Abstract
Structural development of the Motai-Nagasaka area of the South Kitakami Belt, NE Japan is discussed in light of precise mapping and microscopic observation of deformation zones. The following succession of events is recognized in the study area, which is occupied, in apparent ascending order, by the high-P/T type Motai Metamorphic Rocks, 500-440 Ma basement igneous rocks, and Paleozoic strata that cover the basement igneous rocks, 1) the formation of the Boundary Shear Zone along the top of the Motai Metamorphic Rocks and their exhumation through a sinistral or top-to-the-south shearing, 2) initiation of sinistral shearing along the Tsuwamono-zawa and Sarusawa shear zones, 3) asymmetric minor s-folding and the formation of major synclinorium as the result of the drag and/or transpression along the above two sinistral shear zones, 4) formation of slate zones in the western limbs of above minor and major synclines, and 5) cooling of the 120-105 Ma granite in the Kitakami Mountains. A restoration model is finally presented of the Early Cretaceous sinistral displacement in the study area, which suggests that the study area was shortened about 65% in N-S direction and thickened about 150% in E-W direction through Early Cretaceous sinistral shearing.
