The low temperature brittle-ductile transition in a quartzite and the occurrence of cataclastic flow in nature |
| |
| Authors: | Dr J Hadizadeh Dr E H Rutter |
| |
| Institution: | 1. Geology Dept., Garyounis University, Benghazi, Libya
2. Geology Department, Imperial College, London, S.W. 7., Great Britain
|
| |
| Abstract: | The paper describes the mechanical and microstructural characteristics associated with the brittle to cataclastic flow transition in an orthoquarzite (Oughtibridge Ganister), and compares its microstructural development with features of cataclastic deformation of rocks in nature. The brittle to ductile transition in dry ganister occurs at about 600 MPa at room temperature. At lower pressures shear oriented grain boundary cracks form both pre and post peak strength, loosening the microstructure to the point at which axial transgranular cracks develop. Fault zone localization then occurs. At high pressures fault localization is suppressed by friction, and cataclastic flow occurs by the formation of ultracataclasite shear zones around each grain boundary, Rhomb shaped, relatively intact grain cores survive to high (greater than 20%) strains. Hardening mechanisms responsible for the ductility are discussed. It is shown that natural zones of intense cataclasis (fault zones) often develop microstructures comparable with those seen in these experiments, but the less intense cataclastic flow often associated with folding of rocks at high crustal levels in the external zones of orogenic belts is not comparable inasmuch as grain-scale catalaclasis does not normally occur. It is emphasised that finite strain microstructural similarity does not necessarily point to comparable deformation paths and stress history. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
