大陆岩石圈与地球深部动力过程的协同演化  

Co-evolution of continental lithosphere and deep mantle dynamics

作　　者：刘丽军 陈凌[1,3] Lijun Liu;Ling Chen(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Department of Earth Science and Environmental Change,University of Illinois at Urbana-Champaign,Urbana IL 61801,USA;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]Department of Earth Science and Environmental Change,University of Illinois at Urbana-Champaign,Urbana IL 61801,USA [3]中国科学院大学地球与行星科学学院,北京100049

出　　处：《科学通报》2024年第2期200-214,共15页Chinese Science Bulletin

基　　金：国家自然科学基金(42288201)资助。

摘　　要：陆地是人类最主要的栖息地,然而其下方岩石圈的性质仍存在很多未知的因素.传统的板块构造理论认为大陆漂移是受大洋板块运动所控制,大陆岩石圈与对流地幔的物质交换局限在板块边界或热点附近,而大陆内部,尤其是克拉通的构造变形主要是大陆岩石圈对深部动力过程的被动响应.该认识的一个理论基础是tectosphere模型,即大陆内部的克拉通岩石圈地幔密度小而黏度高,从而能够长期稳定存在.然而近期的研究表明,克拉通岩石圈并非如传统认为的长期保持稳定,很多克拉通都发生过不同程度的结构改变,甚至破坏.相应地,对克拉通岩石圈地幔动力学性质的认知也在发生重大转变,如发现其密度高于周围地幔并且具有分层性,而其内部也存在不同尺度的薄弱带/层,在特定的构造扰动下,克拉通岩石圈会发生失稳而形成大规模拆沉.因此,本文认为,大陆岩石圈与深部地幔在超大陆时间尺度上是协同演化的,前者可以通过拆沉和折返的形式主动参与地幔对流,进而更加深刻地影响深浅能量和物质交换.这一认识的转变表明,大陆岩石圈对深部动力过程具有主动作用,因此我们对固体地球演化、环境气候变迁等重大问题的探索需要更多地引入大陆岩石圈本身的贡献.Our knowledge about the continental lithosphere,over which human beings flourish,is still limited.According to the traditional plate tectonics theory,the movement of continental plates is driven by that of adjacent oceanic plates,during which the continental lithosphere only passively drifts around the Earth’s surface while it exchanges mass with the underlying convective mantle only at plate boundaries or hotspots;the continental interiors,especially craton regions,mostly respond to mantle convection passively with its underlying lithosphere remaining intact over geological time.The above understanding was partly based on the traditional tectosphere model,stating that the cratonic mantle lithosphere has low density and high viscosity due to repetitive melt extraction from the ancient process of crustal formation,thus allowing for its longevity.However,recent studies show that the cratonic lithosphere is not as stable as previously thought,with many suffering various degrees of structural deformation,alteration,or even destruction.Meanwhile,reexamination of continental topography,gravity anomaly and global geoid based on updated seismic constraints reveals that the geodynamic properties of the cratonic lithosphere are actually quite different from traditional views.For example,the density of the cratonic mantle lithosphere likely increases with depth,with its mean value being notably higher than that of the ambient mantle;the continental lithosphere bears many weak zones/weak layers,especially the middle lithosphere discontinuity(MLD)at 70–120 km depth that could rheologically decouple the upper and lower cratonic mantle lithosphere during deformation;these properties could collectively promote gravitational instability including large-scale delamination or removal of the dense mantle lithosphere under adequate dynamic perturbations.Geodynamic processes that could trigger prominent lithospheric deformation,especially within the lower mantle lithosphere,include abnormal subduction behaviors of oceanic plates,a

关 键 词：大陆岩石圈 大洋俯冲 地幔柱 拆沉 深浅耦合 协同演化 

分 类 号：P31[天文地球—固体地球物理学] P542[天文地球—地球物理学]