大陆碰撞过程中的多地体变形模式

几乎所有的大陆碰撞造山带都含有多个增生地体,它们是大陆造山带的重要组成部分.前人对地体拼贴过程及其相应地质记录都做过详细探讨,但对后期大陆持续汇聚过程中的多地体之间的变形行为及拆离模式目前研究得仍较为薄弱.为此,我们以"两地体"结构为代表,通过系统的动力学模型试验,来探讨多地体流变结构及其几何参数对大陆碰撞动力学过程的影响.模型结果显示,大陆碰撞过程中的地体变形行为主要受控于靠近主碰撞带的地体流变强度(确切来说是地壳流变强度,下同)及其几何宽度,而与远离主碰撞带的地体流变和几何属性关系较弱.同时,模型结果也揭示出大陆碰撞造山带中地体之间的相互俯冲仅发生在靠近主碰撞带一侧地体较宽的情况下,且总是弱地体向相对强的地体之下俯冲.该研究成果不仅对喜马拉雅—青藏高原造山带中地体变形演化给予重要的动力学启示,也对含有多地体结构的碰撞造山带的动力学演化研究提供一定的理论支撑.

Modes and dynamics of multi-terrane deformation during continental collision

Almost all the collisional orogens are constructed of accreted terranes, which are commonly regarded as an essential component. Previous studies have extensively investigated physical processes of terrane accretion as well as the corresponding geological records, but terrane deformation behaviors and the detachment modes due to continuous continental convergence are still poorly understood. In this work, we built a series of 2D numerical models involving two terranes representing multi-terrane structure of the natural orogens, to explore the effects of rheological properties and geometric parameters of the terrane on itself deformation and dynamic evolution of the collision zone. Model results reveal that the deformation behaviors of the terranes are mainly controlled by the rheological strength and the geometric width of the terrane that neighbors on the subduction zone, whereas the width of the farther terrane won't affect much. More importantly, according to the model results, intra-terrane underthrusting only occurs under the condition of a wide subduction-zone-neighboring terrane, and it is the weak terrane that usually underthrusts the relatively strong terrane. This study not only indicates two contrasting terrane deformation modes that might be applied to western and central Tibet, but also provides significant implications for lithospheric evolution of the natural orogens that contain a number of accreted terranes.