华北克拉通破坏动力学过程研究中的几个构造问题

Selected tectonic topics in the investigation of geodynamic process of destruction of North China craton

华北克拉通破坏问题,是通过对古生代时期和新生代以来华北东部岩石圈厚度、热状态、岩石圈地幔组成与时代等特征的比较研究中,逐渐认识到的一个重大的大陆构造动力学问题。岩石圈厚度的巨大变薄是克拉通破坏的重要标志之一,已有的构造动力学模型从不同角度着重讨论了克拉通岩石圈是如何减薄的问题,但由于岩石圈减薄远不是克拉通破坏的全部,因此,即使已有动力学模型可以对减薄过程给出比较合理的解释,也还难以成为克拉通破坏的综合动力学模型。文中针对目前流行的华北克拉通岩石圈减薄动力学模型存在的问题,提出了在构建克拉通破坏综合动力学模型时需要关注的一些主要构造问题:(1)从构造变形、沉积作用、火山活动及其事件序列特征角度,甄别和评价主动裂谷作用和被动裂谷作用在克拉通破坏过程中所发挥的作用;热-化学侵蚀岩石圈减薄模型可能需要与上述裂谷作用模型相结合,才可能成为克拉通岩石圈破坏的候选模型。(2)从拆沉相关岩浆侵入和火山活动时空演变规律、地壳表层快速隆起及相关沉积作用和构造变形、地壳热状态异常、拆沉引起的热弱化地壳对区域应力场的响应、拆沉导致的局部应力场模拟等方面展开研究,检验、充实或修正岩石圈拆沉模型。(3)从区域构造变形和相关沉积作用、火山活动相结合的综合研究角度,探索华北克拉通的破坏是在古老克拉通基础上的直接破坏,还是在古老克拉通基础上经历了造山作用过程之后的造山带伸展垮塌,这是涉及华北克拉通破坏动力学模型建立的根本问题之一。

The destruction of the North China craton is a key problem in the continental geodynamics, which was realized from the comparison research of the lithosphere thickness, thermal gradient, age and components of the underneath mantle lithosphere between the Paleozoic and the Cenozic in eastern North China craton. As the huge amount of thinning of the lithosphere is regarded as one of the most important indicators of the destruction of the North China craton, several geodynamic models were proposed to account for the process of lithosphere thinning in last two decades. Meanwhile, since many other geological records formed during the destruction of the North China craton could not be explained reasonably by these geodynamic models, they could not be naturally treated as geodynamic models for the destruction of North China craton yet so far. Several important tectonic topics are supposed to be taken into consideration before an integrated geodynamic model for the destruction of North China craton is established, they are that （1） the active versus passive rifting model and the roles they played during the destruction of North China craton are supposed to be reevaluated based on detailed identifications of geological events sequences of tectonic deformation, sedimentation and volcanism, and the combination of the thermal-chemical erosion model with aforementioned rifting model is expected to form an integrated candidate geodynamic model for the destruction of North China craton; that （2） in addition to the geochemical constraints, the spatial and temporal evolution of the plutonism and volcanism associated with delamination, rapid uplift of the crustal surface and related sedimentation and tectonic deformation should be systematically investigated to evaluate, revise and extend current lithosphere delamination model, and identification of high thermal anomaly expected from inferred delamination and the tectonic deformation responses of the thermal weakened crust caused by delamination to regional tectonic stress field, and the variations of stress derived from delamination as well, are supposed to be carried out toward a better construction of a delamination related geodynamic modell that （3） whether the destruction of North China craton was following an old stabilized craton or a mobile orogenic belt is a key to a better understanding of the process and mechanism of the destruction of North China craton, which require integrations of researches in regional tectonic deformation, syntectonic sedimentation and associated plutonism and volcanism; if the predestruction tectonics of eastern North China craton are of mobile orogenic belt characters, the extensional collapse of orogen should be taken into account during reconstructing the geodynamic process of the destruction of North China craton.