碳酸盐岩断层破碎带构造成岩作用——以塔中Ⅰ号断裂带为例

Structural diagenesis in carbonate fault damage zone: A case study of the No. 1 fault zone in the Tarim basin

多旋回叠合盆地断层具有异常复杂的构造变形与成岩演变,跨学科结合的构造成岩作用研究为断层破碎带演变机制与流体-岩石作用分析提供了新思路。结合塔中Ⅰ号断裂带构造解析和地化资料分析,探讨古老碳酸盐岩断层破碎带构造成岩作用的特殊性。结果表明,塔中Ⅰ号断裂带上奥陶统台缘带碳酸盐岩断层破碎带发育多类、多期构造成岩作用,明显不同于围岩。断层破碎带宽度高达2～4km,裂缝类型多样、纵横向变化大、开启程度较高。沿断裂带压实作用较弱且有差异,发现有碳酸盐岩压实变形带发育,并有后期裂缝与溶蚀作用形成的局部高渗透带。断层破碎带观测到多期压溶低角度缝合线与高角度构造缝合线,部分具有渗透性。多达4～5期不同类型胶结作用沿裂缝带发育,大气淡水胶结较多,胶结程度相对较弱。准同生期大气淡水溶蚀与局部风化壳岩溶主要沿断层破碎带发育,而且埋藏溶蚀作用较强,发育大型缝洞体与溶蚀孔洞。构造成岩作用揭示塔中Ⅰ号断裂带东段上奥陶统碳酸盐岩断层破碎带经历断裂萌芽期-形成期-定型期-复活扩张期-局部开启期等5期演变,不同演化期构造成岩作用有明显差异。构造成岩作用的多期差异活动是造成古老碳酸盐岩断层破碎带复杂性的重要因素。

Due to the extremely complicated deformation and diagenetic process in fault damage zone of the multicycle superimposed basin,structural diagenesis of cross-disciplinary approach provides a powerful tool for the study of the mechanism and evolution,and fluid-rock interaction in fault damage zone. Based on the integrated analysis of cores,thin-section and geochemistry data,this paper presents the carbonate structural diagenesis along No. 1 fault zone in the Tarim basin. It is showed that there is multi-types and multistages structural diagenesis in the Ordovician carbonate fault damage zone,which is obvious different from the country rocks. The fault damage zone,having characteristic of fracture zones of multi-types and high degree of opening with frequently lateral variation,is up to2 ～ 4km wide. There is weaker compaction with varied degrees,but compaction deformation bands were identified in fault damage zone,which also occurred localized high permeability by the late fracturing and dissolution process. The stronger pressure solution resulted in low-angle and high-angle stylolites,part of them had seepage performance. There are 4 ～ 5 stages of multi-types cementation,and more of meteoric cements in early diagenesis,and with weaker cement filling in damage zones compared with country rocks. The meteoric dissolution lens in penecontemporaneous diagenesis and localized karstification,and stronger buried dissolution occurred mainly in fault damage zones,which resulted in the development of large scale fracture-cavity reservoirs and dissolution porosity-vug reservoirs in the Upper Ordovician carbonate. It is also indicated by structural diagenesis that there are 5 stages evolution in fault damage zone： fault initiation stage-forming stage-finalizing stage-resurrection stage-local opening stage,and different evolution period has distinct structural diagenesis. Therefore,the discrepancy of multi-phase structural diagenesis process plays a crucial role in the complexity of the ancient carbonate damage zone.