克拉通盆地内断裂走滑变形特征

Strike-slip deformation characteristics of fault in craton Basin

走滑断裂在全球范围不同构造背景下普遍发育,在区域构造、火山地震及能源矿产等领域的研究中具有重要意义。相较于发育于板块或块体边界活动构造背景的大型走滑断裂带的深入研究,发育于稳定克拉通块体(盆地)内部的走滑断层为新近得到关注的一类走滑断层,其研究极为薄弱。该文对近几年通过三维勘探地震在中国3大克拉通盆地(鄂尔多斯盆地、塔里木盆地和四川盆地)新发现的走滑断裂体系进行综合对比研究分析,总结稳定克拉通盆地内走滑断裂的共性特征,讨论其可能的形成动力学机制。结果表明,克拉通盆地内部稳定区走滑断层尽管有时走滑特征典型,但表现出与活动块体区发育的大型走滑断裂的较大不同:①基本特征上具体表现为普遍具有小位移、低发育成熟度的特征,断层在垂向上分层、分期发育,与盆缘构造在方向和动力学特征上明显脱耦;②在形成模式和发育机制上,克拉通盆地内走滑断裂可能是在区域挤压应力下产生的裂缝基础上,经应力-应变调节或斜向挤压或块体旋转下选择性扭动复活发育而成,该发育方式决定其受先存断裂构造的影响弱,记录了断裂从形成到生长发育的较初期阶段;③在动力学过程与意义上,克拉通盆地内走滑断层分层发育特征是断层分期次、上下相对独立活动的结果,是构造应力在克拉通块体内浅表层传递的响应,这不同于传统认识的大型走滑断层由下到上贯穿发育的模式,该特性可以更好地记录克拉通盆地及周围多期次叠加区域应力演化的过程。

Strike-slip faults are widely developed in different tectonic settings around the world,and are of great significance in the study of regional tectonics,volcanic earthquakes,energy and mineral resources.Compared with the investigation of the large-scale strike-slip fault zone developed in the active tectonic background,the strike-slip fault developed in the stable craton block(basin)is a special type of strike-slip fault that has recently received attention;the related research is extremely weak.In this paper,the strike-slip fault systems newly discovered in the three craton basins(Ordos,Tarim and Sichuan basins)in China through three-dimensional exploration seismic data in recent years are comprehensively compared and analyzed.Consequently,the common characteristics of the strike-slip faults in the stable craton basins are summarized,and the possible formation dynamics mechanism is discussed.The results show that the strike-slip faults in the stable area within the craton basin are different from the large-scale strike-slip faults developed in the active block,although their strike-slip characteristics are also sometimes typical.①In aspect of basic characteristics,they are generally characterized by small displacement and low development maturity.The faults have a significant stratified style,and obviously decoupled from the structures of basin margin in terms of direction and dynamics.②For their formation model and development mechanism,it is considered that the strike-slip fault in craton basin may be initiated from the fracture generated under the regional compressive stress;the early fractures is selectedly developed due to the stress-strain accommodation or oblique compression or block rotation,the formation of these faults is less influenced by the preexisting faults,and records the early stage of the fault′s evolution.③In aspect of their geodynamic process and significance,the development characterized by stratified style of strikeslip faults in craton basin is the result of their relatively independent activities in different layers and the response of the tectonic stress propagation in the shallow layer of craton block,this is different from the traditional pattern of strike-slip faults from bottom to top and thus it can better record the evolution process of multistage regional stresses in and around the craton basin.