安徽桐城挂车河镇地区韧性剪切带元素质量平衡分析

Element and mass balance analysis of ductile shear zone in the Guachehe town area,Tongcheng,Anhui

韧性剪切变形对岩石地球化学行为的制约一直是地质学家们关注的问题。安徽桐城挂车河镇(挂镇)地区是大别造山带东缘和郯庐断裂带交汇位置,两个构造体系的韧性剪切带均发育,为开展对比分析研究提供了条件。不同构造体系及构造期次的长英质韧性剪切带在糜棱岩化过程中体积变化和元素迁移规律均相似,随着变形强度的增加,体积亏损和元素迁移越明显,体积亏损可达32.18%,元素迁移表现为SiO2、K2O、Na2O的迁出和Fe2O3、CaO、MgO的迁入;镁铁质脆-韧剪切带在糜棱岩化过程中体积变化和元素迁移规律与长英质剪切带的恰恰相反,体积增加21.63%～186.60%,元素迁移的显著特征是SiO2大量迁入及Fe2O3和CaO迁出。

The constraint of ductile shear deformation on petro-chemical behavior has always been a focus for geolo- gists. The Guachehe town area in Tongcheng of Anhui is a meeting place of the eastern fringe of the Dabie orogen and the Tan-Lu Fault zone, where the two tectonic systems are both developed in terms of ductile shear zone, providing con- ditions for making comparative analysis. Different tectonic systems and different phases of felsic ductile shear zones show similar regularity for volume change and element migration in the process of mylonitization, the volume loss and element migration become even more remarkable as deformation increases, the loss can be up to 32.18% and the migration is shown as move-out of SiO2, K2O and Na2O, and move-in of Fe2O3, CaO and MgO. Compared with felsic shear zone, mafic brittle-ductile shear zone shows a reverse law during mylonitization, i.e., volume increase of 21.63%-186.60% and considerable move-in of SiO2 and move-out of Fe2O3 and CaO.