四川盆地泸州区块构造变形特征及形成过程

Structural deformation characteristics and formation process of Luzhou Block in Sichuan Basin,China

通过对四川盆地泸州区块进行详细三维地震解释以及对五峰组-龙马溪组底界地震构造解析,探讨其构造形成演化过程,为研究页岩气构造保存条件奠定基础。泸州区块以中寒武统膏岩层为主滑脱层,可分为两个构造层,下构造层变形微弱,上构造层向斜宽缓、背斜紧闭,为典型的隔挡式褶皱样式,断层多发育于背斜核部和翼部,形成典型的对冲和背冲构造。燕山期以来,该区块至少经历了两期三幕构造变形,早期(D1)受近N-S向构造挤压,形成了近E-W向构造,具有北强南弱特点,可能与晚白垩世米仓山隆起向南上冲推覆有关;晚期在东、西两侧分别受到近E-W向和NW向的构造挤压,形成了东部以NNE向构造为主和西部以NE向构造为主,可能与始新世太平洋板块向西俯冲和青藏高原向东扩展有关。由于两个组系构造联合过程中,受南川-遵义断裂和华蓥山断裂控制,导致更靠近华蓥山断层的泸州区块内NE向构造形成可能略早(D2~1),由东向西递进的NNE向构造(D2~2)切割了NE向构造或被其限制。

In this paper, 3 D seismic interpretation and seismic structure analysis of the bottom boundary of the Wufeng-Longmaxi Formation in the Luzhou block of Sichuan Basin are carried out in order to discuss the tectonic formation and evolution process of this block and study the structural preservation conditions of shale gas. In the Luzhou block, the Middle Cambrian gypsum layer acts as the main detachment layer, which can be divided into upper and lower tectonic layers. The lower tectonic layer shows weak deformation, while the upper tectonic layer develops comb fold pattern with wide and gentle syncline and tight anticline. Faults with typical combination pattern of ramp fault and backthrust faults mainly developed in the core and limbs of anticline. Since the Yanshanian period, the Luzhou block has experienced at least two stages of tectonic deformation with three episodes. In the early stage, the near E-W trending structure was formed by the near N-S trending tectonic compression, and the strong deformation in the north and weak deformation in the south is considered to be related to the southward overthrusting of the Micangshan uplift in northern Sichuan in the Late Cretaceous. In the late period, the eastern and western sides of the Luzhou block were subjected to E-W and NW direction tectonic compression respectively, forming the NNE-trending structure in the east and the NE-trending structure in the west, which is considered to be related to the westward subduction of the Eocene Pacific plate and the eastward expansion of the Tibetan Plateau. Because the Nanchuan-Zunyi fault and Huayingshan fault controlled the formation of NE and NNE trending structures in the area, the NE trending structure close to Huayingshan Mountain fault may have formed slightly earlier, and the NNE trending structure truncated the NE trending structure or was restricted by the NE trending structure.