迁安铁矿变形岩石的EBSD组构分析

An analysis of the fabric of deformed rock:the application of EBSD(electron backscatter diffraction) in the Qian'an iron mine

迁安铁矿是我国大型沉积变质型铁矿之一,该矿区含矿变质岩系为前寒武纪老变质岩石,时代老,变质程度深,现存岩石的内部矿物发生过多次变形、变质和重结晶等变化,宏观上表现为该区岩石矿物组构的复杂性。为了更深入、清晰地了解该区变形岩石的组构,采用电子背散射衍射(EBSD)技术对该区岩石样品做了分析,通过EBSD系统的配套软件(HKL公司开发的Channel 5),对采集数据进行处理绘制成相应磁铁矿和石英的极图,经分析后重点总结出变形岩石内部石英的组构特点,由此进一步反映出本区构造变形时主要为中温-中高温的变形温度环境,少量组构图反映叠加了中低温变形。

The Qian＇an iron mine is one of the large-sized metamorphic sedimentary iron mines in China. As the ore-bearing metamorphic rocks here are of Precambrian hypometamorphic ones, the minerals in the existent rocks have been deformed,[HJ] metamorphosed and recrystallized several times, resulting in the extreme complexity of the rock microstructure. In order to have a better understanding of the fabric of the deformed rocks, the authors employed EBSD （electron backscatter diffraction） to analyze the samples in the study area. With the help of Channel 5 developed by HKL Co., the authors processed all the data collected and drew the corresponding magnetite polo figures and quartz polo figures. Quartz optical axes, which exist in gneiss and granulite, are basically consistent with the direction of foliation in hand specimen and are also in the same direction or at the small-angle intersection with the elongated direction and wave extinction of quartz under microscope. The analysis shows that the characteristics of magnetite do not show a preferred orientation, while the internal fabric of quartz in deformed rock does. Furthermore, the authors have also obtained the information concerning the conditions during the structural deformation. Most polo figures reflect a circumstance of medium to medium-high temperature, whereas a small number of figures suggest the composition of medium-low temperature deformation. In combination with the knowledge of deformation partitioning which belongs to the deformation field, the authors believe that different minerals in the solid rock such as quartz, feldspar and garnet have different mechanical strength and ductile shear deformation conditions, and such differences would contribute to partition deformation between the light-color deformed quartz and the high mechanical strength magnetite.