Pressure fringes and pressure shadows indicative of progressive deformation

抄録

The geometric forms of pressure shadows (strain shadows) around deformation resistant object involve important information such as sense of shear, degree of non-coaxiality and pass of incremental strains during progressive deformation. Pressure shadows filled with fibrous crystals are known as pressure fringes which commonly occur in slates and pelitic schists.
The growth lines of fiber in mineral veins and in pressure fringes show the incremental strain pass (Ramsay and Huber, 1983; Passchier and Trouw, 1995; Ishii, 1996). There are three types of fiber growth in fibrous veins and pressure fringes; syntaxial, antitaxial and composite. Syntaxial growth occurs inward from the vein wall in veins, and outward from a rigid object in pressure fringes, where fibers consist of the same minerals with the wall/object. In contrast, antitaxial growth occurs outward from the vein center in veins and inward from the matrix in pressure fringes, where fibers consist of other minerals than the wall/ object. Composite growth has a syntaxial and an antitaxial components. Syntaxial and antitaxial pressure fringes are also known as crinoid type and pyrite type pressure fringes, respectively (Ramsay and Huber, 1983).
This pictorial presents pyrite- and crinoid type pressure fringes from the late Paleozoic strata in the South Kitakami Belt, pyrite type pressure fringes from the Sambagawa pelitic schist and porphyroclast-pressure shadow system from granitic mylonites along the Median Tectonic Line in the Ryoke belt. All photomicrographs are taken for XZ thin sections cut parallel to the stretching lineation and perpendicular to the foliation.