晚中生代东亚多板块汇聚与大陆构造体系的发展

EAST ASIA MULTI-PLATE CONVERGENCE IN LATE MESOZOIC AND THE DEVELOPMENT OF CONTINENTAL TECTONIC SYSTEMS

东亚大陆原型形成于三叠纪印支造山运动旋回,其周邻环绕的三大洋(古太平洋、蒙古-鄂霍茨克洋、中特提斯洋)于早侏罗世初期几乎同时向东亚大陆俯冲,开启了东亚多板块汇聚历史。文章通过总结东亚大陆晚中生代构造变形和构造岩浆事件的新近研究成果,简述了东亚多板块汇聚产生的三个陆缘汇聚构造系统(北部蒙古-鄂霍次克碰撞造山带、东部与俯冲有关的增生造山系统、西南部班公湖—怒江缝合构造带)、陆内汇聚构造变形体系和大陆伸展构造体系。在此基础上,重新构建了东亚多板块汇聚大陆构造-岩浆演化的时间框架,将其划分为三个阶段:早侏罗世(200~170Ma)周邻大洋板块初始俯冲阶段和陆缘裂解事件,中晚侏罗世—早白垩世早期(170~135Ma)周邻陆缘碰撞造山或俯冲增生造山作用、陆内再生造山作用和汇聚构造体系的形成;中晚白垩世(135~80Ma)大陆岩石圈的减薄作用和大陆伸展构造体系的发育。研究认为,晚中生代东亚多板块汇聚在时空上的有序演化和深浅构造的复合叠加,不仅产生了东亚大陆复杂的陆缘和陆内构造体系,同时控制了中国东部燕山期爆发式岩浆-成矿作用,也使东亚构造地貌发生东西翘变,早期陆缘汇聚产生的东部高原因晚期大陆岩石圈的减薄和伸展而垮塌。东亚大陆构造体系的形成和演化与联合古大陆的裂解同步,晚中生代东亚多板块汇聚完成了从东亚到欧亚大陆的演替,以东亚大陆为核心的多板块汇聚格局一直延续至新生代,可能成为未来超大陆形成的起点。

The proto-East Asia continent was build up through Triassic Indosinian orogenesis.Its surrounding three oceans,the Paleo-Pacific ocean to the east,the Mongolian-Okhstk ocean to the north,and the Meso Tethys to the southwest,were quasi-simultaneously subducted under this continent in the earliest Jurassic,which marked the beginning of a new tectonic era called East Asia multi-plate convergence history or for short East Asia convergence.In this paper,by integrating the recent research results of tectono-magmatic studies,we briefly describe the basic features of the three marginal tectonic belts generated by the East Asia convergence,i.e.,the Mongolia-Okhstk collisional orogen along its northern margin,the subduction-related accretional orogens along its eastern margin,and the Bangonghu-Nujiang suturing zone along its SW margin,together with widely developed compressional and extensional structures and magmatism produced in the interior of the East Asia continent.A new chronology of the tectonic evolution history was established in which three distinct stages were separated.The Early Jurassic(200~170 Ma)was dominated by coeval landward subduction of the oceanic plates and the development of active continental margins and magmatic activity along the marginal zones.The Middle-Late Jurassic to Early Cretaceous(170~135 Ma)was characterized by the structural development of three marginal orogenic belts(subduction-related accretional and continent-continent collisional orogenesis)and intra-continental orogenic zones,which,as a whole,formed the East Asia convergent tectonic system.The Middle-Late Cretaceous(135~80 Ma)was predominated by crustal extension and lithospheric thinning,with the development of continental extensional tectonic system in East Asia,due in part to the demise of the Mongolia-Okhstk orogeny,and in part to the retreat and/or break off of subducted oceanic slabs of the paleo Pacific Plate.We consider that the sequential evolution and deep-seated processes of Late Mesozoic multi-plate convergence in East Asia not only created complex marginal and intracontinental orogenic tectonic systems,but also controlled the explosive magmatism and mineralization in east China,meanwhile it caused seesaw change of landform in east-west direction.High plateaus possibly generated in East Asia during the middle-Late Jurassic to early Cretaceous convergent orogenesis may have been collapsed during the late-stage extensional tectonism.Coeval with the break-up of the Pangean supercontinent,the East Asia convergence evolved stepwisely from East Asia to Eurasia,then on the way to a future supercontinent.