CHARACTERISTICS OF COMPOSITIONAL MIGRATION IN MYLONITES FROM THE DUCTILE SHEAR ZONES OF THE SOUTHERN TANCHENG-LUJIANG FAULT BELT, EASTERN ANHUI PROVINCE

On the basis of field geology, three typical ductile shear zones in th e southern part of the Tancheng-Lujiang fault belt have been chosen fo r a detailed study. Altogether ten samples of the tectonites have been collected for this study. The paper is focused on a comprehensive stu dy of the tectonites in the medium-lower horizons of the ductile shear zones. The mineral compositions of the rocks are analyzed with EPMA a nd some typical whole-rock samples analyzed by chemical and ICP method s. Based on the comprehensive study of the characteristics of the defo rmation, the mineral assemblages and the changes of chemical compositi on of the bulk rocks, this paper presents a discussion on the relation ship between the volume loss, the fluid flow and compositional changes during mylonitization of the ductile shear zones in this region. Our study shows that there are a large amount of fluids flowing through th e shear zones during the process of mylonization, accompanied by the l oss of rock volume and migration of elements and components. Modelling calculation results under different saturation conditions of fluids s how that the maximum volume loss of the tectonites is about 60% relati ve to their protolith, while the fluid / rock ratio ranges from 10 to 10(3) in different ductile shear zones.