显微构造、EBSD组构及^(40)Ar-^(39)Ar年代学对铧厂沟矿区变形过程的制约

Deformation Process of the Huachanggou Ore District:Microstructure,EBSD Analysis,and^(40)Ar-^(39)Ar Geochronology Constraints

铧厂沟金矿床作为南秦岭地区典型的造山型金矿床,其矿体形态和分布严格受变形作用控制,然而目前对该矿区的变形过程仍缺乏研究。本研究在构造解析的基础上,对铧厂沟矿区岩石进行显微构造、EBSD组构及^(40)Ar-^(39)Ar年代学分析。结果显示,矿区岩石韧性变形分为:①SN向挤压。变形构造包括灰岩的强烈片理化,砂岩紧闭褶皱、无根褶皱及旋转碎斑等。倾向上,砂岩片理的波状弯曲及片理间宏、微观旋转碎斑的形态,指示褶皱过程中的层间剪切作用,弯曲片理面上绢云母的Ar-Ar坪年龄为215.1±0.7 Ma。该期变形在方解石和石英组构图中形成了对称性较好的极密,指示正向挤压的纯剪切过程;②左行走滑。砂岩及灰岩均发育近水平的拉伸线理,结合砂岩片理在走向上的波状弯曲、剪切透镜体及定向薄片内显微构造,指示存在一期左行走滑过程。同时,方解石和石英的EBSD组构图显示极密发生偏转,也代表了简单剪切的产物。结合已有资料,铧厂沟矿区两期变形对应于南秦岭印支期造山引起的正向碰撞和晚期左行走滑。

The Huachanggou gold deposit is a typical orogenic gold deposit in the South Qinling,and its distribution and preservation are strictly controlled by deformation.The deformation process in this deposit,however,remains unclear.Based on the structure analysis of the Huachanggou ore district,we collected samples of deformed limestone and sandstone and conducted microstructure,EBSD,and^(40)Ar-^(39)Ar geochronological analyses.The results indicate that both limestone and sandstone underwent ductile deformation,and their macro-and microstructural characteristics indicate two stages of deformation,i.e.,the north-south compression and sinistral strike-slip.The compressional structures include steep foliation in the limestone,tight folds,rootless folds,and rotated porphyroclasts in the steeply foliated sandstone.The wave-like schistosity and rotated porphyroclasts in dip,as well as the morphology of rotational porphyroclasts in the oriented thin section,imply interlayer shearing during the folding process.Sericite separated from the wave-like schistosity yielded^(40)Ar-^(39)Ar plateaus age of 215.1±0.7 Ma.During this period,the calcite and quartz fabrics exhibit symmetrical maxima,indicating a pure shear process caused by compression.The lenses and wave-like strike schistosity,along with the nearly horizontal stretching lineation in both limestone and sandstone,suggest a sinistral strike-slip movement.The rotated porphyroclasts in the oriented thin sections of the limestone and sandstone also support the view of sinistral strike-slip along the east-west direction.In addition,according to the EBSD analysis of calcite and quartz,the maxima deviated from the axis,indicating simple shear during this stage.Combined with previous data,it can be concluded that the two deformation stages in the Huachanggou ore district correspond to the collision caused by Indosinian orogeny and the sinistral shear caused by adjustment in the South Qinling,respectively.