华南晚中生代大陆变形、深部过程及动力学

Abstract

<p>受控古太平洋板块俯冲及后撤作用，华南晚中生代经历了强烈大陆再造，并伴随幕式岩浆活动，是研究活动大陆边缘构造-岩浆作用、壳幔过程和板块俯冲动力学的天然实验室。本文系统综述了近年来发表的构造变形、岩浆作用和深部结构等多学科成果，以构造解析为主线，深-浅结合，在华南识别出与古太平洋板块俯冲相关的中晚侏罗世弧背缩短和白垩纪弧后伸展系统，厘定了二者的时空格架和叠加改造关系。弧背缩短系统以扬子中部的隔档-隔槽式褶皱、深部多层滑脱和双重逆冲推覆构造为特征，具SE向NW的逆冲扩展变形规律，与古太平洋板块的前进式俯冲有关。白垩纪主体以大陆伸展为主，经历了伸展和挤压变形交替，并伴随着岩浆活动的爆发、迁移和停止，其可能与板片俯冲动力学变化有关。在此基础上，我们分析了白垩纪岩石圈长距离伸展的深部过程及浅表响应，提出了岩石圈随深度变化的分层差异伸展模式。自下而上，从岩石圈地幔到上地壳，应变近一致地表现为（W）NW-（E）SE伸展，反映了垂向变形一致性。可能的垂向应力传播过程：板片后撤诱发长距离地幔流，其在岩石圈底部形成剪切牵引应力，促进下岩石圈地幔被动拉伸；上岩石圈地幔局部发育强应变剪切带，作为应力传播构造，其可有效加强壳-幔间剪切，促进下地壳韧性拉伸，将下地壳和岩石圈地幔的变形关联。我们认为岩石圈伸展、板片后撤和地幔流形成了三位一体的动力学耦合系统，将华南岩石圈长距离伸展的驱动力归结为：（1）古太平洋俯冲带海沟后撤和板片回卷诱发的远程效应，和（2）地幔流在岩石圈底部施加的剪切牵引应力。 <br></p>

In the Late Mesozoic, South China's eastern margin evolved into an active Andean-type convergent margin associated with the subduction of the Paleo-Pacific Plate. The continental crust underwent significant reworking, accompanied by extensive magmatism, providing an ideal natural laboratory to assess the tectono-magmatism, crust-mantle processes, and plate subduction geodynamics along the active continental margin. Here we review the essential constraints of structural deformation, magmatism, and lithospheric architecture. We recognized the Mid-Late Jurassic retro-arc shortening system and the Cretaceous back-arc extensional system, and clarified their spatial-temporal associations and overprinting relationships. The retro-arc shortening involved a northwestward thrust propagation by generating arrays of thin- and thick-skinned thrust systems, multiple decollements, and duplexes in the central Yangtze, possibly associated with the northwestward advancing subduction of the Paleo-Pacific plate. The eastern part