桐柏造山带两侧剪切带构造关系讨论及地质意义

桐柏造山带南北两侧的殷店—马垅剪切带和鸿仪河—桐柏剪切带是分割核部杂岩和高压变质岩石单元的两条重要界限带,通过对其详细的野外观察、显微构造分析、石英C轴组构EBSD(Electron Backscattered Diffraction)分析,发现这两条剪切带有统一的几何学、运动学特征,剪切运动学特征具有对称性,反映了二者可能是同一条剪切带,拥有近EW向伸展的运动特征。一体化的剪切带是一条覆盖于桐柏杂岩之上的拆离剪切带,总体表现为上盘NWW向运动,下部发育大量枢纽近EW向的鞘褶皱和压缩型应变的L型构造岩(L tectonites),剪切带内部则以压扁型应变为主发育大量的S-L构造岩(即糜棱岩系列岩石)。现今桐柏造山带内大量近EW向的线性构造可能源自于平行造山带伸展的构造活动。这种上盘NWW方向剪切拆离的地质特征在大别造山带广泛发育,反映了中国中东部的秦岭—桐柏—大别—苏鲁造山带在早白垩世可能发生过中—下地壳近EW向伸展的构造演化。

The relationship between the shear zones flanking Tongbai orogenic belt and implications for the tectonic evolution

The Yindian-Malong shear zone and the Hongyihe-Tongbai shear zone flanking south side and north side of Tongbai orogenic belt respectively are two most important boundary zones which segmented the core complex and high-pressure metamorphic rocks. Through the detailed field observation, microstructural analysis and quartz C axis analysis, our studies indicate that the Yindian-Malong and Hongyihe-Tongbai shear zones have the same deformed characteristics with symmetric kinematics, suggesting that the two shear zones may derive from a uniform detachment shear zone characterized with nearly EW extension. The L tectonites and sheath fold occurred by constrictional deformation beneath the detachment shear zone. The S-L rocks (mylonitic rocks) formed by flattening strain in the detachment shear zone. The uniform detachment shear zone exhibited a top-to-NWW movement at the top of the Tongbai complex, which suggests an orogen-parallel extension of the Tongbai complex in a nearly W-E direction. This orogen-parallel extension gave rise to the widely development of the linear structure in the Tongbai orogenic belt. The similar features of the top-to-NWW shearing were also widely observed in the Dabie orogenic belt, which suggests that a uniform detachment shearing of the ductile lithosphere may occur in the Qinling-Tongbai-Dabie-Sulu orogenic belt at the Early Cretaceous.