Specification of fabric shapes using an eigenvalue method

Woodcock, Nigel

doi:10.1130/0016-7606(1977)88<1231:sofsua>2.0.co;2

Cited by 524 publications

(420 citation statements)

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“…is the gradient of the radiating lines (Woodcock, 1977).The Flinn-type diagrams of our samples show that the shape of the fabric ellipsoids are mainly in good agreement for the IA-F, IA-S, AMS, the mafic silicates SLD and the magnetite SLD (Fig. 5).…”

Section: Intensity Of Spomentioning

confidence: 50%

“…The shape of fabric ellipsoids delivered by different techniques can easily be compared in a plot of the axial ratios of the ellipsoids (Woodcock, 1977). In such a Flinn-type diagram (Flinn, 1962), the lines radiating out from the origin divide regions of different fabric ellipsoid shapes such as prolate (∞ > K > 1) where the maximum (max) axes cluster in a stereonet projection, and oblate shapes (1 > K > 0) where the maximum and the intermediate (int) axes form a girdle.…”

Section: Intensity Of Spomentioning

confidence: 99%

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The relation between magnetite and silicate fabric in granitoids of the Adamello Batholith

et al. 2015

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Keywords:Rock fabrics in granites; X-ray micro-tomography; Anisotropy of magnetic susceptibility (AMS); 3D shape fabrics (SPO); Magnetic interactions AbstractThe link between the macroscopic silicate fabric and the magnetite-controlled AMS (anisotropy of magnetic susceptibility) fabric in ferromagnetic rocks was investigated through a comprehensive comparison between different fabric measurement techniques. Sample lithologies include tonalites and granodiorites from the Lago della Vacca Complex, Adamello Batholith, Italy. The datasets used to assess the link between subfabrics and the coherence between methods include: 1) macroscopic silicate fabric measured directly in the field; 2) macroscopic silicate fabric derived from image analysis (IA) of outcrop pictures and sample pictures; 3) shape-preferred orientations (SPO) of mafic silicates, 4) SPO of magnetite, and 5) calculated distribution of magnetite grains from computer-assisted highresolution X-ray tomography (X-ray CT) images; 6) fabrics derived from the AMS. Macroscopic mineral fabrics measured in the field agree with the IA results and with the SPO of mafic silicates obtained from the X-ray CT imaging. The X-ray CT results show that the SPO of the magnetite grains are consistent with the AMS data whereas the spatial distribution of the magnetite grains is less compatible with the AMS fabric. This implies that the AMS signal is mainly controlled by the shape of the magnetic carrier mineral rather than by the spatial arrangement of the magnetite grains. An exception is the presence of magnetite clusters. Furthermore, the SPO of mafic silicates and the SPO of the magnetite grains are consistent with the AMS data. Another finding of this study is that the magnetic susceptibility correlates linearly with the amount of magnetite in the samples. The coherent results obtained from a variety of methods reinforce the application of both AMS measurements and IA as robust tools to analyse fabrics in granitic intrusions.

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Section: Intensity Of Spomentioning

confidence: 50%

Section: Intensity Of Spomentioning

confidence: 99%

The relation between magnetite and silicate fabric in granitoids of the Adamello Batholith

et al. 2015

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“…The 3pt method we use hereafter is a variation of the one presented in ref. [24,25], involving an eigenvector decomposition of the arrival directions of all triplets found in the data set [22] . For each cosmic ray we convert the arrival direction into a Cartesian vector r k ={r x , r y , r z }.…”

Section: The Shape Strength 3pt Methodsmentioning

confidence: 99%

A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory

Abreu¹,

Aglietta²,

Ahlers³

et al. 2012

J. Cosmol. Astropart. Phys.

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Observations of cosmic ray arrival directions made with the Pierre Auger Observatory have previously provided evidence of anisotropy at the 99% CL using the correlation of ultra high energy cosmic rays (UHECRs) with objects drawn from the Véron-Cetty Véron catalog. In this paper we report on the use of three catalog independent methods to search for anisotropy. The 2pt–L, 2pt+ and 3pt methods, each giving a different measure of self-clustering in arrival directions, were tested on mock cosmic ray data sets to study the impacts of sample size and magnetic smearing on their results, accounting for both angular and energy resolutions. If the sources of UHECRs follow the same large scale structure as ordinary galaxies in the local Universe and if UHECRs are deflected no more than a few degrees, a study of mock maps suggests that these three methods can efficiently respond to the resulting anisotropy with a P-value = 1.0% or smaller with data sets as few as 100 events. Using data taken from January 1, 2004 to July 31, 2010 we examined the 20,30,…,110 highest energy events with a corresponding minimum energy threshold of about 49.3 EeV. The minimum P-values found were 13.5% using the 2pt-L method, 1.0% using the 2pt+ method and 1.1% using the 3pt method for the highest 100 energy events. In view of the multiple (correlated) scans performed on the data set, these catalog-independent methods do not yield strong evidence of anisotropy in the highest energy cosmic rays.

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“…4) K = r 1 /r 2 (see Woodcock, 1977). 5) % 'plunging': percentage of clast a-axes dipping steeper than local slope dip .…”

Section: Methodsmentioning

confidence: 99%

Rain-generated overland flow as a factor in the development of some stratified slope deposits: A case study from the Pays du Buëch (Préalpes, France)

Steijn¹,

Hétu²

2002

gpq

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A large exposure of stratified slope deposits, and a partly vegetated active talus, both situated near Veynes (Préalpes du Sud, France) were studied. On the active slope, dry grain flows, erosion by rain-generated overland flow, and 'aggregate' flows caused by high-intensity rainstorms are most typical. The term 'aggregate' flow was chosen because of the abundant presence of silty aggregates (diameter 0.5-3 mm) within these deposits which closely resemble small debris flows. These three processes operate in a fixed sequence thus producing a characteristic stratification pattern. Forms and sediments caused by the processes mentioned are described in detail. Subsequently, the results are applied in the interpretation of the sections of the relict deposits. The correlation and the interpretation problems with regard to processes involved between deposits on the active slope and within the relict sediment mass are discussed, together with the traces of other processes recognised within the latter. The results are placed in a wider context of stratified slope deposits and their palaeoclimatic significance.La dynamique de surface d'un talus d'éboulis stratifié partiellement actif a été étudiée en détail dans le but d'en comprendre la stratigraphie, exposée dans une grande gravière à la base du talus. Elaboré à la charnière Pléistocène-Holocène, cet éboulis est situé en France, dans la vallée du Buëch près de Veynes, Préalpes du Sud. Sur le versant actif, partiellement couvert d'arbustes, les processus dominants sont les coulées de pierres sèches, l'érosion pluviale et les 'coulées d'agrégats' associées aux fortes pluies. Ces dernières correspondent à de petites laves de ruissellement comprenant une forte proportion d'agrégats limoneux de 0,5 à 3 mm de diamètre. Ces trois processus interviennent en séquence, définissant une chaîne de processus qui produit des dépôts stratifiés. Les formes et les sédiments associés à ces processus sont décrits en détail. Les résultats sont ensuite utilisés comme cadre de référence lors de l'interprétation des dépôts anciens exposés dans la gravière. Entre les dépôts actuels et les dépôts anciens, on note à la fois des similitudes et des différences. Les premières confirment la validité du modèle proposé ; les secondes soulèvent différents problèmes qui sont discutés (altération des signatures sédimentaires avant et après l'enfouissement des dépôts ; intervention d'autres processus). Ce type d'éboulis stratifié, élaboré par des processus azonaux, n'a en soi aucune signification climatique précise.Ein Aufschluss in geschichteten Hangschuttablagerungen, situiert in der Umgebung von Veynes (Préalpes du Sud, Frankreich), sowie die teils bewachsene, aktive Schutthalde neben der Grube wurden untersucht. Auf der aktiven Schutthalde wurden (trockene) matrixlose Steinströme, durch Regen generierte Abspülung und mit (extremen) Starkregen verbundenen, Murgangähnliche 'Aggregat'-Ströme als die meist charakteristischen Prozesse festgestellt. Die Andeutung 'Aggregatströme' wurde gewählt aufgrund der An...

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Specification of fabric shapes using an eigenvalue method

Cited by 524 publications

References 0 publications

The relation between magnetite and silicate fabric in granitoids of the Adamello Batholith

The relation between magnetite and silicate fabric in granitoids of the Adamello Batholith

A search for anisotropy in the arrival directions of ultra high energy cosmic rays recorded at the Pierre Auger Observatory

Rain-generated overland flow as a factor in the development of some stratified slope deposits: A case study from the Pays du Buëch (Préalpes, France)

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