大别山东南麓韧性剪切构造带

广济县四望、松山咀和黄梅县大河、苦竹及宿松县界岭、二郎河一线存在一条规模较大的平移—推覆型韧性剪切带,其延60余公里,宽约5—15km。该带中糜棱岩岩石的斑晶及眼球体压力影不对称、重结晶石英斜列方式及微褶皱形态特征反映出以左旋剪切作用为主。有限应变沿x方向最大拉伸量为170％,沿z方向最大缩短量为57％。中心部位的糜棱岩明显经历了热加工—恢复作用阶段,是深层次韧性剪切的产物,古差异应力平均值为158.76MPa,应变速率为3.67×10~(-11)～6.17×10~(-12)sec~(-1)。晚期又遭受了脆性薄皮冲断作用。

THE DUCTILE SHEAR ZONES AT THE SOUTHEASTERN FOOT OF DABIE MOUNTAIN

There are several ductile shear zones at the southeastern foot of Dabie mountain. The greatest ductile shear zone, about 60 km long, 5-15 km wide, in NE-NEE trend, is situated between Siwang in Guangji-county and Erlanghe in Susong county. It is called shortly Guangji-Susong ductile shear zone. Results from authors' studies on this shear zone are as follow: 1. Mylonite belt developed in the central of this shear zone. The distorted shapes of auge-nblast stress shadow in mylonite, axialplanes of microfolds and echelon patterns of dynamo-recrysta'llization grains all indicate that the sinistral shear is main in this shear zone. 2. The finite strain measurements of deformed grains in the proterozoic Hongan Group show that the elongation ratio along X-direction is 170% and shortened ratio along Z-direc-tion is 57 % . 3. Authors used transmittion electron microscope (TEM) with accelerating voltage of 80-200 kv to study mylonite in this shear zone. Results show that the mylonite in this shear zone experienced "heat-working and recovering stage" and slow deforming during early period , and it formed in the depth of crust. The average differential flow stress caculated from free dislocation density is 158.76 MPa and the strain rate is roughly of the order of 10-11-10-12/sec. 4. Guangji-Susong ductile shear zone belongs to a strike-slip-nappe typeof ductile shear zones. It experienced a thin-skinned thrusting stage during late period. This shear zone could be produced in the process of Dabie Mountain terrane and Yangzi terrane's moving, colliding and ducking since Mesozoic era.