A previous study of the Dabie area has been supposed that a strong extensional event happened between the Yangtze and North China blocks. The entire extensional system is divided into the Northern Dabie metamorphic complex belt and the south extensional tectonic System according to geological and geochemical characteristics in our study. The Xiaotian-Mozitan shear zone in the north boundary of the north system is a thrust detachment, showing upper block sliding to the NNE, with a displacement of more than 56？km. However, in the south system, the shearing direction along the Shuihou-Wuhe and Taihu-Mamiao shear zones is tending towards SSE, whereas that along the Susong-Qingshuihe shear zone tending towards SW, with a displacement of about 12？km. Flinn index results of both the north and south extensional systems indicate that there is a shear mechanism transition from pure to simple, implying that the extensional event in the south tectonic system could be related to a magma intrusion in the Northern Dabie metamorphic complex belt. Two 40Ar-39Ar ages of mylonite rocks in the above mentioned shear zones yielded, separately, ~190？Ma and ~124？Ma, referring to a cooling age of ultrahigh-pressure rocks and an extensional era later. 1. Introduction Dabie area is well known of owning one largest area of ultrahigh-pressure metamorphic belt (UHPB) in the world, located, as a tectonic zone, between the North China Block and Yangtze Block (Figure 1). Figure 1: Simplified map of late Mesozoic main shear zones in eastern Dabie Mountain, Central China (after Suo et al., 2000 [ 4]). NCC: Northern China Block; YZC: Yangzi Block; NHMB: North Huaiyang metamorphic belt; NDMCD: North Dabie metamorphic complex belt; UHPB: Ultrahigh-pressure metamorphic belt; HPB: high-pressure metamorphic belt; SH-WH SZ: Shuihou-Wuhe shear zone; TH-MM SZ: Taihu-Mamiao shear zone; SS-QSH SZ: Susong-Qingshuihe shear zone; XT-MZT SZ: Xiaotian-Mozitan shear zone; TLF: Tancheng-Lujiang Fault (Tanlu Fault); XF-GJF: Xiangfan-Guangji Fault. The Dabie area experienced a complicated tectonic evolution during the Mesozoic and resulted in thrust-nappe, extensional detachment, and strike-slip structures [1, 2]. Much attention has been paid to the tectonic evolution of the Dabie Mountains, with most tectonic models proposing although compressional tectonism for the formation of the orogen. However, Mesozoic extensional structures in the Dabie Mountains are also obvious and important for understanding the Mesozoic tectonic regime inversion from compression to extension occurred throughout the Dabie
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