北部湾盆地乌石凹陷东区构造转换带识别及其特征

Identification and characteristics of structural transfer zones in the east area of Wushi Sag,Beibuwan Basin

北部湾盆地乌石凹陷东区构造背景复杂,前人对构造转换带类型、特征、定量刻画及形成机制的相关研究较少。为此,在前人研究基础上,从断裂的发育、演化入手,利用地震资料,采用距离—断距曲线、垂向埋深—断距曲线等定量统计方法,对乌石凹陷东区构造转换带进行识别和分类,总结识别标志及其特征,阐述构造转换带的分布规律、形成机制及与油气藏之间的关系,获得以下认识:①该区构造转换带分为平行型、叠覆型、趋近型、转折端型和共线型等5类。②平行型主控断层级序较高,多以“硬连接”的形式调节、传递位移和形变,剖面上呈复“Y”字型;叠覆型在平面上互相平行,断层级序较低,对构造区带的控制较弱,剖面上表现为背斜形式的“软连接”;趋近型以转换斜坡的形式连接主干断层;共线型主断层中段呈手指状张开,东、西两段倾向相反,剖面上断层相互错动,构成“X”型;转折端型在平面上呈马尾状,调节断层向主控断层弯曲部位收敛,具调节主干断层弯曲程度及断距的作用。③不同类型构造转换带受控于构造背景和边界控制条件,分布位置存在差异。平行型全区分布广泛,叠覆型、趋近型分布于东北部,共线型分布于中北部,转折端型靠近7号断层。④NE向基底断裂奠定了形成构造转换带的基础,在哀牢山—红河断裂带走滑、南海扩张、地幔上涌派生的拉张应力的共同作用下,断层分段生长是构造转换带形成的直接原因。该研究丰富了转换带构造体系,填补了乌石凹陷构造转换带研究的空白,对复杂地质环境下转换带的识别及有利区带的选择具有借鉴意义。

The tectonic background of the east area of the Wushi Sag in Beibuwan Basin is complex and there are few previous studies of the types,characteristics,quantitative descriptions,and formation mechanisms of the structural transfer zones in this area.In response,drawing on previous studies and seismic data and starting from the development of faults,this paper identified and classified the structural transfer zones in the study area via quantitative statistical methods such as the distance-displacement curve and the vertical buried depth-displacement curve.The identification marks and their characteristics were summarized.In terms of the structural transfer zones,their distribution laws,formation mechanisms,and relationships with oil and gas reservoirs were expounded.The following understandings were obtained:①The structural transfer zones in this area are divided into 5 types,namely the collateral type,the overlapping type,the approaching type,the hinge zone type,and the collinear type.②As for the collateral type of structural transfer zones,the main controlling faults have high levels of sequence and displacement and deformation are mostly adjusted and transferred by"hard connections",with a complex"Y"shape on the section.The overlapping structural transfer zones are parallel to each other on the plane and their fault sequences are low.Their control over the tectonic zones is weak and the section is in an anticline"soft connection".The approaching type connects the main faults by relay ramps.The middle sections of the main faults of the single-line structural transfer zones are open in finger shapes.The east and west sections are in opposite directions and the faults on the section are staggered,forming an"X"shape.The hinge zone type is in a horsetail shape on the plane,adjusting the faults to converge to the bending parts of the main controlling faults.It has the function of a-djusting the bending degrees and displacements of the main faults.③Different types of structural transfer zones,controlled by the tectonic background and boundary control conditions,have different distribution locations.The collateral type is widely distributed throughout the region.The overlapping type and the approaching type are in the northeast.The collinear type is in the central and northern region and the hinge zone type is close to fault No.7.④The NE basement faults lay the foundation for the formation of the structural transfer zones.Under the combined action of the slip of the Ailaoshan-Honghe fault zone,the expansion of the South China Sea,and the tensile stress generated by mantle upwelling,segmented fault growth became the immediate cause of the structural transfer zones.This study enriches the structural system of transfer zones,fills the gaps in the study of the structural transfer zones in the Wushi Sag,and provides a reference for the identification of transfer zones and the selection of favorable zones in a complex geological environment.