面积平衡法与川东大池干推覆带区域滑脱面预测

THE REGIONAL DETACHMENT OF DACHIGAN THRUST BELT,EASTERN SICHUAN:RESULTS FROM GEOLOGICAL SECTION RESTORATION BASED ON AREA-DEPTH TECHNIQUE

本文详细介绍了面积平衡法的原理与方法,并将该方法应用于川东大池干构造的解释。利用面积平衡法,本文预测出在该地区可能有三个较大的区域滑脱面,它们分别位于3.53km处的中三叠统(由石膏、盐岩和泥页岩组成),7.79km处的下寒武统(由页岩、石膏和岩盐层组成),以及8.67km处的下寒武统(由页岩、石膏和岩盐层组成)地层之中。根据以上滑脱面的分析结果,作者认为大池干构造可以解释为滑脱褶皱和断层转折褶皱两种成因模式。在滑脱褶皱模式中,主滑脱面为8.67km处的非能干层;在断层转折褶皱模式中,该地区被认为具有上下两个滑脱面,其上滑脱面为3.53km处的非能干层,而其下滑脱面为7.79km处的非能干层。两种模式所对应的面积深度直线都具有较好的相关性,表明两种构造解释都具有内部岩层一致性,剖面达到平衡,故具有相对的合理性。

This paper reviewed the principles and procedures of Area-Depth technique, and then applied this technique to interpret Dachigan structure, Eastern Sichuan. Based on the corresponding area-depth diagram and measuring the excess area and depth of seven strata, we propose that there were three potential large-scale regional detachments in this region. The first potential detachment is the middle Triassic gypsum, salt and shale at the depth of 3.53kin. The second potential detaehment has a depth of 7.79 km, which is the lower Cambrian shale, gypsum, and salt. The other potential detachment lies on the lower Cambrian shale, gypsum, and salt, with a depth of 8.67 kin. The above three detachments are corresponding to two different models of the Daehigan structure. The first model is the detaehment folding. In this model, we interpreted the Daehigan structure as an anticline deformed above the regional detaehment of the lower Cambrian at the depth of 8.67 km. Alternatively, we interpreted the Dachigan structure as fault-bend fold with an upper detaehment at the depth of 3.53 km and a lower detaehment at the depth of 7.79km. In both models, the area-depth diagram has good correlation, which means that both interpretations are internally consistent and balanced, and henee reasonable.