatic pressure up to 2 GPa using nonmagnetic high-pressure cells resulted in the demagnetization of the sample by 32-38%. Repeated cycling from 1.8 GPa to atmospheric pressure and back resulted in a total remanence decrease of 44% (after 3 cycles). Pressure demagnetization experiments have important implications for meteorite paleomagnetism and suggest that some published paleointensities of meteorites with non-ideal SD monoclinic pyrrhotite as remanence carrier may be lower limits because shock demagnetization was not accounted for