早白垩世华北克拉通岩石圈减薄与破坏动力学:兼论古太平洋型活动大陆边缘

Dynamics of the Early Cretaceous lithospheric thinning and destruction of the North China craton as the consequence of Paleo-Pacific type active continental margin

早白垩世时期华北克拉通的演化为探索大陆再造提供了典型案例,强烈地壳伸展、岩石圈减薄及克拉通破坏的机理及动力学长期以来一直是争议的焦点。早白垩世岩石圈伸展形成了包括辽南和五莲变质核杂岩在内的地壳伸展构造组合,同时伴随着巨量壳-幔岩浆活动性,这些构造-岩浆活动是克拉通岩石圈壳-幔耦合拆离与解耦拆离作用的结果,可以用克拉通岩石圈壳-幔拆离模型(parallel extension tectonics)解释。与此同时,具有相似特点(时间、几何学、运动学和动力学)的构造-岩浆活动遍布包含东北亚、中国华北和华南及俄罗斯远东地区等在内的整个欧亚大陆东部地区,反映在统一构造环境中发展和演化的本质,而华北克拉通成为早白垩世欧亚大陆东部地区岩石圈伸展的典型案例。广布的早白垩世伸展构造东侧紧邻古太平洋板块俯冲作用形成的陆缘增生杂岩带,构成独特的古太平洋型活动大陆边缘。这种大陆边缘保留和记录了与现今西太平洋型和安第斯型活动大陆边缘全然不一致的构造特点,包含增生杂岩(海沟增生楔处)与面状伸展构造域两个构造要素,但缺乏典型的大规模岩浆弧的存在。地幔分层对流对于古太平洋-欧亚大陆间洋陆相互作用、大陆岩石圈伸展、克拉通岩石圈减薄与破坏提供了重要动力来源,而板块边缘力起着重要的辅助作用。

Early Cretaceous tectonic evolution of the North China craton(NCC)provides a case study for continental remobilization.The mechanism and dynamic processes of lithospheric extension,thinning,and destruction remain hotly debated in the last decades.Extensive Early Cretaceous extensional structures and magmatic rocks in Liaodong and Jiaodong extensional provinces,eastern NCC,including the Liaonan and Wulian metamorphic core complexes,are ascribed to the coupled or decoupled crust-mantle detaching during intensive lithospheric thinning and can be reasonably explained by parallel extension tectonics(PET)model.Sharing similarities in spatial-temporal extension,kinematic features,and dynamic processes,such tectono-magmatic events also widely occurred in eastern Eurasian,from south China,through north and northeast China,to Russian Far East,which is related to the large-scale tectonic extension of regional lithosphere.Realizing the widespread occurrence of extensional tectonics and associate magmatic rocks in eastern Eurasian continent and the narrow arrangement of Early Cretaceous accretionary complexes to its east margin,we defined a new kind of compressive plate boundary,namely the Early Cretaceous Paleo-Pacific type continental margin related to ocean-continent subduction.Being different from other ocean-continent type subduction zone(e.g.,the western Pacific-and Andean-type subduction zone),no remarkable magmatic arcs were found for the Paleo-Pacific one.The stratified convection in mantle depth may provide key force for interaction between the Paleo-Pacific Ocean and Eurasian continent,continental extension,and cratonic thinning and destruction,while plate boundary forces(e.g.,slab-pull and range-push forces)just act as assistants.