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Book Chapter

Biases in three-dimensional vorticity analysis using porphyroclast system: limits and application to natural examples

By
D. Iacopini
D. Iacopini
Geology and Petroleum Geology Department, University of Aberdeen, Aberdeen AB24 3UE, UK
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C. Frassi
C. Frassi
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126, Pisa, Italy
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R. Carosi
R. Carosi
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126, Pisa, Italy
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C. Montomoli
C. Montomoli
Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126, Pisa, Italy
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Published:
January 01, 2011

Abstract

A description of the systematic errors associated with the measurement of the vorticity number from poryhroclasts in natural systems is presented and discussed. We show that strong biases and systematic errors could derive both from some erroneous physical (i.e. no slip across clast/matrix boundary, homogeneity within the matrix) as well as geometrical assumptions (i.e. the radius ratio and angular measurements carried out in two dimensions on outcrop surfaces and thin section). By comparing natural datasets of porphyroclast shape preferred orientation (SPO) with different theoretical curves plots, we suggest that at least one of the Jeffery physical assumptions can be tested when applying vorticity techniques. The comparison of different possible sources of systematic errors indicates that, for medium-to-low vorticity numbers (Wm<0.8), vorticity data are strongly biased and that a minimum systematic error of 0.2 should be taken into account. Finally, we use data from natural shear zones from the Southern Variscan Belt in Sardinia to test and discuss the starting assumptions of the Jeffery model.

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Contents

Geological Society, London, Special Publications

Deformation Mechanisms, Rheology and Tectonics: Microstructures, Mechanics and Anisotropy

David J. Prior
David J. Prior
University of Otago, New Zealand
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Ernest H. Rutter
Ernest H. Rutter
University of Manchester, UK
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Daniel J. Tatham
Daniel J. Tatham
University of Liverpool, UK
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Geological Society of London
Volume
360
ISBN electronic:
9781862394483
Publication date:
January 01, 2011

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