甘肃北山红石山地区扫子山组构造变形特征及其动力学背景

甘肃北山地区扫子山组形成于早石炭世，是红石山蛇绿构造混杂岩的重要组成部分，记录并保存了红石山古洋盆形成及演化的地质信息，是讨论红石山地区晚古生代古地理环境及洋盆构造属性的重要窗口。详细的野外地质调查发现，该套地层构造变形强烈，原始层理难以辨识，为研究该套地层的沉积环境增添了难度。基于此，在查明扫子山组物质组成的基础上，通过详细的构造解析，厘定其构造序列，并通过剥离后期构造改造，恢复原始沉积层理。结果表明，扫子山组经历了3期构造变形，第1期为北北西—南南东向逆冲兼左行走滑，可能为洋壳向北俯冲的产物；第2期为北北东—南南西向挤压兼右行走滑脆−韧性变形，可能为碰撞阶段的产物；第3期构造变形以北东—南西向左行走滑为主，为次一级的晚期构造变形。变形样式及变质程度表明，扫子山组以中浅层次构造变形为主，地层未发生明显的倒转和缺失，该套地层物质成分及空间分布具有明显的规律性，显示裂谷型盆地向南趋于成熟的火山-沉积特征。 结合红石山−蓬勃山断裂以北发育石炭纪—二叠纪弧岩浆岩，揭示了红石山古洋盆向北俯冲的动力学过程，为进一步研究中亚造山带南缘构造演化过程提供地质依据。

Structural characteristics of the Saozishan Formation in the Hongshishan area of the Gansu Beishan and its dynamic background

The Saozishan Formation is developed in the Gansu Beishan area, formed in the Early Carboniferous, as an important part of the Hongshishan ophiolitic mélange, which records and preserves the important information about the formation and evolution of the Hongshishan ocean, also an important window to recover the Late Paleozoic paleogeographic environment and property of the ocean basin. According to the field geological investigation, the strata were strongly deformed, and it is very difficult to recognize the primary sedimentary sequence and also to study on the original depositional environment. Therefore, based on the identification of the material composition of the Saozishan Formation, this study determines its deformation sequences through detailed structural analysis, and restores its original sedimentary bedding by excluding later structural modifications. It is shown that the Saozishan Formation has undergone three periods of deformation, in which the first period of deformation is characterized by top-to SSE thrusting with left-lateral strike-slip motion, possibly as the products of the northward subduction of the oceanic crust in the early period; the second period of deformation is characterized by NNE−SSW compression with right-lateral strike-slip motion, possibly as the products of the collision stage; the third period of deformation shows NE−SW trending left-lateral strike-slip motion. Combined with the deformation and metamorphic characteristics, the Saozishan Formation shows characteristics of middle-shallow level deformation, the composition of the Saozishan Formation shows an obvious regularity in the north-south spatial distribution, indicating that the volcanic-sedimentary characteristics gradually matured towards the south of the rift basin. Together with the Carboniferous to Permian arc igneous rocks on the north side of the Hongshishan-Pengboshan fault, the dynamic characteristics of the northward subduction of the Hongshishan ancient ocean basin are revealed, which also provides geological evidence for further study of the tectonic evolution of the southern margin of the Central Asian Orogenic Belt.