期刊
JOURNAL OF STRUCTURAL GEOLOGY
卷 28, 期 4, 页码 621-640出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jsg.2006.01.008
关键词
strain localization; load bearing framework; phase strength contrast; weak phase interconnection; shear zone; phase fabric
To determine how deformation mechanisms and fabrics evolve during the strain weakening and localization that accompany the transition from a load-bearing framework to an interconnected weak phase, shear experiments were conducted on a fine-grained gneiss (58% quartz, interconnected; 28% plagioclase, dispersed; 13% biotite, aligned but dispersed) at 745 and 800 degrees C, 1500 MPa and two strain rates (2 X 10(-5) and 2 X 10(-6) s(-1)). in experiments with a high phase strength contrast (HPSC, 25 X and 45 X) between dispersed biotite and framework quartz grains, biotite grains become interconnected due to stress concentration at their tips that allow local semi-brittle flow of intervening quartz and cataclasis of intervening plagioclase. In the higher temperature HPSC samples, the biotite partially dehydrated in high strain zones; a single narrow shear zone formed because the PSC between the quartz and biotite/reaction product layers remained high. In the lower temperature HPSC samples there was no reaction, and a penetrative S-C ' fabric formed. The fabric is defined by the many multiply interconnected biotite strands that formed because the PSC between the quartz and biotite decreased as the biotites kinked. In slower strain rate experiments with a much lower PSC (similar to 10X), biotite interconnection occurs by shearing into quartz/quartz boundaries where new, weak strain-free recrystallized grains form. At low strain a weak S-C ' fabric forms, but it evolves to an S-C fabric as the PSC decreases with strain. Thus, the magnitude of the strength contrast between a weak phase and its matrix influences the mechanism of weak phase interconnection, the degree of strain localization and the fabric. (c) 2006 Elsevier Ltd. All rights reserved.
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