以四川盆地西南部宝兴五龙地区中二叠统栖霞组斑马构造白云岩为研究对象,应用岩石学、地球化学等手段对其成因开展综合分析.研究区内斑马构造白云岩主要发育于栖霞组一段上部,斜交或平行层面分布.斑马构造暗带、亮带分别由具残余组构的粉—细晶白云石及中—巨晶鞍状白云石组成,阴极发光分别呈暗红、亮红色,指示晶体生长空间及流体交代过程的元素差异性.斑马构造亮带、暗带白云石有序度均较低,δ18O值负异常明显;暗带的87Sr/86Sr值处于或略高于同期海水范围,亮带明显较高的87Sr/86Sr值指示了深部流体的影响;亮带、暗带均具有低∑REE含量及明显的Eu正异常.综合研究表明,川西南栖霞组斑马构造白云岩属埋藏期热液交代-结晶作用成因,反映了热液流体持续供给下白云石结晶力与岩石抗张强度的动态平衡过程.斑马构造白云岩的形成历经3个阶段:①热液流体沿基底断裂垂向运移,富镁流体顺层进入高孔渗地层并持续溶解-交代石灰岩而形成暗带白云石;②在白云石结晶力大于岩石抗张强度情况下会产生破裂,从而形成一系列裂缝;③溶解作用结束后,裂缝流体中的离子沉淀而形成亮带鞍状白云石.

Taking the zebra dolomite of the Middle Permian Qixia Formation in Wulong area of Baoxing in Southwestern Sichuan Basin as the research object, the genesis of the dolomite is analyzed by means of petrology and geochemistry. The zebra dolomite in the area is mainly developed in the upper part of the Qixia Member 1, which occurs in parallel or oblique to the layers. The dark and bright bands of zebra texture are composed of powder-fine dolomite with residual fabric and mesocrystalline-megacrystalline saddle dolomite, the cathodoluminescence of which is dark red and bright red respectively, indicating the element difference of growth space and in the process of metasomatism. The order degree of dolomite of zebra texture is low, and the negative anomaly of δ18O value is obvious. The 87Sr / 86Sr value of the dark band is in or slightly higher than the seawater range of the same period; the obvious higher 87Sr /86Sr value in the bright band indicates the influence of deep fluid. Both the bright band and the dark band have low ∑REE content and obvious positive Eu anomaly. The comprehensive study shows that the formation of zebra dolomite of Qixia Formation in Southwestern Sichuan belongs to hydrothermal metasomatism -crystallization genesis during burial period, which reflects the dynamic balance process between dolomite crystallization force and rock tensile strength under the continuous supply of hydrothermal fluid. The formation of zebra dolomite undergoes three stages: (1) hydrothermal fluids migrate vertically along the basement fault, and magnesium-rich fluids enter in the high porosity and permeability stratum along the bedding, and continuously dissolve and replace the limestone to form dark band dolomite; (2)when the crystallization force of dolomite is greater than the tensile strength of rock, a series of fractures will be formed; (3)after dissolution, the ions in fluid precipitate to form bright band saddle dolomite in the fracture.