论赣南大余-南康地区断层破碎硅化带的韧性剪切作用

在赣南大余-南康一带,以往未发现韧性剪切带.通过野外工作和室内研究,发现了南北、北东、北东东、北西4组韧性剪切带,其中包括前人划的混合岩带、震旦系顶部某些"硅质岩标志层"及一些断裂硅化破碎带和石英脉.这些韧性剪切带的地质特征表明,它们早期发生过多次脆性变形,并伴随多次热液活动,形成规模不一的断层硅化带.断层硅化带在地壳浅部发生韧性剪切作用形成由石英初糜棱岩、糜棱岩和超糜岩构成的韧性剪切带.韧性剪切带的形成取决于应力强度和应变速率,与形成深度无关,这与Sibson的韧性剪切带双层模式是相悖的.

On ductile shearing in silicified fracture zone in Dayu-Nankang area, southern Jiangxi, China

In Dayu-Nankang area, southern Jiangxi, no ductile shear belt (DSB) was found before. By field survey and microscopic examination, some DSBs are discovered and distributed in SN, NE, NEE and NW strike. They include so-called migmatite zones before, some of silicified fracture zones and quartz veins and some of the siliceous rocks at the top of Sinian System, which are all considered as guide bed (delimiting) between Sinian System and Cambrian System. Their geological characteristics indicate that these DSBs are silicified fracture zones that have different sizes by frequently brittle deformation associated with hydrothermal activity in the early stage. These silicified fracture zones have experienced ductile shear at high level and transformed into DSBs constituted by quartz supermylonite and/or mylonite. This suggests that the formation of DSZs depends on stress intensity and strain rate and is unrelated to the formation depth. This is different from the Sibson's double layer model for DSB.