The structure of suture in orogenic belts and its tectonic implications

缝合带是两个板块之间的分隔带，其规模和形态在不同类型的造山带中多有不同。本文从缝合带和缝合面的定义出发，以典型造山带为案例探讨缝合面的变形及其对造山带结构解析、沉积盆地性质判别的影响。俯冲阶段的主滑脱面是一个没有厚度的应变带，在碰撞后又作为增生杂岩的底界得以保留。这一界面严格区分了上盘和下盘沉积盆地之间的物源亲缘性，因而将之定义作为缝合面可有效帮助解析造山带不同位置盆地的性质。蛇绿岩带、高压变质岩带和大型断裂等线状要素仅能用以大致限定缝合带的位置，而不能用以精确限定缝合面的位置。不同于俯冲阶段相对平直的主滑脱面，缝合面的形态可以在碰撞过程中、甚至碰撞后被逆冲推覆和走滑所改造。在阿尔卑斯、喜马拉雅、东准噶尔等典型造山带中，缝合面都经历了向着前陆方向的远距离推覆及褶皱变形，这一变形的缝合面经历风化剥蚀过程后，在地表的形态呈复杂的指状交叉的特征，甚至由于飞来峰和构造窗的出现而呈现多个出露点。而在双向俯冲系统中，缝合面天然具有Z型的特征，经历后期变形后其形态会更加复杂。在苏鲁-大别造山带，多期次的后期变形叠加在早期的线状缝合面之上，特别是走滑断裂将包括缝合面在内的造山带切割为不连续的断夹块，极大地改造了缝合面在地表的出露形态。综上，在解析造山带结构，特别是进行沉积大地构造研究时，缝合面的复杂形态必须要得到重视。错误的缝合面位置可能造成错误盆地性质判断。;A suture is a tectonic boundary that separates two plates. It varies in size and appearance in different types of orogenic belts. In this study, based on the definition of suture and suture interface, we present several examples of classic orogenic belts and discuss the deformation of the suture interface and the implications to the analysis of the tectonic framework of the orogenic belt and associated sedimentary basins. The decollement formed in the subduction stage is a high strain bond without physical thickness, and it is kept at the bottom of the accretionary complex when the collision happens. Because this surface strictly separated the basins with provenance connections to the upper and lower plates, it would be much convenient to deal with the provenance study if it is regarded as the suture interface. The ophiolitic belt, high-pressure metamorphic belt, and major fault can indicate the approximate location of a suture. Still, they cannot be regarded as the exact indicator of suture interface. The decollement was almost flat in the subduction stage, but its successor, the suture interface, can be deformed by thrust and strike-slip faults at and after the moment of collision. In classic orogenic belts such as the Alps, the Himalayas, and the Eastern Junggar, the suture interface had experienced long-distance thrust towards the foreland, coupled with folding deformation. It leads to the result that the suture interface exposed as a complicated cross-finger shape on the surface after the weathering and erosion and even expose multiple times due to the appearance of klippen and tectonic windows. The suture interface naturally exhibits Z-shape in the opposite subduction system and develops a more complicated structure after the deformation and collision. In the Sulu-Dabie orogenic belt, multiple-stage deformation, especially the strike-slipe fault that cut the whole orogenic belt and the suture interface into separate blocks, was applied to the original simple suture interface, which significantly modified the outcropped suture interface at the surface. The complex structure of the suture interface must be a serious consideration when it comes to analyzing the framework of the orogenic belt, especially with sedimentary tectonic tools. A wrong suture interface could lead to a wrong tectonic interpretation of the sedimentary basin.