Ductile deformation and 40Ar/ 39Ar dating of the Changle–Nanao ductile shear zone, southeastern China

Abstract

An investigation of ductile deformation, mylonitization and 40Ar/ 39Ar geochronology in the Changle–Nanao ductile shear zone, southeastern China, is reported in this paper. At least two phases of ductile deformation occurred in the shear zone in the Mesozoic. The first is a NE-trending foliation widely developed in metasedimentary rocks and orthogneisses, and is associated with metamorphism of amphibolite facies at 165–178 Ma. The second is a strike-slip-related ductile deformation developed both in the metamorphic rocks and the Mesozoic volcanics and includes folds, shear foliation or cleavage, S– C fabrics, NE-striking stretching lineation, and mylonitic microstructures. The ductile deformation and dislocation microstructures of quartz and the brittle deformation microstructures of plagioclase in the mylonites from the shear zone indicate that the second phase of ductile deformation and mylonitization occurred under greenschist facies conditions at temperatures of 300–350°C. 40Ar/ 39Ar plateau ages of five minerals from deformed and mylonitized rocks in the shear zone are in the range of 118–107 Ma. The plateau ages record the time of ductile deformation and mylonitization associated with strike-slip movement along the Changle–Nanao ductile shear zone.