Abstract: Based on the development of Permian Qixia Formation dolomite in Gaoshiti area, it is found that the distribution of dolomite is obviously related to the distribution of main strike-slip faults and multi-stage tectonic activities, but their coupling mechanism remains unclear. The periods of fault activities can be determined based on the geometric and kinematic characteristics of the strike-slip faults, as well as dating data from fracture cements and fracture-filling minerals in the fault zones. Through the comparison with classical diagenetic models, the analysis of elemental geochemical characteristics, and the restoration of geothermal history, it has been confirmed that the Qixia Formation dolomite is of tectonic-hydrothermal origin. The control and significance of strike-slip faults on the development of dolomite reservoirs in Qixia Formation are explored from the perspective of genetic mechanism. (1)The main strike-slip faults extending from the Sinian to the Lower Paleozoic into the Permian in Gaoshiti area were formed through multiple phases of activities along the pre-existing basement faults. These faults mainly experienced three periods of tectonic superimposition, i.e., initial development in the Pre-Sinian period, intense activities during the Late Sinian to Early Caledonian and Late Caledonian to Early Hercynian periods, and localized reactivation in the Late Permian. (2)The distribution pattern, CaO-MgO correlation, order degree, geochemical characteristics of rare earth elements, and paleo-heat flow evidences of dolomites had confirmed that the formation of dolomite reservoirs of Qixia Formation in Gaoshiti area were influenced by the multi-phase activation of main strike-slip faults and the Late Permian Emeishan rifting movement, which was caused by the hydrothermal fluid action related to widespread thermal events. (3)The dolomite reservoirs of the Member 2 of Qixia Formation were horizontally distributed in banded and lenticular patterns near four primary strike-slip fault zones, i.e., F_I-8, F_I-9, F_I-10, and F_I-11. With the Emeishan rifting movement occurring in the Late Permian to end of Early Triassic periods, the deep basement strike-slip fault was reactivated, the fault communicated with the deep thick clastic hydrothermal reservoirs of Chengjiang Formation, and the tight shale of Longtan Formation overburdening Qixia Formation formed a sealing layer, which provided favorable conditions for the development of hydrothermal dolomite reservoir facies, including heat source, fluid channels, and effective sealing. (4)The fault-hydrothermal interaction exerted a significantly greater influence on carbonate rocks on the active side of the fault rather than that on the passive side of the fault. The passive side of the fault might serve as the barrier for the intrusion and penetration of deep upwelling hydrothermal fluid, while the deep Mg-rich fluid would preferentially enter the beach granular limestone with good porosity on the active side of the fault when entering the Qixia Formation along the deep fault, thus resulting in hydrothermal dolomitization.

Key words: Sichuan Basin, Gaoshiti area, strike-slip faults, fault activity, Permian Qixia Formation, dolomite genesis, tectonic-hydrothermal dolomitization

摘要： 基于高石梯地区二叠系栖霞组白云岩在钻井中的发育情况分析,白云岩的分布与主干走滑断裂的分布及多期构造活动明显有关联,但其耦合机理尚不明确。根据走滑断裂带的几何学和运动学特征以及断裂带的裂缝胶结物、缝洞充填矿物的测年数据,判定了断层的活动期。通过与经典成岩模式进行对比、元素地球化学特征分析和地热史恢复,证实栖霞组白云岩为构造-热液成因,并从成因机理上探讨了走滑断裂带对栖霞组白云岩储层发育的控制作用与意义。①在高石梯地区,由震旦系—下古生界延伸至二叠系内的主干走滑断层为基底先存断裂在多期构造活动下形成,断层主要经历了前震旦纪的雏形发育阶段、晚震旦世—加里东早期和加里东晚期—海西早期的强烈活动阶段、晚二叠世局部复活阶段3期构造叠加活动。②白云岩的分布模式、CaO—MgO含量关系、白云石的有序度、稀土元素地球化学特征和古热流证据表明,高石梯地区栖霞组白云岩储层的形成受主干走滑断裂的多期活化和晚二叠世峨眉地裂运动影响,成因为与广泛热事件有关的热液流体作用。③平面上,栖霞组二段的白云岩储层呈带状、透镜状分布在F_I-8、F_I-9、F_I-10和F_I-11这4条一级走滑断裂带附近。伴随着晚二叠世—早三叠世末期发生的峨眉地裂运动,基底深大走滑断裂再次活化,断裂与深部澄江组巨厚碎屑岩热液储库相沟通,而栖霞组的上覆龙潭组致密泥页岩则形成封堵层,这些为热液白云岩储集相的发育提供了热源、通道和封堵的有利配置条件。④断裂构造-热液作用对断层主动盘一侧的碳酸盐岩的影响明显大于被动盘,被动盘一侧可能作为深部上涌热液流体侵入渗透的阻隔层,而深部富镁流体在沿深大断裂进入栖霞组时则会优先选择进入主动盘一侧孔隙度较好的滩相颗粒灰岩中,产生热液白云石化作用。

关键词: 四川盆地, 高石梯地区, 走滑断裂, 断裂活动, 二叠系栖霞组, 白云岩成因, 构造-热液白云石化作用