HR: 1340h
AN: MR23B-1324    [Abstracts]
TI: Automated Quantification of Magmatic Rock-Fabric Anisotropy From Micro to Macro Scale
AU: * Peternell, M
EM: mark.peternell@tum.de
AF: Tectonics and Material Fabrics Section, Technische Universitaet Muenchen, Arcisstrasse 21, Munich, 80333, Germany
AU: Kruhl, J H
EM: kruhl@tum.de
AF: Tectonics and Material Fabrics Section, Technische Universitaet Muenchen, Arcisstrasse 21, Munich, 80333, Germany
AU: Bitencourt, M
EM: fatimab@ufrgs.br
AF: Universidade Federal do Rio Grande do Sul, Instituto de Geociencias, Departamento de Geologia, Av. Bento Goncalves, 9500 - Predio 43126 sala 203, Agronomia, Porto Alegre, 91540-000, Brazil
AB: During the last decade, studies on magmatic fabrics on different scale have been made for analyzing kinematics of melt emplacement and deformation as well as cooling histories of magmatic bodies and their host rocks (Brown 2001). The problem arises for comparing data from structural analysis in thin-sections and fabrics in outcrop scale. Magmatic fabrics in the outcrop scale are often very diffusely developed or show very complex mineral distribution patterns which are mostly not quantifiable with classical field methods. On the other hand the fabrics are too large for thin section investigation. Therefore, methods have to be developed for analyzing microscale rock fabrics like crystal shape preferred orientations on larger image templates, like from outcrop photographs. For analyzing such complex fabrics on different scale, methods of fractal geometry are powerful (Mandelbrot, 1982). Especially methods like map-counting (Kruhl et al., 2004), based on the classical box-counting method, or the modified Cantor-dust method (Volland & Kruhl, 2004) may be used for analyzing meter sized magmatic mineral distribution patterns in granitic rocks and the anisotropic behavior of micro- to macro scale fracture patterns in breccias. Nevertheless, these methods are performed manually and, therefore, not applicable to larger datasets. This study shows the next step towards automated recognition and subsequent quantification of magmatic patterns from micro- to macro-scale. Microstructure shape- and crystallographic preferred orientation measurements on K-feldspar crystals from the Piquiri Syenite Body, Southern Brazil are done manually based on thin-section series parallel to the syenite magmatic foliation. In addition U-stage measurements of K-feldspar indicatrix axis and (010) have been done. Additionally, a slightly changed modified Cantor-dust method was applied on centimeter- to several meter-sized K-feldspar phase distribution patterns, gained by automated image processing of samples and field photographs of the same syenite. The results show that all three methods result in the same shape- and/or crystallographic preferred orientations for K-feldspar, indicating a magmatic lineation, which is not determinable by field observation or in the thin- sections. In addition, the modified and automated Cantor-dust method applied on K-feldspar phase images of a syenite proves the advantage of such type of modified fractal-geometry methods for quantification of magmatic fabrics on various scales. Such automated quantification is fast and precise, and it is suitable for accurate analysis of magmatic fabrics on different scales and for large datasets. References:
Kruhl,J.H., Andries,F., Peternell,M. & Volland,S. (2004): Fractal geometry analyses of rock fabric anisotropies and inhomogeneities. In: D.Kolymbas (ed.), Fractals in Geotechnical Engineering. Advances in Geotechnical Engineering and Tunnelling 9. Logos, Berlin, 115-135. Mandelbrot, B.B., (1982): The Fractal Geometry of Nature. Freeman, San Francisco. Volland, S. & Kruhl, J.H. (2004): Anisotropy quantification: the application of fractal geometry methods on tectonic fracture patterns of a Hercynian fault zone in NW-Sardinia.- J. Struct. Geol. 26, 1489-1500. Brown,M. (2001): Crustal melting and granite magmatism; key issues.- Physics and Chemistry of the Earth. Part A: Solid Earth and Geodesy 26/4-5, 201-212.
DE: 4440 Fractals and multifractals
DE: 4460 Pattern formation
DE: 5104 Fracture and flow
DE: 8094 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting