Magnetic and shape fabrics of magnetite in simple shear flows

Arbaret, Laurent; Launeau, Patrick; Diot, Hervé; Sizaret, Stanislas

doi:10.1016/j.jvolgeores.2012.09.003

Cited by 18 publications

(13 citation statements)

References 84 publications

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“…Hence, AMS has been determined to be a good proxy for the magma flow fabric in some igneous rocks. The determination of flow fabrics and AMS fabrics in analogue models (e.g., Arbaret et al 1996Arbaret et al , 1997Arbaret et al , 2013 confirms the broad correlation between AMS and flow fabrics, at least in the simple shear regime.…”

Section: Principles Of Rock Magnetism and The Origin Of Amssupporting

confidence: 60%

The Significance of Magnetic Fabric in Layered Mafic-Ultramafic Intrusions

et al. 2015

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Anisotropy of magnetic susceptibility (AMS) has been recognised as a well-established fabric analysis tool for intrusive igneous rocks since the 1990s. The AMS technique provides directional information for magnetic foliation and magnetic lineation fabric components of the AMS ellipsoid, potentially coupled with a quantification of the overall fabric strength and geometry. The magnetic susceptibility (and therefore the AMS) of igneous rocks is often dominated by ferromagnetic mineral phases such as magnetite or low-Ti titanomagnetite, even where present in very minor amounts (e.g., ~ 0.1 vol.%). Fe-bearing silicates exhibit subordinate paramagnetic behaviour but are volumetrically much more important constituents of igneous rocks than Fe-Ti oxides, so may also contribute considerably to the AMS.A significant application of AMS is in the characterisation, constraint and quantification of very weak or subtle mineral fabrics related to flow or tectonic deformation. In particular, studies of magnetic fabrics in sheet intrusions and in granite plutons have enormously enhanced our understanding of the magma flow regimes and emplacement kinematics in these settings. Studies of AMS in layered maficultramafic intrusions have been comparatively sparse. This is despite the fact that magnetic fabrics from layered cumulates may provide information on a range of magma chamber processes, from initial magma emplacement to cumulate textural evolution and solidification, if accompanied by careful petrographic documentation and an understanding of the 'magnetic mineralogy' of the rock. A wide array of rock magnetic and complementary quantitative fabric analysis techniques can be employed to support an AMS dataset in this regard. With studies of layered mafic-ultramafic intrusions currently proceeding at unprecedented (micro-)scales of textural and geochemical detail, AMS offers petrologists a unique approach to investigating the microstructure of cumulates and the textural complexity they exhibit.

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Section: Principles Of Rock Magnetism and The Origin Of Amssupporting

confidence: 60%

The Significance of Magnetic Fabric in Layered Mafic-Ultramafic Intrusions

et al. 2015

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“…The even distribution, small size and relative roundness of magnetite grains is strikingly similar to that of artifically produced pseudotachylytes where magnetite is neoformed (e.g., Nakamura et al 2002). Rock fabrics carried by PSD magnetite arise from the 3-D magnetostatic anisotropy, i.e., shape-preferred orientation (SPO) of magnetite grains (e.g., Arbaret et al, 2013).…”

Section: Mineralogic Origin Of the Amsmentioning

confidence: 65%

Deciphering viscous flow of frictional melts with the mini-AMS method

Ferré

Chou

Kuo

et al. 2016

Journal of Structural Geology

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The anisotropy of magnetic susceptibility (AMS) is widely used to analyze magmatic flow in intrusive igneous bodies including plutons, sills and dikes. This method, owing its success to the rapid nature of measurements, provides a proxy for the orientation of markers with shape anisotropy that flow and align in a viscous medium. AMS specimens typically are 25 mm diameter right cylinders or 20 mm on-aside cubes, representing a volume deemed statistically representative. Here, we present new AMS results, based on significantly smaller cubic specimens, which are 3.5 mm on a side, hence~ 250 times volumetrically smaller than conventional specimens. We show that, in the case of frictional melts, which inherently have an extremely small grain size, this small volume is in most cases sufficient to characterize the pseudotachylyte fabric, particularly when magnetite is present. Further, we demonstrate that the mini-AMS method provides new opportunities to investigate the details of frictional melt flow in these coseismic miniature melt bodies. This new method offers significant potential to investigate frictional melt flow in pseudotachylyte veins including contributions to the lubrication of faults at shallow to moderate depths.

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“…). This type of flow imparts a simple shear force that tends to produce a prolate AMS fabric, which has been reproduced both experimentally and numerically46. Because inflation of a magmatic sheet must be supported by an influx of more magma, sheet inflation is covered by this scenario too.…”

Section: Interpreting Ams In Sheet Intrusionsmentioning

confidence: 82%

Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden

Andersson

Almqvist

Burchardt

et al. 2016

Sci Rep

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Magma transport through the Earth’s crust occurs dominantly via sheet intrusions, such as dykes and cone-sheets, and is fundamental to crustal evolution, volcanic eruptions and geochemical element cycling. However, reliable methods to reconstruct flow direction in solidified sheet intrusions have proved elusive. Anisotropy of magnetic susceptibility (AMS) in magmatic sheets is often interpreted as primary magma flow, but magnetic fabrics can be modified by post-emplacement processes, making interpretation of AMS data ambiguous. Here we present AMS data from cone-sheets in the Alnö carbonatite complex, central Sweden. We discuss six scenarios of syn- and post-emplacement processes that can modify AMS fabrics and offer a conceptual framework for systematic interpretation of magma movements in sheet intrusions. The AMS fabrics in the Alnö cone-sheets are dominantly oblate with magnetic foliations parallel to sheet orientations. These fabrics may result from primary lateral flow or from sheet closure at the terminal stage of magma transport. As the cone-sheets are discontinuous along their strike direction, sheet closure is the most probable process to explain the observed AMS fabrics. We argue that these fabrics may be common to cone-sheets and an integrated geology, petrology and AMS approach can be used to distinguish them from primary flow fabrics.

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Magnetic and shape fabrics of magnetite in simple shear flows

Cited by 18 publications

References 84 publications

The Significance of Magnetic Fabric in Layered Mafic-Ultramafic Intrusions

The Significance of Magnetic Fabric in Layered Mafic-Ultramafic Intrusions

Deciphering viscous flow of frictional melts with the mini-AMS method

Magma transport in sheet intrusions of the Alnö carbonatite complex, central Sweden

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