Abstract
The ratio between the viscosities of different types of rocks is one of the important parameters which characterize the structures of not only minor but also large one such as crustal deformation. In this paper, the viscosity ratio between the granitic rocks and the Paleozoic sedimentary rocks, both of which are the elementary rock bodies composing the basements of the Kinki area, are estimated on the basis of the analysis of the large tectonic deformation. The Quaternary crustal deformation of this area has been considered to have taken place in the state of horizontal tectonic compression (HUZITA, 1969; HUZITA et al., 1973). The lateral shortening (layer-parallel shortening) and consequent vertical thickening of the basement rock bodies might have continued due to the horizontal compression. Based on a simplified plane strain model, the rate of thickening, namely the rate of uplift, is in inverse proportion to the viscosity of the basement rocks. Therefore, the difference of the viscosity between the two rock types mentioned above is expected to appear as the difference of the rate of the uplift. The areal distribution of vertical displacement through the whole Quaternary Period, which may be equivalent to that of the average rate of uplift in the same time, was compiled in The Quaternary tectonic map (THE RESEARCH GROUP FOR QUATERNARY TECTONIC MAP, 1969). This map shows that the rate of uplift is larger in the Paleozoic regions rather than in the granitic regions. Inferred from the relationship between the rate of the uplift and the ratio of the two rock types composing the basements, it is derived that the viscosity of the granitic rock bodies is larger than that of the Paleozoic sedimentary ones, and the ratio between them is estimated to be in a range of 2 to 5. This range of the value is nearly coincide with that of the value derived from the deformation of the conglomerates (GAY, 1968).
