摘要
Eclogites from orogens often show strong plastic deformation and high hydroxyl content. We have studied the correlation between crystallographic preferred orientations of garnet and omphacite from natural eclogites with their hydroxyl contents using the electron back-scat- tered diffraction technique. The results show: 1) Omphacite has typical L-type or SL-type crystrallographic preferred orientations, that is, [001] is distributed in a girdle in the foliation plane with a maximum parallel to lineation; (010) is distributed in a girdle normal to the lineation with a maxi- mum parallel to the foliation plane, suggesting a shear dominant deformation regime. Omphacite fabrics do not vary significantly with hydroxyl content, although the hy- drous component may cause lower flow strength. 2) Hy- droxyl can influence significantly flow properties of garnet in eclogite. Garnets behave as rigid bodies under low tempera- ture and dry conditions. Grain boundary processes will dominate the deformation and lower the flow strength of garnet under high water fugacity conditions. Garnets show no crystallographic preferred orientation in both cases. These results may have important implications for a better understanding of deformation mechanisms and associated fluid activities during deep subduction and exhumation processes.
Eclogites from orogens often show strong plastic deformation and highhydroxyl content. We have studied the correlation between crystallographic preferred orientations ofgarnet and omphacite from natural eclogites with their hydroxyl contents using the electronback-scattered diffraction technique. The results show: 1) Omphacite has typical L-type or SL-typecrystrallographic preferred orientations, that is, [001] is distributed In a girdle in the foliationplane with a maximum parallel to lineation; (010) is distributed in a girdle normal to thelineation with a maximum parallel to the foliation plane, suggesting a shear dominant deformationregime. Omphacite fabrics do not vary significantly with hydroxyl content, although the hydrouscomponent may cause lower flow strength. 2) Hydroxyl can influence significantly flow properties ofgarnet in eclogite. Garnets behave as rigid bodies under low temperature and dry conditions. Grainboundary processes will dominate the deformation and lower the flow strength of garnet under highwater fugacity conditions. Garnets show no crystallographic preferred orientation in both cases.These results may have important implications for a better understanding of deformation mechanismsand associated fluid activities during deep subduction and exhumation processes.
基金
supported by the National Natural Science Foundation of China(Grant No.40172068)
the Ministry of Science and Technology of China(Grant No.2003CB716506)
the US National Science Foundation(Grant No.EAR#0003631).
