2004 Volume 110 Issue 10 Pages 608-619
Spatial and temporal deformation sequences based on the deformation facies analysis were revealed in the high-pressure Omi schists in serpentinite melange of the Hida Gaien Belt. The spatial deformation sequence (deformation zoning) represents four deformation zones defined by assemblage of deformed minor structures through schist blocks. High-mean-ductility-facies structures and low-mean-ductility-facies structures appear in every deformation zone, but some high- to moderate-mean-ductility-facies structures show characteristic development in each deformation zone. On the other hand, the temporal deformation sequence indicates that the deformed minor structures had been formed under conditions of decreasing mean ductility. Taking the relationship between development of the deformed minor structures and their lithologic control into consideration, fabric analysis suggests that the deformation zoning is not dependent on lithologic control, but reflects the kinematic history of the schists. Above analyses lead to early, middle and late deformation phases corresponding to each stage during exhumation of the serpentinite melange. That is the early phase represented by high-mean-ductility-facies structures reflecting the layer-parallel shear of the schist along deep subduction zone, the middle phase, high- to moderate-mean-ductility-facies structures, individual progress of ductile deformation in each zone of the exhuming schist blocks, and the late phase, low-mean-ductility-facies structures, brittle deformation in the shallower level of the crust.
