A mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure
A mechanical model for complex fault patterns induced by evaporite dehydration and cyclic changes in fluid pressure
复制标题
DOI：
10.1016/j.jsg.2007.07.015
复制
发表时间：
2007-10
影响因子：
3.1
通讯作者：
N. Paola;C. Collettini;F. Trippetta;M. Barchi;G. Minelli
中科院分区：
文献类型：
--
作者：
N. Paola;C. Collettini;F. Trippetta;M. Barchi;G. Minelli
复杂的断层模式，即表现出不同走向范围的断层，可能在区域构造应力场弱或不存在的条件下形成（例如多边形断层）。本文认为，在翁布里亚-马尔凯亚平宁山脉（意大利）的同沉积断层的复杂系统，几何相似的多边形断层系统，在侏罗纪早期的伸展幕。这种特殊的断层模式不同于许多伸展断层系统，因为它缺乏与经典的双峰共轭“安德森”几何形状发展的结构。提出了一个概念和力学模型来解释复杂的断层模式的发展和演变，其中提出断层主要是由体积不稳定性的发展控制在三叠纪蒸发岩由于脱水过程（anaeritisation）在埋藏。三叠纪蒸发岩的岩性结构，包括互层的钙-硫酸盐层和白云岩，在控制变形过程中发挥了重要作用。循环流体超压的建立/释放以及脆性和脆韧性流动过程的共存导致脱水岩体内部水平各向同性和非平面拉伸应变场，有利于复杂变形模式的发展。提出的力学模型表明，所研究的故障模式下开发的应力场一致，几乎均匀的应力强度内的水平面。所提供的数据表明，局部应变场和瞬态流体压力条件已占主导地位的弱区域伸展构造。这些发现与许多其他地区有关，在这些地区，复杂的断层模式（包括多边形断层）与蒸发岩或富含粘土的沉积序列有关。
Complex fault patterns, i.e. faults which exhibit a diverse range of strikes, may develop under conditions where a regional tectonic stress field is weak or absent (e.g. polygonal faults). The present paper considers a complex system of synsedimentary faults in the Umbria-Marche Apennines (Italy), geometrically similar to polygonal fault systems, developed during an early Jurassic extensional episode. This particular fault pattern differs from many extensional fault systems as it lacks structures that are developed with a classical bimodal conjugate “Andersonian” geometry. A conceptual and mechanical model is proposed to explain the development and evolution of the complex fault pattern in which it is proposed that faulting is primarily controlled by the development of volumetric instability in Triassic Evaporites due to dehydration processes (anhydritisation) during burial. The lithological architecture of the Triassic Evaporites, comprising interbedded Ca-sulphate layers and dolostones, played a fundamental role in controlling the deformation processes. Cyclic fluid overpressure build-up/release and the coexistence of brittle and brittle-ductile flow processes led to horizontal isotropic and non-plane extensional strain fields within the dehydrating rock mass, which favoured the development of complex deformation patterns. The mechanical model proposed shows that the studied fault pattern developed under a stress field consistent with almost homogeneous stress intensities within the horizontal plane. The data presented show that local strain fields and transient fluid pressure conditions have been dominant over weak regional extensional tectonics. The findings are relevant to many other areas where complex faulting patterns—including polygonal faults—occur in association with evaporite or clay-rich sedimentary sequences.