红河断裂带中南段断层活动转换构造岩特征及应力场演化

Tectonite features and stress field variations associated with fault motion transformation in the central southern part of the Red River fault zone

通过对红河断裂带中南段18个糜棱岩、12个角砾岩、10个碎裂岩和8个砂砾岩详细的显微结构观察,部分典型样品的磷灰石裂变径迹(FT)测年及利用断层滑动资料反演构造应力张量的方法,获得了红河断裂带中南段断层活动转换过程微观特征的变化:断层岩为糜棱岩的微结构特征显示红河断裂带早期断层活动为左旋走滑,糜棱岩和未变形的砂砾岩FT年龄均大于20Ma,表明这期间红河断裂带曾发生过一次构造热事件。断层岩为碎裂岩和角砾岩的微结构特征显示红河断裂带后期断层活动为右旋走滑。微结构特征不同的碎裂岩和角砾岩的FT年龄可分为3个时段(9.9～12.7Ma、6.8～8.4Ma、2.0～4.6Ma),测年结果和应力场特征表明红河断裂带中新世以来曾发生过3次断层错动事件,且第1次事件应力结构为走滑型,第2、3次事件应力结构为正断型。

The variations of microstructures associated with the motion transformation in the central southern part of the Red River fault were studied in this paper. The researches included careful observation of microstructures in eighteen mylonite, twelve breccia, ten cataclasite, and eight sandy conglomerate samples from the fault, of which some were dated by the fission track in apatite （FT） method. In addition, the fault slip data were used to infer tectonic stress tensors. The results show that the microstructure of mylonite is indicative of left-slip during the early activity of the Red River fault. The FT ages of the mylonite and undeformed sandy conglomerate exceed 20 Ma, implying that a thermal event occurred in the Red River fault at that time. The microstructures of cataelastite and breccia imply the existence of right-slip during the late activity period of the fault. The above features, the FT ages （9.9--12.7 Ma, 6.8--8.4 Ma, 2.0--4.6 Ma）, and the different stress fields suggest that the Red River fault has undergone three dislocations since the Miocene, of which the first was strike-slip, and the second and third were of normal faulting.