1引言 在最近几年,我们对造山机制的认识有了很大进展。在一篇里程碑文章中,Chapple(1978)把前陆褶皱和冲断带模拟为下伏有弱底层的到处处于临界破裂点边缘的完全塑性楔形体。Chapple(1978)用这个模型证明了水平挤压作为驱动力的重要性,并得出楔形体的形状和地形取决于楔形体物质和底层的相对强度。Davis等(1983)修正TChapple的模型.选定库伦破裂流变为上地壳的较现实流变。他们认为,如果有物质加到楔形体或离出楔形体,那么整个楔形体必定发生变形,以保持临界斜度。自这些早期论文以来,许多作者应用、推广并修改过这个临界楔形体模型,以更好地理解区域规模的造山过程。然而,临界楔形体型模型并不意味能详细预测造山楔形体内变形的运动情况(Chapple,1978),相反,他们推测,造山楔形体的整个形状接近于由连续模型预测的形状。因此这些模型对详细理解变形运动过程是有限的。 近来,在试图设计一般造山过程的较现实运动学模式方面,特别在台湾,Hwang等 (1993)提出一个顺序冲断模式,把造山带当作为一系列前陆倒转,前陆推进的冲断片。此模式是以前陆褶皱冲断带发展的两个基本原则为根据的:(1)主要的缩短作用由冲断作用 1 INTRODUCTION In recent years, much progress has been made in our understanding of orogenic mechanisms. In a landmark article, Chapple (1978) modeled the foreland fold and thrust belt as a complete plastic wedge with a weak base beneath the edge of the critical point of collapse everywhere. Chapple (1978) used this model to demonstrate the importance of horizontal extrusion as a driving force and concluded that the shape and topography of the wedges depend on the relative strength of the wedges and the substrate. Davis et al. (1983) revised the TChapple model and selected the more realistic rheology of the Coulomb failure as the upper crust. They think if there is material added to or leaving the wedge, the entire wedge must be deformed to maintain the critical slope. Since these early papers, many authors have applied, promoted, and revised this critical wedge model to better understand the orogeny-scale orogeny. However, the critical wedge model does not imply a detailed prediction of the deformation of the orogenic wedge (Chapple, 1978). Instead, they hypothesize that the entire shape of the orogenic wedge approaches the shape predicted by the continuous model. Therefore, these models are limited to a detailed understanding of the deformation process. Recently, Hwang et al. (1993) proposed a sequential thrust model in Taiwan to try to design a more realistic kinematic model of a general orogenic process, using the orogenic belt as a series of thrust fragments for foreland reversal and foreland propulsion. This model is based on two basic principles of the development of foreland fold-thrust belts: (1) the main shortening action is caused by thrusting