HR: 08:15h
AN: MR21A-02 INVITED    [Abstracts]
TI: Kinematic and Petrologic Significance of Magma Mixing Structures in Igneous Rocks: Application of Fractal Geometry and Chaos Theory
AU: * Perugini, D
EM: diegop@unipg.it
AF: University of Perugia, Department of Earth Sciences, Piazza Universita', Perugia, 06100, Italy
AU: Poli, G
EM: polig@unipg.it
AF: University of Perugia, Department of Earth Sciences, Piazza Universita', Perugia, 06100, Italy
AB: The last few years have seen an extraordinary growth of interest in complex systems. In most scientific fields a new vocabulary is emerging to describe discoveries about wide-ranging and fundamental phenomena. Many of the terms have already become familiar: complexity, chaos, criticality, fractals, non-linear dynamics, self-similarity, and many more. All together they point to the emergence of new paradigms, cutting across traditional disciplines, for dealing with complex systems. These new concepts have also reached the field of igneous petrology. Magma interaction structures in igneous rocks are analyzed by applying methods of chaos theory and fractal geometry. It is shown that the development of magma mixing processes is closely associated to the onset of chaotic dynamics, the latter being responsible for the generation of fractal compositional patterns. In particular, in both two dimensional sections and 3D reconstructed rock samples, two types of dynamic regions are recognized to coexist at several length scales (from few microns to several meters). The first, defined Active Mixing Regions, are characterized by filaments of magmas showing strong deformation and intimate dispersion. The second, defined Coherent Regions, are characterized by the occurrence of globular portions of magmas showing little deformation and remaining as discrete entities. Microanalysis has been utilized to study the compositional variability within these two types of regions. Within Active Mixing Regions interfacial area between magmas increases exponentially generating strong chemical gradients and producing high degrees of hybridization in short times. On the contrary, Coherent Regions can preserve their composition for a long time due to the low and constant interfacial area between magmas. This feature allows Coherent Regions to survive complete hybridization. Starting from natural observations, magma interaction processes have been simulated by using chaotic dynamical systems in two and three dimensions. These systems reproduce with very good approximation structures and chemical patterns observed in natural samples and allow us to follow in time the development of chaotic dynamics and the generation of fractal compositional patterns in magma mixing systems. Results from this study have been utilized to offer a new hypothesis for the occurrence of magmatic enclaves in igneous rocks. They are interpreted as regions of magma trapped within Coherent Regions that survived the complete homogenization with the host magma. Host rocks, on the contrary, are interpreted as Active Mixing Regions where efficient chaotic mixing dynamics generated volumes of magmas with high degrees of hybridization. In conclusion, it is shown that magma mixing processes exhibit all typical features of chaotic systems and that their evolution occurs as a non-linear cascade of events that, starting from the micro-scale, is non-linearly amplified determining the behavior of magmatic systems at the macro-scale. It is emphasized that chaotic dynamics and fractal geometry are suitable techniques to study the complexity inherent to petrological phenomena, and they represent useful methods that, combined with conventional analysis, can aid in understanding better petrological processes.
DE: 3625 Petrography, microstructures, and textures
DE: 3640 Igneous petrology
DE: 4420 Chaos (7805)
DE: 4440 Fractals and multifractals
DE: 4460 Pattern formation
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting