Magnetic fabric and deformation in the Navia–Alto Sil slate belt, northwestern Spain

Hirt, Ann M.; Julivert, Manuel; Soldevila, Josep Guindo

doi:10.1016/s0040-1951(00)00047-0

Cited by 31 publications

(17 citation statements)

References 23 publications

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“…In the central Coifs Harbour block, 3 out of 4 sites have a down-dip to oblique (>30 ~ magnetic lineation. In the Texas megafold, down-dip magnetic lineations occur close to the hinge of megafold Hirt et al (2000). observed comparable behaviours in the Asturian-Iberian Arc, and proposed that down-dip magnetic lineations in cleaved slates reflect true stretching lineations and strain heterogeneity.…”

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confidence: 86%

“…For proper interpretation of AMS data it is desirable to estimate the matrix susceptibility contribution (non-ferromagnetic grains) from the ferromagnetic susceptibility contribution: both contributions can have a fundamental impact on the AMS of sedimentary rocks at University of St Andrews on April 5, 2015 http://sp.lyellcollection.org/ Downloaded from (Borradaile et al 1986;Hirt et al 2000). We can divide the many sources of low-field magnetic susceptibility (K) into those of matrix origin (Kp), comprising paramagnetic, diamagnetic and antiferromagnetic susceptibilities, and those of ferromagnetic sensu lato origin (K0, which are also responsible for the remanent magnetization (Borradaile & Tarling 1981;Hrouda 1982;Henry 1983;Hounslow 1985;Rochette 1987a).…”

Section: Rock Magnetismmentioning

confidence: 99%

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Magnetic fabric constraints on oroclinal bending of the Texas and Coffs Harbour blocks: New England Orogen, eastern Australia

Aubourg

Klootwijk

Korsch

2004

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We have carried out a magnetic fabric study on deformed, clay-rich rocks from the Carboniferous Texas beds and Coifs Harbour Association in order to test the hypothesis of oroclinal bending of the Texas and Coifs Harbour blocks of the southern New England Orogen, eastern Australia. The magnetic susceptibility is dominated by paramagnetic phyllosilicates, with site-dependent contributions from the ferromagnetic minerals pyrrhotite, magnetite and hematite. Pyrrhotite is ubiquitous in the Texas block and in the central part of the Coifs Harbour block, and may be important as an indicator of the grade of lowtemperature metamorphism. The magnetic fabric results, in general, show good agreement with structural observations in the Texas and Coifs Harbour blocks. The magnetic foliation is related to the pervasive cleavage associated with accretionary deformation prior to oroclinal bending. The magnitudes of the anisotropy parameters and the plunge of the magnetic lineation indicate an increase in the intensity of deformation from east of the Coifs Harbour orocline towards the Texas orocline. An imprint from oroclinal deformation is suggested by a significant increase in the anisotropy parameter and by the development of steeply plunging magnetic lineations towards the hinges of the Texas and Coifs Harbour oroclines. The Terrica beds from the Early Permian (Allandale) Terrica inlier in the Texas orocline also show another, pre-tilt induced, tectonic imprint. Remanence data from volcanics in the Alum Rock inlier (293 Ma) and magnetic fabric data from this inlier tentatively constrain the onset of oroclinal bending as prior to extrusion of the Alum Rocks, and the completion of bending as post-Terrica beds deposition and pre-Illawarra Reversal (est. 265 Ma). et al. 2000). Such a complication has been described by Robion et al. (1995) who showed that an early structural magnetic lineation can From:

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confidence: 86%

Section: Rock Magnetismmentioning

confidence: 99%

Magnetic fabric constraints on oroclinal bending of the Texas and Coffs Harbour blocks: New England Orogen, eastern Australia

Aubourg

Klootwijk

Korsch

2004

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“…Chlorite and epidote most probably resulted from the retrograde metamorphism. This might explain why the correlation between magnetic anisotropy and finite strain axial ratio sometimes deviates greatly from other samples [ Hirt et al , 2000]. …”

Section: Discussionmentioning

confidence: 99%

Study on finite strain and its relationship with magnetic fabric along Ailao Shan‐Red River shear zone

Zhou

Qiu

et al. 2003

J. Geophys. Res.

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[1] The finite strain along Ailao Shan-Red River shear zone has been studied. The axial ratios of strain markers and shear strains vary greatly, arising principally from deformation intensity and from contrasting competencies. Ellipticity of chloritic amygdales in basalt ranges from 6.79 to 10.47 (corresponding shear strain g xz = 2.22-2.93), and ellipticity of garnets from 1.56 to 2.95 (g xz = 0.45-1.14) in core gneiss. The S-C angle of the sheared rocks varies from 2°to 28°(g sc = 1.35-28.60), mostly in a range 2°to 7°. Optical observation, thermal demagnetization, and hysteresis curves were conducted to determine the nature of minerals and the contribution of paramagnetic and ferromagnetic minerals to magnetic susceptibility. The result shows that ferromagnetic minerals and hornblende dominate the magnetic fabric of samples with high to very high susceptibility, and play an important role in the magnetic fabric of samples with low to intermediate susceptibility. The ferromagnetic minerals are mainly pseudo-single-domain and multidomain Ti-poor magnetite. Most samples have their magnetic lineation lying between the C and S surfaces. In the remaining samples, deviations from this common alignment principally resulted from the magnetic minerals being deflected by porphyroclasts, mineral cleavage, and cracks. The axial ratio correlation is very poor between the magnetic and actual or imaginary strain ellipsoid calculated from the S-C fabric. This poor correlation suggests that the shape of the finite strain ellipsoid cannot be evaluated using the magnetic fabric when the latter is a combined result from multiple minerals, and especially when the shape effect of multidomain titanomagnetite is important.INDEX TERMS: 1519 Geomagnetism and Paleomagnetism: Magnetic mineralogy and petrology; 8025 Structural Geology: Mesoscopic fabrics; 8110 Tectonophysics: Continental tectonics-general (0905); KEYWORDS: finite strain, anisotropy of magnetic susceptibility, relationship between petrofabric and magnetic fabric, Ailao Shan-Red River shear zone Citation: Zhou, Y., S. Wu, X. Qiu, and P. Zhou, Study on finite strain and its relationship with magnetic fabric along Ailao Shan-Red River shear zone,

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“…minerals, may result in positive bulk susceptibility for the rock. Reports on purely diamagnetic fabrics are rare in the literature (Almqvist et al 2009;Borradaile et al 1999;de Wall et al 2000;Hirt et al 2000;Hrouda et al 2000;Owens and Bamford 1976;Owens and Rutter 1978). Hrouda (2004) pointed out that commercial instruments rank principal susceptibilities according to their absolute values.…”

Section: Diamagnetic Mineralsmentioning

confidence: 99%

Unraveling magnetic fabrics

Hirt¹,

Almqvist²

2011

Int J Earth Sci (Geol Rundsch)

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The anisotropy of magnetic susceptibility has been proven to be an excellent indicator for mineral fabrics and therefore deformation in a rock or sediment. Low-field anisotropy is relatively rapid to measure so that a sufficient number of samples can be measured to obtain a good statistical representation of the magnetic fabric. The physical properties of individual minerals that contribute to the observed magnetic fabric include bulk susceptibility and intrinsic anisotropy of the mineral phase, its volume concentration, and its degree of alignment. Several techniques have been developed to separate magnetic subfabrics arising from magnetization types, i.e., ferrimagnetism, antiferromagnetism, paramagnetism, and diamagnetism. Susceptibility anisotropy can be measured in low or high fields and at different temperatures in order to isolate a particular subfabric. Measuring the anisotropy of a remanent magnetization can also isolate ferrimagnetic fabrics. A series of case studies are presented that exemplify the value of isolating magnetic subfabrics in a geological context. It is particularly useful in rocks that carry a paramagnetic and diamagnetic subfabric of similar magnitude, such that they negate one another. Further examples are provided for purely paramagnetic subfabrics and cases where a ferrimagnetic subfabric is also identified.

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Magnetic fabric and deformation in the Navia–Alto Sil slate belt, northwestern Spain

Cited by 31 publications

References 23 publications

Magnetic fabric constraints on oroclinal bending of the Texas and Coffs Harbour blocks: New England Orogen, eastern Australia

Magnetic fabric constraints on oroclinal bending of the Texas and Coffs Harbour blocks: New England Orogen, eastern Australia

Study on finite strain and its relationship with magnetic fabric along Ailao Shan‐Red River shear zone

Unraveling magnetic fabrics

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