A new fractal method for the determination of deformation temperatures and strain rates—A case study of the Fuchashan tectonite in the Tanlu fault

Abstract：In this study the fractal method is for the first time used to analyze the Fuchashan tectonite in the Tanlu fault, Feidong, and the results show that the boundaries of the dynamically recrystallized quartz grains in the Fuchashan ductile shear zone in the Tanlu fault are statistically self-similar and have distinct fractal features. Using the “perimeter-diameter method”, the authors conclude that, with an increase in degree of mylonitization of the samples, the fractal dimension value increases progressively from 1.204, 1.213 and 1.222 to 1.229 and the corresponding diameter of the dynamically recrystallized quartz grains is reduced from 33.79, 26.00 and 22.82 μm to 15.01 μm. Comparison between two different calculation methods shows that the corresponding strain rate increases gradually from 4.837×10-13s-1, 7.688×10-13s-1, and 9.682×10-13s-1, to 2.031×10-12s-1. The metamorphism in the study area is generally of high greenschist to low amphibolite facies, and the metamorphic temperature is about 500 ℃. Comparing the results of this study with the previous conclusion, the authors conclude that the Kruhl geothermometer is suitable for the study area, while the Takahashi strain rate meter is unsuitable for the ductile shear zone formed at relatively deep crustal levels.