大别造山带与郯庐断裂带衔接区构造特征分析

Characteristics of structures in the junction area of the Dabie orogenic belt and the Tan-Lu fault zone

大别造山带东部与郯庐断裂带南段的衔接处发育有介于二者之间的转换构造,这些转换构造对于揭示二者之间的转换关系起着非常重要的作用。本文对郯庐断裂带桐城段及其邻区发育的转换构造的构造样式和年代学特征进行了分析,并总结得出该处共出露两种不同尺度的转换构造,分别为较大规模北东向偏转的片麻岩构造带和被北东向糜棱岩带非透入性牵引转换的片麻岩带。发生构造转换的片麻岩、同构造脉体及北东向糜棱岩分别给出锆石U-Pb年龄:812~719 Ma,803~629 Ma、242~208 Ma和176~127 Ma以及735~650 Ma、288~216 Ma。结合前人年代学分析,本文认为片麻岩构造的较大规模北东向偏转活动为郯庐断裂带的初期形成活动,受大别造山活动控制;糜棱岩带的剪切活动的发生始于早侏罗世,主要受太平洋板块向欧亚板块俯冲活动的控制。

At the junction area of the eastern part of the Dabie orogenic belt (DOB) and the southern part of the Tan-Lu fault zone (TLFZ), there exposed a series of transformed structures, which played an important role in revealing the transformation relationship between the two tectonic belts. This paper has studied the geometry and chronology characteristics of these transformed structures, and found that two different transformed structures are separately NE-striking gneiss belt in larger scale and NE-striking gneiss in smaller scale dragged by NE-striking mylonite belts. Zircon U-Pb dating towards transformed gneiss, synchronous vein and mylonite separately gave the results as 812~719 Ma;803~629 Ma, 242~208 Ma, 176-127 Ma;735~650 Ma, 288~216 Ma. Combined with chronological analysis before, we conclude that the transformed structures of larger scale may represent the initial formation of the TLFZ controlled by the Dabie Orogen. The shear activity of mylonite zones developed since Early Jurassic, which basically controlled by the Pacific plate subduction beneath the Eurasian plate.