Abstract:

Subduction-accretionary complex belts are an important component of orogenic belts and have great research values. They record the evolutionary history from the subduction to the collision periods as well as the history of intracontinental evolution after the collision event. Because the formation process of accretionary wedges is complex, and the deformation occurred during the subduction can undergo strong transformation due to the late-stage collision and intracontinental deformation, it is very important to distinguish between the initial and late-stage deformation, although such a task is very difficult. The subduction-accretionary complexes developed in China have all experienced significant late-stage transformations; therefore, the need for reasonable differentiation criteria for deformation of different stages becomes increasingly important in the study of orogenic belts of China continent. Based on the detailed descriptions of subduction-related deformation and its formation mechanism, this study comprehensively compares the similarities and differences in deformations formed in the subduction, collision and subsequent intraplate orogenic stages in terms of their distribution and development characteristics as well as the formation conditions and mechanisms of different structural elements, and puts forward the main principles for distinguishing deformations of different stages. Compared to the collision-induced deformation, deformation in the subduction stage is mainly concentrated in the subduction channels as simple shear or general shear primarily (thrust faults are common), with underplating and duplexing as the important features of deformation. The collision-induced deformation is diffused in matrix during the subduction, with faults, foliations and folds exhibiting dominant structural polarity; but regional-scale large folds are lacking. Pure shear deformation is rare and mainly developed in accretionary wedges above subduction channels. Abundant fluids and strong water-rock interaction directly control the deformation behavior, causing development of strain partitioning, from micro to regional scales. The collision stage mainly occurs in onshore environments, and the main deformation is concentrated near the contact zones between different geological units and large faults or shear zones. The structural polarity of faults and foliations is not obvious, and accretionary wedges are deformed as a whole, resulting in the development of large folds on a regional scale. Although fluids also exist during the deformation, their effects are not as obvious and strong as in the subduction stage, and thrust and strike slip faults are more common. However, many deformation indicators and differentiation criteria are not unique within a given environment; therefore, in practice, it is necessary to consider all aspects of such information so that reasonable judgment can be made.

Key words: subduction, collision, accretionary complex, deformation condition, deformation