活动走滑断裂上断塞塘沉积特征及其构造含义——以西秦岭北缘断裂带断塞塘为例

活动断裂与地震和地质灾害紧密相关,对与其相关的沉积记录进行研究可以认识其活动习性与规律。通过揭露并分析典型断裂地貌——断塞塘的沉积建造特征,能够帮助识别活动走滑断裂作用的信息。选取青藏高原东北缘的西秦岭北缘断裂带黄香沟段,利用组合探槽对沿其发育的断塞塘及其沉积进行研究,分析其沉积特征,并建立断塞沉积序列。研究发现:断塞塘沉积层序由几个沉积韵律组成,一个沉积韵律组合分为下部的粗粒层与上部的细粒层,粒度下粗上细;粗粒层一般为细砂、粗砂和砾石层,具快速堆积的特征;细粒层均为含炭的粘土、亚粘土和粉砂,具湖塘相沉积的特点。断塞沉积层序是分期的,一个沉积韵律组合是一期断塞作用沉积。分析认为,断塞沉积粗细组合的韵律性结构是断裂周期性活动的产物。这一研究是揭示走滑断裂的构造演化与活动习性,反演断裂走滑活动历史并预测其未来行为的基础。

Sedimentary Characteristics of Sag-pond on the Active Strike Slip Fault and Its Tectonic Implications: An Example from Sag Pond along the West Qinling Fault

Active faulting is closely related to earthquake and geologic hazard. Study on relevant deposition records can help understand the active behavior and pattern of an active fault. Therefore, research of sedimentary formation characteristics of typical faulted landform, the sag-pond, can help recognize the information about active strike-slip faulting. Taking the Huangxianggou section of the northern faulting zone of West Qinling in the north Qinghai-Tibet plateau, this study analyzes depositional features using composite trenches and establishes sedimentary sequence of the sag-pond. The result shows that the sedimentary sequence of sag-pond consist of several sedimentary series, each of which contains lower coarse layer and upper fine layers. The coarse layers are commonly constituted by fine sand, coarse sand and gravels, which suggests a fast depositing. The finer layers generally consist of carbonaceous clay, mild clay and silty sand, showing characteristics of lacustrine sedimentation. The sag-pond deposition sequence is multi-staged, and one deposition rhythm corresponding to one sedimentation. Observations indicate that the deposition rhythms were the product of the periodic behavior of the faulting. This study reveals the tectonic evolution and active pattern of strike slip and lays foundation for deducing strike-slipping history and forecasting its upcoming behavior.