Rheology of Orthopyroxene Constrained by Folding of Single Crystals
详细信息
- 责任者：Shaocheng Ji (Département des Génies Civil ; Géologique et des Mines ; Ecole Polytechnique de Montréal ; Montreal H323A7 ; Canada)
- 刊名：Geotectonica et Metallogenia
- 出版年：2013
- 卷期：37(2)
- 关键词：斜方辉石 ; orthopyroxene ; 流变学 ; rheology ; 褶皱 ; folds
- 页码：p.194-205
- 图表：illus., 61 refs.
- 分类号：0300
- issnNo：ISSN1001-1552
- isbnNo：CN44-1595/P
摘要
Ultramylonitic peridotites collected from a high-pressure metamorphic terrain in the Yushugou Massif at the northern margin of the south Tianshan orogenic belt( Xinjiang,China),in which strongly elongate and folded orthopyroxene( En90) porphyroclasts embedded in a fine-grained( d = 10 μm),recrystallized olivine( Fo90) matrix,were optically investigated to constrain the rheological behavior and plastic deformation mechanism of the orthopyroxene. Microstructural evidence suggests that the orthopyroxene deformed dominantly by a single slip system of dislocations:( 100) [001 ],whereas the finegrained olivine deformed most likely by grain-size-sensitive diffusion creep. The development of flexural folds rather than kink bands suggests that the orthopyroxene deformed mainly by the accumulation of geometrically necessary dislocations of same signs without the operation of dislocation climb and diffusion of atomic species. No dynamic recrystallization occurs in orthopyroxene even though the intracrystalline rotation is as high as 140°,implying that the critical shear strain needed to onset dynamic recrystallization is probably above γ = 5. 5 under the conditions of interest. The dislocation creeping orthopyroxene could be at least two orders of magnitude stronger than the diffusion creeping fine-grained( d = 10 μm) olivine under the same conditions.
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