Siegfried Siegesmund; Jörn H. Kruhl; Ewald Lüschen:

The Significance of rock fabrics for the geological interpretation of geophysical anisotropies

Petrophysical and seismic features of the exposed lower continental crust in Calabria (Italy)

1996. 1. edition, 163 pages, 77 figures, 6 tables, 16x24cm, 450 g
Language: English

(Geotectonic Research, Volume 85)

ISBN 978-3-510-50051-2, paperback, price: 65.00 €

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BibTeX file


geoteconics rock fabric anisotropy petrophysics seismic Calabria Italy


Inhaltsbeschreibung top ↑

Das Hauptthema des vorliegenden Bandes ist die Bedeutung anisotroper Gesteinsgefüge für die geologische Interpretation geophysikalischer Anisotropien. Die Richtungsabhängigkeit der physikalischen Eigenschaften basiert auf der engen Wechselbeziehung zwischen der kinematischen Information, repräsentiert durch das Gesteinsgefüge, und ihrer geophysikalischen Erscheinungsform. Die Interpretation geophysikalischer Phänomene durch anisotrope Materialeigenschaften ist für die Charakterisierung der lithologischen, strukturellen und physikalischen Eigenschaften der Erdkruste und des Erdmantels von zunehmender Bedeutung. Im Zentrum der Arbeit steht die Ableitung der physikalischen Eigenschaften der Gesteine auf zwei völlig verschiedenen Wegen: die Berechnung auf der Basis quantifizierter Gesteinsgefüge und experimenteller Ergebnisse.

Content Description top ↑

The main topic of the present paper is a review on the importance of anisotropic rock fabrics for the geological interpretation of geophysical anisotropies. There is a close link between the kinematic information frozen in the rock fabric and its geophysical expression, i.e. the directional dependence of physical properties. Recently, the interpretation of geophysical observations in therms of anisotropy has become a growing interest, because it promises a more refined insight into the composition, structure and physical properties of the Earth's crust and mantle. The central part of this research is the derivation of the anisotropic physical properties of rocks from two complementary methods: calculations based on quantified rock fabric data and those obtained experimentally.

Contents top ↑

Introduction 8
Rock fabrics 12
2.1 Basic concepts 12
2.2 Microstructures 16
2.3 Texture and shape fabric 17
2.4 Microcrack fabric 19
3. Techniques of fabric analysis 20
3.1 Image analysis 21
3.2 U-stage measurements 21
3.3 X-ray diffraction 21
3A Neutron diffraction 22
3.5 Electron diffraction 24
4. Seismic properties 25
4.1 Calculation procedure for properties described by a fourth order
tensor 27
4.1.1 Single crystal properties 29
4.1.2 Experimental determination of elastic wave velocities 33
4.1.3 The Alzenau amphibolite: a case study 36 Lithology and grain shape fabrics 36 Textures 40 Experimental observation and discussion 40
4.1.4 The effect of folding-induced fabric changes on the P-wave velocity
pattern 43 Samples and microstructure 43 Complete Vp-pattern of Sudejov orthogneisses 46 Discussion 46
4.2 Velocity anisotropy of the crustal segment at the KTB drilling site 50
4.2.1 Lithological profile and samples 52
4.2.2 Velocity structure from the KTB pilot hole 54 Laboratory versus sonic velocity data 57 Vp-anisotropy and its relation to the rock fabric 60
4.2.3 Shear-wave splitting 65 Shear-wave experiments at the KTB-site 67 Quantification of the observed shear-wave phenomena 69
4.3 Velocity anisotropy of the uppermost mantle beneath Southwest
Germany 73
4.3.1 Introduction 73
4.3.2 Geophysical model for Southwest Germany 75
4.3.3 Lithological constraints on the upper mantle composition 76
4.3.4 Rock fabrics and textures of upper mantle xenoliths from the
Northern Hessian Depressian 79
4.3.5 Calculated upper mantle properties: a discussion 79
5. Magnetic and thermal properties 84
5.1 Fundamentals 84
5.2 Anisotropy of the magnetic susceptibility 86
5.2.1 Introduction 86
5.2.2 Experimental measurement and representation of low-field AMS 87
5.2.3 Relationship between preferred orientation of the rock-forming
minerals and the AMS 88 Rock samples 88 Texture analyses 89 AMS of the single crystal 89
5.2.4 Experimental results 91 Relation between experimental and modelled AMS 95 1 AMS-strain relation 97 1
5.3 Anisotropy of the thermal conductivity 100
5.3.1 Introduction 100
5.3.2 Relationship between preferred orientation of the rock-forming
minerals and 102
thermal conductivity 102 Rock fabric and texture 102 Single crystal properties 103 Calculated thermal conductivities 104
5.3.3 Discussion 104 1
Acknowledgements 108
References 109